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elektor april 1984

selektorContinuing our look into what future electronics may bring us.

optical memoriesWhy has the optical computer -memory fallen behind the optical audio -memory? We try to find an answer and bring you the latest develop-ments.

controlling the floppy -disk drive motorA circuit to extend the life of certain floppy -disk units, among them ourown DOS for the Junior Computer.

pulse generator .

If you work with digital circuits, a pulse generator is virtually indispens-able. We have designed one that's not too difficult to build and not tooheavy on your pocket.

using the pulse generatorA look at the practical side (use and functions) of the pulse generatoron page 4-26. We show that a pulse generator is not only for use withdigital circuits.

intelligent EPROM eraserA circuit which automatically arranges the erasure of EPROMs in thecorrect time: no longer, no shorter.

missing link

PC board pages

Z80 simulatorOne of the principal features of a microprocessor, its speed, can be ahandicap when a circuit containing a CPU is tested. Our simulator getsaround this problem and can even be used, in a limited sense, withprocessors other than the Z80.

metronome extensionHow to expand our metronome (November 1983) to give one percussivesound with sixteen beats.

real-time analyserWe continue with part 2 of this useful audio instrument: this month,the 'mother board' and the display.

variable a.c. power supplyA power supply with a difference: it provides an a.c. output with variablecurrent limiting.

idlistThis program for cataloguing the files on your data storage tapes also hasa useful error -checking facility.

chip selektA further selection of new integrated circuits to keep you abreast ofdevelopments.

tape contents detectorThis detector tells you at a glance whether a digital cassette has beenwritten into or not.

market

switchboard

EPS service

advertisers index

4-18

4-20

4-24

4-26

4-34

Our April front cover showsthe Z80 simulator which hascome into being partly

4-36 because microprocessors(6502, Z80, etc.) are alsoused for applications otherthan computers. As its nameimplies, it simulates all thefunctions of the Z80 CPU,such as providing variouscontrol signals, feeding dataonto the data bus, andcontrolling the addressbus. It does this either atnormal speed (dynamicmode) or one step at a time(manual mode). This makesit an invaluable aid fortesting any circuit whichnormally contains a Z80, or,in a limited way, any other8 -bit microprocessor.

4-41

4-42

4-45

4-49

4-50

4-58

4-61

4-62

4-64

4-65

4-71

4-80

4-82

A selection from nextmonth's issue: short-wave pocket radio EPROM copier real-time analyser

(part 3) floppy -disk tester mini crescendo video display for the

real-time analyser

4-03

Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CTI 1PE, Kent, U.K.Tel.: Canterbury (02271 54430. Telex: 965504.Office hours: 820 - 12.30 and 13.30 - 16.30.

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The circuits are for domestic use only. The submission of designsor articles to Elektor implies permission to the publishers to alterand translate the text and design, and to use the contents in otherElektor publications and activities. The publishers cannot guaran-tee to return any material submitted to them. All drawings,photographs, printed circuit boards and articles published inElektor are copyright and may not be reproduced or transmittedin any form or by any means, including photocopying andrecording, in whole or in part without prior 'written permissionof the publishers. Such written permission MUST also be obtainedbefore any part of these publications is stored in a retrievalsystem of any nature.

Patent protection may exist in respect of circuits, devices, com-ponents etc. described in this magazine.The publishers do not accept responsibility for failing to identifysuch patent or other protection.

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Copyright © 1984 Elektor Publishers Ltd., Canterbury.Printed in the Netherlands. ABC

Volume 10 - Number 4

What is 10 n?What is the EPS service?What is the TQ service?What is a missing link?

Semiconductor typesA large number of equivalentsemiconductors and ICs existswith different type numbers.For this reason, 'universal'type numbers are used inElektor wherever possible:for instance, '741' stands forpA741, LM741, MC741,MIC 741, RM 741, SN 72741,and so on.

Type numbers 'BC 107B','BC 2378', 'BC 5476' allrefer to the same 'family'of almost identical goodquality silicon transistors.In general, all membersof the same family can beinterchanged.

BC 107 (-8, -9) families (NPN):BC 107 1-8, -91,BC 147 1-8, -9),BC 207 1.8, -91,BC 237 1-8, -9),BC 317 1-8, -9),BC 347 1-8, -9),BC 547 (8, -91,BC 171 1.2, -3),BC 182 1.3, -41,BC 382 (-3, -4),BC 437 1-8, -9),BC414

BC 177 (-8, -9) families (PNP):BC 177 1.8, -91,BC 157 1-8, -91,BC 204 1-5, -6),BC 307 (-8, -9),BC 320 (-1, -2),BC 350 (1, -2),BC 557 1-8, -9),BC 251 (-2, -3),BC 212 (-3, -41,BC 512 (-3, -4),BC 261 1-2, -3),BC 416.

Resistance and capacitancevaluesDecimal points and largenumbers of zeros are avoidedin values of resistors andcapacitors wherever possible.Instead, the following prefixesare used:p (pico-) = 10n (nano-) =

p (micro-) = 10m (milli -1 =k (kilo-) = 10'M (mega) = 10'G (gigs) = 10'

A few examples of resistancevalues:2k7 = 2700 0; 3M3 =3,300,000 0; 820 = 820 0Resistors used are watt,5% carbon types, unlessotherwise stated.

A few examples of capaci-tance values:4p7 = 4,70.000 000 000 004 7 F;10 n = 0.01 J.IF 10-! F=10,000 pF

tprii 1984

ISSN 0308-308X

The DC working voltage ofcapacitors (other than elec-trolytic or tantalum types)is normally assumed to be atleast 60 V. As a rule of thumb,a safe value is usually ap-proximately twice the DCsupply voltage.

Test voltagesDC test voltages shown aremeasured with a 20 kO/V in-strument, unless otherwisespecified.

U, not VNormally, the internationalletter symbol 'U' instead ofthe ambiguous 'V' is usedfor voltage. 'V' is reservedas an abbreviation for 'volts'.For instance, Ub = 10 V,not Vb = 10 V

Mains voltageMains (power line) voltages arenot given on Elektor circuitsas it is assumed that ourreaders know what voltageis standard in their part ofthe world!Readers living in areas whichuse 60 Hz supplies should notethat Elektor circuits aredesigned for operation from50 Hz supplies. This will nor-mally not be a problem, butin cases where the mains fre-quency is used for synchron-isation, some modification tothe circuit may be required.

Technical services to readers. EPS: Elektor printed -circuit

board serviceMany Elektor articles in-clude a layout for a printed -circuit board. Most, but notall, of these boards areavailable ready -etched andpre -drilled. The EPS in thecurrent issue gives a list ofavailable boards, front panels,and software cassettes.

Technical queriesTechnical queries relating toarticles published in Elektormay be submitted by tele-phone (Tel. 0227-53474)on Mondays between 13.30and 16.15, or in writing.The telephone service doesnot operate during July/August. Letters should beaddressed to Dept. TQ Pleaseenclose a stamped self-addressed envelope or, ifyou live outside the UnitedKingdom, an InternationalReply Coupon.

Missing linksAny important modifi-cations to, additions to, im-provements to, or correctionsin, Elektor circuits are gen-erally published under 'MissingLinks' at the earliest oppor-tunity.

4-04

advertisement eiektor april 1984

The Texas Instruments Electronic Library

Words from thewisefor beginners to buffs.

SemiconductorPublications

Optoelectronics Data Book1983 edition.Softbound 470 pages. £5.00Optoelectronics Theory andPractice. 1st edition 1976.Casebound 434 pages.

Linear Control Circuits1980 edition.Softbound 416 pages.

Voltage Regulators1983 edition.Softbound 226 pages.

MOS Memory1982 edition.Softbound 293 pages.

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*TTL Sixth European Edition 1983Volume 2 1983 edition.Softbound 1016 pages. £8.00The Bifet Design Manual 19822nd edition 1982.Softbound 124 pages. £3.95Fundamentals of MicrocomputerDesign1982 edition.Softbound584 pages. £9.009900 Family Data Book1st edition.Softbotaul 770 pages. 00.00The Power SemiconductorData Book2nd edition 1983.Softbound 890 pages. 9.00Software Development Handbook2nd edition.& inbound 434 pages. 12.90

*TMS 32010 Users GuideNew 1984 Edition 14.95

The TI Electronic Library was speciallydeveloped and written to give you an in-depthbowledge of today's world of electronics.

Each book (and there are over 30 on offer)is comprehensive, yet easy to understand.As informative for the electronics buff as forsomeone who's simply interested in what's goingon today.

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Pocket GuidesTTL 1st European Edition 1981Sofrftbound 336 pages. £3.50Linear EL InterfaceSoftbound 256 pages. 2.50

Basic Electricity SeriesBasic AC Circuits Ref. LCW 8168.Casebound 560 pages. 9.50Basic Electricity and DC CircuitsRef. LCW 8161B.Casebound 924 pages. E10.75

Home Computer99/4A. Beginners Basic981 edition. Ref. LCB 4180.Softbound 244 pages. £6.20

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already used it. simply:I. List reference numbers and quantities required.2. Calculate total order value. Add £1.50 forpostage and packing.3. Send the list, plus yourcheque payable to:Texas Instruments Ltd., PO Box 50, MarketHarborough, Leicestershire_Allow 30 days for delivery.

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rib: Texas Instruments Ltd., PO Box 50, Marker Harborough, Leics.

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microelectronics promisesbetter TV picturesThe picture quality of televisionreceivers can be greatly improved,and dormant possibilities realized, bythe use of microelectronic memories.Philips of Eindhoven, theNetherlands, have developed, andare currently testing, an integratedcircuit which can carry out the entireprocessing of the composite informa-tion for a television picture. Thetechnique employed makes possiblemodifications to the video signalduring processing. This would, forinstance, mean the eradication offlicker, 'snow', and the cross -effectsof inadvertent mixing of the bright-ness and colour information. Further-more, the television memory offersthe facility of stopping the picture atany moment, or zooming in on adetail of the image. It makes alsopossible the drastic shortening of thedelay between teletext pages. Theattraction of the chip is that it doesnot require any modification to eitherthe receiver or the transmitter, whichwill simplify its introduction greatly.

The TV standardThe system for transmitting the TVpicture information, the so-called TVstandard, was established some35 years ago for monochrometransmissions (black -and -white pic-tures). The choice of 625 lines perframe, and 25 interlaced pictures(frames) per second, was a compro-mise between the requirements ofpicture quality during normal viewingand technical and economical feasi-bility.The choice of a frame frequency of25 Hz (that is, 25 pictures per sec-ond) ensures a reasonably con-tinuous movement and also mini-mizes interference from the 50 Hzmains supply. Interlacing provides50 rasters per second (that is, a fieldfrequency of 50 Hz), which is acompromise to prevent frame flickerat high brightness. The field fre-quency needs to be low enough toallow as many horizontal lines aspossible and at the same time suf-ficiently high to eliminate frameflicker. Unfortunately, interlacingresults, particularly with largescreens, in line flicker.The 625 horizontal lines which com-pose our TV picture cannot be seenseparately at distances greater than4 . . . 5 times screen height, whichgives the impression of a uniformpicture. Together with a height/widthratio of 3 : 4, and the requirementfor good definition, this results in avideo bandwidth of more than

5 MHz. This was considered accep-table both technically and economi-cally, as was the bandwidth of7 . . . 8 MHz for the transmittedsignal (because there was thenplenty of space available). This stan-dard has been accepted throughoutwestern Europe during the inter-vening years.With the introduction of colourtelevision, one of the first require-ments was that colour transmissionscould be received (without colour)on monochrome receivers.Throughout the world three systemshave been developed for thedecoding of the colour information,each of which has its own advan-tages and disadvantages, but they allare clearly a compromise which fallsshort of requirements under certaincircumstances.It is important, however, that innone of these systems has the re-quired bandwidth been enlarged.Because the colour signal can be ac-commodated in a smaller bandwidththan the brightness signal, it ispossible to contain the decodedcolour information within the band-width of the black -and -white signal.This is normally acceptable, but mayresult in a mixing of the brightnessand colour information. This thenbecomes evident in the cross -effectsalready mentioned.

StraitjacketAlthough these standards for the TVsignal were perfectly acceptablewhen they were laid down, technicaldevelopments since then have beensuch that these same standards arenow often felt as a straitjacket. Thelarger screens and increased bright-ness of modern TV tubes in par-ticular have given rise to this feeling.The 625 lines no longer give a suf-ficiently detailed image, while the25 frames per second show a dis-turbing tendency to flicker.

RemediesAll these imperfections could, ofcourse, be removed by changing thesystem. This would, however, requirea network of new transmitters aswell as new receivers. At the sametime, compatibility with the oldsystem would, of course, have to beretained, which again results inlimitations. Moreover, such drasticmeasures would require internationalagreement, and this can be dis-counted for some time to come.Now, a number of improvementshave become possible, which requireaccess to the receiver only. These

elektor april 1984

make use of large electronicmemories which contain all thenecessary information for a completevideo signal. New developments inmicroelectronics have enabled Philipsresearchers to realize an integratedcircuit which is ideally suitable foruse in a TV receiver. The use of nor-mal computer memories would bemore complicated and require morecircuits. The chip now under test isa video memory with a capacity of308 Kbit and an area of 34.8 mm2,which is 2 . . . 3 times smaller thana comparable computer memory,and is therefore easier to developand cheaper to produce. Such alarge memory allows the increase ofthe field frequency from 50 to100 Hz. The information on the evenlines, which is transmitted in 20 ms,can then be stored in the memory.These lines are then repeated twice:the memory is therefore read twicein succession in 10 ms. This processis then repeated with the odd lines.This prevents field flicker, but notline flicker. Another method, pro-viding alternate even and odd linesevery 10 ms, prevents line as well asfield flicker with still frames. Thismeans, however, that a largermemory is required which can storethe information for the entire videosignal, that is, odd as well as evenlines, in 40 ms. This will probablygive difficulties with moving picturesbecause one has to fall back all thetime on previous movement phases.Electronic means to combat thisproblem are being sought urgently.By using a memory in the decodingsystem it is also possible to reducecross -effects and noise considerably.The signal processes by means ofthe video memory discussed so farare aimed at an improvement in pic-ture quality. It is, however, alsopossible to realize new functions inthe TV receiver. For instance, oncethe frame information has beenstored in the memory, it is possibleto stop the picture or zoom in ontosome detail. It also becomes poss-ible to remove the delay betweenteletext pages.

Philips press notice

World's smallest MicrocomputerThe smallest self-contained CP/Mcompatible microcomputer in theworld has been launched by DVWMicroelectronics Ltd. of Coventry.Weighing just over 1 kg and the sizeof a paperback book the HuskyHunter offers advanced microcom-puting power in a package that canbe carried anywhere. It has the

4-18

elektor april 1984

largest RAM memory of any portableon the market, say the makers.The computer's CP/M compatibilityenables the user to select from thevast range of commercially availableCP/M programs developed for desk-top computers or to write a programin the machine's own interpretiveBasic programming language. Aneight -line 320 -character LCD screenacts as a window on a larger 'virtual'display that emulates popular CRTterminals and this enables applicationsoftware designed for desk -top sys-tems to be operated without modifi-cation. The user can move this displaywindow around the screen at will. Amemory of up to 208 K provides aresource equivalent to that of tra-ditional disc drives, without theirbulk, weight or fragility. This mem-ory, up to ten times that of otherhand-held micros, makes the devicesuitable for many professional appli-cations.The micro is the only hand-helddevice with genuine graphics capa-bility, says the manufacturer. Itslarge screen (240 x 64 dot) is able todraw complex graphic and animatedpictures and show text presentationswith variable character size andfield constructions. Facilities includesynchronous and asynchronous pro-tocols and the implementation of thestandard IBM 2780 bi-sync formatmeans that the micro can 'talk' to atleast 70% of the world's mainframecomputers without intermediate hard-ware.Designed to be used in the field, themicro has a robust diecast aluminiumalloy case, sealed against moistureand immersion. The keyboard has 54rubber keys arranged in four rowswhich are fully waterproof. There is a

choice of four mains -rechargeableNickel/Cadmium batteries with anaverage 14 -hour operating life, oralkaline batteries and there are back-ups charged from the main cells.The complete unit weighs 1.15 kgand measures 216 mm x 156 mm x32 mm.Made in Britain

First undersea fibre optic cableCable for the world's first underseaoptical fibre link, between the UKand Belgium, is to be manufacturedby Britain's Standard Telephones andCables (SIC) comapany under acontract worth £7,250,000. Thecable, which will be able to carrynearly 12,000 telephone calls anddigital computer data, is to be laid inthe spring of 1985 by British Tele-com's cable ship "Alert".Three pairs of optical fibres will eachcarry digital information at speeds upto 280 Mbits per second, giving acapacity of 3,840 64 Kbits per secondcircuits, and total cable capacity of11,520 circuits. Use of single -modetransmission enables a single ray oflaser light to travel a greater distancealong theis needed at a repeater. Three sub-merged repeaters will be installed atintervals of about 30 kilometresalong the 122 kilometres betweenterminal stations.Half of the investment for the cablelink, called UK Belgium 5 because itis the fifth cable link between thetwo countries, is made by BritishTelecom International. The remaindercomes from three telecommuni-cations authorities - those of Belgiumand the Netherlands together with

Germany's Deutsche Bundespost.The cable is the result of co-operationbetween British Telecom's researchlaboratories at Martlesham Heath and

- STC's research laboratories at Harlow,near London, where investment inoptical fibre research and develop-ment has been maintained at con-sistently high levels over recentyears.STC has already been awarded ordersworth nearly £40,000,000 by theconsortium of 28 telecommuni-cations authorities which is to installa transatlantic cable (TAT 8) goinginto operation in 1988. The contractcovers supply of a 520 kilometresegment from Widemouth Bay onEngland's south-west coast, to ajunction box just off the Europeancontinental shelf.LPS.

