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THE INTERNATIONALELECTRONICS MAGAZINE

Elect is

INSIDE:64 -page Greenweld

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Parallel PodsHigh Performance Low Cost PC InstrumentationData Acquisition to 20MHz, 32 bit Logic Analyser to 20MHz

Data Acquisition & Softscope

Connecting to the standard printer port of any PC or compatible, the parallel pods offer 100kHz to 20MHzperformance from as little as £80.00, including software and interconnecting cable. Up to 4 parallel podsmay be connected onto a single printer port. Softscope software is supplied with all units, which is usedto setup, trigger and gather data from up to 4 channels, display in X -Y or in Y -T formats and export tomost industry standard packages.

POD 1 iOuS Single Channel Low CostWhen used with the Softscope software, turns your PC into aversatile oscilloscope for use in real time or storage mode.

POD 2 20uS Dual Channel SimultaneousEffectively two POD1 A -D converters packaged together inone enclosure with a single common trigger. Ideal for X -YPlotting, or as a two channel display.

Logic Analyser & IC Tester

POD 3 1MHz Data Capture with 8k RAMWith 8kBytes of buffer RAM to POD3 gives true 1MHzoperation regardless of the speed of the controlling PC.

POD 4 20MHz Data Capture with 8k RAMAt 50nS per conversion, and with 8kBytes of RAM, highspeed events can be easily captured and displayed with thePOD4, with the features of an expensive storage scope.

In addition to the data acquisition PODS come the Logic Test PODS the POD21 and POD26. Beingcompatible with the other PODS, they may be used in conjunction. For example using the POD4 with thePOD21 provides means of recording both analogue and digital signals together and in synchronism. Aswith other PODS the POD21 and POD26 come complete with operating software and parallel port cable.

POD 21 32Bit Logic AnalyserDesigned to interface with the parallel port of a PC and beused in conjunction with the LogicSoft software, the POD21provides the functions of an expensive logic analyser at afraction of the cost. Full 32 bit trigger signatures areprovided, with internal or external clocks, running at up to20MHz. 8k x 32bit words of RAM are provided for datacapture with a full featured display.

ComputerInstrumentati

Lim

POD 26 Logic I.C. TesterThe POD26 is an invaluable tool for users of 74 series and4000 series logic I.C.s. Simply plug an IC into one of thearray of Dual in line sockets and the software will quicklyidentify and test it. Extensive software and componentlibraries not only identify and test the IC in question, butalso provides a display of the truth table. In addition it maybe used to analyse the truth table of popular PALs.

BLD 3 WOODS WAY TEL 0903 700755GORING -BY -SEA FAX 0903 700788SUSSEX BN12 4QY

July/August 1994ELEKTOR Volume 20TE TS Number 224

ISSN 0268/4519ELECTRUNICE

In the September issue :APPLICATION NOTES 88 Figuring it out - Part 18

Anemometer and flow meter 34 Solid-state temperature sensor 92 Resettable fuse for caravansHome modem 98 Infra -red controlled switchAnalogue rev counter 102 Points control for model railwayLED oscilloscope AUDIO & HI-FI & MUSIC 103 Rear wiper interval switch41/2 digit 1 MHz frequency

counter8

12Surround soundMIDI swell pedal

Reversible a.c. supplyPanda -Wegener stereo

26 Auto -play for CD player POWER SUPPLIES & BATTERY CHARGERS

decoder 28 Programmable amplifier 28 Near -ideal rectifier

PIC programming course - 40 Discrete preamplifier 42 Indicator for lead -acid battery chargerPart 2 48 Robust a.f. power amplifier 55 Power supply for LCD moduleand more for your 50 8th order Butterworth filter 60 Power supply decouplingcontinued interest 54 'Near -perfect' input stage 60 Solar cell powered NiCd charger

56 Two -speaker amplifier 64 Near -ideal supply68 Compressor for guitars 70 Lead -acid battery charger84 Gneral purpose IR volume control 72 Discrete power supply

Front cover COMPUTERS & MICROPROCESSORS RADIO, TELEVISON & COMMUNICATIONSA selection of prototypes of

projects published in this issue.18 PIC programming course - Part 1 6 RC -5 transmitter with 80053538 Senal 12 -bit A -D converter 22 Software emulation for RC -5 code44 80C451 controller board 36 General purpose infra -red buffer52 Joystick -to -mouse adaptor 46 S -VHS -to -VHS converter54 PC over -temperature alarm 71 Stereo decoder62 1-4 Mbyte SIMM adaptor 104 Small loop antennas - Part 266 Centronics input/output interface67 Non-volatile controller chip

TEST & MEASUREMENT

30 Charge meterGENERAL INTEREST 36 Programmable pulse spacing meter

5 Optical doorbell 56 Precision one shot pulse generrator6 Overtone oscillator 63 Frequency indicator

26 Self-starting multivibrator 68 Peak a.f. voltage meter37 Dnve for bistable relay 72 Three-phase indicator42 Heat sink monitor 75 Sweep generator46 Light-sensitive switch 80 Car battery monitor50 Mains -synchronised oscillator 102 PLL controlled ranp generator53 Thermo -controlled hot -plate64 Crystal oscillator

Copyright © 1994 Elektuur BV70 Sensor interface MISCELLANEOUS INFORMATION71 Solder vapour extractor 110 Readers' services

AJ3 CAI III 'I IR RI 1t Oh ( IR( LI %IRAS

7476

Experimentation boards for PICsPolarity reversal protection

112 Terms of business113 Switchboard

CONSUMER PRESS76 Slave switch 114 Buyers' guide78 Water softener 114 Index of advertisers

Elektor Electronics is published monthly, except in August, by Elektor Electronics (Publishing), P.O. Box 1414, Dorchester, Dorset DT2 8YH, England. The magazine isavailable from newsagents, bookshops, and electronics retail outlets, or on subscription at an annual (1994) post paid price of £2700 in the United Kingdom; air speeded:£34.00 in Europe; £43.00 in Africa, the Middle East and South America; £4500 in Australia, New Zealand and the Far East; and $57.00 in the USA and Canada. SecondClass Postage paid at Rahway N.J. Postmaster: please send address corrections to Elektor Electronics, c/o Mercury Airfreight International Ltd Inc., 2323 Randolph Avenue,Avenel, New Jersey, N.J. 07001.

ELEKTOR ELECTRONICS JULY/AUGUST 1994

4 Please mention ELEKTOR ELECTRONICS when contacting advertisers

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ada4al


OPTICAL DOORBELL

his little circuit is for allThis where you can nothear the doorbell, for what-ever reason, but would stilllike to be alerted if someonecalls at you. The reason forbeing unable to notice the soundof the bell may be that you arehard of hearing, blown awayby an old Jesus & Mary Chainsong, or deafened by the noiseof the circular saw in your work-shop as it grinds its way througha piece of wood or metal.Whatever the case, someonewants to see you, and an op-tical warning is a godsend.

The circuit uses the exist-ing bellpush (S1) and associ-ated transformer (Tri), whichis usually rated at 8 V, 1 A,and safe to use for the presentapplication. The secondaryvoltage is rectified and smoothedby D1 -C2 which power the op-tical doorbell driver. When thepush-button is pressed, thebell will ring as usual. At thesame time, transistor T1 isswitched on and off at the rateof the mains frequency (50 or60 Hz). This, in turn, causesa monostable multivibratorformed by ICI a and IC ib to bestarted. The monotime is setto a value of about 15 secondsby C3 and R3. The monostablein turn enables an oscillator,IC which controls ou t -c-ICid,put driver transistor T2.Consequently, the lamp con-nected to the solid-state relay,IC2, will flash for a predeter-mined period. LED D3 flashesat the same rate as a means ofchecking the operation of theoptical door bell. The maxi-mum power of the bulb con-nected to the circuit is about100 W.

Since the mains voltage ispresent on two copper tracksand four solder points on theprinted circuit board, the cir-cuit must be built with dueattention paid to electricalsafety. The completed printedcircuit board is built into asolid ABS enclosure with in-tegral mains socket, so thatthe bulb can be connected viaan ordinary mains cable andplug.

D1

Parts list0

Resistors:R1 = 100 k52R2 -R5 = 1 MS2R6 = 15 Id2R7 = 390 Q

Capacitors:C1,C4 = 100 nFC2 = 100 pF, 25 V, radialC3 = 22 pF, 25 V, radialC5,C6 = 1 pF, 25 V, radial

Semiconductors:DI = 1N4002 944080

D2 = 1N4148 0D3 = LEDT1 = BC547BT2 = BC557B

Integrated circuits:ICi = 4011 block, pitch 7.5mm.IC2 = S201SO4 (Sharp) Si = existing bellpush.

Tr1 = existing bell transMiscellaneous: former 8V/1A.K1 = 3 -way PCB terminal BZI = existing doorbell.

block, pitch 5mm. Enclosure: e.g., BoplaK2 = 2 -way PCB terminal Nicro N12. [Phoenix

Mecano UK Ltd.,Tel. (0296) 398 853.]

PCB Ref. 944080 (p. 110).

Design: E. Verbeek[944080]


6

RC5 TRANSMITTER WITH 800535

rrhe 800535 SBC (single board1 computer) can be adapted

to function as an RC -5 infra -red(IR) transmitter by the addi-tion of some hardware and soft-ware described in this article.

The required carrier waveof 36 kHz is generated by soft-ware: it is, therefore, essentialthat a 12 MHz crystal is usedas the clock for the microcon-troller.

The circuit consists of fourparallel -connected buffersType 74HCT00, followed by aType 2N222 transistor, T1, whichdrives IR transmit diodes D2and D3. The edges of the trans-mitted signal are enhanced byC2.

The IR transmit diodes con-vert the digital code into infra-red signals. Light -emittingdiode DI gives a visibile indica-tion that a code is being trans-mitted.

The connection with theSBC is made via K1.

The circuit is best built onthe printed -circuit boardthat, together with the nec-essary software, is availablethrough our Readers' Ser-vices.

Parts listResistors:R1 = 10 1(52R2, R5 = 330 Q

Quartz crystals are groundby the manufacturers to

oscillate either on the funda-mental frequency or on one ofthe odd harmonics (overtones).Now- adays, this grinding is soaccurate that fundamental modecrystals do not oscillate on thethird or fifth overtone (as theyusually could do in yearspast). However, the present cir-cuit enables fundamental modecrystals to oscillate on an over-tone (third or fifth).

In the design, use is madeof the fact that rectangularwaveforms contain odd har-monics. The signal generatedby oscillator IC la is amplifiedin IC ib. This means that the

01 R1 10 01 R4 10 p.m01 R2 f0 01 R5 I°

R3 = 470 QR4 = 3.3 Q

Capacitors:C1 = 100 pF, 10 V, radialC2 = 1 nFC3 = 100 nF

Semiconductors:D1 = LED, 3 mm, redD2, D3 = LD271T1 = 2N222

Integrated Circuits:IC1 = 74HCTOO

Miscellaneous:K1 = 10 -way straight box

headerPCB Ref. 944106 (p. 110)Software Ref. 946199

OVERTONE OSCILLATOR

C6

IC1 = 74HCU04100n

!Cif 11 13 0

40p

10_CS ,12

5V

(p. 110)Design: W. Hacklander

and S. Furchtbar[944106]

edges of the signal becomesteeper, which gives the sig-nal more harmonics. The wantedovertone is selected by reso-nant circuit L1-05, amplifiedby ICI, and shaped into a propersquare wave by inverterICid.

In the prototype, a funda-mental mode crystal of 4.9 MHzwas used and this oscillated un-failingly on the third as well ason the fifth overtone. The cir-cuit can work on other fre-quencies, but the value of L1 maythen have to be altered by trialand error.

The circuit draws a currentof only a few milliamperes.

Design: K. M. Walraven[944084]


Please mention ELEKTOR ELECTRONICS when contacting advertisers

Modelmkr a synthesis toolkit forSpiceAge for Windows makes models accessible to all.This new model maker includes tools for creating OpAmps, Transformers, Attenuators and Bipolar transistors.Straight from a catalogue...The models are an accessible alternative to SPICE models which may also be used with SpiceAge. But because theinformation needed can be obtained straight out of a catalogue, you need never be kept waiting for a model again.

SpiceAge library Model CreatorElle Edit Zee reit Ea rameters Spice8g

(Untitled)

"P'n con n ectioes "V+""V-" in "in-". and

bias plan-R in ptint, v.2.00A offset 112:i fl v=20.0VCCS (lain -out:se n Se uut:ViR polet pl.Vint GS

Window Hop

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' Meta Mk, Vina

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Input hi as current nA

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Gg Out p 1:0Utv pa:out y=133Di steerl anlsteer ca.v- Input offset voltage, rollDiCCCS

strer2railcurrent

anzsonse Ca:steer-out.v4 Ut:V^

Input lettioce, MOInnoGg isms pl Nint p2v* v=1.0 autput too ishinte. OhmsGg lirn2 pl:sense p2,Vint v7-1.0

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is available inmodules starting from £15 +VAT to £135 + VAT and linkswith version 3 (and later) andlevel 3 (and higher) of SpiceAge

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Unnecessary complexityremoved...The models synthesized aresmaller than SPICE models yetthey are adequate for mostapplications and calculate manytimes faster. This is partlyachieved by exploiting specialpolynomial pragmas (notavailable to SPICE) that definethe limits of validity of non-linearfunctions. The OpAmp models,for example, break new groundin simulation technology byrepresenting many SPICE detailsyet calculating up to five timesfaster.MODELMKR

Produced and published by ELEKTOR Pashley Road GERMANY NETHERLANDSELECTRONICS (Publishing) TICEHURST TN5 7HE Elektor Verlag GmbH Elektuur B V

Telephone (0580) 200 657 (National ) Susterfeld Stralie 25 Peter Treckpoelstrant 2-4Editor- Len Seymoui or +44 580 200 657 (International) 5100 AACHEN 6191 VK BEEKTechnical Editor: J Busting Fax: (0580) 200 616 (National)

or +44580 200 616 (International)Editor E.J.A. Krempelsauer Editor, P H.M. Baggen

Editorial & Administrative Offices: GREECE POLANDPO Box 1414 Head Office Elektor EPE Elektor ElektronikDORCHESTER DT2 8YH P 0 Box 75 Kanskaki 14 02-777 Warszawa 130England 6190 AB BEEK 16673 Voula-ATHENA Skrytka Pocztowa 271Telephone- (0305) 250995 (National)or +44 305 250 995 (International)

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Fax. (0305) 250 996 (National ) Telex 56617 (elekt nI) HUNGARY PORTUGALor +44 305 250 996 (International ) Fax: +31 46 37 01 61 Elektor Elektronikai toly6rat Ferreira & Bento Lda

Managing Director. M M J Landman 1015 Budapest R.D Estefant, 32-1°U.K. Advertising Office' Editor-i n-Chief/Pnblisher Batthyany u 13 1000 LISBOA3 Crescent Terrace P E L Kersemakett Editor. Lakatos Andras Editor: F. Ferreira de AlmeidaCHELTENHAM GL50 3PETelephone: (0242)5 10 760 Distribution: INDIA SPAINFax. (0242)226 626 SEYMOUR Elektor Electronics PVT Ltd Resistor Electronica Aphcada

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8

SURROUND

1.he quality of reproduced sounddoes not result from a single prop-

erty of the audio signal, but fromthe sum total of several charac-teristics. It is not only the fre-quency response, the signal-to-noise ratio and distortion, butalso the breadth and depth ofthe stereo image that determinethe degree to which the repro-duced sound is experienced asfaithful. The breadth of the imageis, within certain limits, underthe listener's control (by placingthe loudspeakers in the desiredpositions). However, since the di-mensions of an average living roomand a concert hall are vastly dif-ferent, obtaining the right depth ofthe image is rather more difficultThere are now amplifiers on the mar-ket that provide 'surround sound', thatis, sound that appears to surround thelistener as it does in a concert hall. It isfortunately not necessary to buy one ofthese modern amplifiers, since the effectcan also be obtained with an existingamplifier as this article shows.

Design considerationsThe ultimate way of producing surroundsound is to make a four -channel record-ing and play this back via four separatechannels: two for speakers in front of thelistener and two for speakers behind him.Several manufacturers introduced thisquad system some years ago, but it wasnot a commercial success. This was mainlybecause of the high cost: the system re-quired a complex decoder, a second stereoamplifier and two extra speakers.

Then, there was a lot of experimenta-tion by manufacturers with matrix cir-cuits that produced a sort of quasi -quadsound from a normal stereo signal. Theresults were encouraging, but the asso-ciated costs were almost as high as thoseof the real quad systems.

906035-11

Design by T. Giesberts

Furthermore, there is the possibilityof driving two 'rear speakers' by an 'aftersound' apparatus. This produces inter-esting sounds, but requires quite a lot ofelectronic circuitry.

Many people create surround soundby connecting two extra loudspeakers,placed at the back of the listener, in par-allel with the existing front loudspeakers.

Fig. 1. An additional loudspeaker connected asshown will reproduce only the difference betweenthe two stereo channels. The difference is called

the L -R (or R -L) signal.

amplifieroutputs

L

R

However, this does not really createsurround sound, since the rear loud-speakers sound exactly the sameas the front ones.Finally, the so-called L -R signalmay be used to drive the rearloudspeaker(s). This yields verysatisfactory results and is rel-atively inexpensive to achieve.This technique is used in thecircuit described. Although thetechnique is not new, its pre-sent application, to the best ofour knowledge, is.

L -R signal

The L -R (or R -L) signal is exactlywhat its name indicates: the dif-

ference between the left-hand andright-hand channels. Note, however,

that only the signals that are exclusiveto the left-hand or the right-hand chan-nel are used. Signals that occur equallyin the left-hand and the right-hand chan-nel are not represented in the differencesignal.

As is well-known, a stereo signal belowabout 200 Hz has hardly any directivity.This does not matter, fortunately, becausethose low frequencies are spread more orless uniformly in all directions by the loud-speakers. In other words, at such low fre-quencies, the reproduced sound is al-ready 'surround sound'.

The situation is quite different at mid -and high frequencies, which are far moredirectional. As it so happens, it is justthese frequencies above 200 Hz that arecontained either in the left-hand or in the

S/a

front

100p/35V

r- - - 100p/35V

II

R

front I S/b

R1

P1

400/10W

220/10W

906035-13

L

rear

R

rear

Fig. 2. The final design. The effect of the loudspeakers at the rear of the lis-tener can be adjusted with P1 from `L -R' to 'double stereo'. If the rear

speakers are too loud, they can be moderated by resistors R.


SURROUND SOUND 9

stereoamplifier

L R

R R

rear front

L L

stereo - expander

906035-12

Fig. 3. Adding a small circuit and two (inexpensive) loudspeakers to an existingaudio system gives a surround sound system.

right-hand channel, not in both.It is clear from this that the difference

between the two channels contains justthe right information to drive one or twoloudspeakers at the rear of the listener.

Figure 1 shows that the L -R signal isobtained by connecting the extra loud-speaker between the two + loudspeakerterminals of the amplifier. The signalsbelow 200 Hz (which are identical in bothchannels) thus appear both in phase andin anti -phase across the third speakerand so cancel one another.

The setup in Fig. 1 could be used in apractical application, were it not that itis rather simplistic.

Final configuration

Figure 2 shows the final setup, which isbasically the same as that in Fig. 1, butthere are now four loudspeakers. It willbe seen that the additional (rear) speak-ers are connected in series across the two+ loudspeaker terminals of the amplifier.The extra loudspeakers can be switchedon and off with S1.

Since sound affects different peopledifferently, and it is, therefore, not cer-tain whether the pure L -R effect will pleaseeveryone, adaptation to individual tasteis made possible by P1. If this control isset to maximum resistance, the effect isalmost the same as if P1 were not there(that is, the loudspeakers reproduce only

the L -R signal). With P1 set to about thecentre of its travel, a sort of spatial stereois produced, while with the control at min-imum resistance the rear and front speak-ers are in parallel, which results in a sortof 'double stereo'. In the latter case, C1and C2 ensure that the (superfluous) lowfrequencies (below 200 Hz) are not re-produced by the rear speakers. Thesebipolar electrolytic capacitors also pre-vent any earth loops.

The potentiometer has a value of about40 f and a rating of 10 W. Shunt resistorR1 increases the load capacity to someextent and gives the control a somewhatrefined character. If a suitable poten-tiometer can not be obtained, a so-calledL -pad can be used (as was done in theprototype).

Suitable drive unitsAs has already been mentioned, the rearloudspeakers do not have to reproducelow frequencies below about 200 Hz. Thismeans that large enclosures are not nec-essary, because these are needed only forbass reproduction. In practice, it is foundthat frequencies above 5000 Hz also donot need to be reproduced by the rearloudspeakers. All this comes down to thefact that the rear speakers can be madefrom a good medium -frequency or wide -band drive unit in an enclosure with avolume of not more than 2-3 litres. Carradio speakers of the better variety areeminently suitable.

It is important, however, that the effi-ciency of the rear speakers is not too high,since, to prevent the effect becoming tooemphatic and unnatural, these speakersshould be only just audible. This is whyin Fig. 2 resistors R are shown in dashedlines: they are for use if the rear speak-ers need to be moderated to some extent.Their value must be determined empiri-cally, but will normally be 2.2-10 Q (10 W).

FinallyIt is advisable to fit the various compo-nents in a small case, which is connectedbetween amplifier and loudspeakers asshown in Fig. 3.

The sound produced by the modifiedsystem is a subjective matter. Tests withthe prototype showed that some peoplelike the sound with P1 at maximum re-sistance (L -R signal), whereas others wereinclined to go to the other extreme. Also,it appears that most people liked it bet-ter for pop music than for classical music.It may well be that only experimentingwith the values of the potentiometer andthe electrolytic capacitors gives a soundthat is just right for you. [906035]

Good quality medium -frequency or wide -band drive units are perfectly suitable.

ELEKTOR ELECTRONICS JulY/AUGUST 1994

10Please mention ELEKTOR ELECTRONICS when contact'ng advertisers

r:1F::Mks 961MMMMM

7440574 0.647460589 1.647460590 0947460592 1.197460593 1067400595 09274HC597 0.987400620 1.627400623 1.627460633 1.627460640 1.327400643 1.3274H0645 1.4074H0646 1.7774110648 1 777490651 1.477400652 1.477460658 4.49

44974H0664 A497460665 4 497460670 1 10

74110677 3 787460678 59174110680 3.83

4.21

5]00 87

74110690 1.6274/10691 1.627400692 1.73

7400693 1.737400696 1.487400697 1.247460698 1147400699 11474004002 0.3574004015 1.0774004016 0.4474404017 0.4274604020 0 5274904022 0 5674004024 0.5074004028 0.5874004040 0.5074404046 1 5474404049 0.48741104050 0.36746104051 0 6474404052 0.6874004053 0.687400405341.1074404060 0.4774604061 2.5274604066 0 467460406640 54741104067 4 7274604072 04574404075 0.3274604078 0.4674604094 0.6474404316 06874604351 0 8974604511 0.5574904514 1.3874604515 1 4274604518 0.804874604520 0.7274004534 POA74604538 0.6874604543 0.8174607001 1.01

74607032 10174607074 1 9974407292 1.1074607294 1 10

746040102 1 10

744040103 1.10744040105 1.40

74601245 0.5274607251 0 8674607253 0 5174007257 0.5474001'258 a72746C7259 07874007273 0.6874007280 0.9874007283 0.9074007297 0.8274007299 1.6474007354 1 2874607356 1 28

74607365 05474HCT366 aao74607367 05474007368 0.8074007373 0.4474007374 0.5074007377 0.6474FICT390 as874607393 0.6874607394 POA74607423 0.6274607533 14474607534 0.75741107540 0.6474607541 0.6474607563 0.9874007564 a-7874001573 0.64

74001574 0.6474007583 POA74007597 1.52740C-1640 1 3474607643 1 3474607646 240741107648 1 9074007651 1 6474407652 PO474401670 1.1074401673 1.64SPG865013674401688 1.10740014002 0.39746074015 1 13

749074016 0 52746074017 ase746074020 0.74740074024 0.6874NC-14040 0.70746014046 2 10

746014051 0 96740014052 0.96740074053 0.84744014059 2.24744014060 0.84744074066 0.66746074067 4.93746074075 am746074094 0.84746074316 0.687411074351 1.04746074510 1 54

746074511 0.94746014514 1.64

746074515 2.50740074516 1.61

74HG-74520 0907411014538 1.02

7411077007 039740017046 2.807400740101 2437440140103 1.487460140104 2.7174hI0140105 102

74F20 0.2874E17 0 2874F30 0.2874F32 01874F37 04174E38 0.44

74540 0.6674F51 04474E64 03274E74 D3074F85 1.4674E86 0.4174E109 0,5874E112 0.72745113 1.3074F114 1.3074E125 0.6074E126 0.9874F132 D5874F138 0.5874B139 0.55

74E148 D9474E151 0.58747153 0.8274E157 158747158 0.7074E160 1.107451604 1.1074E161 1.1074E162 1.2874E163 1.2874F164 1.2874E166 4.3274E166 4.4874F169 30074E174 0.76745175 0.76

74F1131 4.4874E182 1.8074E189 POA74F190 14074,91 3.20

74F192 3.2074F163 3.2074E114 1.4874E195 2.2474E219 4.3874E224 POA

747240 0.6274E241747244 0.6274E245 0.7274F251 0.6274F251A 0.6675,255 0.6274F257 0.627,2574 5.55

74E258 0.6274F259 POA74E260 0.78745259 7.45

74E273 084747280 0.6874E283 0.92747299 POA

74'32' 80474725° 1.50

747352 0.8474F353 1.1474E365 1.28

74E366 1.3074F367 1.4874F388 1.3074E373 0.6274F374 0.6274F377 0.92

74F378 5674E381 3.6874E385 POA74E395 POA74,399 5,5.74F412 POA74F413 POA74E432 POA74F521 1.2074E524 POA74F533 1 2074F534 1.2074E537 1.60747538 1.60747539 1.6074E540 1.9874E54174,549 3.95

74F544 POA74E545 POA74F547 POA74E573 2.9274E574 2.92747579 7.9874E604 4.8474E620 POA74E621 POA74E623 POA747646 5.1574E676 POA74E1321 3.9874E823 POA74F825 POA74F827 4 48

4 4874E843 4.93747845 POA74E1244 3 7574E1245 PO4

7440251 0.607440253 0.607440258 06074,40273 1 107440283 1 407440299 2067440373 0 947440374 0 927440377 0.987440521 POA7440540 0.987440541 0 987440573 1 387440574 1 387440646 POA7440648 PO4

78012 0.4878615 0 55

7905 0.2879054 0.32790554 0.60

7929 ass7912 0.307912A 0 36

7912E4 0.787915 0.3079187924

0.300.30

797124 0.357971240P 0 35

79M05 0 4279M054 04279M05FA 0.6579M12 0.50799124 060on, 77 o 50L,4317,4p 1 05

LM317LZ 0.55

LM338K 4.45

0478G01C 1.020479001C 1.0213041956 1.80

1383.077200V SIL 0.5764/ 100V SIL 1.608A/200V OIL 1.9635N1000 Sqr 2D8KBP01002 1.64

KBPC3502 2.98W005.14/50V 0 32W026-1 54 0402W02 0.40

2KB1310R/S1 0 662KBB2OR/SIL 0 70880C1500/Sq 03568001500017 0.60SK66008/604 PO45606008/604 POA

TT1 Output14pin DIL Layout

Sealed MetI4pin Pkg

Freq.= MHz1MHz £8.90 e0.

4,41151689.8304

10121516.10432, 190808,46204, 25 8 30MHz

' '152 '1'32. 32 768, 33.33,40 8 50, 66MHzPrice: £4.45 ea .

8"419'991919°19Crystal

Oscillators

EX0.3C SERIESSpin OIL Plastic

PackageFreq.. MHz12. 14.31818, 16,16.384,19.6600820MHzPrice: £3.92 ea.

16pin DIL PlasticPackage

Programmable for57 Diff.Frequency

SPG8640460 005 to 600kHz

0PG86408N0.0083 to 1MHz

SPG864001.10.0064 to 768If HzBaud Rate Generator

a000a3 1.100kHz

PX0.6000.005 to 600kHz

px0-10000.008310 1N1HzPrice: E R25 ea.

SPG8651BN0.00003 1 0 If0 1 0 HzCal. Tol. 5ppmprim 2 1080 04.

KM44C2564Z.10 695M5M4464P-15 4

MK41165-54 2.80MK45646-15 1.20NMC37646-15 1.60

UPD41464V12 420UPD41464C-15 4

UPD416C-2 340UPI:511603 3.65UPD4465-1 260

STATIC RAM

2114-37 3

626419,10 2

62647P-12 2

62256LP-12 49562256LP.10 495C0961164E3 5

CDM61174E3 585HM1-6116-5 4

HM3-6116-5 3.60HM6116LP-2 2.60HM61167P-3 2

1-1M6117LP-3 5751-1M612567P-10 7.934M6264ALP.12 195HM626440120 3956M6267P-36 5074M62812802-80

1855HM662041.12 15.80KM62256ALP-10 4.951051640-10i 2.409211447-2 3.40P211441-4 140PCD5101P 3.30UP243258AGU10L

8.33

UPD43256C-12 5

0P043640-15 470

UVPROMS

27C128-25 395270134A-15 395270258-15 3.95270258.25 3

D27256 5402705120.12 6

27010005-12 8.922704096-12 POA

HM270101G-20 9.800192701024HG10

16

FIN27C64FP.201 3H9270640.15 4.20

H5270640.20 4.2005462532P 4.504194827128G-25 4116482764G 3.8092716-151 3.50M5727326 4.409151.27648 3.30MBA/27064-20/21V

4.90mBm 270128-30 4.20MBM27C2513-30 510NMC2702560-25

4.95NM027C640.25 366W025166:45 4

1-MS27128a-25 4.60T96271611-45 480UPD27256821V 5.601116)2732/V21V 4

01:02702560-15 5800P027051212-15 6.96UPD27064D-25 495

EEPROMS

26064.25 9

28064-15 10

28025820 18

280256-15 19

280256-1500 28.50

X2816A0 5.10

X2816412-25 5.10

82864AP-35 12

24001 1

24002 210

24004 2

280044-20 44059011 1

93006 1.12

93006 1.28

93056 1

93066

MISC. MEMORIS

6341-1,1

AM2148.4500AM270281P010171307A -100P 1107713274.100P 1988414EMCM4027AC3682009568201264N68201536682S181AN69065041.9NMC93066P51017-1TBP18S0306TBP24S1ONTEIP24SAIONTC5501PTC55044P-2TC5516PL-15TC551741,2T055651.7-151NI54014J07

60

20

40

4040

.30

38

60

60

95

48

63

40

.

55

58

95

80954060

20

62

98

540

44

52

16

5844

98402095BO

OA49

80

09

40

45

9074.90

.15

50

4020.

20.

6040

TEL 081-471 9338 TLX 929709 VICOM G FAX 081-552 0946

DIGITAL INTEGRATED CIRCUIT SPECIALIST

4000 SERIES 45138 1.20 401601 043 74160 0.94 7470169 0.59 7470669 1 07

40008 0.1640000B 0 1840014 0.1640010 0 1874606594001013 0 2240029 0.184006E1 0.394007UB 0.20400813 0.4040094E 023400906 0.29746068240108 0.29746068440116 0.187460688401106 0.1840124E 0.16401213 0.20

4514B 1 12

45150 1.1245168 0.4445170 1.8445186 aao

45196 0.3645200 0.3645218 0.724522B 0.8645268 0.504527B 0.564528B 0 4945296 0 5745308 1 9245316 1 14

45320 0.44

4017137 0M84018137 078402007 D95402197 0.65402307 aaa402497 0.76402587 038402707 0.45402807 0.56401907 0.864040137 0 78404287 0 74404687 1 41

40470T 1 06404967 106405001 0 48

741614 0.9874163 12874164 1.2074165 1.5774166 1.0674174 15374175 1.2374180 12974184 PO474185 1.7674191 1.4174192 1.41

74193 1.6574221 1.23742592.927 1.46

7470170 PO474L0173 0.397470173A 0.447470174 0.367418175 0.3474L0181 1.8274L0182 2.057470183 2.057413169 2.607413190 0.4974L5191 0.497470192 0.4974L5193 0.487470194 0.5474181944 0.5774181954 0.57

7470670 0 7874L5673 POA7470674 17.607470682 2.627470683 POA7470684 3.8574L5685 7047470686 POA7470687 PO47470688 1.98374L5693 POA3.57954574L5794 POA74L0795 POADIODES74L0796 POA7470797 POA741_5848 POA

7,MtiEs74000 0 6874002 0.6874008 0 6874010 0 6874014 06874°2° 0.9'74030 (19874032 0.68

74042 3 20

74°48 320

740747A013

1.681.40

74076 1.9874C85 2 22

. 1 6074C9-74C93

74C9, 9840

740151 .94

80

74°157 2098

74C16,95

740221 98740240705

74024404

740979 .05

740374 05

740901 1-40740902 40740903 POA

1401 40

740908 2 4415 30

740912 16.80740914 1.24

740915 2.98740922 740740923 74074092, 9-98740926 96

740929 9.98

CRYSTALS

HC49( HC18/U)Freq.MHz1.843200 1.60

2.000000 1.66

2.457600 1.492766.00

1.10

3.686400 1.02

4000000 1.02

4.096000 1

A194304 1

4.433619 1.104.608000 1

4915200 1.20

5.000000/5 1.025.068800 1.105 2428805 888200 1.806.000000 1.02

6.1440006.4000006.5520006 553600 1.21

372"9.000000

8 8672305,3045010 0000010 6950011.0000012.0000013.6750014.0100014 31818/414 74960/S14 7456015 00000/516 0000016 00000/018 43200/S19 66080/S20.00000/S2211840/924.00000/S27 64800/5aa000cos32 00000/0

00001/0s _ 3444.

-U

0.2048000 3072001.000000

8432002 0000002.0971522.4576002.5000003 000000

HC49/U4H

3 2768003.579545

5 06890068643208 00000010 0000011 05920120000014 00000160000090,5000

24.00000

UM -1

8.0000008.19200010.0000011 0000012.20800160000017 7344718.0000020.0000021.0000024 00000

CRYSTALS MISC.

000550

16.1106,1204INDER

WATCH0.032768

0 gg

10

10

10

1.021041.40

0.78.0034

2010

9010.

0.922 401.640.85

10

10.

1002.

20

10

2060.68.82.20

6.991 401 68

8.236.993953614653.71

1 921 922 25

1061.58

2.251.491.142.252401.142.251.141 52

1 90

2.252.022.252.25

2.252 802.502.252252.80

559

L' c.

082

1629869 5 18.20163881 2541939974 655164001 0.04164002

I 64003 21640013

1N4007 2

1N4149164149 D.00164150 2

164448194728A 24164735A 0.24194736A 24164740A 0.2416474311 0.24

0.241647564 0.241952260 0.091N5232B 0 0916513413 00911,d,74 0.4819534913 0 48

0481653570 04011953650 0.4811953668 0.481653708 0.481553808 0.48165401 0.11165402 0.11

87A 1.5516825 2.7516825A 2.7519827 3.14100252 0.205082-2 0.665082-2810 1.4050822835 0.4444119AA144 0.72AA215 0 8

44217 0.584421804010 0.081BAV45

04)(16 0.06BB204 0.32BB212 84813134 058 0.2208809 0.608Y179 042BY261200 3.58BY261-200 3.98Bs/0213-100 0.99BY032 50 1.60

'00080500160 0.40MV1404MV209

1

042001

042020447

1

0490 0.1424018P6KE36AP6KE47A 0.880E053A 0402P02 70 0 06

ZENER DIODESMISC.

BZY9307V5 2.6642093015 2.66BZY93018R 2.66BZY93020 2.66020930240 2 66BZY93033R 266BZ7030120 0.40132061C9V2 0.09BZX61024V 009ZENER DIODES

400111W

24V to 75Vpace 6p each

ZENER DIODES

80091W2 4V to 200VPrme. fip each

ZENER DIODES

13 WATT2.70 to 200VPrice 10p each

ZENER DIODES3.0 WATT

7.50 to 270VPrice.40p eachZENER DIODES

5.0 WATT3.3V to 200VPrice 42p each

ZENER DIODESSTUD MOUNT

20 WATT7.5V to 75V94

PrIce f 4. ea

BRIDGERECTIFIERS

0-94/200000

4013B 0.204534B 2 8245368 1.22

405101 0.78405287 0.64

74273PO4742763.56

7470196 0.6874L0197 0.68

74HC SERIES

4014B 0.42401513 0.4240160 0.2440178 0.3874400440186 0.38740040440190 02640204E 0 36746008402013 0 3840214 0.40

453813 08045398 0624541B 0.524543B 0.574544B 2.1145470 1.684549B PO445510 1 6245530 2.37

405347 0.984060E37 0.84406607 D59406807 0.384069087 038407081 am,407187 0.384075137 0.38407767 0.38

74 1.38

74283 1.2674298 POA74365 0.7074387 1.0674393 2.9474403 POA74423 PO4

7470221 0.44107470224 20.247470240 0.4274015074L0241 0.427470242 0.427401547418243 0.427470244 0 42740164

'

7418245 0.427470247 0 44

.

744000 al97411002 0 19744003 0 24

0.190.24

744005 0.200.20

744010 0.29746011 0.20

40226 04040236 0.20

45540 6.0145550 0.48

407887 0.38408181 0.38

7445 SERIES 747S 248 0.687470249 0.99

740014 0.25741-1014A 0.34

402308 0 2340244E 027402413 0 32

'

40256 0.1940268 0.5440276 0.30401813 am40296 0.3540300 0.214031B 1.044032B 0 704033B 0 584034B 1 10

40356 0 3940366 25740376 1 27

40380 0 7840398 3.2240400 0.42740011240418 ac4041U6 0.3274001234042E1 0.32740012540436 D36

45564 0.4945578 1.8845588 2.1845606 1.51

4561B 1 7445626 5.1545660 1.1045680 5.1745698 3.04457218 0.704573P PO4458013 8.8445810 3 8545820 3 8545830 08645840 0 5745856 0494597CP 6.9045980 6.9045998 5.504720B POA47200 POA47238 POA

409387 0.45409491 0.95450887 2.054510131 1.02451107 1 35451267 0.684514137 2.20451607 1.02451807 1.18452007 1 18

452107 1.074522E17 1.22452807 0.88453400 POA453807 1.0545418T 1.05454387 1D2455587 POA455691 1.05458587 0.954010661 0.534024487 1.3540373131 2.34

747500 0 1874L001 0 18741802 0.18747503 0.18741804 0.2174L005 0.21747506 0.51747007 0.51747008 0.18741809 0.18741010 0.18741_011 0.18741_412 0.18741313 0.19744514 0.24741315 0.36744020 0.18744021 0.1874L022 0.18744024 0.5874L526 0.1874L327 0.18741828 0.24

7470251 0.327470253 0.447470256 0.78164744A7470257 0.34174702574 0 460.447409057470258 .74182584 0.487409077418259 3.487418260 0.2274,9117470266 0.32111535207479273 0.427474275 POA7405279 0.337413280 5.867413283 1457418290 0.4897470292 16.8674LS293 0.38NI74L0294 17.827470295 1.11

74182954 1.1574L0298 0.0879LS299 1.53

7411020 0.2274HC21 0.22741-1027 0.22791-1030 D.2274)1032 D.227411042 0.48740051 0.29746058 0.42740073 0.34740074 0.257411C75 0.407411078 0.40746077 0.51749085 0.48744086 0.28744093 0.4474190107 0.3974110109 0.35

0.4074110113 0.40

0.400.40

7400126 0.47

DC to DCConverters

TDK CE -0344 5.60

'MA 16'15 27.50IPL 5.010 23.40

1 Watt DC/DC5V input output

DIL 8 SIL by

8911/1114.1

''MA'S°5'5VNMA0509d9VNMA0512.12VNMA0515a15VPrice: E 8.55ea.

DC/DC Convertersby Computer

ProductsPM623 24 60PM671 2, 70PM672 26.70PM903 44.00PM951 46.50

74S SERIES

745 00 0.4402 0 44

74003 0.5174504 0.4274508 0.4274009 0.4874510 0.9074511 0.4874520 0.4874532 0.7874340 0.2574S51 0 3674564 03674074 0.9874086 1 12

740112 108740124 2 42745132 0 98740133 07374,1,4 1,95745135 0,0874,139 5.88

740140 0.7874,15, 126749157 1.72745163740174 0.92740175 1.35740182740189 2.10746195 2.40740240 1 007.46241 1 127407

244 1.7740257 1 22

740258 1.22740260 0.70746273 2.44740274 2.42740280 0.96746283 1.90745374 2.18746394 2.10740412 2.10740438 2.62745437 2.62745472 2.32745734 2.62

40446 0.3640456 0.944046B 0.42

4724B 1 904731VP 9 804737VP 18 28

74 SERIES747530 0.18740531 1.58747532 0.20

7413321 3.827475322 POA7418322A POA

7400131 0.5274110132 0.327440133 0.32

4047B 0.384048B 0.8240490 0.244049051 0.28

4050' 0.224051B 0.344052B 0.3340538 0.344054B 0.6840550 0.624056B 0 4840590 2 9840600 0 3840636 0 4240668 0 27

40672 1 8540680 0 204069UB 0 214070B 0.1140710 0.2040728 0.20

40730 0.2040758 0 1940766 0.4240770 92040786 02140816 0.1840828 0 2040858 0 2'40864 0.3840896 0.9840930 0.24

40240 03840950 0 7040960 110

42275 2.7540988 0.4040990 0.4241049 1.01

4162' 0.8541618 0.854174B 1.2741756 1.14

41940 1434409P 11.054410P 18 454411P 21 58441259 POA4412FL PO44412VP POA

04167 9044419P POA4429PB PO444337 POA

'14'13F PO44447P POA4458P POA

4469P 90544899 POA

44229 3.204495P 627

44979 11584499P 62445000 19 45450113 0.32

4738VP 18.5047500028.504752VP 29.254753VP POA475407 POA40085 1.9840097 0.6240098 0.6240100 2.4840101 POA40102 1.2040103 0.8840105 1.8240106 13040107 0.4240108 POA40109 1.2490110 1.0490114 2.6240116 12.0840117 1.8040147 1.2340160 0.5440161 0.5440162 0.5440163 0.5440174 0.3440175 0.4740181 POA40192 0.6240193 0.7440194 1.8240195 2.2440240 2.6240244 1.3640245 1.3640257 0.5440373 1.1040374 1.1045026 4.4245027 5.9945028 4.4945040 POA45041 POA45100 POA4510845109 POA45138 80845145 10.0445146 POA45151 19.5045152 21.4545156 15.6045157 14.3845158 11.9445159 POA45406 2.7345407 6.4745411 POA45414 15 6045428 POA45433 POA45440 POA45441 404

7400 0.367401 0.307402 0.347403 0.347404 0.407405 0.407406 0.6874084 0.727407 0.637407A 0.657408 0.377409 0.8774100.3574120.8474130.767 0.72741674407574170.487420 0.377425 0.5974287427 0.597430 0.357432 0.457437 0.597438 0.4974400.7774420.557445 1.2074461.537447 0.987447A 1.677451 0.577454 0.727470 0.547472 0.387473 0.597474 0.537475 0.677476 0.727480 1 267483 1.107485 0.587486 0.537490 0.767490A 1.347491 2.567492 0.67749257493 0.68741513874934749547497 5.2374104 0.6774107 0.6074110 POA74116 3.1074118 POA74119 POA74121 0.9874123 0.9474125 0.6774126 0.9874120 1.1974132 0.86

744033 0.2074L037 0.18740038 0.18744040 0.18741342 0.32741344 2.11

744547 0.55741348 0.54744049 1.38744051 0.19744554 0.19741355 0.32744073 0.40744073A 0.48744574 0.22744074A 0.24

0.2874L078 0.887443784 0.72744077 0.42741378 0.32740083 0.39740583A 0.39741385 0.38741886 0.27744590 040744591 PDA741392 POA741.093 0.44741.095 0.48741396 0.827405107 0.287413107A 0.38741.5109 0.287445109A 0.327470112 0.287445112A 0.347413113 0.327413113A 0.38744,5114 0.327413114A 0.367400122 0.397475123 0.313

7440125 0.2874451254 0.327449128 0.3274451264 0.367448132 0.297445133 0.16

0.387413137 0.987440138 0.317413139 0.347440145 0.667440147 2.887413148 0.837413151 0.327440153 0.327413154 1.607413155 0.3474131513 0.38743157 0.387440158 0.347413160 0.487405180A 0.54

7410323 3.247400347 2.867449348 1.9874L0352 1.68

7400353 1.687406383 2.107470364 POA7470365 13074703654 1347415366 0.367483664 0,42

5 29747 367 0.

7418367A 13474L0368 0.367418368A 1.7274LS373 0.3874LS374 0.497413375 0.427400377 0.667413378 0.987470379 0.9974703814 4.9874L0385 3.467440386 0.987475390 0.4674L0393 0.407470395 0.667475395A 0 947470396 POA741_5398 POA7470399 0.817470423 0.967445445 POA7413450 10.687440240741_3481A 7.167413485 3.827409467 7.7874L0468 7.787470469 6.1074184694 6.7074402517443490 2. 85

7405491A 12.827413502 POA7413540 0 8°

541 0.807470 .

743589 POA7410573 1.347413574 1.347405590 4.857400592 5.287413593 6.797445595 4.857413597 4.957413621 POA7400622 POA7413623 2.987405624 2.107415825 5.377405826 POA7405627 POA7470628 1.787470629 1.987403631 POA7473639 POA7413640 0.98

7490137 0.787400138 0.3474110139 0.317400141 0.817440147 0.817400148 0.557440151 0.407400153 0.407400154 0.9874001,5 0.697440157 0427440158 0 477440160 0647440161 0 427440162 0.647440163 0.427440164 14274110165 15574410166 0.887400173 0.7874110174 04274110175 0.3674110181 1.997440182 1597440190 0.6774110191 0.527460192 0.777440193 0.547440194 0.8774190195 0.4774190221 0.447400237 0.737490238 0.64

0.447440241 0.447440242 0.807440243 0.887440244 0.437440245 0.44

0.357440253 0.5274410257 0.477460258 0.737400259 0.857400266 0.3674F10273 a547490279 0517440280 0.897440283 0.587440298 0.737440299 1.097440323 1.587440354 0.557400356 a607490365 0.4174110366 0.527440367 1477460368 0527440373 1447440374 0.447460375 0.767400377 0.5174110386 0.297400390 0.387110393 0.41

74HC SERIESSURFACE MOON

740002M 0.32744003M 0.31746004M 0 327460004 0.32

0.32T.,,,,,,,,,nr 91-9-1,11 2 32746014M 0 36741-1020M 036741-1030M 03674HC32M 9 30741-1074A 0 9074#07,M 92471-10135WM 165741-1086M 0.3674110123AM 0.467460125M 0 46..._,....... -

441-2-T d1,i 2-427400138M 018741-1C139M 0 38741-10154WM 004

74,1C'',7M , 9,7460161M 0 48740C164M a4a74601,,M 0977460173M a4874FIC174M 0.30741-1C221AM 00,741-10240WM 055741-10244WM 0.55741-10245AW 06274160251M 042747841604347I1HC259M 2 6974HC273WM , 5,74HC367WM 9,374HC373WM 0.557460374WM ass74110390M 0.577400393M 0.5374110540WM 0.767460541WM 0.767460573WM 109741-10574VYM 0 84741-IC688WM 0 84741-1C4017M 0 48741104020M 0.48

74604040M 0.44740040469 1 68741104960m 04074807474604066W 0.8474604538M 0 70

RESISTORS

METAL FILM0.25W 1%

E24 SenesIOR to 1M 3p eachN 8 Min Ory. Order5pcs per value

METAL FILMPRECISION

0.25 WATT 0.1%

096 Series1006 to 255KPrice: E0.94 each

HIGH PRECISIONNON -INDUCTIVEWIRE WOUND

0.15 WATT OM%

Temp Coeff 3ppm100,500.1009,250R,105.100KPrice: E3.05 each

HIGH PRECISIONNON -INDUCTIVEWIRE WOUND

0.33 WATT 0.1%

TerrficCoeff.3porn10.59.105.200,50RPrice: £3.60 each

1000,120R, 2506.5009,1K, 2K 5K10K,20KPrice: £3.10 each

74FICT SERIES

7400100 0.227400701 0227400703 a257400704 0.227440706 0 22

7460110 0.227440711 0.227400714 o 26

'

7460120 0.2674110721 0.267490127 0.267440130 0 267460132 0.227440142 0.467400173 0.367400774 0.2674110175 0367460785 0.607460186 0.367460193 0 58741107107 0 4074607109 0.4274607112 0.4274401123 0.6474901125 0.5674601126 0.5674901132 0.5074601137 0.5274007138 0.32741501139 0.4574607147 0 68741107151 0 5274007153 0 4474607154 1.24

74401157 0.4474407158 0.4874601160 0.5674001161 0.5674601162 00474607163 0.5674007164 0 5274401165 05274607166 0 5274901173 0.52741107174 05274001175 a5274007181 3.2474407182 0 9674607190 0 6474607191 06474607192 09474607193 0.6474907194 1 13

74607195 1 16741101221 0.98741101237 0.9474401138 0.5174001240 0.5574607241 0.5574601242 0.7674401243 0.7674601244 057

VOLTAGEREGULATORS

78008AP 1 15

7805 0287805A 0 327805E8 0457806 0 287808 0287809 0.327812 0.287812A 0.3278120TC 0.327815 0.287818 0.287824 08878105 024787054 0 287137054CLP0.407870540Z 02878L12 0.2878712A 0.2678712902 0.3078715 0.28713724 0.2878756 1.107890, 0.3278M05A 0.3678M12 0.32784/112A 0.3678M134 06578M15 0.3278505 0.48

74HC SERIESCRYSTAL

OSC. MODULES744000 0.38744002 0.49744004 0.40

.744008 0 40744010 0.40744011 0.40744014 0.40744020 0.40744032 0.40

0407440109 0 647440112 0.817440138 0 657440139 0657440151 0687440153 0.65

0 81

7440158 0.657440163 0 807440169 1.987440174 0.657440175 000744C191 1.387440240 0.927440241 0.927440244 0927440245 1.10

MEMORIES

8pin DILPlastic pkg174 Output

4 Pins spaced atcorners of 8pinDILFreq.= MHz4, 4.9152, 8, 10,12. 16 8 20M07Price: E2.98 ea.24,32.40850M9zPrice E3.40 ea.

8pin DILSealed Metal

PackageHCMOS Output

13

Pins spaced atcOrners ot 8pinD17rreq ,,,,,z

3.6864413.109 2.16.20.24 32,40850MHzPrice 04 20 each

DYNAMIC RAM

4164-10 1 40

4164-12 .20

1 204164-151

41256-8 24041256-10 2 4041256-12 24041264-15 2 244146412 4 4541464.10 4 454464-10 2.80

4142566-70 3.90

440256AZ-10 6.954402560 5.00511000-135 8.45

0M48416AP-154 80

1-0448416AP-20 4 25

HY53025613-80

H15304641380395

HYB511000-85 845

CAPACITORSSURFACE MOUNT

Multilayer Ceramic63 VOLT

Case Size' 1206L2aW1.25mm

10pF.22pFoopF,47pF1000.229)8.33opF

4706F,1000172200p133oopF 4700,F

1000opF. 22000pF220002F

Price, 15p each

47000pF m0000pFPrice: 18p each

74F SERIES

74F00 0.281744015774F02 0.2874E04 0.2874E06 0.7474707 0.7474E08 0.2874E10 0.2874E11 0.2874E13 03274714 0.41

45028 03845036 0 3845048 1 12

4000 SERIESSURFACE

MOUNT

74145 1.1674150 1.874151

74L5161 0.467405161A 0.497405162 0.48

743641 0.9874136419 1.257446842 0.96

74110423 1647440521 0,957460533 0,95

45058 4 424506B 1.144506U 1.1445086 1 '445106 0.5445118 0444512B 0.38

4001 BT 0.32400207 032401107 0.32401!0670.32401287 032401367 0.454015131 0.84

74151A 0.8074153 0.9074154 2.1674155 0.8174157 0.7474158 15774159 398

7445162A 1.077405163 0.4274140183A 0.477400184 0.347413165 0.597470166 0597418168 0.75

74138429 POA7475643 POA7470644 POA7418645 1.127418645-1 1287470646 5.857418652 POA

7400534 0.897400540 0.8974110541 2.607400563 0.887440564 0.887460573 064741105734 072


mPlease mention ELEKTOR ELECTRONICS when contacting advertisers

MICROPROCESSOR& SUPPORT ICs

100114DEC 7.40100141DC 9806303XP 076

6321P 4.2063485CP32/8rn 19.9563603XP 10.076502 3986502A 5.408520P 4.40

801.0165-5 10 96HD146818AP 4.20NM -64026 6 16H03-6440-9 889HD3-6495-9 8.898044883 9.52HD465055P 9.85HD46802P 5.50806321P 4.20HD63485PS32 32.50HD63803XP 11.958068000.9 11.59

R65CO2P3 690R65CO2P4 895R65C102P2 685R65C21 P2 594

.R65C22P2 4805A680032p 5950868155-P 3.82SAB8259AP 159SA880C535-N 1187SA882C54-2-P 412SAB82C554-2-P 4.80SC80C451ccn64 13.60

AD578J5 POAAD581JH 8.92AD581KC5A/56409.97A258540 31 5660592CN POA5059450 16.80AD595AD 15 24AD648JN 3.40AD707JN 3.40AD711J5 2.344,0712J5 3.72A07245JN/KN POA

CM7170IPG 898CM720741PD 7.94CM7207IPD 7.94

M7209IPA 4.95M7211AMIPL 4.68M7211MIPL 4 68

CM7212AMIPL 445M7213I PD 698

CM7216AIJ1 29 32M7217AIPI 1232

CM7217BIJI 12.98M72171J1 12.98

LM386N-3 1.80LM386N-4 2.60LM387AN 590LM3885-1 425LM3895 340LM3900N 1.60LM3909N 2.64LM3914N 440LM3935 0.30LM393P 0.30LM394CN 5.98LM3999Z 2.76

NE592N 1.40

NE592N14 092NE602N/AN 298NE6044N 8.246E6056 880NE61245 2.87NJM4556D 1 20NJM45580)( 1.20NJ8821 DP 12.06OPO7CJ 360OPO7CN 095 95

OPO7CP 095

TL084CN/CP 0.84TL27L2CD/SMD 1 98TL497ACN 344TL507CP 4.03TL604CP 2.90TL7702ACP 2.04TL7705ACP 2.04TL7705CP 2.04TL7709ACP 2.04TL7770-SC 3.82TL783CKC 610TLC15411N 16.03

GRAPHIC LCDDISPLAYS

LM258X 6722LMG63800HGR 6444LM213X8 7744LM313XBN 106.20

INTELLIGENTLCD MODULES

LM087LN 33 10

I-M°91LN 53 04LM092LN 66 82LMO93LN 3]44

8C182 aoe8C1824 008801828 0.08BC182L 0.06BG182LB 0.08BC183 0 08BC183C 008BC183L 0.08BC 184 0 08BC184B 008BC184L 0 08BC184LC 008

BFW10 1 20BFX48 0.49BFX85 059BFX88 0 30BFX89 1 5913E0'50 0.3413M152 0.34BEY90 0.9285107 0.28BS170 0.38BS250 a5265860 0A8

6522 4.406522A 526 HD6845SP 6.92

11068452P 5.60SCN2661bc1n28 3.35SCN266100528 3.35

AD736JN 9.1240741KN 3.69

CM7218AIJI 668M721841P1 8.68

LM399H 7.85LM4250J 11.82

OPO7EP 310OP11GP 585

TLC2201CP 374TLC2274CN 285

ALPHANUMERICDOT MATRIX

BC21218 0.0880212A 0.08

60020 0.3860021 0.48

6551 443HD68821P 4.29 PAL16R4-150N 298 AD7523KN 9.80 M7218DIJI 8.68 LM555CN 028 OP177FP 3/1 TLC251CP 254 LCD MODULES BC212B 0.08 65061 1.85

6551A 4.43H13-7159-5 20.98 TL1 6C552F5 12 58 AD7537JN 34.98 CM7218EIJL 14.76 LM565C5 7 48 0P270P 2.89 TLC2652CP 4 92

LM016L 1569 BC212L 0.08 87136-800 1.1065CO2P2 5.8465CO2P3 699 1113-7159A-5 23.40

HM10422 14 30TMP7002NL-2 497TMP80854P-2 598

427537N POA807542446 36.35

M72241PL 11.92CM7226A1JL 37 20

LM7100H 280LM723CH 2.80

OP42F2 744OP77GP 2.07

TLC2654CP 484TLC271CP 084

LMO44L 34.70MEMO. Buias 0.08BC213 0.08

BUW48 49480211 1.60

65C102P2 7.0065022P2 4.806505161 3.8065051E-2 4.3868000P-10 89868000P-16 1820

082C106H 17 06M6402A1PL 10 20M64021PL 7.75M64031PL 10.80MS2600P-15 4.40

TMS3477NL 668TMS3700NSB 8.78TMS3702ANS 8.78TMS3835ANS 7.55TMS77C015L 10 74

AD7543JCWE PO4AD7578KN 46.15

AD8444N 9.70ADC0804LCN 680ADC804LCWM 12.10

CM72268IPL 32.52M72491DM POAM755518A 1.20M75551P4 0.84

CM75561PD 185

LM72305 0.70LM733CN 265LM741CJ-14 220LM741CN 045LM747CH 240

OPO7CN 0.95PCM63P-K 3580PM7548HP 18.206C41365 0.98RC4193N POA

TLC272CP 1.30TLC272CD/smcl 410TLC274CN 240TLC339CN 198TLC372CP 140

7510749 10275108A5 1.8475110AN 2.4675113N 3.5675114N 3.16

80213L 0.0880214 0.08BC214L 0.11

60231 0.08BC239 0.12

13UZ114 1.62832474 690180214 1.14

IRFZ20 1.77

J113 0.39J175 068

68000P-8 080

68008P-8 7.8568010P-12 POA6802P 3.40

NS82505 780N5825056 780M5M82C51AP 420M5M82C54P6 5.40

TMS9900NL 24.40TMS9901 NL 14.16TMS9902ANL 15.94TMS9914ANL 23.10

ADC0820CCN 22.40ADC0834CCN 10.80ADC84KG-10 38.98ADC908HP 18 42

M64031PL 12 92L272 2.74L272M 2 30L293B 3.64

LM747C9 0.90LM78GCP 2.40LM79GCP 2.40LM833N 2E2

RC4194N 2E58C4207GN 1.921604658 0.90RC4558P 0.60

TLC551 OP 3.68TLC555GP 0.65TLC556GN 1.58TLC7524CN

75115N 2.6975116N 6.2475121N 3.68751226 POA

80307 0.0860327 0.088C328 008BC337 0.08

J270 0 92JA101 0.48MBD501 1 10

6803AP pop.

