TRANSISTOR Ot...TRANSISTOR "k3Ps 47n 441.11, 4 Ot * ij By Louis E. Garner, Jr. IT'S only a few years...

TRANSISTOR"k3Ps

47n

441.11,

4

Ot*

ij

By Louis E. Garner, Jr.

IT'S only a few years since transistorswere heralded as the electronic won-

ders of the future, but that future hasmoved in with a rush. These surprisingcrystals-popping up in new commercialapplications every day-have started tocompete with vacuum tubes in real earnest.Whether you are interested in electronicsas a professional, an experimenter, or acasual hobbyist, the time has arrived to

PARTS LESTTM N.P.N

JUNCTION TRANSISTORTYPE 2N35

ri Ca

50 ppFD.

CERAMIC CAPACITORS

SPINSUBMINIATURETUBE SOCKET'

C6005 St

tmake friends with transistors.

This series of easy -to -assemble projectsis designed to demonstrate basic applica-tions at minimum cost. The circuits areconstructed from a handful of standard,inexpensive parts and because of the knock-down construction you can use most ofthem over and over. Whether you buildone or all these projects, you will get abetter feel for transistor circuitry and op-eration.

The projects, however, aren't just dem-onstraticn circuits; each one is a practicaldevice that is interesting to assemble andfun to use.

Gettirng Ready. To simplify assembly,the projects are put together breadboard -

112 101000 OHMS

R3 COO OHMS

'/ .WATT CARBON

RESISTORS

SP1

TYPE

B2M

SELENIUM PHOTOCELL

("SUN BATTERY")

LI

CR1

1N34

GERMANIUM

DIODE

RI

1.MEGOHM

POTENTIOMETER

(LINEAR TAPER)

TRANSISTOR ANTENNA COIL(LAFAYETTE NO. MS.166)

....:

S.P.S.TSLIDE SWITCH

C3

0.1 OD.PAPER

CAPACITOR

CS O.365.ppFD.MINIATURE VARIABLECAPACITOR (LAFAYETTENO. MS.215)

fashion on a chassis of perforated Ma-sonite. Fats are mounted with machinescrews and nuts to eliminate the labor ofchassis design and redesign.

Mount standard rubber feet in the cor-ners of the 8" by 12" Masonite panel. Thefeet will provide clearance for the mount -

B1

R-YOLT BATTERY(SEE TEXT)

8' x 12- PERFORATEDMASONITE PANEL

STANDARD.

KEY

1,000 -OHMMAGNETIC

HEADPHONE

March, 1956 3t

www.americanradiohistory.com


ing screws and keep the chassis from slip-ping while you're wiring the parts.

Make up a 9 -volt power supply by fittingsix penlite cells into standard clips ortaping them together as shown at theright. Connect the cells in series by solder-ing short leads from the cap, or positiveterminal, of one cell to the negative outershell of the next. Use 8" wire lengths forthe two end connections so you can hookthe power supply into the circuit. If youhave taped up your power pack, you alsohave to bend an aluminum strap around itto serve as a chassis hold-down.

While you're about it, make anotherscrap -aluminum bracket as shown in theproject photos and at the top of the nextpage. Drill it to take a 5 -pin subminiature

Power pack is a 9 -volt battery made up of six se-ries -connected penlite cells. You can tape the cellsTogether as shown or fit them into standard clips.

Parts Substitution. A good set of work-ing components is shown in the parts list,but you can make a number of substitu-tions without altering the circuitry in any

tube socket for the transistor and a 3 -lugterminal strip. Wire the terminal lugs tothe first, third, and fifth socket pins asshown. You can then make-and unmake-connections directly to the lugs withoutany risk of damaging the fragile socket ortransistor leads.

Still another bent -aluminum bracket willcome in handy as a "control panel." Drill%" shaft -clearance holes so you can mounta tuning capacitor or potentiometer asnecessary.

important way. Note, for example, thatin some photos tubular ceramic capacitorsare shown while in others the same unitsappear as discs. The two types are, ofcourse, interchangeable with each other aswell as with paper or mica capacitors ofequivalent value.

In place of the miniature variable capac-itor, C5, you could use any standard 365-Aufd. broadcast -band tuning capacitor, oreven a screwdriver -tuned padder. And forthe 1000 -ohm magnetic headphone, you

rage...0 wean- wawa- -"

ANT.-,GNP

R .