Full -channel teletext gives fastaccessA teletext system having up to16 000 pages of information andgiving access in as little as 16 ms hasbeen developed by Jasmin Elec-tronics Ltd. of Leicester. The systemuses the whole television channelbandwidth, unlike the systems em-ployed in conjunction with regulartelevision broadcasts in which dataare transmitted in the otherwiseredundant lines between frames. Thespecifications of full -channel teletextare standard and therefore thesystem can be used alternatively forconventional television programmesif necessary. Maximum access timeis 1 second per 1000 pages, althoughfor certain individual pages, accesstakes as little as 16 ms.The company is prepared to designand install systems for any purposeand to any specification. Most usersin the UK are large organisationswhich need to disseminate infor-mation rapidly. (One of the earliestand most typical installations was atLondon's Heathrow Airport.)Pages can be created easily in fullcolour with graphics. Not all thepages in a system need to originatein the same studio; pages may becompiled from several locations.Other teletext services, such as thoseprovided by broadcasting services,may be incorporated into the full -channel system.Full -channel teletext systems caninclude feedback from the receivers.This makes possibles such facilitiesas customer authorisation and billing,message services, ordering of goodsand services and travel reservations.Made in Britain.

4-19

optical memorieselektor april 1984

At the right a floppy discdrive unit. At the left theoptical memory drive unitOPTIMEN developed byShugart, which was un-veiled in prototype formin the USA towards theend of 1983. Anticipatedcost of production mo-dels (if they appear in thenext 12 months):about $6000)

optical memorieselectronic filingcabinets

Figure 1. Magnetic tapebelongs to the family of'magnetic coat' mem-ories. The magnetic tapememory functions basi-cally as a multi -tapemachine.

Beethoven's Fifth and Schubert's Unfinished are nowadays availableon compact disc, the optical audio -memory. It is a curious fact thatthe compact disc has appeared so much earlier than opticalmemories for computers, although not so long ago the latter wereexpected to be first on the market. But here we are today with thecompact audio disc reasonably well established but with noindication as to when optical computer memories will appear on themarket. Even the most optimistic prognoses from the industrycontain no hints whatsoever, although there have been murmurs thata read-only optical memory may appear on the American marketduring 1984 at a cost of around 6000 dollars.

As you may remember, the history oflarge -quantity data storage began withpunch cards, punched tape. and themagnetic core memory. Then came the

64436-1

magnetic film store, the magnetic disc,and the magnetic drum. Nowadays, themost widely used memory is that basedon magnetic tape. Operation of thismemory is reasonably well-known, as it isbasically the same as that of tape andcassette recorders. Figure 1 shows theoperation of a magnetic tape memory inschematic form: only one track is shown,although in most equipment nine tracks(that is, the same number as there areread/write heads) are available. Thecapstan is located immediately next to theread/write head. The light barriers in thevacuum guidance ensure that the tapeloops are correctly positioned. Shouldtheir position change, the tape is woundor unwound slightly until the loops areback to normal. The photocells 'recognize'the beginning and end of the tape.Apart from magnetic tape, there is also themagnetic drum. This type of memory con-sists basically of a cylinder coated withmagnetic material. The surface area of thecylinder is divided into tracks. Each trackhas its own read/write head.The classical magnetic disc is made ofaluminium which is coated with a layer ofmagnetizable iron oxide. The data arerecorded (written) on, and retrieved (read)

4.20

from, circular tracks. The flexiblemagnetic disc, called floppy disc, is usedprincipally by hobbyists and in small of-fice equipment.Of late, everybody has been talking aboutthe Winchester disc. This is a memorywith extremely high storage density andcapacity. In contrast to the classicalmagnetic disc, it has one smooth side, butfunctions in all other ways in an identicalmanner. The magnetic head lies on thedisc when this is at rest. When the discstarts to rotate, however, the head,because of its shape, rises and floatsabove the moving surface at a height ofabout 0.5 gm.

Optical memoryIn optical systems, the disc is scanned bya laser beam, as, for instance, the compactdisc and the video disc. The video disc ismade of perspex which is coated with athin layer of photosensitive lacquer. Thedisc is then pressed against a masterwhich produces a spiral track of inden-tations, called pits, as shown in photo 1. Itis then exposed to ultraviolet light toharden the photo -resist. Subsequently, it isloaded into a vacuum chamber where it isimmersed in aluminium vapour for about30 minutes. This vapour produces a finereflective coating on the disc. Finally, thedisc is coated with a protective layer ofclear lacquer. During play -back, the trackis scanned by a laser beam starting at thecentre and moving to the periphery. Thelaser light is bent and deflected at theedges of the pits to such an extent that itis no longer detected by the photodiode.For all practical purposes, the light of thelaser beam is thus intensity -modulated bythe pits. The laser light is polarizedlinearly, so that the beam reflected by thedisc and the primary beam are wellseparated. This type of memory is evi-dently not of much interest to the hob-byist, as it is similar to a PROM.So, what advantages can we expect fromoptical memories? The answer to thatquestion is contained in the followingdescription of two systems which are tobe launched this year.

MEGADOCThe MEGADOC optical memory systemhas been developed by Philips ofEindhoven, the Netherlands, who alsopioneered the compact disc and thevideo disc. The system is intended to belaunched at this year's Hannover Fair.The basis of the system is a 12 -inch diam-eter disc with a storage capacity of1 Gbyte per side. This enables the record-ing of the contents of 50000 A4 size pageson one side!The MEGADOC system consists of a discdrive unit, monitor screen, facsimileprinter, and the memory unit which canhold up to sixty-four optical discs. Such acomplement would enable the recordingof more than six million A4 size pages.According to the manufacturers, the

MEGADOC system offers the followingadvantages: very high storage capacity and density; fast and simple recording of docu-

ments; unimpaired high quality of retrieved

information; fast location of wanted data.Apart from the hardware, there. will, ofcourse, also be a software package for thecontrol and operation. No doubt, thesystem will be of great interest to publicrecords offices, financial institutions, in-surance companies, large multinationals,libraries, and all other organizations whichmaintain large archives.

OPTIMENThis sytem, developed by Shugart, is verysimilar to that of Philips. It also uses a

I

objectivelens

phorodiode laser diode

optical memorieselektor april 1984

Photo 1. The surface of anonerasable opticalmemory disc.

Figure 2. Optical memorydiscs are scanned andwritten by a laser beam.The structure of such adisc is shown in photo 1.

mirror assembly

4-21

optical memorieselektor april 1984

Figure 3. The collectionand telescope lensassemblies focus the lightemission of the laserdiode. Correction prismsshape this to an annularbeam. The routing mirrorassembly deflects thebeam through a polar-izing beamsplitter/ 'AAplate assembly, where theplane of polarization isshifted 90°. The beamthen finally arrives at theobjective lens.The reflected light istaken from the objectivelens, aligned parallel, andfalls onto the 'AA plate.The plane of polarizationis again shifted 90°, andthe beamsplitter directsthe light to the focuserror prism. The detectorprovides the controlsignal for head adjust-ment.

Figure 4. A bubble ariseswhere the laser beam hitsthe surface of the opticalmemory disc. Such abubble represents a bit.

FOCUS ERROR PRISM

DETECTOR

COLLECTION LENS (2)ASSEMBLY

TELESCOPE LENSASSEMBLY (3)

LASER DIODE (1)

OBJECTIVE LENSTWO AXIS (7)

ACTUATOR

CORRECTIONPRISMS (4)

POLARIZINGBEAMSPLITTER/

?.PLATEASSEMBLY (6)

litt136-3

ROUTING MIRROR ASSEMBLY (5)

Metal Polymer Substrate Bubble is one gmor less in diameter

12 -inch diameter disc with a storagecapacity of 1 Gbyte per side.The laser used is a gallium-aluminium-arsenite type which produces a coherent -light beam with a capacity of 20 mW. Thebeam is focused into a point of only about1 µm by a special lens (see figure 3). Thisresults in a storage density of 14500 bitsper inch, which is similar to that ofmagnetic memories. The advantage overmagnetic memories is, however, that thestorage density is also the track density.Table 1 shows that in this way a surfacedensity some seven hundred times that ofan 8 -inch floppy disc can be obtained!During the storing of the data, the writehead (that is, the optical system) focusesthe point of light onto the metallic surfaceof the disc. The laser beam heats the

metal and the ensuing heat is transferredto the acrylic material underneath themetallic layer. This causes a bubble whichcan be read by the laser (see figure 4).

CD-ROMOptical memory techniques offer thepossibility of mass reproduction of soft-ware. Philips and Sony are thereforealready working on the basic model of aCD-ROM. This is a combination of thecompact disc, redeveloped as a digitaldevice, and a ROM. The capacity of sucha digital disc is of the order of 550 Mbyte,which is about five -hundred to a thousandtimes larger than that of a floppy disc! Inother words, this makes it possible tostore 120 000 A4 size pages onto one

4-22

compact disc. Such a digital disc could be Tableread on a modified compact disc machinewhich would at last make an inexpensive Comparison of surface densities

high -capacity memory available forpopular use. Unfortunately, this is a littlewhile off yet.

Floppy disc replacement?We should not forget to mention thatfurther development of the floppy disc isalso taking place. At the end of 1982,Toshiba of Japan presented a 3 -inchfloppy disc with a storage capacity of3 Mbyte per side! In contrast to the con-ventional longitudinal magnetization of thedisc, the Toshiba disc is vertically mag-netized by means of an annular magnetichead. Unfortunately, this interesting tech-nique appears to have died a naturaldeath.A similar situation exists around thedevelopment of an erasable opticalmemory disc. Also at the end of 1982,Philips presented the laboratory prototypeof a 5 -cm disc drive mechanism. This hasso far come to nothing owing to lack ofstandards for optical drive mechanisms.The Philips project is based on amagneto -optical memory with thermo-magnetic storage. The principle of thisconception is best explained withreference to figure 5: it makes use of so-called rare earths of which the magneticproperties are temperature -dependent. Asin the OPTIMEM system, a laser beamheats material but here it causes amagnetic field to be produced. Thischanges the direction of magnetization.After the spot has cooled off, themagnetic state persists. You could, forexample, define this as a logic '1'. If thedata is to be changed, that is, erased, thesame spot is again heated by the laserbeam, a magnetic field arises, and theoriginal direction of magnetization isresumed. Reading of the data is madepossible by the use of the magneto -opticalFaraday effect: when the laser beam hitsthe data location, the direction of polar-ization of the light changes. This directionis ascertained by the analyser and con-verted into a logic '1' or '0' by a detector.This memory holds only 10 Mbytes. Theread rate is of the order of 250 Kbits/s,while writing takes place at a speed ofabout one bit per 3 is.Systems similar to that of Philips havebeen developed in Japan by Sony andKokusai Denshi Denwa. About six monthsago, these companies revealed prototypesof a 30 -cm disc which can store up to30 Gbit. These systems function in thesame way as that of Philips, but the discsare coated with different materials.Before you rush to your local electronicsdealer, we should point out that, unfor-tunately, there is as yet no suitable hard-ware on the market, and at the time ofwriting no information could be obtainedas to when production is likely to start.None the less, we remain optimistic andlook out for the first erasable 5 Mbyte op-tical memory for hobbyists. 14

optical memorieselektor april 1984

bpi tpi urracesi - I

DS/DD-8-inch-Floppy 6 800 48 0.3 x 1065.25 -inch -Winchester 8 800 800 7.0 x 106IBM-3380-Technik 15 200 800 12.2 x 106OPTIMEM 1000 14 500 14 500 210 x 106

bpi = bits per inchtpi = tracks per inch

acrylic body

field coil

Laser

laser beam

- magnetic field

analyser

to detector

Figure 5. Erasable opticalmemory discs utilize thethermo-magnetic proper-ties of so-called rareearths. The direction ofmagnetization shiftswhen the laser beamheats the material whichlies in a magnetic field.

Photo 2. MEGADOC. the'electronic filing cabinet'.

to be introducedon the Hannover Fair 1984by Philips. pioneers ofthe optical disc.

4-23

controlling the floppydisk drive motorelektor april 1984

A look at the technical specifications of certain diskette units willshow that the MTBF (Mean Time Between Failures) indicated by themanufacturer is only valid as long as the drive motor only runs for afraction of the total operating time. The interface published by Elektorhas no way of operating the motor for only a short time. The circuitproposed here enables the motor to run only when the floppy diskdrive is selected, and it is stopped again about a dozen seconds afterthe unit is deselected.

controlling the floppydisk drive motorincrease thelifespan ofcertain disketteunits

Figure 1. The first indexpulses are inhibited byIC3. FF1 and ES2. Theother components makethe motor run when aunit is selected, and keepit running for abouttwelve seconds after thediskette has beendeselected. This preventstime being wasted whenthe floppy disk drive isaccessed several times inquick succession. Also,the whole circuit can bedisabled by connectingthe line between the CLRof IC4 and the R of FF2 tothe positive supply, via aswitch for example.

The floppy disk interface for the JuniorComputer published in Elektor 91,November 1982, was a perfectly feasibleand affordable disk drive, but it did notallow the drive motor to be stopped, evenwhen the floppy disk was not being ac-cessed. This certainly makes the accesstime as small as possible, as there is nodelay while waiting for the speed tostabilize, which is necessary every timethe motor is started from rest. It could,however, be expected to reduce thelongevity of both the motor and thediskettes themselves since the read headis permanently in position.

One second before and twelveseconds afterWhen pin 16 of the connector on a floppydisk drive is logic 'low', the drive motorturns. It does not instantaneously reach itsoperating speed, of course, so the ad-dressing signal (SEL) cannot be used as aDRIVE MOTOR ENABLE or the first fewpulses written to or read from the diskettewould be useless. Furthermore, thismethod of operation switches off the drivemotor as soon the unit is deselected, andthis is a disadvantage if the unit is ac-cessed several times in quick succession.

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4-24

It would be far better if the motor con-tinued to rotate for a short while.These considerations lead us to the circuitshown in figure 1, whose key is switchES2 (and its 'shadow' ES1) driven by flip-flop FF1, which is itself controlled bycounter IC3. When a peripheral unit is tobe activated, signal G1 (pin 6 of IC15 onthe interface) goes high. This signal in-itializes counter IC4 and flip-flop FF2,whose Q output also goes high. Switchingtransistor Ti is saturated and pin 16 of con-nector K2 goes low so the motor selectedstarts to run. Then the first index pulsesarrive, but they are not stable. These donot reach the interface as ES2 is open.The first five pulses are counted by IC3and then its Q4 output goes high. Thiscauses FF1 to flip and PAY receives the in-dex pulses, which have now stabilised, viaES2.During this time, IC4 and FF2 remain in-itiali?ed. As soon as the unit is deselected,signal Cl goes low again and IC4 beginsto count the pulses provided by its ownoscillator. About 12 seconds later, outputQ6 of the 4060 is activated, causing FF2 toflip and Ti switches off. The motor ofwhichever unit was selected then stops.At the same time, a logic 'high' appears atthe Q output of FF2 to reset counter IC3and flip-flop FF1. The result is that ES2opens and ES1 closes, and the cycle isthen complete.

The possibilitiesThe 'after' time can be changed by modi-fying the value of the RC network formingthe time -base for the 4060 (note that R3 =2 ... 10 times R2). The length of the'before' time can also be changed byreducing or increasing the number of in-dex pulses counted before ES2 is closed.All this requires is to connect pin 11 ofFF1 to some output of IC3 other than Q4.If only the motor for the unit selected is torun, a switching transistor (like T1) couldbe included per selectable unit, and thiswould be controlled by a NOR gate (4001)that combines the Q signal of FF2 and theappropriate selection signal, SEL 1... 4.This implies, of course, that line 16 (DriveMotor Enable) cannot be common, butmust have a separate line for each unit inservice.The modifications required on the printedcircuit board for the interface card areshown in figure 2. The line between pin 8of connector K2 and pin 9 of IC5, and theline between pin 16 of K2 and earth, mustbe broken. Don't forget to remake theconnection from earth to pins 6, 8, and 10of IC12 and capacitor Cll. When the cir-cuit from figure 1 has been made up, on apiece of veroboard, for example, it mustbe connected to the interface printed cir-cuit board at points A ... D and '+' and'0'.

A few hintsThe best way of making a neat break in

2

3

rye

the track on a printed circuit board is alsothe least dangerous for the neighbouringtracks. All that is needed is to make twoclean cuts in the copper, spaced aboutone or two centimetres apart, and thenheat this until it lifts. And while we are onthe subject of tips, here is another: asingle -sided diskette is often magnetisedon both sides and there is no reason notto use the reverse side, except, of course,that a second write protect notch must becut and another index hole added (with aperforator or paper punch) in thediskette's dust cover. By the way it is not agood idea to try to remove the diskettefrom its cover! Great care must be takento avoid scoring, or otherwise damaging,the floppy disk surface. These modifica-tions will be simplified by first making upa template, as shown in figure 3. Then,after a few minutes work, your stock ofdiskettes will have become doubly usefuland doubly important.

controlling the floppydisk drive motorelektor april 1984

Figure 2. When the circuitof figure 1, built on apiece of veroboard orsomething similar, isfixed to the track side ofthe floppy disk interfaceprinted circuit board, it isunlikely to interfere withany other boards on thebus. Having broken theconnection to ground atpin 16 of the output con-nector, don't forget toremake the links to theappropriate components.

Figure 3. The reverse sideof a single -sided floppydisk can also be used if awrite protect notch andan index hole are care-fully cut in the dust coverin the same relative pos-itions as the existingones.