6805E3E 10 98

MAB80314H12P 4.56MA680358L-6P 5.98

TMS9928ANL 7.40TMS9995JDL 69.85

ADDACCION PO4800201469 7 35

L293E 482L297/1 6.98

LS285A6 2.40LS288B 3.60

REFO1CP 3.338E001HP 3.33

TLE2061CP 2.20TLE2062CP 3.40

75136N 3.1075140P 3.76

60337-25 008BC4B9 0 24

MJE13070 1 10

MJE340 0.68MJE350

6810P P06 MC10103P 1.98 UA9636ACP 1.98 A00007CN 2.32 L2985 780 LS7210 440 REFO2CP 3.98 TLE2064C 5 345 75150P 1.64 80490 0.30 1.10MJE520 0E0

6821P 152 MC10115L 321 UA96374 1.98 AH0015CD 17.20 L4805CV 289 LT1006CN0 072 REFO3GP 369 TLE2161CP 2.42 751545 1.75 130516 022MPS3638

6840P 3.48

6844P 17.20

MC10115P 198MC146805E2P 9 18

UA9638CP 198UA9639CP 168

AY -3-1270 3.6087-5.1013 4.60

L487 3.76L4960 3.76

LT1010CT 4.58LT1028CN8 7.32

REF25Z 1 12

525604 PO4TMS3477NL 596TPIC2406NE 7.14

75155P 3.2575172ND 4.82

BC517 0.20BC546 055

0.18MPS406 0.12

6845P 4.86 MC68000P12/16 POA UM6845B 4.95 AY -5-1013A 5.98 L7028 3.24 LT1032CN 4.70 5551027 661 TPIC2802KV 9.42 751735 4.82 BC546A 0.05 MPSA13 0.12MPS463 0.32

6845SP 540 MC68010P10/12 PO4 UM9151 POA AV -3-1015D 3.60 LA6250 POA LT1070GT 9.14 SAA1043P 7.98 TPIC62595 3.28 751749 3.68 6054613 0.05MPSA92 024

68800P o04 MC6802P 2.47 UM9151-3 POA 63-5.1250 PO4 LA6358 PO4 LT1083CP 8.82 SAA3049P 9.92 TP1062735 3.28 751745G 4.82 60547 0.08MPSUO5 221

68A09P 4.30 MC6809P 6.78 UP88238 POA A3 -5 -3600 -PRO 9.96 LA6510 PO4 LT1086CT 2.90 SAA5025D 7.65 TP1065955 328 751755 2.60 1305476 0.08MTP8P08 280

68A21P 1,9 MC6821P 1.80 UPB8282C 498 856109 1 68 LA6520 PO4 LT1134CN POA 55560024 10.80 TSC426CPA POA 75176AP 2.18 805478 0.08

68A40P 2.56 MC68401, 505 UPB8284AD 4.98 6A6208 1.40 LC7132 2.98 LTC1052 7.97 5555605 3.40 TSC5000PE POA 75176BP 2.30 1305470 0.08 0C147 1 801

68A50P 298 MC6844P 18 40 UPB8286C 4.98 CA3046 0.51 LC7522 POA LTC1099CN 14.39 SED2000FV4 9.60 TSC7106CPL 881 75177P 488 130548 0.08 0C19 85

68009P 3.98 MC6845P 738 UPD70108C-10 9.10 CA3046(SMD) 0.89 LC7555 POA L7C485CN8 2 16 SFC2301ADC 6.78 TSC7116CPL 5.80 75178P 4.88 605486 0.08 0045 0650.80

68821P 1.99 MC6850P 3.35 UPD70108C-8 6.95 CA3054 0.94 LD111ACJ POA LTC490 4.40 SFC2741 DC 0.18 TSC7126CPL 5.80 75182N 206 BC549 0.08 0072

681340P 2.98 MC68705R3P 25.35 UPD70118C-10 12.90 CA3059 1 20 LF13508121 18.20 M5218AL POA SG3524N 4.60 TSC7660CPA 1.40 751835 296 BC549B 0.08 0078 0.80

8080A POA8085611-2 5.98

MC68A0OP 702MC68A09P 7.62

UPD70116C-8 9.20UPD71055C 4.38

05307857 2.42083079 0.88

LF311H 10.80LF347N 2.40

85220 POAM5238L POA

S17660CJ 1.92SL1452 675

310%8 4.92U20665 2.64

75188N 04875189AN 048

BC550 0.08BC550B 0.08OC81Z

0081M 0.800.92

8086 3.408086-2 3.90

MC8314P 6.60MCM681 OP 3.00

UPD7201AC 11.68UPD7201C 6.80

CA3080E 0.70CA3081 096

LF3515 0.98LF353N 086

M5298P POAM706B1 1.25

SL2364C 3.97SL3117B PO4

324006 550U42240PC 1.40

751895 0487543746 624

805500 0.08BC556 0.0800556A 008

PN3643 018TIC 1068 0.78TICP206D 0.61

800286-121p98 48.50 MCM68A100 5.35MM53200N 340

UPD765AC 5.42UPD765AC 5.42

CA3089E 1 22CA3094AE 2.16

LF355N 1 82LF356N 1.82

MAX134CPL 17.95MAX1232CNG POA

SL4860P 336SL490DP 2.80

UA709CP 0.85UA709PC 0.85

754500N 0.64754515 0.48 6055613 008 71031060 0.24

800286-81p10024.40800854 4.95 MM5816789 10.64 UPD7800-1 4.76 CA3096AE 3.48 LF357BN 4.98 MAX1232CPA 3.57 SL560CDP 3.00 34715HC 4.50 75452Bp 0.80 00557 0.08 TIP115 0.55800854-2 5.940.088118-5CH 7.60

MM5817449 14.80MM58274CN 918

UPD80C39HC 8.42UPD8155H0 5.84

0A3096CE 1 82CA3097E 260

LF357M/SMD 498LF357N 120

MAX1259CPE POAMA0162ACNG POA

SL6270CDP 330SL6700CDP 547

U47230P 0.70UA733CJ 2.98

75452N 0 8075453BP 1 14

805576 0.08

00558

TIP121 0.68TIP145 1.37

93L34DC 7 08

AM251.52588P 2.68

MSM5832RS 339MSM8003565 4.90

UPD8251AFC 409UP08253G-2 3.32

CA3120E PO405313087 1920

LF398N 3.98LF411CN 1.48

MAX2324CPE 4.84MAX232CPE 280

SN5281CN PO4SN5545113JG 2.85

U4741MP 0.80UA741TC 0.28

75454BP 22075462N 1.98

BC558A 0.08BC558B 0.08

TIP2955 0.88TIP30 0.48

AM25LS2589P 2 68 MSM80C39/SMD 6.45 UPD8253G-5 3.32 CA3130E 110 LF412CN .98 MAX232EWE 380 SOC12 0.20 U4748CP 0.36 75462P 1.98 EIC559A 008 7IP3055 088

AM2602PC 2.30 M0M800854 3.95 0P08286C POA CA3140AE 1.34 LF441CN .75 MAX2325 2.80 5P164800 5.53 8A7481C 0.52 754639 3.40 BC559101 0.08 TIP31A 0.38

AM26LS31DC 2.30 MSM80C854-2 5.98 UPD8741AD 12.52 CA3140E 048 LF442CN 99 MAX280CPA 6 94 SP4534 POA UA7700OUIC POA 7546BN 3.53 805605 0 08 TIP32A 0 40

AM26LS31PC 1.26 MSM80C86 7.60 UPD8749HC 13.98 053146E 0.90 LF444CN .71 MAX452CPA 538 SP4740DP 4.46 U4798TC 3.80 75469N 8C560C 008 TI P47 0.80

AM27S191AOC 10 20 MSME1055 4.60 V20-10MHz 9.10 053160E 1.25

CA3240E 1.15LH0002CN 1

LH0032CG 3

.60 MAX627CPA 2.98MAX660CPA 5.72

5P8629DP 3.44SP86600P 4.96

UC55800A 7547051 BC184C 0.08BCY71 0.22

V2751.A10 B92V50104613 0.92

AM27S281PC 620AM2964B0C 12.36AM29650C 6.36

MSM82C51A 3.58MSM82C53-2 3.98MSM82C535 3.56

520-8MHz 6.96V30-10MHz 12.90V30-8MHz 9.20

CA3240E1 2.72CA3260E 1.68

LM101AHLM1OCN

.40

.86

.24M430690ACPA 658MAX693CPE 6 68

STK414111 5.20STK5151 PO4

UCN5801A 2.6075471P30529815UDN2982A 2

3.7675472P 22875473P 3.76

1310131 0..88130135 0.44

VN66AFD 1.40VN90413 2 96

AM2966PC 3.98 M5M82054-2 4.20 V61C300 7.80 CA3280AE 5.94 LM111H .60 MAX694CPA 570 ST6417111 7.10 UDN6118A 1.65 75474P 298 602415 098 VP0104-N3 092VP0104N2 0.98

AM298260C 3.34AM685DL 9.82

MSM82C594-2 3.88MSM82C84A 3.30

VC010658 8.60Z0800110PSC 18.90

CA3280E 3.42CA5550E 0.20

LM136005LM13700N

.60

.60

MA)(697CPE 6.59MAX7219CNG 7.15

07444181-V 9.60ST6419211 7.80

UGN3501M POAULN2001AN 0.44

75477N 29875491N 2 46

B0242C 0.5260243 0.50 VP0104N3 092

AM8238PC 5.60 MSM82C844-2 3.60 Z0868112PSC 3.20 CA7410E 518 LM13915 AO MAX8211CPA 228 57444277SL 10.80 ULN2002A 0.44 75ALS176P 477 BD5' e 0.78 ZTX212 0.18

AM9050CDC 4.95 MSM82C88 12.60 Z180-MPU POA CS5503-KD PO4 LM139J .60 MA)(901BCPE POA TA7215P 7.20 ULN2003AN 0.44 75ALS192N 514 B0675 0.52 27X237 0.26

AM9050CPC 460 N80C286-10/p1 24.50 Z80018 -CPU 11.96 08792513 POA LM1458N .82 MC1377P 4.93 TA7256P 050 ULN2004AN 1.40 75AL5193J 5.14 B0676 0.52 ZTX300 0.18

AM9102CPC 2.82 N80C286-12/pil 29.54 Z8018008VSC 8.25 0169Cd PO4 LM1496N .95 MC1413P 0.74 TA7368P POA ULN2024A 1.40 75C115461 4.55 B0679 0,54 ZTX313L 028

589114808 906 N1801.286-8C2EN 36 20 Z804 -CPU 125 DACOBOOLCN 4.10 LM18015 .92 MC14411P 11 38 TA7658P 1.20 UL52032A 1.40 75014069 394 80680 056 ZTX320 0.38

589551 PC 9.66 N82355 3.68N82645 3.68

Z804-CPU/CMOS 2.98Z80A-CTC 1.98

DAC0832LCN 1067DACO8CP 3.48

LM1881NLM1889N

8040

MC14416L 17.60MC14495P 4.82

TA78005AP 0.48TA8200AH POA

ULN2803AN auUM5100 POA

7501859 3.98 BD743C 1.90

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AM96LO2PC 3.355825126AS! 3.25 280A -DART 498 DACO8EP 5.06 LM18945 16. MC145408P 2 10 TA841 OK 2.80 UM5101 3.80

75C11385 21175C169A0 211 BDX67130X678 278 IC SOCKETS

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C1164/0MD 4.98 NS16450N 4.68 Z804-1°10 1.25 DAC1222LCN 20 40 LM239N 90 MC1455P1 0.60 TA8659AN POA X1611060 9.95 75C1895 211 SF195-C 008

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MIDI SWELL PEDAL

Design by D. Doepfer

Microcontrollers are intended to make life simpler (?!) and theequipment in which they are used more versatile. The swell

pedal presented here uses one and, therefore,can beconfigured rapidly for a number of functions. Musicians will

almost certainly like the design, because it enables astandard swell pedal to be provided with a number of new

features for only a small outlay.

Most inexpensive swell pedals on themarket are no more than a poten-

tiometer in a box. The potentiometer's re-sistance varies according to the degreewith which the pedal is depressed. Thepresent design is, strictly speaking, aninterface between a MIDI system and theexisting swell pedal, that is, it providescommunication between the pedal andthe instrument via MIDI codes. This notonly leaves the quality of the sound un-affected, but it also offers new facilities.For instance, the volume can be influ-enced; the timbre can be adapted; thekeying dynamics can be altered and sev-eral MIDI channels can be driven simul-taneously. Selecting and setting up of thewanted functions and channels remainspossible with the use of a standard MIDIkeyboard.

Circuit descriptionA versatile design as outlined above ispossible only with the use of a micro -controller, for which a Type 80C32 waschosen-see Fig. 1. Since within a MIDIsystem all communication takes place at

a baud rate of 32 kbit 5-1, a clock fre-quency of 12 MHz is used, since the wantedbaud rate is easily derived from this.

The microcontroller, IC1, is linked toEPROM IC3 via busbuffer IC2. The appli-cation software is stored in IC3. The bufferis needed to sort out the multiplexed ad-dress and data bus.

The level of the ALE (Address LatchEnable) line shows whether the bus car-ries address signals or data. The ALE sig-nal ensures that the address informa-tion is stored in IC2 at its trailing edge.

The PSEN signal instructs the EPROMto place the data of the selected addresson to the databus. After a reset, the con-troller automatically executes the pro-gram in the EPROM.

A discrete 7 -bit digital -to -analogue(D -A) converter based on the P1 portsprocesses the position of the swell pedal(potentiometer P2). The 7 -bit width en-ables the digitization of 128 positions ofthe pedal. This number corresponds tothat for the coding in the MIDI protocol.

The output signal of the D -A converter,available across C4, is compared by IC4with the direct voltage at the wiper of P2.

When the output level of IC4 is high, theD -A signal is lower than the potential atthe wiper of the analogue swell pedal. Thisresults in the microcontroller raising thelevel of the D -A signal, by successive ap-proximation, until the output of IC4 goeslow.

When the comparator changes state,the position of the swell pedal is knownand available in digital form. The controlrange of the D -A converter can be alteredto some extent with P1 to ensure that the128 steps fall within the (resistance)range of P2. This arrangement was foundnecessary because in certain circum-stances P2 did not provide the maximumlevel of 5 V at the output. If it is found,however, that it does, P1 may be omitted.

The control program is stored in IC7,a 2 kbit EEPROM. The programming ofthis device will be reverted to. For now, itis sufficient to know that this circuit hasa 'teach' mode. In this mode, a choice canbe made for the function of the pedal andthe MIDI channel in which communica-tion takes place. These choices are storedin IC7 and retained there until new onesare made. The IC has an 12C interface andcommunicates with the microcontrollervia two I/O lines, P3.6 and P3.7. Theselines simulate the communication chan-nels of the I2C interface.

The address lines of IC7, A°, Al and A2,are linked to ground, so that the memoryis set to its base address, Ao(H).

As already mentioned, IC7 is programmedin its teach mode. This mode is selectedwhen Si is closed, which is indicated bythe flashing of D1.

The MIDI input is via K1, and the MIDIoutput via K2. The input is electrically iso-lated from the remainder of the circuitby optoisolator IC6. Such an isolator ispresent in all MIDI equipment to makeit possible for a current loop to be usedfor MIDI communication.

The incoming 5 V power supply is sta-bilized by IC5. Diode D3 protects the cir-cuit against wrong polarity of the supplylines.

ConstructionThe circuit is best built on the double -sided printed -circuit board shown in Fig. 2.The small size of the board allows it to bebuilt into most swell pedals.

Start by soldering all the passive com-ponents into place. Fit IC3 into an ap-propriate socket (this makes updating ofthe application program at a later date asimple matter). All other ICs can be sol-dered directly on to the board, althoughsockets are to be preferred.

When the board is populated (includ-ing the programmed EPROM), the inter-face is ready for use.

Use a mains adaptor with an outputof not less than 8 V. Since the currentdrain should not exceed 300 mA in anycircumstances, most mains adaptors aresuitable.


MIDI SWELL PEDAL Ng

A small modification needs to be madebefore the swell pedal can be connectedto the interface. Normally, a swell pedalhas two connections (it behaves like avariable resistor), but for the present cir-cuit three connections are required. Openthe pedal, solder three wires to the po-tentiometer, and close the pedal again.

If a pedal with an LDR (light -depen-dent resistor) is used, open the pedal andsolder a 5-25 kS1 resistor in series withthe LDR. Solder the +ve line to the re-sistor, ground to the LDR, and use thejunction of the resistor and LDR as the`wiper' of a potentiometer. Close the pedalagain.

Connect the interface to the MIDI sys-tem via two MIDI cables and switch onthe equipment. If all is well, the LED shouldlight twice, the pedal should be active,and MIDI volume commands (MIDI con-troller #7) should be sent when the pedalis moved.

The range of the pedal should be from0 to 127; if it is not, adjust P1 accord-ingly (which may be done by ear).

If the swell pedal can not be turned tozero, the position of P2 must be altereduntil an output voltage of 0 V is obtained.Normally, it will be found possible to adaptthe position of the potmeter or the spin-dle to which it is linked: in practice, it isa matter of a few millimetres at most.

Usage

The interface can be configured entirelyto individual requirements. After it hasbeen connected to the system and themains supply, and this is switched on, itis in the default mode. This means thatthe volume commands are sent via MIDIchannel 1. When the pedal is depressed,the corresponding commands are sentvia the interface. The value at which thishappens varies between 0 and 127. If thepedal emulates a pitch bender, the codevaries between 64 and 127 or between 64and 0. The pedal can also be used to adaptthe velocity and thus the dynamic rangeof the incoming MIDI data. Note that inthis mode data appear at the output onlyif there are data applied to the input.

If the MIDI equipment does not reactto the commands, check the selected chan-nel and ascertain that the polarity of theMIDI cables is correct. Operation of theinterface can be checked by pressing pushbutton switch S1, whereupon the LEDshould begin to flash.

It is also possible that the expanderused does not react to the volume com-mand. There are some expanders, suchas the Yamaha EMT 10, which do not rec-ognize this command. There are also ex-panders that use the command only forgenerating an after -tone. This means that

5V

the volume of an already generated tonecan not be influenced.

After receiving a program change com-mand, the interface always sends an in-struction containing the volume setting.This is necessary because some expandersswitch to maximum volume (127) uponreceiving a program change command.

Teach modeThe default mode, at which the pedalfunctions as MIDI controller #7 and com-mands are sent in MIDI channel 1, canbe altered by setting the interface to theteach mode. This is indicated by the flash-ing of the LED. The teach mode is usedto select the MIDI channel at which theinterface is required to work. This canbe done with a standard MIDI key-board when the interface input is linkedto the MIDI output of the keyboard.

Key36 (C)37 (C#)38 (D)39 (D#)40 (E)41 (F)42 (F#)43 (G)44 (G#)

P2

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P1.3

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P1.6

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24

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26

27

28

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Fig. 1. Circuit diagram of the interface for the MIDI swell pedal.


14 MUSIC & ELECTRONICS

45464748495051

6061626364656667686970717273

(A)

(A#)(B)(C)

(C#)(D)(D#)

(C)

(C#)(D)(D#)(E)(F)(F#)(G)(G#)(A)

(A#)(B)(C)(C#)

1

10 on11 on12 on13 on14 on15 on16 on

74 (D)75 (D#)

15 off flashing and the setting is stored in the16 off EEPROM until the teach mode is selected

again.The wanted command is sent by de-

pressing the relevant key on the key-board when the LED flashes. The dy-namic range properties sent in the MIDIcommand are not used by the interface.

1 off To keep the system easy to use, the note2 off C is chosen as the starting point for both3 off the switch on and the switch off corn -4 off mands.5 off It may of course happen that it is no6 off longer clear which of the channels are7 off active. In that case, there is only one so -8 off lution: switch off all channels and switch9 off on the wanted ones.

10 off After all wanted channels have been11 off selected, the teach mode is discontin-12 off ued when the push button on the inter -13 off face is pressed or when a program change14 off command is sent. The LED then stops

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105

;;

Other functionsSo far, the interface has been used tomodify a simple swell pedal into a mod-ern digital pedal to influence the volumeof the sounds. However, this is the stan-dard configuration: the interface offersother functions, such as velocity con-trol, after -touch or pitch bending.

ProgramNumber

1

23456

0 0 0 00 01Iwo micap cos(E-a mooge saopalsapace

o Q oarpotspace

Function

volume (controller #7)modulation (controller #1)portamento (controller #2)free choiceafter -touch (mono)pitch bend (entire range)

00

CM

00

O

0 0000

00 00

O

00000 cs la0000 la0 0 a0 0 0o o o "0 0O ofo o a a

000

O0

0 0O 000

00

ee

OO

oo 0

Fig. 2. The double -side printed -circuit board for the interface.


MIDI SWELL PEDAL 121

Call us now! We have the widest range ofcomponents available - At competitive prices!

CABLES CAPACITORS VIDEO HEADS

II I/

a.SPEAKERS

'1111le I

CONNECTORS SEMICONDUCTORS

I so :I

IRSA

7 pitch bend (positive)8 pitch bend (negative)9 velocity (touch dynamics)16 data speed

The interface is set to the previously de-fined controller numbers (#7 for volume;#1 for modulation; #2 for portamento)with the aid of program change com-mands 1, 2 and 3. A different controllernumber, if desired, can be set with pro-gram change command 4. With this com-mand, the interface adopts the controllernumber that was sent prior to the pro-gram change command. If, therefore, arandom controller number is desired, aMIDI controller command with that num-ber must be sent to the interface followedby program change command 4.

Program numbers 6, 7 and 8 may beused to imitate the various functions ofa pitch bender. Program number 6 pro-vides the range 0-127 with a neutral zonearound number 64: this simplifies thesetting of a neutral position. Programnumbers 7 and 8 simulate the positiveswing (64-127) and negative swing(64-0) of the pitch bender respectively.

The velocity function is a special onethat can be selected with number 9. Ifthen the pedal is depressed, it will nolonger cause MIDI data to be sent butdata that are being sent on the selectedMIDI channel to be adapted. The veloc-ity value contained in the MIDI commandis then adapted in line with the positionof the swell pedal. In the highest posi-tion of the pedal, the velocity value ismultiplied by 1, that is, it remains un-changed. The more the pedal is depressed,the smaller the factor with which thevalue will be multiplied. This increasesthe touch dynamic range.

This function was found useful be-cause there are MIDI instruments on themarket (expanders, keyboards, and others)that do not support the MIDI volumecommand (controller #7). In spite of thatdeficiency, the interface makes it possi-

ble to influence the sound of such in-struments. Also, keyboards that have notouch -sensitive keys may benefit fromthis function.

Note that the velocity function affectsonly the dynamic range of the note -oncommand; the note -off instruction re-tains its previous value.

Program number 16 influences thefrequency (speed) at which commandsare transferred through the interface.This function is provided because someinstruments, owing to less -than -perfectsoftware, suffer from timing errors if thefrequency is too high.

With the interface in the teach mode,it will be noticed that the frequency withwhich the LED flashes changes when thepedal is depressed. The flashing rate isan indication of the speed at which thecommands are transferred. Sometimesit may appear as if the LED lights con-tinuously. This is because the humaneye can not follow the high frequencyflashing.

Set the frequency with the pedal andgive a program change command 16.This setting is stored in the EEPROM.The default frequency is the lowest: about15 Hz. This means that 15 commandsare sent every second. The precise valueof the highest positions depends on sev-eral factors. Since each MIDI volumecommand consists of three instructions,45 bytes per second are sent at the low-est frequency. If 16 channels are active,16x45=720 bytes per second are sent.Therefore, the ultimate data rate dependson the sampling frequency and on thenumber of active MIDI channels. Themaximum sampling frequency is, there-fore, limited by the number of activechannels. The optimum setting can befound by trial and error only.

Parts list

Resistors:R1 = 10 kS/

R2 = 390 f2R3= 698 kf2R4 = 301 kf2R5 = 2.2 kf2R6, R7, R8 = 220 f2R9, R10, R12 = 100 Ic52R11 = 200 k52R13 = 49.9 kf2R14 = 24.9 k52R15 = 12.4 kf2R16 = 8x1 kf2 arrayP1 = 50 li52 (47 kf2) preset potmeterP2 = 10 kf2 (potmeter in pedal)

Capacitors:C1 = 10 pF, 16 VC2, C3 = 22 pFC4 = 100 pFC5= 2.2 pF, 16VC6 = 100 pF, 25 VC7 = 22 pF, 16VC8 -C11 = 100 nF

Semiconductors:D1 = LEDD2 = 1N4148D3 = 1N4001

Integrated circuits:ICI = 80C32IC2 = 74HC573IC3 = 27C64 (p. 110 - Ref. 946635-1)IC4 = TLC271IC5 = 7805IC6 = CNY17IC7 = 24CO2

Miscellaneous:K1, K2 = 5 -pin DIN socket, 180°Si = push-button switch with single -pole

make contactS2 = single -pole, single -throw switchX1 = 12 MHz crystalPCB Ref. 940019 (p. 110)

(940019]


16Please mention ELEKTOR ELECTRONICS when contacting advertisers

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Scrambled output from this transmitter cannot be monitored without the SCDM decoderconnected to the receiver. Size 20mm x 67mm. 9V operation. 1000m range £22.95

SCLX Subcarrier Telephone TransmitterConnects to telephone line anywhere, requires no batteries. Output scrambled sorequires SCDM connected to receiver. Size 32mm x 37mm. 1000m range £23.95

SCOM Subcarrier Decoder Unit for SCRXConnects to receiver earphone socket and provides decoded audio output toheadphones. Size 32mm x 70mm. 9-12V operation £22.95

ATR2 Micro Size Telephone Recording interfaceConnects between telephone line (anywhere) and cassette recorder. Switches tapeautomatically as phone is used. All conversations recorded. Size 16mm x 32mm.Powered from line £13.45

*** Specials ***IILTX/BLIU( Radio Coat* SwitchRemote control anything around your home or garden, outside lights, alarms, pagingsystem etc. System consists of a small VHF transmitter with digital encoder and receiverunit with decoder and relay output, momentary or alternate, 8 -way dil switches on bothboards set your own unique security code. TX size 45mm x 45mm. RX size 35mm x90mm. Both 9V operation. Range up to 200m.Complete System (2 kits) £50.95Individual Transmitter DLTX £19.95Individual Receiver DLRX £37.95

0M-1 WI Micro BroadcasterNot technically a surveillance device but a great idea! Connects to the headphone outputof your Hi-Fi, tape or CD and transmits Hi-Fi quality to a nearby radio. Listen to yourfavourite music anywhere around the house, garden, in the bath or in the garage andyou don't have to put up with the DJ's choice and boring waffle. Size 27mm x 60mm.9V operation. 250m range £20.95

9

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TLX700 Micro -miniature Telephone TransmitterBest-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble thanUTLX. Connects to line (anywhere) and switches on and off with phone use. Allconversations transmitted. Powered from line. 1000m range £13.45

STLX High-performance Telephone TransmitterHigh performance transmitter with buffered output stage providing excellent stabilityand performance. Connects to line (anywhere) and switches on and off with phone use.All conversations transmitted. Powered from line. Size 22mm x 22mm.1500m range £16.45

TKX900 Signalling/Tracking TransmitterTransmits a continous stream of audio pulses with variable tone and rate. Ideal forsignalling or tracking purposes. High power output giving range up to 3000m. Size25mm x 63mm. 9V operation £22.95

CD400 Pocket Bug Detector/LocatorLED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as youapproach signal. Gain control allows pinpointing of source. Size 45mm x 54mm. 9Voperation £30.95

CD600 Professional Bug Detector/LocatorMulticolour readout of signal strength with variable rate bleeper and variable sensitivityused to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode todistinguish between localised bug transmission and normal legitimate signals such aspagers, cellular, taxis etc. Size 70mm x 100mm. 9V operation £50.95

QTX180 Crystal Controlled Room TransmitterNarrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz andrequires the use of a scanner receiver or our CIRX180 kit (see catlogue). Size 20mm x67mm. 9V operation. 1000m range £40.95

QLX180 Crystal Cointrolled Telephone TransmitterAs per QTX180 but connects to telephone line to monitor both sides of conversations.20mm x 67mm. 9V operation. 1000m range £40.95

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QRX180 Crystal Controlled FM ReceiverFor monitoring any of the '0' range transmitters. High sensitivity unit. All RF sectionsupplied as a pre -built and aligned module ready to connect on board so no difficultysetting up. Outpt to headphones. 60mm x 75mm. 9V operation £60.95

A build-up service is available on all our kits if required.UK customers please send cheques, POs or registered cash. Please add£1.50 per order for P&P. Goods despatched ASAP allowing for chequeclearance. Overseas customers send sterling bank draft and add £5.00 perorder for shipment. Credit card orders welcomed on 0827 714476.

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Advanced 3 -Way Stereo Active Cross -Over, housed in a 19 x 1U case Each channel has three level controlsbass, mid & top. The removable front fascia allows access to the programmable DIL switches to adjust thecross -over frequency, Bass -Mid 250/500/800Hz, Mid -Top 1 8/3/5KHz all at 24dB per octave Bass invert switcheson each bass channel. Nominal 775mV input/output. Fully compatible with OMP rack amplifier and modules

Price £117.44 + £5.00 P&P,1-114:14,1*]1-1KIJ, 1:1-1 .11<tSTEREO DISCO MIXER with 2 x 7 bandL & R graphic equalisers with bar graphLED Vu meters. MANY OUTSTANDINGFEATURES:- including Echo with repeat &speed control, DJ Mic with talk -overswitch, 6 Channels with individual fadersplus cross fade, Cue Headphone Monitor. 8Sound Effects. Useful combination of thefollowing inputs:- 3 turntables (meg), 3miss, 5 Line for CD, Tape, Video etc.

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4

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18

PIC® PROGRAMMING COURSEPART INTRODUCTION

Large designs traditionally required complex and extensive digitalcircuits are now simple to realize by virtue of the small, powerful, PIC®microcontroller developed by Microchip Technology. The mainapplication areas of PICs are automotive electronics, machinecontrols, and test and measurement equipment. Particularly logiccircuits based on time or count pulses often become quite complex ifordinary logic components are used. A single PIC however can do thesame at a smaller outlay, offering a staggering degree of circuitsimplification. Microchip's PIC16C5x family is a class of its own inmicrocontroller land, and forms the subject of the present shortcourse. Apart from programming aspects, the hardware will alsoreceive some attention.

PIC = Peripheral Interface Controller, a registered trademark of Microchip Technology, Inc.

By our editorial staff.

Source: Microchip Data Book, Microchip Technology Inc.

THE PIC16C5x family is aproduct of Microchip

Technology Inc., ofChandler, Arizona, in theUnited States of America.The family consists of a se-ries of CMOS microcon-trollers featuring internaldata and program memories.The program memory has aword size of 12 bits, which isobviously more than that ofcompetitive 8 -bit controllers.As indicated in the 'portraitof a family' inset in our ear-lier article describing a PICprogrammer (Ref. 1), the sizeof the program and datamemory depends on the typeof controller.

The fully static design ofthe microcontrollers allowsthe clock frequency to be re-duced to d.c. The advantageof the 12 -bit word size isthat most instructions re-quire only one 'word', inclu-sive of their operand. Thecontroller has 33 easy to re-member instructions. Withthe exception of jumps (or`branches'), these take onemachine cycle. Conse-quently, Microchip adver-tises the PIC16C5x as adevice which employs aRISC -like architecture (RISC

CERDIPPDIP, SOIC,

WindowPDIP, SOIC,

CERDIP Window

-*-1P. RA2 118,

13

RAI RTCC 28 MCLR fRA3 2 RAO -P-P- Voo 27 OSCI ..-RTCCMCLRVss

PIC 16

16051 15

5 to

OSCI-P-OSC2/CLKOUT

N/C

Vss

N/C 5

P/C

16055

26

25

24

OSC2/CLKOlyr

RCO

-- R130RBIRB2

-- RB3

6 16°55 13

12

8

9 1101

-P-P-11135

RBA --

RAO

RAIRA2

..- RA3RBO

67

10

1605722'2

21

2019

RCS tRCA rRC3-/e-o-RC2-P-oPRC1*-

RBI 18 RCO

17 RB7 -a-o-RB3 16 5136

- RB4 15 RB5

940062-1-11

Fig. 1. Depending on the device, the 'window' type PIC microcon-trollers come in an 18 -pin or a 28 -pin case.

= reduced instruction setcomputer), which is markedby a compact but fast se-quence of instructions, eachof which is executed in onemachine cycle.

Apart from the differencesin memory size, the con-trollers in the 16C5x familyhave different numbers ofI/O lines available, and dif-ferent types of clock oscilla-tor. Furthermore, thedevices come in different en-closures, two of which areshown in Fig. 1. Comparingthe different cases, the mostconspicuous feature is thepresence or absence of aglass window. The window-

less, and therefore cheaper,OTP (one-time programma-ble) versions is suitable forhigh -volume production.The window versions containan EPROM, and are ideal forcode development, sincetheir program memory canbe erased using ultra -violetlight. All devices in the16C5x family offer a copyprotection bit. When set,this bit makes it impossibleto read code from a pro-grammed controller.

Internal hardwareThe PIC architecture isbased on a register file con-

cept with separate bus andmemories for data and in-structions. This so-calledHarvard architecture en-ables the processor to exe-cute one instruction and atthe same time fetch the nextfrom the program memory.Unfortunately this 'look -ahead' mode can not be usedfor a number of branch in-structions. Consequently,these instructions take twomachine cycles instead ofone.

The controller architec-ture is shown in Fig. 2. Theprogram memory and the as-sociated counter, the in-struction register and theinstruction decoder arefound in the upper left-handcorner of the diagram. Belowthese elements sits the ALU(arithmetic/logic unit) withits working register, W.Central to the right is thedata memory (general-pur-pose register file), and abovethat, the clock generatorwith watchdog, and the I/Oregister.

Program memoryThe program memory con-sists of 'pages' of 512 wordseach. The PIC16C54 and16C55 have one such page,while the PIC16C56 has two.Address bit A9 is used to se-lect between the two pages.The PIC16C57 has fourpages, which are selectedwith the aid of bits A9 andA10.

The structure of the pro-gram memory is illustratedin Fig. 3. Sequencing of mi-croinstructions is controlledvia the program counter (PC)using a 9 -bit or 11 -bit wideaddress. Some precautionshave to be taken when exe-cuting branch instructions,or starting a subroutine.Problems may then occur ifit is assumed that the datais 8 bit wide, which makes itimpossible to fit in operandshaving a width of 9 bits ormore.

The effect of a program in-struction on the address bitsof the program counter is il-lustrated in Table 1. The


PIC PROGRAMMING COURSE - 1 19

EPROM512K 12 TO

2048 X 12

INSTRUCTIONREGISTER

INSTRUCTIONDECODER

PC

2

4.1, STACK

STAG 2

IDIRECT ADDRESS

PINCCONFIGURATION EPROM I

OSC1 OSC2 MCLR

'DISABLE) .0SCSELECT'

WATCHDOGTIMER

WDT TIMEOUT T- WEFDRTCC

PRESCALER

"CODEPROTECT'

CLKOUT

OSCILLATOR/TIMING 6

CONTROL

DIRECT RAMADDRESS

IS

FROM W

STATUS .

11140 ALU

TRIS 5

4...ROM W

OATABUS

FROM W

EZIEMRAO RA3

"SLEEP"

GENERALPURPOSE

REGISTERFILE

/.

CONERBO RBY

940062-1-12

4.4

FROM W / a48

TRISC 17 I

RCIORC]IPIC16C55/C57

ONLY)

Fig. 2. General architecture of a PIC16C5x microcontroller. Note thedifferent widths of the internal buses.

programmer should take theabove restriction as regardsword size into account. Withthe exception of one GOTOinstruction, instructionswhich alter the program flowmay only be used in thelower half of the memoryblock (A8=0). Furthermore,bits 5 and 6 of the f 3 regis-ter must be correctly pro-grammed when thePIC16C56 or 16C57 is used.

These bit are not automati-cally modified when the soft-ware jumps between pages.Making sure that they aremodified appropriately is thetask of the programmer.

Data memory andregister fileMicrochip Technology callsthe PIC's internal memory`register file' (RF), because a

PC(12)

GOTO, CALL. INST WITH PC AS DESTINATION .. FROM 13, BIT 6 (PIC16C57 ONLY)

GOTO. CALL, INST WITH PC AS DESTINATION . FROM M. BIT 5 (PIC16C56/C57 ONLY)

-DIRECT FROM INSTRUCTION WORD(° DLACGA°Lil,INST WITH PC AS DESTINATION ... A

_(G,NOsTTO, CALl DFIRROEMCTAFLIRuOM INSTRUCTION WORD

WITH PC AS DESTINATION .

A10 A09 IA08 I A07 -A00

2

RETLW CALL

9.11 BIT

PAGE 0

oo

OFF

100

1FF

STACK LEVEL

STACK LEVEL 2

RETLW

CALL

PAGE 1

200

2FF

300

3FF

PAGE 2

400

4FF

500

5FF

PAGE 3

600

6FF

700

7FF

MAX EPROM ADDRESS FOR.

PIC16C54/191C16C55

PIC16C56

- PIC16C57

940062-1-13

Fig. 3. Structure of the program memory, which is divided into pages.

register is a memory locationwhich can be accessed di-rectly by the ALU. The set ofthe registers is then called afile.

The structure of the regis-ter file is shown in Fig. 4.Registers fall into the cate-gories 'operational', 'I/O' or`general-purpose'. The oper-ational registers not onlyserve to control the core ofthe PIC, but also make re-sults of certain actions avail-able to the program. The I/Oregisters are used to gain ac-cess to the ports. Finally, thegeneral-purpose registersare used to store data. Tothe user, all registers behavein the same way.

OperationalregistersRegister fO, Indirect DataAddressingThis register give the pro-grammer indirect access tothe data. Access is gained inconjunction with the FSRregister described furtheron. A read or write commandto register f0 is treated suchby the controller that theALU selects the location ofwhich the address is con-tained in the FSR register.The combination of registerf0 and the FSR register cre-ates ways to manipulatememory areas in a very effi-cient way. In the (trivial)case of f0 being read throughindirect addressing (FSRthen contains the valueOOH), the value OOH is read.If f0 is written to via indirectaddressing, the result is aNOP.

Register f1, RTCC (Real-time Clock/Counter regis-ter)This register may be com-pared to a location in thedata memory. The content ofthis location is continuouslyincremented using a clocksignal. The clock signal maybe external, and applied tothe RTCC input, or internal,when it is derived from thecontroller's instruction cycleclock. An internal prescalerenables the clock signal tobe scaled as required.Further details on this fea-ture are included in the dis-cussion of the watchdogtimer.

PIC16C5xPROGRAMMING

This short course is aimed atproviding an introductioninto programming and hard-ware aspects of thePIC16C5x family of micro -controllers manufactured byMicrochip Technology Inc.

An assembler will be of-fered on disk later in thecourse. This assembler isdistributed with the permis-sion of Microchip tecnologyInc., and supports thePIC16C5x and PIC16Cxx se-ries of controllers. It offers afull featured macro and con-ditional assembly capacity,It can also generate variousobject code formats includ-ing several hex formats tosupport Microchip's propri-etary devleopment tools aswell as third party tools.Also supported are hex (de-fault), decimal and octalsource and listing formats.An assembler users manualis available from Microchiptechnology distributors fordetailed support.The disk, which will be dis-tributed via the ElektorElectronics Readers' Ser-vices will also contain a soft-ware simulator.

The files produced by the as-sembler can be downloadedto the PIC programmer de-scribed in Elektor ElectronicsMarch 1994.

JOINTHE COURSE!

Register f2, PC (ProgramCounter)The program counter gener-ates the addresses of the lo-cations in the programmemory. Depending on thedevice type, the programcounter and its associatedtwo -level hardware stack is9, 10 or 11 -bit wide, usingbit A8, A9 and A10 as exten-sions of A0 -A7. Table 2summarizes the options.

The PC is normally incre-mented by one after an in-


20 GENERAL INTEREST

PC address Goto CallbitAlO bit of f3 bit 6 Of f3A9 bit 5 van f3 bit 5 of f3A8 from instr. always 0A7 -AO from instr. from instr.

PC instruction

bit 6 of f3bit 5 of f3always 0from ALU

Table 1. The effect of the different instructions on the address bits.

FILEADDRESS

00

D02

03

04

05

06

07

08

09

08

OB

OC

OD

OE

OF

7 6 5 4 3 2 1 0

INDIRECT ADDR (*)

RTCC

A10 (A9 IA8 PC

STATUS

CALL 10 9 8 7 6 5 4 3 2 1 0

RETLW

FSR

PORT A

PORT 13

PORT C n

GENERAL

PURPOSE

REGISTER

FILE

STACK 1

10 9 8 7 6 5 4 3 2 1 0

7 6 5 4 3 2 1

ITRISATRISB

STACK 2

0

5 4 3 2 1 0

TRISC

TO AND FROMREGISTER FILEVIA ALU

OPTION

FROM PROGRAM MEMORY

810 6, 5 OF FSR. BANK SELECT(PIC16C57 ONLY)

00

10 30 50 70

12

13

14

15

16

17

18

19

GENERALPURPOSEREGISTER

FILE(ALL TYPES)

GENERAL PURPOSEREGISTER FILE

(PIC16C57 ONLY)

IA

18

ID

1E

IF

(BANK 0) (...) (BANK I) (-)

3F

(BANK 2) (-)

5F

(BANK 3)1-)

7F

1.) NOT A PHYSICALLY IMPLEMENTED REGISTER,4..) FILE 17 IS A GENERAL PURPOSE REGISTER ON THE PIC16C541/G66(...) BANK 01S AVAILABLE ON ALL MICROCONTROLLERS WHILE RANK 1 TO BANK 3 ARE ONLY AVAILABLE ON THE

PIC16C57940062 - I - 14

1

Fig. 4. The structure of the data memory is fairly complex because itis divided into banks. A key role is played by the FSR register.

struction has been executed.There are, however, a num-ber of instructions which fol-low a different pattern:

GOTOBits A0 -A8 are loaded di-rectly, while A9 and A10 arefetched via bits 5 and 6 ofthe status register (PAO,PA1). When using thePIC16C56 and 16C57, thestatus register must beloaded appropriately.

CALLThe CALL instruction is dif-ferent from GOTO in thatbit 8 is always cleared to 0.Consequently the range ofthis instruction is limited.

All other write instructionsto the PC operate in thesame way as the CALL in-struction, i.e., they clear A8,and read A9 and A10 fromthe status register(16C56/57 only).

Register f3, Status WordRegisterThe C, D and Z flags (bits 0,1 and 2) in this register pro-vide the status of an arith-metic operation carried outby the ALU. The PD flag(bit 3) and the TO flag (bit 4)indicate the reset status,while PAO (bit 5) and PA1(bit 6) are used as auxiliarybits (A9 and A10) for certainprogram counter operations(CALL, GOTO, see above).

Device

PIC16C54

PIC16C55PIC16C56

PIC16C57

PC and stack width

9 bit (A8)9 bit (A8)10 bit (A8,A9)11 bit (A8,A9,A10)

Table 2. The width of the program counter and the associated hard-ware stack.

Register f3

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 'I bit 0PA2 PA1 PAO TO PD Z DC C

Bit FunctionPA2 general purpose R/W, reserved for future use*

PA1 page preselect bits

PAO PIC 16C54 and PIC16C55PA1 and PAO: general purpose read/write*

PIC 16C56PAO:

PM:

PIC 16C57PA1/PAO:

0= bank 0 (000H-1FFH)1= bank 1 (200H-3FFH)general purpose read/write*

00 = bank 0 (000H-1FFH)01 = bank 1 (200H-3FFH)10 = bank 2 (400H-5FFH)11 = bank 3 (600H-7FFH)

TO Time -Out bitSet to 1 during power -up and by the CLRWRT andSLEEP commands. Reset to 0 by a watchdog timertime-out. Not affected by other commands.

PD Power -Down bitSet to 1 during power -up and by the CLRWRTcommand. Reset to 0 by a SLEEP command. Notaffected by other commands.

Z Zero bitSet if the result of an arithmetic logic operation is00H.

DC Digit Carry/Borrow bitCarry/Borrow bit (bit 3) of result of ADDWF andSUBWF instructions.

C Carry/Borrow bitCarry/Borrow bit (bit 7) of result of ADDWF andSUBWF instructions. Also used with RRF and RLFinstructions.

* bits must not be used if application is to run on futuresystems.


PIC PROGRAMMING COURSE - 1 111

Event TO PD

Power -up 1

WDT timeoutSleep instr.CLRWDT instr.

x = don't careWDT = watchdog -timer

Table 4. Status of the TO and PDbits as a function of differentfunctions.

Bits 3 and 4 (TO and PD)in the status word registerare not affected by an 8 -bitwide write action.

If the register is used toindicate the result of anarithmetic operation, itshould be noted that the sta-

tus bits are set after the fol-lowing write.

It is recommended to useonly the BCF, BSF andMOVWF instructions to alterthe status register, sincethese do not affect any sta-tus bit.

Register f4, FSR (FileSelect Register)PIC16C54/55/56: bits 0trough 4 select one of the 32available file registers in in-direct addressing mode, i.e.,using register f0. Bits 5, 6and 7 are read-only, and al-ways at 1.

If no indirect addressingis used, the FSR may beused as a 5 -bit wide general-purpose register.

PIC16C57 only: bits 5 and6 select the current datamemory bank, both in indi-rect and direct addressingmodes. Note that this is only

TO PD Reset caused by:

001

1

x

0

0

x

WDT wake-up from SLEEPWDT timeout (not during SLEEP)MCLR wake-up from SLEEPPower -uplow pulse on MCLR input.

State of TO and PD not affected (x) until an event fromTable 4 occurs.

Table 5. TO and PD status after a reset.

valid for the register ad-dresses 10H through 1FH,since addresses OH throughOFH always point to thesame registers. Finally, bit 7is always at 1.

(940062-1)

Continued in the September 1994issue.