R 2 K;,7. okra -0 R3 Nor -

\'Veft.

4

3 RI

MEG.

MN

iN35repTR]

CI

.0Ipfd.

R2

2N35

10K

EMITTERBASE

COLLECTOR

C2 in Isea ft., KZ

0IPfd. 00 OZ

I C3o-3 aw

-

. I wfd,

KEY e.

(31

9V. 4.7Kr Pi

For learning the sound and touch of aradio ham's second language, nothing takesthe place of a code -practice oscillator. Thissimple job has as good a tone as any you'llfind, and being transistorized, it can keeppouring out dits and dahs practically for-ever on its original power supply.

It takes fewer than a dozen connectionsto put the whole thing together, so investa few extra minutes double-checking allconnections before you fit the transistorinto its socket and press the key. Whenyou do get to it, close the key and adjustR1 for the most pleasing tone.32

This circuit is an adaptation of the fa-miliar vacuum -tube Colpitts oscillator. Ca-pacitors C2 and C3 in series are shuntedacross the inductance of the headphone.The combination forms both a tuned cir-cuit and an impedance -matching network.The latter matches the high impedance ofthe collector -emitter output to the lowimpedance of the base -emitter input. Thebias current is fixed by R2 and the tonecontrol, Rl. Resistor R3, in series with thepower supply, isolates the tuned circuitfrom the battery and serves also to limitthe collector and base currents.

POPULAR ELECTRONICS



Each time you wire in the 1N34A diode,pinch the lead you are soldering with apair of pliers. Holding pliers somewherebetween the body of the diode and the wiretip being soldered serves to trap the heatand keep it from damaging the delicatecrystal.

For safety, install the transistor last in

Transistor -mounting assembly can be made bybending a piece of scrap aluminum to hold 3 -lugterminal strip and 5 -pin subminiature tube socket.

could substitute any magnetic phone ofhigh impedance.

Miscellaneous items, such as knobs, rub-ber feet, binding posts, machine screws,

all projects-after you've double-checkedthe wiring. Make sure, also, that batterypolarity in every case follows that indicatedin the diagrams.

An n -p -n junction transistor (type 2N35)is used in this first group of experiments.It requires battery polarity just opposite tothat of the more familiar p -n -p units.Schematic symbols are similar for the twotypes except that in this one the arrow

solder lugs scrap metal, and the like aren'tlisted and you can use whatever type youhave on hand.

Wiring. In these experimental circuitsthe parts layout and lead dress aren't crit-ical. You can follow the illustrations orrearrange :he pieces in any way.

If you want to reuse the parts in severalprojects, it is best to leave the leads andpigtails full length except or. the transistor.These should be trimmed to about '4" sothey'll fit the socket.

identifying the emitter electrode pointsaway from the base line.

The common -emitter circuit - roughlysimilar to the grounded -cathode vacuum -tube circuit-is used in all these experi-ments. As you might imagine, the hookupgets its name because the emitter electrodeis common to both the input and outputsides of the transistor. When it is con-nected directly to circuit ground, this basicarrangement is sometimes called thegrounded -emitter configuration.

ANTEHNA

50 ppf4.

r CS-, y365rd.

LIIf

Is

Is

I000.n.

2N35HEADPHONES

T RI - Er 0.,"

CR i r- A K II... F 8

1N34 L AE,

81

9V.

Though this simple receiver has a lotmore gain than a crystal set, it still needsa good antenna and a ground for best re-sults. A commercially available "transistorantenna coil"-tapped to provide a goodimpedance match to the input of the tran-sistor-is used in the tuned circuit.

When you wire up the set, pay specialattention to the polarity of the diode. Onsome 1N34's the cathode end is marked bya broad stripe or the letter "K"; on otherdiodes the terminals are identified by asmall schematic diagram similar to theone which is used here.March, 1956

Signals picked up by the antenna -groundsystem are coupled-through C4-to thetuned circuit made up of L.1 and C5. Vari-able capacitor C5 is used for station selec-tion as in any conventional receiver. Thetap on L.1 is designed for good selectivityas well as maximum energy transfer to thetransistor circuit. Detection-the separa-tion of the audio and radio components ofthe tuned signal-takes place in the 1N34diode and the base -emitter circuit of thetransistor. The program that comes throughshould be heard clearly and with goodvolume in the headphone.

33



1 - ,

yC

ANTENNA.

4

GNO.