4.25

pulse generatorelektor april 1984

An electronics home workshop is usually started with a universalmeter. Then follow a variable (regulated) power supply, a sine wavegenerator, and an oscilloscope. After that, who knows? There arehobbyists' workshops which would make many a professional greenwith envy. It is, however, fairly certain that among what follows is apulse generator which is virtually indispensable when you work withdigital circuits.

pulse generatorA pulse generator, like every measuringinstrument, must be of good quality, andthis is one of the starting points of ourdevelopment described. Reliability,without exotic frills, and operatingfacilities for coping with most imaginablerequirements, are others.To start with. however, a recap of pulseterminology which may refreshen many amemory!A pulse is a voltage or current which in-creases from a constant value to a maxi-mum and decreases back to the constantvalue in a comparatively short time. Theconstant value (which may be zero) in theabsence of a pulse is called the baselevel. A pulse may be rectangular,triangular, square, sawtooth-shaped, andso on.The portion of the pulse that first in-creases in amplitude is the leading edge.The time interval during which theleading edge increases between ten andninety per cent of the pulse height is call-ed the rise time. The pulse decays backto the base level in a finite decay timebetween the same limits as the rise time.The major portion of the decay time istermed the trailing edge of the pulse. Thetime interval between the rise time anddecay time is the pulse width (sometimescalled pulse duration). The amplitude ofthe pulse taken over the pulse width isthe pulse height.

Featurespulse REPETI:ION TIME

1 pis10 ps

100 ps1 ms VAR: 0.1 . 1(CALI

10 ms100 ms

1sMAN ua triggerEXTernal trigger (2 .. . 20 VI

jitter 0.5% (at PRT = 1 ms)

PULSE WIDTH1 piS

10 p5100 ;Is

1 ms VAR: 0.1 . 1(CAL)10 ms

100 ms1s

SYMmetricaljitter 0.1% (at width of 1 ms and duty

factor = 80%)duty factor variable up to 100%

OUTPUT voltageTTLVAR 11 . . . 15 V)EXTernal OUTPUT CONTROLVOLTAGE (1 . . . 15 VIchoice of inverted and non -invertedoutput signal

CONTROL ERROR indication SYNC OUTPUT (TTL) TRIGGER INPUT (20 V max) rise time about 10 ns (load = 50 4 in parallel

with 33 pF)

4-26

A group of identical pulses is a pulsetrain which is normally named, accordingto the type of pulses it contains, squarewave, triangular wave, sawtooth wave, andso on. The time interval between cor-responding portions of the pulses in atrain, for instance, the decay times, is thepulse spacing or pulse -repetitionperiod, T. The pulse -repetition frequencyor pulse rate is the reciprocal of theperiod (that is, the rate at which pulsesare transmitted in the train) and ismeasured in hertz.The duty factor (NOT duty cycle!) of apulse train is the ratio of the averagepulse width to the average pulse spacingin a train and is normally expressed in percent. A rectangular pulse train is often er-roneously called a square wave: itbecomes a square wave only, however,when the duty factor is fifty per cent.A spike is an unwanted pulse of relativelyshort duration superimposed on the mainpulse; ripple is unwanted small periodicvariations in pulse height. Jitter is minorvariations in the pulse spacing.The pulse generator described here pro-duces rectangular pulses or waves. Thepulse rate as well as the pulse width arevariable. Such a generator is basicallyquite simple as shown in figure 1 and con-sists of three main parts: a voltage -

controlled oscillator (VCO), a monostablemultivibrator (MMV), and art amplifier.The VCO generates pulses at a rate whichcan be varied over a wide range. Thesepulses are used to trigger the MMV. If themono -period of the MMV is variable, thepulse width may be varied at will. Theamplifier raises the output pulses of theMMV to the required height, and that's allthere is to it!Two additional facilities indicated infigure 1 should, in our opinion, be fitted toeach and every pulse generator howeversimple: external trigger input and manualmode. The latter enables single pulses tobe generated by pressing a spring -loadedpush-button. A three -position switchenables selection of the three modes:VCO, external trigger, and manual.

The concept

To be sure, an instrument as shown infigure 1 is somewhat spartan, and someother very desirable, if not necessary,facilities have therefore been added:these are partly technical necessitiesbecause we have painted the picture infigure 1 a little too simple, and partlyniceties which make using the generator alittle easier.The technical necessities concern thevariability of the VCO and MMV. It is, un-fortunately, not possible to achieve a suf-ficiently wide range of pulse rates andpulse widths with just one potentiometer.A switch and a potentiometer form aminimum combination and this has far-reaching consequences on the design ofthe VCO.Of the 'niceties', we would mention the

1

PULSE

REPETITIONPERIOD

MANUALTRIGGER

tte

0-.4)0

MMV

ULSE

EXTERNALTRIGGER INPUT

114037-1

variable output voltage which is normallynot provided on inexpensive generators; aswitch which sets the output voltage toTTL level; and finally, a facility to makethe output voltage identical with the sup-ply voltage of the circuit under test whichis a very convenient feature for testingCMOS circuits which do not operate from5V.Next, we felt it would be useful to provideselection of inverted and non -inverted out-put pulses, and of variable or fixed (50 percent) duty factor. Finally, there is an in-dicator for operational errors, and aseparate sync output (TTL level) which isintended for use as a trigger signal for anoscilloscope or as drive signal for aneventual frequency read-out.

The block schematic

Adding these additional featurestransforms the block schematic of figure 1to that shown in figure 2.The VCO should have a fairly wideoperating range which can be achievedby either switching the VCO itself or by achain of dividers in the VCO output. Ascan be seen, we opted for the dividers.The VCO is controlled by potentiometerPI which enables the VCO output periodto be varied between 0.1 µs and 1.0 pis.This output is fed to six cascaded decadescalers. With PI in position KCAL), that is,a VCO output period of 1.01.1s, REP-ETITION TIME selector SI enables theselection of pulse periods of 1 µS ... 1 s indecadic steps. Periods between thesesteps may be set by Pl. Selector Si alsoenables selection of MANual pulses andan EXTernal trigger signal. The manualpulses are generated by flip-flop FF2when spring -loaded switch S2 (MANUAL)is pressed. The external TRIGGER INPUTsiganl is provided via amplifier TI/N1.As the output of the VCO is a pulse train(often called wave) with a duty factor of50 per cent, a square wave is available atthe wiper of Si and this is, of course, aperfectly suitable SYNC OUTPUT (TTL)signal. It is also applied to a monostablemultivibrator (MMV) which provides the

pulse generatorelektor april 1984

Figure 1. A pulsegenerator in its simplestform: the VCO enablessetting the pulse rep-etition period and theMMV the pulse duration.

4-27

pulse generatorelektor april 1984 2

IC2 's IC3 7SIC3 :i1C4 :SIC4

Figure 2. The blockschematic of the pulsegenerator described inthis article. The desig-nations correspond withthose in the circuitdiagram.

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vco -4114P =10 =10 ÷ 10

REPETITION TIME PULSE WIDTH

51,3=1,s 55 = 1 .61b10 b=10 LAc - 100 LA c=100 nsd I rns d = 1 rns

10 nu s 10 an100 em I 100 ms

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P1=0.1_ .. I (CA1-1

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134037.2

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variable pulse width. The MMV is fired bythe leading edge of each pulse in thewave emanating from Si. The pulse dur-ation may be varied between 0.1 pis and 1 sby PULSE WIDTH selector S5 and poten-tiometer P3. The output signal of theMMV, together with the square wave fromSI, is fed to an electronic switching cir-cuit, N2 ... N4, from where either asquare wave (SYM) or rectangular wave(VAR) may be selected by S3. The signal isthen taken to XOR gate N6 which enablesselection of inverted or non -invertedsignals by S4.The output stage, T2 ... T4, ensures thatthe TTL level of the output signal can beconverted into a variable or externallycontrolled level. This is effected by IC11 inthe power supply. The IC provides theoutput stage with a variable supplyvoltage which is controlled by an externalvoltage, or by potentiometer P4, or byVAR/TTL selector S7. When S7 is in posi-tion TTL, the output voltage is about 4.8 V,

while in position VAR it may be variedbetween 1 and 15 V by P4. When an exter-nal control voltage is connected, the out-put voltage is identical to it. When, for in-stance, work is being carried out on aCMOS circuit, it is sufficient to connectthe supply voltage of that circuit to theEXT. OUTPUT CONTRol VOLTAGE.Flip-flop FF2 is a divider circuit whichdetects and signals operational errors bythe CONTROL ERROR indicator LED. Thishappens, for instance, when a longerpulse duration is selected (S5) than ispossible with the pulse period selected(S1). As the circuit diagram is not muchdifferent from the block schematic for thiscircuit, it's as well to describe the opera-tion here.During normal operation the Of output ofFF2 is logic 1. The flip-flop is clocked ateach leading edge of the MMV signal,because its D input is connected to the Qoutput of the MMV (provided S3 is in posi-tion VAR). This leading edge arrives

4-28

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slightly later than that of the sync outputsignal at the CLK input of FF2. At the in-stant the CLK input becomes logic 1, theD input is still logic 0: the 0 outputtherefore remains high and the LED staysextinguished. If the selected pulse dura-tion is longer than the pulse period, theoutput of the MMV (and therefore the D

input of FF2) will still be logic 1 when thenext clock pulse arrives at FF2. The flip-flop then changes state and the LEDbegins to blink indicating that an error hasbeen made. With S3 in position SYM, thistype of error cannot occur because the Dinput of FF2 then always goes logic highafter the CLK input.

Parts list

Resistors:

R1,R2,R6,R7,R9 = 5k6R3,R4,R5,R17 = 1 kR8 = 4k7R10 = 220 QR11,R23 = 220 Q/1 W (notwire -wound!)

R12 = 2k2R13,R14 = 100 9/1 W (notwire -wound!)

R15 = 47 QR16 = 330 QR18 = 10 kR19 = 390 QR20 = 1k5R21 = 150 52R22 = 680 Q

Capacitors:Cl. = 82 pC2 = 2 . . 20 p trimmerC3 = 100 pC4 = 10 pC5 = 560 pC6 = 6n8C7 =- 68 nC8 = 680 nC9,C26,C27,C31 =10 p/10 V

C10 = 22 y/10 VC11 = 100 y/10 VC12 = 220 y/10 VC13 = 68 pFC14 = 470 y/25 VC15 = 220 p/25 VC16,C24 = 330 nC17 = 2y2/25 VC18,C21,C25,C28,C30,

C32 . . . C35 = 100 nC19 = 1 y/10 VC20 = 220 y140 VC22 = 10 y/40 VC23 = 1 y/25 VC29 = 10 y/25 V

Semiconductors:ICI = 74LS6241C2,1C3,IC4 = 74LS390IC5 = 74LS74106 = 74LS00IC7 = 74LS86IC8 = 74122 (not LS!)IC9,1C12 = 7805IC10 = 79L05IC11 = LM 317T

Figure 4. The circuit hasbeen divided over twoprinted -circuit boards: theone illustrated here con-tains the parts of the cir-cuit in dashed lines.

Figure 5. This board con-tains the remainder of thecircuit. To ensure goodstability it has been madedouble -sided: the largecopper area at the com-ponents side is an earthplane.

4.30

pulse generatorelektor april 1984

T1,T2 = BSX 20T3 = 2N2219AT4 = 2N2905AD1,D2 = 1N4148D3 = flashing LEDD4 = LEDD5 . . . D11 = 1N4001

Potentiometers Er switches:P1 = 10 k lin. stereoP2 = 10 k presetP3 = 50 k lin.P4 = 1 k lin.S1,S5 = 12 -position,1 -pole, rotary switch

S2 = push-button, change-over contact

S3,S4,S7 -- single -polechange -over switch

S6 = double -pole mainsswitch

S8 = integral with jacksocket (see below)

Miscellaneous:

Trl = mains transformer,secondary 12 V/400 mA

Tr2 = mains transformer,secondary 24 V/400 mA

Fl = fuse. 500 mA, delayedaction

3 BNC round chassissockets panel mounting

1 jack socket with integralchange -over contact

2 heat sinks for IC11 and T3Vero case, 205 x 140 x75 mm, code 75-1411D

Printed circuit boards84037/1 and 84037/2

Front panel foil 84037/F

Figure 6. This front panellayout is available as aself-adhesive foil throughthe EPS service. It is, ofcourse, not essential forthe operation, butaesthetically right.

The circuit diagramAs we have already gone through manydetails in the description of the blockschematic, analysis of the circuit diagramin figure 3 will be quite brief.At the top left is the VCO, ICI, which ob-tains its drive voltage from IC12, a voltageregulator type 7805. At the top centre isthe chain of decade scalers, IC2 ... IC4,while the MMV, IC8, is located in the cen-tre of the diagram. Stepped adjustment ofthe pulse duration is effected by switchedcapacitors C4 ... C12. At the right of theMMV you see the three NAND gatesN2 ... N4 which, together with S3 enablethe switching between square -wave andrectangular -wave output. At the extremeright you'll find the EXOR gate N6 andpulse inverter switch S4, followed by theoutput stage consisting of T2 ... T4.At the bottom is the power supply com-plete with output voltage control (S7 andP4) and the input for the external controlvoltage (S8).The remaining parts of the circuit are er-ror detector FF2 with indicator LED D3,MANUAL push-button S2 with debounceflip-flop FF1, and the pre -amplifier for ex-ternal trigger signals consisting of Tl andNl.A note about the VCO: its pulse repetitionfrequency is controlled by a stereo poten-tiometer, P1, the two halves of which areconnected in opposition. This enables theVCO output to be adjusted over a range ofa decade, which would be impossiblewith a single potentiometer.The MMV is an IC type 74122 (NOT a74LS122!) which allows a duty factor of upto 100 per cent. As the pulse duration isvariable down to 0.1 µs, the 74LS122 wouldbe working at the limit of its capabilities.A few notes about the power supply. To

obviate cross -effects, the supplies to thevarious sections of the generator havebeen kept separate wherever possible. Forinstance, ICI has its own regulator, whilethe supply to the MMV is taken fromregulator IC9 by independent lines.The output stage has a separate supply,the voltage level of which may be ad-justed with P4 if ST is in position VAR; inposition TTL the supply voltage is fixed atabout 4.8 V. The level set by P4 is about1.25 V above that of the desired outputvoltage: this is so arranged to compensatefor the voltage losses in the output stage.The input socket for the external drivevoltages is provided with a change -overcontact, S8. As soon as a plug is insertedinto the socket, S8 opens, so that the ex-ternal voltage is applied to the centre ter-minal (c) of the socket. The output voltageof the generator is then identical to theexternal drive voltage plus the compen-sating voltage of 1.25 V.

The printed -circuit boardsThe generator uses two printed -circuitboards (figures 4 and 5) which, togetherwith the front panel, form a three-tiersandwich (see figures 7 and 8).The sections of the circuit diagram(figure 3) contained in dashed lines arelocated on the front pc board (figure 4),the remainder on that shown in figure 5.The latter is a double -sided board, so thatthe components side functions as a largeearth plane.With the exception of the three BNCsockets and the mains transformers, allcomponents, inclusive of the switches andthe potentiometers, are mounted directlyonto the boards. Switches S1 and S5 aresoldered onto the rear board (figure 5),whereas the remaining switches and the

6

ELEKTOR

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4-31

potentiometers are mounted onto theother board. Suitable holes have been pro-vided in the front board to allow thespindles of Si and S5 to pass through.Note that the screw thread of the switchesand potentiometers should not protrudemore than necessary (about 3 ... 4 mm) toprevent difficulties during the mounting ofthe front panel.A number of components have to besoldered at both sides of the rear board:this is in all locations where no isolatingislands have been provided in the copperat the component side.An extra hole has been drilled -beside pin8 of IC2 ... IC4: this serves to pass apiece of blank wire with which the twosides should be electrically connectedtogether.Keep the connections of the componentson the double -sided board free of theearth plane unless, of course, they shouldbe connected to earth.All points on the double -sided boardwhich are to be connected to the otherboard should be provided with pc halfpins; those for the transformer connec-tions are best fined at the track side. DONOT fit pc pins to the other board to pre-vent your running into difficulties duringthe final assembly.Voltage regulator IC11 must be mounted atthe track side of the double -sided boardwith its heat sink and spacers! (seefigure 8). Because of possible space pro-blems, it is best to fit C11 and C12 also atthe track side of the board.Make sure that the metal housing of P1and P3 is in good contact with the earthplane.Because of cooling requirements, mountR13 and R14 floating (about 5 mm) abovethe board.LEDs D3 and D4 must be mounted suchthat they can be pushed, housing and all,through the hole provided below the rele-vant terminals. If you use a normal insteadof a flashing LED, the wire bridge besideR7 (indicated by a resistor in dashedoutline) should be replaced by a 330 Qresistor.

CalibrationWhen both boards have been completed,they may be connected together as in-dicated. This is best done with lengths offlexible wire 3 ... 4 cm long. Do not yet fitICI ... IC8 into their sockets. Connect transformer Trl to the mains

and check on the boards that the ± 5 Vsupplies are available. If that is all right, connect Tr2 to the

mains, set S7 to VAR and checkwhether the generator output can be ad-justed between 2 and 16 V with P4. If that's also all right, measure the

voltage across C26 which should beabout 5 V. Next, insert ICI in the relevant socket

and check that a rectangular pulse ispresent at pin 8. Set P1 in position 0.1 andadjust the frequency to 10 MHz with trim-

mer C2. Turn PI to 1(CAL) and adjust thefrequency to 1 MHz with P2. Insert IC2 ... IC4 into their respective

sockets and measure the frequency atthe wiper of Sl. When this switch is turn-ed from position a to position g, the fre-quency should descend in decadic (-1O)steps from 1 MHz (a) to 1 Hz (g). Next, insert IC5 into its socket and set

SI to position h. The wiper of Sl shouldthen be logic low until S2 is pressedwhen the level should be 1. Then, insert IC8 into its socket and set

Si to position b and S5 to position a.Check at pin 4 whether the pulse widthcan be varied between 100 ns and 1µswith P3. With Sl in position c and S5 inposition b, it should be possible to varythe pulse width between 1µs and 10 piS.