Reference:1. PIC programmer. ElektorElectronics March 1994.

MICROCHIP ANNOUNCES FURTHER IMPROVEMENTS IN MICROCONTROLLERS

Microchip's PIC16C54 8 -bitmicrocontroller is now avail-able with reduced powerconsumption, improvedelectrical characteristicsand denser packaging.Using an advanced 0.9 -mi-cron double -layer metalwafer fabrication process,the new one-time program-mable PIC 16C54A can bepowered from a singlelithium -ion battery, makingit an ideal solution forportable aplications such aspagers and remote controls.

The PIC16C54A is thefirst of the PIC16C5x familyto be manufactured usingthe 0.9 -micron process. Thehigh-speed RISC -like 8 -bitdevice operates at up to 20MHz, and provides faster in-struction execution thanany other 8 -bit microcon-troller in its price range. Anon -chip EPROM fuse config-urator allows designers toselect on -chip R/C timingcircuits and crystal/res-onator options to reducecomponent count, cost andboard space requirements.On -chip memory facilitiesinclude 512 words ofEPROM for program storage

and 25 bytes of static RAMfor data. On -chip peripher-rals include an 8 -bit real-time clock/counter withprogrammable prescaler, awatchdog timer, and 12 I/Olines with individual direc-tional control. ThePIC16C54A operates be-tween 2.5 and 6.0 volts, andincludes a power -down orsleep mode which reducescurrent drain to less than 4pA when executed.

The new PIC16C54A isavailable in plastic DIP andSOIC, and also in a compactSSOP configuration.

Further information from

Microchip TechnologyInc., 2355 West ChandlerBlvd., Chandler, AZ85224-6199, USA. Tel.602 786-7200. Fax: 602899-9210.

UK Headquarters:Arizona Microchip Techno-logy Ltd., Unit 3, TheCourtyard, Meadowbank,Furlong Road, Bourne End,Bucks SL8 5AJ. Tel.: (0628)850303. Fax: (0628)850178.

UK distributors:Farnell Electronics, tel.(0532)792715, fax: (0532)63340.Future Electronics, tel.(0753) 687000, fax: (0753)689100.H.B. Electronics Ltd., tel.(0204) 25544, fax: (0204)384911.Hawke Components Ltd.,tel. (0256) 880800, fax:(0256) 880325.ITT Multicomponents, tel.:

(0753) 824131, fax: (0753)824160.Polar Electronics PLC, tel.:(0525) 377093, fax: (0525)378367.

Sweden:MEMEC Scandinavia AB,tel.: 08 6434190, fax: 086431195.

Denmark:Exatec A/S, tel. 044 927000, fax: 044 92 6020.


SOFTWARE EMULATION OF RC5INFRA -RED CODE

A set of programs is described that allows a PC to send infra -red remote controlcommands to a TV set, video recorder or hi-fi stereo chain, using the RC5

standard. As regards hardware, all you need is one infra -red transmitter LED.

ONE very obvious trend in audio/vi-sual consumer electronics is the

use of remote controls. Designed tomaximize user comfort, infra -red re-mote controls enable nearly all func-

Codes for frequently used addressesand commands

System address Apparatus

0 TV2 Teletext5 Video recorder7 Experimental16 Preamplifier17 Receiver/tuner18 Tape/cassette recorder19 Experimental20 CD player

Command number Command

0-9 0-912 Standby13 Mute14 Presets16 Volume +17 Volume -18 Brightness +19 Brightness -20 Colour saturation +21 Colour saturation -22 Bass +23 Bass24 Treble +25 Treble -26 Balance right27 Balance left48 Pause50 Fast reverse52 Fast forward53 Play54 Stop55 Record

Design by M. Claessen

tions of audio/video equipment to beselected and controlled from 'armchairdistance'. This article shows that re-mote control is not only a 'luxury', butalso makes it easy to set up links withother equipment, say, a PC.

Using suitable software, a videorecorder, TV set or stereo rack can becontrolled by a personal computer (PC)without having to change a thing onthis equipment. The hardware exten-sion required at the PC side of the linkis, indeed, minimal, consisting of asingle infra -red light emitting diode (IRLED), which is connected in serieswith the loudspeaker found in any PC.A small program then ensures that theright RC5 commands are generatedand transmitted by the LED. The loud-speaker will function as before.

RC5 is a system developed byPhilips for communication using infra-red light. The system is also used by anumber of other manufacturers ofaudio/video equipment. For the pre-sent project the designer has based thesoftware on the RC5 standard andcode set. The source code contained ondisk should enable experienced pro-grammers to adapt the program sothat it can be used for, say, Sony orPioneer equipment.

The programThe function of the program is totranslate instructions or commandsinto a pulse code signal that can beapplied to the loudspeaker connectionon the PC's motherboard. This loud-speaker output is fairly rudimentary,and usually consists of an 'power' in-verter only, which drives a miniatureloudspeaker directly. The maximumpower delivered to the speaker is about150 mW .

In a normal infra -red remote controllink, the encoding of selected com-mands is performed by a simple inte-grated circuit contained in the

MAIN SPECIFICATIONS

Code used:Range:PC requirements:PC type:Source code:Emulation:IR diode:Transmit power:

RC5

5 to 13 mMS-DOS

XT/AT/386/486on disk

Philips RC5903LD271 or LD274

max. 150 mW

handheld unit. In the present case, theencoding function is assumed by aprogram running on the PC. Since gen-erating the digital code is time -critical,a machine -language program is usedfor that purpose. That allows the pro-gram, ELEKFUNC.EXE, to be called byroutines written in 'higher' languages,for instance, Turbo Pascal.

Apart from ELEKFUNC.EXE, thediskette supplied through the ReadersServices (order code 1901) containstwo more programs: SWITCH.EXE andRC5.EXE. The latter enables you to se-lect and transmit RC5 commands in asimple manner. SWITCH.EXE may beused to transmit a system address anda key code 'manually', for instance,'SWITCH 24 35'.

The diskette also contains thesource code of all three programs(Pascal for SWITCH and RC5, and as-sembler for ELEKFUNC). The sourcecode files should enable you to fine-tune the software to personal require-ments. In this context, Ref. 1 shouldbe mentioned, since that design en-ables you to set up a complete wirelesscontrol system capable of switchingapparatus in the home on and off. Oneapplication would be a lighting controlsystem managed by the PC while you

li



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are away on holiday. One condition forsuch a system to work is, of course,that the transmitter diode connectedto the PC 'sees' the receiver diode inthe apparatus to be controlled.

The hardwareAs already indicated, an infra -redtransmitter LED must be fitted insidethe PC. In most PCs, the loudspeakeris connected to the motherboard via athin cable and a 4 -way connector.Usually, only three of the four wiresare used. The fourth connector pinserves to polarize the connector so thatit can not be fitted the wrong wayaround. As far as we have been able toascertain, the pin functions on thisconnector are as follows: pin 1 is data,pin 2 is not connected, pin 3 isground, and pin 4 is +5 V. Connect theIR LED in series with the loudspeaker,making sure that the cathode goes tothe PC ground connection. Alternati-vely, the diode may be connectedacross (i.e., in parallel with) the loud-speaker. In particular when the loud-speaker (or buzzer) is fitted on themotherboard, that may be the only vi-able option. (930097)

PC/AT>>>>»

EMULATOR PHILIPS INFRARED REMOTE CONTROL RC 5903RC5 ««« COPYRIGHT 1993 BY ELEKTOR

MODE TV

PPREFS MUTE TIMER STANDBY TIME HOLD TXT OFF

EXT TV TXT EXT 1/2 DISPLAY DOUBLE MIX NEXT

1 2 3 00 * TREBLE BASS

4 5 6 00 * TREBLE BASS

7 8 STEREO 4 BAL BAL VOL A

0 * PP I/II PROG PROG P. VOL

RECORD STOP 14 REW FFWD *P. PLAY TV/VCR EXIT

930097-11

Fig. 1. Screendump showing how the program RC5.EXE enables an infra -red remote controlto be simulated on an MS-DOS PC.

Reference:1. Universal RC5 code infra -red re-ceiver. Elektor Electronics January1992.



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LOW COST PIC ICE (In -Circuit Emulator)Plugs into the printer port and runs in conjunction with the PIC development simulator software.Appears on the target system as a normal Pic device including OSC2 and RTCC in/out. Runs inreal time from IBM PC changes made to File registers reflected on target. Supplied software ofyour choice Pic54-57 or Pic7 1 /84 Only L89,95

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26

AUTO -PLAY FOR CD PLAYER

Many CD players are equip-ped with a timer, which

starts the player automati-cally as soon as the mains isswitched on (perhaps by a timeswitch). There are, however,several makes that do not havethis facility: the present circuitis intended for these.

The circuit is based on adual timer Type NE556. The 5 Vsupply is derived from the CDplayer. When switch Sl is closedand the mains is switched onto the CD player, the presentcircuit will be powered via con-nector K1.

Immediately upon the supplyvoltage becoming available,IC lb receives a trigger signal vianetwork RI -C1. The timer thenprovides a pulse of about 1.2 s(time constant R2 -C2). Duringthis short period, the CD playeris initialized. After the pulse hasdecayed, ICib triggers the othertimer, which in its turn switcheson the transistor in optoiso-lator IC2 for 0.2 s (time constantR4 -C4). The transistor is con-nected in parallel with the con-tacts of the play switch on theD player, so that this startsplaying the CD in the disc com-partment.

Since the switch circuit ofmost CD players is multiplexedone way or another, the op-toisolator is imperative as it

5V)R5

EITIM

R1 R2

10

R3 R4

13 DISIC1 b

1 MS

12 THR our 9 THR

8 1n 6

CNTR

Cl C2 C5I=1

TI6T1

prevents the other signals beingaffected or even short-circuitedto earth.

Since the transistor in theoptoisolator conducts in onlyone direction, wiring it up cor-rectly to the play switch mustbe done by trial and error. Inother words, if it does not work,interchange the two wires fromthe transistor to the play switch.It is also possible to operate a

I=1

18V

1µ 116V

IC1aOUT

CNTR

3

C6

10n

R8

D1

R6 R7

IC26

K2

5V

reed relay via IC2 to short-cir-cuit the contacts of the playswitch.

Light -emitting diode D 1serves as pulse indicator. Itlights the moment IC la gener-ates a pulse. The diode is notessential and, together withRg, may be omitted.

Use an NE556, not a TLC556,since this does not provideenough current to drive two

CNY174

ICI = NE556

944016 - 11

LEDs.The circuit should preferably

be fitted inside the CD player,with switch Si mounted on thefront or rear panel.

The 5 V line is taken fromthe 5 V power supply in theplayer. The circuit draws acurrent of not more than 40 mA.

Design: G. Renker[944016]

SELF-STARTING MULTIVIBRATOR

It is not too well-known thatif the characteristics of the

two transistors making up amultivibrator are near -identical,it is very difficult to get themultivibrator started.

The present circuit showshow a small modification canmake the basic cicuit suffi-ciently asymmetrical to en-sure that he multivibrator al-ways starts unfailingly. Theonly drawback is that the dutyfactor is affected slightly, butin practice this will normallynot be very important.

In the diagram, resistor R4connects the base and collec-tor of T1, so that this transis-tor can no longer become sat-

urated. Instead, it works as aself -setting amplifier. A con-sequence of this is that theamplified noise on the collec-tor of T2 also appears on the col-lector of T1. Because of thiscoupling, T2 is provided afreshwith the amplified noise signalvia C1. This ensures tat thenoise level increases rapidlyso that the multivibrator starts.

Putting values to the cir-cuit elements is straightfor-ward. Take a collector currentof 1-10 mA. If it is 1 mA, thevalue of R1 and Rg is equal tothe supply voltage times 1000.The value of R1 and R4 shouldbe equal to a quarter of theamplification factor of the tran-

sistors, multiplied by the valueof R1. The value of C1 and C2is the same and is calculatedfrom

C = f / (1 .4xR3).

Design: C. Clarkson[944096]



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28

PROGRAMMABLE AMPLIFIER

The principle of the amplifieris simple: take a common -

or -garden operational ampli-fier and make the feedback loopswitchable with the aid of amultiplexer. Supplying the mul-tiplexer with a 3 -bit binary wordenables one of up to six differ-ent amplification factors to beselected.

In the diagram, IC b is theamplifier stage proper. Its feed-back loop is split into a num-ber of discrete resistors, R4 -R10,which can be switched by mul-tiplier IC2. With the specifiedvalues, there is a choice of sixgains: +20 dB; +10 dB; 0 dB;-10 dB; -20 dB; and -30 dB.

The amplifier/multiplexer

R1

16V5

OD1

I1N4148

16V5

is preceded by an input buffer,ICia. The input is protectedagainst overload by R1, DI andD2. Conversely, the high inputimpedance of ICI, obviates over-loading of the output of a con-nected apparatus by the pre-sent circuit.

Although the channel re-sistance of the multiplexer isfairly high at 220 S-1 comparedwith the values of R4 -R10, thishas no detrimental effects sinceit is in series with the relativelyhigh input impedance of IC lb.

The capacitances of the dis-crete analogue switches in themultiplexer have some adverseeffect on the signal, but thisstays well within acceptable

R3

IC1 a

C1 C2

O 22 25V 100n

'ClO C3 C4

22u 25V 100n

Occasionally, an ideal full -wave rectifier is required,

for example in a dynamic com-pressor where switching thresh-olds and non-linear behaviourare not acceptable. The pre-sent circuit approaches thisideal.

The circuit consists essen-tially of two parts: the rectifierproper, IC ib, and a differentialamplifier, ICI,.

The rectified voltage ap-pears acrossR2. Opamp IC lbensures that rectifiers D1 -D4

16V5

16V5

R4

1%

R5

limits. Up to 100 kHz, the cir-cuit performs well; only abovethis frequency does a sine wavebegin to resemble a triangle.

Harmonic distortion is0.001% at 1 kHz and 50.01%

at 20 kHz. With the gain set to+20 dB, the signal-to-noiseratio is 95 dB referred to 1 Vwith the input short-circuited.

Te rather unusual supplyvoltage of ±16.5 V was chosendeliberately to obtain a maxi-mum input voltage of 10 V r.m.s.with gains of -20 dB and -30 dB.If this is considered not veryimportant, the supply may belowered to ±15 V.

The circuit draws currentsof +18 mA and -9 mA.

R6 R7 R8 R9

IMEEI EMI EMI 1213 CBI1% 1%

16V5

16V5

13

3

CIO 0

1:1? Q1 0

020

9 10

1/

11 12

1%

7

1%

6

R10

34052

1%

The relationship betweenthe binary word and the resul-tant gain is:

Q2 Q 1 QO gain

1 +20 dB1 1 0 +10 dB1 0 0 dB1 0 0 -10 dB0 -20 dB0 1 0 -30 dB0 00 0 0

* smaller than -90 dB at 1 kHzand 10 V r.m.s. input.

Design: T. Giesberts[944005]

5 4

Nit

IC2

MUX08 DRAIN

0

16 15

5V

14

IC1 b

IC1 = NE5532

NEAR -IDEAL RECTIFIER

R6

-0

944005 - 11

function as ideal componentswithout switching thresholds.

Since most circuits requirea direct voltage with respect toearth, IC la functions as a dif-ferential amplifier. Its output car-ries the rectified voltage acrossR2. Assuming that the supplyvoltage is ±10 V, the level of thealternating signal at the inputmust not exceed 16 VPP'

The circuit draws a currentof only a few milliamperes.

Design: H. Bonekamp[944079]



ESR ELECTRONIC COMPONENTSStation Road, Cullercoats, DEPT. EETyne & Wear NE30 4PQTel. 091 251 4363 Fax. 091 252 2296

74LS-Series74LS0074LS0174LS0274LSO374LSO474LSO574[50874LS0974 [01074LS10774LS109741_01174LS11274LS11374LS11474LS1274LS12274LS12374[5125741_0126741_51374L413274[513374LS13674LS13874[513974LS1474LS145741_514774LS148741_51574LS15174LS15374LS15474LS15574LS15674LS15774LS158741_516074LS16174[516274LS163741_516474[516574LS17074LS17374[5174741_517574LS19074LS19174LS19274LS19374LS19574LS19674[519774L02074LS21741_52274LS22174LS24074LS24174LS24274LS24374LS24474LS24574LS24774LS25174[525774LS25874LS2674LS26674L52774LS27374LS27974LS3074[03274[536574LS367741_536874LS3774LS373741_537474LS375741_537774[037874LS3874LS39074[S39374LS39574LS39974LS4074LS4274[04774[S51741_067074L073741_07474[S7574[57674LS8374LS8574[08674LS9074LS9274LS93

£0.22£0.14£0.14£0.14£0.14£0.14£0.14£0.14£0.14£0,23£0.21£0.17£0.21£0.21£0.21£0.14£0,31£0.31£0.21£0,21£0.14£0.21£0.18£0.16£0.24£0.25E0.18£0.56£1.26£0.70£0.14£0.25£0.25£0.70£0.25£0.36£0.25£0.25£0.32£0.32£0.32£0.32£0.26£0.48£0.30£0.24£0.24£0.24£0.25£0.24£0.42£0.24£0.24£0.24£0,24£0.16£0.14£0,14£0.36£0.32£0.32£0,32£0,32£0.32£0.36£0,32£0.24£0.24£0.24£0.140.14£0.14£0.32£0.25£0 1 4£0.14£0.21£0.21£0.21£0.14£0.32£0.32£0.34£0.32£0.62£0.14£0.25£0.24£0.26£0.62£0.14£0.25EC '2£0.14£0,69£0 .1 7S;2_£0.19£0.25£0.31£0.35£0.20£0.23£0.35£0.25

ENAMELLEDCOPPER

WIRE

All 2oz Reels14 SWG £0.6316 SWG £0.6718 SWG £0.6720 SWG £0.7222 SWG £0.7624 SWG £0.8026 SWG £0.8928 SWG £0.9130 SWG £0.9332 SWG £0.9334 SWG £0.9936 SWG £1.0438 SWG £1.1040 SWG £1.22

4000 Series4000400140024006400740084009401040114012401340144015401640174018401940204021402240234024402540264027402840294030403140334034403540404041404240434044404640474048404940504051405240534054405540E.:406340664067406840694070407140724073407540764077408140824085

409340944095409740984099450245034508451045114512451445154516451845204521452645274528452945324534453645384541454345554556456045664572458445854724401064010940163401744017540193

£0.17£0.21£0.17£0.40£0.28£0.31£0,19£0.23£0.26£0.16£0.21£0.30£0.31£0.18L0.27£0.27£0,19£0.31£0.31£0.32£0.16£0.21£0.1510.59£0.18£0.22£0.36£0,17£0,70£0.56£1.24£0.31£0.29£0.31£0.22£0.28£0.35£0 31£0.25£0.31£0,20£0,20£0.36£0,25£0.25£0.56£0.34frr LE£0.29£0.18£1.91£0.16£0.20£0.17£0.20£0.17£0.17£0.17£0.30£0.17£0.14£0.21£0.28£0.26£0.55L0.18£0.31£0.56£1.20

£0.38£0.38£0.31£0.90£0,26£0.32£0.32£0.77£0.98£0.31£0.27£0.26£0.62£0.40£0.40£0.40£0.44£0.32£2.48£1.00£0.37£0.33£0.46£0.34£0.34£1.18£1.96£0.25£0.24£0.32£0.70£0.31£0.50£0.46£0.34£0,36£0.60

TRANSISTORS2N16132N17112N18932N2218A24221902N2222A2N2646242904A242905A2N29072N29262N30532N30542430552N34402N37022N37032437042N37052N37062N37712N37722N37732438192438202439042439052439062440362452962N5321246107AC126AC127AC128AC187AC188ACY17AD149AD161AD162BC107BC107BBC108BC1 08ABC108CBC109BC109CBC114BC115BC116BC118BC132BC1344C135BC140BC141801424C1438C149BC154BC15780159BC160BC170BC1701980171BC1716EiC172BC17215BC177BC178BC179BC182BC182LBC182LBBC183BC183LBC183LBBC184BC184L

£0.31£0.26£0.29£0.28£0.25£0.16£0.80£0.25£0.23£0.20£0.16£0.27£0.90£0.62£0.50£0.09£0,10£0.10£0.10£0,10£1 .44£1 .51£1.79£0.40£0.58£0.10£0.10£0.10£0.31£0.57£0.57£0.60£0.30£0.30£0.28£0.45£0.37£3.84£1.67£0.92£0.92£0.14£13.15£0.13£0.14£0 t5£0,14Er;,£0,41£0.41£0,41£0.41£0.36£0.36£0.36£0.25£0.27£0.31£0.34£0.21£0.36£0.12£0.12£0.28£0.16£0.16£0.11£0.16£0.13£0.13L0.18L0.18£0.17£0.08E0.08£0.08£0.08£0.08£0,08£0.08£0,08

TRIACSZ0105DA £0.42T102060 £0.65TI C2260 £0.7301408.6008 £0.841102360 £0.96DIAC £0.20

VOLTAGEREGULATORS78L0578L1278L1579L0579L1279L15780578127815790579127915LM3177LM723L200CVLM323KLM338K

£0.24£0.24£0.24£0.28£0.28£0.28£0,28£0.28£0.28£0.38£0.38£0,38£0.56E0.29£1.16£2.70£5.52

OPTO DEVICES5mm Red LED5mm Green LED5mm Yellow LED5mm Orange LED3mm Red LED3mm Green LED3mm Yellow LED3mm Orange LED5mm Flashing Red5mm Flashing Green5mm Br Colour5mm Tri Colour5mm Plastic Bezel3mm Plastic Bezel0 r 7 Segment Display Redcommon anodecommon cathode

£0.09£0.10£0.10£0.10£0.08£0.12£0.13£0.13£0.50£0.54£0.360.48£004£005

£1 14

BC18680204013020613BC207CBC208BC209ABC212BC212LBC212LBBC2138C213LC00214BC214LBC2378BC238CBC239CBC251BC252BC261BBC2626BC267B0C307BC308BC327BC328BC337BC338BC414CBC441BC461BC463BC478BC479BC490BC516BC517BC527BC528BC537BC546CBC547CBC548CBC549CBC550CBC556ABC557CBC558CBC559CBC56013BC637BC638BC639BC640BCY708CY71BCY72BD135BD136130137BD138BD139BD140BD150C13016500166BD187BD201BD202BD203BD204BD222BD225BD232BD237BD238802406B 0243B802440BD246Ei 0441BD442

£0.33£0.72£0.72£0.72£0.72£0.72£0.08£008£0.08£0.08£0.08£0.08£0.08£0.09£0,09£0,10£0,13£0.13£0.24£0.24£0.30£0.10£0.10£0.10£0.10£0.10£0.10£0.13£0.40£0.40£0.29£0.32£0.32£0.24£0.22£0.20£0.20£0.20£0.20£0.08£0.09£0.08£0.10£0.08£008£0.08£0.08£0,08£0.09£0.21£0.21£0,21£0.21£0.21£0.20£0.20£0.20L0.21£0.22£0.22£0.23£014£0,82f 0.42£0.35£0.39£0.40£0.40E0.40£0.40£0.40£0.42£0.38£0.32£0.32£0.37£0.50£0.53£1.06£0.41£0.41

BD534BD535BD536BD64613764863650B D707B D807BDX32BDX33CBOX34CBDX53CBOX54C6E1808E1826E1858E1948E1958E2448E2578E2598E337BF3558E4238E4518E4598F469BFX29BFX84BFX85B FY50B FY51B FY5206107B6170BSW66BU126BU205BU208ABU326A80500BU508ABU526BU806BUX84IRF540IRF740MJ11015MJ11016MJ2501MJ3001MJE340MJE350MPSA13MPSA42MRF475TIP121TIP122TIP125TIP127TIP132TIP137TIP142TIP147T192955TIP29CTI P3055TIP30CTIP31CTIP32CTIP33CTI941ATI P42CTI P47TI P46TIP50VN1OKMVN66AF7TX300ZTX500

THYRISTORSP0102AATICI 06DT1011601101260

£0.30£0.40£0.66£0.77

£0.47£0.48£0.65£0.52£0.52£0.53E0,42£0.80£1.78£0.46£0.50£0.47£0.50£0.31£0.31£0.31£0.19£0.19£0.35£0.33£0.33£0,36£0.38£0,13£0.19£0.29£0.36£0.29£0,31£0.31£0.29£0.26£0.28£0.21£0,21£1.35£1.70£1.82£1.73£1.80£2.32£1.76£2.24£1.36£0.78£1.60£1 .63£2.11£2.11£1.60£1.52£0.40£0.42£0.12£0.17£6.21£0.35£0.37£0.37£0.37£0 46£0.46£1.08E1.12£0.63£0.31£0.63£0.31£0.34£0.32£0.72£0.36£0.38£0.48£0,62£0.53£0,44£1.50£0,16£0.16

HARDWARET2 Box 75 x 56 x 25mmT3 Box 75 x 51 x 25mmT4 Boo 111 x 57 x 22mrnMB1 Box 79 x 61 x 40minMB2 Box 100076x 41mmMB3 Box 119 x 98 x 45rnmMB5 Box 150 x 100x 60mm

£0.82£0.82£0.98£1.44£1.56£1.82£2.50

LINEAR ICs00311ECA324CA555CA741 CECA747CECA3046CA3080CA3130003130ECA3140CA3240ICL7621ICM7555ICM7556LM301ALM348NLF351 NLF353LM358NLM377LM380NLM381L M386[41387LM392NLM393NLM748CNLM1458L M3900LM3914LM3915MC3340MC4558NE531NE556NNE567NN£5532NE5534TBA120STBA8106TBA820MTDA2030TL061TL062TL064TL071CPTL072CPTL074CNTL081TL082CPTL084CNUA733ULN 2003ULN2004ZN414ZZN425EZN426EZN427EZN428EZN435EZN448E

£0.28SC 35£0.22£C, 26£0.39£0.37£0.72£0.98£0.98£0.56£1.22£1.70£0.43£0.96£0.25£0.31£0.36£0,41£0,27£2.57£1.12£2.70£0.48£1.60£0.79£0.28£0.31£0.26£0.72£2.70£2.70E1.60£0.36£1.56£0.36£0.36£0.80£0.66E0.77£0.68£0.39£1.35£0.35£0.42£0.46£0.32£0.34£0.48£0.33£0.34£0.46£0.64

£0.52£0.48£1 .04.£4.68£2.61£8.82£6.12£5.31£7.92

EPROMS &RAMS

271627322764 2527C64-2521728-2027C128-2027256 2027C256-20

27C51227C0106116 106264-1062256-104164 1541256-10511000-8514256-8

£4.46£4.84£3.00£2.80£3.69£3.31£3.99£3.57

43.69'4.97£1.53L3.06£4.83£1.78/2.80£5.61L5.61

DIL SOCKETS8 Pin14 Pin16 Pm18 Pin20 Pin24 Pin28 Pm40 Pm

£0.07£0.11£0.15£0.15£0.16£0.19£0.22£0.25

ELECTROLYTIC RADIAL CAPACITORS

uF 16V 25V 63V 100V 450V0 47 £0.05 £0.071 0 £0.05 £0.06 £0.152 2 £0.05 £0.06 £0.184 7 £0.05 £0.08 £0.3010 £0.05 £0.05 £0.06 £0.08 £0.4822 £0.05 £0.05 £0.0947 £0.06 £0.06 £0.11100 £0.06 £0.09 £0.11220 £0.09 £0.12 £0.31470 £0.15 E0.19 £0.571000 £0.22 £0.292200 £0.37 £0.574700 £1 .11

ELECTROLYTIC AXIAL CAPACI FORS

uF 16V 25V 63V 100V 450V0 47 £0.1510 £0.10 £0.10 £0.192 2 £0.10 £0.10 £0.224 7 £0.09 £0.10 £0.10 £0.3410 £0.12 £0.12 £0.12 £0.4822 £0.09 £0.13 £0.17 £1.0647 £0.10 £0.11 £0.16 £0.20 £1.33100 £0.10 £0.13 £0.21 £2.46220 £0.13 £0.18 £0.42470 £0.21 £0.24 £0.691000 £0.33 £0.40 £1.052200 £0.52 £0.64

£1.14 4700 £0.90

SOLDERING IRONSAntex Soldering ironsM 12 WattC 15WanG 18WattCS 17WattXS 25WattST4 STAND35Watt Gas IronDesolder PumpAntistatic Pump22SWG 0 5Kg Solder18SWG 0 5Kg Solderlmrn 3 yds SolderDesolder Braid

£7.75£7.78£7.96£7.88£7.96£2.85

£11,58£3.00£4.30£7.40£6.6060,62£0.87

RF CONNECTORSBNC Solder Plug SOBBNC Solder Plug 75RBNC Crimp Plug 50RBNC Crimp Plug 75RBNC Solder SktBNC Chassis SktPL259 5 2rnmPL259 11mmRND UHF socketSOP UHF socketF Plug RG58F Plug RG6N Plug RG8N Socket RG8BNC Crimp Pliers

£0.93£0.96£0.68£0.68£1 08£0.80£0.68£0.62£0,68£0.45£0.30£0.27£1.60£1.40

£15.50

PCB EQUIPMENTUV EXPOSURE UNITPLASTIC DEVELOPING TRAYPHOTO RESIST AEROSOL SPRAY (100m1)FERRIC CHLORIDE CRYSTALS (0 5Kg)TIN PLATING POWDER (90g)ETCH RESIST PENPCB POLISHING BLOCK

STRIPBOARD 0.1 PITCH64mm x 25mm £0.2764mm x 95mm £0,9064mrn x 431mm £3.2295mm x 127mm £1.5095mm x 95mm £1.1095mm x 431mm £4,80100mmx 160mm £1.60119mm x 454mm £6,20

PHOTO RESIST BOARD(G. Fibre)

£67.38£1,35£3.90£2.45

£10.80£0.72£1.84

BREADBOARD81 mm x 60mm175mm x 42mm175mm x 67mm203mm x 75mm Includesmounting plate & posts £7.36

COPPER BOARD (G. Fibre)10Ornm x 160nur £0.90110mm x 220mm £1 .24

PHOTO RESIST BOARD(Paper)

£0.86£1.62£2.09£2.41

CAPACITORSCeramic Mini Disc 100 & 63V

1 OpF to 100nE1pF.1nF £0.06. 1 n2 -2n7 £0.07,3n3 -4n7 f 0.12.1 On & 1 2n £0.07

Polystyrene 160V 5% 47pF to 10nF47p -2n2 £0.09, 2n7.1 On£0,12

D CONNECTORSPlug Socket

9 Pm £0,29 £0,3015 P. £0.39 £0.3915 Pon H D £0.81 £0,9023 Pin £0.40 £0.4925 Pm £0.48 £0.50

9 Way plastic cover £0.3015 Way plastic cover £0.3323 Way plastic cover £0.3625 Way plastic cover £0.36

BRIDGERECTIFIERS

W005 1 5A 50VWO2 1 5A 200VBR32 3A 200VBR62 6A 200V1004 1 OA 400V

£0.19£0.20£0.36£0.64£1.39

x10

£3.06£3.74£5.56

£0.67£1.24£1.58£4.63

SWITCHES3amp 250v 6 4rnm (f, mountingSPST Toggle £0.58SPDT Toggle £0.60SPOT CO Tog £0.64DPDT ToggleDPDT CO Toggle £0.76DPDT CO Toggle(biased) El .20DPDT CO Toggle(biased 1 way) £1.20DPDT mini slide £0.15Rotary Wafer 1P -12W, 2P -6W,3P -4W. 49.3W £0.78Key Switch SPOT £2.70Push to make £0.25Push to break £0.28Latching Push Sqr £0.63PCB Tact 6 x Sole £0.25

£0.68

RESISTORS025W 5% CF El 2 Series £0.60/10005W 5% CF E12 Series £0.95/1000 25W 1% MF E24 Series £1 .72/100POTS Log or Lin 4709 1 MO 25mm dia 0 251n

shaft £0.42PRESETS Enclosed Horz

or Vert 100R 'IMO 0.15WPRESETS Skeleton Horz

or Vert 100R IMO 0 1 W £0.11* PLEASE STATE VALUE REQUIRED *

COMPUTER ACCESSORIES

Parallel Printer Lead tieRS232 Lead (all pins) Male MaleRS232 Lead (all pins) Female MaleCornrow, 36 Way Lead Male MaleGender Changers9 Way D Mir, Female to Female9 Way D Mini Male to Male25 Way D Mini Female to Female25 Way D Mini Male to Male9 Way D Female to Female9 Way D Male to Male25 Way D Female to Female25 Way D Male to MaleAdaptors9 We-, Male to 25 Way Female9Way Female to 25Way Male25 Way Male to 9 Way Female25 Way D Male to 36 Way Centronic25 Way Null Modem Female Female25 Way Null Modem Male to Female25 Way Null Modem Male to MaleRS232 Surge Protector Male FemaleRS232 Jumper Box Male to FemaleRS232 Tester IT LEDs) Male FemaleDate Switch BoxesSerial Switch box 2 Way A/BSerial Switch box 3 Way A/B/CSerial Switch box 4 Way A/B/C/0Serial Switch box Cross overParallel box 2 Way A/BParallel box 3 Way A/ 13/C;Parallel box 4 Way ArBrC.DParallel box Cross over

£6,90£3.75£3.80£4.78

£1.81£1.98£2.23£2.23£2.33£2.33£2.71£2.71

C2.71£271£2.33£3.56£3,02£3.02£3.02£6.12£3,02£6,59

£9.20£13.16£15.15£19.69£11.134£17.11£18.43£20.42

£0.15

DIODESZener Diodes 2V7 33VBZY88400Mw £0.08BZX85 1.3W E0.141 44001 £0.061614002 £0.071 44003 E0.071440041 N40051 N40061 N400714 54001454011 N54021N54041 N5406145407145408149141N9161 N4148Bri 330A4700900A910A202BA157BA158BA1591 44149O4200

£0.07£0,07£0.08£0.08£0.09£0.09£0.09£0.11£0.11£0.14£0.15£0.06£0.06£0.05£0.13£0.28£0.07£0.100.27£0.10£0.10£0.10£0.06£0.10

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30

CHARGE METERDesign by H. Bonekamp

Electrostatic discharge in a workshop or laboratory can lead toa great deal of damage. Even the electrostatic charge on the

human body can give rise to voltages of up to 20 kV. Mostsemiconductors and integrated circuits can not withstand suchpotentials. With the meter described in this article the presence

of unwanted electrostatic charges can be detectedso that protective measures can be taken.

Nhough work on circuits containingemiconductors and integrated cir-

cuits should always be carried out withan earthed soldering iron and an earth-ing wrist strap, it is still good practice toascertain whether anti-ESD (electrosta-tic discharge) measures are necessary.The meter described, an accurate elec-trometer with two ranges, 0-5 pC and0-500 nC, is perfect for this task.

Design considerationsWith reference to Fig. 1, consider an ob-ject (or person), C1, with a certain elec-trostatic charge, which is used to chargea (previously uncharged) capacitor C2. Ris the inevitable transfer resistance. Provi-ded that the value of C2 is not less than10 times that of C1, the larger part of thecharge on Clwill have moved to C2 withina relatively short time. The potential acrossC2 can then be measured to form a mea-sure of the charge the capacitor has re-ceived.

Since the charge is the product of ca-pacitance and potential, Qi = C1U1 andQ2 = C2 U2. When the switch is closed, aftera theoretically infinite time, U1 = U2, thatis, U2 may be taken as the original po-tential across C1, multiplied by the ratioC : (CI-FC2). Using this in the formula forthe charge on C2:

Q2 = Ul(CIC2)/(C1+C2).

Assuming that C1 is negligibly small com-pared with C2:

Q2= clui.

Resistance R merely delays the chargetransfer, but has no effect on the amountof charge ultimately transferred.

Circuit descriptionIn the circuit diagram in Fig. 2, capaci-tor C1, corresponding (confusingly) to ca-pacitor C2 in Fig. 1, functions as the mea-suring element. Each measurement startswith closing S1, so that C1 is dischargedvery rapidly via R1. If the (charged) objectis connected to the input pin (or a persontouches this pin), a transfer of chargetakes place. As described earlier, C1 willthen be charged to a potential that formsa direct measure of the charge originallyon the object or person. Since the 'earthy'side of C1 is at half the supply voltage,

1.151.16 C7L81.19

71 71 air lp

RESET ,(Si 0

C1

4)17

100V

1/211b

S2 R3

-0-0.110-0-1=11--

R2

3

R4

the capacitor may be charged in a posi-tive as well as in a negative sense. Notethat the capacitance of most people is inthe range of 100-200 pF, so that the valueof C1 more than meets the requirementmentioned earlier that it should be at least10 times that of the object or person.

The potential across C1 is applied tothe non -inverting input of IC la, which,because of its high impedance, hardlyconstitutes a load on the capacitor. The

R5

10

D8

1N4148 S3 Ub 1/2Ub

En1

EMI9V

100p 100n

IC1 = TLC274

P1

25k

Ub

= 1N4148

D6-O.

R6

D2

O1/2Ub

Ub

R8

R9

D5

1/2Ub

940033- 12

Fig. 1. The principle of the charge meter. Fig. 1. Circuit diagram of the charge meter.


CHARGE METER EaElectrostatic discharge (ESD)

Electrostatic discharge (ESD) may notonly interfere with the correct operationof equipment, but can also lead to ir-reparable damage to certain components.

The discharge is obviously precededby the forming of an electrostatic charge,which is normally caused when a con-ductive and a non-conductive materialare rubbed together. Typical examplesare the human body and nylon carpetsor car upholstery, terylene clothing andplastic wrapping material. The conse-quent electrostatic voltage may be ashigh as 20 kV,

The phenomenon depends stronglyon the humidity of the ambient atmos-phere. The drier the air, the higher thevoltage. Research has shown that in thisrespect the human body may be con-

sidered as a capcitor with a value of100-200 pF. During an ESD, people havean internal resistance of 150-1500 O.The electrostatic charge appears to beconcentrated in protruding parts of thebody, such as the hands. Because of thisand the speed of the discharge pulses,ESD can rapidly damage semiconduc-tors when these are touched by hand

Recognition of the phenomenon is noteasy, because shocks are felt only whenthe potential is higher than 2-3 kV, butthis level of voltage can already seriouslydamage sensitive semiconductors.

Electrostatic charges may be preventedby replacing non -conducting carpets,cloth-ing or packing by conducting materials.Also, the use of an earthed wrist strapis advisable when semiconductors arehandled.

Fig. 3. Printed circuit board for the charge meter.

amplification of IC la can be switched be-tween x2 and x20 by S2, which switchesR3 into the feedback loop, or disconnectsit from the loop.

From the output of IC la, the signaltakes two paths: one to the metering net-work and the other to comparator IC lc.

The inverting input of IC is carries halfthe supply voltage as reference poten-tial. In this way, the output of the com-parator indicates the polarity of the mea-sured charge. If this is negative, D6 lightsand when it is positive, D7 lights.

The part of the output of IC la fed to themetering network is applied via R5 andP1 to IC ib, which drives the meter, M1.The diodes ensure that the meter pointeralways deflects in the same direction, ir-respective of the polarity of the originalcharge. Diode D3 protects the meteragainst too high a potential across it.

Power is derived from a 9 V battery,which is buffered by C2 and decoupledfor r.f. by C3. S3 is the on -off switch, whileD8 protects the circuit against a wronglyconnected battery.

The stabilized half supply voltage men-tioned on a few earlier occasions is ob-tained from potential divider R.8 -R9 andbuffer stage IC id. It is essential for thecorrect working of the circuit that the out-put of ICI,/ is connected to a good earth-ing point (mains earth or water pipe).

ConstructionThe charge meter is best built on the printed -circuit board shown in Fig. 3. The designof the board allows either a single 4.7 pFcapacitor (C1) or five 1 pF capacitors(C5 -C9) in parallel to be used as the in-put capacitor (see Fig. 4).

When the board has been completed,mount it in a small case as shown at thebeginning of this article and in Fig. 5. Asuggested front panel is shown in Fig. 6(which is not available ready made).

It is absolutely essential that the cir-cuit is properly earthed, either to the mainsearth or to a water pipe.

The input (touch) terminal can be, forinstance, a non -insulated audio socket.

Calibration and useA variable power supply is required forcalibrating the meter.

Set the meter to the 5 pC range (S2closed).Adjust the variable power supply togive an output of exactly 1.06 V if C1is used and of 1.0 V if C5 -Cg are used.Check the output with a digital volt-meter.Connect the output of the variable powersupply across CI or C5 -C9, as the casemay be.Adjust P1 for fulll-scale deflection(f.s.d.) on MI.

Fig. 4. Completed printed circuit board.


When the earth wire has been connected,the power supply has been switched on,

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and reset knob S1 has been pressed,the charge meter is ready for use. Themeter should then be at 0. Touch theinput, or connect an object suspected ofhaving a static electric charge to the input.

Never forget to press the reset buttonbefore making a measurement. Also, it isadvisable to start a measurement withthe meter set to the higher range.

Parts list

Resistors:R1 = 100 S2

R2 = 1.00 kl), 1%R3 = 1.051(52, 1%R4 = 19.1 kt2, 1%R5 = 27 IcS2R6, = 2.7 kS2Rg, R9 = 100 liS2131 = 25 Id/ preset potmeter

Capacitors:C1* = 4.7 pF, 100 V, polystyreneC2 = 100 pF, 16 V, radialC3 = 100 nFC4 = 10 pF, 16 VC5 -C9* = 1 pF, 63 V, polystyrene

1,

* alternatives - see text

Semiconductors:D1 -D5, Dg = 1N4148D6 = LED, green, low currentD7 = LED, red, low current

Integrated circuits:ICI = TLC274CN

Miscellaneous:S1 = miniature spring -loaded

push-button switchS2 = slide switch, 1 make contact , PCB

modelS3 = single -pole, single -throw switchM1 = moving -coil meter, 50 pABti = 9 V battery with terminal clipPCB Ref. 940033 (p. 110)

[9400331

01 0:: 0,3 04

0 \\4\41111111111104/04;/ 5"NC

0 J_KI 2 0

RESET

0.5µC SRC

0 0+_CHARGE

METER

Fig. 5. Suggested final assembly of the charge meter. Fig. 6. Suggested front panel.


A A

6.00 U

AC4, u0

OSCILLOSCOPE LIVE CHOP Page 0.0046.6 U

C4uA.0

2.00 4.0 Psec 33.3

0.00 ] Nes10.0 ysec

26,620.0 msec

-2.00 50.0 msec 20.0

-4.000.1 msec

13.30.2 msec

-6.00 0.5 msec 6.66

-8.001.0 msec

0.002.0 msec

-10.0 5.0 msec .6.66

11.00(psec) 12.00 10.0 nsec

FREEZE ONE SHOT MODE CH1 SET CH2 S20,0 msec

50.0 msec

TIME/DIU TIME-MAG. TIME-OUT HYSTERESIS SLOPE 0.1 sec CH 10.2 sec

PRINT COMMENT READ DISK WRITE DISK DEVI CEITSE7TTNGS

11 " IConnect the HANDYPROBE to the parallel printer portof the PC and start the software Measuring can becarried out at once The HANDYPROBE does not needan external power supply Some technical parameters0 5-400 V softwareselect input range;one input channel;8 bits resolution(overall accuracy 2%);A complete softwareprogram consisting ofa digitalstorage oscilloscope,spectrum analyzer,voltmeter and atransient recorderis provided.The HANDYPROBE iseminently suitable forservicing andeducational purposes.

The TP5008 is an interface cardthat provides an analogueoutput in addition to two inputchannels. This output incombination with the twoinputs may be used for thesetting up of a completecontrol loop The outputmay also be used as a -function generator.The TP5008 has aresolution of 8 bitsand a sampling rateof 200,000 samples/sec (200 kHz) The input range may be set to 0.5-20 Vfull-scale deflection. The output range covers 1.25-2.5 V.The TP5008 is fitted with BNC connectors and isdelivered complete with a user manual and softwareSeparately available are 1 1-1 10 probesand 1 100 oscilloscope probes

4

I 99

197

TiePie engineering manufactures a completerange of computer -controlled measuring instrumentsConnecting these units to a PC (MS DOS 3 0 or higher)results in a number of compre-hensive test instruments - 0Sci I FOSCOPC

- voltmeter;- spectrum analyzer;- frequency meter;- transient recorder.

All measured data can be storedon disk or run off for documentation Because of themany trigger possibilities, a variety of signals can bemeasured, while the powerful software enables amultitude of measurements to be carried out in astraightforward manner Application areas includeservice, medical research, automatic test systems,research and development, and education

1 II IIA

I P

The HANDYSCOPE is connected to the parallel printerport This makes it possible to carry out measurementswith a laptop or notebook PC Because of its highresolution (12 bits), the HANDYSCOPE is a very accurateinstrument The measuring rate is 100,000 samples/secEither of the two channels can be set independentlyover a range of 0 5-20 V (with a 1 10 probe up to 200 V)The advanced software enables many measurements tobe carried out Two probes (switchable 1 1-1 10) areprovided The HANDYSCOPE is constructed as a smalltable model with two BNC connectorsThe length ofthe cablelinking thePC and theHANDYSCOPEis 1 8 m,which can beextendedto 3 8 m 299

The TP208 is an interface cardwith a measuring speed of2x20 Megasamples/sec(8 bits) Phenomena shorterthan one millionth of asecond can still bemeasured wellThe completely digitizedtriggering ensures verystable triggering withmany triggerpossibilitiesThe TP208 has aninput range of5 nnV/div to 20 V/div in 12 steps and an auto calibrationfunction Since both channels may be sampledsimultaneously, phase differences can be measuredvery accurately Even single phenomena can bemeasured since each channel has a32 KByte memory Comprehensivesoftware is provided

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34

PPLI Ti N N TE

Temperature sensors and switches in theTC62x series from Teledyne Compo-

nents make some interesting applications prac-ticable. They are particularly suited for ap-plications where, owing to shock and vibra-tion, mechanical devices can not be used. Bothsensors and switches operate from supply volt-ages in the range 4.5-18 V.

The TC620/621 can react to an upper anda lower temperature setting with the aid oftwo resistors. Three outputs serve to controlthe external load (fan, heating).

The TC626 is a 3 -pin thermal switch in-tended for operation in the frequency range0-125 °C.

The accuracy of the switching tempera-tures, according to the manufacturers's data, is±3 °C.

Sensors TC620/621

The internal circuit of sensors TC620 andTC621 is shown in Fig. 1. Whereas in the TC620an internal PTC (positive temperature co-efficient) detector converts changes in the tem-perature into changes in resistance, theTC621 operates with an external NTC (neg-ative temperature coefficient) resistor as de-tector. This makes the operation independentof the chip temperature, and makes it pos-siblel for the detector to be sited in the mostconvenient position for the particular ap-

The content of this note is based on information received from manufacturers in the electricaland electronics industries, or their representatives, and does not imply practical experience by

Elektor Electronics or its consultants.

SOLID-STATE TEMPERATURE SENSOR TC62X

By G. Kleine

FUNCTIONAL DIAGRAM1

NC 1

120REF

CC

THERMISTOR

e(PTC) 1.20

MP

TC620

0 -

(RTC)

LOW LIMITCOMP

HIGH SETAMP

LOW SET

HIGH UNITCOMP

3LOW SET

AMP

HIGH SET

-4/1/1e-- S ROCONTROL

CND LATCH15-4

CND

RLOW RHIGH

NOTE: LATCH 0 la "C" (STANDARD)LATCHTS "H" (OPTION)

plication.Inputs LOW SET (pin 2) and HIGH SET (pin 3)

serve to set the two threshold temperatures.This only requires a resistor to the +ve supplyline, V. The value of the resistor determinesthe position of the threshold according tothe formulas:

R = 0.783T+91 (T<70 °C)

R = T+77 (T>70 °C)

MP

AMP

COMP

COMP

TC621

Vcc

HIGH LIMIT

6LOW LIMIT

S R

LATCH 5CONTROL

RLOW RHIGH

NOTE: LATCH ISM "C" (STANDARD)LATCH 0 M :14" (OPTION)

940012-11

where R is the resistance in kCI and T is thethreshold temperature in °C.

The TC620/621 circuits have three out-puts: LOW LIMIT, HIGH LIMIT, and CONTROL.

The first two are used to indicate whether therelevant threshold is being exceeded. In theTC620 they are logic low when the ambienttemperature is below the threshold and logic1 when the ambient temperature is above thethreshold. The third output, in conjunctionwith a bistable, has an hysteresis function.

TI C R/Ics-2

3IC2 = 74HCT04

0 91 IC2d IC2e

10 99 * multiturn 8 10

20 107

30 115

40 122 9

50 13060 138

HIGH HIGHSET LIMIT

TC620GND CONTROL

IC2f

12

13

940012-13

5V

CONTROL


Table 1Type Case DetectorTC620 Cxxx internalTC620 Hxxx internalTC621 Cxxx externalTX621 Hxxac external

COA = 8 -pin SOICEOA = 8 -pin SOICCPA = 8 -pin plastic DIPEPA = 8 -pin plastic DIPMJA = 8 -pin ceramic DIP

Controlnormal polarityinverse polaritynormal polarityinverse polarity

0 °C - 70 °C-40 °C - +85 °C0°C - 70 °C-40 °C - +85 °C-55 °C - +125 °C

4

5

1144002 A

.7;1_VALVE

120 VAC 311 24 VAC

12V

A 1144002

STANDBY

2.a

944002 A j 194002

1144002

11733055E 91.3k 5

TypeTC626 yyy CABTC626 yyy EABTC626 yyy VABTC626 yyy CZBTC626 yyy EZBTC626 yyy VZB

Table 2Case3 -pin TO -2203 -pin TO -2203 -pin TP-2203 -pin TO -923 -pin TO -923 -pin TO -92

Ambient temperature0 °C - 70 °C-40 °C - +85 °X-40 °C - +125 °C0 °C - +70 °C-40 °C - +85 °C-40 °C - +125 °C

where yyy indicates the switching temperature.Switching temperatures between 0 °C and 125 °C are available in5 °C steps; for instance, a Type TC626 045 VAB is housed in aTO -220 case and has a switching threshold of +45 °C

12V

POVNicAD

PIN CONFIGURATIONS

TO -220

1 2 3

TO -92

1 2 3

6

1 = OUTPUT

2 = VCC (CASE)

3 = GROUND

940012-168

When the HIGH LIMIT threshold tempera-ture is exceeded, the bistable is set, where-upon it can start, say, a cooling system viapin 5 (that is, the CONTROL output), which isthen logic high. Only after the temperaturehas dropped below the LOW LIMIT thresholdagain, is the bistable reset (when the CON-TROL output becomes logic low)-see Fig. 2.

In the Type TC620-H the CONTROL out-put is active low.

The operation of the TC621, owing to itsexternal NTC resistive detector, is exactly

940012.15

SYSTEM OVERTEMPERATUREPROTECTION

5V TO 18V

NC

SYSTEM POWER

NC = NORMALLY CLOSED940012-16a

the opposite. Compared with the TC620, itsHIGH LIMIT and LOW LIMIT are reversed, as arethe allocation and polarity of the three out-puts. This means that in this IC the outputgoes logic low when the ambient temperatureexceeds the set threshold. The CONTROL out-put will have the same polarity as that in theTC620 if the other Q output of the bistableis used. Thus, pin 5 becomes logic high whenthe HIGH SET threshold is exceeded and logiclow when the temperature is below the LOWSET threshold.

Table 1 gives a correlation of the vari-ous versions of the TC620 and TC621 and therelevant temperature ranges.

The TC620 may be tested with the simplecircuit shown in Fig. 3. The two resistors thatdetermine the threshold temperatures areconnected in series with preset potentiome-ters, which enable accurate settings to be ob-tained (set the resistance with the aid of anohmmeter).

Because of the PTC detector, it is impor-tant that the chip does not warm up. There-fore, the manufacturers permit an outputcurrent of only 1 mA. In the prototype cir-cuit, each output is connected to a driverstage contained in IC2.

Since the TC621x uses an external NTCdetector, its output current can be up to10 mA.

Figure 4 shows how simple an applica-tion circuit using a TC620/621 chip can be.Here, dependent on the ambient tempera-ture, a fan is switched on and off. The CON-TROL output of a TC620 drives a power MOS-FET, which functions as the on/off switch forthe fan.

Figure 5 shows how a thermostat isswitched by a TC620. In the diagram, the powerMOSFET switches a valve in the heating sys-tem. The circuit is powered by the 24 V supplyof the heating system. When the power MOS-FET is on, a standby battery comes into cir-cuit.