Transistors are so efficient they can op-erate in radio receivers on electrical powertaken from the sun. If you'd like to testthis for yourself, you only have to substi-tute a selenium photocell for the 9 -voltpower -supply used in project 2. The unitshown (marked SP1 in the diagram) is theB2M "sun battery" made by InternationalRectifier Corp.

In addition, you may want to substituteC3 for the germanium diode. Whether thisextra change will improve reception de -

ANTENNA

C4

.010fd.

TR I

rC6

005pfd.

r-3 8 9V

a/Sit/11Ni

You can greatly increase the sensitivityof the receivers shown in projects 2 and 3by adding regenerative feedback. A coupleof simple wiring changes will do the trick.

One, new part-"tickler" winding L2-appears in the diagram and photo abovebut not in the parts list because you makeit yourself by winding 10 to 15 turns ofplastic -covered hookup wire around themiddle of Ll.

Two other parts-R/ and C6-are addedto the circuit of project 2, and a .01-µfdcoupling capacitor (C/) is substituted for

Circuit operation is similar to that' ofother regenerative receivers. Signals pickedup by the antenna -ground system arecoupled through C4 to the tuned circuitconsisting of C5 and Ll. Varying the fre-quency of C5 selects the desired signalwhich is then transferred (through C/) tothe base -emitter of the transistor. Thiscircuit amplifies the radio frequencies anddetects the audio.

But as the name "regenerative" suggests,the amplified r.f. signal is routed back tothe tuned circuit through the feedback

the 1N34 germanium diode.After you have completed the wiring

changes, slip on the headphones and slowlyturn potentiometer R1 through its entirerange. At some point you should hear a"putt -putt" or oscillation tone. If you don't,reverse the connections from L2.

This feedback tone is a sign that the setis regenerating the way it should. Back offthe potentiometer until the "putt -putt"sound just disappears, then carefully tunethe station you want by adjusting capaci-tor C5. Readjust R1 for maximum volume,34

winding of the coil. On its repeated jour-neys through the transistor it picks upever greater amplitude.

The resistance across potentiometer R1governs the amount of energy that is fedback through the "tickler." Advancing thesetting of the potentiometer-that is, in-creasing its effective resistance-boosts ther.f. feedback and thus increases the gain.Capacitor C6 serves to bypass any r.f. thattries to sneak off in the wrong direction(through the headphones and battery). andcarries it back to the transistor circuit.

POPULAR ELECTRONICS



p _lids on the characteristics of the indi-vidual transistor and on the antenna andground that you use. The only way to makesure is to try both arrangements and seewhich gives better results. Keep in mindthat a sun battery doesn't deliver as muchpower as six penlite cells-don't expectas much output from the receiver.

And notice that the circuit doesn't in-clude a switch. When you want to turn thisset on, you just expose the battery to directsunlight.

'ANTENNA

C

0 <I

-re-. CND

4

KEY

1_2 (SEE TEXT)

er I MREIG.r C0 II CI

pfd..01

2N3 -tTRI 81 9V

91.31111MT_s

74lasnitalefac #

4-,,: TR

,

If you've ever built a regenerative re-ceiver like the one shown opposite, youknow that misadjustment of the feedbackpotentiometer can make the set squeal likea stuck pig.

Squealing occurs when the circuit isthrown into oscillatior. The high-pitchednoise can be a bit of a nuisance in a re-ceiver, but it does have this use-it per-mits you to turn a receiver into a trans-mitter by making a few minor changes.

As you can see by comparing the circuit

from home base. To hold the range down,use only a short antenna lead.

To set up the -transmitter, place its an-tenna a few feet from any broadcast re-ceiver. Turn the receiver volume full onand tune it to a dead spot near the middleor the lower end of the dial.

Next, switch on the transmitter, closethe key, and set R1 at nearly maximumresistance. Tune C5 gradually till you heara high-pitched tone in the loudspeaker ofthe receiver. You can now adjust the sound

above with the one at the left, the most im-portant alteration is that a hand key andresistor R3 tAke the place of the head-phone. In addition, capacitors Cl and C6have been interchanged to improve thetone quality of the broadcast signal.

Sirrpl?. as it is, this transmitter is ca-pable of radiating a weak modulated signalat almost any frequency in the standardbroadcast band; you can pick your fre-quency by adjusting tuning capacitor C5.Keep it mind, however, that the circuitisn't stable enough for :Ise as a ham trans-mitter,. so don't let it broadcast too farMarch,, 1956

to your taste by resetting R1 and sharpen-ing receiver and transmitter tuning.