Finally, insert IC6 and IC7 into theirrespective sockets. All settings should

now work as indicated on the front panel.If the pulse width is not in exact accor-dance with the stated values, it may bemade so by changing the value of therelevant capacitor, C4 ... C12. The largerthe capacitor, the longer the pulse width.

Final assemblyNote that the final assembly can be car-ried out in many different ways, but if youfollow our suggestions and guidance youshould not encounter any undue prob-lems.We have used a Vero box consisting of atop and bottom moulding in plastic withfront and rear aluminium panels which arepositively retained in the two halves.Bosses and guides are moulded into thecase for printed -circuit board mounting.Note, however, that a small part of the fourcorners of the board in figure 5 must befiled away at an angle of 45°

7

pulse generatorelektor april 1984

Figures 7 and 8. Thesephotographs illustrate thefinal assembly. The sizeof the printed -circuitboards was determinedby the Vero case used forour prototype.

4-32

8 pulse generatorelekior april 1984

The assembly is illustrated in figures 7 and8. Right at the front is, of course, the frontpanel; then follows the first pc boardbetween the bosses and first set ofguides, and finally the pc board offigure 5 in the guides. Make sure that thetrack side of the first board does notmake contact with the front panel and thatthe connections to the mains switch arewell insulated. As a further precaution,spray the back of the front panel with aproprietary insulating lacquer. To preventa short-circuit at the sync output plug,stick some insulating tape around the holein the front pc board (track side) providedfor that plug.The two mains transformers should be fit-ted in the lower half of the case and thefuse carrier in the rear panel. A suitablehole must be drilled in the rear panel formains cable entry.Since all potentiometers and switches aremounted on the pc boards, all that re-mains to be done is to drill suitable holesat the right location in the front panel.These holes should have a diameter slight-ly larger than that of the screw threads ofthe relevant component. The front pcboard may be used as a template.The components that are mounted on thefront panel itself are the three BNC inputand output sockets. Switch S8 is an in-tegral part of the external output voltage

9

control socket. This component is passedthrough the front pc board and then stuckto it with fast drying glue.To ensure adequate ventilation, drill anumber of holes in the top and bottom ofthe case (between the two pc boards), aswell as in the rear panel.Finally, attach the self-adhesive foil to thefront -panel, the layout of which is given infigure 6.

Figure 9. Although theuse of the pulsegenerator is described indetail elsewhere in thisissue, this photograph il-lustrates the capabilitiesof the generator. At thetop is the square waveavailable at the SYNCOUTPUT (TTL); under thisa signal with short pulsewidth, then a squarewave (S3 in positionSYM), and a signal with arelatively long pulsewidth. At the bottom theinverted mode of thesignal right above it (S4!).The horizontal scale is2 pis per division, the ver-tical one is 5 V perdivision.

4-33

using a pulse generatorelektor april 1984

Elsewhere in this issue we have described our pulse generator projectand dealt with all the constructional details. In this article, we willlook at some of the possible uses for, and the various functions of, apulse generator. We will, of course, concentrate on our own design,but the principles are the same for virtually all designs.

using a pulse generatorwith particularreference to theElektor pulsegenerator

Figure 1. If the output ofthe pulse generator isloaded with 50 0 thepulse shape will improve,but the output voltage isthen halved.

Figure 2. The resonantfrequency of an LC circuitcan be defined with theaid of this little circuit.

The name 'pulse generator' tends to con-jure up images of an instrument that isprimarily (if not entirely) intended for usewith digital circuits. It is, of course,perfectly suited to providing all sorts ofpulse shapes for digital circuits, but apartfrom this there are many more appli-cations that must be considered. In thisarticle we aim to give a few practicalexamples of these. as well as a fewgeneral observations about using a pulsegenerator. It should be noted, however,that some points are intended solely forthe Elektor design.

General (digital) useThe output impedance of the pulsegenerator (like most other generators) is50 Q. To get the optimum pulse form, thisoutput should be fed to a 50 i2 load. A50 cable should be used to connectgenerator and circuit, and the terminationat the circuit should, again, be 50 Q. If thisis not done there is a risk of degradationof the waveform by overshoot on thepulses. The difference is clearly visible infigure 1. The upper trace shows the output

2

85042-2

on-WascopeV -input

through a cable which does not have 50impedance, the lower trace shows thesame signal fed through the correct cable.In the second case the output amplitudeis halved, but this is to be expected whena 50 0 output is loaded with 50 Q. Actuallyfor most applications, the wave form willbe good enough without the 50 0 load.The pulse generator will often be used incombination with an oscilloscope, so theremay be a temptation to use anoscilloscope cable to connect the pulsegenerator to a circuit. We strongly adviseagainst this as the impedance of theoscilloscope probe cable is very high.This could cause problems particularly inTTL circuits because of the relatively'large' currents that can flow so that thelogic levels may not be reached.The output voltage of the Elektor pulsegenerator can be set to TTL level orswitched to another position where theoutput level is variable with a preset. Inthe TTL position the output is, of course,5V.For CMOS circuits that work at somevoltage other than 5 V. the pulseamplitude can be set to the correct levelby adjusting P4 -with reference to anoscilloscope. A special input has beenprovided to automatically adapt the outputvoltage to the supply level of the circuit:the External Output Voltage Control input.A special lead could be made up for thisinput, it will need a small plug (with theearth in the middle) at one end and twocrocodile clips at the other end for con-necting to the voltage supply of the cir-cuit. If this control input is used, theoutput voltage is automatically equal tothe supply voltage, irrespective of theposition of switch S7. The generator doesnot have to be terminated with 50 0 bothfor CMOS and TTL circuits as minimal dis-tortion of the square wave is not importanthere.The sync. output provides a square wavethat can be used to trigger anoscilloscope or to measure the frequencyof the output signal. This enables theoscilloscope to be properly triggeredwhile the 'real' output is kept free tosupply the 'measuring' pulses.

A few digital applicationsFor TTL and CMOS circuits the pulsegenerator can be used, among otherthings, for the following points:- Simply to provide pulses (such as clock

4.34

signals). Refer also to the photo in thearticle on the pulse generator.-To provide a single noise -free pulse (S1

in position MAN., S3 in position VAR.,and press 52 for each pulse). The pulsewidth of the output signal can be set be-tween 100 ns and 1 s.- Edge delay. A positive edge applied to

the trigger input will appear delayed atthe output if S1 is set to EXT., S3 to VAR..and S4 toll. The delay time can be setwith S5 and P3.This delay can, for example, be used asthe trigger delay for an oscilloscope.Assume we want to examine a videosignal. We then trigger the pulsegenerator with the vertical sync. Theoutput of the generator supplies the exter-nal trigger signal for the oscilloscope(which is switched to external triggering).The video signal is simply fed to the Y in-put. By varying the pulse width of thegenerator the whole of the video infor-mation can be shifted across the screen(the time -base of the oscilloscope couldbe set to 201.is/division for example).

Other possibilitiesThere are, of course, other non -digitaluses for the pulse generator:- Defining the resonant frequency of an

LC circuit (see figure 2). The sync.output of the generator supplies the exter-nal trigger signal for the oscilloscope. Thephoto in figure 3 shows what will bedisplayed on the screen. Given theperiod, T, of the oscillation, the resonantfrequency is easily found from fres = 1/T.Remember that the capacitance of theprobe is in parallel with the LC circuit andthis must be taken into account if thevalue of the capacitor is small.- Defining RC times (see figure 4). If the

input voltage is selected so that thevoltage swing of the output signal isexactly eight divisions (vertically), the RCtime is the time needed to rise from zeroto five divisions. The value of R mustalways be much larger than 50 9.-A fairly specific but interesting appli-

cation: testing the quality of a supply. Inthe example we give in figure 5, thesupply to be tested is alternately loadedwith 4.7 Q and 100 Q - with a 5 V supplythis gives currents of 1 A and 50 mArespectively. The pulse generator is usedhere to provide the switching signal forthe transistor. The stability of the outputimpedance can then be examined on theoscilloscope (figure 6). The upper traceshows the driving signal, and the secondtrace is the voltage across the load. Thelower trace in figure 6 shows how a 4701./Felectrolytic capacitor in parallel with theload cleans up the output. All that remainsis the voltage variation resulting from theoutput impedance of the supply (andleads). The impedance is then: Z =If the supply is not very stable someoscillations will remain visible every timethe load is changed.

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- The generator, of course, provides goodpulses with straight edges for testing

power amplifiers. The stability of theamplifier can then easily be establishedand the slew rate measured.There are many more applications for apulse generator that we have not men-tioned. The examples given here merelyserve to show that a pulse generator is amany-sided instrument.

using a pulse generatorelektor april 1984

Figure 3. This is whatappears on the oscillo-scope if the circuit fromfigure 2 is connected tothe generator. The uppertrace is the input signal,and the lower trace is theoutput oscillation of theLC circuit.

Figure 4. This is how RCtimes can be measured.

Figure 5. This circuit isused as an aid to examinethe quality of a supply. Itis used to alternately loadthe supply with 4.7 2 and100 Q.

Figure 6. When the circuitof figure 5 is connectedto the generator, this iswhat appears on theoscilloscope. The uppertrace shows the driversignal for the BD 139.Under this is the voltageacross the load; in thiscase the high frequencybehaviour is not verygood. Connecting a470 uF electrolytic acrossthe load improves thesituation, as the lowesttrace shows.

4-35

intelligent EPROM eraserelektor april 1984

intelligentEPROM eraserThe circuit described checks that during the erasure process,that is, when the EPROM is subject to ultraviolet (UV) ra-diation, even the last bit has been erased. As soonas this is so, the circuit arranges for the UVradiation to be continued for an ap-propriate period to ensure thatthe long-term stability of thenew data is guaranteed. In otherwords, erasing is only carriedout for as long as it is reallynecessary: no longer, noshorter. Furthermore, the circuitindicates whether the EPROM(new or used) is in goodworking order.

An intensity of radiation of12 000 µW/cm2 gives anenergy of 0.012 Jicrn2 everysecond, as 1 Joule) =1 Wlattlstecond). The requi-red dose (energy) is15 J.Icm2 and this will there-fore take 1510.012 seconds= 1250 seconds = 20 min.

50 sec.

SI

Erasure of EPROMs can be a confusingmatter: one manufacturer states an erasureperiod of ten minutes, the next one of acouple of hours. You might get the imnres-sion that the first gives short times oncommercial grounds, while the second isovercautious. This is, however, notnecessarily so: because of differences inmanufacturing and materials, there isbound to be divergence in erasure timesquoted by various manufacturers. Apartfrom all that, the erasure time is depen-dent upon the intensity of radiation, whichdecreases with age and wear of the UVlamp, and the distance of the erasewindow from the lamp. In the circuitshown in figure 1, the post -erasure time ofradiation has been fixed at three times theperiod necessary for the erasure of all thebits. It is possible to shorten the post -erasure time, but please read to the endof the article first.It may happen that an EPROM is defectand that consequently total erasure is im-possible: this is indicated by an LED inthe circuit.

Floating -gate EPROMThe most common type of EPROMnowadays is the floating -gate EPROM, inwhich the basic memory cell is a metal -oxide semiconductor which has two gate -electrodes separated by a layer of silicondioxide. The lower gate is entirely sur-rounded by oxide: it 'floats' in it, whencethe name. A charge can be placed on thefloating gate by applying a voltage of

The construction andassembly of a suitablehousing is trickier thanthat of the printed -circuitboard.

about 20 ... 25 V between the gate elec-trode and the drain while the substratematerial is held at a much lower voltage.Some electrons gain sufficient energy tocross the potential barrier of the insulatingsilicon dioxide and charge the floatinggate. Silicon dioxide is such an excellentinsulator that the charge, without externalinfluences, could be kept virtually forever,but most manufacturers guarantee aperiod of ten years. The charges can beremoved by exposure to UV radiationwhich causes the silicon dioxide tobecome sufficiently conductive to allowthe stored charges to leak away.As stated, a good -quality EPROM canretain its charges for many, many years,but this is, of course. only so if it is pro-grammed under suitable conditions.Suitable here means well -protected fromdaylight and UV radiation and an ambienttemperature not higher than 70°C.

Erase conditionsDuring erasure, the erase window of theEPROM is exposed to radiation from anUV lamp operating at a wavelength of0.2537 mm at a distance of 2 ... 3 cm. Atypical dose (energy) of UV radiation re-

quired with a 27xx EPROM is 15 J/cm2.The intensity of radiation is stated inpW/cm2: if this is, say, 12 0001.1W/cm2, theerasure time is 20.8 min. The time actuallyrequired may deviate substantially fromthis figure as explained before; EPROMmanufacturers are always at pains to pointto the decreasing intensity of the UV lamp

4-36

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IC3 and oscillator N3/N4,the measuring sectionwith up/down countersIC8/1C9 and oscillators N6and N7, the driver sectionwith N9 ... N14,T1 ... T3, D1, 02, andRe, and finally thesupply -voltage clockingsection with 1C11 and T4.

437

intelligent EPROM eraserelektor april 1984

Parts list

Resistors:

R1, R5 = 100 kR2,R6.R8,R10,R17 = 10 kR3 = 22 kR4 = 270 kR7,R9 = 220 kR11,R12,R13 = 47 kR14 = 820kR15 = 8k2R16 = 1k

Capacitors:

Cl = 100 pC2,C3 = 220 ir/10 Velectrolytic

C4 = 1000 14/16 Velectrolytic

C5 = 10 i.r/10 V electrolyticC6 = 22 p/16 V electrolyticC7 = 10 nC8 = 100 n

Semiconductors:T1,T2 = BC 56073 = BC 550T4 = BC 328D1 = LED, redD2 = LED, greenD4 . D7 = 1N40011C1,1C2 = 4040IC3 = 4068IC4 = 4011IC5 = 4093IC6,1C7 = 4001IC8,1C9 = 4516IC10 = 7805IC11 = 555

Miscellaneous:

Tr1 = mains transformer,secondary 8 . . . 9 V,500 mA

Fl = fuse, 500 mARe = relay, 5 V.a.c. contacts

La1 = UV lamp, 6 WSi = rotary switch,3 -pole, 5 -position

S2 = mains on/off switchS3 = push -to -make switch,lid -operated, spring -loaded

S4 = push-button switch,push -to -make,spring -loaded

S5 = push-button switch,push -to -make,spring -loaded

CaseIC socket, 24 or 28 pinFuse carrier, panelmounting type

Printed -circuit boardtype 84017

over its life.Furthermore, it should be noted that youcannot simply stop erasing when all thebits have become 'I, because both theerasure and the subsequent rechargingare temperature dependent. This cannotbe explained in a few words, so pleasetake our word for it. All manufacturerstherefore state a post -erasure time of threetimes the erasure time. A shorter post -erasure period may well suffice but, tocoin a phrase, prudence is the mother oflong-term stability.

