CANADA'S OWN ELECTRONICS MAGAZINE - World Radio ...

CANADA'S OWN ELECTRONICS MAGAZINE

ectronics todairFEBRUARY 1978 =sr lissilissittottiisto incorporating

PROJECTSDigital Panel MeterFreezer AlarmTachomonitorCB Power Supply

PETComputerReview

k $1 25

Ourn

FONT NW

BIRTHDAY

ETI!

COLOR ORGANKIT

WIROCN COLORTHE RAJ Ij

f

3 CHANNEL

$1995

5 CHANNEL

. 29.95

Creates beautiful psychodelic lighting effects from any sound source.Easily connects to your stereo system, musical instrumests amplifier,PA system, etc. divides the sound into three separate chan-nels, low, med. and high frequency. You plug three lights or threesets of lights into the back of the controller (not to exceed 500 wattsper channel). Each set of lights can be individually controlled.

Standard Octal Bose

Thermal Delay RelaysSTANDARD

Bottom ViewSchematic Diagram

VOLTS6.3 v.115 v.

115 v.

115 v.

115 v.

115 v.115 v.

CONTACTS DELAYN.O. 5 sec.N.O. 10 sec.

N.O. 15 sec.

N.O. 20 sec.N.O. 30 sec.N.O. 60 sec.N.O. 90 sec.

2.95EACH

YOUR CHOICE

10 for

$20.00

oto-

Receiving Tubes

.992D21

3AU6

3BC53CS63CK63DT64BZ64C136

4DT66AK66AS5

1.29 1490Z41BC2

1S2A1S5

3GK54CS64DK64EH74EJ74HM64HS8

6EA8

6EH76EJ76EM56GH86GK66HZ66J4

6J W8

6KZ86T8

1R5 6GX7154 6HA5114 6HB71U4 6HD72AF4 6HA53AF4 6HS83AT2 6HZ63BU8 6JC63HA5 6JD63HQ5 6JU84BU8 6JV8

1111Illlllli1s6.9

Panel Meters4f" scale

A.C. VOLTMETER 0 - 234 v.A.C.

A.C. MILLIAMMETER TWO SCALESLOW 0 - 27.5 ma.

5 HIGH 0 - 242 ma.

5 for $30.00

7.5 R.P.M. MOTOR

$649* Enclosed Geer draft,* Vs" Diameter Shaft* Clockwise Rotation* Self.Sterting* Site: 51/2":123/4".23/4"

110.120 V. A.G. 60eta. MPG. Wt. a it.

HIGH TORQUESHADED

7_,L, POLEMOTOR

1

* SelLsterting* Bronze Bearings* Neavy Doty 11/4" Core* Dia. Spline Shaft

Sloe: 2y." x 2y x 2. 110-120V. AC. 60 II.. Slaw. wt. 2 II..

$395

AC MOTOR115 v. AC 60 cyc.

1)' shaft3/16" dia.

3"x24"xli"

195with MOUNTING BRKTS.

Computer

Grade

4:) Capacitors4t)

1119YOUR CHOICE

Plastic Cased

Motorized Controls115 v. AC REVERSIBLE DIRECTION

3 VALUES 1. mfdAVAILABLE 200 v.

1k ohm10k ohm50k ohm

1195 4 for $10.00

USE FOR REMOTE CONTROL

Ill V. AC SOLENOIDS

* OperatesMOW.

Switches. Th.LARGE: 2%. x lye^ X W

Stroke: to P

$2.95 ea. 3/$8.00SMALL: 114" . 254"

stroke: W

$1.95 ea 3/$5.00

FM Variable CapacitorCapacitor range

6.6-23 mmfd.

79c4 for $3.00

SPRAGUE, MALLORYSANGAMO and G.E.

GUARANTEED FOR ONE FULL YEAR

14" dia. x 44"

2,500mfd. 45 v.5,500 19 v.

7,000 13 v.

7,750 10 v.

8,000 15 v.

10,000 10 v.

11,000 10 v.

3" dia. x 4f"74,000mfd. 10 v.

2" dia. x 44"

250 mfd. 350 v.

500 200 v.1,500 100 v.

1,500 150 v.

2,000 50 v.

2,000 100 v.

3,500 75 v.

3,750 75 v.

5,000 55 v.

11,000 mfd 19 v.

14,000 13 v.

15,000 10 v.

15,500 10 v.

19,000 8 v.

25,000 6 v.

36,000 4 v.

"MOOVIT"THE

SUPER LUBRICANTfor tuners - switches - changersremoves rust - inhibits corrosionpermanent lubrication for every mech-anical or electrical situation.

uses A cows.

CJM CAPSULED LENLINE JELLIEDMOOVIT 20 INDIVIDUAL APPLICA-TIONS OF MOOVIT IN FIRE ENGINERED CAPSULES. IN A RE -USABLEROUND PLASTIC BOTTLE. NET PRICE

PER PLASTIC JAR 42:99-

C:=7. SPECIAL 1.75

THIS IS PROBABLY THE BESTCLEANER LUBRICANT PRESERVA-TIVE AVAILABLE. FOR THE ELEC-TRONIC TECHNICIAN THE MECH-ANIC OR THE TINKERER

Miniature LampsFLASHLIGHT BULBS

4ePR -2 2.4v.PR -3 3.6v.PR -13 4.75v.

10 for 65¢100 for $4.50

PRE -FOCUSED BULBS# 112 1.2v.# 222 2.2v.-

10 for 65¢100 for $4.50

BAYONET BASE BULBS12 for $1.00

# G590 14 v.100 for $7.00

.06 A.

SCREW BASE BULBS

40E)# 248 12 for $1.00

2.5 v. 100 for $7.00

FUSETRON FUSES,

DUAL -ELEMENTcoA# SLOW BLOWING Taal

v. W

Ott x 14"* 14 amp.

100 for* 10 amp $10.0Q

ADA GLOBE ELECTRONICSCORP. LTD.4. 440

DISTRIBUTORS OF ELECTRONIC EQUIPMENT AND PARTS1925 AVENUE ROAD - TORONTO, ONT. M5M 4A1

783-1801 783-1832

VOL. 2 NO. 2FEBRUARY 1978

EditorSTEVE BRAIDWOOD BSc

Assistant EditorGRAHAM WIDEMAN BASc

Accounts DepartmentSENGA HARRISON

Subscriptions DepartmentBEBE LALL

Marketing Manager and AdvertisingPETER E. PRIEST

Advertising ServicesSHARON WILSON

Layout and AssemblyGAIL ARMBRUST

Advertising RepresentativesJIM O'BRIEN, ALAN FLANCMAN.

Eastern Canada JEAN SEGUIN &ASSOCIATES INC., 601 Cote Vertu.

St. Laurent, Quebec H4L 1X8Telephone (514) 748-6561.

Editorial Director TOM GRAHAM.

Published by Electronics TodayInternational (Canada) Ltd.

EDITORIAL AND ADVERTISINGOFFICES

Unit 6, 25 Overlea Boulevard.Toronto, Ontario, M4H 1 B1Telephone (416) 423-3262

Printed by Livingstone Printing Ltd.

News Stand Distribution Gordon &Gotch. Toronto.

Subscription Rates $12.00 per year,$20.00 for two years. Send to Sub-

scription Dept.. ETI Magazine. Unit 6.25 Overlea Blvd.. Toronto,

Ontario, M4H 1B1.

INTERNATIONAL EDITIONSElectronics Today International

25-27 Oxford St., London W1 R 1 RF, UK.Editor Halvor Moorshead.

Electronics Today International,Ryrie House, 15 Boundary St.,

Rushcutters Bay, Sydney, Australia.Editor Collyn Rivers.

Electronica Top Internationaal,Postbus 260, Emmen, Holland.

Editor Denis Loos.

Elrad,Kommanditgesellschaft, Bissendorfer

Strasse 8, 3000 Hannover 61, Germany.Editor lJdo Wittig.

electronicsWongCANADA'S OWN ELECTRONICS MAGAZINE

PROJECTSTACHOMONITOR 25A simple guide to effective gear -changingDIGITAL PANEL METER 29An accurate digital voltmeter with liquid crystal displayCB POWER SUPPLY 44A heavy-duty design for using your mobile rig at homeFREEZER ALARM 48A simple way to safeguard against accidental defrosting

FEATURESTHE COMMODORE PET 10Answers to the questions everyone is askingELECTRETS EXPLAINED 20The magic ingredient of many microphones, cartridges and headphonesCLASS G AUDIO AMPLIFIER 22A new technique used in the Hitachi 'Dynaharmony' rangeDATA SHEET 32The Intersil ICL7106/7107 digital parel meter ICTRANSFORMERS 52How to choose them, how to use themBITS, BYTES & BAUDS 57Bill Johnson's computer introduction

SINCLAIR CAMBRIDGE PROGRAMMABLE CALCULATOR 60A cheap programmable with conditicnal branchingTECH TIPSIdeas for experimenters

66

NEWS & INFORMATIONNews Digest 4 ETI Circuits Book 67Microfile 7 Free Readers' Advertising 68

ETI Publications 24 ETI Panel Transfers 72Club Call 27 Classified Ad Rates 72Next Month's ETI 28 Mini -Ad Rates 72

Subscriptions Information 43 Reader Service Information 74Transistor Equivalents 47 Classified Advertising 74

ETI Binders 55

Cover: Computer graphics, cover photo, and PET review by Graham Wideman. Turn to page 10for full story.

Second Class Mail registration number 3955.Return postage guaranteed. Post Office returnsto Unit 6, 25 Overlea Boulevard, Toronto,Ontario, M41-i 181.

Copyright: All material is subject to world-wideCopyright protection. All reasonable care istaken to ensure the accuracy of the information.

ETI CANADA - FEBRUARY 1978 3

TENS DIGEST

Interfacing CalculatorA new computing data acquisitiondevice that combines an HP program-mable calculator with interfacingtechnology has been introduced byHewlett-Packard

The HP 97S I/O calculator, based onthe HP97 programmable printingcalculator, uses BCD interfacing togather data from a wide range ofinstruments. The HPS then manipu-lates the data according to user -designed programs and produces aprinted hard -copy report. With theHP97S, the user can take aninstrument measurement and compare

DPM Module

it to a standard or calibrate in data, docomputation on each individualreading, or take multiple measure-ments and conduct computation andstatistical analysis.

The list of products that can be usedwith the HP97S, includes electronicbalances, photometers, densitome-ters, thermal conductivity measure-ment devices, strain gauge systems,colorimeters, devices that measure ionactivity, titrators and pH meters,coordinate measuring equipment andphysical parameter measuring equip-ment.

The logic is TTL compatible and maybe configured with either positive or

negative trueness. The ten BCD inputlines allow entry of numeric data, signinformation, the exponent, and thedecimal point. Four output lines aid inthe instrument control. These outputlines may be set and cleared undersoftware control. (For example, whenconnected to a peripheral device theymight open or close a relay, providepulses for a stepper motor, signal thatan event has taken place or perhapschange ranges on a measurementinstrument.)

The basic system costs $1744 inCanada (duty and taxes extra). OEMdiscounts are available. Delivery is 12weeks.

A 2" x 2" x 0.4" module that offers all ofthe electronics necessary to constructa 3 -digit digital panel meter with thedesigner's choice of external displaysis now available from the Instrumentsand Systems Group of Analog Devices.

Requiring only a +5 V supply, theunits accept input voltage between -99mV and +999 mV with automaticpolarity indication. Two differentoutput versions are available. Themultiplexed seven -segment versioncan drive a 3 -digit LED display directly;

the only additional part necessary is again pot. The BCD output versionallows the user to add decoder/drivercircuits as required to drive a variety ofdisplays such as LED, LCD, and gas -discharge. Microprocessor interfacingis also simplified with the BCD output;application details are provided in thedata sheet.

US prices for the AD2023 with 7 -segment output is $28 in 100s, $39 1-9;the AD2023B for BCD output is $27 in100s, $37 1-9.

The Canadian agents are TracanElectronics, Downsview, Ontario.

4 7TI CANADA - FEBRUARY 1978

Pocket DigitalThermometer

TEMP -MASTERmomt ific

For vie With

TYPE K CiA

ther11.04.01.011A

PIO InstrumentsOtA,ANSWEAV. CAI ARM

A new Pocket Size Digital Thermome-ter has been introduced by PIDInstruments. The Temp -Master 100will read temperatures from -55 to+999° C and the 10F will read within thesame range in °F.