The transmitter works just like a regen-erative receiver that has gone into oscilla-tion. It puts out a modulated signal, how-ever, because of a blocking action in thebase -emitter circuit of the transistor. Thefrequency of the audible signal is governedby the amount of feedback plus the timeconstant of the RC circuit composed of C6and the input resistance of the transistor.Since the potentiometer determines theamount of feedback, it serves as a simplecontrol over the modulation tone. --130r-

35



FIVE NEW JOFOR TWO

1

.4fiat

TRANSISTORSYou'll find many practical

uses for these simple,low-cost circuits

°

PART II

It

By Louis E. Garner, Jr.

TRANSISTORSwere born with a couple

of important advantages that vacuumtubes never enjoyed. They're tiny and theydraw very little current you can use two,three, or a dozen with a very modestpower supply.

Each of the five projects described lastmonth was built around a single tran-sistor. Most of the circuits on the follow-ing pages employ a second transistor anda few additional parts. The small increase

In an n -p -n transistor (such as the 2N35Used in the first group of projects), thebase or central layer is a p -type semicon-ductor and the outer layers are both n -typematerial. The p -n -p transistor (like theRaytheon CK722 added to these circuits)is exactly opposite-its n base is flankedby two p -type layers.

As you've probably guessed, the lettersp and n stand for positive and negative. Ina p -type semiconductor, one or more elec-trons are missing from the crystal struc-ture; each missing electron leaves a posi-

in bulk and cost makes possible a greatincrease in the range, the power, and thevariety of new devices you can build. Asbefore, these breadboard units are de-signed for knock -down construction.

Transistors-p and n. A junctiontransistor is a sort of sandwich made upof three layers of semiconductor material(a material which is neither a good con-ductor nor a good insulator) such as ger-manium. The center of the sandwich,known as the base, is flanked on one sideby the collector and on the other by theemitter. The two types of junction tran-sistors available to hobbyists can be distin-guished by the way the layers are ar-ranged.54

tive charge that is known as a "hole." Inthe n -type semiconductor there is a sur-plus of electrons which are free to move,or "diffuse," through the material.

Aside from polarity, the two types oftransistors are very much alike and can beused in similar circuits. In general, n -p -nunits have somewhat better high -frequen-cy response.

From a construction point of view, themain difference between these two kindsof junction transistors is that they needopposite d.c. voltages on their electrodes.As you'll see in the projects that follow,this fact can actually simplify couplingcircuits, when n -p -n and p -n -p transiistorsare used in combination.

POPULAR ELECTRONICS

J www.americanradiohistory.com


of antenna coil LA.The n -p -n transistor, TR1, serves here as

an r.f. oscillator, and its frequency is deter-mined by the tuned circuit made up of Li.and variable capacitor C5. "Tickler" wind-ing L2 provides the feedback needed tostart and sustain oscillation. Base biascurrent-governing amount of feedback-can be regulated by potentiometer R.I.

The p -n -p transistor, TR2, acts as bothaudio amplifier and modulator. Since thetwo transistors are effectively in seriesacross the d.c. power supply, the same

middle or lower end of the dial. Set Ri atnearly maximum resistance. Then gradu-ally tune C5 and listen for either a livebackground hiss or a motorboating "putt -putt" sound. If you get no signal, reversethe connections to L2 and tr.), again.

If the set "putt -putts," back off R1 untilthe sound just disappears. Then recheckthe tuning of the receiver, and you shouldhe ready to go on the air.

Use the headphone as a mike. It's nottremendously efficient, hOwever, so hold itclose to your mouth and talk up.