The circuit diagramIf we now look at the circuit diagram(figure 1), we see that ICI and IC2 form anaddress counter. At the onset of operation,all outputs of these counters are logic '0',and the lowest address of the EPROM ischecked by IC3. This is an eight -inputNAND gate of which the output is invertedby Ni, so that the overall function is ANDAs soon as all data on the data bus of theEPROM are logic 1, the output of NI(pin 3) is also high. This opens gate N2which operates as a switch. The outputpulse of oscillator N3/N4 is then appliedto the clock input of ICI. Output QO of theaddress counter goes high and the nextaddress is checked by IC3 and Ni. If allthe bits of this are logic 1, the followingaddress is checked. And so it goes onuntil an address is reached which containsone or more logic zeros. The clock inputto the address counter is then disabled byN2 until the address contains nothing but1 s.A point to note: the sequence in whichthe store addresses are read is not thenatural ascending order of the binarynumbers as that would lead to many un-necessary bridges on the printed -circuitboard. In any case, it would have beenmeaningless, because, as there is no pro-gram being read, the order is irrelevant: itis only necessary that all addresses arebeing read.The checking process only comes to anend when all the addresses on theEPROM have been read a couple of times,that is, when output Q5 of the addresscounter is logic 1.Fortunately, the time required for thisdouble -security procedure is relativelyshort: when after the first reading of theaddresses all bits are '1', the few subse-quent check readings take only seconds.As soon as output Q5 of the addresscounter is 1, four things happen: output Q5 is inverted by N5 and stops

oscillator N3/N4; the inverted output Q5 disables

oscillator N7; output Q5 starts oscillator N6; test counter IC8/IC9 is switched from

upward to downward counting.Let us now have a closer look at themeasuring section. CMOS-ICs 8 and 9 arepresettable 4 -bit up/down binary counters,of which the direction of countingdepends upon the level at their U/D ter-minal (pin 10). The connection between

pin 7 of IC8 and pin 5 of IC9 combinesthe two circuits into a cascade counter.Both U/D outputs are connected to the in-verted output signal at Q5 of the addresscounter.Everything has now been switched overby the Q5 output signal. Gate N6 providesthe clock, and the counter is countingdownwards.As the clock frequency of oscillator N6 isonly about a third of that provided by N7,it takes three times as long for the counterto reach 0 again. Note that this factor isdetermined by the value of R4: eachkiloohm gives a post -erasure time of oneper cent of the erasure time. Thus, if R4 is10 k, the post -erasure period is one tenthof the erasure time.It now remains to ensure that the UV lampis switched off by the relay when thecounter reaches 0. This is, however, not assimple as it sounds, because how can adistinction be made between 0 at theonset of upward counting and reaching 0in the downward mode?The solution to that little problem takes usto the third functional pan of the circuit.The output (pin 3) of the NOR flip-flopconsisting of N9 and N10 is made logichigh by the reset switch at the start oferasure. A logic 1 at pin 1 will cause it tochange state. NOR gate NI2 provides thislevel when both its inputs are 0. Duringupward counting, line U/D is at high level,so that N12 retains its state. Duringdownward counting the output CO(carry out) is also logic low, but when thecounter jumps from 0 to -1, it emits ashort low-level pulse. And becauseline U/D is also at low level duringdownward counting, N12 gives a shorthigh-level pulse which causes flip-flop N9/N10 to change state, the relay isactuated, and the UV lamp is switched off.At the same time, the low level at pin 3 ofN10 causes driver transistor T2 to conductso that (green) LED D2 lights to indicatethat erasure has been completed. RedLED Dl indicates a defect EPROM or oneof which the erasure time is longer thanone hour. The control circuit for drivertransistor T1 is identical to that of the relayor that of D2, except that line U/D insteadof U/D is usecLSo far, so good. And then we discoveredduring the testing of the prototype that itdid not work! Certain bytes were beingset to 0 (sic!). So we took a couple ofbrand-new EPROMs and checked these inthe prototype. And lo and behold, we ap-peared to have stumbled upon a new wayof programming: with UV light! Fortunate-ly, the process cannot be controlled,otherwise we would immediately havelodged a patent application.We can assure you that this is not anApril Fool's Day hoax, nor are we gettingsoft in the brain. It seems, however, thatsolid-state physics plays tricks when thesupply voltage to the EPROM is leftswitched on continuously during erasure.Whether this is engendered by too highan operating temperature or by internal

4-38

2 intelligent EPROM eraserelektor april 1984

capacitances in the EPROM which arecharged by the supply voltage and in thatway cause programming pulses, we can-not be certain; it's probably a combinationof the two. We have, however, ascertainedthat the effect disappears when the supplyvoltage to the EPROM instead of con-tinuous is pulsed.This is effected by means of a switchingcircuit based on a type 555 timer-IC(11).The duty factor (width/period ratio) hasbeen fixed at 1: 100 by means of R14 andR15. The pulse duration is about 130 ms;the pulse spacing, about 13 s. In the caseof an erased EPROM, the total test cyclecan be run through a couple of timesduring one of these periods, because thefrequency of oscillator N3/N4 is highenough. In other words, the operation ofthe circuit as a whole is delayed veryslightly, but the erasing process hasbecome error -free.At the same time, we have taken the op-portunity to add switch 55. When this isclosed, the supply voltage is continuouslyconnected to the EPROM; we'll return tothis under `operation.

ConstructionIf you use the printed -circuit board shownin figure 2, the construction of the elec-tronics part of the eraser should not pre-sent too many difficulties. When it comesto the mechanical construction, however,things become a little trickier as may beevident from the drawing on the title page(note that this is given for illustrative pur-poses only!). The total height of the caseis dependent on several factors: themounted height of the board, that of theEPROM socket, and so on. In any case,with the lid closed, the UV lamp shouldbe about 2 ... 3 cm above the erasewindow of the EPROM. With the excep-tion of S3, all switches, the two LEDs, andthe fuse carrier (F1) should be fitted in thefront wall of the case. When choosing thecase, bear in mind that in addition to theabove, it also has to house the mainstransformer, and that it should be possibleto close it light -tight (UV light is harmful toyour eyes!).Switch S3 should be fitted such that it isclosed when the lid of the case is com-pletely shut, but always open otherwise.

Figure 2. The electronicpart of the EPROM eraseris easily built with theuse of the printed -circuitboard shown here.

pulse width = pulseduration

pulse spacing = pulse repe-tition period

4.39

intelligent EPROM eraserelektor april 1984

Figure 3. This part viewof the printed -circuitboard clearly shows theconnections of theEPROM selector switchS1 as well as the switchpositions for the varioustypes of EPROM.

3

S1

2

S1: 1=2716,25162 = 25323 = 2732, 27644 = 271285 = 27256*

27EPROM

005

11 y 94121 3i

* see text

8 4 017-3

As soon as the lid is even slightly open,and S3 therefore also, the relay cannot beactuated so that your eyes are protectedagainst UV light.The EPROM socket should be a 24 or28 pin type: this depends, of course, onthe types of EPROM likely to be used.The type of EPROM is selected by Si: asdrawn, the circuit is suitable for erasing2516, 2532, 2716, 2732, 2764 and 27128EPROMs. It may also be modified toenable erasing type 27256 EPROMs,although these are not yet freely available:Sl should then be a 3 -pole 5 -positionrotary switch and the pulse duration ofIC11 changed from 130 ms to 65 ms. Theswitch positions and wiring for the variousEPROMs are shown in figure 3.NOTE: the Texas TMS 2716, which needsadditional operating voltages, cannot beerased without a further modification. Ifthis, or similar, type of EPROM needs tobe erased, a switch should be connectedbetween the collector and emitter of T3.In this way, it will be possible to carry outerasure as stated in the Texas data sheetwith the aid of a watch or alarm clock.Make sure, however, that the mains supplyis switched off before you open the case,as S3 is inoperative!

OperationInsert the EPROM into its socket, selectthe type with Sl, close the lid, switch onthe mains with S2, press reset switch S4,and wait until D2 lights (there's no need tosit near the eraser for this).

Switch off the mains, open the lid, andremove the EPROM from the socket.Before taking it into use again, it is strong-ly recommended to let it cool off for atleast half an hour, as this is beneficial forthe long-term stability of the data.If Dl instead of D2 lights, do not throw theEPROM into the wastepaper basketstraight away. If it is a Texas type, repeatthe erasure by pressing the reset switchagain: Texas indicates a total erasure timeof two hours for many types. It maytherefore happen that after one hour notall bits have become logic 1; this will par-ticularly be so if the erase window is notsufficiently clean.Furthermore, check that the distance bet-ween the UV lamp and the EPROM is cor-rect, that the IN lamp is not past it, andthat the EPROM window is clean. If allthat is in order, you may safely throw theEPROM into the wastepaper basket.Apart from erasing used EPROMs, the unitmay also be used to check new ones. In-sert it into the socket, leave the lid andtherefore S3 open, switch on the mainssupply, and close S5 (check).Then press the reset switch briefly. Shortlyafterwards - even with the 27128 it onlytakes seconds - LED D2 lights to indicatethat the EPROM is blank. If not, you bettergo back to the dealer to change theEPROM. 14

4-40

elektor april 1984

7 -day timer/controller(April J983, page 4-42)It happens occasionally thatthe first minute of theday (00.00 . . . 00.01) lastsfor 1 min. 15 sec. If yourtimer suffers from this,replace the 47 pF capacitorin the C9 position by oneof 33 pF.

Tape timer(March 1984 - page 3-60)Note that the base resistorin figures 4a and 4b shouldread 100 k.The diode bridge in figure5 consists of diodes type1N4001.The caption of figure 5should be extended asfollows.... NiCd cells (c). Thesecells should be of thesintered type. The value ofcharging resistor Flv sin-tered type. The value ofcharging resistor Rv iscalculated from Rv = 50/capacity of cells in Ah(ohms).

4-41

elektor april 1984

The following pages contain themirror images of the track layout ofthe printed circuit beards (excludingdouble -plated ones as these are verytricky to make at home) relating toprojects featured in this issue toenable you to etch your own boards. To do this, you require: an

aerosol of 'ISOdraft' trans-parentizer (available from yourlocal drawing office suppliers;distributors for the UK: Cannon& Wrin), an ultraviolet lamp,etching sodium, ferric chloride,positive photo -sensitive boardmaterial (which can be eitherbought or home made by applyinga film of photo -copying lacquer tonormal board material). Wet the photo -sensitive (track)

side of the board thoroughlywith the transparent spray. Lay the layout cut from the

relevant page of this magazinewith its printed side onto the wetboard. Remove any air bubbles bycarefully 'ironing' the cut-out withsome tissue paper.

PC board pages

The whole can now be exposedto ultra -violet light. Use a glass

plate for holding the layout in placeonly for long exposure times, asnormally the spray ensures that thepaper sticks to the board. Bear inmind that normal plate glass (butnot crystal glass or perspex) absorbssome of the ultra -violet light so thatthe exposure time has to be in-creased slightly. The exposure time is dependent

upon the ultra -violet lamp used.the distance of the lamp from theboard, and the photo -sensitiveboard. If you use a 300 wattUV lamp at a distance of about40 cm from the board and a sheetof perspex, an exposure time of4 ... 8 minutes should normallybe sufficient. After exposure, remove the

layout sheet (which can beused again), and rinse the boardthoroughly under running water. After the photo -sensitive film

has been developed in sodiumlye (about 9 grammes of etching

cs1OOoo

CO

40tJte

0

0

4-42

elektor april 1984

A.Pf-84029

PC board pages

sodium to one litre of water), theboard can be etched in ferric chlo-ride (500 grammes of FeCl3 toone litre of water). Then rinse theboard (and your hands!) thoroughlyunder running water. Remove the photo -sensitive film

from the copper tracks withwire wool and drill the holes.

pulse generator 84037-184037-2

tt.

BB MOB IBMIIl Mel win map alm

O

II II II

Please note the pc boardsof the UHF video andaudio modulator (840291which were omitted fromthe March issue owing tolack of space. This monthwe have nor been able toinclude pc boards 84024-3and 84024-4 (real-timeanalyser); they are, how-ever, given in the article.

e.E0AEI

/1":_91,1

elektor april 1984

PC board pages

4-44

4

The prime objective of a microprocessor is to operate quickly.However, when the operation of a circuit (memory, input/output, etc)must be tested, it is preferable to be able to move slowly, step-by-step, in order to isolate and examine suspect occurrances. There isexpensive equipment available for this, of course, but our simulatorperforms the same task. Furthermore, our design has both a manualmode and a dynamic mode. A sequencer provides the Z80 signalswith the correct timing relationships, whether in continuous or step-by-step mode.

4101 '17 0 PS 0

. -

EP

Z80 CPU simulatorelektor april 1984

fig

Z80 CPU simulatorMicroprocessors, such as the 6502 andZ80, are often used in specific automationapplications other than computers. Theyare not suitable for programming in thelarge sense of the word, and they are verylimited as regards communicating with theoutside world, except in specific appli-cations. Two cases in point are thedarkroom computer (using a 6502) and thedigital polyphonic keyboard for a syn-thesizer (using a Z80). The operation ofsuch a device cannot be checked with an'interactive' monitor program as the soft-ware is ignorant of the environment sur-rounding it. That is why this CPU simulatorcame into being. It could be consideredas a sort of hard -wired monitor program,which is used to simulate (and check) theoperations normally carried out by theprocessor. Even thought our simulator wasdesigned for the Z80, it could, with somerestrictions, also help users of other CPUsby programming address and data lines.This applies particularly, of course, to thestep-by-step mode.

Generating the signalsThe polarising circuit for address linesA15 ... AO, with the corresponding logiclevels, is shown in figure la. All it is, infact, is an inverter, a LED, a switch and aresistor, per address line. Below this is ananalogue circuit for the data lines. Thistime the buffers are bi-directional, and thedirection of data transfer is determined byflip-flop N33/N34 which is controlled bySI.

When the data are placed on the bus bythe simulator, the LEDs indicate the logiclevels of switches S-DIL3. If, on the otherhand, the data are read from the bus, buf-fers N17 ... N24 are blocked, and thelogic levels come from the system bus.Looking closely at flip-flop N33/N34, wesee that N34 is also fed the RD signal sothat 'write' mode can only be selected -

when RD is inactive (Le. logic 'high'). Thisleads us to figure lb, which, as could beexpected, provides the WR, RD, MREQand IOREQ signals. This circuit consists oftwo sub -assemblies: at the left are the anti -bounce flip-flops to generate the signals,and at the right is the logic for combiningthe static and dynamic signals, and a cir-cuit for displaying and preventing errors.Notice that there is one line common toall the flip-flops, and if this is low itprevents all static operation. The true out-put of each flip-flop is then high and thecomplementary output is low.At the right, the same combination ofthree gates and an inverter is repeated foreach of the four control signals. Thesignals provided by the flip-flops, whichare manually controlled, and the dynamicsignals given by the simulator in real-timeare combined by AND gates N45 ... N48.Any prohibited configurations, such asWR and RD or MREQ and IOREQ activeat the same time, are prevented by ORgates N49 ... N52. The inverter and theNAND gate signal any errors that may bedetected. The pins indicated are, ofcourse, the numbers on the Elektor bus,and this should be taken into account ifthis simulator is used with another system.

P addresses,data, andcontrol signalsin either static(manual) ordynamic (real-time) mode.

4-45

Real-time cyclesThe circuit shown in figure 2 has twomodes of operation: continuous and step-by-step. In the latter case, it only producesone cycle at a time. The cycle in questionis one of the four cycles from figures 3and 4; reading or writing to memory or toa peripheral device. In the other mode itproduces the same cycles, but in anuninterrupted stream. The possibility alsoexists of introducing a WAIT signal duringeach cycle.The cycle generator is clocked by theastable multivibrator around inverters 1and 2, and this signal is also available inPHIEX form, the well-known Z80 time -base.The type of cycle selected is determinedby the user by means of changeoverswitches S3 and S4, which are connectedto flip-flops N1/N2 and N12/N13 respect-ively. The sequencer proper consists ofIC1, IC2, and gates N3 ... N7, N14, N15and inverter 5.The BCD counter, IC1, is fed the clocksignal (on pin 2) and it feeds the binary in-puts of BCD to decimal decoder IC2. Atleast one of the decimal outputs 1... 3 ofthe 74LS42 applied to N5 is logic low dur-ing the first counting cycle (see thediagram of figure 5, signals 3 ... 5). Thenthey all remain high until the start of thenext counting sequence. Thus we get abase signal equal to three clock pulses;when this in inverted by Nl4 it becomesMREQ, as long as S4 is in position 'MEM.If S4 is in the 'I/O' position, however, thesignal becomes IOREQ via N15.It is clear from figure 3 that the RD (read)signal of the Z80 occurs at the same timeas MREQ and IOREQ. The base signal wementioned a moment ago (the output ofN5) also controls gate N3 which gives theRD signal, provided S3 is in the correctposition.The WR (write) signal is slightly more in-volved than the rest. In fact, if WR co-incides with IOREQ, a clock cycle ap-pears after MREQ. Consequently, a parti-cular logic set-up is needed to generatethis signal. In order for the output of N4 tobe low, switch S3 must be the right pos-ition (to give a high at pin 9 of N4) andalso the output of N6 must be high. As thetiming diagram shows, this only occurs onthe one hand if IOREQ is active (WR co-incides with IOREQ) and on the otherhand when MREQ is active, but then onlyduring the last two clock cycles: output 1of IC2 is applied to N7 after inversion by IS,so that the first clock cycle is eliminated.The combination of gates N8 NIO areused for generating a WAIT signal. This isdone if ICI is stopped counting by takingpin 7 (PE) low during a read or writecycle.The other enable input of ICI, TE (pin 10),is taken high via R5 as long as S2 is not inthe step-by-step position. If this is thecase, however, TE is controlled by output9 (pin 11) of IC2. In other words, wheneverICI counts the tenth pulse in a sequenceoutput 9 of IC2 goes low and this stops

la

N1 ... NB = IC1 = 74LS240N9 ... N16= IC2 =74LS240N17 ... N24 = IC3 = 74LS240N25 ... N32 = IC4 =74LS240N33 ... N35 = IC5= 74LSI0N37 ... N40 = 2/3IC6 =74LSO4N41 ... N44 = IV = 74LS00N45 ... N48 = IC8 = 74LS08N49 ... N52 = IC9 = 74LS32N53 ... N56 = IC10 = 74LSO1N57 ... N59 = IC11 = 74LS10

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Z80 CPU simulatorelektor april 1984

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ICI from counting. Pressing Si resets IC1to zero and starts it counting again. This ishow we generate a single cycle at a timewithout affecting the tinting relationshipsbetween the signals. The length of timethat Sl is pressed is of little importance aslong as output 0 of IC2 is not used.

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Figure la. The simplestpart of the simulator isalso the most effective.The DIL (or other) microswitches allow the userhimself to select the logiclevels on the addresslines, and those on thedata lines in 'write' mode.The levels are indicatedby means of LEDs.

4-46

lb Z80 CPU simulatorelektor april 1984

5V

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Why simulate?A simulator is some device which allows areal function to be artificially represented.In our case it is a substitute for a CPU(which must then, of course, be removedfrom circuit). and it reproduces all its

signals, as we have seen. It is simply con-nected to the system's bus, and the supplyvoltages are also tapped from here. Ifthere is no bus, all the signals are wiredto a wire wrapping type IC socket andthis is mounted in the actual socket forthe CPU IC. The result is that, equipped

Figure lb. In manualmode switch S6 must beopen or the flip-flop willbe blocked. If you onlywant to use the circuit inthis mode, gatesN45 ... N48 are omitted.Then, of course. you haveto do without thedynamic mode of oper-ation obtained with theaid of the circuit offigure 2.

4-47

Z80 CPU simulatorelektor april 1984 2

5V iT4 IOREO

Figure 2. The signalgenerator consists mainlyof a clock (11/12), a se-quencer 11C1, IC2,N5 . . N7 and 15) and thecircuitry for switchingbetween access to thememory or to peripherals,and between reading andwriting (Ni . . N4,N12 ... N151.