Thermal switch TC626

The Type TC626 thermal switch is availablefor operation in the temperature range0-125 °C. It is housed in a TO -220 orTO -92 case-see Fig. 6a. The switching out-put delivers op to 10 mA in the TO -92 ver-sion, and up to 50 mA in the TO -220 version.Table 2 gives an overview of the variousversions and the associated temperatureranges.

The switching output of the TC626 is logiclow as long as the threshold temperature isnot exceeded. When the ambient tempera-ture reaches the threshold, the output becomeslogic high. This makes it possible, for in-stance, to protect an apparatus by having arelay switch off its supply voltage when a giventemperature is exceeded-see Fig. 6b.

[940012]


36

GENERAL PURPOSE INFRA -RED BUFFER

The buffer enables 'stretch-ing' the signal of any infra-

red (IR) remote control. Thismakes it possible, for instance,to control a video recorder inthe living room from the bed-room or kitchen. The high -fre-quency modulated binary sig-nal is converted by an IR re-ceiver/decoder (see point 1 inthe diagram) into a serial sig-nal without that high frequency

The trailing edge of the re-ceived signal is delayed by RI -C1,since the IR receiver delaysthe leading edge. Without thiscompensation, the bits wouldbecome slightly wider thanthey were originally. This mayresult in errors in the receiverwhich ultimately must decodethe signals, or a contraction ofthe distance to be spanned.Owing to D1, the RC networkdoes not affect the leading edge(2).

To retransmit the decodedsignals as IR signals, the lowerperiods of the signal must befilled with the basic frequencyof the detected signal, whichin the RC -5 code is 36 kHz.This is done with the aid ofIC la, IC 1, and ICid.

When pin 8 of IC lc is high,this gate will generate the car-rier frequency with the aid ofR2, P1 and C2. This signal is usedvia gate ICid to switch outputtransistor T1. This high fre-quency is transferred whenthe received signal is low, be -

IR - IN

R6

14 C4U5

C3

IC1

\;l TUUn 4V7 25V

R1

1N4002D4 K2 7...15V

500mA

IC1b

1 11 FiLE 40

40

L_Th_ 40

FR EQ1:1-:1E1Cy IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

IR OUT _11111111 1111111LJ11111111111111111L11111111_ 40

cause the output of IC la is thenhigh.

Gate ICid is needed to switchthe transistor off when oscil-lator IC 1, is disabled.

Fit D2 and D3 close to theequipment that is to receivethe IR signals. The link be-tween the LEDs and the pre -

R5

SFH505A

-I li-

sent circuit can be simply ofloudspeaker cable.

The power supply may be amains adaptor that can de-liver a current of about 0.5 A.

Preset P1 may be adjustedby 'ear': simply vary it untilthe largest required distancecan be spanned. If an oscillo-

SFH506 IS1U60

+ s 1V1.

944098 - 11

scope is available, comparethe frequency of the original sig-nal with that of the oscillatorand adjust P1 until they areidentical.

Design: A. Rietj ens[944098]

PROGRAMMABLE PULSE SPACING METER

1.he meter can measure thespacing between the trail-

ing edges of not fewer than two,nor more than, nine pulses ina train. The number of pulsesis selected by a rotary switch.

The interval is measuredwith the aid of a 1 MHz pulsegenerator, IC4. During mea-surements the generator signalis present also at the output ofthe circuit to enable an exter-nal counter to be used.

Decade scaler IC2 is resetwith switch S1, whereupon

pin 1 (output 0 ) of BCD -to -decimal converter IC3 goes,while the level at all the otheroutputs of this circuit go high.This results in the output ofICid becoming high, so that D2lights. The 1 MHz pulses fromIC4 (arranged as a :16 divider),or the external generator sig-nal, depending on the positionof S3, are then blocked by IC id.

On the trailing edge of thefirst pulse that reaches the cir-cuit after this has been reset,IC2 is set to position 1. The level

at pin 1 of IC3 then goes high,resulting in the clock signalappearing at the output of thecircuit. On the trailing edge ofthe second pulse, pin 3 of IC3goes low, whereupon IC i d blocksthe clock pulses if rotaryswitch S2 is in the positionshown in the diagram. Settingthis switch to a different posi-tion determines at which clockpulse the transfer of the 1 MHzpulse train is blocked. Thepulse input is then disabledvia the pole of S2 and gate ICI,.

The counter connected tothe output of the circuit indi-cates how much time haselapsed between the first andthe next desired (2-9) pulse.At the specified reference fre-quency this will be in steps of1 p s. If the clock signal were1 kHz, the steps would be 1 ms.

The circuit draws a currentof about 20 mA, which makesbattery operation possible.

Design: K. Dietrich[944002]


21 S3

1

CTR143

5 1MHzX1IC4I16MHz

11 !G

R4 R5 RCX10

714

9 CT 4 13CX 8

59

C9 C102

CT=0MIM 2

IME MIM 74HCT100p 22p 4060

3

2

5V®

S1

ffs,

IC1 a

O

MIM

astable relays have the greatLi advantage that once theyare in the wanted position theydo not need power to maintainthat status. Another advan-tage is that their position is re-tained when the power fails oris switched off. This means thatsuch a relay can be used as asemi -permanent memory.

The present circuit is in-tended to drive a bistable relay.Typical of such relays is that theyhave two windings.

Since only a short voltagepulse is needed to switch the relayto its wanted position, the drivecircuit contains two mono -stable multivibrators (MMV).One of these consists of IC ib,C1 and R2; the other of gates ICI,and ICid and C2 and R3. BuffersT2 and T3 ensure that the MMVscan provide sufficient current.

5V

51p

CIA ci A414 1. D2IC4

1:IC1 IC2 IC3

10077 1007. 111) 11) .17100n (1..? .1700n

5V

R3

R2T1

4k7

IC1bIC1 c 12

8

BC547B

IC1d

.8 9

10

11 N CTR DWI 0

IC2>2+

G2

4tG1

841) BCD/DEC

0

2

14 ff&Si if&13

153D

3 153

48- 2 14 IC32 4

10 6 134 5

74HCT428

7

8

S2O

IC1 = 74HCT1327 12

[i96.4.9 613

12

2CT=0

1CT=9

0\JO 130V1 7s

74HCT192 98 0

0s' 01 011 12 944002-11

DRIVE FOR BISTABLE RELAY

The digital input signal isbuffered and inverted by T1,so that a leading edge of thesignal at the base rises, whereasthat of the signal at the draindecays. A decaying leadingedge triggers MMV IC lb, where-upon the output of IC lb brieflygoes high. This level switcheson T2, so that the associatedwinding of Re1 is energizedand the relay switches. A trail-ing edge at the input causesthe other MMV to be triggered,which results in the other wind-ing of the relay being ener-gized. The relay then switchesto its second position.

Diodes D1 and D2 protectthe output transistors againsvoltage peaks caused by theswitching of the relay.

Design: G. Kleine1944111)

TTL

5...15V

IC1 a

0 d&'944111 - 51

5...15V


38

SERIAL 12 -BIT A -D CONVERTER

rre MAX187 is eminentlysuitable for building a good -

quality 12 -bit A -D converter.Communication with the com-puter is serial, but not via thestandard RS232 protocol. Allthat is needed are three freeI/O lines. In the prototype, theCentronics port was used.

The diagram shows a ther-mometer designed around theMAX187 with an AD592 serv-ing as the sensor. Because of thepotential across IC2 and re-sistor R1, a supply voltage of 8 Vis required. The A -D converterworks from 5 V, however. Thisis why there are two voltageregulators. For other applica-tions, IC I can, therefore, beomitted. Although the circuitdraws a current of only a fewmA, the power supply is nottaken from the Centronics port.

The A -D converter is enabledby making pin 3 high. If this pinis left open, the IC is enabled,but the internal reference volt-age (4.096 V) is disabled. Inthat case, an external refer-ence voltage must be applied topin 4.

A start -of -conversion pulseis generated by making pin 7low. This pin must remainlow until the conversion datahave been read. During theconversion, the clock input(pin 8) must be low. The dataoutput (pin 6) is high impe-dance when pin 7 is high. Pin6 is low as long as the conver-sion lasts, but goes high assoon as it is ended.

The associated software mustbe able to detect the going highof pin 6, whereupon it mustcommence with reading the 12data bits, starting with the MSB.Thirteen clock pulses at pin 8are needed for this. The datachange at the trailing edges ofthe clock.

The MAX187 is quite fast:8.5 ps for the conversion: 13times 0.25 ps for reading anda pause of 0.5 ps: a total con-version time of 12.25 ps. See alsothe timing diagram.

For use as a thermometer,the QBASIC program shownindicates the measured tem-perature on the monitor. QBA-SIC is delivered free of charge

MINIMUMCYCLE TIME

DOUT

CS

maxwrite = &H378maxread = maxwrite+1

WHILE 1OUT maxwrite, 128: REM CS highOUT maxwrite, 0: REM start conversion

WHILE 1NP(maxread) AND 128 = 0: REM wait for EOC (input inverted!)WEND

OUT maxwrite, 1: REM clock high, extra clock to startOUT maxwrite, 0: REM clock lowtotal = 0FOR clocks . 11 TO 0 STEP -1OUT maxwrite, I

value% . (NOT 1NP(maxread)) AND 128: REM inverted input!IF value% <> 0 THEN total = (2 clocks) + totalOUT maxwrite, 0: REM next clock

NEXTPRINT total

WEND

I ze

94417,3

SCLK - L,

ee 14- EOC

4

CIDOIDCIOGIOGICICIC1300

INTERFACE IDLE -IV 14-2,==÷4--1

EOC CLOCK OUTPUT DATA

A / D STATE TRACK4.1.4_CONVE0RSION 1.14 TRACK OxilF CONV.1

8.5psUCONV 414- Op. -19+4 12 x 0.250us = 3.25ss 04- Ops 0.5us(1cs I

TOTAL = 12.25ps14

12V D1

1 N4001

78L08ici

CI

IM100/25V

78L050 IC30

1.TRZVII3-1(1)T .14-IDLE

AD592 78LXX

+1NC

4

IC2

AD592

2

C2 C3oT1Op 100n6V

Al

-g

V+

SD SCLK

IC4

CS

MAX187AN DO

with MOS-DOS versions 5 and6.

Design: K.M. Walraven[9440701

GND REF

5 4C4

4/716V

14 02

D7

O

O

3-016 0

501 8

6-0

/_020

21

9

07

944070-11

22O

1C0O

23

" 024

11_025

110

id 944070-12


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53-55 Main St, Grassington, North Yorks. BD23 5AA.


40

DISCRETE PREAMPLIFIER

1guality-conscious audio buffsstill prefer discrete designs.

And quite rightly so, becausealthough there are very good op-erational amplifiers available,discrete designs offer just thatlittle bit extra.

The present preamplifier isa symmetrical Class A design.The input is a double differentialamplifier consisting of dualtransistors Type MATO2 orMAT03. A stable d.c. operat-ing point is ensured by currentsources T3 and T4, which useLEDs as reference-D 1 and D2respectively.

The current through the LEDsis held stable by current sourceT5. It is essential for good ther-mal stability that the transis-tors and associated diodes (T3and D 1 , and T4 and D2) aremounted in close contact.

The input signals are ap-plied to push-pull drivers T6and T7, which feed the outputstages, consisting of emitterfollowers T10 and T11. Transis-tors T8 and T9 ensure a constantquiescent current through theemitter followers. It is necessaryfor good thermal stability thatT8 and T10, and T9 and Ti 1, aremounted in close contact. To thisend, their flat sides, with heatconducting paste in between,are juxtaposed. The pairs areheld together with a loop of barecopper wire.

Before the mains is switchedon, set P1 to maximum resis-tance. Switch on the mains,wait for about a minute andthen adjust P1 for a quiescentcurrent through T10 and Ti 1 of15 mA, corresponding to a volt-age drop of 150 mV across R23and R24.

Since the amplifier is d.c.coupled throughout, the like-lihood of a fairly high directvoltage at the output wouldbe great, the more so becausethe input transistors are nottruly complementary. This is,however, obviated by an actived.c. correction that holds the di-rect voltage at the output atzero in all circumstances. Forthis purpose, the output signalis passed via low-pass filterR26 -C13 to integrator ICI. Tisarrangement does not affectfast variations of the signal. If,however, the output signal hasa d.c. component, T12 will con -

A = OV

B = 2V

C = 1V76

D = 1V4

E = 8V6

F = 1V43

0

L27p

to be coupled thermally

* see text

MATO2

MATO3

T12

BC55OC

00k

15V

BC560C

BC550C

115

:100n

IC17

0P77

15V C)

2p2

:16 r4

TOOn

3

7

15V

BC560C

BC55OC

D3

2x 1N4148

15V

C)

BC337-40

C8 7-sIN=

1p

T10

R23

R25 0

BC327-40

2200 1100p

15V

D4 C13mw

72

R26

475k

Fig. 1. Circuit diagram of the discrete preamplifier

duct to some degree, so thatthe bases ofT1 and T2 are pulledinto a negative direction. In anegative direction, because Ti(n -p -n) has an inherently greatervoltage amplification (x3) thanT2 (p -n -p).

Adjust P2 immediately onswitch -on for as low a directvoltage at the output as possi-ble. From then on, any varia-tions caused by temperaturechanges will be corrected by IC 1.The speed at which the cor-rection takes place can be in-creased by giving R26 and R27lower values.

It is important for optimum

rs C)15V

944063 - 11

Some parameters(measured with an output of 1 V r.m.s. across 47 MI)

THIS

THD N(B = 22 Hz -80 kHz)

Signal-to-noise ratio(B = 22 Hz-22 kHz)

BandwidthSlew rateRise timeInput impedanceSensitivityPeak output voltage

50.00005% (at 1 kHz)5.0.0004% (at 20 kHz)<0.0012% (20 Hz -20 kHz)

>104 de

1.5 Hz -3.7 MHzabout 200 V us -1about 0.1 us47 kit150 mVabout 9 V r.m.s.


41

clepz

LeL IOIin011O,14

T1 (..bo 16 it!Ai RS

0o

00

C13

6

0-0

olio

T9

T11

011 SI 1

Fig. 2.Printed circuit board for the discrete preamplifier.

Fig. 3. Completed printed circuit board.

symmetry that the currentsthrough T1 and T2 (and thus thevoltage drops across R9 andRIO are equal. This can only beif the potentials across D 1 andD2 are equal, and it is, there-fore, advisable to match thesediodes for equal voltage with atest current through them of3 mA. When the diodes arematched, the drops across R13and R14 should not differ bymore than a few millivolts.

The same applies to T6 andT7: for good symmetry theyshould be matched for equalbase/emitter voltage, with a

current through them of 5 mA.This matching can not be donein the circuit, because the volt-age drops across R17 and R18will be equal whatever, other-wise the output would not bezero.

Low-pass filter R2 -C2 is des-digned for maximum slew rateat a cut-off point of 9-10 MHz.If this large bandwidth resultsin high sensitivity to interfer-ence, it may be advisable tolower the cut-off point. If the valueof C2 is increased to 680 pF,the cut-off point drops to about400 kHz. At the same time, the

slew rate deteriorates to about20 V ps-1.

The preamplifier is best builton the PCB in Fig. 2, which isavailable ready-made.

The supply lines should bestabilized by a suitable voltageregulator.

Parts list

Resistors:R1 = 47.5 kQ, 1%R2 = 470 52R3 = 1.00 kQ, 1%R4 = 5.62 MI, 1%R5, R6, R9, R10 = 806 Q, 1%R7, R8, R11, R12 = 80.6 S-1, 1%R13, R14 = 221 Q, 1%R15 = 2.7 kQR16 = 820 QR17, R18 = 249 Q, 1%R19, R20 = 10.0 k52, 1%

R21, R22 = 390 QR23, R24 = 10.0 S2, 1%R25 = 47 QR26, R27 = 475 k4, 1%R28 = 27 lc4R29 = 3.9 k4R30 = 100 lc4R31, R32 = 392 IcQ, 1%P1 = 10 1W preset potmeterP2 = 100 IcQ preset potmeter

Capacitors:C1, C13, C14 = 2.2 pF, 50 V,

pitch 5 mmC2 = 33 pF, 160 V, polystyreneC3 = 10 pF, 160 V, polystyreneC4, C5 = 100 pF, 6.3 V, radialC6, C7 = 150 pF, 160 V,

polystyreneC8 = 1 pF, pitch 5 mmC9, C11 = 220 nFC10, C12 = 100 pF, 25 V, radialC15, C16 = 100 nF

t00

Semiconductors:D 1 , D2 = LED, red, flatD3, D4 = 1N4148T1 = MATO2T2 = MATO3T3, T6, T9 = BC560CT4, T7, T8, T12 = BC550CT5 = BF256CT10 = BC337-40T11 = BC327-40

Integrated circuits:ICI = OP77

Miscellaneous:PCB Ref. 944063 (p. 110)

Design: T. Giesberts

[944063]


42

HEAT SINK MONITOR

e monitor is intended es-pecially for force -cooled

power resistors mounted on aheat sink. Such construc-tions are used, for instance,to test audio output ampli-fiers. Since it may be forgot-ten to switch the associatedfan on during testing, the re-sistors can overheat with allthe consequences of this.

It is, of course, possible touse in series with the re-sistors a relay that is ener-gized only when the power tothe fan is switched on. Thisis, however, not feasible withlow -value resistors (e.g., s1 52)because the transfer resis-tance of the relay may thenplay too large a role.

Another method is the useof a battery -powered alarm,which actuates a buzzerwhen the temperature risesabove 80 °C. When the mainsto the fan is switched on, thealarm is disabled. The pre-sent circuit then ensures thatthe fan is operated when thetemperature reaches 80 °C.The advantage of this ar-rangement is that there is no(electrical) fan noise at lowpowers.

The circuit is powered bybattery Bt1 via diode D4 ifthere is no mains voltage pre-sent. Stage T3 is not poweredand the logic level at the in -

0 12V

R5

g

IC1 = 4093

IC1C9 IC1b

106d&

R4 R3

5

C1

ffs,

R2

4 1

IC1a

d&

+V C)Bz1

R1

'3 MI (FL.

BC547

K101

BAT85

12V 0R7

14.2W5BD240

BC3371N4001

0

D2

05 12V

T1

0R8

Bt1

0 Di

9V

C

13

1N4148

IC1 d

D3 -O.-Ow

R9

0IC1

0

1N4148

C2

100n

012V

0

puts of gate ICI, is 0. This en-ables oscillator IC lb, but thiscan not yet oscillate becauseC1 is short-circuited by athermal switch connected to

944001.11

K1. The output of IC la is thuslow, so that T1 is off and the(direct -current) buzzer is notenergized. When the tempera-ture rises above 80 °C, the

thermal switch opens andICib begins to oscillate,whereupon the buzzersounds intermittently.When the mains is switchedon, a 12-V potential is ap-plied to the emitter of T3,whereupon the level at the in-puts of IC lc goes high. Thiscauses the oscillator to bedisabled, so that the buzzer isdeenergized. At temperaturesbelow 80 °C, the sensor con-tacts are closed, so that T2and T3 are switched off.Above that temperature, thesensor contacts open, where-upon T2 arranges for the fanto be switched on via T3.When the temperature dropsbelow 80 °C, the sensor con-tacts close and the fan isswitched off.

Gate ICid provides alow -battery indication (whichoperates only when the mainsis switched on).

The sensor must be fittedon to the heat sink close tothe resistors. Any thermalswitch whose contacts openat 80 °C can be used.

The current drawn fromthe battery is only about10 pA, which rises to around10 mA when the buzzer is en-ergized.


INDICATOR FOR LEAD -ACID BATTERY CHARGER

his unit is intended as anadd-on for the many lead -

acid battery chargers that haveno charge indicator. A greenLED shows that the battery isconnected with correct polar-ity. A red LED indicates that thebattery voltage has reached itsoperating voltage, that is, thebattery is fully charged. A yel-low LED functions as on/offindicator, that is, shows that themains is connected.

The operation of DI and D3is straightforward and needs no

explanation. In the prototype,D2 glowed faintly at 13.5 V andbrightly at 14.4 V. Because ofthe tolerances in the zener andLED voltages, it may be neces-sary for a more positive indi-cation to add another diode inseries with DX or even to omitD. Owing to the vast differ-ences between commercialchargers, this can be ascer-tained only by trial and error.

Most standard chargers for12 V lead -acid batteries pro-vide a voltage of 13.8 V, while

fast chargers provide 14.4 V.Standard LEDs can be used.The + and 0 terminals in the

diagram must be connected tothe corresponding terminalsof the battery. The - terminalmust be linked to the secondarytransformer winding with good -quality cable. Make sure thatit is connected to the secondaryand not to the primary, becausethat could be fatal.

Design: K. Walraven[9440437]

D6

D3

GR E EN YELLOW

944037.11



oin

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44

80C451 CONTROLLER BOARD

The 80C451 from Signeticsis one of the many derivates

of the 'generic' 8051 originallymanufactured by Intel. Theobsolescent SC80451CCN64was first discussed in Ref. 1.The '451 has several ports morethan the 8051. Here, a smallcontroller board is presentedbased on the 68 -pin PLCC ver-sion of the 80C451, theSC80C451CCA68 (12 MHz) orSC80C451CGA68 (16 MHz).

As indicated by the circuitdiagram, the microcontrollerboard has all the 'typical' in-gredients: memory formed byan EPROM, IC3, an addresslatch, IC2, a power supply, IC5,a reset circuit, Si -R2-05, anRS232 interface, IC4, and con-nectors (boxheaders) K1 -K6,which allow you to hook upextension circuits. Perhapsless common is the on -boardI2C interface around mini -DINconnector K7.

Boxheaders K2 -K6 give ac-cess to the controller's plethoraof port lines. Boxheader K6 iswired to allow easy connec-tion of an LCD display. Sucha display can be used in 4 -bitmode only, while the contrastadjustment pot must be lo-cated on the unit itself. Also notethat the associated 'contrast'pin, number 3, of the LCD mod-ule is not connected to thecontroller board.

If a flatcable, a 40 -pin DIPheader and a 40 -way IDC socketare used, boxheader K1 givesa 1 -to -1 correspondence withthe pins of the 'standard' 8051controller in a 40 -pin DIL en-closure. However, to preventproblems, the '451 clock sig-nal is not copied to the socket.Jumper JP1 allows you to con-nect the 5-V supply of the '451system to the 8051 system.The 40 -way DIL socket enablesthe controller board to be turnedinto a simple 8751 emulator (seealso Ref. 1). In that setup, port 0of the emulated 8751 equalsport 5 of the '451. Similarly,port 2 of the emulated 8751 thenequals port 4 of the '451.

Although an I2C socket is pro-vided on the board, that shouldnot be taken to mean that the80C451 has built-in hardwareto interface with an I2C bus. Itshould be noted that the I2Clines of the controller board

5

5V

OPI

21 AL

\C' P

' 42'2 `4vaa 2

C'' :1.4.7 \/

N/P27 P46 /2 P3 4N/

P.5 \ P5.0 44

a.,..." 30 3.5',....P5.1 45

'' :'2

P4.4 \.../P5.2 46

P3.6 \''P5.3

P3.7 P5.5 49

C:1_33'6P4.2...../P5 6 50

\44.,p,.7

°4i713 N.1 \ / PS.6ti 67

4 7

23

5V

80C451

BST

PIA/

P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

P1.7

MOM°en. rex o

P3.4.70

P3 5.71

P3.80/1

5V

O

ICI

DI

P3.7/T1-0

80C451

4.6

P5.0

P5.1

P5.2

P5.4

P5 5

P5 6

P5.7

ALEIPPOG

Bottom View

oon

PO

P2 D

P2

P2 2

P2 3

P2 4

P2 5

P2.6

P2 7

P6

P6

P6

P6

P6

P6

P6.6

P6

EANPP

ODS

B LAG

A LAG

X2 VS.

54

IC5

PI

///

IC274FICT573

v

JP2

I ze 7

VPP

AO

A2DO

IC3 on

132

25

26 EPROM27

28 27C6429

07.10

211

112 .22 I,4

K6

1,059 P6 0

60 P6 Rs0

81 P6 FUT/

62 P60

B21-24

4 P6 02,267o

OA 9

66 P6 7 OAT, 0

O

,ALI

5V

10,

2 "V

Wee

SV

O

5788 88

5V/ 944009 - 11

pin 27C64 27C128 27C256 27C512

1 (JP2) Vcc Vcc Vcc A15

26 xx A13 A13 A13

27 (J P3) Vcc Vcc A14 A14


45

are capable of supplying up to 1.5 mA,which is less than a standard I2C line(3 mA). However, this need not causeproblems because 3.3-k52 pull-up re-sistors are used here. On the same tack,the switching thresholds of the '451 in-puts are not to I2C standard, but no realproblem there, either. Fortunately, anumber of elementary software routinesto implement I2C communication usingthe 80C451 are available from the PhilipsSemiconductors databank (bulletin board)

in Holland which can be contacted bymodem on (+31) 40 721102. Dial up anddownload the file I2CBITS.EXE.

The RS232 channel is a standard ap-plication of the MAX232 single -chip RS232interface. Although only RxD and TxD areimplemented, this should work in most,if not all, cases where a simple link is de-sired to a PC running a terminal emula-tion program.

All of the popular EPROM types 2764through 27512 may be used in this cir-

0 00 00 8O

t"."00 000

0 00 0 0

0 \000 oNa oooooo c0

S M M M oo oo. aC M E M : ; o o00 .'00. ., 000fN

t 00 00:0000:bbQ 00000 0

o[o

8888

.

888888881 8888 8

O

0 00

O 0O

0a

?o 0

O

0O9,00 00

000oo

0 00 000 00 0O 0 0O

0 0

O

CM ima

8888'-88888

O

w *OM

cuit - the selection is made with twojumpers, JP2 and JP3 (see table). Notethat pin 26 (n.c. on the '64) is perma-nently tied to address line A13.

Finally, the quartz crystal frequencyis 12 MHz or 16 MHz, depending on thecontroller type used. Capacitor C3 ismounted at the underside of the boardfor maximum decoupling efficiency. Currentconsumption of the board is of the orderof 30 mA, depending on clock speed andconnected extensions. In practice, a 100 mApower supply will be adequate for all andsundry applications.

Parts listResistors:R1 = 8 -way (9 -pin) 10 Id2 SILR2 = 10052R3, = 3.3 ki2R4 -R6 = 330 Q

Capacitors:C1, C2 = 33 pFC4 = 100 nFC3 = 100 nF (fit at underside

of board)C5 = 4.7 pF, 10 V, radialC6 = 100 pF, 10 V, radialC7 -C11 = 10 pF, 16 V, radialC12 = 100 pF, 25 V, radial

Inductors:L1 = 100 pH choke

Semiconductors:D1 = 1N4001

Integrated circuits:ICI = SC80C451CCA68

(12MHz) orSC80C451CGA68(16MHz)

(Signetics/Philips)IC2 = 74HCT573IC3 = 27C64 (see text)IC4 = MAX232IC5 = 7805

Miscellaneous:JP1 = 2 -way jumper.JP2, JP3 = 3 -way jumper.K1 = 40 -way boxheader.K2 -K6 = 10 -way boxheader.K7 = 6 -way mini DIN socket,

PCB mount.Kg = 3 -way PCB terminalblock.Kg = 2 -way PCB terminalblock.S1 = push-button 2CTL2X1 = 16MHz or 12MHz

crystal.PCB Ref.944069-1 (p.110).

Reference:1. 8751 emulator, Elektor ElectronicsMarch 1992.

Design: K.M. Walraven[9440691


46

S -VHS -TO -VHS CONVERTER

Most modern video unitsare provided with an S -VHS

or Y/C output. This output fur-nishes the black -and -white in-formation (luminance or Y) andthe colour information (chromi-nance or C) of a video pictureon separate pins. This separa-tion of data improves the qual-ity of a picture generated by anS -VHS signal appreciably com-pared with a standard CVBS sig-nal. Unfortunately, older tele-vision receivers without anS -VHS input can not processsuch a signal. It is for ownersof such older receivers that thepresent circuit was designed:it recombines the Y and C com-ponents into a CVBS signal.

The two components of theS -VHS signal are applied to theconverter via K1 and K2. Thelevel of the luminance compo-nent is 1 Vpp and that of thechrominance component is0.5VPP' For that reason, a weight-ing factor is applied in the re-combination of the components.The output signal is composed

The switch is typified by thevery few components needed

and its high sensitivity. Becauseof this, it has some limitations:

It is suitable for use with in-candescent lamps only.It has no switch -on delay, sothat the lamp will light alsoduring the day if the sensorbecomes shaded.It has no switching threshold,so that the lamp will lightup gradually.

The circuit is connected in se-ries with the lamp. The bridgerectifier ensures that both pe-riod halves of the alternating volt-age can be switched with the aidof thyristor Thi. The gate of Thlis driven via R1 -C1 and diacDi1. At the onset of each periodhalf, CI is charged rapidly viaR1. As soon as the potentialacross the capacitor has reachedsome tens of volts, the diacswitches, whereupon Thi beginsto conduct. It continues to do

C K1

of 1/3 of the luminance com-ponent and 2/3 of the chromi-nance component. The level ofthe signal at the base of T1 isthus 666 mV. The amplificationof the circuit is x3 (Rg:RRJ, so thatthe level of the signal at the col-lector of T2 is about 2 Vpp Thepotential divider consisting of

R11 and the input impedanceof the receiver (75 Q) halve thesignal being applied to the re-ceiver, whose level is, there-fore, 1 Vpp again.

If the input of the televisionreceiver is adequately decoupledfor d.c., capacitors C4 and C5 ,as well as R10, may be omitted.

LIGHT-SENSITIVE SWITCH

so until the next zero crossing,when it gets a fresh gate pulse,and so on.

When transistor T1, which isin parallel with C1, begins to con-duct, the potential across Ci re-mains virtually nil, so that thethyristor can not be ignited.

When the light -dependent

resistor (LDR) between the baseand collector of T1 is in light, ithas a low resistance so that Tiis on. The thyristor, and thusthe lamp, is off. When the LDRis in darkness, T1 is off and thethyristor, and thus the lamp, ison. The value of resistor R2 de-termines the moment of switch

A F,100n K3

I 010220µ16V

This presupposes that the inputimpedance is 75 Q for both thea. c . and the d.c. component.

The converter draws a cur-rent of about 25 mA.

Design: J Kircher[944004]

on, so it can be chosen to indi-vidual requirements.

The circuit is so sensitivethat great care must be takento ensure that the LDR can notreceive any light from the lamp(if it did, a sort of oscillator ef-fect would ensue).

The LDR should be a type thathas a resistance of about 60 Qwhen it is in bright light and ofabout 2 MS in darkness.

It is best to use a TypeTIC126D thyristor, not a TypeTIC106D, because this is sosensitive that the lamp wouldremain on. If a TIC106D mustbe used, its sensitivity can bereduced by soldering a 220 Qresistor between gate and cath-ode.

Since the full mains voltageis present at various points inthe circuit, it is essential thatthe switch is built into a well -insulated enclosure.

Design: J. Von te.19440171



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48

ROBUST A.F. POWER AMPLIFIER

rrilis is a no -frills audiopower amplifier based

on inexpensive transistors. Itis short-circuit protected, andhas a maximum power out-put of the order of 50 W into4 Q. As shown by the circuitdiagram, the amplifier is aclassic push-pull class -B de-sign.

To minimize the offset cur-rent which flows throughfeedback resistor R10, zenerdiodes D1 and D2 should bematched for equal zener volt-ages. Similarly, transistors T7and T8, the complementarypair BD139-BD140, shouldbe matched for equal base -emitter voltages, Ube. Theyare fitted on a commonheatsink to ensure that theyare always at the same tem-perature. If T7 and T8 are notmatched, or if D1 and D2 havedifferent zener voltages, itmay not be possible to com-pensate the offset voltage atthe amplifier output despiteadjustment of preset P1.

To negate the effect of theinput stage off -set variation,the feedback line is decou-pled by two parallel con-nected bipolar electrolytic ca-pacitors, C6 and C7.

Like T7 arid T8, the inputtransistors, T1 and T2, mustbe thermally coupled. Thiscan be achieved in a simpleway by clamping the twotransistors face-to-face withthe aid of a small band of alu-minium, copper or brass.

Because of their floatingbias, the input transistors aresensitive to supply voltagefluctuations. Each transistoris, therefore, provied with itsown regulator consisting of acurrent sources (T3 -T4) and azener diode (D1 -D2). Note thatthe tolerance on the FETsand the zener diodes maywell cause a deviation of upto ±1 V from the nominalsupply voltage required,which is ± 18 V.

Capacitors C8 and C9 inthe cascade stages formed byT2 -T6 and T1 -T5 serve to mini-mize the adverse effect of thebase -collector capacitances ofT1 and T2. The base -collectorjunctions of transistors T7and T8 are shunted by capac-itors (C10 -C11) because the

BD1 39 and BD1 40 altoughelectrically complementarytypes do not have the sameswitching speed.

When the amplifier is firstswitched on, the voltageacross R17 and R18 will settleat a certain value, and thenrise slowly by about 0.15 V.This is normal and mainlyowing to the simple designand the inevitable thermal ef-fects in T1 -T2 and T7 -T8. Thisvariation, however, calls for agood zener device to keep thequiescent current stable. Inother words, the zener voltagebetween the bases of T13 andT14 must be independent ofthe current variation throughT9 and T10. The quiescentcurrent is adjusted with pre-set P2. The 'super' zenerformed by T9 and T10 has ana.c. resistance which is aboutfive times lower than that of aconventional one -transistorstabilizer. For obvious rea-sons, both transistors are fit-ted on the same heatsink as

BF256

G D

Main parameters

Input impedanceInput sensitivity:Cl not fitted:rise timeslew rate:Cl fitted:slew rateBandwidth:THD+N:1 W/8 0:25 W/8 0:

25 W/8 0:

S/N (1 W/8 0):

max (THD+N = 0.1%):

47 ILO

1.25 V (30 W/8 SI)

<0.7 ps>40 Vps<1.5 ps>24 ps(30 W/8 0): 10 Hz - 180 kHz<0.005% (1 kHz)<0.02% (1 kHz)

<0.07% (20 Hz - 20 kHz)

>100 dB (B = 22 kHz)30 W into 8

56 W into 4 0Damping (20 Hz - 20kHz); 8 0):>350

Measurements conditions:Amplifier powered by a regulated ±25-V supply. Quiescent cur-rent (T13/T14) set to 200 mA; bandwidth 10 Hz to 80 kHz un-less otherwise stated.

the power output transistors.SOAR (safe operating area)

protection is provided bytransistors T11 and T12.Resistors R22 through R27have values which enable the

ac517 , BC516BC547B , BC557B

BC639 , BC640

C

R

BD139 , BD140

E LB

BDV64B BDV65B

C

C

B

BF256A

18V500mW

500mW

BF256A

*0V15

BD140

g

BC557B

R1±01/15

BD140

BD139

BD139

currents through T13 and T14to be kept within reasonablelimits when the amplifier out-put is short-circuited or con-nected to a too low im-pedance.

BDV65B

BDV64B

R25

944075-11

R28

J4

0O25V

C13

2200440V

714

40V25V


49

c;°111=6

0

+0

01-132L-10(nT11

R24 10

R28

33ro

0

-1co

2tin:20120o

WO R2110

I

The construction of theamplifier should be evidentfrom the circuit board layoutand the photograph. Tran-sistors T9, T10, T13 and T14must be fitted with ceramicwashers to keep their metaltabs isolated while still main-taining a low thermal resis-tance to the SK85 heatsink.T7 and T8 must also be fittedwith washers (mica types areo.k.) on their common heat -sink.

Be sure to set P2 for maxi-mum resistance (wiper fullycounter -clockwise) before ap-plying the supply voltage.Next, carefully adjust P2 for aquiescent current of about200 mA through T13 and T14,which should correspond toabout 200 mV across R28 andR29. Finally, the minimumloudspeaker impedance thatcan be used with the ampli-fier is 4 0.

Parts list(One channel)

Resistors:R1 = 470 S2R2 = 100 k1R3, R4 = 220 k12R5, R6 = 1 MS2R7,Rg = 470 kl2R9=6852R10 = 820 S2

[11

R11, R12, R17, R18 = 22 QR13 = 1.5 k.(2R14 = 1.8 Id2R15, R16 = 270 IIR19 = 1 k52R20, R23, R26 = 220 S2R21 = 100R22, R25 = 12 IcS2R24, R27 = 330 QR28, R29 = 0.1 0, 5 WP1 = 1 kt2 preset HP2 = 250 Q preset H

Capacitors:C1, C8, C9 = 1nFC2, C3, C12 = 1 pF, pitch

5 mmC4, C5 = 680 nFC6, C7 = 100 pF, 10 V,

bipolar, radialCio,Cii = 100 pF, 160 V

polystyreneC13, C14 = 2200 pF, 40 V,

radial

Semiconductors:DI,D2 = 18 V zener, 0.5 WT1 = BC517T2 = BC516T3, T4 = BF256AT5 = BC547BT6 = BC557BT7, T10 = BD140T8, T9 = BD139T11 = BC639T12 = BC640T13 = BDV65BT14 = BDV64B

Miscellaneous:Common heatsink for T7 -T8

Type SK12/50 mm(15 K W-1; Fischer).

2 TO -220 style ceramicwashers.

2 TOP -3 style ceramicwashers.

2 TO -220 style micawashers (cut to size).

-71

Heatsink 0.65 K W-1 forT9 -T10, T13 -T14,e.g, SK85/75 mm(Fischer).

PCB Ref. 944075 (p. 110)(two required for astereo amplifier).

Design: T. Giesberts1944075]

\


50

8TH ORDER BUTTERWORTH FILTER

usual in RC filter designs,esistors R1 -R4 and R5-Rg

are given equal values. Unfor-tunately, again as usual, thisleads to rather awkward valuesof the capacitors. However,rounding off these values tothe nearest El2 value leads toripples in the transfer charac-teristic. The specified compo-nent values give a cut-off fre-quency of 1 kHz.

The frequency characteris-tic is rather different from thatof a Bessel filter, as is the tran-sit time. Moreover, there is a ten-dency to ringing. This is be-cause the second section hasa 3 dB peak in its gain just be-fore the cut-off point. However,in practice this is hardly no-ticeable: the prototype was foundto be usable up to full drive ofthe opamps. The only noticeableeffect was a (very) slight dete-rioration in the signal-to-noisefigure around the cut-off fre-quency.

Although the NE5532 proved

11mim

18n807

R1

10k0

R13

MI6

0

R2

10k0

R3

10k0

C2MIM

76n732

IC1 = NE5532 IC1

13n016

R4

10k0

well up to the task, it may beworthwhile to use opamps withFET inputs. These generaterather more noise than bipolartypes, but, since the noise in the

3

C4

Tn1355

15V

15V

15MOM

18n724

filter is caused mainly by the re-sistor, this would not mattermuch.

Each of the NE5532 chipsdraws a current of about 4 mA.

1117

14n355

R8

IC1b6

C8

75318

944025 - 11

n

n

R11

R12


MAINS -SYNCHRONISED OSCILLATOR

e mains -synchronised os-cillator has certain advan-

tages over a simple zero cross-ing detector. For instance, thebrief failing of input pulsesdoes not immediately cause adisaster and spurious pulseson the mains have hardly anyeffect on the circuit.

Because of the feedback tothe positive input of ICI via R5,the opamp has some hystere-sis. This causes the output tochange state when the poten-tial across C1 exceeds the upperhysteresis threshold and tochange state again when thatvoltage drops below the lowerhysteresis threshold. Since C1is continuously charged via RI,the output of IC I continuouslychanges from one state to theother, so that the opamp behaveslike a rectangular -signal gen-erator. The duty factor dependson the threshold voltage; withvalues of R3 and R4 as specified,it is not greater than 50%. The

frequency of the oscillations isdetermined mainly by R1 andC1 and should be just a littlehigher than the mains frequency(55-60 Hz).

The oscillator is synchro-nized with the mains frequencyby connecting the anode of Dito the secondary winding of thesupply transformer (that is,prior to the bridge rectifier).The positive pulsating directvoltage causes the dischargetime of C1 to lenghten, so thatthe oscillator frequency dropsand synchronises with the mainsfrequency. The synchronisa-tion causes a phase shift thatdepends on the strength of theinput signal and on the differ-ence between the mains andoscillator frequencies.

If the level of the 50 Hz inputsignal is <5 V or >20 V, thevalue of R2 should be changedaccordingly.

Before the circuit is taken intouse, check the frequency of the

5 2ov

of50Hz D1 R2

freewheeling oscillator (inputshorted to earth): this must beslightly higher than 50 Hz. Thefrequency depends to some ex-tent on the opamp used.

Suitable opamps are the typesLM358, TLC272, TLC271 andthe TLC2201; note that a 741is not suitable. If fast edges atthe output are desirable, anLM339 is a good choice. Note,

however, that this type has anopen -collector output, so thata resistor of a few IcS2 must beadded between the output andthe positive supply line.

The circuit as shown drawsa current of only a few mA.

Design: K. Walraven[944029]


kmPlease mention ELEKTOR ELECTRONICS 11.15c1/ conitictin,c; odrcrliNers

= z == z = == == === =.=

= = Z = = = = = = == = Z = = = = =

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TYPE W L H PRICET2 75 56 25 C0.77

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MB5 150 100 60 C2.35

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MB8 150 80 50 0.22ALL SIZES ARE IN MILLIMETRES

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VOLTAGE W D PRICEI2V D.C. M 120mm x 38mm E6.96

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VOLTAGE REGULATORS1 amp 7805/7812/7815 33p each7905/7912/7915 39p each2 amp 78S05/78S 12 54p each100mA 78L0S/78412/78L15 all 26p each. 79L05/79LI2/79L 15 29p eachAdjustable LM3I7T 70p each LM723 29p each L200 £1 .28 eachTransistors TIP2955 70p each TIP3055 70p each2N3053 29p each, 2N3055 70p each 2N4403 28p each, 2N3819 40p each

OPTODEVICES -LEDS -ETC

CRYSTAL OSCILATORS4.0mhz, 7.5mhz, 10mhz 12mhz, I 8.432mhz, or

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MICRO IC'SZ80A CPU 1.20;

Z80A PIO L1.50;Z8OB SI 0 £4.00

10p each 12 for L1.00 any mix20p each 6 for CI.00 any mix

red 60p each, yellow/green 70p each35p each, tri-colour 45p each

30p each 4 for CI.0025p each 5 for C1.00

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EPROMS 27C256-30 27C512-25. Once programmed but never used. Mounted on a plastic carrier,can easily be removed from the carrier or used with a low insertion force socket. 27C256 £1.00 each6 for 05.00 27C5 I 2 LI .20 each 5 for 05.00Suitable low insertion force socket 28 pin. 40p each 3 for C1.00EPROM 27C010-120 (EX NEW CIRCUIT BOARDS) 64.96 EACH

SAB 800535MICRO CONTROLLER f 11.75 EACH (EX -STOCK)

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65.95 eachMOSFET

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68000 HIGH PERFORMANCE VMEBUS BASED MICROCOMPUTER BOARD68000 CPU (8MI-1.), 256K Dual ported RAM expandable to I mega byte. Up to 2 kbyte eprom space, 8 bitstatus register, Fast multiprotocol comms interface link, (RS232 compatible),VEMBUS INTERFACE, on -boardsingle chip floppy disk controller. On -board monitor ROM. Real time clock, 24 -bit parallel 110. Can be used asa stand-alone microcomputer Over 350 pages of data supplied. 688.50 each

ALARM CONTROL PANEL 5T3000Wire free alarm control panel, detectors communicate with the panel bymeans of radio transmitters. Speech synthesis for programming andgeneral operating guidance. Built in user programmable telephone dialler*Up to 32 transmitters can be used* Programmable exit/entry and belltimers. Programmable user codes* Many other features* Full installationdata supplied.The only thing that has to be handwired is the output to thesiren/bell unit (not supplied)* These control panels cost over £300.00.

Yours for only 659.95.PASSIVE INFRA RED SENSOR/TRANSMITTER UNIVERSAL TRANSMITTER For connectionC25.85 each. Battery operated, available in 8mm of normally open or closed contacts for door/

range, 10m range or 25m range. window switches, pressure mats etc. LI7 .63 each

ALARM CONTROL UNITSingle zone alarm control unit built into a domestic light switch box. Ideal for home, caravan, boat, garage, shede.t.c. Facilities - Normally closed and Normally open loops. 24 -hour personal attack loop. Visual indication thatthe system is operational. Automatic entry/exit delay. Automatic system reset. Alarm output cmos logic level.PRICE COMPLETE WITH FULL INSTRUCTIONS 68.95 eachEX INSTALLATION SENSORS tested workingTYPE I. Measure 130ram x 70mm x 50mm with walk test led, relay output and tamper protection.12 volt dc supply required £6.50 each

TYPE 2.As above but a smaller unit 85ram x 75ram x 50 £13.50 each

TYPE 3. Ceiling mounting passive, infra red sensor 360° detection 12v d.C. supply relay output, tamper circuitand pulse count option. Data supplied. 01 2.00 eachPlease note: There may be variations in the size of she above FIR'S depending on stock at the time of orderings But the unit will

certainly be within the stated sizes.

DUAL TECH SENSOR Microwave and passive infra -red combined. led indication for each function.Measure 120 x 75 x 50ram 12 volt d.c. supply. Relay output. Tamper protection. £21.15 eachSUB -MINIATURE PASSIVE INFRA -RED SENSORBrand new passive infra -red sensor, measures only 33mmW x 24mmHx 29minD. Logic level output.Full data and application notes supplied. £7.95 eachSOUND BOMB Two tone alarm sounder incorporating four piezoelements in white plastic box. 100db I2v d.c. C5.99 each

MINIATURE HORN SIREN 100db two-tone piezo siren 12v d.c. 05.I7 eachVIBRATION SENSITIVE ALARMBOARD WITH PIEZO SOUNDEROriginally a bike alarm There is a short delay after activation then the piezo sounder operates for a presetperiod. E3.76 each or the above alarm board with a custom designed case fixing clip and keyswitch £995UNIVERSAL BELL TIMER 10 or 20 minute bell cut off +ve or ve trigger timed relay contacts 0496 eachMERCURY TILT SWITCH Standard on/off 2 CONTACT CI 00each 4 contact (directional) (150 each PIEZO VIBRATIONDOOR/WINDOW CONTACTS Surface or flush mounting white L 1 10 each SENSOR with data

JUNCTION BOX White 6 way 60p each PERSONAL ATTACK BUTTON C320 sheet CI 00 each

SIREN 12 volt dc forexternal use I I6db 68.95

PIEZO SOUNDER100db 3-I2v d.c. 40Ma,45ram dia. x 26mm 61.76

TEMPERATURE PROBEHigh quality probe consists of a resistire sensor mounted in a plastic covered probe with a I meter curled lead.Temp. range -40 to 150°C. Resistance at: I50°C 188.3 ohms; - 40°C 336.5 kohm; 25°C 10.0 kohm 70 ohms.

The original price of these probes was over £24.00. Full data supplied. OUR PRICE 63.76

POWER SUPPLIESASTEC AC9232-0I Switch mode PSU 50 watts input 230V 0.6A 50-60hz outputs + I 2V 2.5A, +5V6.0A, ± 5V 0.5A, ± I2V 0.5A. C17.80 EachSOLAR CELL 2 volt 150mA max, size 60 x 100mm CI.35 each 5 for £6.00BNC SOCKETS SO ohm single hole fixing 50p each 10 for C4.00MULTITURN PRESETS 20mm RECT, I K, 5K, 10K, 20K, 50K,100K, IMO 40p each, 3 for CI.00MINIATURE TOGGLE SWITCHESspdt 60p each spdt 3 position c/off 70p eachdpdt 70p each dpdt 3 position c/off 80p eachspdt biased 60p each spdt 3 position c/off biased both ways 70p each

dpdt 3 position c/off biased one way 80p eachMIN PUSH TO MAKE SWITCH 50p. MICRO SWITCH roller arm spdt 40p .

DIL RELAYS 5 volt dp/changeover 60p each 10 for C5.0012 volt dp/changeover 80p each 10 for 66.00

CAR HORN RELAY in metal can with fixing lug s/pole on 10 amp contacts CI 00 each 6 for 05.0020 AMP RELAY dp on 12 volt L1.50 each 4 for C5.00REED RELAY 12 volt Op each 10 for C4.00240 VOLT AC RELAY 3 -pole c/o 10amp contacts L1.50 each 4 for C5.00

RECHARGEABLE BATTERIESAA (HPT) 600mAH £1.02 each C(HPII) 1200mAH £2.99 eachD(HP2) I 200MAH f2.40 each PP3 8.4V 100mAH £4.77 eachFLUORESCENT LIGHT INVERTOR Drives an 8 watt tube directlyfrom 6v d.c. Data supplied. C4.50 each

BREADBOARDS173 X 65mm 840TP

C5.2.5 each9V D.C. CASSETTE

MOTOR40mm Dia 30 H

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6 FOR £5.00

BULK LEDSOFFER

500 5mm roundRED LEDS 125.85

£ 1.00 BARGAIN PACKSBO 1 4 x SUB -MINIATURE TOGGLE SWITCHES S.Pole P.C.B. MountingB02 3 x SUB -MINIATURE TOGGLE SWITCHES D.Pole P.C.B. MountingB03 3 x SUB -MINIATURE TOGGLE SWITCHES D.Pole 3 pos, centre offB004 3 x DILL SWITCHES 4 -way s.p. onB005 2 x DILL SWITCHES 8 -way s.p. on8006 2 x DILL SWITCHES 12 way 90' s.p. onB007 12 x PP3 BATTERY SNAPSB008 I x CAPACITOR I FARAD 5.5 VOLT 20mm dia. x 7mm highB009 5 x INSTRUMENT KNOBS (0.25" SHAFT) High quality grey plastic knob, collet fixing ISram dia.B010 3 x INSTRUMENT KNOBS (0.25" SHAFT) High quality grey plastic knob collet fixing 29mm dia.

8011 4 x MAGNETIC EAR -PIECE 8 ohm with 3.5mm plug13012 4 x 28 -WAY TURNED PIN DIL SOCKETB013 15 x 12 VOLT WIRE -ENDED LAMPSB015 2 x LIGHT DEPENDENT RESISTOR less than 200 ohms in day light, greater than 100

megohms in darknessB016 I x KEYPAD 20 -key in 5 x 4 matrix bubble type switch contactsB017 2 x PIEZO BUZZERS approx 3 to 20 volt d.c.B018 5 x 78M12 VOLTAGE REGULATORS positive I2V 500mA8019 4 x TLO82CP bi-fet op -ampsB020 20 x ASSORTED LEDS full spec. various shapes and sizesB021 3 x INFRA -RED DIODE TX/RX PAIRS made by Honeywell (no info)8022 3 x CONSTANT CURRENT LED 5mm round, red 2-18V d.c.or a.c. nominal 14mAB023 50 x IN4148 DIODE8024 2 x INFRA -RED TRANSISTORS FPT51338025 5 x DIACS8026 3 x BDX33C lOamp 100V npn transistor8027 12 x 2N3702 TransistorB028 12 x 2N3904 TransistorB029 12 x BC337 TransistorB030 4 x LM3 I7T Variable regulator mounted on a small heatsink13031 2 x MAN6610 2 digit 0.6" 7 segment display Com anode, amberB032 3 x PHONO TO PHONO LEADS 63cm longB033 15 x RECTANGULAR RED LEDS 6 x 6 x tram stackableB034 I x PHOTO SENSITIVE SCR mounted on a PCB, data sheet suppliedB035 4 x IECPANEL MOUNTING MAINS PLUG Snap fix8036 5 x ASSORTED PIEZO TRANSDUCERSB037 5 LENGTHS OF HEATSHRINK SLEEVING 8mm dia. 400mm long13038 25 x CERAMIC DISC CAPACITORS 0.1 mfd 63VB039 15 x MONOLITHIC CERAMIC CAPACITORS 0.1 mfd 63V, in a dill packageB040 25 x ASSORTED ELECTROLYTIC CAPACITORS PCB mounting useful valuesB041 25 ASSORTED PRE-SET RESISTORSB042 6 x 3.5MM LINE JACK SOCKETS (mono)B043 6 x 3.5mm JACK PLUGS (mono)8044 8 x 3.5mm CHASSIS SOCKET (mono)8045 2 x TRIACS 800V 8 amp8046 12 x BC2I3L Transistor8047 12 x MIN SLIDE SWITCH dpdtB048 IS x MIN CERMET TRIMMER POTS (good range of values)13049 I x PCB WITH TWO LARGE LEDS 15mm square, one red one green8050 I x I2VDC RELAY 4 pole c/o with plug in baseB051 4 x LM324 quad op -amps8052 4 x 555 TimerB053 5 x 741 op -amp8054 25 x IN4001 diodeB055 20 x IN4007 diodeB056 I x SLOTTED OPTOB057 I x DAC08 digital to analogue convertor with dataB058 4 x OPTO ISOLATORB060 3 x C106D THYRISTORB061 5 x 78M05 VOLTAGE REGULATORS positive 5 volt 500mAB062 10 x TACTILE SWITCHESB063 25 x 0.0IMFD 50V CERAMIC DISK CAPACITORS

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A

II

' : :


JOYSTICK -TO -MOUSE ADAPTOR

Although most PC gamesd more serious programs

are perfectly suited to mouse con-trol, there are applications,such as flight simulators, wherejoystick control would give afar more realistic feel'. Unfortu-nately, not all programs wherejoystick control would be de-sirable actually support sucha device. In these cases, onlymouse control is available. Also,in more general terms, the fol-lowing problems are often en-countered when running flightsimulators:

opto-mechanical mouse. Themain board, the LEDs (or theirseries resistors) and the pho-totransistors are removed fromthe mouse. The phototransis-tors are replaced (electrically,that is) by four optoisolatorscontained in IC5. This is achievedby connecting points XA, AB,YA and YB to the emitter or col-lector of each phototransistorremoved. The adaptor boardshown here has a number ofjumpers to allow the collectorand emitter of each photo -

although the resolution ofthe mouse is adequate foraccurate control, the expe-rience of flying is not simu-lated;

the analogue joystick is far tooinaccurate, and is pro-cesseddigitally in any case;

the digital joystick with D -Aconverter in principle simu-lates full deflection of theanalogue joystick.