Input is from an ISA type K (chromel-alumel) thermocouple sensor. Thisinstrument comes with a metal linedleather case for $275.00 (whichincludes a ye" stainless steel immersiontype thermocouple).

For more information contact PIDInstruments division of R H Nicols CoLtd, 214 Dolomite Drive, Downsview,Ontario M3J 2P8.

Motorola's LM148Motorola is now a source for theLM148/248/348 series of quad opera-tional amplifiers. The four independentop -amps feature 741 -like true differ-ential inputs, internal compensation,and low supply current (0.6 mA peramplifier). Available from stock, the100 -up pricing is LM348J (0 to +70°C,ceramic) $1.15 each, and LM348N (0 to+70°C, plastic) $.87 each.

Circuit Protector for$1.00 Plus a Blown FuseHeinemann Electric Co., Trenton, NewJersey, has announced a programwhereby it will send a sample of its new'Re-Cirk-It' circuit protector for a dollarand a blown fuse.

The Re-Cirk-It protects like a fusebut is resettab:e. It installs in the samepanel space as a conventional 5/8"

diameter fuseholder, and it tripsinstantaneously on short circuits andwith delay on sustained overloads. Itcan only be electrically tripped, and itcan't be turned off or held against afault.

The use of a circuit protector helpsequipment manufacturers and usersby eliminating nuisance service callsdue to blown fuses. For the equipment

IC Temperature SensorAn integrated circuit temperaturesensor capable of 1°C absoluteaccuracy over a -55 to +150°C rangehas been introduced by AnalogDevices Semiconductor. The companyclaims that the device represents thefirst application of thin film resistortechnology and laser trimming to an ICtemperature sensor.

The AD590 is a two -terminal devicethat produces an output currentproportional to absolute temperaturewhen driven by a DC supply voltagebetween 4 and 30 V. The device is lasertrimmed at the wafer stage to producean output of 298.2 uA at 25° C; theoutput changes 1 uA/°C from thatpoint.

Power requirements for the newdevices measure only 1.5 mW with a 5volt supply at 25°C, which means thatsensor self -heating effects are kept toan absolute minimum. This low powerconsumption, combined with thedevice's high level output and small

user, it ends the bother of finding afresh fuse and the danger that thewrong size replacement will be used.

The protector is available in a widerange of current ratings from 0.25through 10 A. It is UL -recognized andCSA-approved as a componentprotector.

To participate in the special offer(which runs through December 1978) ablown fuse and $1.00 should be sent toHeinemann Special Re-Cirk-It Offer,PO BOX CN01908, Trenton, N.J.08608. For further information aboutthe Re-Cirk-It protector, requestBulletin KD-4001 from HeinemannElectric Co, Magnetic Drive, Trenton,NJ 08650.

Delta Design AppointsNational ElectrolabDelta Design, Inc of San Diego,California, has appointed NationalElectrolab Ltd as their exclusiverepresentative for Western Canada.National Electrolab also providescomplete repair and calibrationservices.

Delta Design Inc is a manufacturer ofenvironmental temperature chambers,semiconductor handling equipment,and burn -in systems. National Electro-lab are at 1536 Columbia St, NorthVancouver, BC, V7J 1A4 (phone (604)985-0511).

two -terminal package, make theAD590 ideal for remote probeapplications and as a replacement forthermocouple probes.

Three models of the AD590 areavailable. The high -precision "L"version is guaranteed to a calibrationaccuracy of +1°C linearity over therange of -55 to +150°C; the "K" versionoffers 2°C calibration accuracy with+1°C linearity; and the "J" versionoffers 5°C calibration accuracy and a+2°C linearity.

Initial versions of the device will beoffered in a T052 metal can or in chipform; miniature ceramic packages willbe offered at a later date. US pricing ofthe three versions of the AD590 in theTO52 can is $1.95 in 100 -piece ordersfor the "J" version; $3.95 for the "K";and $7.95 for the high precision "L". Allare available to MIL -STD -883A ClassB.

Canadian Agents are Tracan Elec-tronics Corporation, 558 ChampagneDrive, Downsview, Ontario M3J 2T9,(Tel: 416-638-0052).


Order Your Copy Now!

Top Projects fromETI-Canada

Audio LimiterBalanced MicrophonePreampBurglar AlarmCeramic CartridgePreampDigital Voltmeter

Double DiceFive Watt StereoFuzz BoxGeneral Purpose PreampG.S.R. MonitorHead Phone AmpHeart Rate MonitorInjector TracerMaster MindMetal LocatorMixerModular DiscoOver LEDPhaserReaction TesterSound Light FlashTouch OrganVU Meter Circuit50W/1 00WAmplifier Module

Available from your nearest Radio Shack Store,suggested retail price $3.00 or order directly from ETI, send $3.00 to:

Canadian Projects Book,ETI MagazineUnit 6, 25 Overlea Blvd.,TORONTO. OntarioM4H 1B1

DO NOT SEND CASHCheque, Money Order, Master Charge, Chargex (Visa).Please include Card No., Expiry Date, and Signature.

6 ETI CANADA - FEBRUARY 1978

8 -Bit Monolithic CMOSDAC8 -bit multiplying CMOS digital/analogconverter has been introduced byAnalog Devices BV. This is also thecompany's first device to be designedat its recently established integratedcircuit operation in Limerick, Ireland.

The new AD7523 uses thin-film-on-CMOS technology to provide 8 -bitresolution, 10 -bit accuracy and verylow power dissipation.

A

The ICs are housed in a 16 -pinplastic DIP and are priced at $2.00,$5.00 and $7.50 for the AD7523JN, KN,and LN (with linearities of +1/2LSB, +1/4LSB and +1/2 LSB).

The Canadian agents are TracanElectronics, Downsview, Ontario.

TM -990/100M- CompatibleAnalog I/O BoardsThe first family of analog input/outputsubsystems compatible with TexasInstrument's TM -990/100M 16 -bitmicrocomputer has been introducedby the Instruments and Systems Groupof Analog Devices.

The family of six devices isfunctionally, electrically, and mech-anically compatible with the TM -990/100M and allows users of the TIseries to interface that device to analog

Each of the subsystems can beaddressed as a memory -mapped I/O

Video Card KitCybernex inform us of their newTH6416 video terminal card kit. This 5"by 12" logic card generates 16 lines of64 characters from a parallel inputfrom a keyboard or microcomputer; orfrom serial data, via its on -card UART.Eight baud rates from 110 to 9600 areselectable at the edge connector.

The TH6416 displays 64 character USASCII and with thelower case option it displays 128 character USASCII and hastransparency mode. The 75 ohm video output is formattedfor a normal TV set or overscanned monitor. Composite andnon -composite video with H and V drive are available on theboard. The optional on -card power supply powers theTH6416 and has 200 mA in reserve to supply to a keyboardrequiring 5 volts.

The TH6416 sells in Canada for $184.00 plus $15.00 for thelower case option and $16.00 for the power supply option.For more information contact Cybernex, 3221 Council RungRoad, Mississauga, Ontario, Canada L5L 1L5. Dealerinquiries are invited.

interface device, offers convenientaddress and feature selection withwire -wrap jumpers and is availablewith an optional dc -dc converter whichallows the board to operate off the +5 Vlogic supply.

The RTI-1242 and RTI-1243 will beavailable in the USA at $395 and $675.The RTI-1240 and RTI-1241 modelswill be priced from $445. Canadianagents are Tracan Electronics, Downs -view, Ontario.

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NEWS DIGE ST

40:00P."

A13. n"410'

Another new feature hits the ETIplanning sheet! Softspot is ETI'ssoftware department, where we willpublish readers' programs. Ourlimits are pretty wide: any programsusing some form of conditionalbranching that can be entered inany common programmablecalculator. And so that readers withother calculators can adapt theprogram for their machines we askyou to draw a flow -chart of yourprogram. And any additionalexplanation about executing theprogram would be helpful. So if youhave devised a game or otherinteresting program that's not beenpublished elsewhere please send itto ETI Softspot, Unit 6, 25 OverleaBlvd., Toronto, Ontario, M4H 1B1.

FLOW CHART SYMBOLS

Information Output

/ Data to be Input

Branch

A Accumulator (Display)M Memory

Operations

Memory Exchange

Program Entry PointFor A or M

End


IC Test SystemA new combination of a micro -programmed integrated circuit devicetester, desktop computer and printerhas been announced by Hewlett-Packard. It gives the user the ability towrite or modify IC test programs for hisspecial needs in addition to performinga wide range of functional andparametric tests.

With this new HP 5046A system, theuser is able to write one -of -a -kindprograms, change test parametersquickly, create special componentevaluation programs or modifyexisting test programs. In-houseprogramming capability not only savestime but allows the user to keepproprietary information confidential.

The system includes an HP 5045Adigital IC tester, an HP 9825A desktopcomputer, and an HP 98666 printerand appropriate software. Full hard-ware and software manuals -areprovided which include startup andoperating procedures and self -instruction on the system software.

Programs can be written for, andtests performed on, logic families such

as ECL TTL (including low power TTLand other subfamilies), CMOS, RTL,HTL and DTL. A built-in thermalprinter provides a permanent record ofIC failure information.

Tests can be run manually on the5045A IC tester alone. However, thetester is also designed for high -volumetesting using automatic IC handlers.Over 800 standard (catalog) testprograms are a!ready available.

The Canadian price of the Hewlett-Packard Model 5046A Digital IC TestSystem is $30,200. Delivery is tenweeks. (duty & taxes extra whereapplicable.)

Bendy FM AntennaA new Bosch car antenna, designed toimprove fringe FM reception, is beingintroduced to the Canadian market bythe Blaupunkt car radio division ofRobert Bosch (Canada) Limited.

Approximately 40 cm (or 16 inches)long, the new antenna has a highdegree of flexibility - as demonstratedin the photo - making it particularlysafe in automatic car washes.

The antenna features low loss leads

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The Watt ShopP.O. Box 434,

shawa, Ont. L1H 7L5

ORDERS UNDER $25 ADD $1.00 FOR POST. AND PACKING.ONT. RESIDENTS ADD 7% PST. PRICES ARE IN CANADIANFUNDS AND INCLUDE FST. PRICES SUBJECT TO CHANGE3,ITHOUT NOTICE. WRITE FOF LATEST BARGAIN FLYER.

VISA (CHARGES) AcceptedMINIMUM ORDER $5.00 PLEASE

and separate preamplifiers for AM andFM. It must be installed with adashboard switch (not included), sothat the preamp section can beswitched off to reduce overloading ariacross modulation in strong signalareas.

BERT BOSCH (CANAD1411 CINTIAY 498

Nichols in EdmontonR H Nichols has opened a new salesoffice and service centre at 100-11 80thAvenue, Edmonton, Alberta. P6E 1T4(phone 403-432-7746).

CORRECTIONS ANDNOTESEqualiser - Oct. 77 Issue: The circuitdiagram as published does not agreewith the pcb overlay. In most respectsthis is simply a case of differentsections of the quad op -amps beingused, which of course are inter-changeable. However, some pins wereincorrectly numbered. Below we givethe changes to make the circuitdiagram match the pcb which iscorrect. On IC 2, change pin 1 to 5, 2 to6, 4 to 3, 3 to 4, and 5 to 2 and 6 to 1. OnIC 3change pin 1 to 2, and 2 to 1.

50D 50 Amplifier Dec. 77 Issue The textrefers to a 65V power transformer,while the Parts List and circuit diagramcorrectly show a 50V one. Seems likean extra factor of root 2 slipped into thecalculations!!

Digital Thermometer Nov. 77 Issue: Inaddition to those notes given lastmonth, some readers have informed usof problems with Radio Shack 3911sensors. It appears that the packagingis incorrectly printed, showing thepinouts for the metal can version ratherthan the Mini -DIP one. Our pinnumbers are correct.


Inside TheCommodore PETWe don't feel that "Personal Electronic Transactor" completely describes it, but we likedwhat we found in this machine. Review by Graham Wideman and Mark Czerwinski

LOOK WHAT HAPPENS when anaggressive, popular -market calculatorcompany joins forces with a lowprofile, high technology micro-processor manufacturer! Commodoreand their mpu wing, MOS Technology,have come up with a product whichwhile technologically unsurprising isrevolutionary from a packaging andmarketing point of view. Never beforehas a company tried to convince thepublic that a computer is anacceptable, fun, useful, perhaps evenan essential thing to have around thehouse.