STEP

51

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Figure 3. The timingdiagram for the read andwrite to memory cyclesshows a time lag be-tween the MREQ and WRsignals, and this issimulated by a particularcombination of logicelements.

Figure 4. The read andwrite to peripheralscycles representedsimultaneously herecannot appear togethereither in the Z80 or in thesimulator, which rejectsforbidden configurationsboth in static anddynamic mode.

Figure 5. The function ofthe sequencer is obviousfrom this timing diagram.Output 0 of IC2 is notused in order to preventthe length of time forwhich S1 is pressed fromaffecting the duration ofthe counting cycle.

5V

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with this simulator in place of the pro-cessor, a fairly complicated circuit such asthe polyphonic keyboard can easily bechecked with quite simple test equipmentwhich would be useless in other cir-cumstances (logic probe, multirneter,single or double trace oscilloscope, etc.).It is impossible to establish a universaltest protocol as this depends entirely onthe type of circuit and the tests that haveto be made. However, as the simulatorpossesses enough 'intelligence' to preventforbidden configurations, there is nodanger of this sort of problem.Even though we have so far avoided anymention of using this simulator for trouble-shooting processor systems other thanmicro computers, this simulator is, in fact,perfectly suited to checking memorycards, VDU cards, and so on.

4-48

The metronome featured in our November 1983 issue (page 11-48) canbe programmed to give two simultaneous pulse trains each witheight beats. If you find this inadequate for your requirements, wepresent an extension which will enable you to obtain one pulse trainwith sixteen beats. In addition, we will tell you how it is possible totime two or more instruments simultaneously.

metronome extensionelektor april 1984

metronome extensionvariations in tick -tack

The first requirement is met by a smalllogic circuit with which all sixteenswitches (Sla S8a and Slb S8b) are'scanned' alternately. This circuit consistsof IC6 and IC7. An integral flip-flop in IC6has its clock input (pin 3) connected tothe 'carry -out' output (pin 12) of IC1. As themetronome printed -circuit board has noprovision for this connection, it has to bemade by means of a short length of circuitwire. The flip-flop ensures that after thefirst eight steps output Q, and after thenext eight steps, 0, becomes logic 1. Theoutput state (pins 1 and 2) of IC6 is com-municated to pin 5 of NAND gate NIO andpin 1 of NAND gate N9 respectively. Theother input of these gates is connected toterminals Q and S on the metronomeprinted -circuit board respectively.When pin 2 of IC6 is high, gate N9 passesthe output information of gate N2; whenpin 1 is high, the output of N4 becomesavailable at pin 4 of gate NIO. So, irrespec-tive of whether Q or 0 is low, there isalways a logic 1 at one of the inputs ofNAND gate N11. As the two inputs of thisgate can never be low simultaneously, ourlogic circuit produces a previously pro-grammed 'tick' sixteen times in succes-sion.The sixteen 'ticks' are used to drive afilter without N11, the output sound duringthe first eight 'ticks' would be differentfrom that produced during the next eight'ticks'. This means that the output of NII isconnected to either terminal T or terminalR on the metronome printed -circuit board.DO NOT FORGET TO REMOVE THEWIRE BRIDGE BETWEEN S and T AND Qand R!

More 'tick' and 'tack'The original metronome is intended forone or two instruments. It is possible toextend the circuit 'downward' by addingmore metronome printed -circuit boardsfrom which ICI and associated com-ponents have been omitted. The switchesare then controlled by the inputs fromdata lines QO ... Q7. These additionalprinted -circuit boards may also be pro-vided with the extension for sixteen beats.The filter is then omitted and the board,including extension, is connected to theredundant band-pass filter (IC4 or IC5) onthe original metronome board. The func-tion of switch S9 (selection of time -signatures) is retained at all times.

1

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As already mentioned in the Novemberarticle, the tone and timbre of the per-cussive sounds may be altered to in-dividual requirements. It is even more in-teresting to connect the output to the trig-ger input of a synthesizer instead of to afilter: the sound nuances are then almostunlimited. 14

Literature:Drum Interface, Elektor, November 1982,page 11-20.

4

FF1 *i1C6 = 4013N9... N11 = iiIC7 4011

JUL

O1OIC7

000

mimO44.itS 1

Figure 1. This simpleextension circuit enablesthe production of sixteenbeats instead of twotimes eight as in theoriginal metronome. Ifmore metronome boardsare connected together, itmay be necessary toenlarge the power supply.

4-49

real-time analyserelektor april 1984

Last month we started this real-time analyser project and describedthe printed circuit boards for the input amplifier and filters. Thismonth we have a couple of bigger boards, the base board, whichserves as a mother board for all the others, and the display boardcontaining the complete read-out section (LEDs plus electronics).With these two boards the analyser is effectively finished, except forone or two refinements.

read -tire analyserbase board anddisplay board

(parr -1 2)

The two sections we will describe in thisarticle are not only physically large, theyare also very important within the totalconcept of the real-time analyser. As wespent a lot of last months's article describ-ing the layout of the project, we will skipit this time and just get on with thetechnical side of the two boards.

The base boardFor once. it will probably be easier tounderstand this circuit if we first look atthe printed circuit board and then exam-ine the circuits that are fitted to it. Theboard is shown in figure 3, but this is notthe actual size as it is, in fact, slightlylarger than one of our pages. This boardserves as the 'mother board' for the sevenothers, and contains a separate supply forthe read-out and the thirty active rectifiersfor the filters.The circuit diagram does not show verymuch, and there is a good reason for this.As the board contains thirty identical ac-tive rectifiers, it would be an unnecessarycomplication to indicate more than one of

these and the power supply.Each rectifier is built up around an op -amp with a diode in its feedback path.This combination behaves as an 'idealdiode' with no threshold voltage. This'diode' half -wave rectifies the filter signal.The feedback to the op -amp travels viathe wiper of PI to enable the amplificationto be adjusted. The relationship betweenPI and R2 is chosen so that the con-trollable range is about 10 dB. Somemeans of adjustment is necessary to pro-vide compensation for voltage differencesbetween the filters due to componenttolerances and the open -loop bandwidthof the op -amps used.The active rectifier is followed by aresistor and an electrolytic capacitor. Thiscapacitor, which is charged via R1 anddischarged via RI, P1 and R2, forms a'memory' for the rectifier to keep themeasured voltage displayed for a shorttime (it has a short charging cycle andlonger discharging cycle). The chargingtime is trimmed to the centre frequency ofeach filter, which means that the charging

4

4-50

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resistor has a different value in each rec-tifier (for the first rectifier it is R1). Thecomponent numbering for all the rectifiersis given in the table in figure 1. Thedischarging resistance (P1 + R2) is thesame for all rectifiers. Because the charg-ing resistance is in series with P1 and R2during discharging, the discharging timeis slightly longer for the lower filters thanfor the higher ones.With the component values stated, thecharging time is a compromise betweenpeak and average value measuring. Thiswas intentionally done to enable theanalyser to measure both music and noisesignals. The read-out gives approximatelythe peak values of a music signal,

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840242-1

Figure 1. The circuit ofthe rectifiers and thesupply, which are con-tained on the base board.The component number-ing of the thirty rectifiersis given in the table.

4-51

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whereas if pink noise is used the averagevalue of the measured voltages is shownto prevent the display from continuallyjumping.The charging time can also be modifiedto suit any particular needs. If the real-time analyser is only to be used to exam-ine audio signals, the rectifiers can beconverted into peak meters by reducingthe values of the odd -numbered (charg-ing) resistors, R1 ... R59, by a factor of 10.For purely noise applications, the read-outcan be made somewhat 'darner' by givingall the odd numbered resistors values of220 ...470 k.The power supply here is identical to thaton the input board, except that theregulators used here are 8 V types andthe voltage supplied from the transformeris 10 V a.c. It should be noted that thispower supply is not required if the real-time analyser is to be used with the videodisplay that will be published (hopefully)next month. The LED display is then, ofcourse, also superfluous.The way in which the various boards arefitted together is shown in figure 5. Thisrequires some clarification, but that issomething we will get around to in duecourse.

The LED displayCompared to the base board, the circuitfor the display section seems very full.That is not really surprising consideringthat 30 LED columns are needed todisplay the output voltages of all 30 filters.The most obvious part of the circuit is the11 x 30 LED matrix. In last month's articlewe went into the reason for using all theseLEDs and, in practice, both the dimen-sions and the price of this 'discrete'display seem quite reasonable.Quite a large multiplexer system isneeded to switch all these LEDs. First wehave the 16 -to -1 line multiplexers, IC1 andIC2, which are connected 'in series' sothat all thirty outputs from the rectifiersare connected in turn to the read-out.Each multiplexer has one unused outputand they are both clocked by the signalfrom IC5. This counter/oscillator providesthe control signals for the channel selectinputs, A, B, C, D and E (enable). The Esignal to IC1 is inverted by EXOR gate N12so that only one of the two multiplexers isenabled at a time. The timing componentsaround IC5 (R53, R54 and C4) ensure thateach channel of the multiplexers isselected for 0.2 rns.The LED columns are multiplexed via1 -to -16 line decoders IC3 and IC4. The ad-dress inputs, AO ... A3, and enable inputsE of both ICs are connected to outputsQ3 ... Q7 of the 4060 (E of IC3 via N12).The operation of this circuit should nowbe fairly clear. Whenever a particular filteroutput is selected via the multiplexers, theLED column corresponding to this filter isactivated by taking the appropriate output(QO ... Q14) low. The multiplexers anddecoders therefore keep the thirty filtersand the LED columns synchronized.

Because of the large number of LEDcolumns that must be multiplexed. thepeak current flowing through each LED isvery high: about 300 mA! The average cur-rent per LED is about 10 mA. Using a suit-able type of LED and keeping the multi-plex frequency high makes this possiblewithout adversely affecting the lifespan ofthe LEDs. Because of the large currents,the outputs of the decoders feed into dar-lington.s, T12 ... T41, and the actual currentis defined by the value of resistorsR23 ... R52.As we have implied, the type of LED usedis very important and there are relativelyfew LEDs that can handle such a highpeak current. Mostly they are normal redLEDs. Other colours may not be used.High efficiency LEDs are also out; their -

maximum permitted current is50 ... 100 mA which is much too low. Themoral of this is to look for LEDs that havea peak curent of 1 A.The outputs of the multiplexers, which areconnected together, are followed by acomparator circuit built up aroundAl ... Al2. The inverting inputs of the op -amps are connected to a precise voltagedivider (R2 ... R14). This divider is fed a5 V reference level from voltage regulatorIC9. The non -inverting inputs of the op -amps are all connected to the outputs ofthe multiplexers. If the input signal (whichis to be measured) at the non -inverting in-put is greater than the voltage on the in-verting input, the output of the op -ampwill go high. The values in the voltagedivider are selected such that the com-parison occurs in steps of 1 dB, while avoltage of 0.5 V is taken as an internal0 dB level. The LED rows are driven bythe op -amps via EXORs N1 ... N11 anddarlingtons T1 ... T11. The EXORs ensurethat only one LED, per column, lights at atime, the idea being to keep the currentconsumption within reasonable limits.If the signals offered to the display areoutside its range, one of two auxiliaryLEDs will light. Darlington T42 switches

4.53

real-time analyserelektor april 1984 3

Figure 3. The base boardis shown here, but.because it is very big, itis not given full size.

S -61

on LED D1 if the signal is 'above' thedisplay. and D3 lights via T43 if the signalis 'below' the display or if there is nosignal at all present. A capacitor and adiode are included in each case to keepthe LED lit long enough for it to be seen.The resolution of the display can beswitched to a coarser range by means ofSI. Flipping this switch places an extraresistor in parallel with the upper andlower resistors in the divider chain. Therange is then from +3 to -20 dB insteadof --2 to -8 dB. When reading the display

it is important to remember that the LEDslight to indicate that the input voltage levelis within a certain range, not that thevoltage is above the nominal valuerepresented by the LED. If, for example, a-2 dB LED lights it means that the inputvoltaae is between -2.5 and -1.5 dB. Inthe other switch position. the -7 dB LEDhandles the range of -6 ... -8 dB.

ConstructionAssembling these two printed circuit

4-54

real-time analyserelektor april 1984

boards is a very straightforward process.The base board, as we have said, containsthe supply section and the thirty rectifiers.The two voltage regulators must bemounted on a heat sink. Soldering pins(veropins) should be fitted where theother boards are to be mounted (with theexception of the display board). Thewiper of each preset should now be ro-tated to the limit on the 'diode side.All the components, except for the LEDsand resistors R23 ... R52. can be solderedin place without further ado. Only after

this is finished should the LEDs be fitted.These should be mounted a row (30 LEDs)at a time. Care taken now to line the LEDsup correctly will pay dividends later whenthe completed display is something to beproud of. Finally, resistors R23 ... R52 aresoldered on the reverse side of the board.Each resistor is soldered vertically and isconnected to the pin of the last LED inthe row.Provision has been made for mounting therange changeover switch on the board,but this is only feasible if it has a long

Parts list:-Base board 18402441

Resistors:

RI = 100kR3 = 68 kR5 = 56 kR7 = 47 kR9 = 39kR11 = 27 kR13 = 22 kR15 = 18 kR17 = 15 kR19 = 12 kR21 = 10 kR23 = 6k8R25 = 5k6R27 = 4k7R29 = 3k9R31 = 2k7R33 = 2k2R35 = 1k8R37 = 1k5R39 = 1k2R41 = 1 kR43 = 680 QR45 = 560R47 = 470 QR49 = 390 QR51 = 270 QR53 = 220 QR55 = 180 QR57 = 150 QR59 = 120 QR2, R4, R6, etc., R60= 30 x 220 k

P1 . . P30 +500 k preset

Capacitors:

CI . C30 = 4u7/10 Vtantalum

C31 . C38, C41, C42 =100 n

C39. C40 = 220011/25 VC43 = 10011/25 V

Semiconductors:D1 . D30 = 1N4148D31 . . D34 = 1N4001ICI . IC8 = TL084IC9 = 7808IC10 = 7908

Miscellaneous:

2 Heatsinks for IC9 andIC10, 10°C/W

4-55

real-time analyserelektor april 1984 4

Parts list:

-Display board (84024-31

Resistors:

R1 = 64k9 1%R2 = 34k8 1%R3 = 576 Q 1%R4 = 523 Q 1%R5 = 464 2 1%R6 = 4122 1%R7 = 365 2 1%R8 = 324 Q 1%R9 = 287 Q 1%R10 = 261 Q 1%R11 = 232Q1%R12 = 205 Q 1%R13 = 182 Q 1%R14 = 1k5 1%R15 = 215 2 1%R16. R17, R20 = 1MR18, R21 = 10 MR19,R22=5602R23 . . R52 = 33R53 = 270 kR54 = 27 k

Capacitors:

CI, C5 ... C8 = 100nC2, C3 = 22 nC4 = 330 p

Semiconductors:

DI, 03 = LED, 3 mm redD2, D4 = 1N4148330 un-numbered LEDs, red3 mm le.g. COY 85N8)'

T1 T11. T42 = BC5I7112 ... T41, T43 = BC 516ICI, IC2 = 4067BIC3, IC4 = 4515BIC5 = 4060BIC6 . IC8 = 4070BIC9 = 78L05IC10 ... 1C12 = TL084

Miscellaneous:

Sta. Sib = double polechangeover switch

'see text

Figure 4. The displayboard is double -sidedwith through -platedholes. The finished ap-pearance is greatly im-proved by ensuring thatthe LEDs are all in line.Resistors R23 ... R52 aremounted on the reverseside of the board, withone lead of each resistorsoldered directly to therelevant LED column.There is no separate holeon the board for this, asspace on the board,which is shown here inreduced size, is at apremium.

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operating spindle. Otherwise it is better tomount this switch directly on the frontpanel.

Assembly and testingThe positions and orientations of thevarious boards relative to the base boardare indicated in figure 5. If you have beenpaying attention up to now the connection

points for the pink noise board, the inputboard and the filter boards should havesolder pins. Similarly, the connectionpoints on each board should have solderpins. The input board is the first to beconnected to the base board, with thecomponent side facing the power supplyon the mother board. This simply involvessoldering the veropins together. The con-nections to the transformer can now bemade; two 15 1.,,v lines and earth to the in -

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4 -56

5 real-time analyserelektor april 1984

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put board, and two 10 Vti lines and earthto the appropiate points on the baseboard. The supplies can now be checked.When the mains has been switched onthere should be + and -12 V at the +and - points on the input board. Thesupply connections for the display boardmust have + and -8 V with respect to the0 V on the base board.If everything is correct so far, the powercan be switched off and we can continuewith mounting the filter boards. Theseshould already be numbered, with thelowest filters on board I and the higheston board IV. Note that the componentside of boards I and III face towards theinput board, whereas the track side ofboards II and IV face this board.Finally, the display board must be con-nected. It is a good idea to make this linkwith a sufficient length of cable (andpossibly a connector) to facilliate accessto the back of the display. You will prob-ably be grateful for this later. Rememberthat there are two supply connections atthe left side of the board.The analyser is now finished, except forone 'extra' - namely the pink noisegenerator -, so we can now actually 'fireit up' and see if it works. The twoswitches and the potentiometer must beconnected to the input board. With SI we

select 'line, S2 is in the +10 dBm position,and the power cart then be switched on. -

If the whole circuit is working, a largenumber of LEDs should light and slowlydrop out of sight below the display. Con-necting a sine wave generator to the lineinput and running through the frequencyrange will verify the operation of all theLEDs. Select an appropiate frequency foreach filter in turn and vary the inputvoltage to check that each LED lights. Inprinciple, the rectifiers can now be ad-justed by feeding a 0.775 V a.c. signalto the input (S2 at 0 dBm) at the centre fre-quency of some filter and then setting theappropriate rectifier so that the 0 dB LEDis lit. Not everybody can get their handson a sine wave generator, however, so wewill leave this subject of adjustment untilnext month. Then we will have the pinknoise generator, and we can deal with ad-justment in detail.The important thing is that the analysernow functions. To try it out, you can feeda music signal, from a radio, for example,into the input and look at what the displayshows. Even though it is not yet accurate,you can already get quite a good idea ofthe frequency content of various audiosignals. However, to expand this to seriousmeasurements, you will have to be patientfor one more month. 14

Figure 5. Here we seehow the various boardsare mounted onto thebase board.