P LIST'BI -9 -volt battery (6 series -con-.

nected penlite cells)112, 83-Penlite cells (divided into

7.5- and 1.5 -volt batteries; seeProject 2, "Photocell Relays")

*CI, C2 -0.131 -pfd. capacitor*C3-0.1-µfd., 200 -volt paper ca-

pacitor*C4-50-gmfd. capacitor*C5-365-gµfd. miniature variable

capacitor (Lafayette MS -215)*C6-0.005 µfd. capacitorC7-25-ftfd., 25 -volt electrolytic

capacitorC8-0.005 fifd capacitorC9 -0.25-4c1.

pacitor200 -volt paper ca -

OF_*CRI-IN34A germanium diode'LI-Transistor antenna coil (La-

fayette No. MS -I66)12-Feedback winding (10-15 turns

hookup wire; see Project"Wireless Microphone")

R1-1-megohm potentiometer, lin-ear taper

`R2 -10,000 -ohm 1/2 -watt resistorR3 -4700 -ohm, *ft resistor

R4 -100,000 -ohm, att resistor125 -100 -ohm, 1/2-wAtt resistorRLI-S.p.d.t. relay, 4000 -ohm coil

(Advance No. SO/IC/4000D orequivalent.)

91-S.p.s.t. slide switch*SPI-Selenium photocell or "Sun

Battery" (International RectifierCorp. Type B2M)

*TRI-Junction transistor, n -p -n(Sylvania Type 2N35)

TR2-Junction transistor, p -n -p(Raytheon Type CK722)

"*I -1000 -ohm magnetic headphoneI-8" x 12" perforated Masonite

2 -5 -pin subminiature tube socketsI-Sensor plate (see Project 3,

"Rain Alarm")I-Flashlight lensI-Piece of cardboard tubingMisc. solder, binding posts, rub-

ber feet, knobs, machine screw;*Asterisks in parts list and diagrams indicate components used in Part I of this series.

TRANSSTOUR' spintojters

\:k\ \\.\ \ '

1/44

ANT

IC365PPM.

GAO

4R2104

ANT:RiC14

I

Eb,

QTR_igalcaW- --

HEADPHONEA4 IDOK mowase.a

HEADPHONE(USED AS

250d.

Good party fun and serious electronicsexperimenting have a happy meetingground in this wireless mike. For with thelow -powered voice transmitter, you cansurprise or amuse your friends by broad-casting hum e-gr own announcementsthrough any AM receiver in the house. Theheadphone, generally used for listening,doubles here as an inexpensive microphone.

The circuit requires a feedback winding(L2) in addition to the store-bought parts;make this coil by winding 10 to 15 turnsof ordinary hookup wire around the center

emitter current flows through both units.Normally, current variations in one wouldappear in the other. Bypass capacitor C8,however, grounds r.f. variations in thecommon emitter. It thus keeps r.f. out ofthe audio stage while permitting the signaldeveloped in TR2 to modulate the r.f. inTR1. This arrangement eliminates theneed for a modulation transformer.

To use the wireless mike, connect it toa good ground and run an antenna lead towithin a few feet of a standard receiver.Tune the receiver to a dead spot near the



wiring assembly foreach transistor bymounting a 5 -pin sub-miniature tube socketand a 3 -lug terminalstrip on an L-shapedstrip of scrap alumi-num. Wire the lugs tofifth socket pins. Make alto the lugs.

the first, third, andI circuit connections

e Trim transistor leads to I/4" to fit the

Would you like your porch lamp toblink on automatically when the sun goesdown? It's no trick to use light-or theabsence of it-to flip a switch.

A selenium photocell-used in the sun -powered receiver last month as a powersource-does a little switch of its own inthese layouts and becomes a signal source.Actually, of course, the sun battery con-tinues to do exactly what it did before: it

sockets. Leave the pigtails of other com-ponents full length so you can wire-andrewire-them in different circuits.

CK722

EDDOT

CK722 4:: CB

tV-11. :2N35' \

B

Pay special atten-tion to the wiring ofthe two transistors.Socket connectionscan be identified bylead spacing on the2N35 and a red doton the CK722.

Always install transistors last-after dou-ble-checking the wiring. Don't switch onthe power until you're sure the right tran-

generates current when it is exposed tolight. After it's amplified, the currenttriggers a relay.

Two photocell units are shown here:Un-der strong light conditions, the one -tran-sistor amplifier is all you need. However,the two -stage circuit will give better re-sults over a wider range of applications.

Adjustment screws on the relay switchallow you to vary both spring tension andthe spacing of the contacts. In general,lowering spring tension and narrowing thegap between armature and pole piecesmake the relay responsive to smaller sig-

sistor is in the right socket.

Each time you wirethe I N34 diode(CRI ), grip the leadwith a pair of long -nose pliers to carryoff the heat of thesoldering iron.

Use simple lap joints when soldering ledds.