In the past it's happened with radios,TVs, automobiles, calculators, digitalwatches. We really are now seeing theintroduction of the personal computerto widespread use.

We were dying to get some hands onexperience, and managed to borrowone of the few (one or two) PETs thatCommodore had in Canada. Here's thestory, with some surprises!

IT'S COMING, IT'S ALMOSTHERE . . .

No doubt many of our readers will haveheard so much about this machine thatthey feel it's a little late to do a reviewand call it news. Certainly literature,advance press releases, tantalizinghints and the like have been with us forover six months, but the real machineis still only almost just arrived. A fewwords with MOS Technology inPennsylvania put us in the picture.

By early December about 500 to 600PETS had rolled off the assembly line,being produced at a rate of about 30per day. These were almost all beingshipped in the States and withoutcomplete manuals. A temporarymanual was being issued, whichcontained little more than a descrip-tion of BASIC, and a few elementaryexplanations for how to operate themachine. There was no sign of acomplete manual in mid -December,nor much hope of its appearancewithin the near future.

As for sales of the PET in Canada, noone seems to know very much. Theprice fluctuates (mostly upwards) fromweek to week, and availability??? Theprice started at $695 and $895(Canadian) for 4k and 8k models withdelivery in January. At the time ofwriting (mid -December) the price is upto $850 and $1,100 for those samemachines, and no CSA approval hasbeen granted, which means nodeliveries to consumers. A couple ofmachines have appeared in very eagerstores, but these outlets can still onlyaccept orders.

In view of the low speed ofproduction, and the incredible demandwe expect will have developed for thisequipment, it is likely that the USdemand will exhaust most of thesupply and Canadians will have a longwait. March is our optimistic guess forfirst delivery, but then it's just a guess.

THE MACHINE ITSELFThe actual, non -imaginary, not -just-promised hardware we borrowed ispictured on the cover. We have severalassurances that what's in that one iswhat you'll get if you order one. It does

Fig. 1. An "old" (and not very good) Commodore press release photo. Note rounded case.


Fig. 2. Our first sight of the insides. It's areal pleasure to open it up and discover a"prop" already in place to hold up the top.

however look significantly differentfrom that pictured in Fig. 1., chiefly incase styling, recessing of the keyboard,and cassette deck. In addition thekeyboard in Fig. 1. has completelydifferent graphics symbols. In any case(?), it appears that our model is closerto a production machine, or may evenbe one, having regard to the fact thatdates inside indicate it was built inearly October, and the main pcb isnumbered 0109. The cassette worriedus a little though (see below).

So what do you get? Basically, whatyou see, and a few other features.Inside is a microprocessor system, andit's hooked up to an alpha -graphicskeyboard, numeric -and -moregraphics keyboard, CRT display, andcassette recorder. The microprocessorsystem uses the (big surprise) MOSTechnology 6502 mpu, with 14k ofROM containing everything to operatethe hardware, and purportedly a veryfast interpreter for BASIC. As statedabove 4k or 8k of RAM is provided foruser program and data storage.

HOW DID WE LIKE ITThere is no doubt that this package ofmicro -pieces is well thought out, anddesigned with the idea that the userneeds to know very little aboutcomputers to get "into" the PET.Remember the increased popularity oftape recording when cassettes cameout? Make it simpler to use, easier forthe human being. Same philosophy atwork here, and that is what will sell it.Needless to say in spite of the fact we

Notice neat cabling and connecting plugs,making for cheap efficient assembly andservice.

had very little documentation, we werehighly impressed.

First of all there is no wiring up to do.When you plug in and switch on thePET, after only a couple of seconds it'sready for action. No BASIC to loadfrom tape, it's already in there. This isone great headache reliever if the

Fig. 3. Here we've detached some of theparts from their mountings so we diJn't have

program you've written bombs out andwrites all over memory in selected vital(of course) locations. No waiting for a20 minute BASIC reload. 14k of built-insoftware is worth ten times its weight insilicon.

So after "power up" you can startprogramming, (more about that underSOFTWARE) or load from a cassettethe software you want. Presumably inthe future, tapes for various usefulsoftware packages will be widelyavailable, so you will infrequentk, needto write your own, but it's lots of tui i suyou'll actually want to.

TAPEDUpon entering the LOAD instruction,the machine tells you to stick the tapein and press the "PLAY" button. Here'swhere a compromise has been made.Although the PET can switch thetransport motor on and off, it tells youto do the muscle work. Commodorehave saved money by using a standard(cheap) cassette recorder, which issensible for the consumer market theyare aiming at. In fact, as you can see inFig. 3., our cassette was so standard ithad a grille for "condenser mike", andthe corner had been somewhatroughly cut off for the wires to enter itsbody.

The cassette feature worked quitewell, although a couple of demonstra-tion tapes did not load properly (wesuspect over -worn tapes due to heavy

to draw a block diagram. Video monitor boardis above.

ETI CANADA - FEBRUARY 1978

use). One feature we would have liked,(which could not have been includedwithout a large extra cost) would be afast forward search. Without it themachine took a long time to find aprogram if the tape was started at thebeginning and the program happenedto be near the end. For this reason itseems most economical (time wise) toonly use C30 cassettes (these arethicker and stronger anyway) and thenrecord only one or two programs nearthe start of each side, unless programsare recorded in some long sequence inwhich they are to be used, or forstorage of little used data etc.

KEY FEATURESAnother cost saver is the keyboard,being of calculator type constructionand feel. An idea of its size and actionmay be gathered from Fig. 5. All ourreviewers disliked the feel (nofeedback, you have to look at thescreen to see your entry) particularlysince we had a lot of problems with areluctant "N". On the other hand thesereviewers were all used to sitting downat expensive IBM terminals for days(and nights) on end, so perhaps thecomments are unfair.

The keyboard arrangement has allthe rows of keys lined up instead ofoffset as in a normal keyboard, whichwould appear to be a big disadvantageto experienced typists. However, oneis unlikely to enter vast quantities oftext, and this turned out to be lessannoying than anticipated.

To solve all these problems, it wouldbe a simple matter to replace the mainkeyboard with a "proper" one. Sincethere are no electronics inside, it wouldsimply be a question of configuring theswitches the same way. How long will itbe until some one comes out with aPET soup -up kit, come on, we'vestarted counting . . . !

Fig. 4. Peeking /I the back of the video monitor reveals i fairly standard set of works.

A CRT-ICAL LOOKThe video monitor appears to be quitestandard, Fig. 4 is a view in the back.The 9 inch CRT provided us with highresolution for the 25 lines of 40characters. A brightness control islocated at the rear.

ELECTRONICSFor the electronics enthusiasts (well,you're reading this magazines aren'tyou?) we've got Fig. 6. Most of theimportant features are shown on thisphoto, from which a basic idea of thesystem configuration can be gleaned.All the big chips are plugged intosockets, something nice to see,especially for ROMs. (When's APLcoming???)

Commodore appears to be pro-ducing mostly, if not exclusively 8k

models at the moment, but the hefty($250) price difference between 4k and8k models means that it could besignificantly cheaper to buy a 4k modeland plug your own 4k worth of RAMinto the sockets, or holes, left vacant.No doubt 4k buyers will be offered theoption of having an extra 4k installedlater, and they may as well save bydoing it themselves. In addition, a

option is a 24k memory unitwith its own power supply, to connectonto the expansion connectors.Commodore literature says this unit"cannot be described as static ordynamic but somewhere between thetwo". This we take to mean dynamicmemory chips with additional hard-ware to handle the refresh indepen-dently from the PET. This would allowsimple interface, servicing, and greatsavings in the power supply using lowpower cheap dynamic RAMs. The6502, like 6800 does not use the entireclock cycle, thus allowing (throughsuitable synchronizing circuitry)memory refresh to occur in the unusedpart of the cycle. Ciever and cheap;economy attainable in such a largememory unit.

The keyboard is accessed via a 16line Peripheral Interface Adapter (6520like a 6820 for Motorola fans) which weexpect uses 8 outputs and 8 inputs fordecoding 64 keys, and then also acouple of the PIA "handshaking" linesfor the rest of the work. In other wordsmost of the keyboard decoding is doneby software.

The cassette recorder as previouslymentioned is a customised standardone, with a new pcb inside full ofelectronics suitable for data recording.

Fig. 5. We call this one "Finger on the keyof *". Portrays finger pushing down key all theway to illustrate keyboard action.


14k of ROMcontainingBASIC and other ............software(2k x 8 ROMS)

These two chips total1k bytes of RAM,presumably screenmemory (25 x 40characters)

Another 2k x 8 ROM, 0...presumably the charactergenerator for video. Eachcharacter is 8 x 8 dots,requiring 64 bits storage.Therefore one ROM hasspace for 256 characters.Hmmm!!

Area for RAM, 16 x MPS6550 k chips (4k bits)

6522 Versatile InterfaceAdapter including timerwhich counts 60Hz linefrequency, and more I/O

In fact two cassette interfaces areincluded (second cassette recorderavailable for about $100.00 sometime)with input, output, and motor on/offlines. This uses six lines of the 16 onthe second 6520 PIA (we assume)leaving 10 lines, 8 for parallel I/O, and 2

Commodore PETCable to keyboard

6520 PIA for 1,0

Zener diodes for powerline transient and over -voltage protection.

.7r, Cable to power supply....

Socket for cassette cable

.. Peripheral Interface.............. Adapter, 6520

LED, probably for.... diagnostics

Cable to video monitor

..Crystal clock oscillator

Power transistors: turncassette motors on and Power supply voltageoff regulators and heat sinks.

Fig. 6. This is the main PET board, conraining all the electronics except for video monitor andcassette circuitry. Note well thought out layout, and edge letters: numbers for easy location ofareas on the board.

serial, at TTL levels. Both cassettesrecord at 1000 baud, but using built insoftware any program is recordedtwice in series for reliability, cctting theeffective rate to 500 baud. Thus an 8kprogram takes about 2. miiutes toload.

In addition, the PET is probably thefirst popular micro -computer to usethe IEEE 488 bus for instrumentationcommunications, making it compat-ible with many existing and futuredigital instruments, printers etc.Commodore themselves plan to hang


on this a printer ($1,000.00?), floppydisc (mini $1,000.00, "full size"$2,000.00??) and telephone interface($?) available when we don't know, butwith a standard bus you can be surethere will be a swarm of cheap add-onsfrom other sources in the not too farfuture, just like when the S100 buscaught on.

A final note of the hardware. Unlikesome of the early hobby computerequipment the inside of this machinelooks like it's built for business, and forthe manufacturer to stay in business.Constructed with quality electronics,and chassis and pcb arrangement foreasy assembly and service.

SOFTWARE

As stated before, one of the beauties ofthe PET is its built in ROM - full ofsoftware. The 14k includes 8 k BASIC,4k Operating System, 1k MachineLanguage and 1k Diagnostic routine,according to Commodore's literature.

First there's 8k of "extended" BASIC.The correct term is "BASIC interpre-ter". In simple terms an interpreter is amachine language program whichtakes your BASIC program as data,"translates" it to machine languagesubroutines and then executes it. Thisprocess actually occurs in a line -by-line translate -execute manner. Theterm "extended" refers to the fact thatmany statements are included that areomitted in some versions of BASIC.Using BASIC means that program-ming can be conducted in a civilizedmanner, using statements that arealmost readable in English, with baseten numbers. The machine does thework of converting to machinelanguage and 8 bit binary arithmetic.As encouragement to skeptics we'veincluded a description of the languageand how (easy it is) to use it.

Commodore claim that their BASICis significantly faster than anybodyelse's which we cannot attest to, but forgeneral use the PET performedadmirably as compared to thereasonably typical IBM 360 and 370interactive, multi-user systems that thereviewers were familiar with. (But wedo like APL!)

The cassette I/O, keyboard, video,and other functions are handled by the8k operating system.

Lacking documentation, we can onlyguess at the other two ROM items. Thediagnostic routine we assume verifiesthe operation of the hardware, anduses the LED as an indicator for thistask.