4-57

a.c. Dower supplyelektor april 1984

a.c.alternatingcurrent withbuilt-inprotection

power supplyJust for a change, this is a power supply that provides not d.c. buta.c. voltages. The most important characteristic of the circuit is itsadjustable current limiting. If the current exceeds a preset value, thepower is instantaneously switched off. That makes the circuit a veryuseful aid for trying out newly built or repaired circuits. It is designedto reduce the anxiety symptoms that often appear just before youplug in some circuit.

This circuit was actually designedbecause we wanted it ourselves. It oftenhappens when trying out a new circuitthat not everything is exactly as it shouldbe. This results in high-speed changing ofblown fuses, always assuming of coursethat the correct fuses are to hand. In-evitably, Murphy has a part to play, andthere is nothing more annoying than beingsnookered by something as trifling (butessential) as a fuse. Also, it doesn't doyour technical self-exteem any good tokeep blowing fuses.There comes a point where this simplygets to be too much, so it's on with thethinking cap to come up with a design foran a.c. power supply with adjustable cur-rent limiting. It then takes the place of thesupply transformer in the new (or justrepaired) circuit, and the first tests can bedone with a voltage lower than the

nominal circuit voltage. If there issomething wrong and the current tries toexceed the maximum desired level, thesupply automatically switches off. Theproblem can now be sought at leisurewithout any risk of permanent damage.

The circuitAs we have already said, this circuit wasborn of a purely practical need. Westarted with a transformer with a largenumber of secondary tappings (figure 1).The output voltage is changed in steps of3 V by means of S3. It is, of course, yourprerogative to use a transformer with dif-ferent voltages if you wish. The currentsupplied by the transformer flows throughRI via the rectifier, with the result that apulsed d.c. voltage is seen across thisresistor. This d.c. voltage, which is pro -

4 -58

portional to the value of the a.c. current,serves as the driver voltage for the currentlimiting circuit.The lower part of the circuit is the currentlimiting, and this has to be powered froma separate transformer. Failing to do thiscould cause problems when the a.c. isconnected to the protection circuit. Theprotection circuit itself is very simple. Avoltage regulator (IC2) is followed by acomparator circuit which compares thevoltage across RI to a voltage set with PIand P2. The maximum value of currentlimiting is set with preset Pl. Dependingon the transformer used, this will normallybe adjustable between 2.7 and 5.4 A(Irms = 1.9 ... 3.8 A). This value can thenbe further adjusted so that the actualrange of values for current limiting is0.27 ... 5.4 A (peak value) or 0.2 ... 3.8 A(rms value). Short noise pulses are nodanger to transformer, circuit, or fuse soC3 prevents the current limiting from oc-curing under these conditions.As soon as the maximum (set) value ofcurrent is reached, the output of the com-parator flips. A pulse is then fed via R6and R7 to the gate of thyristor Thl, whichfires and powers the relay. The relay nowcuts off the primary winding oftransformer Trl, and LED D6 lights to in-

dicate that current limiting has takenplace.Once a thyristor is caused to conduct itcontinues to do so after the gate pulse haspassed, which means that the only way to'reset' the circuit is to press Si. Before do-ing this it is wise to try to find the reasonfor the problem, and also set the currentlimiting to a different value if necessary.

ConstructionBuilding this a.c. power supply should notcause any problems. Most of the time willprobably be involved in the 'mechanical'work: housing the supply transformers ina case, making a front panel with connec-tors, switch, and indicator LEDs, andfinishing the whole unit off. The printedcircuit board for this project is shown infigure 2. The left side of the componentlayout shows the input and output for thesupply, and these are connected respect-ively to the ground of Trl and one of theconnectors on the front panel. Thesepoints can, of course, be freely inter-changed. The cathode (k) connection forthe 'power' LED (D7) is also clearly visible.The anode connection for this LED istapped off the 3 V winding of Trl. If a dif-ferent transformer is used, the currentlimiting resistor (R8 ti U/0.04) will have to

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84035-1

a.c. power supplyelektor april 1984

Figure 1. Most of the cir-cuit for the a.c. powersupply shown here isused for the currentlimiting.

4-59

a.c. power supplyelektor april 1984

Figure 2. The printed cir-cuit board layout andcomponent overlay forthe circuit are shownhere.

Figure 3. This is how thecircuit looks when it is allput together.

Parts list

Resistors:

RI = 0.22 QI5 W or 2 x0.47 Q/3 W in parallel

R2 = 100 kR3,R9 = 1 kR4,R7 = 10 kR5 = 1MR6 = 47 kR8 -= 82QP1 = 100 k presetP2 = 10 k fin. pot.

Capacitors:C1 = 470 p/25 VC2 = 220 nC3 = 100 n

Semiconductors:D1 ... D4 = 1N4001D5 = 1N4148D6 = LED, redD7 = LED, green81 = bridge rectifier, siliconin line 80 V at 5.0/3.3 Ae.g. 88005000/3300(available from Gemotronikl

IC1 = 3140IC2 = 7812Th1 = TIC 106

Switches:Si = push to break pushbutton

S2 = double pole mainsswitch

S3 = single pole six waywafer switch, must berated 5 A

Miscellaneous:

Trl = transformer, 60 VA,secondary = 3 V, 6 V.9 V. 12 V, 15 V. 18 V

Tr2 = transformer,15 V/100 mA

Fl = fuse. 500 mA slowblow

Rel = relay, 12 V/8 A(Maplin order no. HY2OWI

Figure 4. When we testthe power supply withthe aid of anoscilloscope, we see howthe current limiting cir-cuit trips if the currentexceeds a pre -determinedvalue.

4

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be changed. If the voltage is higher than3 V it is also a good idea to connect anordinary silicon diode in series with D7,as a protective measure.The relay contact (points X and of Relis connected in series with the primary oftransformer Trl (so there are mainsvoltages on the printed circuit board!).

also cutoff the primary of Tr2 when it operates.The voltage regulator (ICI) andthyristor (Thl) do not need to be mountedon heat sinks as they are not likely to getvery warm in this circuit.A final note: problems can be caused withthis kind of (experimenting) supply circuitwhen connecting to the earth line of sometypes of equipment. The best thing to do,therefore, is to house this supply in ametal case and connect the mains earth tothe case, but do not connect it to eitherthe a.c. supply section or the protectioncircuit.

4-60

It may seem somewhat unusual, now thatthe Junior Computer has its own floppydisk interface, to publish a program forthe cassette interface. Even though manyJunior users do have a DOS on their com-puter there are still others who only usecassettes. And then there are even somewho use both systems in parallel, but notwithout the occasional eloquent excla-mation about the difficulty of remember-ing the exact contents of all the cassettes.This program, like some of our other re-cent software offerings (especially lastmonth's GET & GO), is a modification of anexisting program (certain TM and PMroutines) to achieve something new onyour familiar computer. It makes a com-plete list of all the identification numbers(ID), complete with start and finish ad-dresses, of all the files stored on acassette. Each search operation alsodoubles as a systematic check of the datain a file.To run the program, simply load it andstart it at address 50200. Load a cassetteinto the player and press some key on thekeyboard ... and wait for IDList to displaythe information you require and signal anypossible incorrect data.Stopping IDList in the course of a run issimply a matter of pressing 'BREAK', andthen, to restart it, pressing 'R'.

Familiar labels

Once again we plead lack of space as anexcuse for not providing a completesource listing for this program. The hex -dump in table 1 contains all the software,including messages and the author's

IDList

elektor april 1984

The more you use your personal computer, thegreater the number of filled cassettes youaccumulate, and only by keeping a detailed cataloguecan you hope to keep track of anything.Unfortunately there are few people, even amongmicro computer users, who have the patient,meticulous soul of a librarian.What you need is a program which likes nothingbetter than sorting out the tangled mess of data on acassette. And if this program just happened to checkthe data at the same time your proverbial cup wouldbe running over.

IDListsignature (starting at S0369). The S77 foundat 50368 and S03FB is an end -of -file in-dicator. The main part of the program con-tains a lot of instructions borrowed fromRDTAPE, as TM users will undoubtedlysee. For those who may be interested indisassembling this program, here is a listof the labels used. Even though some ofthem are not used in TM, they do not re-quire any explanation. 0200: START 0203:RESET 0206: BRKTST 022A: INIT 0247:RDTAPE (see the source listing of TapeMonitor) 0310: IDSA 032D: SUMERR 033B:CORDAT 0349: MESSB 0357: MESSEND0358: CLS 0362: CLSA.

0 1 2 3 4 5 6 7 8 9ABCDEF0200: 4C 2A 02 20 BC 14 2C 80 lA 10 FB A2 FF 9A 86 F20210: AO 80 20 49 03 A9 5F 8D 7C lA A9 10 8D 7D lA A90220: 02 85 FB A9 00 85 FA 4C 6A 10 A9 03 8D 7C lA A90230: 02 8D 7D IA 20 58 03 EA EA EA A0 00 20 49 03 200240: AE 12 AO 48 20 49 03 A9 32 8D 82 1A 8D 78 lA A90250: 7E 8D 83 lA A9 7F 8D 81 lA A9 00 8D 6E lA 8D 6F0260: IA A9 FF 8D 6B lA 2C 80 IA 10 61 20 C2 OB 6E 6B0270: lA AD 6B IA 20 E8 OB C9 16 DO EB A0 0A 8C 69 lA0280: 2C 80 lA 10 47 20 36 0C 20 5D OC C9 16 DO D2 CE0290: 69 IA DO EC 2C 80 IA 10 33 20 36 OC 20 5D OC C902A0: 2A FO 07 C9 16 FO ED 4C 47 02 20 5D OC 20 F3 0B02B0: 8D 79 lA 20 F3 08 20 4B OC 85 FA 8D 70 IA 20 F302C0: OB 20 4B C 85 FB 8D 71 IA 4C CF 02 4C 03 02 2C02D0: 80 1A 10 F8 20 F3 OB 30 62 FO OF 20 4B 0C E6 FA02E0: DO 02 E6 FB 20 64 OC 4C CF 02 20 F3 OB CD 6E lA02F0: DO 3B 20 F3 OB CD 6F IA DO 33 20 BC 14 20 10 030300: A5 FB 20 8F 12 AS FA 20 8F 12 20 E8 11 4C 47 020310: AD 79 lA 20 8F 12 AO 8A 20 49 03 AD 71 lA 20 8F0320: 12 AD 70 IA 20 8F 12 AO 8E 20 49 03 60 20 BC 140330: 20 10 03 AO 5E 20 49 03 4C 47 02 20 BC 14 20 100340: 03 AO 6F 20 49 03 4C 47 02 B9 69 03 C9 03 FO 070350: 20 34 13 C8 4C 49 03 60 A9 0C 20 34 13 A9 84 8D0360: F7 1A 2C D5 IA 10 FB 60 77 22 49 44 4C 49 53 540370: 22 0D OA 42 59 20 50 41 55 4C 20 53 20 4A 45 4E380: 4B 49 4E 53 20 20 OD OA 54 55 52 4E 20 4F 4E 200390: 54 41 50 45 20 28 50 4C 41 59 29 20 41 4E 44 2003A0: 50 52 45 53 53 20 41 4E 59 20 4C 45 54 54 45 5203B0: 03 OD 20 OD OA 49 44 20 20 20 53 54 41 52 54 2003C0: 20 45 4E 44 0D OA 03 43 48 45 43 4B 53 55 4D 2003D0: 45 52 52 4F 52 OD OA 03 43 4F 52 52 55 50 54 4503E0: 44 20 44 41 54 41 OD 0A 03 OD OA 42 52 45 41 4803FO: OD OA 03 20 3A 20 3 20 2D 20 03 77 2C

gives the JuniorComputer anautomaticsearchprocedure tolocateidentificationnumbersmagnetic tape

R Jenkins

Table 1. This is the hex -dump for IDList thatshould be loaded at $0200.It not only shows theidentification numbers.start and end addressesof the files on the tape.but also checks the dataand signals for any poss-ible differences from thecheck -sum (CHKL/CHKH:$1A6E/1A6F).

4-61

Please note that the following ICs may notyet be commercially available. They aregiven here to keep you abreast ofdevelopments.

infra -red remote -controlpreamplifier type XL 486(Plessey Semiconductors Limited)The XL 486 has been designed to form an inter-face between an infra -red receiving diode andthe digital input of remote -control receivingcircuits. It contains an output pulse stretcherfor use with microprocessor decoders.

FeaturesIII Fast -acting automatic gain control (a.g.c.) to

improve operation in noisy environments. Output pulse stretcher for use with micro-

processor decoders. On -chip stabilizer allows operation with

ML 920 remote -control receivers.

Electrical characteristics(typical over temperature range 0°C ... 70°Cwith supply voltage, Ub = 4.5 ... 9.5 V unlessotherwise stated)Supply current (pins 4, 7) 5 mA (Ub = 5 V)Regulated input voltage (pins 7, 13) 6.4 VDifferential sensitivity (pins 1, 16) 5 nACommon mode rejection (pins 1, 16) 30 dBMaximum signal input (pins 1, 16) 4 mA (plc)A.G.C. range 68 dBUnregulated input voltage (pins 7, 12) 16 VOutput pull-up resistor (pin 9) 56 kStretched output pulse width (pin 9) 2.4 ms

bicycle computer basedon microprocessor typeMC146805G2(Motorola Semiconductor Products Inc.)The MC146805G2, complemented by a liquid -crystal display (LCD), two push-buttonswitches, and two sensors, forms a novelbicycle computer. The two sensors are re-quired to provide an interrupt and to pulsecertain counters. Each sensor is a normallyopen reed switch which is actuated by amagnet mounted on the wheel and the pedalcrank respectively.The program for the, computer is included onthe chip and uses 1300 of the available2100 bytes. Functions of the computer that canbe selected and displayed are: instantaneous speed to the nearest mile or

kilometre per hour;average speed (calculated by dividing thedistance travelled by the time) to the nearest

mile or kilometre per hour; resettable trip odometer, giving the dis-

tance since the last trip odometer reset (orpower -on reset) to the nearest tenth of a mile orkilometre; resettable long distance odometer, giving

the distance since the last long distanceodometer reset; cadence, that is, the number of rev/min of

the pedal crank;II English or metric unitsIM wheel size, that is, the current wheel

circumference to the nearest 1/2 inch.

XL486: microprocessor interface pcb

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bicycle computer: schematic diagram

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TDA3800: block diagram and test circuit

17

real-time clock plus RAMtype MC146818(Motorola Semiconductor Products Inc.)This chip combines three features: a completetime -of -day clock and one hundred year calen-dar, a programmable periodic interrupt andsquare -wave generator, and 50 bytes of RAM. Ithas two distinct uses: (a) as an independentbattery -operated CMOS circuit offering RAM,time. and calendar, and (b), with a CMOSmicroprocessor to relieve the software of thetimekeeping workload and to extend the avail-able RAM where appropriate.

FeaturesMI Internal time base and oscillator.II Counts seconds, minutes, and hours of the

day. Counts days of the week, date, month, and

year. Operation from 3 ... 6 V supplies.II Binary or BCD representation of time and

calendar.II 12 or 24 hour clock with AM and PM in

I2 -hour mode. Automatic end -of -month recognition.II Automatic leap year compensation.II Microprocessor bus compatible. Multiplexed bus for pin efficiency. Three interrupts (separately maskable and

testable):time -of -day alarm, once per second toonce a day;periodic rates from 30.5 ps to 500 ms;end -of -clock update cycle.

IN 24 -pin dual -in -line package.

stereo/dual TV soundprocessing circuit typeTDA 3800(Philips)Features 2nd i.f. limiter/amplifier and FM demodu-

lator (5.742 MHz) for the second soundchannel.

II Level adjustment of the demodulated sig-nal for channel matching.

Pilot carrier processing with digital identi-fication, hysteresis, and short switchingtimes.

II Mode selection of stereo/audio orsound I/sound II with storage of selectedmode.

Two dual channel, independently controllable a.f. outputs.

III Low -resistance a.f. outputs.Il Switched output for controlling external

video/audio equipment.Electrical characteristics(typical values measured at an ambient tem-perature of 25°C and a supply voltage of 12 Vwith an input signal of 1 kHz unless otherwisestated).Onset of limiting, pins 28-15 50 NVAM suppression 60 dBAttenuation of the demodulator output

signal AF2 at audio/video mode 75 dBAF1 input voltage, pins 1-15 6 VAF1 input resistance, pins 1-15 14 kMaximum a.f. output signals (r.m.s.) 2VSignal -plus -noise to noise ratio 80 dBCrosstalk attenuation, in stereo mode 40 dB

in dual sound mode 60 dB

4-63

tape contents detectorelektor april 1984

tape contents detectorfor digitalcassetterecorders

M. Hefner

BCD = binary codeddecimal

Figure 1. The circuit con-sists of three common -or -garden ICs and a handfuldiscrete components. Ifthese are all fitted on asmall piece of wiringboard, it will be possiblewith a little luck to housethe detector in therecorder case.