Make up a 9 -voltpower supply (BI) bywiring six penlite cellsin series. Batteries B2and B3 (in the photo-cell relay on the op-posite page) are madeby using one cell sep-arately and five in se-

nal impulses. It is worth noting, however,that relay adjustment can be very tricky.If you haven't worked with these switch-ing devices before, you will probably findit best to go along with the "factory ad-justment" of the spring and gaps.

Under "no -light" conditions (with eitherof these circuits), there is very little basecurrent flow in TR1. The emitter -collectorcircuit of the transistor therefore has ahigh resistance and current in the coilisn't enough to operate the relay.

However, when light strikes the selen-ium cell, current in the base -emitter cir-cuit increases and is amplified by thetransistor so it can close the relay.

Any interruption of the light source re-stores the circuit to a no -current condition

ries. and lets the relay drop open. Resistor R5and capacitor C7 are connected across the

P

56

our

°°..

POPULAR ELECTRONICS

r-i1

WIRING HINTS Make a breadboard 6,1



close the relay as soon as light strikes thecell and open it when the beam is broken.

You can also "tune" RI to a less sensi-tive spot. With the right adjustment. theunit should operate as if it were a"latched" switch. That is, once the con-tacts are closed, they will stay closed evenif the light beam is Or conversely.the relay will open when the light goes offand stay open after it comes on again.

To control a lamp, snip one conductor inthe power cord and wire the cut endsacross the relay's output terminals. Plugthe altered appliance cord into a 117 -voltoutlet as usual.

If you want the controlled device to turnon when no light strikes the photocell,

ScrewCenterchange

it-LS1:: COIL0j- TERMINALS

adjustments vary the relay's sensitivity.screw alters spring tension; outer onesgaps on "open" and "closed" contacts.

FRS.i71( CM 727

t13.2

/.5Y62

ed ki4-1Pr,

Light -shield tube can be 3" to 12" long. Paintthe inside flat black. For maximumsensitivity, in-sert a flashlight lens in tube to concentrate rays.

c;, RIOgiis) p

.0

..arrk... ITRII

100fqRS tO

0 I

-.07. 6a SI

RI I

83FG .4

I SY.MFG. o

connect the lamp cord in series with the"normally closed" contacts. For a directlyopposite switching service that is. if youwant a lamp to turn off when light readiesthe photocell-use the "NO" pair.

2N T

SPI

Ir

.3- :ow" lose

441:" I'4183-1.

u1.1

,1

J

\ \ N

relay's coil to absorb any inductive "kicks"that may develop because of suddenchanges in coil current.

Because of its greater sensitivity, thetwo -stage layout can be used where it isnecessary to focus on a single source oflight. Thus, if you want sunlight to switchsome appliance, you can shield the photo-cell from surrounding glare that mightgive a false signal. Use a cardboard tubefor a shield. Mount it over the cell andpoint its open end at the "control" light.

To allow for a wide range of operatingadjustments, a potentiometer is includedin the two -stage circuit and the 9 -volt bat-tery pack is tapped to provide a 71/2 -volt(5 -cell) "B" supply and a 11/2 -volt (1 -cell)bias voltage. To set up the switchingmechanism, close battery switch S/ andfocus the control light on the photocell.You should be able to set the potentiome-ter to an almost hairline balance that will

Make a bracket for the relay from scrap metalSpace mounting holes to match your relay andleave top screws accessible for adjustment.

OPEN-

CLOSED'

SPRING'ADJUSTMENT



If you built the simple battery -poweredreceiver described last month, you needonly make a few additions to complete thisde luxe version. To the earlier model itadds a direct -coupled stage of audio am-plification for greatly increased stationpickup, sound power and clarity.

Since the receiver isn't regenerative, it

doesn't need the tickler winding (L2 of the"Wireless Microphone" project). However,if you have added these extra turns of wire,just leave its two leads unconnected.

The most interesting feature of this cir-cuit is the direct coupling between the col-lector of the n -p -n transistor (TR1) andthe base of the p -n -p unit (TR2). This

TR2i

HEADPHOW

58

$CO rOmill

PNT

X 05

365 1

P.

GNI)

2N35

IN34CRI

" FB'

A K

'LI

4 R34.7K

CK 722TRZ

C

POPULAR ELECTRONICS

\\

R210K

aa0

2N35 IRS!URI OTK

oc 722TR2

NO

JIa.

0

It's no fun getting up in the middle ofthe night to close windows, but it's a lotless fun when you have to mop the floorsin the morning because you slept througha rainstorm the night before.