The 1k machine language we guessrefers to an assembly language

("machine language" is what the mpuuses, "assembler" is one step higher,using mnemonics for each instruction,and is generally more readable anduseable). There is also a mention ofnext year's "assembler device", to beplugged into the expansion port for"machine language" (?) programming.The advantage of machine or assem-bler language programming is in-creased efficiency of programs overthose "interpreted" from BASIC. Thiscould be critical in case of a routinewhich runs several thousand times in aloop, or for a frequently used function.

BASIC BASIC(INTERACTIVE)

One can think of the PET as operatingin one of two modes: "calculatormode" in which the operator asks themachine to execute and give theresults of one statement; and "pro-grammed mode" in which theprogrammer enters a series ofstatements, then has the machineexecute the entire set at one go. Thesecond mode requires a little morestructure for "administrative" pur-poses.

A list of the available statements andcommands with comments may befound to the right for reference.

CALCULATOR MODE

Known by this name because it is theprocess of getting a quick answer froma small formula, (similar to calcula-tors), or telling the machine to do onething.Example: PRINT 3+4The machine works out 3+4 and"prints" the result on the screen.Another example: LOAD FREDThis causes the machine to obtain aprogram called "FRED" from thecassette, including giving you instruc-tions about what buttons to push onthe recorder.

PROGRAM MODE

Problem: Figure out the sum of theintegers zero to ten.

Program: 10 J% = 020 FOR I% = 1 TO 1030 J% = J % + 1%40 NEXT50 PRINT J%60 END

The numbers down the side are linenumbers which can be any integers,and they keep the lines in order. Wehave chosen multiples of ten as itmakes for easy editing at a later date byinserting line numbers in between if

necessary. The variables are J% and10/0. The % signs identify them asintegers.

The FOR = NEXT pair signify a"loop" to be executed many times. Thefirst time 1% has the value 1, thesecond time 2, and so on up to 10.

On each iteration the value of 10/0 isadded to the accumulated total J%.After the 10th interation the programcontinues to line 50, prints the answer,then stops at 60. A simple task, a simple

BASIC

Commodore claims that their full floating pointBASIC is the fastest yet implemented on amicrocomputer. Here are the statements andfeatures included.

Standard Dartmouth BASIC Statements: LET,READ, PRINT, DATA, IF, THEN, FOR, NEXT,DIM, END, GOTO

Extended BASIC Statements: RESTORE, REM,GET, GOSUB, DEF, RETURN, STOP, STEP,INPUT, FN, ON GOTO, ON GOSUB

Scientific Functions: SGN, INT, ABS, SQR,RND, SIN, COS. TAN, ATN, LOG, EXP, PI

Logical Operators: AND, OR, NOT

Operation Commands: RUN, NEW, CLR, LIST,CONT, FRE

Formatting Functions: TAB, POS, SPC

Machine Level Statements: PEEK, POKE; Allowthe user to examine and store at specificmemory locations. USR, SYS; Link BASIC tomachine language subroutines with parameterpassing or developmental subsystems. WAIT;Monitors status of a memory location such as anI/O port until specified bits are set.

String Functions: LEFT$, R1GHT$, MID$:Returns substrings (of specified length andposition) of string acted upon. CHR$, ASC:CHR$ returns a character, given a numericcode. ASC returns a numeric code corres-ponding to a character. LEN: Returns the lengthof a string. VAL, STR$: Convert decimal valuesto numeric strings and vice -versa.

Extended I/O Statements: OPEN, CLOSE:Control association of a logical file number to aphysical device and, optionally, a file name onthe device. SAVE, LOAD, VERIFY: Store andretrieve a program, with optional file name, on aphysical device. Load allows for programoverlay, VERIFY compares contents of memoryto stored program. PRINT#, INPUT#, GET#:Allow communication with logical devicenumbers other than keyboard or screen. GET#inputs one character. CMD: Permits communi-cation with multiple devices simultaneously.

VariablesTYPES: Real, Integer (%), String ($)NAMES: Variable names are uniquely given as aletter or a letter followed by a letter or digit.

SpeCial VariablesTI, Tl$: Time of day. ST: Status word for I/Ooperations.


Commodore PETM::.i.Erlt:::' :'.....ii.M. nD'"-'.

e e 1 c,le el 1 1 1 ol.lel e1 il

1 lol1 0 1

1 1 11 1 W 1 I I I 101LI LJ LI 1...1

4

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Fig 8. The PE T's impressive array of graphic symbols makes game playing or creating quite a pleasure.

EXF1MPLE OF GRIPHING:ETI BUSINESS REPORT

..... -++++ S 9=ETI44

q- 4. 9 +=THE

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44 94 V

2 - 9+4

1 - 9999 44

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Fig 9. Ne were even more impressed when we saw the machine produce this graph!

Fig 7. The two PET keyboards. We found it quite handy to have a separate numeric padhaving hassled with other arrangements on in eractive terminals and keypunch machines.

program. With the program stored inthe machine, the operator keys in"RUN" and the answer appears. Howboring. But it does illustrate the ease ofprogramming.

Of much more interest to people arefun programs like games, and businesssoftware which helps you make (more)money. These can also be simple, or ofcomplexity running to many hundredstatements. These programs not onlydo simple calculations, but manipulatecharacter data, set up filing systems ontape draw fancy graphics on thescreen and other entertaining activ-ities. And you can exercise yourimagination writing your own pro-grams. A computer can be a verycreativity promoting toy, requiringvery little activation energy (other thanoriginal outlay) to get you involved,alot more healthy than a TV set, that'scertain!

GRAPHICS

We suspect some pretty creative,intelligent people sat down andworked out the graphics character seton tilos machine. Figure 7 shows thekeyboard and all the characters youcan Key in.

The display system is based upon8x8 dot units, which may contain 5x7dot upper case letters, or assortedsymbols which are so designed toprovide very versatile diagram andgraphing capabilities. Because the 8x8blocks fit together both horizontallyand vertically, it means that adjacentlines of text look a little crammedtogether, but this can be avoided byjudicious line spacing if necessary.


Commodore PET

The "cursor" is a flashing "element"or character that can be moved aboutthe screen, and it normally indicatesthe next space to be typed in. Aftertyping in that space the cursor movesto the next adjacent spot and so forth."RETURN" causes the cursor to moveto the first position on the next line, justas a carriage return does on atypewriter. Additional cursor control isprovided to move it quickly up, down orsideways. The cursor is useful alsofor editing and correcting programsalready written on screen, with thefacility for inserting and deletingcharacters. When the cursor attemptsto move below the bottom of the"page", the screen "scrolls up". That isto say each line moves up one, with thetop line disappearing.

In addition to the normal characters,each may be "reversed", that is appearas black on white, which can be used toadvantage on some occasions.

Finally, here's our big surprise! Ifyou've been counting keyboard char-acters, there are alot less than the 256possible with the character generatorshown in Fig. 6. Quite by accident wefound a whole set of lower case letters!Very interesting. We're not quite surewhat does it but check the pictures foryourself. That still doesn't add up to256 characters, so there may be yetmore we don't know about. In fact ourFig. 1 photo, upon close scrutiny of thekeyboard shows another set of graphicsymbols including assorted Greekletters, could they be inside as well?We don't know, but it all depends onwhat's in the character generator. Wewonder if Commodore has lower caseletters planned as a future "add-onoption?" For that matter you couldalways burn your own PROM . . .

WHAT MORE CAN WE SAY?It looks like computers are startingtheir march into the homes of themasses, which sounds very science -fiction and scary to some. We hope thatthe familiarity with computers this maybring to the man/woman/child in thestreet will reverse the widespread fearof THE COMPUTER as an enemy.Perhaps man will once again feelmaster over objects. There was after alla time when the automobile wasregarded as an evil fire breathingmonster, until everybody got one.

Fig. 12. No kidding, we really turned ourmachine info a labour saving device,designing our pcb layouts for us!!! Any errorsin future . . . "Well, it was the computer'sfault".

HERE IS AN EXAMPLE OF THE -EXT THAT ISPSSIBLE AITH THE COMMODORE PET DISPLAYTHERE ARE ALSO NUMBERS AND SYMBOLS.123456789a.-=+*/!"4$%sa\0.-t?)<=2"AND GRAPHICS:

I H I 11049+44.111"1_1ETV. :=& r - -r1 I I I 1

IN AD: I ION ALL CHAFAC TER'S MAY BE REV-E.P.!EED

IIIMUNIMMORg C F

THESE ARE ALL THE CHARK7ERS NORMALLYAVAIL-=IBLE ON THE KEYBOARL

Fig. 10. rest can look a little cramped as thelines of capita! lettevs are quite close. It'sdesigned that way sothat the graphicsymbols will join together.

Fig. 11. OK, we'll have to admit it was luck,but there they are, lower case letters and howto get them. Go and impress your local PETdealers. Don't forget to tell them where youread it . . .

....ETI'S REVIEWERS DISCOVERED. THAT

BY EXECUTING THE STATEMENT: -

POKE 59500,72

you can have lower case letters

INSTEAD of graphics. YOJ can't have

both on screen at once, tut can

alternate them in one program.


Electrets in AudioElectrostatic headphones have long been acknowledged as the ultimate insound transducers, but are restricted in usage by needing a high vcltagesupply to operate. Recently electret headphones have appeared,and are claimed to give a similar performance with no drawbacks.Cartridges and microphones too have begun to see the advantages ofthis new technology. But what exactly are electrets? Ian Sinclair explainsthe principle and its applications.

SEASONED CONSTRUCTORS are fairly used to theproblem of a noisy transformer or choke. In some casesthe noise is caused by laminations which are notsufficiently tightly clamped together, and so vibrate atline frequency. Transformers which work at higherfrequencies may cause sound to be emitted because ofmagnetostriction, meaning that the cores change in sizeas they magnetise. In our experience, capacitors do notcause such problems and yet some recent research workties up capacitance with microphonics, loudspeakersand even a new method of measuring temperatures.

PUTTING IT ABOUT, AND CHARGINGIn its simplest form, a capacitor consists of twoparallel metal plates insulated from each other by air orsome other non -conducting material between the plates.If we bring an electric charge, meaning a few electrons,from one of the plates and put it on the other, socharging the capacitor, this causes a voltage to appearbetween the plates.

QUANTITY

CHARGEVOLTAGECAPACITANCE

SYMBOL UNITS

O COULOMBSV VOLTSC FARADS

It is the ratio of the amount of charge to the value ofvoltage which is the quartity which we call capacitance.The relationship can be described more formally asQ= CV, where C is the capacitance in farads, Q is chargein coulombs, and V is the voltage in volts (see Fig. 1).When a capacitor has charged, the charge will staywhere it is unless there is some conduction between theplates of the capacitor which will allow the electrons totravel back to where they started. While the capacitor ischarged. there will be energy stored in the form ofelectric field between the plates.

For any simple capacitor of this type, the value ofcapacitance is proportional to the area of the plates andinversely proportional to the distance between them;mathematically this is

0AC- (see Fig. 2).

Fig. 1. The parallel -plate capacitor. (a) Charging consists of shiftingelectrons from one plate to the other (b) A graph of charge transferredplotted against voltage is a straight line and its slope is the value ofcapacitance.

AMOUNT OFCHARGETRANSFERRED

VVOLTAGE BETWEEN PLATES


Electrets in Audio

A

t111111111111111111111.11111111IIIIII1111111,,

n

C-(10

QUANTITY SYMBOL UNITSCAPACITANCE C FARADSAREA A METRES2SEPARATION d METRESPERMITTIVITY OFFREE SPACE 0 FARADS/METRE

PERMITTIVITY CONSTANTLY

The constant here (pronounced epsilon nought) iscalled the permittivity of free space, and applies whenthe capacitor plates have air (strictly, a vacuum) betweenthem; if any other material is used, then a numericalmultiplier, called the relative permittivity,constant will also appear, making the formula:

_ (,)Ad

C .

In each of these formulae, A represents the area ofoverlap of the plates in square metres, and d is thespacing between the plates in metres. The effect of therelative permittivity is to increase considerably thecapacitance between two plates which were formerlyair -spaced.