C6

The circuit about to be described makesit possible to ascertain whether a digitalcasstte has been written into or not. It hasbeen tested on a Commodore computer,with a ZX81, and with a Junior Computer.Not only does it enable you to distinguishbetween blank and recorded tape, butalso, by alternate switching between play-back and fast forward wind - or rewind- to find the beginning of a program onthe tape.When used with the Commodore orJunior Computers, the circuit shows bymeans of three LEDs whether the tape isblank (D2), contains a leader (D1), or hasbeen recorded (D3). The leader, or pilottone, is a signal which precedes therecorded information, or, in the Com-modore, is interjected between the pro-gram coding (name, length, and so on)and the actual recorded data.The leader is not available with the ZX81which in itself is a serious disadvantage.On the other hand, it makes the construc-tion of the detector a lot easier, as shownbelow.

The circuitThe input of the detector (see figure 1), isconnected to the output of the cassette

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recorder. The signal from the recorder istaken via C6 to the input (pin 3) of a tonedecoder, ICI, and to the input (pin 2) of amonostable, IC2. There are three possiblestates: No signal. The ouput of ICI (pin 8) is

then logic 1, and that of IC2 (pin 3) islogic 0. The signal at the inputs (pins 12,13, 14, 15) of the BCD -to -decimal decoder,IC3, is then a binary signal 0010 (as 12 and13 are connected to earth which is logic0). This causes the output (pin 3) for thedecimal number '2' to be actuated, that is,to become logic 0. A current then flowsthrough R3 and LED D2 into this pin; theLED lights to indicate that the cassette isblank. Leader present. The constant frequency

of the pilot tone is recognized by IC1,causing its output to go low. At the sametime, IC2 receives a stream of triggerpulses, which causes its output to go high.The binary number at the inputs of IC3 isthen 0001, which makes pin 2 go low. Acurrent then flows through R3 and LED Dl:the LED lights to indicate 'leader present'. Data present. The output of ICI remains

logic high, because the input frequencylies outside the bandwidth of the tonedecoder. The monostable remains trig-gered, so that its output remains logic I.The binary number at the inputs of IC3 is0011 causing pin.4 to become logic 0. TheLED D3 then lights to indicate 'datapresent'.The centre frequency, fc, of ICI is deter-mined by P1 and C5 and can be calcula-ted from fc = 1/P105 (Hz) where P1 is thepreset value of Pl. The bandwidth, B, ofthe tone decoder is calculated fromB = 1070 \fUi/fcC4 (Hz.), where Ui is ther.ms. value of the input signal in volts, C4is the value of C4 in µF, and fc is thecentre frequency in Hz. It should be no-ted that Ui should be smaller than 200 mV.When the ZX81 is used, Dl, ICI, Pl, R2,and C3 ...C5 can be omitted. Pin 14 of IC3is then connected to the positive supplyline.

CalibrationThis section need not be read by ZX81users, as in their case there is nothing tobe calibrated. Otherwise, connect yourhome computer to the cassette recorderand write a program of a few dozen singlefigures (as close together as possible) ontothe tape: this gives you a leader on thecassette. Rewind the tape, and then playback. Starting from centre setting, adjustP1 slowly until LED D1 lights for 2...10seconds for each leader.

4-64

Digital logic pulserThe PLS-1 logic pulse; will superimpose adynamic pulse train (20 pps) or a single pulseonto the circuit node under test. There is noneed to unsolder pins or cut printed -circuittraces even when these nodes are beingclamped by digital outputs. This product is amulti mode high current pulse generatorpackaged in a hand-held, shirt pocket por-table, instrument. It can source or sink suf-

' 1.1.111114)1101.11114)

ficient current to force saturated output tran-sistors in digital circuits into the opposite logicstate. Signal injection is by means of a pushbutton switch near the probe tip. When thebutton is depressed, a single high -going orlow -going pulse of 2ps wide is delivered to thecircuit node under test. Pulse polarity isautomatic: high nodes are pulsed low and lownodes are pulsed high. Holding the buttondown delivers a series of pulses of 20 pps tothe circuit under test.

Too!range Limited,Upton Road,Reading,Berkshire, RG3 4JA.Telephone: 0734 22245 12894 MI

80 column needlemechanismDED of Lydd has introduced a true 80 columnmechanism which can also print at 96 and 132characters per line. Previously designers havehad to allow space for a complete free-standing unit which can be expensive andreduces the software flexibility.

The D119 has a 9 needle head with steppermotor drive for the pen carriage and paperfeed. Paper can be fed forward and reverse.Printing is bi-directional in character mode andunidirectional in high resolution graphic mode.Print speed is 100 characters per second. It ac-cepts paper 414 to 10 inches wide and hasboth friction feed and pin feed as standard aswell as printing on original plus two copies. A4single cut sheets can also be fed. The ribbonis in cassette form for ease of changeability.Each cassette can print 2 million charactersminimum. The two stepper motors and printhead only require 24 V DC hence power sup-

ply requirements are simplified. This ruggedmechanism has very high reliability andmeasures 380 mm wide, 209 mm deep and74 mm high (excluding lever arms). It weighs3.1 kg.

DEO,Mill Road,Lydd,Kent TN29 9EJ.Telephone: 0679 20636 (2892 Ml

Isolation amplifierOffering a new and safe way of makingmeasurements on floating circuits up to 1,500 Vfrom ground. The input amplifier offers sen-sitivities from 10 mV/division to 5 V/division(50 V with probe set to X10) AC or DC coupled.Signals from the input amplifier are coupled tothe output amplifier by a pair of differentiallyconnected opto-couplers thus ensuring goodlinearity and high common mode rejection. Theoutput remains constant at 100 mV/division giv-ing a useful gain boost for older less sensitive

101111111.1.-

oscilloscopes. The amplifier will find great ac-ceptance in such diverse fields from powerengineering examining SCR and triac gate firingpulses, switch mode power supplies,eliminating ground loops to medical researchwhere complete isolation between subject andmeasuring instrument is essential. Batteryoperation from PP3 batteries means that theamplifier can quickly and easily extend youroscilloscope's performance at any time.

Otter Electronics Ltd.,Otter House,Weston Underwood,Olney,Buckinghamshire MK46 5JS.Telephone: 0234 712445 (2893 M)

New cataloguesMarshall's 1984 catalogue contains56 pages filled with over 8,000 line items, andcrammed from cover to cover with new pro-ducts, new data and new ideas. This is one ofthe biggest catalogues ever produced by Mar-shall's and costs 75p to callers, £1.00 post paidwithin the U.K., and £1.50 for the rest of theworld.Marshall85 West Regent Street,Glasgow G2 20D,Telephone: 041.322.4133.

Electrovalue A -Z product list is regularly up-dated and is available free to anybody on re-quest. Its 36 pages contain everything fromadhesives to zener diodes and everything inbetween.

Electrovalue Ltd.,28 St. Judes Road,Englefield Green,Surrey TW20 OHB,Telephone: 0784.33603.

µ AmplifierNow signals as minute as 10011V from DC to2 MHz can be viewed and measured on mostoscilloscopes. The amplifier offers sensitivitiesfrom 100;N/division to 50 mV/division with ACor DC input coupling and maintains a constantoutput of 100 mV/division. To make full use ofthe high sensitivity a differential input is pro-

vided so that common mode signals can beminimised, also to improve the display a band-width limiting switch is provided to reduce theupper frequency limit to 20 KHz or 1 kHz. Thisamplifier will find many uses in audio andvideo work enabling monitoring of signalsdirect from playback heads and measuringripple. Even physiological signals come withinthe amplifier's wide performance. Batteryoperation from PP3 batteries means that theamplifier can quickly convert your oscilloscopefor very low level signal observation.

Otter Electronics Ltd.,Otter House"Weston Underwood,Olney,Buckinghamshire MK46 5./S.Telephone: 0234 712445 12886 M1

6502 Micro controllerControl 65 is a small low cost micro controllerPCB allowing: stand alone terminals to haveintelligence and flexibility. A 5 V supply is allthat is required to make the 75 mm x 100 mmPCB into a versatile controller offering 16 TTLcompatible Input/Output lines, up to 8kB ofEPROM decoding. 2kB of user RAM plus thepopular 6502 microprocessor. Onboard finksallow 2716, 2732 EPROM type devices to beused. PIO interupts are serviced for fast I/Oresponse times.

Applications within industry are countless andalso extend into educational and experimentalspheres, thus providing an ideal opportunity togain familiarity with the 6502 microprocessor.It can easily be programmed using Interface 84(Multiplexed RAM Card) from most computersystems.

J. P Designs37 Oyster Row,Cambridge, CB5 8L-1.Telephone: 0223 522234 12895 M1

465

FL100 work lightIdeal for illuminating dark work areas and inac-cessible corners, OK's FL -100 work -light has ahigh -intensity bulb and reflector system whichmeasures only 1iin (12 mm) diameter. It has a4in (102 mm) flexible shaft to position the lightin any position. The handle, which also holdsthe two AA batteries, has a clip to attach toany suitable point at the work area. Being bat-tery operated the FL -100 is safe in all situations.

OK Industries UK Ltd.,Dutton Lane,Eastleigh,Hants S05 4EE.Telephone: 0703 610944 (2896 MI

Wide range of knobsThe Mentor range of top-quality instrumentknobs, supplied by West Hyde, has now beenextended to include three new products.The first is a series of plastic collet knobs,featuring a raised, knurled band to ensure aslip -free grip. This knob is available in black orgrey in seven sizes from 10 to 50 mm diameter.Mentor aluminium collet knobs are nowavailable with a black anodised finish in ad-dition to the original silver version. These highquality knobs are machined from aluminiumalloy and are suitable for use under the mostarduous conditions. Both colours are availablein seven sizes from 9 to 36 mm diameter. Boththese new series can be fitted with caps, dials,pointers and many other accessories from theexisting wide range.For applications where a wide variety of ac-cessories is unnecessary, there is now an'Economy Series' knob available. These areavailable at low cost in a matt, textured blackor grey finish. Four sizes from 12 to 28 mmdiameter can be supplied, with or without anut cover. Caps in three colours with an op-

tional indicator line are also available to fitthese knobs. All these knobs can be chosen tosuit a wide variety of spindle sizes and featurea precision brass collet which ensures themaximum grip on the spindle.

West Hyde Developments Ltd.,Unit 9, Park Street Industrial Estate,Aylesbury,Buckinghamshire HP20 1E7:Telephone: 0296 20441 (2890 M)

Compact low-cost frequencycountersDigiMax 500 series frequency counters arecompact inexpensive instruments offering arelatively large 8 -digit display and an accuracyof 1 p.p.m. Little more than pocket sizemeasuring only 5'.:""x 5"x 114", separatemodels cover ranges of 10 Hz to 512 MHz and50 Hz to 1 GHz with resolutions of 1 Hz and10 Hz respectively.

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Powered by a rechargeable battery pack or byway of a mains adapter, the 500 series can beused equally well on the bench or in the fieldand serve as a useful addition to the serviceengineer's tool kit. With sensitivity of 15 to50 mV and 50 ohm inputs the frequencycounters are particularly well suited to check-ing transmitter and receiver frequencies atbase stations or for example in motor vehiclesor boats.

Aspen Electronics Limited,2/3 Kildare Close,Eastcote,Ruislip,Middlesex HA4 .9UB.Telephone 01-8681188 (2891 M1

Ultra miniature microswitchAn ultra miniature 50 -volt microswitch with ac-tuator arm is announced by SemiconductorSupplies International, Sutton. This 300 MAsingle pole changeover switch weighs0.3 grams. Dimensions are height (inclusive ofpins and with lever comprpcqPd) 10 mm, width8 mm, thickness 3 mm. The actuating lever ofthis switch is shaped for cam follower applica-tions as well as for ordinary compression ap-plications. Other possible uses include thetamper proofing or safety switching of smallequipment including security equipment suchas sensors and for switching scale models and,indeed, in any other miniaturised equipment.

Semiconductor Supplies International Ltd.,Davison House,128/130 Carshalton Road,Sutton,Surrey SM1 4RS.Telephone: 01 634 1126 (2888 Ml

Safe voltage indicatorOK's new Combi-Check two -terminal voltageindicator is the high -resistance type with anauxiliary voltage source, providing the degreeof user protection favoured by safety experts.Shock protected by the high input resistanceand safe against voltage surges, this productswitches on automatically when an externaltest voltage is applied. Furthermore, it isfoolproof and no conceivable wrong operationwill endanger the user or instrument, andvoltages at the terminals are always indicated.It can be used for detecting a.c. and d.c.voltages at 6, 12, 24, 50, 110, 220. 380, 660 V,phase -to -ground testing, polarity testing, con-tinuity up to 2 megohm and polarity -depen-dent continuity testing.A major feature, a complete performancecheck of the instrument and display levels canbe carried out before or during a vohage test,enabling the unit's accuracy to be continuallyverified. Its rated voltage is 6 - 660 V AC/DCbut is surge proof to VDE standard 0.433/111.

OK Industries UK Ltd.,Dutton Lane,Eastleigh,Hants 505 4AA.Telephone: 0703 619841 12887 MI

4-66

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Ctl-S'ARR Cappy Ole capaloe, capacitor

The fir5i-, electronic comic -bookRESI & TRANS

BANISH THE MYSTERIES OF ELECTRONICS !Excitement, entertanment, circuits. Complete with pr.nted circuit board and Resirneter.

Further adventures and circuitscoming soon - starring Resi & Transi,of course!

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Elektor Publishers Ltd., Elektor House, 10 Longport, Canterbury CT1 1PE, Kent, U.K.Tel.: Canterbury (02271 54430. Telex: 965504. Office hours: 8.30 - 12.30 and 13.30 - 16.30.

(-Invilagniinthepeople for Atari

`MP

3 Consoles available:Atari 400 with 16K RAM(AF36P) £345Atari 400 with 32K RAM(AF37S)£395Atari 800 with 16K HAM (AFO2C) £599Lots of other hardware: 16K RAM Module (AFO8J) £64.00Cassette Recorder (AF28F) £50.00 32K RAM Module (AF44X) £125.35Disk Drive (AFO6G) £345.00 32K Upgrade for 400 (AF45Y) £75.00Thermal Printer (AFO4E) £265.00 Floppy Disk £2.75Printer Interface for 400 (AF4111) £49.95 Le - (AC45Y) £24.95Printer Interface for 800 (AF42V) £49.95 Joystick Controllers (AC37S) £13.95Interface Module (AF29G) £135.00 For full details ask for our hardware leafletVersawriter fAF43W) £169.00 (XH54J) SAE appreciated

Et RTC

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-C- 16K -(80388) £19.95-C-16K-18039N) £19.95

-C-16/C-(9340T) £19.95_

. ;___ a -C -16K-1804114) £19.95,11., Satan 25 5':grams) -C-16X-180490) £18.95AunGatan(25PrLyelm) -0-19K-0050E1 121.95/kW 90991erS(3Prtgrarrs) -C- 16K -(Y1.388) £8.95Music ProgramsMUS4CCITVOMf -E-8K-(Y648C) £32.50Mcrae Themes (use .071

Music Composer) -C- 16K -1933418) £9.95

£8.95 Sr.:ohne Gallery -C-16K-(8036P) £14-95 Computer Languages£8.95 Wotan 9Kot -C-1611-(80129) £10-95 0 -48K -(6031J) £52.50

Jawbreaker -0-48K-(80260) £22.95 System A+ D -48X-(80301) £52.50Basketball -E-8K-(Y0618) £29.95 Bas-: 4 - 5

£32 50 Tank Trap C 16K -(Y130.1) £8.95 vi; Systern A + -0-48K (8032K) £99.50£32.50 mk Trap -032K-(113501 £11.95 OSFsctr -D- 24K - IYL2981 £44.90£32 9)£32.50£14.95£8.95

Horn. Clams Programs-C-16/24K- (MVO £12.95

-C-321(-(3020W) £22.45-C- 16K -180376) £10.95

Not -E.S2C-8X-IYGE9A) £49.50Utilities30 -Super Graphecs D -48X -119028F1 £29.9530 -Super Graphics -C -48X -00290 £29 95

£8.95- -C-16K-18048C) £14.95

-C-16X-(80165) £10.95AtanWorld(Graphcs) -0-48K-03027E) £43.95Assentder EON -6-8X-(Y868Y) £34-50

-C-16X-(8046A1 £29.95 Asseroder -C-16K-(YL32K) £14.95£11.95 Sac.7-z Ocrnmander -C- 16X -1804781 £24.50 65020isass,E-: -C-8X-IYL3OH) £8.95£995 Sert.a, ' -C-16X-18013P) £10.95 65026sas,, _ er -D-8K-(Y1.31J) £11 95

£10 95 Darts -C-161c-(8042V) £19.95 - -C 16K - ert.270 £9 97£1895 Tourr..1---C- 16X -03045Y) £19.95 -D- 16K -(Y128E) £12 50£19.95 SnC44 '_. anis -C-16X-(8044X) £19.95 T13e r. E- 8/(11,059P) £14 55£9.95 ChESS -E-8K- (Y663T) EN.%

Key: c=r...,....pne. E Cartridge.OD.% 3,, -C- 16X- (YL40T) £15.952C = 2 CaS-SigteS BX: 16X etc sh2=s£9.95 -C- 16K -(YL41U) £15.95

£10.95 -C-19X-(91043W1 £14.95 rrirernum rnenory rectioenitint

Send sae now for our new software leaflet with details of all the above programs. Order As XH52G - Issue 2Lots of exciting new software titles available soon. Keep in touch with Maplin!Subscribe now to America's leading Atari -only magazine - Analog -6 issues per year for just £9 CO Order as GG24B.

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