You don't have to be caught with yourwindows up, however, if you provide your-self tx ith an electronic rain watcher. Thisone will flash a warning when moistureshort-circuits its "sensor" plate.

The transistorized relay circuit, similarto that of the two -stage photocell layouton the preceding page, has a rain -sensitive

signal source in place of the light-sensitivesource.

You can make a suitable rain "sensor" inseveral ways. The basic plate consists oftwo exposed, narrowly separated conduct-ing elements on an insulating board. Adrop of moisture that bridges the gap be-tween the conductors completes the circuitand causes the relay to snap closed.

One way to make the moisture detector isto start with a sheet of copper -clad plasticof the kind used for printed circuits. Withan etching compound made for this pur-



WW,1-WE _ "tki-t rern,4.-tr's!''''

simple hookup is made possible by theopposite d.c. characteristics of the twotypes of transistors. As far as operationis concerned, in fact, you could omitthe coupling network consisting of R3and C7 and wire the collector of TR1directly to the base of TR2. ResistorR3 is used for safety only; it serves tolimit the current on the electrodeswhich might otherwise run too highunder some conditions. When it is in-cluded, bypass capacitor C7 is also need-ed to minimize the effect of the resistoron the signal level.

Broadcast signals picked up by a good

9 I

Le

If you can't get the metronome to pulseout the beat rate you want by adjustingpotentiometer R1, experiment with slightlydifferent values for fixed -resistor R4 andfeedback capacitors C3 and C9.

RI.

4` Ns+ -

,_CW; '

antenna -ground system are coupledthrough CI, to the tuned circuit. Vari-able capacitor C5 selects the desiredsignal and the low -impedance tap on Litransfers it to the base of TR1.

The germanium diode detector (CR1)and the base -emitter circuit of the firsttransistor separate the audio signalfrom the r.f. The sound is amplified byTR1 and is fed through capacitor C7 tothe input of TR2. In this audio -amplifierstage, the signal is given a further boostand is then routed to the headphone. 4)

April, 1956

V4 L -g

C9 I(.25 old.

SC3 I .11.1a.

2N35II TR! R3

CK722TR2

R001(

7K

t New 4 I HEADPHONE

91 21.0

59

7 a

it

Yh'

Music students-and even advanced per-formers-can make good use of this elec-tronic timekeeper. Its tempo beat, heardthrough a single headphone, is clearly sep-arated from distracting outside sounds.

Rain "sensor" can be made by etching cop-per -clad plastic as above, or by painting orcementing conductive strips on a non-conductor.

pose, you can cut a narrow insulatingcanal through the metal face.

Or you can turn the procedure upsidedown and "print" conducting lines on abase of non-conductive plastic. Use asilver paint (such as General Cement's

it

Essentially, the metronome is an oscilla-tor circuit similar to one you might use forpracticing code. The frequency of the met-ronome's "beat rate" is determined by thefeedback capacity and the total resistancein the return path of TR1. To bring theoperating frequency well below that of acode oscillator, two feedback capacitors-C3 and C9-are wired in parallel.

Potentiometer R/ can be used to tuneNo. 21-1) or cut strips of aluminum foiland cement them to the base. Leave anarrow insulating gap between the con-ductors and lay them out in a windingpattern to increase the total area of ex-posure.

Wire the leads from the "sensor"plate to the terminals marked "control."For the alarm, connect a lamp, bell, orbuzzer to the "normally open" relaycontacts. The alarm itself, of course,must be plugged in to a suitable powersource.

the metronome; its, series resistor, R4, isincluded merely 10 limit the frequency -adjustment range. If R4 were omitted (orrather replaced by a direct -wire connec-tion), tuning might be slightly more criti-cal. Otherwise there should be no differ-ence under normal operating conditions.

Resistor R3, between the collector of thefirst transistor and the base of the second,plays a similar role. It could also be re-placed by a direct -wire lead. But while itdoes not affect operation, it does protectthe transistors against excess current.



TRANSISTOR Ot...TRANSISTOR "k3Ps 47n 441.11, 4 Ot * ij By Louis E. Garner, Jr. IT'S only a few years...

Documents

Transcript of TRANSISTOR Ot...TRANSISTOR "k3Ps 47n 441.11, 4 Ot * ij By Louis E. Garner, Jr. IT'S only a few years...