The circuit shown here allowsa digital (ex -Commodore 64)joystick to be used for playinggames that support mouse con-trol only. The interface is basedon electronics salvaged froman inexpensive (10 or less)

P1

470k

R1

7

C3M1M

100n

F13--.7 4

R2

YI6

2

C2MIM

TOOn

0 RDI5

IC1

TLC OUT

THR 555T R

.6 CV

00110 N1 Ri

C4

100n

16

14

5

C1MIM

110n

11b

0

CTRDIV10/DEC

3

104

IC2 5

40176

T=0 98

119

CT?.5s12

transistor in the CNY74-4 tobe wired to +5 V or ground.Jumpers E/C therefore deter-mine whether the drive signalcomes from the emitter or fromthe collector. The exact con-nections will depend on theelectronics available on themouse.

The circuit uses a TLC555astable multivibrator and a4017 divider to generate a pulsetrain which simulates the ro-tating slotted disc in the opto-mechanical mouse. This

0 0 0 00 O 0 0000

000

00

000

00

0 450

00

-100+0400.0g00

EN IC3a

10

x:10

S2

o v-0-0

54

N IC4a

4

5

6

10

vN

12

14

EN IC4b

5

13

nal is routed to the optoisola-tors via two 4503 buffers. Thedesired direction (up /down;left/right) is selected with thedigital joystick, via the enableinputs on the buffers. The speedof the cursor on the screen isset with preset P1, since that de-termines the clock frequency ofthe TLC555.

The supply voltage for the in-terface is taken from the mouse,and can be found where theLEDs and their series resistorsused to be connected. The

IC3,1C4 = 4503

R7

R9

El=

R108

7

IC515

r

110n16V

16

0O+5V

14

13

10

0

XA

0 0

XB

° 0

YA

0 0

CNY74-4

MIM

OYB

0 0944040-11


mouse/fire keys are wired di-rectly, while the second 'fire'key (which is not available onthe digital joystick) may be in-tegrated into the adaptor en-closure.

Parts list

Resistors:R1 -R6 = 10 IcS2R7 -R10 = 4.7 Id2P1 = 470 IcS2

Capacitors:C1 = 10 nF

C2 -C6= 100 nF= 10 pF, 16V

Integrated circuits:IC1 = TLC555IC2 = 4017IC3, IC4 = 4503IC5 = CNY74-4

Miscellaneous:S1 -S4 = switch in C64

joystick.PCB Ref.944040 (p. 110).

THERMO-CONTROLLED HOT -PLATE

TOe hot -plate was designedkeep a tray with developer

for print material warm. It mayalso prove useful in a photog-rapher's dark -room. It is con-tained in a small metal case,which also contains the elec-tronics. The plate, which is madeof aluminium and measuresabout 25x15cm (10x6 in) ismounted about 2 cm above themains transformer. Four par-allel -connected 22 C2, 25 W re-sistors screwed to the undersideof the plate function as heatingelement. The current throughthe resistors is switched on anoff by an electronically con-trolled relay, which is also fit-ted in the metal case.

A Type LM335 tempera-ture sensor is connected tothe negative input of com-parator IC1. The voltageacross the sensor is directlyproportional with the tem-perature, so that when thehot -plate cools off, it will at agiven moment drop below thereference voltage set by P1 atthe positive input of IC1. Theoutput of the comparator willthen go high, so that afterthree inversions in IC2a,, IC2band IC2c, there is a low logiclevel at the base of T2. Sincethis is a p -n -p transistor, itwill begin to conduct, where-upon T3 is also switched onand relay Re 1 is energized.The heating resistors (repre-sented by R12), connected toK1, are then connected to themains transformer via K2and heat the hot -plate.

When the temperaturecauses the voltage across D1to exceed the reference volt-age at pin 2 of IC1, the com-parator output goes low and

4LM335

12V

08IC2

IC3

7812

C8

25V

22n

IC2 = 4093

*see text

R5

C7

TOOOtt40V

C6

22n

B80C1500

D3 I Ref

1N4148

K1

K2

0

'R12

Design: C. Wolff[944040]

2x 15V2x 2A66

IC2a IC2bR6 1 5

LM335

T2 and T3 are switched off.The hysteresis provided byR5 ensures that the on andoff thresholds are far enoughapart to prevent relay clatter.

An optional indicator isformed by IC2d, T1 and D2.When the heating resistorsare not switched on, thecomparator output is low.Pin 13 of IC2d is then alsolow and the gate functions as

C1MIM

720n

IC2c

R7

10M

C2OEM

TOOn

BC557R11

"O`

T3

(41

an inverter, so that T1 isswitched on and D2 lights.When the heating resistorsare on, pin 13 of IC2d is high.Network R7 -C2 then causesthe gate to function as a rec-tangular -signal generator sothat D2 flashes in sync withit.

In the prototype, a toroi-dal mains transformer fromILP (2 x15 V, 2 x2.66 A) was

944031 - 11

used.The power resistors were

aluminium types providedwith fixing holes.

The relay was a 24 V typefrom Siemens that canswitch currents of 6 A orgreater.

Design: R. Lucassen[944031]


54

PC OVER -TEMPERATURE ALARM

.ny PC, however old, is toovaluable to break down

as a result of inadequatecooling, usually caused byfan failure. The alarm causesa buzzer to sound when thetemperature inside the PCreaches a predefined level.Obviously, this early warningshould prompt you to switchoff and take a very seriouslook at the cooling of the PC ifyou do not want it to beturned into a lot of siliconjunk. You may have fitted toomany insertion cards, or thefan has failed. In any case,the cost of the present circuitis always lower than that of anew motherboard or a powersupply.

The temperature sensorused is an NTC (negative tem-perature coefficient) resistor,which is fitted at a suitablelocation in the air flow beingmaintained by the fan insidethe power supply. The NTC isconnected to a comparatorwhose output swings high ifthe resistance value of theNTC is smaller than the sumof preset P1 and fixed resistorR3. The switching tempera-tures are29 °C or 50 °C (84 °For 120 °F) with the preset setto maximum or minimum re-sistance respectively.

The alarm is adjusted byfirst turning P1 to minimumresistance (wiper electricallytowards R3), heating the NTCto the desired alarm tempera-ture (approx. 45 °C or 113 °Fas a guide), and then adjust-ing P1 until the buzzer just

sounds.The board is cut into two

to enable two alarms to bebuilt. The SMDs (surfacemount devices) are fitted atthe copper side of the board,and the conventional parts atthe top side, as shown by thecomponent overlays.

The circuit is powered viaa 3.5 -inch drive connector,which can be connectedeither way to the board with-out affecting the operation orthe temperature range of thealarm. The NTC may bemounted directly on to theboard, or off the board at asuitable location in the PC. Inthe latter case, the device isconnected to the board viatwo short wires.

Parts list

Resistors:R1 = NTC 100 kS2, Siemens

series K164, B=4600K, R2,R4 = 100 kc2, SMTR3 = 33 1c51, SMTR5 = 1 M52, SMTR6 = 10 kf2, SMTP1 = 50 (47) IcS2 preset

(Bourns)

Capacitors:C1 = 100 pF, 16 V, radialC2 = 100 nF, SMTSemiconductors:T1 = BC847B, SMT

Integrated circuits:ICI = TLC271CD, SMT

Miscellaneous:K1 = 4 -way SIL connector

(3.5" drive supply).Bz1 = 5V DC buzzerPCB Ref. 944076 (p. 110).

`NEAR -PERFECT' INPUT STAGE

far as audio enthusiastsre concerned, striving for

perfection is a never-endingquest. The present circuit shouldappeal to them.

The designer of amplifiersaims for the best possible sym-metry, because that provides theoptimum performance. Inputstages often consist of two dif-ferential amplifiers that areeach other's complement.

The d.c. setting of each dif-ferential amplifier is effectedby a single -transistor currentsource, whose reference is azener diode or LED. In itself, thisis an excellent design, partic-ularly when an LED is used, be-cause this has a temperaturecoefficient virtually identicalto that of the transistor. However,in practice, these values willhardly ever be exactly the same.

Since, moreover, the thermalcoupling normally leaves some-thing to be desired, it is clearthat there will be variations inthe d.c. setting in practice.Furthermore, as each differ-ential amplifier has its own cur-rent source, these adverse ef-fects are doubled. The inevitableresult is that thetwo stages donot operate in perfect symme-try.

5V

12V

Design: L. Lemmens(9440761

In the present circuit, thedifferential amplifiers have acommon current source. Anyvariations in this have a sym-metrical effect, producing as itwere automatic compensation.This means that the d.c. oper-ating point is far more stable andthe offset drift caused by tem-perature variations is muchsmaller. The only factor thatstill causes troubles is that


there are no true complemen-tary dual transistors on themarket. Even in the MATO2and MAT03, the hFEs are too farapart, but better types are notyet available.

The 'near -perfect' input stagein its simplest form is shown indiagram A. The current source,

built from a JFET is enclosedby two current mirrors. Theupper mirror fucntions as thecurrent source for the lowerdifferential amplifier and viceversa. The stability of the JFETsource can be improved asshown in diagram B. Here theJFET is replaced by two tran-

sistors with a common emit-ter resistance. Two LEDs pro-vide the setting of the base volt-age; the current through thesediodes is held constant by twoJFET current sources. The cur-rent mirrors are built frommonolithic dual transistors.

The collector -emitter volt-

age of the MATO3 must not ex-ceed 36 V.

The current drain of circuitA is three times the currentsource setting. That of circuitB is the same plus the currentdrawn by the LEDs.

Design: T. Giesberts)944065]

POWER SUPPLY FOR LCD MODULE

Bwilding an LCD moduleinto an equipment (for in-

stance, a voltmeter into a powersupply) is often not straight-forward, because its supplycan not be taken from the supplyof the equipment (perhaps be-cause floating voltages are tobe measured).

This difficulty is reso I \ I I Ar

the present circuit, wh R (lc -

rives a direct voltage from theexisting d. c. supply and keepsit isolated with the aid of ca-pacitors. This enables the LCDmodule to measure floating di-rect voltages.

The circuit is based on anastable multivibrator, T1 -T2, ina traditional configuration. Thealternative charging and dis-charging of capacitors CI andC2 will cause T1 and T2 to beswitched on and off in turn.This results in rectangular,

944039 - 11

944065 11

anti -phase pulses at the col-lectors of these transistors.These pulses are applied toT3 -T4 and T5 -T6 respectively.

The signals at the emittersof these buffer stages are ap-plied to a bridge rectifier via C3and C4 respectively. The directvoltage taken from the bridgerectifier is smoothed by C5 andstabilized at 9 V by regulator ICI .

The current that can be drawnfrom the circuit is only a fewmA, but this is sufficient formost LCD modules.

The input voltage must be inthe range 12-15 V. If it islower (8-12 V), IC I should bea Type 7806, assuming thatthe LCD module used can workfrom 6 V.

Design: R. Baltissen[944039]


56

PRECISION ONE SHOT PULSE GENERATOR

is simple non-retrigger-able pulse generator

(`one-shot') is designedaround an inexpensive digi-tal watch crystal and twocommonly available CMOSintegrated circuits. Com-pared with the ubiquitous74121/ 123 'external RC'mo-nostables and their de-rivates, this design is re-markably immune againstsupply voltage and ambienttemperature variations. Theoutput pulse width is de-fined with the aid of a 12 -stage binary counter TypeCD4040, at a precision equalto the period, Tc, of the crys-tal frequency.

NOR gate ICI, is wired asa crystal oscillator, whileICI, and ICI form a bistable.Diodes at the outputs of thecounter provide a logic ANDfunction. The bistable is setby a low -to -high transition atthe trigger input of the cir-cuit, whereupon the counteris enabled. When the coun-ter reaches the count atwhich all cathodes of thediodes connected to the Qoutputs of the counter are atlogic high, the bistable and

The design of this amplifieris based on the assump-

tion that, since the collectorcurrent of a transistor is, roughly,the same as the emitter current,the transistor can drive twoloudspeakers.

In the diagram, T1 is a simplevoltage amplifier, followed byemitter follower T2 and class Aoutput amplifier T3. Negativefeedback is provided by RI -R2 -P1.The amplification is about unitywhich can be altered slightlywith P1.

Noteworthy of the design isthat the d.c. operating point ofT3 is determined by the base -emitter voltage ofT1. This volt-age and the potential acrossLS1 are virtually identical andthe d.c. operating point of T3 isthus practically independent

IC1 = 4001

R1 R4

82k

X1

C2

40p

C3M1M

120p

X1 = 32.768kHz

5...12V

Oso

12

IC1a

or >

IC1 d

D1...D5 = 1N4148

,3.10N7,

CTR12

>+

IC2

CT

4040

CT=0

0

1

2

3

4

6

7

8

9

10

11

244,2L,7

6

5

C4

3 D3

13

12

14

15 D5

4n7R2

D1

IC1 c

0

the counter itself are reset.Complementary one-shotpulses are available at thetwo outputs of the generator.

Up to 12 diodes may beconnected to the counteroutputs to program the divi-sor, n, that determines thewidth T,, of the complemen-tary output pulses:

n = / Tc.

A crystal frequency of32.768 kHz will be one of themost cost effective, and re-sults in a pulse width resolu-tion of 30.5 ps and a maxi-mum pulse width of124.9 ms. Alternatively,crystals of higher frequen-cies up to 10 MHz may be

TWO -SPEAKER AMPLIFIER

R1

EMI

0

C3

10p

5...9V

LS1

8...3252

T3

11IN=

C5

1000pBC461 boy

C4

TOp8...3252

LS2

944049 - 11

944022-110

used to increase the pulsewidth resolution. The gener-ator works at a supply volt-age range from 5 V to 15 V ata current consumption of afew milliamps, dependingmostly on the quartz crystalfrequency.

Design: M.S. Nagaraj[944022]

of the supply voltage.Inserting a second loud-

speaker into the collector cir-cuit of T3 doubles the poweroutput of the amplifier. Theoutput power is 2 x 23 mW witha supply voltage of 5 V and2 x 40 mW with a supply volt-age of 9 V. In the latter case, dis-tortion amounts to 0.1%. Thefrequency range extends fromabout 15 Hz to 200 kHz.

Since the feedback loop ref-erence is the positive supplyline, the power supply needs tobe decoupled well (whence thehigh value of C5).

The current drain dependsprimarily on the setting of T3and amounts to 100 mA at 5 Vand 120 mA at 9 V.

Design: Amrit Bir Tiwana[944049]



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60

POWER SUPPLY DECOUPLING

In many advanced electroniccircuits, speed and accuracy

are of the utmost importance.It is sometimes overlooked thatto achieve these, good decou-pling of the power supply linesis an absolute must. 'Fast' ICsare particularly sensitive inthis respect.

It can not be overempha-sized that the connections ofthe decoupling elements to thesupply pins of the IC must beas short as possible: every mil-limetre counts! Usually, thesupply pins are located at op-posite corners of the housing.As a rule of thumb, it may betaken that if the distance be-tween these pins is doubled(owing to the layout of the PCB),the level of the resulting volt-age variation is also doubled.That is significant.

Ideal, but expensive, are ICsockets with integral decouplingcapacitor. It is, however, nor-mally possible to achieve thesame effect by soldering a smalldecoupling capacitor directly

across the supply pins. It maynot look nice, but it is effective.A value of 100 nF per (TTL, HCor HCT) IC is sufficient. Now-adays, there are capacitorsdesigned specifically for de -coupling on the market: theSibatit series from Siemens isan example.

In circuits where the fre-quency is higher than 50 MHz,the effect of the decoupling ismagnified when a 10 nF ca-pacitor is soldered in parallelwith the 100 nF capacitor.

A practical difficulty oftenarises in a hybrid circuit, that

is, one with a digital section andan analogue section (e.g., ananalogue -to -digital converter,ADC). Ideally, these sectionsshould have separated sup-plies, but this is often not pos-sible. If, therefore, only a singlepower supply is used, branchoff a positive and a negative linefor the analogue section im-mediately after the voltage reg-ulator. In other words, neveruse combined supply lines ina hybrid circuit. As shown inthe diagram, the effectivenessof the decoupling can be im-proved by inserting a resis-

tance or inductance in the pos-itive supply line. An induc-tance screens the analoguesection from the spurious sig-nals arising in the digital sec-tion.

It is essential that the en-tire analogue section is de -coupled properly. This may,however, cause the inductanceand capacitance to form a res-onant circuit. This may be pre-vented by using a much largercapacitor and damping the cir-cuit with a small series resis-tance. In practice, an LC filterconsisting of a 100 pH induc-tor and a 10 pF capacitor worksvery satisfactorily. As shownin the diagram, the 10 pF ca-pacitor is connected in paral-lel with the 100 nF capacitor(which remains essential!). Aminiature choke (same size asa resistor) is perfect, becauseits internal resistance of 1-212is just right for damping the cir-cuit.

Design: K. M. Walraven[944082]

SOLAR CELL -POWERED NiCd CHARGER

Alcciattery of solar cells canharge a NiCd battery with

better than 80% efficiency, pro-vided the solar battery voltageexceeds the fully charged NiCdoutput by about 0.6 V. For thatcase, a simple blocking diodeprovides the charging path be-tween the two batteries. Thoughinflexible, such dedicated sys-tems are simple and effective.

The simple approach, how-ever, is impractical if adjust-ment of the charging voltage isimpossible or inconvenient.Badly mismatched voltages(« 0.6 V) cause a low level ofpower transfer and consequentslow charging of the NiCd bat-tery.

Adding a step-down switch-ing regulator enables a givenbank of solar cells to chargebatteries of various terminalvoltages at optimum rates andwith efficiencies approachingthat of the regulator itself.

The IC used for this pur-

R1

1%

6

v+SHDN

3LBI LBO

R2\'12 xQ B12

C1 iC 1

MI= VOUT

1000 40V MAX6391%

VFB

R3 GND

4

1%

pose, the MAX639 from Maxim,operates in an unorthodox fash-ion, regulating the chargingcurrent such that the solar bat-tery's voltage remains near thelevel required for peak powertransfer.

The device therefore regu-lates its input voltage, ratherthan its output voltage as iscustomary. Potential divider

R4

2

L1

D1

1N5117

D21N5117

C2o16V

B11

1 5 xNiCd

944089-11

R2 -R3 disables the internal reg-ulating loop by holding VFB low.Voltage divider R1-(R2+R3) en-ables the low battery input (LBI)to sense a decrease in the solar-batteryvoltage. Such decreases,which represent a move awayfrom the solar cell's peak out-put power, cause the low bat-tery output (LBO) to pull theSHDN input low and disable the

chip. The LBI input then sensesa rising input voltage, LBO goeshigh, and the resulting pul-sating control maintains max-imum power transfer to theNiCd battery. Current limitingin the IC limits the output cur-rent to 200 mA.

With the IC enabled, the reg-ulator passes current frompin 6 to pin 5 through an internalswitch resistance of less than1 SI Combined with the regu-lator's low quiescent current(typically 10 pA) and high effi-ciency (typically 85%), this per-formance allows the circuit todeliver as much as four timesthe power of a single -diode cir-cuit.

Note that the circuit shouldbe used only to charge NiCdcells that can be charged con-tinuously with a current of200 mA, that is, have a capac-ity greater than 1700 mAh.

Maxim Application[944089]


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TELEPHONE TAP ALERT TTA1 Visual warningof any invasions of privacy on your telephone line.Dimensions: 38 x 52mm

RF DETECTOR RFD1 Highly sensitive hand-helddetector. Range between 10Mhz and 600Mhz. Silent

' operation. Dimensions: 70x 50rnm

CAMERA DETECTOR CD8 Detects hidden videocameras (even miniature CCD models).Dimensions: 63 x 38mm

RECORDING BRIEFCASE R BC1 Completelydiscreet recordings at a value for money price.

SHOTGUN MICROPHONE AMPLIFIER SMAIdeal for surveillance. The amplifier will pick up soundsfrom a long distance.

SIGNALLING TRANSMITTER SIGT Sends acontinual audio pulse. Can be integrated into alarm,tracking or warning systems. Dimensions: 20 x 50mm

TELEPHONE AMPLIFIER TA5 Connected directlyto the telephone, this unit will amplify both sides of atelephone call. Dimensions: 25 x 52mm

PROFESSIONAL SOUND TO LIGHT UNITSK72 Custom built for disco or home use. Audio signaldivided into bass, mid and treble bands, with internalmicrophone and spotlight option.Dimensions 210 x 45mm

MICRO METAL DETECTOR MMD Detect thepresence of ferrous and various non-ferrous metals.Useful for all those DIY jobs. Dimensions: 40 x 25mm

14.74

31.50

16.80

34.96

21.95

42.75

69.00

24.95

21.95

10.95

21.95

9.95

45.50

25.90

31.50

69.00

89.00

36.00

34.89

16.95

32.49

16.95

PROFFINISHED

19.00

45.00

25.00

29.00

65.00

39.00

69.00

45.00

95.00

125.00

145.00

45.00

45.00

19.95

44.95

Please add £2.00 P & P to all orders and 17.5% VAT on all U.K. orders.

For full catalogue please send two 1st class stamps or 2 IRC'S

172 Caledonian Road London N1 OSGDept EL

CANAL BRIDGE AUDIO071-837 4423


62

1 4 MBYTE SIMM ADAPTOR

Memory upgrades for PCscan present unexpected

problems. For instance, if youare upgrading with 4-MbyteSIMMs (single -in -line mem-ory module), the existing1-Mbyte SIMM will be uselessin most cases. A waste ofmoney? Not if you build thecircuit shown here, which en-ables four 1-Mbyte SIMM mod-ules with eight or nine DRAMchips, to act as a single 4-MByteSIMM, and occupy only onememory expansion socket. Thecircuit is not suitable for usewith three -chip SIMMs.

The memory of a 486 -basedPC has a width of 32 bits, whilea SIMM has a 'width' of only8 bits (well, 9, if you include theparity bit). Consequently, mem-ory modules can only be addedfour at a time. If 1-MByte SIMIVIsare used, that allows memo-ries of 4, 8, 12 or 16 MByte tobe created, or 16, 32, 48 or64 MByte if you can afford touse 4-MByte modules. In somecases, 4-MByte and 1-MBytemodules may be 'mixed', for in-stance, to give 20 MByte, con-sisting of four 4-MByte andfour 1-MByte SIMMs. Thus,upgrading from 4-MByte to16 MByte means that you haveto exchange the four 1-MByteSIMMs with four 4-Mbyte mod-ules. If you are lucky, the moth-erboard still has four socketsto insert your 1-MByte SIMMs,so that you can extend thememory up to 20 MByte. Inother cases, for instance, whenit is desired to upgrade a12-MByte memory to 20 MByte,you may be left with eight1-MByte modules for whichthere is no room on the moth-erboard.

Before deciding to build thepresent circuit, be sure to casta look inside your PC to makesure that it has sufficient roomin the memory expansion areafor the circuit board and theSIMMs fitted on it. Particularlyin mini -tower cases space maybe tight, and the circuit can notbe used.

Apart from the memory ICsused, the difference betweena 1-MByte and a 4-MByte SIMMis that the latter has one moreaddress line, A10. This line isused in conjunction with thetwo refresh signals RAS (row

2

IC7a

12

TT?

5V

CI CZN 4 ci 4IC7 IC6 IC5.7 10.7 p 10.7 9

T4 5V

IC5a

ff )CR

DM00

2

5 3

IC5 = 74HCT74 5V

K1

01

OOOOO

OO

00

O

O

O

IR IR

OMUX

1163

IC6a

3

2

'5

IC6 = 74HCT139IC7 = 74HCT04

3

IC15V

01-0-4

0

5

6

7

O

3

IC2

4

02

0

OOO

O0

2

3

O

0O

4

5

16

7

OOO

O

6

O

O

3

IC3

O

IC4

3

0

4

0

10 MTM

O

O

5

7

0

2

3

4

O

0

9

OOO

6

0

19

O

OOOOOO0OO

0

20

21

22

23

24

O9

O

O

20

O

O

2

3

4

5

6

00

7

19-0-21

00

25

26

27

OOO

28

29

30

0O

22

23 Min

0O

20

0 4 4O

O

O0O0000000000

19 19-000000000000

- 944094-11

OO0OO

0O

OOO00O

5

6 6

7 7

8 8

0 10

11

12 12

13 13

14 14

15 15

16 16

17 17

18 18

-0-21

22

24

25

26

27

28

0 29

O23

OO

24

25

OOOO

26

27

28

29

0 30- 5V - 30

address select) and CAS (col-umn address select) to selectbetween the four 1-MbyteSIMMs in the circuit. The levelof A10 is latched in IC5a (rowaddress line A10). Togetherwith column address line A10,it is decoded into a 1 -of -4 se-lection signal for the respectiveSIMM module. This happenswhen the CAS signal is actu-ated. The contents of the SIMMsare refreshed by the briefly ad-dressing all rows. Hence, all RASconnections on the SIMMs areinterconnected.

The adaptor board shouldbe fitted with standard SIMMsockets, which can not bemounted the wrong way aroundbecause they are polarized.The SIMM module can also be

00

O

0OO

OOO0

20 20

21 21

22 22

23 23

24 24

25 25

26 26

27 27

28 28

29 29

30 30

0-

',MAD

"etita.*

-C7-- .1"

3 3 3

3Yfr

944094-1 0 0

fitted with the correct polar-ization only.

If you use more than oneadaptor board, these can notnormally be fitted alongsideeach other in adjacent slots.That is why the PCB is double -sided, allowing you to mountSIMM sockets at both sides, andfit adaptor boards next to eachother. The ICs are, of course,fitted at one side only.

O O

944094-1

Parts listCapacitors:C1, C2, C3 = 100 nF

Integated circuits:= SIMM socket,

30 -way.IC5 = 74HCT74IC6 = 74HCT139IC7 = 74HCT04


63

0 0 000 0-11-100

OD

00

00

4)

000110

ICI

El

n711tcroplaO 01

0 0 0110011 00 0 oNo 0

=MI 113 0=MI

01 vs 0-0

00

8010001

01100

=MIVI

=MI=MINMI CI

113=MNMM1B=MI

CI=MIIn=MON

MENCI-CB=MI

=MI1003MUMMIES 0 0 0 0 0

he circuit gives a coarse in-dication nof the frequency

by a tricolour LED, the TypeLF-59EBGBW from Kingbright.When the frequency of the inputsignal is 50 Hz, the two blueLEDs light; when the frequencyrises to 500 Hz, the red LED alsolights, and when the frequencyrises above 5 kHz, the greenLED lights, too. The resultinghue is thus indicative of thefrequency of the input signal.

The setting of P1 deter-mines the threshold of oper-ation of the red LED. Sincethe green and blue diodesneed a higher threshold volt-age, the offset voltage of thered LED is increased by thestatic voltage amplification ofthe opamp.

Networks in the feedbackloops of the opamps providecut-off points of 50 Hz (ICI,);500 Hz (IC%) and 5 kHz(ICIa). These networks en-sure frequency -independentbrightness of the LEDs.

The stability of the op -amps is enhanced by net-works R4 -C2, R7-05 andR11 -C7.

Since the brightness ofblue LEDs is appreciableless than that of red or green

Miscellaneous:PCB Ref. 944094 (p. 110)

FREQUENCY INDICATOR

types, two of them are fittedin the LF-59EBGBW. Thesecond blue diode has itsown buffer opamp, IC id. Inspite of the fact that thereare two blue diodes, thesealso draw twice as high acurrent as the red and greento give the same brightness.It is for that reason that thevalue of resistors R13 and R14is lower than that of R6 andRg.

The level of the input sig-nal should be 1 V

PP'

C3

OA I330n

9V

5

C5

ICI

IC1 = TL0847

3n3 R8

C4

:3n

10

R2

C7

9IC1 c

R11

Design: A. Rietjens[944094]

9V

C8

100p16V

C9

100p16V

9V

R9 R6

o

01 iozi

VR13 R14

33n R12

C6

130n

10k

R10

When all LEDs light, thecircuit draws a current ofabout 100 mA.

12

IC1 d13

14

944088-11



64

R2 R3CRYSTAL OSCILLATOR 0

single non -buffered HC in-verter can be made to func-

tion as a stable oscillator. Thecrystal may be either afunda-mental type (low frequencies)or an overtone model (high fre-quencies).

Circuit 1 in the diagramshows an oscillator that oper-ates on the third overtone ofthe crystal. Note that oscillationis possible even on the seventhor ninth harmonic. The 'U' inthe type number of the IC in-dicates an unbuffered output;this type of IC is more suitablefor use as an oscillator thanthe HC model. The crystal hasa capacitance, CxL, of 30 pF. Thisvalue is important, because thecapacitance and inductance L1form a resonant circuit that istuned to a frequency just belowthe wanted crystal frequency.This arrangement preventsthe crystal oscillating spon-taneously on its fundamentalfrequency. The value of resistorR1 is specified as 3.3 MQ, butmay lie anywhere between 1 MQand 10 MQ.

Circuit 1 may be used withpower supplies of 5 V at fre-quencies up to 40 MHz. TheHCUO4 chip is not suitable foroperation above 40 MHz.

A crystal that oscillates atits fundamental frequency

Arti ideal power supply main-ains its e.m.f., irrespec-

tive of whether it is providingcurrent or sinking it. The pre-sent supply approaches thisideal. Its output voltage maybe set between 2 V and 16 V,while the output current mayvary between -1 A and +1 A.

The supply is based on IC1,a Type L165V operational ampli-fier from SGS Thomson. A sta-ble reference voltage is pro-vided by zener diode D1. Thisvoltage can be varied between0 V and 2.5 V by Pi.

The opamp magnifies its in-put voltage x6.45. In theory,its output voltage should, there -

(which may be up to 17 MHz)does not need a tuned circuit.Both circuit 2 and 3 may beused. The difference between thetwo is the use of either a re-sistor or a capacitor at the out-put. For frequencies up to 2 MHz,circuit 3 is more suitable; forhigher frequencies (up to17 MHz), circuit 2 is better.

Calculating the componentvalues for Circuit 1 is simpli-fied by the BASIC program inFig. 2. This program com-putes the values of C1, C2 andC3 from the input frequencyand capacitance, CXL, of thecrystal. Normally, the com-puted alue of C1 is about halfthat of C2 and C3.

IC1 = 74HCU04

Note that the oscillatorsshown here are not suitable foruse with watch crystals thatoperate at about 32 kHz.

5V

944013-11

Design: L. Pijpers[944013]

10 DIM I$(8): PI = 3.14159320 CLS : PRINT "Calculating crystal oscillators."30 LOCATE 3, 1: PRINT "An inverter type 74HCU04 (unbuffered) is used."40 LOCATE 6, 1: INPUT "Crystal frequency in MHz "; F: IF F = 0 THEN 2050 LOCATE 9, 1: INPUT "Capacitance C(1) of the crystal (Return=30pF) "; CL60 LOCATE 12, 1: PRINT "R1 = 3.3 MOhm"70 IF CL = 30 OR CL = 0 THEN Cl =80 IF CL = 8 THEN Cl = 6.8: C2 =90 IF CL = 12 THEN Cl = 10: C2 =100 IF CL = 15 THEN Cl = 12: C2 =110 IF CL = 20 THEN CI = 18: C2 =120 IF CL = 50 THEN Cl = 39: C2 =130 IF CL = 100 THEN Cl = 82: C2 = 180: GOTO 150140 Cl = .45 * CL: C2 = 2 * Cl150 PRINT "Cl ="; Cl; " pF": PRINT "C2 ="; C2; " pF": PRINT "C3 ="; C2; " pF"160 IF F < 17 THEN PRINT "No need for inductor.": GOTO 180170 T = 1111 / F: K = T * T / (4 * PI * PI): L = K / Cl: PRINT "Ll ="; L; " uH"180 LOCATE 20, 1: PRINT "More calculations (y/n) "; : INPUT 1$190 IF 1$ = "N" OR IS = "n" THEN END ELSE 20

27: C2 = 56: GOTO 15015: GOTO 15022: GOTO 15027: GOTO 15033: GOTO 15082: GOTO 150

NEAR-IDEAL SUPPLY

2<Uo<16VL1A

C2 C3 IQM=7207100m

25V

MI 944078-11

944013.14

fore, be 0-16.1 V. In practice,this is not wholly realizableand the output voltage is lim-ited to 2-16 V.

Series network R4 -C2 pre-vents the opamp oscillatingspontaneously.

The opamp has various in-ternal protection circuits, sothat, provided it is mounted ona suitable heat sink of about4.5 KW -1, nothing serious cango wrong.



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66

CENTRONICS INPUT/OUTPUT INTERFACE

Tabe Centronics interface avail -le on almost any IBM PC

or compatible lends itself tosimple input/output functionsprovided the drive capacity ofthe output lines is consider-ably boosted. In principle, thefive inputs on the Centronics in-terface can be used straightaway because they are TTL-compatible. However, for addedsecurity, a resistor and a volt-age limiting zener diode maybe hooked up as shown here.It should be noted that thisworks on modern PCs only, i.e.,those having CMOS inputs. Ifyou have a very old computer,it is likely to have standard TTLinputs. If so, consider donatingit to your nearest science mu-seum, or reduce the value of theprotection resistors to a fewhundred ohms (or omit them al-together). A simple test to seeif this is necessary is to mea-sure the voltage drop acrossthe 2.2-Id/resistors when ap-plying a '0'. If the voltage dropis greater than 0.8 V, you havean 'old' computer, and chang-ing the resistors to low -valuetypes is in order, as well as dri-ving the inputs from low -im-pedance sources.

The inputs are pin 11 (BUSY;bit 7), pin 10 (ACK; bit 6), pin 12(PAPER EMPTY; bit 5), pin 13(SELECT; bit 4), and pin 15(not connected; bit 3). The pinnumbers refer to the 25 -waysub -D connector on the backof the PC. The corresponding pinnumbers on the 36 -wayCentronics connector may befound in the circuit diagram. Thelogic state of the above bits may

K1

1 STROBE

,K1.43 2 OUT 0\

.__.21 G3 our l\4 OUT 2\

23 5 OUT 3\24 c) 0 6 OUT 4\

.._21._0 o-7 MT 5 \2fi o-8 OUT 6 \

9 OUT 7\222._<3 10 C ACK \

29 11 C BUSY\32o 12 C PEN

____01 13 C SEL \

a0 14 AUTO F \

3L0 12215 \3L0 0_,6

31_00_1L36 0_18

SEL IN/C ERROR/

INIT/

be interrogated by reading theLPT base address + 1. In thisword, bits 0, 1 and 2 are 'don'tcare', that is, they do not con-tain relevant information.

The eight (data) outputs onD25 connector pins 2 through9 are normally capably of sourc-ing 2.6 mA or sinking 24 mA.The outputs can be controlledby writing the correspondingeight databits to the base ad-dress of the LPT port. In addi-tion to the eight databits, fourextra outputs can be addressedvia base address + 2: pin 1(STROBE; bit 0), pin 14 (AUTOFEED; bit I, pin 16 (INIT; bit 2),and pin 17 (SELECT IN; bit 3).Originally these are control lineoutputs with an internal pull-up of 4.7 lit), and a currentsink capacity of 7 mA. Note thatthe four higher -order bits (4through 7) must be kept at '0'to prevent an interrupt withunexpected results.

Darlington transistors typeBD679 are used to boost the cur-rent sink and source capacityof the twelve programmableoutputs. The BD679 is capableof switching up to 4 A at a col-lector voltage of 80 V. In prac-tice, it is recommended to staybelow 2 A or so, and fit the tran-sistors with heatsinks if con-siderable dissipation is expected.Remember that the collectorof a darlington can never pullthe load lower than 0.6V, or even0.8 V at a current between 1 Aand 2 A.

The auxiliary voltage used forthe BC547 driver transistorsis not critical, and may lie be-tween 5 and 15 V. At 5 V, the

0 5V0

C=41

16V

05V

K2

ERROR SCT PE ACK

R25

5V1

R26 1R27

5V1 I 15V

total current consumption isabout 50 mA,

The loads to be controlledby the Centronics port are con-nected between the collectorsof the BD679s and the positiveline of the external power supply(max. 80 V). If inductive loads(such as relay coils) are con-nected, do not forget to shuntthese with (reverse connected)free -wheeling diodes. This isnecessary to protect the dar-lingtons against reverse-emfvoltage surges.

As regards programming,you may start in the simplestpossible way in BASIC, for in-stance, with the following pro-gram which reads your four in-puts, and presents the corre-sponding value in hexadeci-mal on the screen:

REM read Centronics inputs,display in hex

LPT1 address=&H378

R2B

5V1

WHILE 1cent=INP(LPTladdress+1)PRINT hex$(cent)WEND

Or, equally simple, control theoutputs:

REM square waves on D0 -D7,DO has highest frequency

LPTaddress=&H378count=0WHILE=1OUT LPTI address, countcount=count+1IF count>255 then count=0WEND

Parts list

Resistors:RI,R3,R5,R7,R9,R1I,R13,R15,R17,R19,R21,R23 = 1 ki2R2,R4,R6,R8,R19,R12,R14,R16,R18,R20,R22,R24 = 10 kitR25 -R27, R29 = 2.2 kQR28 = 820 Q

R29STR FEED

BC T17 BC 119 BC

5478

co547B 44 5478

135 118 T20

I) RN aR18

11114,

C ERROR / C SEL JCPE jC ACK jC BUSY

OUTS bOUT1

R2 IR1

T1

BC547B

BD679

DO

OUT 2

R4 IR3 IR6 IR5

BC5478

BD6

T3

D1

r

T5

C5478

BD679

D2tl

OUT 3

R8 IR7

17

BC5478

BD679

r 5VSE L

T21

C4547B

R22


67

160

0kiz

ERROR SCT PE ACK BUSY

00 00 0 0,,

3

5

D4

R18R16R14R12R10R8

R6R4

R2

944067

Capacitor:C1 = 10 pF, 16 V, radial

Semiconductors:D1 -D5 = 5.1 V, 400 mWT1,T3,T5,T7,T9,TII,T13,T15

CMIC) 2

21

CM R18 0 1

CO Biz 10 1

T1

T9

R T7

or R5 10 T5

01 R3 K> T3

01 R1 10 Ti

T17,T19,T21,T23 = BC547BT2, T4, T6, T8, T10, T12,T14, T15,

T18, T20, T22, T24 = BD679

Miscellaneous:K1 = Centronics socket, PCB

mount, angled pins.K2 = 3 -way PCB terminal

block, pitch 5 mm.18 PCB solder pins or 9 PCB

terminal blocks, 2 -way,pitch 5 mm.

944067

O

PCB Ref. 944067 (p. 110)

Design: K.M. Walraven)[9440671

NON-VOLATILE CONTROLLER CHIP

e DS1210 controller chipfrom Dallas Semiconduc-

tor, in combination with a CMOSRAM and a lithium battery,forms a memory module thatwill retain its data for manyyears.

The controller performs sev-eral functions. It provides volt-age to the RAM IC from V orfrom the battery, depending onthe voltage levels. The loss acrossthe internal electronic change-over switch is smaller than 0.3 V.

If the supply voltage fails,the controller prevents any fur-ther writing to the memory. Thebattery is then used as a tem-porary power supply. To makethe circuit absolutely immuneto power failure, a second bat-tery may be used, which takesover when the main batterygoes flat.

There is a facility to indicateto the user (via the software) thestatus of the main battery. Ifthat voltage has dropped below2 V, the controller blocks allread and write operations tothe memory from the secondread/write cycle onwards. Inother words, if it proves im-

possible to change the contentof the memory, the main bat-tery is flat.

The diagram shows how thecircuit can be used in an existingapparatus. Note that IC2 is thesocket into which the memoryto be protected is to be inserted.

Dallas SemiconductorApplication

[9441071

AO

VCCI

3V

IC3

DS1210

VCCO

6

10

O0

0

0

O0 00000000000 0

IC2*O0000000

28

20 CE

22

.t

MEI3V

20

OE 22

28

27 WE 27

11

12

DO 1

D1 12

13 D2 13

15 D3 15

16 D4 1

17 D5 17

8 D6 1

19 D7 19

14

CE

OE

WE

D1

D2

D3

D4

05

D6

D7

IC1

AO

Al

A2

A3

A4

A5

RAM A6

A7

62256A8

A10

AllAl2A13

A14

14

10 AO


944107-11

68

PEAK A.F. VOLTAGE METER

The meter described can mea-sure peak voltages from a

few millivolts to several voltsat frequencies up to 200 kHz.

The peak detector is formedby a comparator IC with open -collector output-see Fig. 1.Capacitor C will be charged toa certain potential. When thelevel of the incoming signal isbelow this voltage, the outputtransistor begins to conduct,whereupon the voltage acrossC will rise rapidly to the level ofthe negative supply line. WhenLIc is equal to the input voltage,charging will cease. In this man-ner, Lk will always correspondto the most negative level of theinstantaneous input signal. AsC is discharged gradually viaR, Uc will follow any variationsin the input signal. Of course,the circuit in Fig. 1 can mea-sure only half the peak -to -peakvoltage. Adding an identicalcircuit for the positive halvesenables the whole signal to bemeasured.

In Fig. 2, IC1 is the positive -peak detector and IC2 the neg-ative -peak detector, whose'memories' are C1 and C2 re-spectively. Low-pass filtersR3 -C3 and R6 -C4 remove any un-wanted peaks. The positivevalue is inverted by IC3 andsummed with the negative halfin IC4, where the signal is in-verted again.

The top end of the frequencyrange is limited only by thespeed of ICI and IC2; in theprototype, the upper frequencywas about 200 kHz, even withrectangular and triangular sig-

nals.The lower end of the frequency

range is determined by the valuesof C1 and C2. With the valuesas shown, the lower limit wasabout 500 Hz. If measurementsdown to 20 Hz are desired, thevalue of these capacitors mustbe increased to 220 pF-butthis will be at the cost of the re-action time. Following a rise inthe input signal of 1 V will thentake 2-3 seconds.

Note also that capacitorsC1 and C2 are bipolar types.Only if there is certainty thatthe input signal will always befree of direct voltage can normalelectrolytic types be used.

The supply voltage may beas low as ±6 V, but if input sig-nals exceeding 4 Vpp are to bemeasured, or if the signal hasan appreciable d.c. offset, it isadvisable to use a higher supplyvoltage. Although not strictly nec-essary, it is also advisable to sta-bilize the supply lines. Sincethe current drain does not ex-ceed 20 mA, two 9 V batterieswill suffice.

To calibrate the meter, short-circuit the input to ground,connect a millivoltmeter acrossC1 and adjust P1 for a readingof 0 V. Next, do the same withthe voltmeter across C2 andadjust P2. This needs to be donecarefully, because it is a mat-ter ofjust a few millivolts. Then,adjust P3 and P4 for a voltageof 0 V at pin 6 of IC3 and IC4 re-spectively. Remove the short-circuit from the input.

Design: V. Mitrovic[944056]

1

2

0-

2k2

R1

2k2

C11

R7 1%

R8 1%100k

LM741

4

P3

10k

IC3

6

6...15V

C8 C7

100n 100p25V

C10 C9

100n 100p25V

6...15V

5

R15

2k2

2C12

MIM10n

MEI

1%R 0

®

COMPRESSOR FOR GUITARS

Many guitarists still swearby the good old valve ampli-

fier. It is fact that valve ampli-fiers produce a sound differ-ent from that of a solid-stateamplifier. This is caused mainlyby the fact that in valve ampli-fiers the transition from thelinear to the non-linear part oftheoperating range is more grad-ual than in solid-state ampli-fiers, in which the transition

is sudden. In other words, in valveamplifiers, the distortion in-creases with increased drivelevels and may thus be seen asa sort of dynamic compression.This phenomenon does not occurin solid-state devices, wherethe transition is quite sudden:the resulting sound is un-pleasant.

Before the arrival of voltage -controlled IC amplifiers, dy-

namic compressors were oftendesigned with diodes as thecontrol element. Since a certaindegree of distortion is desir-able, diodes are very suitablefor use in a guitar compressorwith 'valve sound'.

In the diagram, input ampli-fier ICI drives two pairs of diodesvia R5: D1-D3for the positive halfperiods and D2 -D4 for the neg-ative half periods. Capacitors

R12 1%

LM741

4

P4

10k

IC4

6

944056-12

C3 and C4 short-circuit any a.c.signals: they hold the level of thecontrol voltage constant andthus determine the speed ofthe control. The diodes obtaina bias voltage (which is inde-pendent of the drive level) fromthe output of IC2a via D5 and D6.

When Sea is open, the dy-namic compression is disabled.

The stage based on IC2b com-pensates the output level at


69

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various positions of the switchesand potentiometers (the twohalves of which turn in oppo-site directions). It is thus pos-sible to take the output signaldirectly from the output of IC2a.

The onset of compression isset with P1. This control should

be set, by trial and error, to aposition where the 'pluckingpeaks' are just beginning todistort.

The amplification of IClis al-tered with S1 to enable instru-ments with a single as well asa double coil to be used.

R8

IC2 = TL072D1, D2 = 1N4148D3..D6 = BAT85

80C166 MicrocontrollerThe RMB-166 is an evaluation board for the Siemens 80C16616 -bit high performance microcontroller running at 40MHz withno wait states. The RMB-166 board comes with monitor andPC host software to allow downloading of user code.

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Although the prototype per-formed to the taste of the de-signer, individual modifica-tions are, of course, possible.Note, however, that the BAT85diodes must not be replacedby common -or -garden diodeslike the 1N4148, which produce

a far less pronounced 'valve ef-fect'. This is because the dis-tortion sets in more abruptlyand at a higher level.

Design: W. Teder[944048]

944048 - 11


70

SENSOR INTERFACE

Connecting a sensor to an A -D(analogue -to -digital) con-

verter is not always as straight-forward as may be expected.Often, an interface is requiredto amplify the signal and toprovide some offset control.The present circuit was de-signed on that basis.

Most A -D converters have areference input; the voltage ap-plied to this is fed internally toa potential divider. This meansthat the converter does not workwith absolute values, but withthe ratio of input voltage to ref-erence potential.

If, for instance, a tempera-ture sensor is required, it isbest to base this on a resistorwith positive temperature co-efficient (PTC) connected in abridge circuit. If the supply tothe bridge is taken from thesame source as the referencevoltage, the reading of the A -Dconverter will be immune tosmall variations in the level ofthe reference voltage. In other

words, the reference voltageneed not be regulated.

If a sensor sensitivity of about0.'75%°C-1 is sufficient, abridgeas described earlier will be ad-equate. If greater precision isrequired, the bridge voltagemust be amplified, which canbe arranged with any opamp thatcan operate from +5 V. In the

prototype, a modern, low -dis-sipation type was used as shownin the diagram. This model,which has very low noise andvery small offset, can be drivento 0.2 V with small loads (1 mA)from a negative as well as apositive supply.

The A -D converter used anunregulated +5V supply. Diodes

D1 and D2 make sure that thereference voltage remains closeto the supply voltage.

One branch of the bridgecontains preset potentiometerPI, while the other contains thePTC resistor, R3. Resistor R2does not only form part of thebridge, but also serves to makethe temperature -to -voltagecharacteristic of R3 linear. Withthe type of PTC resistor in thediagram, R2 needs to be 4.1 Id2to obtain a linear curve around20 °C. If the KTY81- 1 is used,the value of R2 should be 2 IcaCapacitor C2 suppresses anynoise.

The amplification of theopamp is determined by feed-back resistor R6, whose valueis up to individual requirements(within reason). With values asspecified, the amplification isabout x14.

The circuit draws a currentof only a few mA.

Design: K. Wairaven[9440361

LEAD -ACID BATTERY CHARGER

part from use as a stan-ard charger, the present

unit may also be used for con-tinuous trickle charging to keepa 12 V lead -acid battery in topcondition.

The charger is based on a pre-cision voltage source, whichhas been given a negative tem-perature coefficient by a tem-perature sensor. This meansthat the charging voltage is re-duced when the ambient orbattery temperature rises.

According to the electrical firmof Bosch, a temperature coef-ficient of -8 mV °C-1 is the mostbeneficial for charging a lead -acid battery. In the present cir-cuit, this is achieved by usinga common -or -garden transis-tor as sensor.

The operation of IC 1 dependson the property that three -pinregulators tend to keep the volt-age difference between theirinput and output at a constant1.25 V. This means that thecurrent through R1 is constant.Normally, this characteristic

is made use of to set the desiredoutput voltage by means of a fixedresistor between the adj (ust)pin and ground. In the presentcircuit, this resistor is madevariable by inserting T1 in thelink. To keep the circuit sta-ble, potential divider, R3 -R4 -P1controls the base voltage of Ti.

Since the base -emitter junc-tion ofTi , in common with everyother semiconductor, has atemperature coefficient of about-2 mV °C-1, the output also hasa negative temperature coeffi-cient. This is, however, fourtimes as large because the base -emitter variation of T1 is mul-tiplied by the scaling factor ofR3 -R4 -P1.

Diode DI shows whether thepower is available.

Transistor T2 prevents thebattery being discharged viaR1 in the absence of a supplyvoltage (T2 is switched off).

The wanted output voltageis set between 13.5 V and 14.5Vwith P1. This range may be shiftedto some extent by altering the

17V5...30V

3A D2

1N5401

LM350

adj

R5

C1

10035V

IC1

LM350

adj.

L/_

T1

D1

--N

R2C2

10µ16y

BD140

T2

BC547

R3

R4

P1

2k2

LI 2V_,

value of R4.To prevent Ti being warmed

by its own base current, it is ad-visable to fit the transistor ona small sheet of metal.

If T1 is intended to monitorthe ambient temperature only,it suffices to mount it just in theopen air. If it is intended to corn-

944033 - 11

pensate a rise in battery tem-perature, it must be mountedas close to the battery as pos-sible.

Linear Technology Application[9440331


SOLDER VAPOUR EXTRACTOREn

Soldering is an unhealthyactivity: when the tin melts

it releases harmful vapours. Itis, therefore, advisable, to in-stall a small 12 V d.c. extrac-tor fan on or near the work-bench. The present circuit is in-tended to control the fan.

The rotational speed of thefan is adjusted to a few hun-dred r.p.m. with P1. Pressingpush-button switch S1 duringsoldering raises that speed tomaximum to give added ex-traction of the vapours. Thelength of time during which thefan rotates at maximum speeddepends on the time constantR2 -C3. The fan will also rotateat maximum speed for a timeR2 -C3 when it is switched on.After that, its speed drops to afew hundred r.p.m.

The circuit is a typical ap-plication of an LM317. The out-put voltage is determined byP1 when T1 conducts and bypotential divider R3/ (R4 -P1 -R5)

xtracting the separate left-12/hand and right-hand sig-nals from a multiplexed stereosignal is a complex process. Itrequires an auxiliary carrier ofexactly the same frequency(38 kHz) and phase as that inthe transmitter. A voltage -con-trolled oscillator (VCO) by it-self is not good enough. It needsto be synchronized with the19 kHz pilot tone in the multi-plexed (MPX) signal. Further-more, a mono/stereo convertercontrolled by the pilot tone,preferably with an optical in-dicator, is required.