INSULATION ON A PLATE

The reason for this behaviour of insulating materialsis that the electric field between the plates of thecapacitor acts on the atoms of the dielectric, that is theinsulator which is placed between the plates, so thatthere is a force trying to separate the electrons from theremainder of each atom in a direction which is towardsthe positive plate of the capacitor. These electronscannot shift very far; if they could, the material woundnot be an insulator but a conductor. The result of thisslight shift is to "polarise" each atom or molecule,meaning that one end of the molecule is slightly negativeand the other end slightly positive, and the amount ofthis polarisation which takes place depends very muchon how the atoms of the material are constructed.

Polarisation causes another electric field to appear,this time inside the material and in the opposite directionto the field between the plates. Because these two fields

Fig. 2. Capacitance values. The value of capacitance of aparallel -plate capacitor is decided by the area of the plates and thespacing (when no dielectric is used). Tubular capacitors are simplyparallel plate types, with a thin film dielectric, which are rolled upwith another layer of insulation.

Fig. 3. Dielectrics. (a) The electric field between the plates of acapacitor. (b) Representing a dielectric; the molecules are randomlyarranged. (c) In a polarised dielectric, the direction of the field insidethe dielectric opposes the field (of the capacitor plates) which hascreated it.

la)

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ORIGINALFIELD

ELECTRICFIELD

FIELD WITHINDIELECTRIC


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e,,t,EPOUrationCrouncil

Name Age

Address

City

Employed by

Type of Present Work

Prov Code

1

19

Electrets in AudioHEAT, THEN COOL

HEAT

m. m. 5 0 ,m4T. r r#4

are in opposite directions, their effect subtracts, and thetotal electric field between the plates is less than it wouldbe if the dielectric were not present. Because the field isless, so is the voltage and so the capacitance is greater.

BEING SENSITIVE TO SIZE

The use of dielectrics in this way makes it possible forus to manufacture capacitors of comparatively largevalues in a reasonably small size, , but can causeproblems, one of which is voltage sensitivity.

We may find, for example, that the amount of theshift between the atom and the electrons of the dielectricvaries with the voltage we apply to the plates of thecapacitor, in which case the amount of polarisation willchange as the voltage is changed. A capacitor like thiswill be voltage -sensitive, and its capacitance will changeas the applied voltage changes. If such a capacitor,typically the high -K ceramic type, is used as a by-pass,this variation of capacitance is of no great consequence,but it makes such capacitances useless for tuningresonant circuits. (The experienced constructor willknow that certain types of capacitors are specified forvarious purposes.)

CAUSING A SPARKMost observable effects work in both directions, anddielectrics are no exception. In this case, the opposite ofthe normal action of the dielectric occurs in piezoelectriccrystals, where we apply a force which shifts atomsslightly out of place relative to their electrons, andcauses a voltage to develop across the crystal of thematerial. This voltage can be detected by connecting tometal plates formed on opposite sides of the crystal. Inthis case it is the force which causes the field, and thefield which then causes the voltage.

In many types of piezoelectric crystals, the voltageswhich are generated can be quite high, high enough tocause a spark, which is why piezoelectric crystals can beused as igniters for gas fires.

Another variation on this effect, of course, is thefamiliar piezoelectric crystal pickup cartridge, where amuch smaller force is applied from the stylus through thecantilever, and the voltage between the plates is thesignal output.

Piezoelectric effects, however, last only as long as thenormal structure of the material has been distorted, andthey disappear as soon as normal conditions areresumed. Electrets are materials which haVe a structure

COLD

ELECTRET

+

Fig. 4. Forming an electret.

which has been changed permanently, and whichtherefore have permanent amounts of charge displaced.Such materials have been known for sixty years or so,and the name comes from the resemblance to themagnet.

DUSTY PICK UPS?

A slab of electret material will pick up the dust orpowder of most materials. insulating or conducting, andso is rather useful in dust -collecting devices, and if weuse an electret as a dielectric in a capacitor then therewill be a permanent DC voltage between the plates of thecapacitor, though we will not be able to draw anymeasurable current if the plates are connected together.

Now there have moleculeswith a natural and permanent polarisation, water is oneof them, yet these are not electrets. The reason is that insuch materials these permanent polarisations are not

Fig. 5. An electretmicrophone orloudspeaker incross-section.

ELECTRET

0

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held in one particular direction, so that the electric fieldswhich are caused by each molecule simply cancel eachother out, with no overall effect. What makes a materialan electret is the combination of a polarised moleculewith a fairly low melting point and a very high resistivity,so that the material can be heated, the moleculesbrought into line by an external field, and the materialallowed to solidify again so that the molecules arepermanently "frozen" into position again. The highresistivity then ensures that there is no movement ofcharge which could reverse the process.

GETTING INTO HOT PLASTIC!

Many modern plastics materials are ideal electrets,some even have their charges established during themanufacturing process simply because of the electricfields which exist while the material is cooling. In mostcases, however, the plastic has to be made into anelectret by the combination of heating, applying anintense field, and cooling while the field is applied.

Such plastics sheets will "stick" tightly to each otherand to other plastics, will pick up dust, and show all theother behaviour which is normal to electrets. (It may wellbe that some of the problems we experience withmodern vinyl phonograph records are due to partialelectret formation during pressing.)

As far as the applications of electrets to electronics isconcerned, these arise because an electret is sensitive toanything which disturbs the arrangement of itsmolecules. A capacitor containing an electret asdielectric, for example, should be sensitive to vibration,i.e. microphonic. The opposite effect should also be true;if we apply AC between the plates of an electret capacitorwe should be able to cause vibration of the electretmaterial (if it is free to move) the capacitor would thenact as a loudspeaker.

As well as these AC effects, there is also a DC effect.Any electret capacitor will have a steady voltagebetween its plates which is caused by the field whichpermanently exists across the electret.

This voltage can be detected only by an electrostaticvoltmeter or by a very high input resistanceelectrometer, because the internal resistance of thecapacitor is extremely high. The voltage, however, willchange as the temperature difference between thesurfaces of the dielectric material changes, and this isparticularly obvious when the electret is struck byradiant heat; the effect is called the pyroelectric effect.

HOT AIR AND TELEPHONES

A pyroelectric detector consists of an electretsandwiched between a solid metal plate and a metalgauze, or between two transparent conducting plates,with an electrometer connected between the plates.Changes in air temperature will not cause any change inthe voltage reading if they affect both sides of theelectret. If we shine radiated heat on to one side of theelectret a difference in temperature will exist across theelectret, causing a difference in voltage. The sensitivityis quite remarkable. Placing your hand at a distance ofabout 1 metre from this pyroelectric detector radiatesenough energy to cause a reading of about 1V.

With some DC amplification, a temperature

difference of a millionth of a degree caused by radiatedheat can be detected, so that the pyroelectric effect hasimmense possibilities for measurements. Even withoutamplification, detectors using pyroelectric effect haveapplications in burglar alarms, fire alarms, detecting hotspots in machinery, even possibly for replacing fuses.

It was recently announced that some phone companiesintend to replace the old carbon microphone intelephones by an electret type, and presumably theearpiece can be replaced similarly. Some electret pickupcartridges have now appeared, but we are still waiting fora range of electret loucspeakers which would need nopolarising voltages and hence no AC supply.

STOCK QUESTIONThis is one of the fields of modern materials researchin which it is possible for almost anyone to get into theact. So many modern plastics form electrets easily that itis not impossible to manufacture them for yourself,though the effort would hardly be worthwhile on aone-off basis. Ready made electret materials are by nomeans easy to obtain, though there is always a

possibility of manufacturers of plastics sheeting forelectronics use, or capacitor manufacturers, havingsmall quantities in stock. (Perhaps one of ourenterprising surplus dealers might be able to obtain someof this material.)

Finaily, suppose one were able to manufacturecapacitors with a permanent voltage across them, howmuch would this save us on high value bias resistors forFETs?

WANTTOHOOKUP ACIRCUITQUICK?

Proto-Board ® 100760 solderless tie -points

Kit $28.75

The PB-100 is only one of our family of solderless Proto-Board breadboarding units, designed to help you assemble,test and modify circuits as fast as you can push in or pullout a lead. Preassernbled sockets with durable 5 -pointterminals provide low -resistance interconnections you canarrange and re -arrange at will.Resistors, capacitors, transistors, DIP's, TO -5's, LED'setc. plug in without damage to leads. And jumper con-nections, where required, are lengths of No. 22 AWGsolid wire. Models from 630 to 3060 tie -point (6 to 3214 -pin DIP) capacity available.

Write today for complete CSC Catalogue and Dist. List

len finkler ltd25 Toro Road, Downsview, Ontario M3J 2A6Telephone 14161 630-9103 Telex 065-24010


Class GA new amplifier technology from Hitachi. What is it and how

does it sound? Ron Harris reports.

HITACHI 46A-UNI %ILIA t t iVt tt ttt.$1.

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HITACHI NOW HAVE three units inthe hi-fi market employing this newamplifier configuration, which theyhave entitled Dynaharmony. Basically,class G is an improvement on the olderclass B circuit, specially designed toeliminate 'clipping'.

Since clipping is a form of distortionwhich occurs when an amplifier runsout of watts, to avoid it means pro-viding more power when a peak occurson the signal. There are two ways ofdoing this. One is to use an amplifier offar greater power than is needed norm-ally, so that in the 5% of the time whenthe peak power capacity is necessary itis there to be called upon.

Hitachi are now proposing thesecond solution, that of adding a secondamplifier in the same case, so configuredto operate only on the peaks, and henceto avoid the main circuit clipping off

-VAT

the waveform.When we first heard details of the

scheme, we wondered whether theswitching in and out of circuit of th ssecond amplifier would cause anyaudible degration of the sound, and sopolitely requested Hitachi to lend usan SR903 which is their 75 + 75 WDynaharmony receiver. This unit lis

capable of supplying some 160 W ofgood clean power when it mattersmost, and sounded superb - but moreof that later, let's look at the circuitin more detail first.

OUTPUT ON A G-STRINGFigure 1 shows the version of the classG output stage employed in the SR903receiver. 02, Q6 and Q3, Q7 constitutethe normal 75 W RMS amplificationstage. When the input voltage is lower

0.V2 (67V)

Figure 1. Theoutput stage of theSR903 receiver,showing how thetwo powersupplies areconnected to thetransistors. Inputsignal ei is showngoing into thebases of 01, 2 and03, 4. Otherwaveforms arethen given,showing how thecircuit handleseach half cycle.

than V1, 05 and Q8 are cut off, and theload current is supplied by Q2 and Q6,and by Q3 and Q7 on the -ve halfcycle.

Once the input exceeds V1 ie. 31.5 V01 and Q5 are switched in on the +vehalf cycle and Q4 and Q8 come in ona -ve half cycle. As this occurs V1 isshut off, and V2 (67 volts) is now em-ployed to handle the signal.

REALISING POTENTIALIn effect we now have a much higherpower amplifier operating than prev-iously. Once the incoming signal nolonger requires this, and the potential atQ5 emitter drops to 31.5 V, V2 is shutoff and Vi once more supplies theoutput current.

For music operation, the amplifieroperates with V1 90% of the time,thus keeping power dissipation low.This enables the unit as a whole to bepresented smaller and lighter as a result.(Mind you, hauling the SR903 aroundnearly ruined a few lives here - thatthing is HEAVY.)

Very fast diodes are employed forD1 and D2 so that the changeover isas rapid as possible. Residual spikescaused by the switch can be designedout, say Hitachi, and so do not appearon the output signal at all. We coulddetect none, certainly.

Class G efficiency is close to 80%for most of the time, which comparesvery favourably with the 65% peakefficiency of class B. This comes aboutbecause in the former circuit eachtransistor in the output stage is working

22-V21-67V)


close to its optimum efficiency pointall of the time, while in class B thisonly occurs close to rated outputpower.

A SOUND CHOICEIn order to see where all this ingeniousengineering has put the final soundquality, we put SR903 through itspaces in a domestic situation. Lab-oratory measurements were not taken,as we were entirely concerned with howthe unit sounded, not how manyzeroes are packed in between thedecimal point and the distortionfigures.

We believe that the most importantspecification for any piece of hi-fi is

its sound. Specifications are a useful,nay vital, guide in choosing a piece ofhi-fi, and can indicate whether or notX lies within the band you intend toselect from. And that's all!

Make up a shortlist from paper per-formances by all means, but do yourchoosing by earhole alone! Whateverthe equipment, cartridge, turntable,amplifier, tuner, tape deck - what itwill do to the sound of your system iswhat matters, not the fact that itsoutput power is 5.031 W higher thanyour old one.

ALL IN CONTROLAnyway sermon over, back to theSR903. This is a receiver of 75 W RMSnominal power, and with a good qualitytuner to boot. The multiplicity offacilities provided can be read off Figure3, suffice to say here they are mo-e.than enough for any domestic set-up.

The tuning action is smooth andtotally free of backlash, and the meterballistics good. The Auto -Lock facilityworks well too, and is controlled bytouching the tuning knob. All that isrequired is that you tune roughly intothe station, and let go the control.The circuit then locks on to the correctfrequency by itself. Neat and effective.

Volume and tone controls are both'click action' with positive indents at

Figure 2. Simplified version of the output stagewhich more clearly shows the operation of classG. 02 and 02' switch on when the input VINdemands a higher level than +V1, and switchoff again as the level passes VI going down.

Class G24 23 22 21 20 19

r.

;Figure 3. Front panel layout of the SR 903 receiver. To explain the numbers. 1. Power on / off switch.2. Headphone output (1/4- jack socket). 3. Protection indicator lights up when the protection circuit isoperating, ie first few seconds after switch on, and whenever an illegal condition exists at the output.4. Speaker controls (both pairs) 5, 6, 7 tone controls 8, 9 Filters. 10. Step attenuation volumecontrol. 11. Concentrically mounted balance control. 12. Tape copy switch. 13. Tape monitorswitch. Overrides function control (14) whenever put into either position 1 or 2. 15. Mode control.16. Loudness switch. 17. Adaptor control. Can be used to add Dolby, or even a third tape deck

the graduations. They are beautifulto use, and are of very high qualityindeed, as are all aspects of the controls.Everything about it has been carefullythought out, and the finish is immac-ulate. Personally pushbuttons are notmy favourite type of switch at all, butif you must have them, Hitachi's arenicer than most peoples, showing notendancy to be 'sloppy' or 'touchy'in use.

A CASE, A TAILOR AND ALEAPEven though the case is large by anystandards, an amplifier capable ofthese sort of powers would normallybe larger and heavier and riddled withheatsinks. Maybe Dynaharmony didsave us a few trusses (trussi?) after all.

In use the first thing to prove itselfwas the midrange tone control, allow-ing more exact response tailoring to theroom being 'bombarded'. The balancecontrol however is far too sudden inoperation. One touch either way, andthe sound leaps sideways at incrediblevelocity! All the action seems restrict-ed to about 1/8th rotation either sideof the centre. How about it Hitachi?

Musically the amplifier section of theSR903 is very good indeed, being quiteneutral in tone with good transientbehaviour and a solid, tight bass.

MUSIC TO BE EVICTED BYComparing the 903 to anotherreputable 70 W amplifier really beganto show the advantages of class G. Longafter clipping became painfully evidentfrom the other, the Hitachi soaredgracefully on unperturbed by thedemands made of it.

The loudspeakers used, CelestionDitton 66s, were very efficient and thelevels reached were quite horrendous attimes! On heavy rock or full blownorchestral splendour the 903 would un-doubtedly lose any similarly specifiedamplifier for sheer power o4 delivery.

Its sound is clear and open, and hasgreat 'bite' without ever becominghard. At very high levels, however, aslight thickening could be detected inthe upper midrange - but this is a veryslight effect indeed, and it took a greatdeal of A-B comparison to uncover itat all.

TUNING UP AND INOnto the tuner. Reference here wasdrawn with respect to a PioneerTX9500 FM/AM tuner which is ETI'sstandard quality reference. This waswired into the AUX input on the 903,so that straight A-B work could becarried out.

The first difference to becomeapparent is that the Hitachi is not assensitive, and even in full limiting thenoise level slightly higher. Both para-meters though are perfectly acceptableand astounding in a receiver of thisprice. Sound quality is high overall, buta bit hard in nature and prone to slightsibilance. Again though it comparesmore than favourably with the opposit-ion around in its own price range.

Sensitivity and selectivity were goodenough to allow usage for good stereoreception in fringe areas, and over aperiod of time listening remained a

pleasure.

G, WOT CLASS!Overall the 903 is an excellent pro-duct, and quite amazing value at itsprice. Think of it as a 160 W + 160 Wreceiver, with a good FM/AM depart-ment, and you can see that the 903 ischeap!

Class G amplification too comes outof this very well, a good example ofa sound piece of technical innovationhaving played an important part inimproving the sound subjectively.

It gave the 903 a sense of ease whenhandling peak signals, and allowed itto cruise happily at sustained levels ithad no right to in the first place!


PublicationsCircuits No. 1 $5.00

A brand new concept from the house of ETI. More than 100 pages packed with a wide range of experimenters circuits.Based on the 'Tech Tips' section carried in the overseas editions of ETI, Circuits 1 is the first of a series of specials -produced for the enthusiasts who know what they want, but not where to get it! Circuits 1 will also act as a catalyst forfurther development of ideas, ideal for the experimenter. The collection of more than 200 circuits is complemented by acomprehensive index, making searches for a particular circuit quick and simple. Also, similar circuits can be comparedeasily, due to the logical layout and grouping used throughout. Last and by no means least, Circuits 1 has no distractingadvertisements in the main section!

Top Projects No. 3 $2.50Now available in Canada, this book contains 27 projects reprinted from the UK edition of ETI. Includes WaaWaa, HifiAmp, Car Alarm, Audio Millivoltmeter, Pushbutton Dimmer, Expander -Compressor, Dual Tracking Power Supply,Photo Timer, Car Amp, Touch Switch, Exposure Meter, etc.

Top Projects No. 4 $2.50Twenty-eight projects from the UK edition of ETI. Includes Twenty -Five Watt Hifi Amp, FM Tuner, Line Amp, DualBeam Scope Adapter, Impedance Meter, DVM, Ignition Timing Light, Colour Organ, Radar Intruder Alarm, ElectronicIgnition, Fluorescent Light Dimmer, Drill Speed Controller, etc.

Electronics - it's easy Volume 1 $3.50*The best introductory series to electronics ever published in a magazine. Volume three completing the series, will beavailable in a few months. Volume One introduces electronics to the beginner by going through the systems approach,basic concepts, meters and measurements, frequency and wavelengths, electronics and communication, capacitanceand inductance, capacitive and inductive reactance, resistance, capacitance and inductance in combination, detectionand amplification, elements of transistor amplifiers, emitter followers and DC amplifiers, and basic operationalamplifiers.

Electronics it's easy Volume 2 $3.50*Volume Two introduces the sources of power, simple power supplies, how regulated power supplies work, generalpurpose supplies, generating signal waveforms, generating non -sinusoidal waveforms, all about electronic filters,more about filters, introducing digital systems, the algebra of logic, integrated circuit forms of logic functions. digitalsub -systems, counters and shift registers.

These publications are at presentonly available from ETI

Send your order, with payment (not cash), to

Please specify which publications you require,and print your name and address clearly.

$6.00 For Both*

ETI PUBLICATIONSElectronics Today International

Unit Six25 Overlea Boulevard

Toronto, OntarioM4H 1B1


Project Rev. Monitor -Counter

Rev. Monitor-CounterThis design uses light bulbs to indicate the upper and lower limits of idealrev ranges. Details are also given of an optional analogue tacho which caneasily be added.

WE HAVE HAD many requests topublish the design of a digital tacho-meter for use in cars. However, acouple of factors make this less thana practical proposition.

The most important drawback isdifficulty of reading the digital display.Many cars can rev out over a 5000rpm range in less than two seconds;even with 100 rpm resolution thiswould have the second digit changingevery 0.04 seconds.

Additionally, the simplest designprinciple - counting the number ofpulses from the distributor over aperiod of time - would not offeracceptable resolution for a reasonablesampling rate. On a four -cylinder car,a two -digit readout, i.e. 100 rpmresolution, calls for a sampling time of0.3 sec, while 3 sec is needed for athree -digit readout.

Analogue meters are easier to readbut may be a little sluggish with carswhich can rev out quickly in first gear.We therefore decided to design ananalogue tacho and add three indicatorlamps to give an instant indication orwarning of engine speed. One of these ison below a set rpm indicating that themotor is below the ideal minimum, asecond which is on between certainlimits indicating the working range ofthe engine and the third comes on abovea set rpm indicating too high an enginespeed. All the limits are adjustable andby overlapping the limits five bands ofengine speed can be indicated.

Where the vehicle is already fitted

with a tacho, or one is not wanted, thelights can be used by themselves. Thisreduces the cost considerably, while thelights still give an indication of enginespeeds and when to change gear.

CONSTRUCTIONThe electronics can be assembled onthe printed circuit board with the aidof the overlay in Fig 3. Due to thenumber of components, the use ofthe printed circuit board is recommen-ded. The value of R4 should be selectedfrom Table 1.

The mechanical arrangment for the

lights and meter we have left to theconstructor as variations in stylerequired make it difficult to give anydetails.

ADJUSTMENTThe potentiometer RV1 should beadjusted to give stable readings over theentire rpm range. Calibration of themeter is done by RV2 and this shouldbe done against a known instrument.The lights are adjusted by RV3, RV6,RV4 and RV5 (from the lowest to thehighest limit) to whatever levels arerequired.


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electronics tpdayComing up in

March's ETI

''HAMMER THROW-`F0

2 A U 23

THROW 100 )

ON PL AY

0 RESET0

eff

Hammer ThrowPress the play button and the hammer spins,first slowly then faster and faster. But don't letthe speed build up too much or you will not beable to release the hammer at the correctplace.

The straight line of LEDs shows you how faryou throw the hammer; the faster the hammerat the time of release the further it travels.

Free Message Service

House AlarmProtect your possessions with this sophisticated project.CMOS technology monitors your home as you leave,when you are away and when you return. The basicsystem has seven perimeter sensors and four internalones, but these are all expandable - see the full projectnext month.

Do you know how, for the cost of a local phone call,you can send a message by radio to anyone in NorthAmerica? Read more about this alternativecommunications network in ETI.

Equalization

Graphic equalisers, parameters equalisers, disc, tape,etc.. . . It is a wide subject but Wally Parsonsmanages to give you all the basic concepts in thisinformative article.

CANADA'S OWN ELECTRONICS MAGAZINE28 ETI CANADA - FEBRUARY 1978

Project Digital Panel Meter

Digital Panel MeterThis simple, economical yet highly accurate voltmeter uses a large liquidcrystal display for easy reading and low power consumption. It can be thebasis of many projects as well as being a useful meter in its own right.

WE INITIALLY purchased a number ofIntersil evaluation kits for our own usebut soon realised that while they werevery good electronically, the physicallayout wasn't too hot. We thereforeredesigned the PC board, reducing thesize dramatically, adding the decimalpoint drive circuitry and some droppingresistors and zener diodes to allow theboard to run from a dual power supplyof +/- 5V or more (e.g. with op -amps).

This resulted in a very useful devicewhich we decided to run as a project.It is basically a panel meter suitablefor DC voltage and current (with ashunt) and could be used in a varietyof projects.

t'"'" .

1.'1.'44 ,"'!"'1".1414$

tt-T44441444+144144t4-,

CONSTRUCTIONTo save on real estate, the main IC ismounted under the display. We used theMolex connectors supplied with theevaluation kit for the display andsoldered the IC directly into the board.If you want to mount the IC in a socketa low profile type should be used, witha high one for the display. As a socket isnot available for the display a standard40 pin one can be cut up to f t.

However before fitting either thedisplay sockets or the IC, fit all the othercomponents first. The over lay in fig. 3.shows the positioning of the com-ponents. Most of the components comewith the evaluation kit. The largecapacitors are laid on their side tominimise height.

When fitting the IC solder pins 1 and26 first (the power supply pins) so thatthe protection diodes on the inputs canoperate, thus preventing damage bystatic electricity. It is necessary that asmall tipped iron and fine solder be usedto prevent bridging tracks. The Molexsockets can now be fitted in two stripsof 20 with the top connecting piecesbeing broken off using long nosed pliersafter they are soldered in.

As there are no polarity marks on thedisplay it is necessary to hold it at anangle to the light and look for the outlineof the digits. The full format of thedisplay is shown in fig. 2. In this unitthe arrow, semicolon and the verticalpart of the + sign are not used.