Fortunately, ready-made ICstereo decoders have been avail-able for some time. Neverthe-less, these decoders normallyrequire quite a few externalcomponents and, moreover,their calibration is often notsimple.

Modern decoder ICs, however,are simplicity itself. As the di-agram shows, one of these,

D1...D4 = 1N4001

when the transistor is off. Withvalues as specified, the output

MONO

voltage ranges from about 4 Vto around 11 V.

STEREO DECODER

81 13o

C4

I=14µ725V

7

P1

5k

R1

4

to

D1

-O.

6

MPX cl

GO -ID10p25V

Vcc Vco PILOT

LPF2

IN

IC1

LPF1

OUT R

TA7343POUT

GND

2

C2 C10 1_1919 8V

imm

25V 5VR6

120µ25V

2p221µ

5

Toshiba's TA7343P, needs onlya few external components.

The MPX signal is applied topin 1, whereupon the separateleft-hand and right-hand sig-nals are available at pins 8 and9 respectively. When the in -

R5 I C

15n

C7

4p725V

C8

4p7R4

944050-11

25V

0

ternal pilot -tone detector reg-isters the presence of the 19 kHzsignal, D1 is driven into con-duction and the internal 'stereoswitch' is actuated. When thereis no pilot tone, DI remains offand the circuit remains in the

When S1 is pressed, the po-tential across C3 drops to 0,whereupon T1 stops conduct-ing. After a little while, the volt-age across C3 has risen suffi-ciently to cause T1 to begin toconduct again. It then forms aresistance in parallel with R4and the upper half of P1. As T1begins to conduct harder andharder, its parallel resistancebecomes smaller and smalleruntil it is a short-circuit. Theoutput voltage then dependson the ratio between R3 andthe lower half of P1 plus R5. Thepotentiometer is thus used toset the minimum output volt-age. With values as specified,the minimum output voltagecan be set between 4V and 8 V.This minimum voltage is usedto drive the fan at low speed. Ifthe fan stops, adjust P1 to givea slightly higher output voltage.

Design: A. Rietj ens[944090]

mono mode.Manual switching to the mono

mode is possible with SI. Whenthis switch is closed (pin 7 to+8 V), both outputs carry theL+R signal.

The VCO is adjusted withP1 and does not require any in-struments or expertise: simplytune the receiver to a stereotransmitter and turn P1 tillD1 lights.

In spite of its simplicity of ap-plication, the parameters ofthe TA7343P are very good.Harmonic distortion is 0.08%(typical); auxiliary carrier sup-pression is 70 dB; and the sig-nal-to-noise ratio is 74 dB. Thesefigures were measured with asupply voltage of 8 V.

The supply voltage can rangefrom 3.5 V to 12 V. The currentdrain (excluding that throughthe LED) is 11-18 mA, depend-ing on the supply voltage.

Toshiba Application[944050]


DISCRETE POWER SUPPLY

In these days of integratedvoltage regulators, many con-

structors will enjoy this old-fashioned power supply builtfrom discrete components. Itprovides an accurately pre-settable output voltage of 13.8 Vat a peak current of 10 A andis short -circuit -proof.

Ignoring the stage round T1for a moment, the design is tra-ditional. Transistor T2, in con-junction with potential dividerR6 -R7 -P1 and zener diode D7,forms a variable voltage sourcethat is followed by three emit-ter followers. The last of these,T5 and T6, consists of two par-allel -connected golden oldiesType 2N3055, which togetherprovide the output current.

What is new is the mannerof current limiting provided byT1. The base voltage of this tran-sistor is derived from the out-put voltage via R4. If the outputvoltage drops below 5 V, for in-stance through overload, T1will switch off. Transistor T2 isthen driven hard via D6, whichresults in T3 -T6 only j ustcon-ducting, so that the output volt-age and current become neg-ligibly small.

To get out of this situation,a 50 Hz signal is applied to thebase of T1 via D3. The level ofthis signal is limited to 1.3 V byD4 and D5. This causes Ti toswitch on periodically, which willreenable the circuit if the over-load or short-circuit at the out -

en a three-phase mo-toris being installed, it is es-

sential to know the sequence ofphases R, Y and B, since anerror may have disastrous con-sequences. The letters R, Yand B are abbreviations of 'red','yellow' and blue', that is, thecolours used to identify thethree phases. Also, red -yellow -blue is the sequence univer-sally adopted to denote thatthe e.m.f. in the yellow phaselags that in the red phase by

put has been removed. Thismeans, of course, that evenduring a short-circuit fairlylarge current pulses flow throughthe load, but these are so short(about 2 ms) that they can notcause any harm.

Instead of the usual emitterresistors, the connecting wiresto the emitters of T5 and T6function as potential divider. Theymust, therefore, both be about10 cm long and have a diame-

ter of 0.7 mm.Because of the fold -back cur-

rent limiting, the heatsink forT5 and T6 need not be large: a10 cm long Type SK01(2.5 K W-1) will suffice.

Choose transistors with aT03 case for T5 and T6 and mountwith the aid of insulating wash-ers.

Preset P1 should preferablybe a multiturn type.

Buffer capacitor CI may con -

THREE -PHASE INDICATOR

120° (a third of a cycle), and thee.m.f. in the blue phase lagsthat in the yellow phase also by120°.

In the present circuit thephases are indicated by threeneon lights mounted in a cir-cle. If this 'running light' movesclockwise, the phase sequenceis correct; if it moves anti -clock-wise, the sequence is incorrect.

Each neon lamp is in serieswith a phase via a resistor. Thethree phases are simply inter-

connected after being rectifiedby D1 -D3. Their junction is con-nected on and off to N(eutral)by T3. The remainder of the cir-cuit arranges for the switch-ing to occur in a manner bywhich the neon lamps are short-circuited to neutral in the cor-rect sequence.

Transistor T3is controlled bya monostable formed by T1 andT2, which provides a switchingsignal at a frequency of about48 MHz. It works as follows.

944034 - 11

sist of three parallel -connected4700 pF electrolytic capaci-tors: this is at least as good asal5 mF type and much cheaper.

Diodes D1 and D2 must be10 A types: it may be cheaperto use two diodes from a 10 Abridge rectifier.

Finally, make sure that thelarge currents can not enterthe control circuits.

Design: Altai[944034]

After the phases have been rec-tified by D 1-D4, capacitor C2 ischarged via Rg. As soon as thepotential across C2, and thusthat at the emitter of T2, risesabove the level set by R8 -R15 -P1,T2 begins to conduct. Thiscauses C2 to be discharged viaT2, R11 and the base -emitterjunction of T3. Transistor T3 isthen on briefly so that one of theneon lamps, depending on whichphase is active at that instant,is short-circuited to neutral


r1

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Standard charger charges 4 M cells in 5 hours or 4Cs or Dsin 12-14 hours +1xPP3(1,2,3 or 4 cells may be charged at atime)

. £5.95

High power charger as above but charges the Cs and Ds in 5hours Ms Cs and Ds must be charged in 2s or 4s ...... £10.95Male Metal Hydryde M. cells high capacity with no memory1000mAH . .... £3.85 1200mAH . £4.40

Special offers please check for availability42x16mm dia 1.2v . £1.45stick of 4.171mmx16mm dia with red 8. bask leads 4.8v...£5.95

Computer grade capacitors with screw to rninals38000uf 20u . £2.50 87000uf 10v . £1.9568000uf 15v . £2.95 10000uf 16v . £1.505800uf 60v £4.95

7 segment common anode led display 12mm . £0.45LM29314T5.0 low drop out 5v regulator T0220 package £0.857812 and7912 12v IA regulators £26.00 per 100LM337K 103 case variable regulator ...£1.95 £1.44 100+GaAs FET low leakage current 58873 . £12.95 each£9.95 10+ £7.95 100+BS250 P Channel moefet

. £0.45BC559 transistor £3.95 per 10074LS05 hex invertor . £10.00 per 100used 8748 Microcontroler

. £3.50SL952 UHF Limiting amplifier LC 16 surface mounting packagewith data sheet . £1.95AM27S02 £1.25 each, 90p 100 +CD400706 10p 100+. 6p 1000+Sinclair light gun terminated with jack plug and PP3 clip gives asignal when painted at 50hz flickering light with output waveform chart £3.95DC -DC convertor Reliability model V12P5 12v in 5v 200maout 300v input to output isolation with data £4.95 each or packof 10 .. £39.50

Hour counter used 7 digit 240v c 50 Hz .. £1.45

OWERTY keyboard 58 keys good quality switches new£5.00

&pax 482903-C large stepping motor 14v 7.5 step 27ohm68mm dia body 6.3mm shaft £8.95Or £200.00 for a box of 30Polyester capacitors box type 22.5mm lead pitch0.9uf 250vdc 18p each, 14p 100+, 9p 1000+luf 250Vdc 20p each, 15p 100+, 10p 1000+2.2uf 250Vdc (27.5mm pitch) 30p each, 20p 100+, 15p1000+3.3uf 100Vdc 30p each 20p 100+, 15p 1000+luf 50v bipolar electrolytic axial leads 15p each, 7.5p 1000+0.22uf 250v polyester axial leads ......_.15p each, 7.5p 100+Polypropylene luf 400Vdc (Wima MKP10) 27.5mm pitch32x29x17mm case .. 75p each, 60p 100+Phillips 123 series solid aluminium axial leads

33 of 10v & 2.2uf 40 v 40p each, 25p 100+Phillips 108 series 22uf 63v axial 30 each 15 p 1000+Multilayer AVX ceramic capacitors all 5mm pitch 100v

100pf, 150pf, 220pf, 10,000010n) 10p each, 5p 100+,3.5p 1000+, 500pf compression trimmer 60p

40uf 370Vac motor start capacitor (dialectrol type containing

no pcbs) £5.95 or £49.50 for 10Welwyn W23 9W 120 ohm 35p each, 20p 100+

680ohm 2W metal film resistor 4p 100+, 2p 1000+

solid carbon resistors very low inductance ideal for RF drcuits27ohm 2W, 68ohm 2W 25p each, 15p each 100+ we have arange of 0.25w 0.5w 1w and 2w solid carbon resistors pleasesend SAE for list

P.C. 400w PSU (inter pad 201035-001) with standard

motherboard and 5 disk drive connectors, fan and mains inlet/

outlet connectors on back and switch on the side (top fortower case) dims 212x149x149mm excluding switch £26.00each . £138.00 for 6MX180 Digital Multimeter 17 ranges 1000vdc 750 vac2Mohm 200mA transistor Hfe 9v and 1.5v battery test £12.95AMD27255-3 Eproms £2.00 each. 1.25 100+DIP switch 3PCO 12 pin (ERG SDC-3-023) 60p each,40p 100+

Disk drive boxes for 5.25 disk drive with me for a powersupply light grey plastic 67x268x247mm £7.95

Or f49.50 for 10Handheld ultrasonic remote control . £3.95

CV2486 gas relay 30x10mm dia with 3 Ore terminals will alsowork as a neon light 20p each or £750 per 100A23 12v battery for car alarms or lighters .... 75p each

£50.00 per100All products advertised are new and unused unless

otherwise stated. Wide range of CMOS TTL 74HC 74F

Linear Transistors Kits rechargeable batteries

capadtors tools etc always in stockPlease add f1.95 towards PEP

VAT included in all prices

tt1 :

I.

and lights. The lamp lights until is because the collector of T2 so that junction R8 -R15 is alsoat neutral. When C2 has been

discharged completely,T2 and T1 switch off andthe neon lamp goes out.This continues untilthe next phase becomesactive.

R2 R7 Provided that good -470 k quality components are

D2 D4 used for R8, R9, R15, PI

R9and C2, the monostablewill ensure a reliableindication.

The circuit is cali-brated as follows. Con-nect it to the three-phase

T2 supply (neutral first!)after having turned P1fully atiticlockwise.Then, slowly turn the

R12 preset clockwise until56k the running light formed

C3 by the neons appearsR10 to be at a standstill.

C2 Next, turn P1 a little720n

Ifurther clockwise untilthe neon lights appearto move in a clockwise

C2 is virtually discharged. This

R1 *

D1...D4 1N4007

*see text

T3

TIP50

R11

keeps T1 switched on as well,

D5

0

ill 13

0

1 N41482N3906

120p 2N3904

R14

O

R8

R15

P1

50kMT

944018 - 11

Cl

4µ7350V

direction at about two revolu-tions per second. Lock the pre-set in that position with somelacquer.

Because of the required ac-curacy, Rg, R9 and R15 must bemetal film types; C2 should bea polyester type and P1 must bea multiturn model. The neonlamps should have their seriesresistors integrated. CapacitorC1 must be a high -voltage type.Resis-tors R4 -R6 must be spe-cial 500 V types (it is, of course,possible to connect two stan-dard 250 V types in series).

Finally, the entire circuit isconnected directly to the three-phase supply so the utmostcaution is necessary duringconstruction, testing and cal-ibration. It must be installed ina good -quality synthetic en-closure.

Design: R. Kahne19440181


74

EXPERIMENTATION BOARDS FOR PICs

In view of the popularity ofgeneral purpose PICs (Peri-

pheral Interface Controllers),two experimentation boardsare presented: one for the 18 -pin models (Fig. la), and theother for the 28 -pin models(Fig. ib).

The layout of both boards isgiven in Fig. 2; the board avail-able from our Readers' Servicecontains both versions. Theboards are indispensable forthe practical application of thenew PIC Programming coursestarted in this issue.

Each board has provisionfor the 5 V power supply withpolarity reversal protection:any mains adaptor that can pro-vide 9-15 V and a current of300 mA is suitable.

The board also has provi-sion for the 8 MHz clock gen-erator, reset circuit and de -coupling capacitor.

The pin headers on the boardensure that access to the I/Olines is good.

Finally, extra soldering padsare provided for any additionalhardware that may be needed.

Note that in the EPROM ver-sion of the PICs no choice hasbeen made as regards the typeof oscillator. This means that dur-ing the configuration of thefuses (in the programming) thecorrect type of oscillator willhave to be chosen and pro-grammed (here, the XT).

Parts list

Resistors:R1 = 270 S1R2= 10 IcS2

Capacitors:C1, C2= 22 pFC3= 10 pF, 16VC4, C5 = 100 nFC6= 100 pF, 16 V

Semiconductors:Di = I N4002

Integrated circuits:ICI, = PIC16C54/56 (board a)IC lb = PIC16C55/ 57 (board b)IC2 = 7805

Miscellaneous:K1 = 8 -way single row headerK2 = 10 -way single row headerK3 = mains adaptor connectorK4 = 10 -way single row header

a b 155V

:100n2

K1

5V

0

C5

:00n14

0 5V

5V

08

RBO

RAO

RAI

RBI

IC 1 RB2=mommmri RA2 PIC16C54 RB3PIC16C56RA3

MCLR

RB4

RB5

RTCC RB6

8137OSC2/

OSC1 CLKOUT

15 5

5V R2X1

1 2MHz0 OEC3 C1 C2

10p 22p16V

IC2K3 D

(board b only)X1 = crystal, 8 MHzPCB Ref. 944105 (p. 110)

rc

5V

0C4

100n

1Y Cita° 12a/K2 C6

(0 0 0 0 0 0 0 0 0 01

KiC2 C4

olio

K2

RAO

RAI

RA2

RA3

MCLR

RTCC

SCI

5V

K1

o -

O

O

0OOO

6

8

28

K3 DI

Design: A. Rietjens[944105]

CC

C6 IC,

K3

944105-1a PIC16C54/56000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

00000000000 sl00 0 00 0 0 0 0 0 0

K2

C3

0 880

RBI

RB2

RB3

IC1 RB4

PIC16C55 R85RB6

RB7

OSC2/CLKOUT

RCO

RCI

RC2

RC3

RB4

R23

RC6

RC7

C5 OFe)

0000000

'Cl

PIC16C55/57 944105 -lb0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

143000000000000000000000000000000000000000000000000

5V

10 K211

00

12 013 014 015 016 017 0

O

18 O K419 O20

O21 O22

O23

O24

O25

O

0

5V

100n

944105 - 11

C2 -Z-10.6

4

e6C4 1C2

K4


SWEEP GENERATOR

Phase locked loop IC TypeCD4046 enables a simple

rectangular wave generator withvariable frequency to be de-signed as shown in the dia-gram. Careful computing andchoosing of the componentvalues results in a usable sweepgenerator.

Capacitor CI is charged viaR1; the resulting potential acrossit is applied to linked pins 9and 14 of the IC. Pin 14 is the

input to the phase comparator,while pin 9 gives access to thecontrol input of the voltage -controlled oscillator (VCO).

When the input to the IC be-comes logic high, the bistablein the phase comparator isreset. This results in the levelat pin 13 going high and C1being discharged via T1.

At the same time, the highlevel at pin 13 causes C2 to becharged via R3. When C2 has at-

tained a given charge, pin 3goes high, so that the bistableis reset.

Diode D1 then causes C2 tobe discharged rapidly. At thesame time, C1 is chargedagain and the whole cycle re-peats itself. The potential acrossC1, which has an exponentialwaveform, ultimately providesthe sweep of the VCO frequency.

The minimum VCO frequencydepends on the values of C3, R4

and R5; with values as specified,it is 2.2 kHz.

The maximum frequency de-pends on C3 and RI; with valuesspecified it is 11 kHz.

The sweep time of about600 ms (with a supply voltageof 12 V), is determined by C1 andR1.

The supply voltage may be7-15 V. The circuit draws acurrent of not more than 5 mA.

Design: M. Nagaraj[944091]

6V8 -

09, 14 IC1

OV -

12V -

013 ICI

OV

6V8

03 IC10

04

12V -

OV-944091 12

944105-1944105-1 00000000000000000000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000 00000000000

1............0 0000000000000000 0 0 00000000000 00000000000000000 00000000000


76

POLARITY REVERSAL PROTECTION

Rversal of the supply lineso a circuit normally has di-

astrous consequences. The pro-tection described here can pre-vent such a disaster occurring.It consists of an enrichmentMOSFETthat is connected closeto the negative supply input.The transistor conducts onlywhen it receives a positive gatevoltage from the positive supplyline via R1.

Use is made of an n -chan-nel transistor, which usuallyhas a lower Rds(on) than p -chan-nel types. This low transfer re-sistance is vital because it meansthat even with large loads thepower loss is kept low.

If breaking into the negativesupply line is difficult, a p -chan-nel device can be used in the pos-itive supply line.

There are several n -chan-nel FETs that are suitable for

It is often handy if two or moresets of equipment that work

together, such as a computerand a printer, or a tuner, ampli-fier and CD player are switchedon and off together. This canbe done with the aid of a slaveswitch, which is easy to build.The simplest type uses a resistorin series with the mains leadas sensor. As soon as a currentflows, a voltage is developedacross the resistor and this isused to switch on a triac. Thisarrangement is not only waste-ful (power dissipation in the re-sistor), but also dangerous inthat there is a risk of the en-tire load current flowing throughthe gate of the triac, which def-initely can not cope with this.

It is much better to use a cur-rent transformer as sensor. Inthe present circuit, an old 1 Abell transformer with secondaryvoltages of 3 V, 5 V and 8 V wasused. The 3 V winding is con-nected in series with the (neu-tral) mains line to the com-puter (amplifier). Note, however,that with certain computer -printer combinations, theprinter should, according tothe manufacturer, be switchedon first. As soon as the corn -

the present application; theIRF520 is but one of them - theIRF540 and BUZ11 are two al-ternatives.

Designing the protection sothat, strictly speaking, the cur-rent flows in the wrong direc-tion (from source to drain) is de-liberate, since it prevents the in-ternal protection diode con-ducting when the polarity ofthe supply is reversed acci-dentally. This diode will, however, conduct when the cur-rent becomes large. This is notmuch of a problem, because itcan cope with the same level ofcurrent as the drain -sourcechannel. In the IRF520, this is9.2 A; the IRF540 can handleup to 28 A. The table shows thepotential drop with and with-out heat sink: it is clear fromthis that at relatively large cur-rents a heat sink (21 K W-1) is

a sensible addition. The figuresin the table were obtained witha battery voltage of 12 V; if a lowervoltage is used, the dropsacross the FET may be slightlyhigher.


IRF520 944044 - 11

Current (A) Drop withoutheatsink (mV)

Drop withheatsink (mV)

0.012 2.2 2.40.120 21.9 260.240 43.3 500.450 87.3 900.980 223 2101.870 500 4202.610 1 1002.740 640

SLAVE SWITCH

puter is switched on, the sec-ondary current will be trans-ferred to the primary winding.Since this winding has manymore turns than the secondary,the current through it is muchsmaller than that in the sec-ondary. For a voltage ratio of3:240, the transformer ratio is1:80, that is, the primary cur-rent is 1/80 of the secondary cur-rent. This current is largeenough, however, to start asensitive triac like the TIC206D.

MASTER

(Emigticam.\

TIC206D

2

The starting current of thetriac has the same waveformas that through the primary ofthe transformer. If this is aclean sine wave, the triac willstrike just after the zero cross-ing as it should. In other cases,the triac might not strike untilmuch later and that is not theidea. To ensure that the triacconducts continuously, a bridgerectifier and reservoir capaci-tor have been added.

The prototype needed a si-

nusoidal current of about100 mA to start the triac. Thevoltage loss amounted to 95 mV,which increased to 295 mVwith a current of 500 mA.Without a transformer, thatis, with a series resistor, thiswould have been at least 2 V.Larger currents may be ob-tained by the use of the 5 V or8 V winding. Note, however,that the current must not ex-ceed the rating of the trans-former.

Since mains voltage is pre-sent in the circuit, great caremust be taken when workingon the circuit, which, whenfinished, must be enclosed ina non-metallic housing.

There is a further dangerin this circuit in that the trans-former is used 'the wrong wayaround', so that when it is notloaded, very high voltages mayarise across the primary wind-ing. It is, therefore, strongly ad-visable to use a bell trans-former, because this complieswith stringent safety require-ments.

Design: K. M . Walraven[944083]



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CARETAKER VOLUMETRIC Alarm, will cover the whole ofthe ground floor against forcred entry. I nd udes mai ns power supplyand integral battery backup. Powerful intemal sounder, will takeexternal bell if req'd. Retail £150+, ours? £49.99 ref MAR50P1.TELEPHONE CABLE White 6 core 100m reel complete with apack of 100 dips. Ideal 'phone extns etc. £7.99 ref MAR8P3.VIEVVDATA RETURNS86 made by Tandata, indudes 1200.75modem, k/bd, RGB and comp o/p, printer port. No PSU.E6 MAG6P7

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UNIVERSAL SPEED CONTROLLER KIT Designed by usfor the above motor but ok for any 12v motor up to 30A. Completewith PCB etc. A heat sink may be required. £17.00 REF: MAG17VIDEO SENDER UNIT. Transmitsboth audio and videosignalsfrom either a video camera, video recorder, TV or Computer etc toanystandard TVsetin a 100' range! (tune TVto a spare channel) 12vDC op. Priceis£15 REF: MAG15 12v psu isE5 extra REF: MAG5P2'FM CORDLESS MICROPHONE Small hand held unit with a500' range! 2 transmit power levels. Reqs PP3 9v battery. Tuneableto any FM receiver. Price is £15 REF: MAG15P1LOW COST WALKIE TALKIES Pair of battery operated unitswith a range of about 2C0'. Ideal for garden use or as an educationaltoy. Price is £8 a pair REF: MAO BPI 2 x PP3 req'd.

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'SOME OF OUR PRODUCTS MAY BE UNLICENSABLE IN THE UK

SPEAKERW IRE Brown 2 core 100 foot hank £2 REF MALED PACK of 100 standard red 5m leds £5 REF MAG5P4

UNIVERSAL PC POWER SUPPLY complete with fly,switch, fan etc. Two types available 150w at E15 REF:MAG(23x23x23mm) and 200w at £20 REF. MAG20P3 (23x23x23mFNITFtANSMFTER housed in a standard working 13Aadaptertthe bug runs directly off the mains so lasts forevert why pay £700?or price is £26 REF: MAG26 Transmits to any FM radio.*FM BUG KIT New design with PCB embedded coil for extrastability. Works to any FM radio. 9v battery req'd. £5 REF: MAG5P5'FM BUG BUILTANDTESTED supenordesign to kit. Suppliedto detective agendes. 9v battery req'd. £14 REF: MAG14TALKING COIN BOX STRIPPER originally made to retail at£79 each, these units are designed to convert and ordinary phoneinto a payp hone. The units have the locks missing and sometimesbroken hinges. However they can be adapted for their original useor used for something else?? Price is just £3 REF: MAG3P1100 WATT MOSFET PAIR same spec as 2SK343 and 2SJ413(8A,140v,100w) 1 N channel, 1 P channel, £3 a pair REF: MAG3P2TOP QUALITY SPEAKERS Made for HI Fl televisions theseare 10 watt 4R Jap made 4' round with large shielded magnets.Good quality. £2 each REF: MAG2P4 or 4 for £6 REF: MAG6P2TWEETERS 2' diameter good quality tweeter 140R (ok with theabove speaker) 2 for £2 REF: MAG2P5 or 4 for £3 REF: MAG3P4AT KEYBOARDS Made by Ap ricot these quality keyboards needjust a small mod to run on any AT, they work perfectly but you willhave to put up with 1 or 2 foreign keycaps! Price £6 REF: MAG6P3PC CASES Again mixed types so you take a chance next one offthe pile £12 REF:MAG12 or two the same for £20 REF: MAG20P4COMMODORE MICRODRIVE SYSTEM mini storagedevice for C64's 4 times faster than disc drives, 10 times fasterthan tapes. Complete unit just £12 REF:RAci2P1SCHOOL STRIPPERS We have quite a few of the aboveunits which are 'returns' as they are quite comprehensive unitsthey could be used for other projects etc. Let us know how many youneed at just 50p a unit (minimum 10).HEADPHONES Ex Virgin Atlantic. 8 pairsfor£2 REF: MAG2P8PROXIMITY SENSORS These are small PCB's with what looklike a source and sensor LED on one end and lots of components onthe rest of the PCB. Complete with fly leads. Pack of 5£3 REF: MAG:3P5 or 20 for £8 REF: MAG8P4SNOOPERS EAR? Original made to dip over the earpiece oftelephone to amplify the sound -it also works quite well on the cablerunning along the wall! Price is E5 REF: MAG5P7DOS PACKS Microsoft version 3.3 or higher complete with allmanuals or price just £5 REF: MAG5P8 Worth it just for the verycomprehensive manual! 5.25' only.DOS PACK Microsoft version 5 Original software but no manu-als hence only £3 REF: MAG3P6 5.25' only.CTM644COLOURMONITOR MadetoworkwiththeCPC464home computer. Standard RGB input so will work with other ma-chines. Refurbished £59.00 REF:MAG59PIR DETECTOR Made by famous UK alarm manufacturer theseare hi spec, long range internal units. 12v operation. Slight marks oncase and unboxed (although brand new) E8 REF: MAG8P5WINDUP SOLAR POWERED RADIO AM/FM radio completewith hand charger and solar panel! £14 REF: MAG14P1COMMODORE 64 TAPE DRIVES Customer returns at E4REF: MAG4P9 Fully tested units are £12 REF: MAG12P5.MAINS CABLES These are 2 core standard black 2 metre mainscables fitted with a 13A plug on one end, cable the other. Ideal forprdects, low cost manufacturing etc. Pack of 10 for£3 REF: MAG3P8Pack of 100E20 REF: MAG20P5MICROWAVE TIMER Electronic timer with relay output suitableto make enlarger timer etc E4 REF: MAG4P4MOBILE CAR PHONE £6.99 Well almost! complete in carphone excluding the box of electronics normally hidden under seat.Can be made to illuminate with 12v also has built in light sensor sodisplay only illuminateswhen dark. Totally convi nd ng! REF: MAG6P6

ALARM BEACONS Zenon strobe made to mount on an externalbell box but could be used for caravans etc. 12v operation. Justconnect up and it flashes regularty)E5 REF: MAG5P11FIRE ALARM CONTROL PANEL High quality metal casedalarm panel 350x165x8Omm,VVith key. Comes with electronics butno information. sale price 7.99 REF: MAG8P6REMOTE CONTROL PCB These are receiver boards forgarage door opening systems. Another use? E4 ea REF MAG4P56"X12" AMORPHOUS SOLAR PANEL 12v 155x310mm130mA. Bargain price just £5.99 ea REF MAG6P12.FIBRE OPTIC CABLE BUMPER PACK 10 metres for £499ref MAG5P13 ideal for experimenters! 30m for£12.99 ref MAG13P1

LOPTX Line output transformers believed to be for hi res colourmonitors b ut useful for getting high voltages from low ones! £2 eachREF: MAG2P12 bumper pack of 10 for £12 REF MAG12P3.

BOTH SHOPS OPEN 9-5.30SIX DAYS A WEEK

BULL ELECTRICAL250 PORTLAND ROAD HOVE SUSSEX

BN3 5QTMAIL ORDER TERMS: CASH PO OR CHEQUEWITH ORDER PLUS £3.00 POST PLUS VAT,

PLEASE ALLOW 7 - 10 DAYS FOR DELIVERYTELEPHONE ORDERS WELCOME

TEL: 0273 203500FAX: 0273 323077

PORTABLE RADIATION DETECTOR

£49.99A Hand held personal Gamma and X Ray detec-tor. This unit contains two Geiger Tubes, has a 4digit LCD display with a Piezo speaker, giving anaudio visual indication. The unit detects highenergy electromagnetic quanta with an energyfrom 30K eV to over 1,2M eV and a measuringrange of 5-9999 UR/h or 10-99990 Nr/h. Suppliedcomplete with handbook.

REF: MAG50


78

WATER SOFTENER

Exposing hard water to anelectrical field causes cal-

cium -carbonate crystals andother minerals to join and formlarger crystals. At least, that iswhat researchers claim to havediscovered in their efforts tocombat the cause and ill ef-fects of hard water.

The good news is that therisk of calcium compound de-posits reduces with crystal size.If your home is on a hard watersupply (which depends on thearea you live in), you will prob-ably be aware of the disastrouseffects of solidified calcium com-pounds, which form green de-posits on just about anythingthat runs hot and supplies water,i.e., heating elements in wash-ing machines (expensive to re-place!), taps, shower heads andkettles. Water softeners areavailable commercially, butunfortunately cost an arm anda leg.

A dual astable multivibrator(AMV) type TLC556 is used inthe softener circuit to gener-ate a swept -frequency rectan-gular waveform which is ap-plied to a coil, Li, wound arounda length of plastic water tubingwhere the water supply entersyour home. Alternatively, thecoil is fitted on the water inlettube of a certain apparatus, forinstance, a washing machinethat is to be protected againsthard water. The oscillator out-put pulses are rectified by D1,and cause D6 (a green LED) tolight as an assurance that thecoil is fed with pulses. The os-cillator frequency is swept be-tween about 800 Hz and 2,5kHz. The coil, L1, consists of14 turns of solid, insulatedwire, spaced at about the di-ameter of the water pipe. Someexperimentation with differenttypes of electromagnetic field

TR1

that work on the hard water isworthwhile.

Figure A shows two open-ended coils connected to K2.This is the traditional arrange-ment of forming an electro-magnetic field, i.e., a field withan electric and a magnetic com-ponent. Figure B shows threecoils connected to K2. This causestwo mutually interacting elec-tromagnetic fields. Lastly thearrangement in Fig. C producesa magnetic field only. All ofthese arrangements should betried to ascertain which one givesthe best results on plastic or cop-per water pipes. All coils are14 turns each, spaced as statedabove.

The circuit is powered by aconventional mains supply con-sisting of a transformer, a rec-tifier, and a 12-V voltage regu-lator.

Since the mains voltage is pre-sent on the printed circuit board(at the primary pins of trans-former Tri), the completed PCBshould be fitted into a robustplastic case. The coil wires arekept as short as possible andconnected to PCB terminal blockK2. The circuit can safely beassumed to work if the green LEDlights.

Parts list

Resistors:R1, R2, R3 = 101(12R4= 39 kQR5= 22 liS2R6= 220 SIR7= 18 lcS2R8= 1.2 IcS2

Capacitors:C1 = 10 pF, 16 V, radial02, C3 = 10 nFC4 = 100 pF, 16V, radialC5, C7, C8, C10 = 100 nFC6= 47 pF, 50 V, radial

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80

CAR BATTERY MONITORThe lead -acid battery forms the heart of the electrical system in any car. If you

are on a camping or caravanning holiday, it can happen that the battery isdischarged so deeply by extra loads that the amount of energy left is too small to

start the car. The car battery monitor described here prevents this problem bydisconnecting extra loads in time, ensuring a battery condition which is always

good enough for a reliable engine start.

FORGOTTEN to switch off the carlights? Not to worry, they will go

out by themselves, very slowly. Goodfor your physical shape, too, becausethe car is bound to need a push-startthe next morning.

For campers and caravanners thecar battery is a welcome source of en-ergy, because it allows many 12-V op-erated devices to be used, for instance,a small vacuum cleaner, your mother-in-law's mini hair dryer, a coffee ma-chine, a portable TV, an extra bedsidelight, an electric shaver, and, ofcourse, the mini stereo rack. Relishingthe use of all these luxury devices(which you have become used to athome), no one thinks of recharging thecar battery. The joy lasts till the nextmorning, when the car, after a few fee-ble and discouraging sounds of thestarter engine, refuses to start becauseof a totally exhausted battery. The onlyway to get 'on the move' again is tolend some battery power from theneighbours' car, or team up and push-start the car. Obviously, such eventsare to be avoided at all costs, particu-larly when you are on holiday.

The preventive action of the car bat-tery monitor described here can beachieved at a very small outlay, and

Design by K. Walraven

with a small effort as regards con-struction. The circuit measures thedischarge level of the car battery bymonitoring the battery voltage. If thevoltage is in danger of becoming toolow for the car to be started, the extraloads (lights, radio, etc.) are discon-nected from the battery. So, if youhappen to have forgotten to switch offsomething, that will not cause a totallydrained battery.

The lead -acid batteryBefore we tackle the description of thecircuit proper, a short description isgiven of the discharge behaviour of alead -acid car battery - see Fig. 1.Note that the graph shown is typical ofa battery that has been in use for sometime. The shape of the curve of an oldbattery is totally different from thatproduced by a brand new battery.

The graph indicates a relation be-tween the charge condition (rangingfrom 'discharged' to 'charged') and theopen -circuit battery voltage. This fea-ture is exploited by the present batterymonitor. If the battery voltage dropsbelow a certain threshold, the load isdisconnected to save the remaining en-ergy. The exact value of the threshold

18

V

16

14

12

100 20

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battery voltage(load=2.2A)

40 60

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80 100 %

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936042X-11

Fig. 1. Typical lead -acid battery dischargegraph. The shape of the curve depends onthe battery's age and condition.

differs from battery to battery. Hence,an adjustment is provided in the cir-cuit to enable any threshold to be set,depending on personal requirements.

Circuit descriptionLooking at the circuit diagram of thebattery monitor, Fig. 2, you aregreeted by an old faithful, the Type 723voltage regulator in position IC1. ThisIC is used to compare a part of the bat-tery voltage with an internal referencevoltage. This is done with the aid of aninternal opamp. The reference voltageis fixed at 7.15 V, and appears atpin 6. It is applied to the invertinginput (pin 4) of the internal opamp.The non -inverting input is connectedto the wiper of preset P1. In this way, apart of the battery voltage appears atpin 5 of the 723. The actual size of the


CAR BATTERY MONITOR 81

Fig. 2. The battery saver is based on the familiar 723 voltage regulator, which contains,among others, a stable 7.15-V reference and an opamp.

part is determined by voltage dividerR2 -P1 -R3.

The battery voltage measured by theopamp is decoupled by capacitor C2,which suppresses interference acrossP1 and R3. The output of the internalopamp is connected to pin 10 of ICI.This output is `high' if the stepped -down battery voltage at pin 5 is higherthan 7.15 V. The opamp output swings`low' when the voltage at pin 5 dropsbelow the reference level. That alsocauses the relay, Ref, to be switchedoff, and LED D5 to go out. Diode D4suppresses the back-emf voltage gen-erated by the relay coil as the currentthrough it is interrupted. The loadsconnected to the relay contacts aredisconnected from the battery. Ourgoal has been achieved: if the batteryvoltage drops below a certain level, anumber of loads are switched off auto-matically via a relay.

Switch S1 is intended for emergencycases, and allows you to switch theloads on (briefly) after they have beendisconnected by the circuit. Fuse F1protects the relay contact, the PCBtracks and the connecting wiresagainst too high currents. LED D7 isthe `fuse intact' indicator. If it does notlight while D5 is on, the fuse is blown.

The use of `sense' lines requires aseparate discussion, which is aided bythe drawings in Fig. 3 and Fig. 4. InFig. 3, the battery monitor `sees' thevoltage across the load. At first glance,this voltage is equal to the battery volt-age, but there is a snag. Assumingthat the wires between the battery andthe load have a resistance of about0.5 c2, and the load draws a current of1 A, the cable `drops' 0.5 V. The voltageapplied to the monitor circuit is, there-

fore, 0.5 V lower than the battery volt-age, causing the load(s) to be discon-nected too early. In Fig. 4, the circuit

monitors the battery voltage via twosense wires. This setup eliminates theabove measurement error, and enablesthe monitor to keep an eye on the ac-tual battery voltage, ensuring thatextra loads are switched off when it isreally necessary.

ConstructionAlthough the printed circuit boardshown in Fig. 5 is not available ready-made through our Readers Services,the construction of the battery monitorshould not present problems.Alternatively, the circuit may be builton a piece of stripboard. The trackswhich carry the load current must betinned and sufficiently wide. The `Amp'type spade terminals are secured tothe PCB using bolts and nuts (Fig. 6) .

Once the screws have been tightened,the nuts may be soldered to the re-spective copper areas. The `Amp' typeterminal has three advantages: it issuitable for high currents; it enablesan easy connection to clamp -on cablereceptacles; and it is widely used forelectrical systems in cars.

The IC is fitted in a socket, and the

Fig. 3. If the sense wires are connected across the load, the cable resistance may cause thebattery monitor to measure a voltage which is lower than that on the battery terminals.

Fig. 4. The proper connection: the sense wires go directly to the battery terminals.


82 POWER SUPPLIES AND BATTERIES

Fig. 5. Track layout (direct reading) and component overlay of the PCB designed for the bat-tery monitor (PCB not available ready-made through the Readers Services).

Fig. 6. Illustrating the use of car -type 45° an-gled 'Amp' terminals and cable receptacles.

mounting of the other parts on theboard will not present problems. Donot forget the single wire link on theboard, because the circuit does notwork without this 'component'.

Once the PCB is fully populated(Fig. 7), it may be fitted into a suitable Fig. 7. Fully populated board, ready for mounting into an enclosure.

enclosure, using the front panel layoutgiven in Fig. 8. Make sure the termi-nals remain accessible without havingto open the case.

To prevent voltage loss in the con-necting wires, the circuit is bestmounted as close as possible to the car

Resistors:R1;R7;R8 = 21(02R2 = 3k09R3 = eksaR4= 1k0R5 = 15kk2R6 = 41(07P1 = 10kO preset H

Capacitors:Cl = 10uF 25VC2 = 1001iF 25VC3 = 1nFD1;D7 = LED, 5mm, greenD2;D3;D4 = 1N4148D5 = LED, 5mm, redD6 = 11\14001IC1 = CA723CE

Miscellaneous:S1 = push -to -make button.Ref = V23127 -A2 -A101 (12V;Siemens).Fl = 6 3A slow4 'Amp' cable sockets and PCB -mountspade terminals.Enclosure Pac-Tec HM -kit 6600-902.

battery. Use heavy-duty copper wirewith a cross-sectional area of at least4 mm2, or 6 mm2 if very high currentsare switched. Such wire may be ob-tained from hi-fi shops as loudspeakercable.

Connect the circuit to the load(s)and the battery as indicated in Fig. 4.If you want the LEDs and the press -key on your car dashboard, they mustbe connected via wires if the battery


CAR BATTERY MONITOR 83

monitor is mounted close to the bat-tery. Alternatively, if these parts arefitted on the board, the front panel lay-out shown in Fig. 8 may be used.

Adjustment

Strictly speaking, preset P1 can only beadjusted by trial and error. Unfortu-nately that may take quite a lot oftime, whence our suggestion to adjustthe circuit as follows.

Connect the circuit to an adjustablepower supply, and make the outputvoltage equal to the desired switchingthreshold, for instance, 11.5 V or 12 V(guidance values). Adjust P1 until therelay is just de -energized. If, aftersome time, it is found that the switch -off voltage is too low or too high, thethreshold may be corrected a little bycarefully adjusting the preset.

Attention!Car batteries are capable of deliveringextremely high currents which cancause fire and other hazards. The cir-cuit discussed here is only suitable for12-V car batteries. For higher battery

Al\S

S

936042 - F

Fig. 8. Suggested front panel layout and lettering (not available ready-made through theReaders Services).

voltages, for instance, 24 V, the relaymust be replaced by a suitable type,and voltage divider R2 -P1 -R3 requiresdifferent resistor values.

(936042)

ELECTRONICS WORKBENCH THE ELECTRONICS LAB IN A COMPUTER

Electronics Workbench (version 3)from Interactive Image Technologies(IIT) is a CAD package specificallygeared to rapid design and verificationof analogue and digital circuits. Sincethe circuit is simulated on a computer,making changes to it is much quickerthan the traditional breadboardmethod, i.e., scouring for components,fitting them, soldering and connectingthe test equipment after every change.None the less, no electronics designprogram, including EWB, does awaywith the need to build a prototype fromreal components, since the proof of thepudding is in the eating. EWB shouldbe of great interest to students, as wellas to the reasonably advanced hobby-ist. Once a circuit is known to functionproperly using EWB, you have thegreen light to actually build it.

Drawing a circuit in EWB is helpedby a `parts bin' containing most com-monly used electronic parts. Althoughthe drawing phase is pretty fast and ef-ficient, producing the circuit response(measured by various instruments, in-cluding an oscilloscope and a bodeplotter) is sluggish. Tests were carriedout on a Macintosh Ilci computer.Digital circuits, by contrast, producedtest results much faster.

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Adding parts to the library is easy ifyou duplicate the existing 'ideal' ver-sion of a particular component, andthen assign parameter values to the`real' part to be added. From then on,the part is available for all new work.

Although the components pick andplace operations work fine, the pro-gram sometimes has a quirk in theway in which the parts are actually po-sitioned and connected. Also, althoughthey are electrically correctly con-

nected, the leads to the test bench in-struments sometimes take surprisingpaths criss-cross through the circuit.

Among the shortcomings of the pro-gram that should be mentioned are theinability to read netlists and so put cir-cuits generated by other programs onthe test bench, and the unusually sim-ple shapes assigned to some ICs likethe 555. Also, it would be desirable tohave a rather more elaborate parts li-brary, and to be able to mix linear withdigital electronics. Fortunately, a li-brary extension (Model Set 1), and aset of 150 `standard circuits' can beobtained from ITT.

None of these criticisms, however,can alter my opinion that ElectronicsWorkbench is well worth considering ifyou are after a drastical reduction ofcost and time spent on the design ofanalogue and digital circuits of up tomedium complexity. tech. ed.

Electronics Workbench costs £199(excl. VAT and p&p), and is availablefor DOS, Windows and Apple plat-forms, from Robinson Marshall(Europe) Ltd., Nadella Building,Progress Close, Leofric BusinessPark, Coventry CV3 2TF. Telephone:(0203) 233216, fax: (0203) 233210.


84

GENERAL-PURPOSE INFRA -REDVOLUME CONTROL

Home made audio amplifiers are rarely equipped with a remotely controlledmotor -driven volume control. Curious, because motor -driven pots are high -quality products, and consequently should appeal to the 'high -end' audio

fraternity. Fortunately, prices of motor -driven volume controls have come downto acceptable levels, while infra -red remote controls can be obtained fairly easily

from TV spare parts sources. Time to put two and two together.

HE number of electronics hobby-ists sinterested in building audio

amplifiers and related items is tradi-tionally fairly high. It may thereforesafely be assumed that a fair numberof readers have been waiting for a pro-ject of the kind described here.

A relatively simple circuit is dis-cussed that enables the volume of, forinstance, a home-made amplifier or asimilar circuit (Audio DAC, Ref. 1) to becontrolled via an ordinary infra -red re-mote control. The remote control unitmay be any type, as long as it is RC5compatible. The self -learning (or 'intel-ligent') brand offered by some radio andTV retailers may also be used.

Thanks to the use of integrated circuits,the number of components in the projectis small, while motor -driven potentiome-ters are available at reasonable pricesthese days. All in all, many high -end audioenthusiasts will find the remote -controlledvolume control a worthwhile upgrade foran existing preamplifier.

Design by T. Giesberts

The drive circuit

The circuit diagram of the infra -redvolume control is shown in Fig. 1. Thecircuit consists mainly of three ICs forreceiving and decoding the infra -redsignal, and a couple of transistors todrive the motor. The circuit has itsown power supply, which is fed by thesecondary winding of the mains trans-former used in the preamplifier. Thatis done to save you the cost of an extratransformer, while the preamplifiersupply will happily supply the smallextra current drawn by the volumecontrol.

The infra -red signal transmitted bythe remote control unit is picked up byICI. The IS1U60 from Sharp not onlycontains an infra -red sensitive diode,but also a complete receiver consistingof an amplifier, a limiter, a 38 -kHzpass -band filter, a demodulator andan output stage - all in a case with asize of only a few millimetres.

Furthermore, the IS1U60 is fullyscreened against electromagnetic in-terference, and features a lens elementto bundle and focus infra -red light.Sharp Electronics in their datasheetsspecify a minimum operating range of5 metres, while 3 metres is guaranteedat a horizontal angle of incidence of30°, or a vertical angle of incidence of15°. In practice, the range achieved bythe receiver is much larger - our pro-totype easily covered 15 m. The highsensitivity of the IS1U60 makes thedevice just the thing for the presentapplication.

The received and filtered drive sig-nal may be applied directly to the de-coder, a SAA3009 (IC2). The SAA3009is related to the SAA3049, which wasused in earlier projects in this maga-zine, including a multi -purpose RC5infra -red receiver (Ref. 2). The maindifference between the SAA3009 andthe SAA3049 is the higher output cur-rent capacity of the former: 10 mA

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MULTI -PURPOSE INFRA -RED VOLUME CONTROL 85

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Fig. 1. The circuit of the IR volume control consists of three sections: an infra -red receiver, a decoder and a driver for the motorized poten-tiometer.

against 3 mA for the SAA3049.Obviously this is reflected by the3009's total current consumption,which can go up to 70 mA.

The function of the SAA3009 is toconvert the received data into a binarycode. The serial RC5 signal containstwo important data: the system ad-dress and the command proper. In theRC5 set of codes, the function 'pream-plifier' is assigned system address 16.As a matter of course, every user isfree to assign a different address to theamplifier (or, in more general terms,the volume control), if '16' is already inuse, or if the potentiometer is fitted ina circuit which is not an amplifier. Theaddress is set with the aid of inputsA0 -A4 on the SAA3009. Address '16' isselected by making AO through A3logic low (jumpers fitted), while nojumper is fitted for A4. The address re-served for TV sets is '0', which is se-lected by fitting all four jumpers onjumper block K1.

The SAA3009 operates in single -

system mode (SSM), which means thatit responds to only one address. Short-circuiting resistor R5 causes the IC toswitch over to combined system mode(CSM). The decoded address is thenavailable on pins AO through A4,which then function as 'active -low'outputs.

In the RC5 protocol, the system ad-dress is followed by the commandproper. That is decoded in IC2, andmade available at outputs A throughF. In principle, the IC is capable of de-coding up to 64 commands in additionto the 32 system addresses. In the pre-sent circuit, however, only two com-mands matter:

address1617

F EO 1

O 1

D CO 0O 0

B A CommandO 0 vol. upO 1 vol. down

Outputs A -F are connected to the `P'inputs of a digital comparator, IC3. Theoutput of this comparator, labelledP=Q, goes low when the dataword at

the `P' inputs matches the dataword atthe 'Q' inputs. That happens whenP=0010111. The least significant bit,A, forms the only difference betweenthe 'volume up' and 'volume down'commands. This bit is connected tothe PO and the QO pin of the compara-tor, to make sure that they are alwaysat the same level. It also drives thegate of MOSFET T3 and so determinesthe left/right rotation of motor M1.

If the dataword at the P inputsmatches the preset dataword at the Qinputs, T4 is driven, and the motor dri-ver is powered. Next, the level of the`volume up/down' bit, A, determines therotation direction of the motor. If A=0,T5 conducts. Consequently, T3 isswitched off, so that the base of T6 ispulled to ground, causing this transis-tor to be switched off also. However,since a voltage of 5 V is present on thecollector of T6, T8 is switched on, and T7is switched off. The upshot is that a cur-rent flows through the motor winding,via T4, T5, T8, and into the ground rail.


86 AUDIO AND HI -El

If A=1, the above state is reversed:T5 is then off, so that T3 and T6 areswitched on. T6 pulls the base of T7 toground, so that T7 starts to conductalso. Consequently, current flows inthe opposite direction through themotor winding, via T4, T7, and into theground rail again, this time via T6. Inthis way, the level of bit A determinesthe direction of the motor. LED D6lights any time the motor operates.

The sub -circuit around T1 and T2,between the CA output of IC2 (`com-mand received', pin 19) and the enableinput (G) of IC2, affords additional pro-tection against noise, and also servesto detect when a new system addressis received. If a system address is de-

coded, the CA output supplies a rec-tangular signal which is low for 15 ms,and high for 105 ms. Because of thelarge time constant of network R7 -C7,transistor T2 operates as a rectifier onthis signal. Its collector will thereforeremain logic high as long as the signalis present at pin 19. As soon as thesignal disappears, IC3 is immediatelydisabled.

Immediately after the supply isswitched on, IC1 is reset via capacitorC2. Diode D1 ensures that C2 is rapidlydischarged when the supply is switchedoff. The toggle bit (pin 18), whichchanges state on every command re-ceived, is not used in this circuit.

The power supply is conventional.

Fig. 2. The PCB may be cut into two, separating the driver board from the potentiometerboard. The IR receiver circuit, IC1, and the potentiometer are best mounted onto the pream-plifier's front panel. This printed circuit board is available ready-made through the ReadersServices (see page 110).

Diodes D7 and D8 rectify the alternat-ing voltage supplied by the secondarywinding of the preamplifier's mainstransformer, and C11 smooths the di-rect voltage. Resistor R15 reduces theregulator input voltage so that the dis-sipation of the 7805 is kept withinspecifications. The value of the 5 -wattresistor depends on the transformer'ssecondary voltage. For example, if thesecondary voltage is 30 V, the rectifiedvoltage will be of the order of 40 V.Since the maximum input voltage of a7805 regulator is 35 V, resistor R15 willhave to drop at least 5 V. The currentconsumption of the IR volume controlbeing about 50 mA, R15 then takes avalue of 5 V/50 mA = 100 52.

Resistors:R1 = 470R2 = 2522

R3 = IMOR4 = 331(0R5 = 6841R6 = 5426R7 = 10MilR8 = 10k0R9 -R14 = 142R15 = see textP1 = 20k52 log. stereo potentiometerw. motor drive (Alps type 20KAX2)

Capacitors:Cl = 220pF 10V radialC2 = 22pF 25VC3;C4 = 27pFC5 = 10pF 25V radialC6 = 47nF ceramicC7 = 33nFC8 = 100pF 10VC9 = 100nFC10 = 220nFC11 = 470pF 40V

Semiconductors:D1 -D5= 1N4148D6 = low -current LEDD7;D8 = 1N4002T1;T2 = BC547BT3 = BS170T4;T5;T7 = BC640T6;18 = BC639IC1 = 1S1U60 (Sharp), or SFH506-38(Siemens)IC2 = SAA30091C3 = 74HCT688IC4 = 7805

Miscellaneous:K1 = 10 -way boxheader w. 5 jumpers.X1 = 4MHz quartz crystalPrinted circuit board 930099 (see page110).


MULTI -PURPOSE INFRA -RED VOLUME CONTROL 87

Fig. 3. Three different types of infra -red re-ceiver IC may be used with the wireless vol-ume control. Note the different pinnings,which are catered for by a 5 -way SIL socketon the driver board.

Construction

The printed circuit board of which theartwork is shown in Fig. 2 consist oftwo sections which are separated witha jigsaw. The combined board is avail-able ready-made through the ReadersServices. The larger board contains thedrive electronics, while the smaller oneserves to mount the motor -driven po-tentiometer. Solder pins may be fittedat the solder side of the potentiometerboard. The small board is useful if youwant to fit the pot at the back of thepreamplifier case. The PCB is notstrictly necessary if you decide to se-cure the pot behind the front panel, inwhich case the wires may be soldereddirectly to the tags on the motor.

As long as you do not forget to fitthe wire links, and take care to fit thepolarized components the right wayaround, no special problems should beencountered in the construction. Workcarefully, and follow the parts list andthe component overlay.

An alternative for the IS1U60 is theSiemens SFH506-38. As shown inFig. 3, the two ICs have different pin-nings, so take care when connectingone to the input of the control board.The SFH505A appears to be obsolete,and should not be used in conjunctionwith the SAA3049.

Once populated, the circuit boardmay be fitted into the preamplifier en-closure. Replacing the existing poten-tiometer in the preamplifier with themotorized type is fairly easy in mostcases. The PCB with the drive electron-ics is best fitted behind the preampli-fier's front panel, so that the infra -reddiode contained in ICI can 'look out'

through a hole. If space is tight, thePCB may have to be located a little fur-ther away from the front panel. In thatcase, ICI may be connected to theboard via a short length of screenedcable.

Final notesThose of you who are wondering howto program an existing remote controlunit for system address 16 may findthe information in Ref. 2 of use, sincemodification details are given in thatarticle.

Finally, just before the present de-sign was finalized for publication, in-formation was received from PhilipsComponents that the SAA3009 is sup-plied in limited quantities only. A suit-

able equivalent is the SAA3049, whichdoes not suffer from supply problems.However, the use if the 3049 does re-quire a number of resistors to beadded, as shown in Fig. 4. Eleven 10-ki2 pull-up resistors are fitted at termi-nals A0 -A4 and A -F of IC2, and a68-kS2 resistor in parallel with D1.Components R3, C3, C4 and the quartzcrystal may be omitted.

(930099)

References:1. AF digital -to -analogue converter,parts 1, 2 and 3, Elektor ElectronicsJuly/August, September and October1992.2. Universal RC5 code infra -red re-ceiver, Elektor Electronics January1992.

IC1

SFH 506

5V R2

® ® 12 I L* K1 "7

5mm22p

Idl 44_0 5

.1_0 3 8

2_0 1 7

NIS1U60 .4_0 7 N

.2 900 N

2

20

Cl

220p 110V

D1

I1N4148

AO

Al

A2

4

IC2

SAA3049

RESET

A

CA

TO

MODE

X1 X2 L

S.

L 1_1 L 16

10p 25V 475

12 13

,19

18

11

Cl

7n

930099 - 132 x

BC547B

Fig. 4. If a SAA3049 is used instead of a SAA3009 you have to add 12 resistors.


88

FIGURING IT OUTPART 18 THE LAPLACE TRANSFORM

By Owen Bishop

This series is intended to help you with the quantitative aspects of electronic design:predicting currents, voltage, waveforms, and other aspects of the behaviour of circuits.

Our aim is to provide more than just a collection of rule -of -thumb formulas.We will explain the underlying electronic theory and, whenever

appropriate, render some insights into the mathematics involved.

Systems of many kinds, fromelectronic circuits to the mo-

tion of planets and the spend-ing patterns of supermarket cus-tomers, may be modelled withdifferential equations. Settingup the equations is usually fairlyeasy. Solving the equations maybe unexpectedly dfficult. Ob-viously, a solution may be morereadily reached if we assumethat certain values are zero or re-main constant, but this may makethe model unrealistic, or at leastlimit its applicability. Varioustechniques have been devisedto assist the solution of differ-ential equations. One of theseis the operator D, described inPart 14. Another technique, knownas Euler's method, is easy to usebut, since it relies heavily on ap-proximations, is not entirely re-liable. A third and powerful tech-nique is the Laplace transform.

Transforms

Given a set of values, we trans-form them by performing a spec-ified mathematical operation oneach of them. A well-known ex-ample is the logarithmic trans-form. Take this set of numbers:

0.5, 2, 3.5, 7, 20.22.

The logarithmic transform ofthese is obtained by taking thenatural logs, or logs to any otherbase, if preferred. Natural logscan be found with a pocket cal-culator and we obtain the trans-formed set (shown here to 4 dec-imal points):

-0.6931, 0.6931, 1.2528,1.9459, 3.0067.

The members of the original setmap in a one-to-one manner withthe members of the transformed

set. We can also perform the in-verse transform, using the exfunction on the calculator, andrecover the original set.

At one time, logs were usedextensively to assist in calcula-tions, either in the form of logtables, or on the slide rule. Thisis because they have the prop-erty that adding logs is the equiv-alent of multiplying ordinarynumbers. For example:

ln 2 + ln 3.5 = 0.6931 + 1.2528= 1.9459 = In 7.

Taking logs, adding them, andtaking the antilog of the sum, hasgiven us the product. Adding iseasier than multiplying, espe-cially when there are many dec-imal places.

Finding a fractional power ofa number is a troublesome op-eration. For example, find thevalue of 3.52.4. The log transfor-mation comes to our aid becausemultiplying a log by a numberis the equivalent of finding thepower. In this example:

2.4 x ln 3.5 = 2.4 x 1.2528= ln 20.22

that is,

3.52.4 = 20.22.

Multiplying the log, then findingthe antilog, has given us thepower. Multiplying is easier thantaking powers, especially whenthey are fractional. Summingup, we use the log transform be-cause it makes certain mathsoperations easier to do. We usethe Laplace transform for thesame reason.

Laplace transformThe Laplace transform operates

on a time function. By this wemean that a quantity (such asvoltage) is specified by a functionf(t), in which time is the inde-pendent variable. For example,u = 3 sin cot. We say that u is inthe time domain. We sometimeswrite u(t) and i(t ) for the functioninstead of f(t), the lower caseletter indicating the quantityinvolved. The Laplace transformof a time function f(t) is F(s),where:

F(s)=-o f ( t) e st dt

[Eq. 132]The main condition attached tothis transform is that the inte-gral must be convergent, whichmeans that the integral must ap-proach a definite limiting valueas t becomes large, and not be-come infinitely large itself. Mostof the time, functions met in elec-tronics conform to this require-ment. It is also specified thatf(t) = 0 when t = 0. If it is not,we insert starting conditions intothe equations.

Unit step functionThe Laplace transform is notunduly complicated when thetime function is a simple one.As an example of the transform,we look at the unit step func-tion, which, in effect, is equiva-lent to just turning on the powerswitch-see Fig. 147a. Up tothe instant of the starting time,the switch is open. The voltageacross the resistor is u = 0. Theswitch is closed when t = 0 andthe voltage across the resistor in-stantly rises to u = 1. We have aunit step-see Fig. 147b. Thefunction describing this is piece -wise:

u(t) = 0 < t < 0-

a

b

930010-XVIII-147

Fig. 147

u(t) = 1 0+ < t < +00.Note that we specify u up to theinstant before the switch is closed(t = 0-) and from the instant afterthe switch is closed (t = 0+). It isundefined for the instant of clos-ing. The second of the two func-tions above is the one we trans-form. Substituting in Eq. 127:

U(s)=.1e-Stdt

1[e -.St==1/sAs t approaches infinity, e-st ap-proaches zero; when t is zero,e-st = e0 = 1. The integral re-duces to 1/s. Similarly, if the stepis other than a unit step, for ex-ample u = a, the transform isa /s.

Other transformsIn a similar way, we can find thetransforms of other common func-tions. As might be expected, theintegrations required are morecomplicated than that for thesimple step function above.However, there is no need to worryabout this as the transforms of


FIGURING IT OUT - PART 18 89

all the most frequently met func-tions are available in a table(see Box 1). The transforms inBox 1 are mostly needed whenwe are performing the reversetransform, as we shall see later.Since our calculations usuallybegin with a differential equa-

tion, we need to know how totransform these. Box 2 shows thetransforms of the terms of a dif-ferential equation and the wayto use these and the transformsin Box 1 is explained in the ex-ample below.

A differential equation con -

Function Transform Conditions1 (unit step function) 1/s 91(s) > 0

a (step function) Ws 9Z(s) > 0

t (ramp function) 1/s2

eat (growth function) 1/(s -a) 91(s) > a

e -at (decay function) 1/(s+a) 9l(s) > -a

1 -eat als(s-a) 91(s) > a

1 -e -at als(s+a) 91(s) > -a

sin a coi(s24.(02) s 0cos wt si(s2+(0 ) s > 0

91(s) is the real part of s in those cases where s is a complex

number.a and co are constants.

Box 1 - Laplace transforms of functions.

TermConstant aFunction 1( t)

First derivative f '(t)

Second derivative f"(t)rr

Integral f (t') dt

Transformed terma/s

F(s)

sF(s)- f (0 )

s2F(s)-sf (0+ )-/"(0± )

P(s)/s+ f (0+ )/s

Box 2 - Laplace transforms of differential equations.

1. Factorise the denominator of the original fraction, if possible2 Match the factors against one or more of the formats shown in

Box 4.3. Box 4 sets out the form of the partial fractions; write them out

as an identity.4. Clear fractions by multiplying both sides of the identity by the

original denominator.5. Equate coefficients of each power of x, obtaining equations for

constants A, B, etc.6. Solve these equations to find A, B, etc.

Example: Express (3.r+5)/(x2-x-12) as a partial fractionStep 1: (3x+5)/(x2-x-12) = (3x+5)/(x+3) (x-11)Step 2: There are two factors, both have the form (x+a). So,

there are two partial fractions, both with the formA(r+a).(3x+5)/(x+3) (x-4) = A/(x+3)+B/(x-4).3x+5 = A(x-4)+B(x+3)

Ax-4A+Bx+3B.Equating coefficients of x: A+B = 3.Equating constants: -4A+3B = 5.A = 4/7 and B = 17/7; partial fractions are:(3x+5) / (x2 -x-12) = 4/7: (x+3)+17/7 (x-4).

Step 3Step 4:

Step 5:

Step 6:

Further worked examples appear in the text.

sists of several terms, usually in-cluding a constant, a first fiffer-ential (dy/dt), a second differen-tial (d2y/dt2), and possibly dif-ferential terms of third or higherorders. An example taken fromPart 13 is a model of a seriesLCR circuit in which R = 500 S2,C = 2 pF, and L = 100 mH. Thedifferential equation, based onEq. 94, is:

d2i(t)/dt2 +5000 (di(t)Idt)+ (5x106)i(t) = 0

[Eq. 1331Note that we have replaced i inEq. 94 with i (t) to emphasise thati varies in the time domain - itis a function oft - but it repre-sents exactly the same quantity.Our aim is to discover the way ivaries with time. In other words,to obtain the function i (t). Tosolve this equation, we will firstfind its transform. It can be shownthat, if we find the transform ofeach term individually and sumthe transforms for each side ofthe equation, this gives the trans-form of the whole equation.Working from right to left:

The transform of 0 is 0 (a unitstep in which a = 0 - see Box 1)

The transform of (5x106)i(t)presents a problem because, untilwe have solved the equation, wedo not know the form of the func-tion i. Represent it by a symbol,using the corresponding capitalletter, and say that its trans-form is I(s). Note that the trans-form is in the s domain, whichcan be shown to be the frequencydomain. Since any constant mul-tiplier also multiplies the trans-form, the transform of (5x106)i (t)is (5x106)/(s).

The transform of 5000(di(t)/dt)can be obtained by integrationaccording to Eq. 132. Skippingover the intermediate stages,which are a conventional inte-gration by parts, we find that thetransform of di(t)Idt is sI(s)-i(0+).

As above, we have had to statethe transform in terms of/(s), be-cause we do not yet know theform of i(t). The term i(0+) is thecurrent flowing at the instant

that timing begins. Again, wemultiply the transform by the co-efficient of the original term, sothe transform of 5000 [di(t)/dt]is

5000s/(s) - 5000i(0+).

In Part 13, we stipulated thatthe current is 2 mA when tim-ing begins, so i(0+) = 0.002 andthe transform is 5000s/(s)-10.Note that instead of having to dif-ferentiate i(t), we have simplymultiplied its transform by s togive sI(s). Multiplying by s ismuch easier than differentiat-ing, which is the reason for usingthe transform.

The transform of the extremeleft-hand term, d2i(t)/dt2, is alsomade according to Eq. 132 and,assuming that no current is flow-ing at the instant the power isswitched on, it produces

s2/(s)-si(0+)-di(0+)/dt.

The second differential is ob-tained by multiplying sI(s) by s;as before, it is much easier to mul-tiply by s than it is to differen-tiate. In this expression, i(0+)= 0.002, as above. di(0+)/dt is therate of change of current whentiming begins. In Part 13, wesaid that this is 0.05 A s-1-, sothe tranform under these start-ing conditions becomes

s2/(s)-0.002s - 0.05.

Summing the transforms ofthe terms on each side ofEq. 133, we obtain a new equa-tion in the frequency domain:

s 2i(S)-0. 002 s -0.05+5000 s/( s )- 10

+(5x 106 )I(s)=0

The next step is to simplify thisin order to find /(s), the Laplacetransform of Eq.133. Examinationshows that I(s)is a factor in threeof the terms. The equation be-comes:

{s2 +5000s+(5x 106 )}I(s)=0.002s+ 10.05

Factors in denominatorx+a

x2+ax+b

(x+a)2

(x+a)3

(x2+ax+b)2

Partial fractionsA/(x+a)

(Ax+B)/(x2+ax+b)

A/(x+a) and B/(x+a)2

A/(x+a), B/(x+a)2 and C/(x+a)3

(Ax+B)/(x2+ax+b) and

(Cx+D)/(x2+ax+b)2

Box 3 - Partial fractions.


Box 4 - Formats for partial fractions.

90 GENERAL INTEREST

so that:

/(s)-=0.002s +10.05

6s2 +5000s+(5x 10 )

The expression below the line canbe factorised, using the quadraticequation formula (available onmany scientific calculators) togive:

/(s)= 0.002s+ 10.05(s+1382)(s+3618)

[Eq. 134]We are working toward gettingthe terms of the equation into thesame form as one or more of thetransformed expressions in Box 1.Many of these have a single fac-tor, such as (s -a), beneath theline. The equation above couldbe turned into this form by ex-pressing the fraction as partialfractions. When this is done, wefind that:

/(s)= 0.003258 0.001258-s+1382 s +3618

(To confirm this working, add thetwo partial fractions and verifythat you get back to the fractionof Eq. 134). A search through thetable of Box 1 shows that ex-pressions of this form are trans-forms of the decay function,i(t) = e -at. We are ready to per-form the reverse transform, read-ing from right to left in Box 1and substituting appropriatevalues for a and s:

i(t)=0.003258e-1382

-0.001258e-3618

This is precisely the same re-sult as was obtained in Part 13using the straightforward tech-niques for solving differentialequations. It serves to confirmthat the Laplace transform doesgive the correct result, in spiteof the apparently roundaboutroute from start to finish. The ad-vantage of the Laplace methodis that it can be used with dif-ferential equations that do notyield readily to the ordinary tech-niques.

It has taken several paragraphsto work through this example,but the steps in the calculationare few:

1. Transform the differential equa-tion, using Boxes 1 and 2.

2. Simplify the equation to ob-tain an expression for I(s).

3. Insert initial values and re-cast the expression so that itconsists of terms of the sametype as the transforms in Box 1.

4. Find the inverse transforms,

using Box 1, to obtain an equa-tion for i(t).

The important point to no-tice is that at no stage is thereany need to differentiate or in-tegrate. The tables of transformscover almost every case, and ta-bles more extensive than Boxes1 and 2 are available for the in-frequently used functions. Theonly maths required is simple al-gebraic manipulation, mostlythe finding of partial fractions.This does not seem to appear inGCSE maths syllabuses, so asimple routine for this is out-lined in Boxes 3 and 4.

Transformed circuits

930010-XV111-148

Fig. 148

Figure 148 shows a circuit inwhich the switch is in positionA long enough to reach a steadystate. The switch is changed toposition B when t = 0. At anyinstant the voltage across the tworesistors is 120i(t) and, becauseit depends on the rate of changeof current, the voltage acrossthe inductor is 0.5di(t)/dt. Applyingthe rules for networks that wefirst met in Part 4, we can statethat by KVL, and with the switchin position B:

120i(t)+0.5di(t)/dt = 0lEq. 135]

This differential equation de-scribes the behaviour of the cir-cuit but, since it does not takeinto account the initial state ofthe circuit, we do not yet havean equation for i(t). Because thevoltage source is now switchedout of the circuit, it is hard tosee how we can allow for it. Thisis where the transform helpsout. Transforming Eq. 135:

120/(s)+0.51s/(s)-i(0+)} = 0[Eq. 136]

Now we can take the initial cur-rent, i(0+), into account. We findits value by noting that in thesteady state with the switch atA, assuming that the resistanceof the inductor is negligible, avoltage of 6 V across a resis-tance of 100 Q causes a current

30mV930010-XVIII-149

Fig. 149

of i(0+) = 6/100 = 0.06 A. Sub-stituting in Eq. 136:

120/(s)+0.5s/(s)-0.03 = 0or

120/(s)+0.5s/(s) = 0.03[Eq. 137]

Equation 137 is the equationwhich woulld be obtained by ap-plying the network rules to thecircuit of Fig. 149. In other words,Fig. 149 is the circuit ofFig. 148transformed into the frequencydomain. Note how the induc-tance depends on s, which hasthe dimensions offrequency. Thecircuit includes a voltage source,representing the voltage due tothe initial current. From Eq. 137:

/(s) = 0.03/(0.5s+120)

Before we can reverse the trans-form, we must multiply the nu-merator and denominator of thefraction by 2 to obtain s in thedenominator instead of 0.05s:

i(s) = 0.06/(s+240)

Box 1 shows that this is the trans-form of the decay function. In thetransform, a = 240 and:

i(t) = 0.06e -240t

The graph of this function is givenin Fig. 150. It shows that the cur-rent starts at 0.06 A and decaysexponentially, being very close tozero after 20 ms.

60

InIA]

SO

20

10

10

Fig. 150

Next month we look at howto model capacitors and how to

calculate initial and final cur-rents and voltages.

Test yourself1. Use the table of Box 1 to find

the transforms of (a) 2e -6t,and (b) 3cos4t.

2. Use the table of Box 1 to findthe inverse transform of (a)3/s(s-3), and (b) 28/(s2+49).

3. Write the transform of thisequation and solve it, usingthe starting conditions given:d2i(t)/ dt2+di(t)/dt-6 = 0, giventhat i(0+) = 0 and di(0+)/dt = 5.

4. In the circuit of Fig. 151, theinput voltage is 10 V at t = 0,and ramps down accordingto the equation u = 10-200t.(a) Express the current in thiscircuit as a differential equa-tion; (b) find the transformof the equation and simplifyit; (c) find the inverse trans-form to obtain an equationwhich shows how the currentvaries in time.

930010-XV111-151

Fig. 151

Answers toTest yourself (Part 17)

la Eel& = 2+3y;& 1 &y = 2x+3.

lb &z/&x = 3x/2y;&I Sy = -3x2/4y2.

2. Charge decreases by 0.2 pC,from 198.0 pC to 197.8 pC.

3. dr/dt = 0.75;du/dt = 100x10-6;Si 1 ou = -1r;

1 &r = (u -10)/r2;di/dt = 86.7x10-9 wheni =1 mA, equivalent to a tempcoof 86.7 ppm °C-1.

[930010-XVIII]


91


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46 Smear solder on starter for utensil!(3-6)

47 No vice in hearsay! (5)48 Type of small Sovereign? Fifty

about her planners (9)49 Russian gets hotter about flier (5-4)

Down:1 On top of the way? (7, 5, 9)2 Typed in order (6)3 Dictator of the year? No, head

stupid (7)4 Drug Squad issue 500? No.

Thought they knew! (6)5 Little Christopher, say, has ten

letters. So it does! (10)6 And others have no alien carpet.

Not sharp (6)7 Calling all cards! (7)8 Imagined not being at home.

Pictured (6)9 Grapple coracle, then hoe for Top

Chart! (21)10 Altering?! (8, 9)12 Coastal cartographers? (7, 10)19 Give vase the runaround (3)21 Could it trigger infra -red zebra

crossing? (7)22 Danced to the fourth track (7)24 Financial cartel compromising

foreign sea (3)25 We hear it's safe (5)26 A news item (5)31 Geometric car light (3)32 Yet, how trivial is this theory? (10)33 Polo? Not quiet round here (3)37 Mum's clean with a clasp (7)38 Dynasty one Scot would have in

explanation (7)40 500 in Andes does not make one

happy (6)42 Veers around point to find birds (6)43 Do campers mean this here? (6)44 Inferior odd Continental (6)

The solution will be published in theSeptember 1994 issue.


92

RESETTABLE FUSE FOR CARAVANS

Considering the increasing volume of electrical equipmenttowed along by today's caravanners, people franticallysearching for torchlights and then the spare fuses box can beobserved almost any night on any camping site. If you have acaravan, and want to keep that unpleasant aspect of holidaymaking at bay, you are well advised to extend the electricalsystem with a resettable fuse as described here.

From an idea by E. Bosman

THE true spirit of caravanners andcamping enthusiasts seems to

have vanished if you look at what somepeople bring with them to their holidaydestination: an electric coffee machine,a hot water boiler, an electric iron, acolour TV sets and even a satellite TVreceiver, to mention but a few things.Obviously, the modern holiday makerdoes not want to forfeit the comfortand luxury he or she has come tovalue so much at home. At the sametime, most of you would also like tothink of camping as a 'primitive' pas-time: back to nature, idyllic places, el-ementary cooking, and making coffeeon a smoking little fire made from wetwood, that is what it should be about.Unfortunately, as in so many cases,modern technology has changed allthat. For better or for worse, that is foryou to judge.

In any case, the arrival of more andmore electrical equipment in andaround the caravan or mobile homegreatly increases the risk of fusesblowing at unexpected times. A blownfuse is not a very serious event in itself

P

controlcircuit

Fig. 1. Basic elements that make up an elec-tronic, resettable, fuse.

if it is just the caravan fuse, since thatis fairly easy to replace. Provided, ofcourse, you have your torchlighthandy when disaster strikes (most ofyou will know that fuses usually blowwhen it is dark).

Far more trouble, indeed, if the fuse

in the caravan connection post on thecamping blows. That can happen if ithas a lower rating than the caravanfuse. Undesirable as it may be, ablown fuse is often difficult to forestallin the hubbub of getting your caravanparked, connected, and so on. A lot oftrouble can be prevented by first ask-ing the camping proprietor about therating of the fuse installed in the con-nection post, and install a lighter fusein your caravan before actually con-necting up to the mains network. Forexample, if the mains outlet is said tohave a 10-A fuse, it is best to use a 6-Afuse in the caravan. Undoubtedly thebest way to prevent trouble with themains supply is to insert a resettable,adjustable fuse in series with the(fixed) caravan fuse. The resettablefuse is then adjusted for a trip currentjust below that of the fixed fuse. Oncethe resettable fuse is installed, all youhave to do is press a button if you aresuddenly in the dark as a result of anoverload or an short-circuit.

The electronic fuse described here isfairly easy to build, as reliable as canbe achieved with simple means, andadjustable for currents between 4-Aand 16 A. In other words, a 'must' forall caravanners!

General layoutAlthough there are several options todesigning an electronic alternative to afuse, there is no way to go round cer-tain basic 'ingredients'. For example, acurrent sensor is always required todetect the overcurrent level, as well asa device to break the supply. In otherwords, the design is basically asshown in Fig. 1.

A series resistor, R, and a relay con-tact are inserted in the supply line tothe load. The voltage drop across R de-pends on the current which flowsthrough the resistor. All that is re-quired in addition is an electronic cir-cuit which monitors the voltage acrossR, and actuate the relay if a certainthreshold is exceeded. What remains,is, of course, the question how theelectronic control is realized in prac-tice.

Comparators with amemoryTo be able to check if a voltage exceedsa certain level, that level needs to bedefined as a threshold. Although thatcan be achieved with the aid of a com-parator, it is also desirable for the load


RESETTABI,E FUSE FOR CARAVANS 93

R1

R2

0 1771 2x 1N4148

L

Tr1

12V 3VA

R11 R5

R6

Pi 0

IC3

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1N41484

C3

100n

T1

BD140

940061 - 12

Fig. 2. Circuit diagram of the resettable fuse for caravanners.

voltage to remain switched off (after anoverload condition) until the reset but-ton is pressed. In other words, somekind of memory function is in order.

A cursory look at the circuit dia-gram in Fig. 2 will inform you thatboth basic elements mentioned aboveare present in the circuit. There areeven two comparators, so that the cir-cuit responds to the positive as well asthe negative half cycle of the mainsvoltage. Briefly, the operation is as fol-lows. The series (`sensing') resistor isformed by R12. When the voltage

across R12 rises above +100 mV or-100 mV, the respective comparatorIC la or IC b toggles, causing bistableIC2 to be triggered, and to change statealso. Consequently, the relay is de -en-ergized, and the bistable holds its stateuntil the 'start' key is pressed.

Let us examine the circuit in moredetail. The sensing resistor, R12, has alow value to prevent too much powerbeing wasted by dissipation. Resistorswith such a low value are fairly easy tomake yourself from (enamelled) copperwire of a known diameter or wire gauge

number. Since the value of R12 deter-mines the trip level of the electronicfuse, Table 1 indicates how values of18 mil down to 5 rnS2 may be producedfor maximum fuse actuation currentsof 4 A and 16 A respectively.

Comparators IC la and IC b jointlycompare the input voltage with a refer-ence voltage derived from the 12-Vsupply with the aid of R3 -R6. Of theseresistors, R4 and Ry drop about2x100 mV. The alternating voltagedropped by the sensing resistor arrivesat the voltage monitor via R1 and R2.


94 GENERAL INTEREST

R Pm:am) c.s.a. wire dia. length

4 A 18 mil 0.3 W 0.5 mm2 0.8 mm (22) 52 cm

6 A 12 rni2 0.5 W 0.5 mm2 0.8 mm (22) 35 cm

10 A 8 mil 0.7 W 0.5 mm2 0.8 mm (22) 23 cm

16 A 5 mil 1.13 W 0.75 mm2 1 mm (20) 22 cm

c.s.a. = cross-sectional area.Nearest SWG value in brackets.

Table 1. Design data to help you make your own shunt resistor.

This voltage is limited by diodes D1and D2, while capacitor C1 suppressesfast pulses and RF noise. The sensitiv-ity of the fuse is adjusted with presetP1. The preset acts as a kind of 'fineadjustment' of the fuse value, bearingin mind that the maximum current de-fined by R12 can only be increased, notdecreased, by the preset.

As soon as the positive or negativehalf period of the voltage across R12 ex-ceeds the reference level of 100 mV,one of the comparator outputs swingsfrom high to low. Next, bistable IC2, a

Fig. 3. Track layout (direct reading) and component mounting plan of the printed circuit board designed for the resettable fuse (PCB not avail-

able ready-made).


RESETTABLE FUSE FOR CARAVANS 95

Resistors:R1,R2,R6,R7,R8,R10 = 10kiIR3 = 10041R4,R5 = 1k1R9 = 1MC1R11 = 47klR12 = see table 1P1 = 47k11 preset H

Capacitors:C1,C3,C4 = 100nFC2 = 470nFC5 = 470uF 25VC6 = 10pF 16V

Semiconductors:D1-05= 1N4148T1 = BD1401C1=TLC272IC2 = TLC555

= 7812B1= B400500

Miscellaneous;K1 = PCB terminal block, raster

7.5mm.S1 = push -to -make button.RE1 = relay, 12V, w. make contact

240V/16 A (e.g., Conrad KacoRY-T1L or Siemens V23008 se-ries).

Tr1 = mains transformer, 12V/3VA(e.g., Block VR3112, MonacorVTR3112 or Velleman1120038M).

La1,La2 = neon light w. series resistor.Enclosure: dimensions 150x80x55mm(e.g., Bopla E440).

'good old' 555, is triggered via low-passfilter R8 -C2. The high level at the Qoutput of the 555 then swings high,causing transistor T1 to be switchedoff, and the relay to be de -energized.The 555 now acts as a 'memory', whichretains its state until a short pulse isreceived at pin 6. That happens whenthe 'start' key is pressed. The relay isthen re -energized, and the fuse is`whole' again, re-establishing the cur-rent flow. If, however, the short-circuitor overload condition still exists, therelay will be de -energized again in-stantly. Keeping SI pressed has no ef-fect, since only a pulse resets the 555.In other words, it is necessary to re-lease the key and press it again in anycase. Before you do that, however, in-vestigate and clear the cause of theoverload.

Short transients in the comparatorinput signals are suppressed by C1.

Futhermore, the trigger signal for thebistable is purposely delayed a little toprevent the fuse being actuated on

Fig. 4. Completed prototype of the caravan fuse. Note that the current sense wire is insulatedand folded. Also note the use of heavy-duty grommets and strain reliefs on the mains in andout cable.

every current surge. This is achievedwith the aid of network R8 -C2. Theneon lights (with internal resistors),La 1 and La2, are added to the circuitto be able to check at any time if themains voltage is present at the inputand output of the fuse. If you wish,you may omit these lights, althoughwe found them very useful on the pro-totype.

The power supply is entirely con-ventional, consisting of a mains trans-former, a bridge rectifier, a smoothingcapacitor and a fixed voltage regulator.

ConstructionThe artwork of the printed circuitboard designed for the resettable fuseis given in Fig. 3. Unfortunately thisboard is not available ready-madethrough the Readers Services, so youhave to have it made, or etch it your-self. Populating the board will presentno problems using the componentoverlay and the parts list.

The main attention during the con-struction should go to the sensing re-sistor, R12, the relay, and the way thecurrent -carrying connections aremade. Table 1, apart from indicatingthe diameter and length of the copperwire needed for a particular resistancevalue, also shows the maximum powerdissipation. Clearly, the wire will runquite hot at high load currents. Therelay is not an 'off -the -shelf compo-nent either, as already indicated by thespace reserved for it on the printed cir-cuit board. Most Siemens `E -card' re-lays used in Elektor Electronicsprojects are capable of switching up to8 A. However, the contact rating is re-

duced to 4 A for continuous use. Thatmay be just sufficient for a 'small' fuse,but is certainly inadequate for the pre-sent application, where much highercurrents are required. Hence, a muchlarger relay is used here, the connec-tions of which are formed by clamp orscrew terminals. that brings us to thethird matter of attention: the electricalconnections in the fuse circuit.

At currents of between 10 A and16 A is it no longer possible, or evenallowed (in the interest of safety), to es-tablish electrical connections by sol-dering. PCB terminal blocks are notsuitable either. Normal terminalblocks may be used, although youmust be sure to use 16-A types, notthe smaller (and cheaper) 6-A versions.

By far the best way to connect andwire the circuit is to use car -type 6.3 -mm (0.25 -in.) wide spade terminalsand sockets known as 'AMP' types.These terminals are also used on therelay specified in the parts list. Neveruse an ordinary pair of pliers to clampthe socket on to the cable - it willyield an unreliable and possibly dan-gerous connection. Instead, use spe-cial 'AMP' type crimp pliers, which alsooffer a cable stripper and cutter. Onthe cable sockets, make sure that thehole is properly filled with wire beforecrimping. If necessary, double thewire.

As a matter of course, great atten-tion should be paid to electrical safety,because the present circuit carries themains voltage at several points. Theenclosure must be a sturdy all -plastic(ABS) type. The prototype was housedin a Bopla Type E440 case, which pro-vides a neat fit for the circuit board


96 GENERAL INTEREST

o

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Ref

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0

O 940061

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2.11' o --c2

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O940061 - 13

Fig. 5. Wiring diagram. Be sure to use 'amp' type push -on cable sockets and spade terminalsto make the current -carrying connections.

and the 16-A relay. The mains inputand output cables (220/230/240 V)are three -wire types passed throughgrommets, and fitted with a strain re-lief at the inside of the case.

The internal wiring of the fuse isshown in a separate diagram, Fig. 5.Do not forget to make a through con-nection for the protective earth.

AdjustmentThe circuit should be functional after acareful check on the wiring and theconstruction of the printed circuitboard. The adjustment of Pi is not par-ticularly difficult, although it may in-volve quite a bit of work. A suggestedadjustment procedure is given below.In the example, it is assumed that themains voltage is 240 V.

The preset is set to the centre of itstravel, and the fuse is installed.Pressing the start key should close therelay. Both neon lights should then beon. Next, arrange a load which draws acurrent corresponding to the desiredfuse trip level. In case you require arelatively high trip level, say, 12 A, a 2 -kW electric heater is good to beginwith, since it draws just over 8 A. Add

a paint stripper, an electric iron orsimilar load of about 800 W, and youhave a load drawing a current closeenough to 12 A.

Turn the wiper of P1 until the fuse isjust actuated (counter -clockwise: lesssensitive; clockwise: more sensitive).Be very careful while adjusting thepreset, and do not touch any part ofthe circuit. If the span of Pi is toosmall, switch off, and change thelength of the sensing resistor as re-quired.

While testing you are will probablynotice that the fuse value is a littletemperature dependent. The reason issimple. As the circuit heats up, the re-sistance of the sensing resistor rises,so that the fuse becomes more sensi-tive. Fortunately, that is no cause foralarm, since the effect occurs with nor-mal fuses also.

(940061X)

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and jumpers select the ECONET address Only £29.95the video output. On board DIP switches

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Of,

98

INFRA -RED CONTROLLED SWITCHInfra -red remote control units for TVs and video recordersusually have a large number of press -keys to select astaggering variety of functions. For simple on/off remotecontrol applications, such as opening a door or controlling alamp, these transmitters are far too complex. That is why amuch smaller transmitter and an associated receiver aredescribed here. The system is suitable for switching loads upto 1,000 W using a simple toggle on/off function.

Design by A. Rietjens

,

MOST infra -red remote controlssupplied with today's audio and

video equipment use the so-called RC -5 code. The RC -5 standard is based ona set of codes which are used to con-trol the plethora of functions availableon modern audio and video equip-ment.

The pulse codes generated by re-mote control units are conveyed to thereceivers in the audio/video equip-

ment by infra -red light. The transmit-ter contains an infra -red LED which isswitched on and off at a rate of about36,000 times per second by an oscilla-tor and a switching transistor. In thissetup, the oscillator is actuated bycode pulses.

The 'packets' of infra -red lighttransmitted in this way are received ona diode or transistor which is sensitiveto infra -red light. Next, the signal is

converted back into electrical pulsesby a 36 -kHz receiver and an associateddetector. The pulses are applied to adecoder which is capable of recogniz-ing the transmitted code. Dependingon the received (and recognized) code,one of the functions of the audio/videoequipment (volume, contrast, pro-gram, etc.) is switched.

The encoder contained in the IRtransmitter monitors the keypad onthe remote control, and converts thecode of the key pressed by the userinto a corresponding pulse train.

The IR receiver described belowuses an unmodulated carrier with afrequency of 32 kHz, which is a sim-pler signal than the RC -5 code. Theinfra -red remote control system has a'toggle' type on/off function, whereevery key action produces a short 32 -kHz burst.

A miniature infra -redtransmitterThe circuit diagram, Fig. 1, already in-dicates that the infra -red transmitteris a compact unit.

At the far right in the diagram aretwo series -connected infra -red LEDs,D7 and D8. These LEDs are powered,and start to emit infra -red light, whentransistor T2 conducts.

T2 receives base current and isswitched on when the output ofSchmitt trigger NAND gate IC4d(pin 11) goes logic high. Since its twoinputs, pins 12 and 13, are intercon-nected, the NAND gate functions as aninverting buffer.

As already mentioned, the IR LEDsare switched at the rate of a 32 -kHzcarrier. This carrier is generated by asquare -wave oscillator built aroundIC4,. If pin 9 of IC4, is made high(which happens briefly any time S1 ispressed), the gate starts to oscillate ata frequency determined by network R7 -C9 -P1. The preset, P1, allows the car-rier frequency to be 'tuned' accuratelyto the operating frequency of the inte-grated IR receiver contained in the re-ceiver (IC5, see further on).

Since pressing switch S1 shouldproduce a short infra -red signal ratherthan a continuous one, the 32 -kHzcarrier generator built around IC4, hasa time limiter consisting of R5, R6 andC8. When S1 is not pressed, the inputsof IC4a are low because the charge volt-age on Cg has disappeared via resistorR5. As soon as S1 is pressed, the trans-mitter is powered. After a short while,C8 is charged sufficiently by R6 tocause the start state of IC4a to be


INFRA -RED CONTROLLED SWITCH 99

changed. The voltage at both gate in-puts (pins 1 and 2) is then highenough for the output of IC4a to dropfrom high to low, causing the square -wave oscillator, IC4,, to be switchedoff. For a new pulse to be generated viaS1, you have to wait a short while forC8 to be discharged again via R5.

Since the IR LEDs are switched onand off by short 32 -kHz bursts, theydo not need the usual current -limitingresistor required for continuous (d.c.)operation. Here, the internal resis-tance of the battery helps to keep thepeak LED current within specifica-tions.

IR receiverThe circuit diagram of the receiver as-sociated with the small IR transmitteris shown in Fig. 2. The upper part ofthe diagram shows the power supply,while the receiver proper is drawnbelow.

The power supply consists of trans-former Tri, bridge rectifier Di -D4,smoothing capacitor C3 and voltageregulator IC3. The latter provides thereceiver electronics with a regulated 5-V supply voltage. The relay coil voltageis taken directly from C3, and appearsacross the relay coil when transistor T1is switched on by the receiver electron-ics. T1 then receives base current frompin 9 of IC2b, via resistor R3.

D -type bistable IC2b is wired as a di-vide -by -two scaler. As illustrated bythe timing diagrams in Fig. 3, eachpositive -going edge at the clock inputof IC2b (pin 11) produces a level changeat the outputs (pin 8, inverting input;pin 9, non -inverting input).Consequently, the rectangular signalwhich arrives at the clock input is di-vided by two before it appears at thebistable outputs. The first clock pulseat pin 11 causes output pin 9 to gohigh, while the second clock pulsecauses it to go low again. In this way,the relay is alternately energized andswitched off again, resulting in thepreviously mentioned 'toggle' functionof the remote control system. The ap-paratus connected to the relay con-tacts may be a mains operated device.The connection with the relay contactsis made via terminal block K1.

SelectionThe 'on' and 'off clock pulses which ar-rive at the clock inputs of IC2b (pin 11)emanate from D-bistable IC2a.Together with monostable IC la, thebistable forms a selection circuit whichserves to ensure that only 32 -kHz sig-nals with a certain minimum burstlength cause a clock pulse at pin 11 ofIC2b. Noise and other spurious pulses

I TRANSMITTER

si

I 011

Fig. 1. Circuit diagram of the one -channel on/off infra -red remote control transmitter.

RECEIVER

5VIc

I

T00n

I (2) IC1 = 74HCT123 12

IC2 = 74HCT74 LI ®I I

SFH505A SFH506

O1S1 U60

936066X-11

;i!

Fig. 2. Circuit diagram of the infra -red receiver, and pinouts of the three IR receiver ICs thatare suppressed by the selection circuit may be connected to the input.


100 GENERAL INTEREST

noise or different source rt.rin936066-12

Fig. 3. Timing diagrams of the main signals in the circuit. (1): an IR 'burst' emitted by the re-mote control, switched on and off at a rate of 32 kHz; (2): the same burst, after detection byIC5; (3): monostable pulse produced by IC1a; (4): an on/off switching pulse; (5): a high levelwhich causes relay Re1 to be energized.

0

0

I -

1C5

C1

0

Ut.e.

C3

°11°° 000C5

+ A 0

ill, 01 R1 10

IS °IBR 101

R5 10

clo

©in© %pp R7 pi

0 Ei 0

I it 87

=6+

+ A D

Cr C.,

8 '8

S

Fig. 4. Track layout (direct reading) and component mounting plan of the printed circuitboard for the infra -red controlled switch. This board is available ready-made through ourReaders Services (see page 110).

because they are nearly always shorterthan the on/off pulses transmitted bythe IR remote control.

Figure 3 should help you to under-stand the operation of the selectioncircuit. The upper signal, (1), is the 32 -kHz carrier. Every time S1 is pressed, ashort burst is generated. The receiverIC, IC5, contains a complete detectorwhich turns the infra -red light into anelectrical signal which is subsequentlyrectified.

The output of the IR receiver IC isnormally high, and swings 'low' onlywhen S1 on the transmitter is pressed.This 'low' pulse is drawn in Fig. 3 (2).The positive going edges of the pulseserve to control the previously men-tioned selection circuit, ICia-IC2a.

The positive going edges supplied bythe IR receiver IC are applied to the

COMPONENTS LIST

Resistors:R1 = 1000R2 = 220141R3;R8 = 10k0.R4;R7 = 142R5 = 1M0R6 = 47kilP1 = 5k0 preset H

Capacitors:Cl = 100pF 16VC2;C5;C6;C7,C10 = 100nFC3 = 220pF 16V radialC4 = 330nFC8 = 1pFC9 = 10nF

Semiconductors:D1 = LED 3mm redD2 = 1N4148D3-06 = 1N4001D7;D8 = LD271T1;T2 = BC547B(Cl = 74HCT123IC2 = 74HCT74IC3 = 7805IC4 = 4093IC5 = SFH505A, SFH506-30 (Siemens)or IS1U60 (Sharp)

Miscellaneous:K1;K2 = 2 -way PCB terminal block,

raster 7.5mm.51 = push -to -make presskey.Re1 = 12V card relay, 1 changeover

contact.Bt1 = 9V battery with clip.Tr1 = 9V/100mA, e.g., VTR1109

(Monacor/Monarch).Enclosure: e.g. Bopla type SE432DEPrinted circuit board 936066 (see page110).


INFRA -RED CONTROLLED SWITCH 101

input of monostable IC la as well as tothe clock input of D -type bistable IC2a.Every positive going edge supplied bythe IR receiver IC causes the mono -stable to be triggered. The response isa `low' output pulse at the invertinginput, pin 4. The length of that pulse(number 3 in the timing diagram) isdetermined by R2 and C2.

The selection circuit around ICI andIC2a will only feed an on/off pulse topin 11 of IC21, if IC5 supplies a pulsewhich is longer than the mono -time ofIC la. In that case, the D -input (pin 2)and the reset input (pin 1) are bothlogic high when a clock pulse (positivegoing edge) arrives at the clock input ofIC2a (see also Fig. 3). Consequently,the high level at the D input of IC2a is`copied' to the output of IC2a (pin 9),which goes high. As already discussed,the high level at the output of IC2acauses IC2b and the relay circuit T1 -Re I connected to it to be switched onor off.

In the above example, it was as-sumed that a regular transmitter pulsewas received, i.e., one with a lengthwhich exceeds that of monostable ICia.The response of the circuit to interfer-ence is illustrated to the right in Fig. 3.Noise (signal 2 in the drawing) isshorter than the monotime of IC1a. Theinstant the noise is already passed, aclock pulse has been generated atpin 3 of IC2b, although ICia is stillgoing through its monotime, so thatthe MMV output, pin 4, is still low.This level keeps IC2a in the 'reset'state, preventing short noise pulsesfrom being clocked through on to theoutput. Interference is effectivelyblocked in this way because the indi-vidual pulses are shorter than themonotime of ICI,.

ConstructionThe artwork of the printed circuitboard designed for the infra -red trans-mitter, the receiver and the associatedpower supply is shown in Fig. 4. Theprinted circuit board is availableready-made through the ReadersServices. The three sub -sections(transmitter, receiver and power sup-ply) are separated with the aid of a jig-saw. Cutting is made easy by thedashed lines on the component over-lay.

The construction of the transmitteris unlikely to cause problems. MountIC4 as the last component, and then doa careful check on your solderingwork. To test the transmitter, tem-porarily connect 'ordinary' LEDs, forinstance, red ones, instead of the IRLEDs. The LEDs should light brieflywhen Si is pressed. If this works,mount the IR LEDs, and you can safelyassume that the transmitter is func-

Fig. 5. Prototype of the infra -red transmitter.

tional. As a matter of course, the IRLEDs are fitted in a position that al-lows them to radiate their invisiblelight in one, common, direction.

Although the transmitter may be fit-ted in almost any small, plastic casewith room for the PCB and the battery,the receiver must be housed in an en-closure which is electrically safe. If youwish, the receiver and the power sup-ply may be fitted in separate cases,when a three -wire cable is used to in-terconnect these units.

The construction of the receiver isalong the same general lines as that ofthe transmitter, i.e., the ICs should befitted last. The LED indicator (D1 -R4) isvery useful for testing the receiver.Connect the 5-V supply to the receiver,point the transmitter at the IR re-ceiver, IC5, and press Si repeatedly.LED DI should go on and off. Increase

the distance between the transmitterand the receiver, and adjust P1 untilno further increase can be achieved.

Since the power supply PCB carriesthe mains voltage at several points, itmust be mounted with great attentionpaid to electrical safety. All mains car-rying wires should be properly isolatedusing heat -shrink sleeving. Also besure to use grommets and strain re-liefs on the mains cables that enter thecase.

The power supply section is thesimplest to test: you only have tocheck if the relay operates (clicks), andDI goes on or off, when the transmitkey is pressed. If that works, the loadto be switched may be connected toterminal block K1 for a 'final test'. Themaximum load power that can beswitched is 1,000 W.

(936066)

.0

Fig. 6. Fully populated receiver and power supply boards.

ELEKTOR ELECTRONICS ,JULY/AUGUST 1994

102

PLL-CONTROLLED RAMP GENERATOR

e CD4046 is integratedanphase -locked loop (PLL) with

integral voltage -controlled os-cillator (VCO) that is used inmany digital circuits. In thepresent circuit, the VCO is usedto generate a sawtooth signal.Normally, the VCO producesa triangular signal that is com-pared with an external digitalsignal. The VCO in the standard4046 can be used for digitalsignals up to 1 MHz; in the HC

1

or HCT version it is usable upto 38 MHz.

In the present circuit, theVCO generates a triangular sig-nal whose rise time is 1000times longer than its decay time:actually, a sawtooth signal.

Figure 1 shows a section ofthe internal structure of the4046, while the complete cir-cuit of the generator is given inFig. 2. The single capacitornormally connected between

944019-11

pins 6 and 7 of the chip is re-placed by two capacitors, C1and C2, whose values have a ratioof 1000:1. Capacitor C2 is dis-charged rapidly through T1,which is switched on and off bythe signal from the VCO. Thecapacitor is charged by a FETin the 4046 that functions asa current source.

The frequency at which Ti isswitched is, of course, also thefrequency of the sawtooth sig-

2

nal. It can be set with P1, withvalues as shown, between 20 kHzand 200 kHz.

Since the output is connecteddirectly to the timing section ofthe circuit, a buffer stage, con-sisting of a simple FET or op-erational amplifier, may provedesirable.

The circuit draws a currentof about 3 mA.

Design: M.S. Nagaraj[944019]

POINTS CONTROL FOR MODEL RAILWAY

Electric points of a modelrailway system contain two

small magnets. To set the pointsin a given position, one of thesemagnets must be energizedbriefly (say, 0.5 s). Any elec-tronic control must, therefore,translate a a change in logiclevel into a short pulse.

In the present circuit, thedigital input signal is appliedto XOR gates IC a (pin 1) andICib (which functions as an in-verter) and to AND gate IC2a. Theinput signal is also applied tothe other input of IC la (pin 2)via a delay network, R1 -C1. Aslong as the input signal is con-stant (whether 1 or 0), the levelsat the inputs of ICI, are equaland the output, pin 3, is low.The AND gates, IC2a and IC2b,have at least one low level at their

IC1 IC213TOOn TOOn

IC1 b4 IC2b

5 F716 65

inputs, so that their outputs arealso low and the transistors,T1 and T2, are off.

When the level of the inputsignal changes, the output ofIC la is high during the time C1

is being charged. If the input levelchanges to 1, the output ofIC2a becomes high; if it changesto 0, the output of IC2b goeshigh (because the input is in-verted by IC lb).

Depending on which ANDgate has a high output, relayRe1 or Reg is energized by T1or T2 respectively. The dar-lington transistor can switchup to 1 A, which for mostpoints is more than ade-quate.

It is important that HCtypes are used for IC1 andIC2, because these ensurethat the switch -over point isclose to half the supply volt-age. If standard types areused, T1 will conduct formuch longer than T2.

The supply voltage for thepoints relays should beabout 15 V.

Design: M. Averkvist[944023]

ELEKTOR ELECTRONICS JULY/AUGST 1994

REAR WIPER INTERVAL SWITCH

103

Many cars have a rearwiper that is controlled

by a switch with a make -break combination. In mod-ern cars, the wiper is oper-ated simply by pressing apush-button (with a makecontact). In such a case,there is an electronic circuitbetween the switch andwiper motor, to which an in-terval circuit can be added.The present circuit allowsthe time interval to be set be-tween 2 s and 22 s with apotmeter. Operation of thewiper remains via the push-button. If this button ispressed briefly, the wipertravels once and then stops;if the button is held down formore than 2s, the intervalcircuit comes into operation.Pressing the button brieflyagain switches off the inter-val circuit. The advantage ofthe design is that the exist-ing push button is used: itneeds no additional switchesas many other designs do.

In the diagram of Fig. 1,SI is the existing push-but-ton. When this is pressed,T1, which functions as an in-verter, is on. The level atpin 1 of ICia is then pulledlow via debounce networkR4 -C1 -D1 -D2, whereuponmonostable multivibrator(MMV) IC ia-IC ib is started.Its mono time is determinedby R5 -C2, which here isabout 2 s.

At the same time that theMMV is started, D -typebistable IC2a is set via C3,whereupon pin 2 goes low.This results in the output ofICI, going high: the relay isthen energized via IC id andT2 for as long as S1 ispressed.

After the mono time haselapsed, the output of IC lbgoes high again and thebistable receives a clockpulse. At that instant, thestatus of SI is read in via theD -input of ICia. If S1 waspressed briefly, a logic iswritten and pin 2 remainslow. This means that therelay can not be energized,so that the wiper makes onlysweep.

If S1 was depressed whenthe bistable was clocked,

1

S1

IC1 = 4093IC2 = 4013

BC547B

C

01 2V

D1

104148

IC1a

2

pin 2 goes high and astablemultivibrator (AMV) ICi, isenabled. The relay is ener-gized briefly after every fewseconds, depending on theposition of P1, so that thewiper sweeps again andagain. That situation per-sists until SI is pressedagain. The bistable is thenreset and ICi, ceases con-ducting.

Network R6 -C4 provides apower -on reset

The power supply has sev-eral provisions for keepinginterference on the car'selectrical system from thepresent circuit. Inductor L1blocks high -frequency inter-ference pulses, while zenerdiode D6 ensures that thelevel of signals filtered out byL1 does not rise above 27 V.

Figure 2 shows how thecircuit is connected in thecar (here a Renault Espace).The connection betweenpush-button switch and

12V

C2 IC1b3 5

R10

0 I

C9 C0 0 C7 C6

100n

IC2100n

IC1To10 10u

25V 27V

mim100n

14

R

./T>C

IC2a

wiper motor is broken,whereupon the two resultingwires are soldered to pointsA and B.

If one of the terminals ofthe push-button switch isconnected to ground, it func-tions as S2 in the circuit: R1,R2 and T1 can then be omit -

D5

104004

L1

im 12V O+

N4148

IC1d2 R9 (4

NH

04 Re1

1=1=104148 ?

BC547B

944095-11

JI

O

pole contact of Refis then connected to ground,while the switching contactis linked to the wiper motor.

The only item that has tobe fitted on or near the dash-board is the knob of P1.

Design: J. Seyler19440951

ted. The


104

SMALL LOOP ANTENNAS FOR MWAM BCB, LF AND VLF RECEPTION

PART 2 (FINAL): PRACTICAL CONSTRUCTION

Last month we examined the basic theory of loop antennas,and demonstrated some of the basic forms of loop antenna,resonating methods and coupling methods. In this second andfinal installment we will take a look at the actual constructionof practical loop antennas, some representative looppreamplifier circuits, and a couple of interesting, if odd,applications of loop antennas.

By Joseph J. Carr, B.Sc., M.S.E.E.

Loop construction

Discussing antennas is all well and good,and indeed somewhat intellectually sat-isfying, but, as they say, 'the devil is inthe details'. Unless the loop antenna is toremain a theoretical construct you readabout in this magazine, it must be some-how rendered into practical form. Andthat is where the going can get a mightsticky.