SPECIFICATIONSFull scale reading

Resolution

Accuracy

Display

Input impedance

Input bias current

Polarity

Conversion method

Reference

Power supply

200 mV

100µV

<1 digit

3'/ digit LCD

> 1012 ohms

pA

automatic

dual slope

internal ± 100 ppm

±5V to± 15V dc1mA@±5V


Project

HIGH

+Ve

R61k

ZD15 1V

INPUT

0

851M

R124k

RVI1k

R4

LOW(COMMON)

T510

470riC2

-"I 3A 2C20n

ZD2 ......T5 I V

R247k

0-MA/-'

'Clloon

ALL VOLTAGESARE REFERREDTO PIN 1.

36 (-2.8V)

35 (-2.9V1

32

31

30 (-4.8V)

29

28

27

ICIIC L7106

34 1 -2.8V 1

21

(-4.9V) 37

33 )-2.9V 126 (-9.6V)

2022

25

40

39

R84M7

R9100k

01BC549

C610n

R3100kAA/S-

C4100p

38

Fig. 1. Circuit diagram of the completepanel meter.

-Ve

IC UNDERDISPLINY

Fig. 2. Component overlay with the display in place.Points marked A, B and C are the unused displaysegments - the vertical part of the + sign, the arrowand the semicolon respectively.

RIO4M7

BACKPLANE

I CDDISPLAY

LDECIMALPOINT

NOTES: MOT USED FOR 200mV

1DOk FOR 20V10k FOR 200V

R7 THESE POINTS CANNOT BE1k MEASURED WITHOUT AFFECTING

OPERATION EXCEPT BY A VERYHIGH IMPEDANCE) 1Gi!)VOLTMETER

DECIMALPOINTDRIVE

-HOW IT WORKS.Not much can be said on how this projectworks as everything is done by one ICand if anything goes wrong it is usuallythe IC. We have included some waveformdiagrams and voltages for referencepurposes. The conversion works on thedual -slope integration technique, whichis the most reliable of the simple methodsavailable. A capacitor is charged up at arate proportional to the input voltage fora predetermined time (in this case 1000clock pulses), then it is discharged at aconstant rate until it reaches the startingpoint again. The time taken to do this(i.e. the number of clock pulses) isproportional to the input voltage.

It is a true dual polarity system wherethe integration direction depends on thepolarity of the input voltage. ProvidedAC ripple on the input averages to zeroover 1000 clock pulses it will be rejected,hence where 61111/ AC is to he rejected a 48k Ili clock should he used. giving 83 ISISsample time (5 cycles of 60 Iii). the clockcan he adjusted by varying R3 it desired.R3 if desired.

For further details of the IC see thedata sheet in this issue.

1

Re:*tittlitaillitt.'Cl

l I

C60DECIMALPOINTDRIVEfltif..yrill.illill e.r},c

21 4° lrr 01t Dm --Dp2--DP3 I

b

41't ' ?".1 Ti

llikr,

-Ve R7 4.01,ZD2

HIGH

U

-CM*ZO1

LOW(COMMON)

INPUTS

+Ve Fig. 3. The component overlay without the displayshowing the positioning of the integrated circuit.

+Ve

30ETI CANADA - FEBRUARY 1978

OV Ine-mnend to pin I --

1111 11 itr Itn 1111- Iff

CALIBRATIONVERTICAL I V; disHORIZONTAL,....Noss dw.

Fog. 4. The waveform at pin 27 with a negative inputvoltage of about 170mV.

IV (rokossool to pm

Ill 1}t HIV ifft

CALIBRATIONVERTICALHORIZONTAL. / AIL

Fig. 5. The waveform at pin 27 with a negative inputvoltage of about 30mV. Compare this with Fig. 4.

I'll

iTtrofonoolool to pis

fill

CALEBRAT ONVERTICAL IV110011/0111TAL Mw

Fig. 6. The waveform at pin 27 with a positive inputvoltage of about 170mV.

The Intersil evaluation kit containingmost of the parts for this project isav-ailabie from Zentronics Ltd 99Norfinch Dr., Downsview, Ontario,also in Montreal and Ottawa. The partnumber is 7106 EV/KIT, and it costsaround $42. The 7106 itself, (and 7107LED version) costs around $15.

Digital Panel Meter

fill fl

OV (rohootod b vim II-I

1111_1111 till II II1tjm1r

CALIBRATIONVERTICAL I V /dmHORIZONTAL Bins/der.

Fig. 7. The waveform at pin 28.

IV (oNonomml to pie Ie

ill Ills 11 I'll

JI

till

CREMATIONVERTICALMORIZONTAL !Ao / Mu.

F g. 8. The output of the master oscillator on

Iilf II

I

V orkw....i b oio I

H it I II

CALIBRATIONVERTICAL . ..... IV /ay...... thd 10.

Fig. 9. The input of the oscillator - pin 40.

PARTS LISTRESISTORS all Y. or 1/2 W, 5%R1' 24kR2* 47kR3* 100kR4 see circuit diagramR5* 1MR6 1kR7 1kRE 4M7R9 100kR10 4M7

POTENTIOMETERSrIV 1 " 1k $0 turn trim

SEMICONDUCTORSiC1* ICL710601 2N3904ZD1,2 . . 5.1V 300mWMISCELLANEOUSPC boardLCD display Socket for LCD display

' These components are supplied withthe Intersil ICL7106EV evaluation kit.


ETI DATA SHEET

INTERSIL ICL7106/7107Digital Panel Meter ICThese chips provide all the worksfor 31/2 digit LED or LCD panel

meters using low power CMOS

THE ICL7106 and 7107 are highperformance, low power, CMOS 31/2 digitA/D converters that contain all thenecessary active devices on a singlemonolithic IC. Each has parallel seven-

segment outputs which are ideal for usein a digital panel meter. The ICL7106will directly drive a liquid crystal displayincluding the backplane drive. TheICL7107 will directly drive instrumentsize LEDs without buffering. With sevenpassive components, display and powersupply, the system forms a completedigital voltmeter with automatic zeroconnection and polarity (see figs. 3 and4).

Both ICs use the time -proven dualslope integration technique with all itsadvantages, i.e. non -critical components,high noise rejection, non -critical clockfrequency and almost perfect differentiallinearity. Both the ICL7106 and 7107can be used not only with its internalreference, but true ratiometric readingapplications may also be accomplishedover a full scale input range of 199.9 mVto 1.999 V.

The accuracy of conversion isguaranteed to plus or minus 1 countover the entire plus or minus 2000 countsand the auto -zero facility provides aguaranteed zero reading for 0 voltsinput. However, the chip does provide

Fig. 1. Pin Configuration.

1.1 SUPPLYD (UNITS)C (UNITS)II (UNITS)A (UNITS)F (UNITS)G (UNITS)E (UNITS)D (TENS)C (TENS) (TENS)A (TENS)F (TENS)E (TENS)CI (1001)

(1001)F (1001)E (1001)

AO (1000)POLARITY

(MINUS)

32

IOSIIIOILIElIU

wIti

62ID

7106 LCD

7107 LED

0Si)

IDL)

LhLD

LiiFit

La

FLI

ciLnLII

OSC. 1OSC. 2OSC 3TEST REF- REF.

REF. CAP.- REF CAPCOMMONINPUT HIINPUT LOAUTO -ZEROBUFFERINTEGRATOR(1 SUPPLYG (TENS)C ( 1001)A (100')G 000')BACKPLANyDIGITAL GND(7106) (7107)

IN

TP5O O

TP1 TP224K)) 1M()

TP30

1K))

CS

01

C,110.1IF

C2

0

9V

R2C3

ID -0TP4 016P1.icv

INTERSIL 7106

0 W 0

Fig. 3. LCD Digital Panel Meter Using ICL7106.

a true polarity output at low voltagesfor null detection. Both chips have anon -board clock and reference circuitry,as well as overrange detection.

DISPLAYS AND DPsThe additional components required tobuild a DPM are a display (either LCDor LED), 4 resistors, 4 capacitors, andan input filter if required. Liquid crystal

Fig. 2 Analogue Section Block Diagram.

INPUTHI

ANALOGCOMMON

INPUTLO

-- V

6'

I T

I T

®AZ

A/2 ®A/2

displays become polarised and damagedif a DC voltage is continuously appliedto them, so they must be driven with anAC signal. To turn on a segment, a

waveform 180 degrees out of phase withthe backplane drive (but of equalamplitude) is applied to that segment.The 7106 generates the segment drivewaveform for all digits internally, butdoes not generate segment drive for the

2.00

R6

v

I T

C3

C2H F.>>1071,2

6 2V OUTPUTOF

COMPARATOR


TO LCDDECIMAL POINT

TO LCDBACK PLANE

Fig. 5. Simple Inverter for fixed decimal point.

BP

7106

TEST

DECIMALPOINT

SELECT

)D-

CD4030

GND

Fig. 6. Exclusive -OR gate for DP drive.

TO LCDDECIMALPOINTS

decimal point. This must be done usingan inverter or exclusive -OR logic (seefigs. 5 and 6). For use with LED displaysthe 7107 pull -down F ETs will sink about8 mA per segment, which produces abright display suitable for almost anyindoor application. A fixed decimalpoint can be turned on by tying theappropriate cathode to ground througha 150 ohm resistor.

CAPACITORSThe integration capacitor should be a

6.8 VOLTZENER

(a)

Fig. 7. Using an external reference.

(b)

5V

TPS0

R

-4_

TP1 TP20 0

R. R24101 1MII

TP3

R.

C,I10.1w F1

IN-

Cs

01

C2R

-5V

0-0TP4

R6

ISO!! TO

I

DECIMALPOINT

-=

PLAY

INTERSIL 7107

'LinnI I,

Fig. 4. LED Digital Panel Meter Using ICL7107.

low dielectric -loss type, such as a poly-propylene. Mylar capacitors are suitablefor the reference and auto -zerocapacitors.

THE CLOCKThe chip carries the active parts of anRC oscillator which runs at about 48 kHzand is divided by 4 for use as the systemclock. The integration period (1000clock pulses) is therefore 83.3 ms. Eachconversion requires 4000 clock pulses,

1.2 REFERENCE(L811.13 ORMICPOPOWERSYSTEMSMPS 5010)

i.e. 3 readings per second. This isOptimum for rejecting 60 Hz line fre-quency, 1000 clock pulses being 5cycles.

THE REFERENCEFor 200.0 mV full scale, the voltageapplied between REF Hi and REF Loshould be set at 100.0 mV. For 2.000 Vfull scale, this should be 1.000 V. Thereference inputs are floating, and theonly restriction on the applied voltage

V- -3.3v

Fig. 8. Generating a negative supply from +5 V.


ETI DATASHEETis that it should lie in the range V-to V+.

For many applications, the internalreference of 2.8 V between V+ andCOMMON is adequate, but powerdissipation in the 7107 LED version canwreck this. However, an external refer-ence can be added as shown in fig. 7.

POWER SUPPLIES

The 7106 will run from a single 5 to12 V supply. If INPUT Lo is shorted toCOMMON, this will cause V+ to sit2.8 V positive with respect to INPUTLo, and V- at 6.2 V negative withrespect to INPUT Lo.

The 7107 requires dual supplies,+4.5 to +6 V and -3 to -6 V at 1 mA.A negative supply may be derived from+5 V using the circuit given in fig.8.

FURTHER INFORMATIONEvaluation kits for the 7106 and 7107are supplied with a data sheet andapplication note. In addition, Intersilproduce three other ApplicationBulletins: A016 'Selecting A/D Con-verters', A017, 'The Integrating A/DConverter', and A018 'Do's and Dont'sof Applying A/D Converters'.