Hoop loopsPerhaps the stickiest form of loop tomake is the low frequency circular loop.At higher frequencies, a single length ofRG52/U coaxial cable can be formed intoa satisfactory single -turn loop antenna.Indeed, the amateur radio literature con-tains numerous examples of 14 through54 MHz amateur band portable 'foxhunting' RDF loop antennas made fromcoaxial cable. At lower frequencies, how-ever, the problem becomes a bit more dif-ficult, although not impossible as youwill soon see.

A solution that I found is shown inFig. 13a and Fig. 13b. A schematic ofthe hoop loop is shown in Fig. 13a, whilethe actual antenna that I built is shownin Fig. 13b sitting at my ham radio sta-tion. A black plastic box contains a pre-amplifier and resonating capacitor (boxshould have been metal, by the way).

The core of this loop construction ideacame to me while visiting a crafts storefrequented by my wife: it is an embroi-dery hoop. These products are two-piececircular wooden or plastic hoops sizedsuch that one fits inside the other. The

larger outer hoop is broken at one point,and fitted there with a thumbscrew as-sembly for tightening the outer loopagainst the inner loop in order to holdfast the fabric the embroiderist is work-ing on.

The first version that I built usedmulti -conductor ribbon cable with eachwire cross -connected to its adjacent mate(more later). In Fig. 13b you can see theouter edge of the ribbon cable protrudingbeyond the width of the wooden hoop.

Picture frame loopAnother approach is the planar woundloop of Fig. 14. This loop antenna wasbuilt with supplies from the same craftsstore, but this time wooden picture framematerial was used. The frame material isintended for do-it-yourself framers, andcomes in 2 -foot and 3 -foot lengths. Eachlength is cut with tongue and groove, andslanted 45 degrees at each end, so thatthey joined to form either a longerstraight section or a right angle joint. Iused four 2 -foot sections to form thesquare loop shown in Fig. 14.

The winding of the loop antenna inFig. 14 is ribbon cable, as before, but inthis case it is thumb tacked to thewooden frame. Care must be taken topush the thumb tacks through the ribboncable between conductors in to not harmthem. I could discern no effect on the per-formance of the loop antenna from thethumbtacks passing through the cable.Note that the cable is folded over on itselfat each corner in order to make the turn.This also had little or no noticeable effecton the performance, although I should

PII

Fig. 13. Embroidery hoop loop antenna: (a)schematic; (b) photo.

imagine that performance deteriorates atleast somewhat.

Ribbon cable windingsThe previous two antennas, and one to beshown shortly, use computer ribboncable as the antenna windings. The ideais to cross -connect wires in order to form


SMALL LOOP ANTENNAS FOR MW BCB, LF AND VLF RECPTION - 2 105

rftf4A,akros.

Fig. 14. Picture frame loop antenna.

Fig. 15. Cross -connection of ribbon cableconductors to form a continuous loop.

a continuous loop. In the 50 -conductorversion shown in Fig. 15, the connec-tions to the loop at wires 1 and 50. At thebeginning of the loop, the other end ofwire no. 1 is soldered to wire no. 2, theother end of no. 2 to no. 3 and so on untilone end of no. 49 is soldered to one end ofno. 50, ... with the remaining free end ofno. 50 becoming the connection for theloop.

For small loops (under 1 metresquared), which use only a few turns, one

might want to purchase the pre-cut typeof ribbon cable that has a single -row in -line connector on each end (female on oneend and male on the other). The connec-tors can be wrapped around the loopframe and then fastened together one pinoff (see inset to Fig. 15). The loop end at`A' is a normal pin from the male connec-tor, while that at 'B' is a loose pin or wireinserted into the opposite end of the fe-male connector.

Cross loop

Figure 16 shows several aspects of thetraditional cross loop. I made several ofthese loops from spruce wood purchasedfrom hobby shops that cater to modelbuilders. The spruce is typically sold inthe same display as balsa wood stock.The stock that I purchased from anAmerican source was 24 inches (60 cm)by 3 inches (7.6 cm), and was 3/16 inch(4.8 mm) thick. Two lengths wereneeded. Each length was notched at themiddle (`c') half the width, so that the

two pieces could be fit together to form across as seen in Fig. 16b. At the ends ofthe wood pieces small slits, the width of ajeweller's or jigsaw blade, were cut to adepth of 6 mm. These slits hold the #26(0.45 -mm dia.) enamelled wire that formthe main loop. Holes 0.042 -inch (1 -mm)in diameter are drilled 12 mm from eachend, in the centre of the piece. Theseholes are for the single turn of the cou-pling loop.

Figure 16b shows the basic assem-bled structure of the cross loop. At thejunction of the two pieces a set of four 1 -cm square stiffeners are glued into place.For better strength, a small screw pass-ing through stiffeners on opposite sidesof the same wooden member might be inorder.

Figure 16c shows the finished loopwith the wires strung. The support forthe loop (besides the dead pine tree be-side my house) is a 2.5 -cm wooden dowelabout 1.5 metres in length. This antennaproved quite useful on 75/80 metre ham

a

T

notch

smell hole forcoupling loop

C

b

3,

slits for wireof mein loop

\

b

d

rnoln loop

A : end gusset plates8 centre gusset piste(coupling loop not shown)

.4002sN-14d

Fig. 16. Cross loop antenna: (a) form of each element; (b) assembly; (c) photo; (d) improvedform.


106 RADIO AND TELEVISION

bands, and could be used for fox huntingapplications.

Subsequent use of this antennaproved the design to be mechanicallyweaker than I prefer. In order to over-come this defect, I added the corner gus-sets and a centre plate gusset, as shownin Fig. 16d. The gussets were cut with45 -degree angles from the same type ofstock as formed the cross pieces.Additional 1 -cm pieces can be placed be-hind the corner gussets to improve sta-bility, if necessary.

Large box loopAt VLF frequencies a large box loop issometimes in order. Loops with dimen-sions of 1.5 to 3 metres squared are foundin the literature. Large square loops aresomewhat more difficult to build becausemechanical stability becomes a largerissue, especially when the loop is in-stalled outdoors. When wind is a factor,the 'sail area' of the loop becomes a seri-ous issue. In this section we will take alook at a large box loop made with sub-stantial materials (Fig. 17).

The basic design of the loop is asquare frame stabilized by corner gus-sets, as shown in Fig. 17. The sectionedview is shown in the inset. The sides ofthe elements (`A') are made from cornermoulding of the sort sold to homeownersat do-it-yourself lumber stores. Use0.625 -inch (1.6 -cm) to 1 -inch (2.54 -cm)stock. The stock is glued and screwed tothe backplate (`B'), forming a U-shapedchannel. The backplate can be anythingfrom 0.25 (6 mm) to 0.625 inch (1.6 cm)thick, and as wide as needed to accommo-date the moulding and the wires (`D').The wire is laid into the channel, and canbe either wound enamelled wire or rib-bon cable. In the case of the ribbon cable,for VLF operation, two or more layers ofribbon cable can be wound over top one

C

wood channel

A : right-anglewood mouldingB : wood panelC : copper foilD : ribbon cable

gusset plate

metal tuning box

940028A-15

Fig. 17. Form of large loop antenna.

Fig. 18. Low capacitance winding separatesgroups of conductors.

another (although this approach can se-riously increase stray capacitance).

If the loop antenna is to be shielded (agood idea), then line the U-shaped chan-nel with copper foil (`C') prior to in-stalling the wire. Once the wire (13') isinstalled, inspected and tested, then thefree foil ends can be folded over on itselfand soldered together, completing theshield. Keep in mind to leave a 1-2 cmgap in the foil shield opposite the feed -point of the loop.

Once the loop is completed, cement acover (`E') over the U -channel. This covercan be of the same stock as the backplate(`B'), although thinner stock would alsosuffice. The cover plate can be slotted atthe feedpoint in order to bring the cableinto the tuning box, where all connec-tions are made and both the tuning ca-pacitor and preamplifier (if either areused) are located.

Reducing stray capacitanceAll coils have a certain amount of un-wanted capacitance along with the nor-mal inductance. This stray capacitancemakes the coil self -resonant at some fre-quency that is hopefully far higher thanthe normal operating frequencies. Loopantennas are no exception, and can ex-hibit rather large stray capacitance num-bers.

The stray capacitance does not nor-mally bother loop constructors, and in-deed may help. For example, when thevariable tuning capacitor (400 pF or so)is insufficient to resonate the loop atsome desired frequency. The stray capac-itance of the loop may well permit use ofsmaller add-on capacitors to achieve res-onance. But at other times, such as whenthe self -resonant point is forced too low,

centre conductor oflast turn connectedto shield of first turn

Trl80/100011 audio transformer

940028-11-17

Fig. 19. Coaxial cable 100 kHz loop: (a)schematic. Note that the centre conductor ofthe far end is connected to the shield at thefeedpoint; (b) close up.

the stray capacitance has a bad effect onoperation of the loop.

Conversations with some radiosolarobservers (Taylor and Stokes 1992),while researching another article,showed me that stray capacitance was abig problem for them ... and one whichthey had overcome. A typical 20 to 30 -kHz VLF loop used by radiosolar ob-servers to detect sudden ionosphericdisturbances (SIDs) are square, 1 to2 metres on a side, and wound with 100to 150 turns of wire. They use anarrangement similar to Fig. 18 to reducethe stray capacitance effect. Whether rib-bon cable or free winding is used, the



windings are separated into groups of 20to 50 turns, and each group is spacedabout 2 cm from the adjacent groups. Allof the groups are connected in series witheach other in order to form a single con-tinuous loop antenna.

Coaxial cable 100 KHz loopA reader wrote to me and provided thedesign of Fig. 19 (Ingram 1993). Theoriginal antenna was designed to receiveLORAN -C navigation signals in thevicinity of 100 kHz. The antenna elementconsists of 16 turns of RG-59/U 75-acoaxial cable (in Fig. 19a only one turn isshown), on an average diameter of 2 me-tres, connected such that the centre con-ductor of the last turn is soldered to theouter shield of the first turn at the feed -point. The introductory photograph withPart 1 and the drawing in Fig. 19b showthe mechanical structure of this antenna.Coupling is provided through an8:1000 Q audio transformer. Although abit large, the coaxial cable antennashould provide very good, low -noise re-ception because of the Faraday shieldmanner of the construction. The designerclaimed that a 500 -kW 100 -kHz stationat a distance of nearly 500 km produceda signal of 1,000 pV into the 50-Q inputof the receiver.

Coupled ferri-loopA loop antenna that is a modification ofone of Marris' designs (Marris 1992) isshown in Fig. 20. The circuit is shown inFig. 20a and the actual antenna is inFig.20b. This antenna is made by embed-ding 7.5 -inch (19 -cm) ferrite rods in 10 -inch (25.4 -cm) lengths of PVC plumbingpipe. Each ferrite rod is wrapped withelectrical or masking tape to support itwhen it is force -fit (`gently') into the pipe.I found that a 1 -cm diameter rod, wheninserted into a 2.5 -cm o.d. pipe, requiredabout 14 turns of 3-M brand black elec-trical tape to hold it firm when pressedinto the pipe.

The windings consist of whatevernumber of turns are required for opera-tion at the desired frequency. In an an-tenna meant to work in the 2 to 5 -MHzregion, including 75/80 -metres perMarris' design, I used ten turns of wire,and the ferrite rods were the p=800 type.Lower frequencies would require highernumber of turns, and possibly thep=1,200 or p=2,000 ferrite rods.

Three of the four sides of the ferri-loopare identical to each other, and are simi-lar to Marris' design. The sides are heldtogether with cemented 90 -degree PVCpipe elbows. The fourth side, however,differs from the other three. It is fittedwith a tee -connector. The winding on thisside is split into two halves of five turnseach. Like the other windings, these areexterior to the PVC pipe. The couplingwinding (L5) consists of 5 turns of wirewound directly on the ferrite rod thatforms Li, and Lis. The connections to L5

Fig. 20. Ferriform antenna: (a) schematic; (b)photo.

are connected to very thin shielded wireor coaxial cable, and routed to the re-ceiver or preamplifier.

Loop preamplifier circuitsThe signal levels obtained by loops isquite low, even when the loop is tuned tothe received frequency. As a result, it iscommon practice to boost loop outputusing a preamplifier stage. Although al-most any preamplifier will suffice, if itcover the desired frequency range, thereare several designs which seem mostpopular, and these will be discussedbelow.

Whichever amplifier is selected, itmust be capable of amplifying the rangeof frequencies covered by the loop. Theamplifier that might be right for the VLFamplifier may or may not also be suitablefor operation in the LF or MW portion ofthe spectrum. Several devices presentthemselves quite well in this respect,however. For example, the Mini -Circuits MAR -x series of MMIC chipsmay be designed for VHF through low -microwave applications, but they alsowork well at VLF through HF as well.Similarly, some specialist integrated cir-cuits houses, such as Burr -Brown, offeroperational amplifiers and operationaltransconductance amplifiers with gain -bandwidth products of 150, 200, 350 and500 MHz. These amplifiers can easily beused at VLF through MW frequencies.Another Burr -Brown product is the35 MHz VCA-610 voltage controlled am-plifier. This device features a high im-pedance input, a low impedance output,and is voltage controllable over a rangeof ±40 gain for a control voltage range of±2 V. The VCA-610 was designed for ul-trasonic medical imaging applications atfrequencies similar to those used by VLFthrough MW radio stations.

As appealing as the above approachesmight be, however, except for the MAR -xchips these solutions are also a bit expen-sive for hobbyist applications. So let usnow turn our attention to some circuitsusing easy -to -obtain components that arelow in cost.

Figure 21 shows the circuit of a loopantenna preamplifier that can be built

Fig. 21. Single -ended loop preamplifier.


108 RADIO AND TELEVISION

with ordinary hobbyist grade compo-nents, yet functions at frequencies up to70 kHz or so. This circuit uses an ordi-nary garden variety NPN silicon transis-tor for amplification. I have used2N2222, 2N3904 and 2N4401 (latter pre-ferred) for this application, all success-fully. The biasing is the ordinaryresistance voltage divider (R1 -R2) withemitter stabilization (R3).

The capacitor across resistor R, is setto have a reactance at the lowest operat-ing frequency of <0.1R3, or 47 Q The ideabehind setting the value of C2 is to keepthe a.c. path to ground as low a reactanceas possible, while maintaining the d.c.level caused by the current flow in R3. Inpractice, this goal is very easy to achieve.At 10 kHz, for example, a 1-pF capacitorhas a reactance less than 16 Q, so fallswell within the R/10 rule of thumb.Using a 2.2 pF or 3.3 pF comes closer to amore ideal R/100 rule.

For VLF receivers in the <100 -kHzrange, almost any electrolytic capacitorwill suffice for C2, although tantalumsare preferred. At higher frequencies,however, other forms of capacitor are inorder. The Panasonic V -series capaci-tors are available in values up to 1 pF,but are not electrolytics (and thus are notpolarity sensitive). These capacitorsmake a better choice for higher frequencyunits. Also, some builders actually paral-lel a 1 pF tantalum with a 0.1 pF disk ce-ramic for wider frequency coverage. Forthe <70 kHz bandwidth of this circuit,however, a single 1 pF tantalum capaci-tor seems sufficient.

Some people who are located close toAM BCB stations, or other large signalsources, may wish to control the gain ofthe front-end by deleting C2 altogether.`Whistler' hunters, i.e., those who seek toreceive natural radio signals (Mideke1992), often leave the emitter resistor ofthe first stage unbypassed for exactlythis reason. It cuts the gain, but is alsocuts the level of the interfering signal.

Transformers Tr, and Tr2 are ordi-nary transistor radio audio transformers.In the circuit shown here, Trl is an audiooutput transformer used in reverse; i.e.,the 8-Q winding is connected to the loopand the 1,000-a winding is connected tothe input of the amplifier. In some loopantennas, a 1000:1000 Q transformer isused to couple the loop to the receiver orpreamplifier, and can be used in place of

Both Tr, and Tr2 can be ordinary tran-sistor radio grade transformers for workup to 70 kHz or so. At frequencies to150 kHz, however, these transformersmust be replaced by high grade commer-cial audio transformers that are guaran-teed to be ±1 dB to that frequency.Several such transformers are seen incommercial electronics parts catalogs.

Two output circuit configurations arepopular for this preamplifier. One is thetransformer coupled version shown in

the main circuit, while the other is theresistor -capacitor coupled version shownin the inset. The RC coupled version re-places the transformer with a 10-M2 re-sistor, and couples the signal to the nextstage (or receiver) through a 1-qF capaci-tor (C4).

Cascode preamplifierA cascode two -stage amplifier is shownin Fig. 22. This circuit uses a junctionfield effect transistor (Ti) at the input,and an NPN silicon transistor for theoutput stage. Common devices such asMPF102 for Ti and 2N4401 for T2 aresufficient. Transistors T1 and T2 are di-rect -coupled, with d.c. bias applied to T2through R2 -R3.

Fig. 22. Cascode loop preamplifier.

The input circuit in this example istuned to a specific frequency, although insome cases a transformer arrangementsuch as shown earlier in Fig. 9 might alsobe used. The inductance needed to tunethe loop may be a little hard to come byat the lowest frequencies, in which casetwo or more coils can be connected in se-ries. In some cases, a xenon tube triggertransformer, such as Maplin JE15R,provides a part of the inductance (6 pH),and the rest can be made up with coils inthe 10 to 100 pH range. The transformerprovides the coupling loop needed to iso-late the amplifier from the loop.

Alternatively, the loop itself can beused as the inductor for this circuit. Suchan arrangement is not at all uncommon,and works out well, especially when theloop antenna is not located at a remotesite from the amplifier (co -location is theusual, and best, practice).

Another alternative is to provide ahigh impedance antenna input to thepreamplifier. If you plan to use a whip,random length wire, or other non -loopantenna, then connecting the antenna tothe top of the resonant LC tank circuit

through a small value disk ceramic ormica capacitor will achieve your purpose.

Push-pull and differential preampli-fiersA lot of loop antenna builders prefer touse push-pull or differential amplifiersfor the loop preamplifier job. Any num-ber of possibilities present themselves.For example, an operational amplifier inthe differential configuration can beused, if it has a sufficient gain -band-width product. Devices such as the CA -3140 (and related chips) or the SigneticsNE5534 device, are easily available andwill work well into the VLF region. Also,devices such as the CA3028, which ispopular in amateur radio circles, is alsouseful for this purpose.

Figure 23 shows a circuit based oncommon JFET transistors. Each transis-tor operates in the common source con-figuration, with the inputs tied to theloop outputs and loop shield. The JFEToutputs are combined in a trifilar woundthree -winding transformer (Tr,). TheMini -Circuits RF transformers can beused in this application, although at VLFthey have a substantial loss (-3 dB or so).One can also wind a variant of Tr1 usingeither toroidal or bazooka forms made oflow frequency ferrites. The number ofturns will depend on the frequency used,and some experimentation is needed. Ifound that 50 trifilar turns of #30(0.31 mm dia.) enamelled wire over anFT -68-72 form worked well at 60 kHz ina WWVB receiver, but I have not checkedit at frequencies lower than 60 kHz.

Special loop applicationsThe loop antenna is sufficiently differentfrom other antennas to suggest some in -

Fig. 23. Push-pull loop preamplifier.



teresting applications. The normal looppattern is a figure -8 with very deep nullsbeing present at the broadside aspect tothe antenna. The use in nulling interfer-ing signals and in radio direction findingwere described earlier. In this section wewill describe two additional applications:the sports fan's loop and the monodirec-tional loop.

Sports fan's loopThis application uses a special form ofloop antenna to boost the performance ofAM BCB portable radios. It apparentlyoriginated when sports fans wanted tolisten to ball games on distant AM sta-tions that were normally out of the rangeof their portable receivers. The loop an-tenna is a square box loop, typically 60 to150 cm on each side. A 100 -cm squareloop, with 8 turns of wire spaced to oc-cupy 2.5 cm, produces an inductance ofabout 330 pH, which can be resonated to550 kHz with 240 pF. No preamplifier isneeded, although the resonating capaci-tor should be placed inside of a shieldedmetal box.

Fig. 24. Sports fans' loop.

The radio in the sports fan's loop isplaced such that its internal loop stickreceives in the same direction as thesquare loop (see Fig. 24). While a squareloop has its nulls perpendicular (orbroadside) to the loop, the loopstick hasits nulls off the ends. Signals picked upby the larger loop are coupled into theloopstick antenna, providing a strongersignal for the radio to receive than is nor-mally available with the loopstick alone.

At first, the version that I built (whileresearching my book Joe Carr'sReceiving Antenna Handbook) did notwork, so I wondered at the stories I hadbeen told. However, the problem wassoon found out: I had failed to knowwhere the loopstick was inside the radio.I had assumed it was along the top of theradio, and ran from left -to -right relativeto the front panel. However, it was actu-ally mounted vertically along the rightside of the radio near the tuning capaci-tor. Replacing the radio with one that

Fig. 25. (a) Monodirectional tardioid'pattern, (b) omni/monodirectionalcombination circuit.

had the loopstick antenna as shown inFig. 24 solved the problem.

Monodirectional receptionThe normal loop pattern is bidirectional,figure -8, with deep nulls broadside to theloop. This pattern permits the antenna tonull out, i.e. attenuate, any signal in thedirection that the nulls point.Unfortunately, the bidirectionalitycauses two problems. In radio directionfinding there is a directional ambiguitybecause RDF is typically done by point-ing the null at the station until minimumsignal level is achieved. The line perpen-dicular to the loop face contains the loca-tion of the station, but the station couldbe either in front of or behind the loop. Insome cases, RDFers will take the direc-tional measurement from three loca-tions, and note where the three linescross, which is the location of the stationto a good precision. But in other cases,multiple location measurements are notfeasible. In those applications, a monodi-rectional loop with but one null isneeded.

Another problem caused by the loop isseen not in RDF, but when the loop useris at a fixed location that is on or near a

line that runs between two stations. Ifyou desire to listen to one of the stations,and the other is strong enough to causeinterference, then nulling one with theloop also nulls the other. Assuming thatthe ratio of the signal levels is not suchthat nulling both places one below somecomfortable threshold (a situation that Ihave never seen), one needs a monodirec-tional loop that has but one null.

There are two approaches to solvingthis problem. The classic approach isshown in Fig. 25. In this situation, theloop is paired with a small whip antennaused as a sense element, resulting in thecardioid pattern of Fig. 25a. The signalfrom the omnidirectional loop antenna iscombined with the signal from the bidi-rectional loop antenna, in a network, asshown in Fig. 25b.

In use, the null is pointed at the of-fending station, while the maxima ispointed at the desired station.

The other approach is to use a spoilerloop in the manner of Fig. 26 (Levintown.d.). Here we have the undesirable situ-ation of a pair of stations on the same oradjacent channels located such that thereceiving site is on the line between thetwo stations. Two antennas are needed:the small ferrite loopstick and a 60 to150 cm resonant box loop. The ferrite an-tenna can be a special antenna coupledto the receiver, e.g., when a receiverwithout an internal antenna is used, or itcan be the normal loopstick inside of aportable receiver. The loopstick is placedsuch that it is broadside to the desiredstation. The box loop is placed 30 to150 cm away from the loopstick, and inthe direction of the offending station; theexact distance must be found experimen-tally for each situation. When the boxloop is rotated through an angle of about30 to 90 degrees with respect to the linebetween radio stations, a point will befound at which the offending station isnulled.

(940028-2)

Fig. 26. Use of a secondary loop to nullinterference.


110 'The publishers reserve the right to change prices without prior notification. Prices shown in this issue supersede those in previous issues. E. & O.E.

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'COMPONENTS

Components for projects appearing in Elektor Elec-tronics are usually available from appropriate advertis-ers in this magazine. If difficulties in the supply ofcomponents are envisaged, a source will normally beadvised in the article. It should be noted that thesource(s) given is (are) not exclusive - other suppli-ers may also be able to help.

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SHELFElektor Electronics shelf box

BOX

$6.00£2.95

FRONT PANEL FOILSPROJECT No. Price Price

(£) (US$)

4MB printer buffer card 920009-F 8.25 16.50LC meter 920012-F 11.45 22.90Guitar tuner 920033-F 8.80 17.60NICAM decoder 920035-F 8.25 16.5012VDC to 240VACinverter 920038-F 16.15 32.30

Audio DAC 920063-F 10.00 20.00Dig. audio/visual system 920022-F1 10.00 20.00

920022-F2 19.40 38.80920022-F3 28.80 57.60

1.2 GHz multifunctionfrequency meter 920095-F 13.80 27.60U2400B NiCd batterycharger 920098-F 8.75 17.50Workbench PSU 930033-F 17.00 34.00Inexpensive phase meter 930046-F 17.25 34.50Mini preamplifier 930106-F Not availableAF rms voltmeter 930108-F 17.25 34.50

PROJECT No. Price Price(£) (US$)

EPROMS / PALS / MICROCONTROLLERS

EMON51 (8051 assemblercourse) (1 x 27256+disk 1661) 6061 20.00 40.00EMON51 (8051 assemblercourse) (1 x 27256+disk 1681) 6091 20.00 40.00FM tuner (1 x 27C256) 6101 15.30 30.60Multi -purpose Z80 card:GAL set (2 x GAL 16V8) 6111 11.15 22.30Multi -purpose Z80 card:BIOS (1 x EPROM 27128) 6121 15.30 30.601.2 GHz multifunctionfrequency meter(1 x 27C256) 6141 11.45 22.90Digital audio/visual system(1 x 27C256) 6171 10.30 20.60TV test pattern generator(1 x 27256) 6151 13.00 26.00DiAV system. Package:1 x 27512; 2 x GAL; 1 xfloppy disk (MSDOS) 6181 30.50 61.00PAL test pattern generator(1 x GAL 20V8-25) 6211 9.40 18.60800535 assembler course(1 x EMON52 EPROM and1 x disk 1811) 6221 17.05 34.10Watt-hour meter (1 x 27256) 6241 10.00 20.00Four fold DAC (1 x GAL) 6251 10.75 21.50Multipurpose display decoder(1 x 2764) 6261 11.50 23.00Telephone -controlled switch(1 x 2764) 6271 14.50 29.00Relative humidity meter(1 x 2764) 6301 14.50 29.00535 card w. EPROM emulator(1 x PAL; 1 x GAL) 6311 26.00 52.00Copybit eliminator (1 x GAL16V8 and 1 x MACH110) 6321 42.25 84.50RDS decoder (1 x 27C64) 6331 14.50 29.00I2C tester (1 x GAL 6001) 6341 30.75 61.50Mains signalling system(1 x 27C64) 6371 13.25 26.508751 programmer (1 x 8751) 7061 46.40 92.80Microcontroller NiCd charger(1 x ST62E15) 7071 10.00 20.00Maxi micro clock (clock) 7081 11.50 23.00Maxi micro clock (darkroom timer) 7091 11.50 23.00Maxi micro clock (cooking timer) 7101 11.50 23.00Mini micro clock (clock) 7111 11 50 23.00Mini micro clock (darkroom timer) 7121 11.50 23.00Mini micro clock (cooking timer) 7131 11 50 23.00VHF/UHF TV tuner(1 x 87C51) 7141 25.75 51.50Microntroller-driven UART(1 x ST62T10) 7151 17.25 34.50PIC programmer(1 x PIC17C42 and 1 x disk) 7161 52.75 105.50MIDI swell pedal (1x27C64) 946635 13.75 27.50

DISKETTES

8051/8032 Assembler course(IBM version) 1661 7.65 15.308051/8032 Assemblercourse (Atari version) (3.5") 1681 7.65 15.30AD232 converter 1691 7.65 15.30GAL programmer (3 disks;upgrade: June 1993) 1701 11.15 22.30Multi -purpose Z80 card 1711 7.65 15.30Fuzzy Control One 1721 7.75 15.50Pascal library for MMC 1751 9.70 19.40Speech/sound memory 1771 7.65 15.30PC -aided transistor tester 1781 7.50 15.00IR receiver and DTMF decoderfor 80C32 SBC 1791 9.00 18.00800535 assembler course 1811 8.80 17.6012C opto/relay card 1821 7.65 15.30Video digitizer for PCs 1831 14.50 29.00GAL programmer for Amiga 1841 11.00 22.0012C alphanumerical display 1851 8.50 17.00Philips preamplifier 1861 8.50 17.00GAL programmer (excl. OpalJr. disks) 1881 10.75 21.50Precision clock for PCs 1871 8.50 17.00X2404 -to -8751 interfacing 1891 8.50 17.00RC5 software emulation 1901 10.75 21.50Mains signalling system 1911 9.75 19.50SIM - an 8051 simulator 1931 34.25 68.50800535 SBC extension 1941 9.75 19.50

PROJECT No. Price Price(£) (US$)

800535 SBC 12C display 946197-1 9.75 19.50Small loop antennas 1951 10.75 21.50RC5 transmitter w. 800535946199-1 9.75 19.90

PRINTED CIRCUIT BOARDS

Printed circuit boards whose number is followed by a+ sign are only available in combination with the as-sociated software item, and can not be supplied sepa-rately. The indicated price includes the software.

FEBRUARY 1994800535 single -boardcomputerCopybit eliminatorincl. MACH and GAL 930098+ 46.25 92.50

Mini preamplifier 930106 29.25 58.50Bidirectional RS232 -to -Centronics converter 930134 14.00 28.0024 cm FM ATV transmitter PCB available from author

MARCH 1994PIC programmerincl. software set 7161

100W AF amplifier- adaptor board 930039- amplifier board 920135-1- protection board 920135-2

Mini I/O card for CasioFX850/880P 930090AF signal tracer 940006Electronic fuse 936071

924046 14.10 28.20

APRIL 1994Mains signalling system - 1

(receiver) 940021-168HC11 processor boardRS232 speedometerStroboscope lightHeadphones amplifierHalogen light dimmerRS232 interface foruniversal bus

930123930119940022940016940034

940048+ 66.00 132.00

8.25 16.5019.40 38.80

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924048 Not available

MAY 1994Diffferential probe foroscilloscopes 940018 7.75 15.50Mains signalling system - 2(transmitter) (incl. disk1911 and EPROM 6371) 940021-2+ 33.25 66.50Morse decoder contact Velleman distributorGeneral-pupose sensormonitor 916107 Not availableTV sound to light unit 936038 Not available

JUNE 1994800535 SBC extension12C bus boosterRS485 interfaceFuel consumption monitorIntelligent EPROMeraser

940025+ 19.75 39.50940057 7.25 14.50940035 6.25 12.50940045 6.00 12.00

940058-1 9.00 18.00

JULY/AUGUST 1994Gen. purpose IR volumecontrol 930099IR controlled switch 936066MIDI swell pedal,incl. EPROM 946635 940019-C+Charge meter 940033Water softener 944011-1Joystick -to -mouse adaptor 944040-1Discrete preamplifier 944063-1Centronics I/O interface 944067-180C451 controller board 944069-1Robust AF power amp 944075-1PC over -temperature alarm944076-11-4 MByte SIMM adaptor 944094-1Optical doorbell 944080-1PIC experimenting board 944105-1RC5 transmitter w. 800535incl. disk 946199 944106-C+Car battery monitor 936042Resettable fuse for caravans 940061

9.00 18.009.75 19.50

26.75 53.505.75 11.506.00 12.007.00 14.008.50 17.008.75 17.50

15.00 30.009.75 19.504.25 8.50

15.50 31.006.25 12.50

17.75 35.50

13.00 26.00Not availableNot available

IA list of all PCBs, software products and front panels available through the Readers Services ispublished in the March, June, September and December issues of Elektor Electronics


x anPlease send this order form to *Elektor Electronics (Publishing)P.O. Box 1414Dorchester DT2 8YHENGLANDTel. (0305) 250995Fax (0305) 250996

`USA and Canada residents only: use $ prices, and sendorder form to:Old Colony Sound Lab, P.O. Box 243, Peterborough,NH 03458.Tel. (603) 924-6371. 924-6526, Fax: (603) 924-9467

ORDER FORM 7/8-94

VAT No.GB 454 135 463

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Please supply the following. For PCBs, front panel foils, EPROMs, PALs, GALs, microcontrollers anddiskettes, state the part number and description; for books, state the full title; for photocopies of articles,state full name of article and month and year of publication. Please use block capitals.

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Send this form toElektor Electronics, World Wide Subscription Service Ltd, Unit 4, Gibbs Reed Farm,

Pashley Road, Ticehurst TN5 7HE, England7/8-94 (Registered in the UK under the Data Protection Act, 1984)


TERMS OF BUSINESSHOW TO PAYUnless you have an approved credit accountwith us, all orders must be accompanied bythe full payment, including postage and pack-ing charges as stated on page 70, section I.

Payment may be made by cheque drawnon a London clearing bank (but see para. 4below), postal order, VISA, ACCESS, MAS-TERCARD or EUROCARD (when paying bycredit card, the order must go to the card-holder's address). Do not send cash throughthe mail. Cheques and postal orders should becrossed and made payable to 'Elektor Electronics(Publishing)'.

Payment may also be made by direct trans-fer from a private or business Giro account toour Giro Account No. 34 152 3801 by com-pleting and sending to the National Giro Centre,in a National Giro postage paid envelope, aNational Giro transfer/deposit form. Do not sendGiro transfers direct tolls, as this will delay yourorder.

If you live outside the UK, payment mayalso be made by Bankers' sterling draft drawnon a London clearing bank, Eurocheque madeout in pounds sterling (with holder's guaran-tee card number written on the back), or US orCanadian dollar cheque, but such cheques, ac-cepted at the exchange rate prevailing at thetime your order is received, must be increasedby the equivalent of £15.00 to cover our hankers'negotiating fee.

If you pay by Bankers' sterling draft, makeclear to the issuing hank that your full nameand address MUST be communicated to theLondon clearing bank.

Our bankers are National WestminsterBank PLC, 100 High Street, BRENTFORD

r

TW8 8AY, England. Our account number is4285 0134.

DELIVERYAlthough every effort will be made to dispatchyour order within 2-3 weeks from receipt of yourinstructions, we can not guarantee this time scalefor all orders.

RETURNSFaulty goods or goods sent in error may be re-turned for replacement or correction, but notbefore obtaining our consent. All goods re-turned should be packed securely in a paddedbag or box, enclosing a covering letter statingthe dispatch note number. If the goods are re-turned because of a mistake on our part, wewill refund the return postage. Goods returnedfor refund must be in resaleable condition andwill be subject to a 10% handling charge witha minimum charge of £2.50.

DAMAGED GOODSClaims for damaged goods must be received atour Dorchester office within 10 days (UK); 14days (Europe) or 21 days (all other countries)from the date on our "Recorded Delivery" slip.

CANCELLED ORDERSAll cancelled orders will be subject to a 10%handling charge with a minimum charge of£2.50.

PATENTSPatent protection may exist in respect of circuits,devices, components, and soon, described in ourbooks or magazines. Elektor Electronics (Publishing)do not accept responsibility or liability for fail -

Mg to identify such patent or other protection.

COPYRIGHTAll drawings, photographs, articles, printed -cir-cuit boards, EPRONIS, and cassettes published inour books or magazines (other than in third -partyadvertisements) are copyright and may not hereproduced or transmitted in any form or byany means, including photocopying and record-ing, in whole or in part, without the prior per-mission of Elektor Electronics (Publishing) inwriting. Such written permission must also beobtained before any part of these publicationsis stored in a retrieval system of any nature.

Nothwithstanding the above, printed -circuitboards may be produced for private and personaluse without prior permission.

LIMITATION OF LIABILITYElektor Electronics (Publishing) shall not beliable in contract, tort, or otherwise, for anyloss or damage suffered by the purchaser what-soever or howsoever arising out of, or in con-nexion with, the supply of goods or services byElektor Electronics (Publishing) other than tosupply goods as described or, at the option ofElektor Electronics (Publishing), to refund thepurchaser any money paid in respect of thegoods.

LAWAny question relating to the supply of goodsand services by Elektor Electronics (Publishing)shall be determined in all respects by the lawsof England.

Mar /994

Annual subscription rates (1994)

United Kingdom £27.00Rest of the world (surface mail) £33.00AIRMAILEurope & Eire £34.00USA & Canada $57.00Middle East & North Africa £43.00Central & southern Africa £4300Central & South America £43.00Australia & New Zealand £45.00Far East & South Pacific regions £45.00

Payment may he made by cheque in sterling drawnon a London clearing bank (but see below), postalorder, VISA, ACCESS, MASTERCARD or EUROCARD (in whichcase the subscription must be sent to the cardholder's ad-dress) or by direct transfer to our Giro Account no. 34152 3801. Do not send cash through the mail. Chequesand postal orders should be made payable to `ElektorElectronics Publishing'. Giro transfers should be made bycompleting and sending the appropriate transfer/depositform to the National Giro Centre (UK) or to your nationalGiro Centre.

If you live outside the United Kingdom, payment mayalso be made by Bankers' sterling draft drawn on a Londonclearing bank or Eurocheque. Eurocheques should bemade out in pounds sterling and have the holder's guaranteecard number written on the back.

only may pay in $US cheques.

The standard subscription order period is twelve months.If a permanent change of address during your subscrip-tion period means that copies have to be dispatched by amore expensive service, no extra charge will be made.Similarly, no refund will be made, nor expiry date extended,if a change of address allows the use of a cheaper service.

Student applications, which qualify for a 10% (ten percent) reduction in current rates, must be supported by ev-idence of studentship signed by the head of the college,school or university faculty.

Please note that new subscriptions take about four weeksfrom receipt of order to become effective.

Cancelled subscriptions will be subject to a charge of25% (twenty-five per cent) of the full subscription price or£7.50, whichever is the higher, plus the cost of any issuesalready dispatched. Subscriptions cannot be cancelled afterthey have run for six months or more.

Our bankers are National Westminster Bank PLC, SortingCode 60-03-23, 100 High Street, Brentford TW8 8AY,England. Our account number is 4285 0134.

May 1994

US dollar cheques. Subscribers in the USA and CanadaL


SWITCHBOARDSwitchboard allows all PRIVATE READERS ofElektor Electronics one FREE advertisementof up to 108 characters, including spaces,commas, numerals, etc., per month

Write the advertisement, which MUSTrelate to electronics, in the coupon on thispage; it MUST INCLUDE a private telephonenumber or name and address; post officeboxes are NOT acceptable.

Elektor Electronics (Publishing) can not ac-cept responsibility for any correspondence ortransaction as a result of a free advertisementor of any inaccuracy in the text of such an ad-vertisement.

Advertisements will be placed in the orderin which they are received

Elektor Electronics (Publishing) reservethe right to refuse advertisements withoutgiving reasons or without returning them.

WANTED -Technical help with simple automative/motorsport projects. Please phone Peteon (0621) 853 070

FOR SALE-Yaesu 747GX, CW filter, FMboard + mic, c/w HB VSWR bridge and QRDpower meter VGC - £ 499. Also, Drae 12 V,24 A PSU , £ 70. Please phone Dennis Cannings,on (0280) 701 562.

WANTED -Back issues of Elektor Electronics.Please contact William Wallace, 934 SharonDrive, Lebanon, Ohio 1045636 USA. Telephone1 513 932 1877.

WANTED-software/hardware for Apricot Flcomputer. I have most manuals but disks arecorrupt.Please phone B. French on (0507)607 333.

FREELANCE ENGINEERS team leader re-quired. Contact NTP, 1 Mid Brae, MountMelville, St. Andrews, Fife KY16 8NT.

WANTED AT bios information of any kind; alsoAT boards 386, etc. not working. Cash paid. Phone(0268) 524 968.

FOR SALE. Toroidal mains transformer, 50+50 V,6.25 A sec. ILP no. 93033, £20. PhoneNorthampton (0604) 710 268.

WANTED manuals, software, info on Cifer1800 range of CP/M computers. Please call(0283) 34678 after 7 p.m.

FOR SALE Telequipment oscilloscope, fullworking order, single beam, 10 MHz, 10 mV,TV trig., ext. Y calibrator. £60. Phone (0438)729 054.

WANTED The Eternal Summer by A. Baker,published by Collins. Write or phone Petrie, 54Clober Road, Milngavie G62 7SR. Tellephone041 956 1041.

FOR SALE Harry Moss remote car alarmMS705 circuit dia. £7. Send P.O. or cheque toG. Smith, 83 Avenue Vivian, Fence Houses,Houghton le Spring DH6 6HZ.

HELP. Urgently need circuit plan for Hillspin 4ch.STL controller. Write to A. Hall, 19, NewarkDrive, Pollokshields, Glasgow G41 4QB.

Send this coupon toElektor Electronics (Publishing)

P.O. Box 1414Dorchester DT2 81-1

England

B ock capitals p ease - one character to each box

ELEKTOR ELECTRONICS 07/94

Name and address MUST be given

FOR SALE Fluke 8060A multimeter c/w calibration certificaate. £100. Also, FG3 LFP1function generators £50 each. Call Mark on (0274)871 571.

WANTED data onCT5002 and MM5456 clockchips. Write to M. Hooker, 59 Thornton Place,Horley, Surrey RH6 8RZ.

Books from Elektor Electronics (Publishing)

The following books are currently available:301 Circuits £9.95 $14.50302 Circuits £9.95 $14.50303 Circuits £10.95 $17.90304 Circuits £12.95 $23.95305 Circuits (published in May 1994) £14.95 $27.70SMT Projects 9.95 $14.50Microprocessor Data Book £10-95 $19.90Data Sheet Book 2 £9.95 $18.50Data Book 3: Peripheral Chips £10.95 $19.95Data Book 4: Peripheral Chips £10.95 $19.95Data Book 5: Application Notes £10.95 $19.95

How to order:UK and Overseas private customers (NOTin USA and Canada) from:Elektor Electronics (Publishing)PO Box 1414 Dorchester, England DT2 8YHTelephone (0305) 250 995Fax: (0305) 250 996

UK and Overseas bookshops, schools,colleges, universities and bulk orders

(NOT in USA and Canada) from:Gazelle Book Services LtdFalcon House, Queen Square, Lancaster,England LA 1 1RNTelephone (0524) 68765Fax: (0524) 63232

USA and Canada ONLY from:Old Colony Sound - please see order formon page 111 for details

ELEKTOR ELECTRONICS .IULY/AUGUST 1994

114

ELEKTOR ELECTRONICS is available from, among others:

CRICKLEWOODELECTRONICS LIMITED40 Cricklewood Broadway,

London NW2 3ETTelephone 081 450 0995

Fax 081 208 1441

L.P. HANNEYYour electronic componentspecialist for Avon, Wilts &

Somerset.77 Lower Bristol Road, Bath,

Avon, Telephone 0225424811

AAGE NIELSEN1 Sortedam DosseringenDK-2200 Copenhagen,

Denmark,Telephone 01 39 30 10

Fax 031 39 05 02

TABACCARIA BRITANICAPraca do Duque da

Terceira 191107 Lisboa, PortugalTelephone 932 4752

MK KNJIGARNASlovenska 29

LjubljanaSlovenia

Telephone 061 150 196

THE ELECTRONIC SHOPElectronic components, test

equipment, telephoneaccessories, computer

accessories, microphones,disco lighting, speakers, turntables, mixers, meters, stylus.

29 Hanging Ditch,Manchester M4 3ES,

Telephone 061 834 1185

HELMHOLT ELEKTRONIKFarvevej 2

DK-7600 Struer, DenmarkTelephone 97 85 26 11

D.P. HOBBS (NORWICH)LTD

Electronic componentspecialists. Amateur radio

equipment.13 St. Benedict Street,

Norwich NR2 4PE,Telephone 0603 615786

RCE ELECTRONICCENTRE

Boulevarden 34DK-9000 Aalborg, Denmark

Telephone 98 16 07 10

TECHNICAL BOOKS &MAGAZINES

289-299 Swanston StreetMelbourne, Australia 3000

Telephone 663 3951MANCOMP

240 Platt LaneManchester M14 7BS

EnglandTelephone 061 224 1888

GREENWELD27 Park Road

Southampton SO1 3TBEngland

Telephone (0703) 236 363Fax (0703) 236 307

VEJLE RC ELEKTRONIKSdr Brogade 42

P 0 Box 332DK-7100 Vejle, DenmarkTelephone 75 83 25 33

INEL Co.P.O. Box 1397

JL. Hariang Banga No. 3Bandung 40116

IndonesiaOMNI ELECTRONICSStock a wide range of

electronic components.174 Dalkeith Road,

Edinburgh EH16 5DX,Telephone 031 667 2611

BEBEK ELECTRONICSHirsimetsantie 26SF -15200 Lahti 11

FinlandTelephone (18) 33 99 46

Advertising Standards AuthorityAutonaBadger BoardsBaylinB K ElectronicsBull ElectricalCanal Bridge AudioC -I ElectronicsCIL GroupCirkit DistributionCricklewood ElectronicsCrossware ProductsDisplay ElectronicsElektor ElectronicsESR Electronic ComponentsEurocomHitexHSPICE TechnologyInstrutekJPGLabcenterLloyd ResearchMaplin Electronics PLCMailtechMegalab/MegatronMicroAmpsMilford InstrumentsMorrison MicrosNumber One Systems LtdPico Technology LtdPOWERware

INDEX OF ADVERTISERS

6947325717776123

Inside front cover47155797

11329696143

Inside back cover33733927

Back cover5196254325

42427

Remote Imaging GroupRobinson MarshallSigCadSmartSpeaker BuilderSquarewave ElectronicsStewart of ReadingSuma DesignsTelnetThose EngineersTsien (UK) LtdUltimate TechnologyViewcom ElectronicsYork Equipment

915825577332431665

77959

10, 1143

ADVERTISING SPACEfor the September 1994 issue may be reserved not later

than14 July 1994 by

Elektor Electronics (Publishing)Advertisement Office3 Crescent Terrace

Cheltenham GL50 3PEEngland

Telephone (0242) 510 760; Fax (0242) 226 626to whom all correspondence, copy instructions and

artwork should be addressed.

THEME OF THE MONTH in the September issue will beHOMEBUS.


THE BEST LOW COST PROGRAMMERSDESIGNED & MANUFACTURED IN THE UK

FOR MORE DETAILS, DEVICE LIST AND DEMO DISK CALL NOW ON

TEL +44 (0)226 767404 FAX +44 (0)226 370434 REPLY NO. 28 FAX: 081-429 3117

SPEEDMASTER 1000SPEEDMASTER 1000E

UNIVERSAL PROGRAMMER Superfast PC based programmer Programmes; EPROMS UP TO 8M BIT,

FLASH EPROMS, EEPROMS, BPROMS,NVRAMs, MICROs (8748/51),PALs, GALs, EPLDs, PEELS,MACHS, MAPLs, MAX

Plugs directly intoparallel port

101000E Version has ROM/RAMemulator built in: 128k(1 Mbit) standard,optional 512K (4Mbit)

4,1

MICROMASTER 1000MICROMASTER 1000E

UNIVERSAL PROGRAMMERIII Programmes: EPROMS UP TO 8M BIT.

FLASH EPROMS, EEPROMS,BPROMS, NVRAMs, PALs,GALs, EPLDs, PEELs, 0. o.i(e%MACHs, MAPLs, MAX etc. 50,S1

PLUS over 80 different Microsincluding 8748/51, 68HC705, 68HC711,PICs, Z86, TMS320, TMS370 etc DIPsWITHOUT ADAPTORS ORPERSONALITY MODULES!

II Package adaptors available. 1000E Version has ROM/

RAM emulator built in: 0128K (1Mbit) standard, CCIPoptional 512K (4 Mbit)

SPEEDMASTER 8000GANG/SET PROGRAMMER

8 way, Pc or stand alone Super -fast programming times,

manufacturer recommendedalgorithms

32 pin devices as standard Support for 8748,51,

TMS370, PIC Micros and40 pins.

WHY BUY AN INFERIOR IMPORTED PROGRAMMER WHEN YOU CAN HAVE A MANUFACTURERAPPROVED UNIVERSAL PROGRAMMER/EMULATOR DIRECT FROM ICE TECHNOLOGY!

E We offer the best range of low-cost programmers available, now including our uniqueUNIVERSAL PROGRAMMERS WITH BUILT IN EMULATORS

E Unrivalled device support, for example the Micromaster 1000 programmes PICS, Z86, 87C705, 68HC705,TMS370, 77C82 ETC WITHOUT ADAPTORS, as well as the full range of Eproms, PLDs etc supported byall our universal programmers.

E Approved by National Semiconductor for their full range of PALs, GALs, and MAPLs - other programmersclaiming approval are often only approved for EPROMs - a much less exacting specification!

E All our programmers and programme/emulators work off the standard parallel port with any IBMcompatible PC, even laptops

E Unbeaten programming times: Programme a 27256 in just 5 SECONDS including download and verify.E Easy upgrade path between Models. 0 Y

0

V

ICE TECHNOLOGY LTD, UNIT 4, PENISTONE COURT, STATION BUILDINGS, PENISTONE, S. YORKS, S30 6HG, UK.

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I -1 1 PSI 1 CEOA , STORAGE M 6/ENU 0 SAW

1.1.16-'71 giell iPTH` I

GoictStar DIGITAL STORAGE. OSCILLOSCOPE OS4020 mow

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SELECT ISOT '[CALL 111460t 1'1 1M AN 2$0.*

FOSMON P4.1111011,MOMIK.41114

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Model OS -3020 illustrated above

Star Quality, Reliability,and World ClassPerformance

P.O.; £269-95Maplin Electronics are pleased toannounce their superb new range

of precision, laboratory gradeOscilloscopes from Goldstar.

The range starts with the superNE value -for -money, 20MHz Dual -trace

Oscilloscope, OS -9020A. Featuresinclude a large 6in., high luminanceCRT with internal 8 x 10cm graticule,TV field or line triggering and X -Ymode producing Lissajous patternsfor phase shift measurements.

For higher frequency applications,N1 the 40MHz Dual -trace Oscilloscope,

OS -9040D, is ideal for TV and videosignals and a trigger delay facility allowsobservation of fast leading edges.YJ For RF signals and high-speed logic

1\1 applications, the highly specified 100MHz triple -trace Oscilloscope,

OS -9100D, has 3 independent inputchannels and is ideal for simultaneousdisplay of 3 logic pulse trains fortiming comparison.

/tithe dual -trace, 40MHz Oscilloscope,NE" OS-904RD, is similar in specification

to OS -9040D, but with the additionalfacility of a digital readout on the CRT.The readout displays information suchas timebase and attenuator settings,and on -screen measurements can beperformed using movable cursors, thevalue appearing on the CRT screen.

NE 20MHzTop -of -the -range is the excellent

Nr' 20MHz Digital Storage Oscilloscope,OS -3020, with on -screen digital read-out and measurement facilities. Thedigital storage function enables one-offevents to be captured and stored fordetailed analysis. Stored waveforms canbe printed out on a suitable X -Y plottervia the built-in RS232 interface.Repetitive high-speed waveformsup to 20MHz can be digitised usingequivalent sampling techniquesand pre -trigger mode allows eventsoccurring before the triggering pointto be captured.

All models are supplied complete with probes, mains lead, spare fuses and detailed operating manual. Full detailsand specifications can be found in the 1994 Maplin Full Colour Catalogue, available from WHSMITH andselected branches of RSMcColl in Scotland for £2.95 (£3.45 by post direct from Maplin). To order, Phone the CreditCard Hotline, 0702 554161, or send your Mail Order to P.O Box 3, Rayleigh, SS6 2BR, or visit your local Maplin store.Please note latest models all now cream in colour as Model OS -3020.

ffNIctplin ELECTRONICS. UK AGENTS FOR GoldStarVisit our stores in: Birmingham, Brighton, Bristol, Cardiff, Chatham, Coventry, Dudley, Edinburgh, Glasgow,Ilford, Leeds, Leicester, London (Edgware, Forest Hill and Hammersmith), Manchester (Oxford Road andCheetham Hill), Middlesborough, Milton Keynes, Newcastle-upon-Tyne (The Metro Centre, Gateshead),Nottingham, Portsmouth, Reading, Sheffield, Slough, Southampton, Southend-on-Sea, and Stockport. Plus newstores opening soon in Preston and other areas. Phone (0702) 552 911 for further details.

C, t.,) 10 1, 11

OS -9020A GWO3D 1269.95

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0S-91) 11)1) ( A\ 0 1399.95

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C. 4 4,. C to (3 r 0

OS-904RD GWO6G £499.95

OS -9100D GWO5F £699.95

OS -3020 GWO7H £749.95

GoldStarAll items subject to availability; prices include VAT and are subject to change. Carriage charge per order £5-70. Handlingcharge £140 per order. Overseas customers please phone +44 702 552 911.

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