New C BSound Saddle

let's you hear

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Electrical Specifications: ICL7106/7107

Full Scale Voltage Rating

Full Scale Digital RangeAccuracy with external reference10° to 50° CNoise referred to inputInput circuitInput Bias CurrentInput ImpedanceReference (Internal)

Conversion Characteristic

T200 mV (5.0 V min V+ to V-)-T2.0 V (6.0 V min V+ to V-)-T2000 counts<1/2 count

15 µV typicalDifferential2 pA>1 TS22.8 V, referenced to V+Temperature Coefficient 100 ppm

typicalDual Slope with Auto -zeroIntegrating Time = 1000 countsReference Time = 0 - 2000 countsAuto -zero time =

1000 + 2000 - Ref. Time

Recommended External Components:200 mV full scale

Integrating Cap (C3) 0.22µFAZ Cap (C2) 0.47µFRef. Cap (C1) 0.1 µFClock Cap (C4) 100 pFIntegrator Resistor (R6) 47 k1-2Clock Resistor 100

Clock FrequencyPower Requirements

Read Rate

2 V full scale0.22 µF0.0470.1 /IF100 pF470 kc2100 Id -2

48 kHz, internally divided by 4LCD: 1 mA at 4.5 -6 VLED: 1 mA at 4.5 -6 V, plus LED

currentAccurate from .1 to 15 readingsper second

Oaktron Industries puts your CB radio ,nthe SB Sound Saddle to give you reception younever before thought possible. The speciallymade, built-in 3" x 5" voice communicationspeaker virtually eliminates unwanted high andlow frequency interference - then directsthe sound to you, not to the floor.

Oaktron's CB Sound Saddle is fully adjus-table to almost any transmission hump. Even

if it is not permanently attached, it's designedto ride out any kind of trip with ease, yet isfully portable if you want to remove entireunit.

CB Sound Saddle includes all hardwareneeded, takes 4-6 minu:es for custom assembly.No tools needed. Your choise of grilles; BlackEnamel, Walnut Woodgrain or Chrome Plated.All American made for dependability's sake.

Meet a wholenew conceptin CB soundand convenience.1. Powerful 3" x 5"voice communicationspeaker aims clear,crisp sound directly at

you.

2. Puts your CB radiocontrols within easyreach.

3 Custom -fits com-pletely secure on mostany transmission hump.

4. Permanent or porta-ble installation

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Photo Enlarger Timer

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Knob included

MODEL TRAVEL

JJ-10006 10K 30mmJJ-10006B 100K 30mmJJ-10006C - 500K 30mfmJJ-10006D - 1 MEG 30mm

JJ-10007 10K 45mmJJ-10007A 50K 45mmJJ-100078 - 100K 45mmJJ-10007C - 500K 45mmJJ-10007D - 1 MEG 45mm

ROLS49c Rotary 69c

PIH ER

kilvondsmaro

Available in10 K ohms50 K ohms100 K ohms

log or linear taperMatching Knob

SLIDER

CONTROLS

60mm Travel

49c

SINGLES

100

220

470

500

750

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lmeg

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1 meg - 500K

200K -dual

10K -5K

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1. AUTOMATIC HEADLIGHT REMINDERNovel circuit to remind you to turn your headlights off if they are left on when the ignition is off. $ 4.25

2. BATTERY OPERATED FLORESCENT LIGHT KITUseful circuit that can be built into small (20 W max) fluorescent fixture in mobile vans & campers for 12 VDC

$14.25

3. BUG SHOOProduces a sound to keep annoying bugs away

$ 5.25

4. CODE OSCILLATORPractice up your "Morse Code" with this simple project.

$ 5.55

5. CRYSTAL RADIOCrystal radio receiver picks up local AM radio stations.

$ 4.95

7. CURIOSITY BOX IEGreat for parties - a novelty electronic item.

$ 7.25

8. DALLY LIGHTERTime delay circuit for turning a light circuit off after a predetermined length of time.

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10 FISH CALLERA real fisherman's lure - not guaranteed to catch the big one but only to make it more interesting.

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11. HI POWER 12 V DC FLASHERElectronic signal flasher circuit for warning lights, etc.

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12. PHOTO ELECTRIC NIGHT LIGHTNight watchman - turns lights on at dusk and off at dawn.

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13. 6V POWER SUPPLYRegulated & filtered 6V DC power supply 1/2 amp.

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14. 9V POWER SUPPLYRegulated & filtered 9V DC power supply 1/2 amp.

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15. 0-24 V POWER SUPPLYVariable regulated & filtered power supply @ I amp.

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16.'

SINGLE CHANNEL COLOR ORGANDancing lights are possible by connecting this to your HiFi and adding a light bulb.

$ 5.75

17. ELECTRONIC SIRENPolice siren simulator.

$ 4.59

18. SHIMMER STROBE LIGHTShimmer light is great for special lighting effecs.

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19. TONE GENERATORAudio tone generator produces different tones by "waving your hand".

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20. 5 TRANSISTOR 1 WATT AMPLIFIERHiFi quality amplifier - great for many uses.

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21. TUBE CONTINUITY CHECKERTube filiament tester for 7, 8 and 9 pin tubes.

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22. XENON STROBESuper strobe effects are possible with this Xenon strobe.

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23. LI 12016A COLOR ORGAN3 Channel color organ complete with PC board & instructions. 300W per channel.

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24. LOUDMOUTH SIRENVarious siren like tones are produced with an ear shattering noise level MEW $11.25

25. ROULETTE WHEELGreat party item - duplicates the real Vegas game, electronically. NEW

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Jana projects have been developed and refined over the past few years with the helpand assistance of teachers in the

school system. Many of our projects are part of the electronics teaching programs in many provinces. Each of the projects

illustrate a principle of electronics. These principles may be covered in depth or they may be just accepted as is.

LAMP

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3300 .(-,,,,t, - 2,-)

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33 -1,-; n,-\ .'n47 . 2;1 -)0

. 0'7 on100 ')7 .222 .30 .32220 .20 .25 .1,:0 , f;0330 -..-n ) .2') . 50470 .0,0 .35 .70

1000 ,-i r- ..) .60

2200 .60

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2200 1.P:7) '7) cn I. (-)03300 1. Po 7.20 3.00 5.'C04700 ?.00 7.50 3.5n 4. nn

.6800 2..50 3.00 4.50 8.5010000 3.00 3.50 6.0015000 3.50 !,..50 8.5022000 L.50 5.5033000 5.5047000 _ r-,, -,0

PR/CE INCLUDES MOUNTING CLAMPS

Note: WV -Rated Voltage (V )SV -Surge Voltage (V)C -Rated Capacitance (ul)

DIPPED SOLID TANTALUM

Capacitance Tolerance -20 +20

DC Leakage Current(uA) 0.02 or 1.0

:7i4\vj 16(20) 25(32) 35(46)

0.22 'Th --,-

0.33 .'15

0.47 _nr:

0.681.0 .

1.5 n:.;

2.2 .253.3 .2,4.7 -),._;

_ .306.8 . '15 30

10 . 20 35 .3015

_n ., ,,.:-. r,r1

22 .2n . r)0 .7033 . 50 .70 1.1047 .7n 1.1n 1.2068 1 .1 n 1. c'

100 1.50 1..90

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100 of each value -LESS 10 0101000 mixed values-LESS.15 °lc,1000 of each value - LESS ,20.°I0

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25 of each value -LESS 10%100 mixed values -LESS 15°10100 of each value - LESS 20 010

TANTALUM CAPACITORS50 of each value -LESS'10°10

100 mixed values -LESS15010100 of each value - LESS 20%

ALL ABOVE ARE PER UNIT PRICES

DOMINION RADIO & ELECTRONICS COMPANY

66.

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$149

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SEMICONDUCTORSPower

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60 Volts

NPN

7rTO -3

Metal canPNP

MJ2955

$159

RF PowerTransistor

14 - 30 MHz

1995SD 1024

50 Watts Output12 Volt Supply10 db Gain

WO 2

69'1.5 Amp200 PIV

BRIDGESFO 1

$1,95 Amp100 PIV

KO 1.

45°25 Amp

100 PIV

OUTLINE

WO

MIL 30

3 mm dia

3

LED'SDIFFUSED LENS

REDYELLOW

GREEN

.29

.339

.9.8 mcd at 20 ma.

MIL 50

5mm da

BargainTransistors

2N22212N22222N35652N37032N37042N3707

2N37082N39002N39042N40582N 51722N5526

E

Zener Diodes6 volt 1 watt6.8 volt 1 watt7.2 volt 1 watt8.2 volt 1 watt9.1 volt 1 watt12 volt 1 watt15 volt 500mw22 volt 1 watt100 volt 350mw

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2.25Thermal shut -down 2 .50

Fully protected 5.95

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Voltage regulators

L200 AOJUSTABLE MONOLITHICVOLTAGE & CURRENT REGULATOROUTPUT VOLTAGE 3 -30 VOLTSOUTPUT CURRENT 1.8 AMPSPACKAIIE PEntawart

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master chargeTHE INTERBANK CARD

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175-300 OHMMatchingTransformer

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Project

CB Power SupplyHere's the answer if you want to run the mobile rig off the line as a base station

WITH THE EXPLOSION in the popu-larity of CB radio there is a growingdemand for a power supply designed tooperate mobile transceivers as a basestation. In the mobile situation theseoperate off a 12V battery but while abattery can be used for the base stationthe problem of keeping it charged is anuisance. Some people have triedsimply a transformer, rectifier andfilter capacitor but have run intoproblems with hum.

This power supply has been de-signed to operate the base stationand can supply up to 2.5A at 13.5Vof well regulated and filtered power.While it has been designed for CB useit is a good general purpose fixedvoltage regulator. By changing a fewcomponents voltages from 5 to 50volts at up to 3 amps can be achieved.Current protection is of the foldbacktype which gives less current into ashort circuit than at the nomina out-put voltage so giving more protectionto the output transistor without affect-ing normal operation.

DESIGN FEATURESWhile we could have designed thissupply using a special voltage regulatorIC such as the 723, we decided to usetransistors as it allows a wider range ofinput - output voltages and froman educational point of view it is moreworthwhile. By changing the value ofAll the output voltage can be alteredprovided the input voltage is suitable.We chose foldback current protectionas it minimises the power dissipatedif the output is shorted, reducing theneed for a large heatsink.

SPECIFICATIONSNominal output voltage

Adjustment range

Nominal output current

Load regulation

Ripple @ 2 A

Short circuit current

13.5 volts

12V - 14.5V

0- 2.5 amps

0 - 2.5 A 150mV

0.8mV

1A


16

14

12

10

8

OUTPUTVOLTAGE

6

4

2

0 1 2 3

OUTPUT CURRENT - AMPS.

Graph showing relationship between outputvoltage and current. Note that the currentinto a short circuit is less than that availableat 13 V.

IV

4

1:701:"......"."""....."'"... 0 0

A

TRANSFORMER

B

D2

15V

Fig. 3. Component overlay and wiring diagram.

O o

TERMINALBLOCK

CB Power Supply

Fig. 2. Printed circuit layout.Full size 80 x 75 mm.

POWERCORD

c b e

2N39042N3905Bottom View


Project CB Power SupplyI 1 5V ,30Vc t

0

0GROUND I

T1D2

C14700p35V

Fig. 1. Circuit diagramof the supply.

C

0

-HOW IT WORKSAs high regulation is not required forCB use or most applications, we delib-erately chose not to use a high gain circuitwith its stability problems. The regulatoris of the series pass type with Q3 dissipa-ting the excess power. The gain of thistransistor is increased by Q2 and the Q2/3pair appears as a high gain (> 1000) PNPtransistor.

The voltage reference in the supplyis a 5.1 V zener diode and the majorityof the current needed for this comesfrom the regulated output. To enablethe unit to start RI and R2 supply somecurrent from the unregulated supplyand C2 provides additional filtering tohelp eliminate 120 Hz ripple from thereference voltage. The output voltageis divided by R11, 12 and RV1 andthen compared to the reference vol-tage by Q4 and Q5 which act as a com-parator. There is a 1.2V difference be-tween these two voltages due to thebase emitter junctions of the two tran-sistors. The comparator then controlsthe output stage Q2 and Q3 maintainingthe output voltage within limits.

Overload protection is given by 01which measures the voltage across R4(current) and the voltage across thetransistor and if the sum exceeds a setlevel Q1 will bypass some of the currentfrom the base of Q2 so limiting the out-put current. This technique allows highoutput currents at normal output voltagesbut reduces the current, and powerdissipation, if the unit is shorted.

R1 R21k 1k

4. C210025V

C

04

05C

CONSTRUCTIONThe layout of the circuit is not criticaland any construction method can beused. We have given a printed circuitboard layout which will make it easierespecially if you are not experienced inelectronics. When assembling note thatall the components except the resistorsare polarised and that the orientationof the small transistors should bechecked carefully.

We used a simple folded aluminiumbox to house the supply as anythingmore fancy was a lot more expensive.The transistor Q3 should be mountedon a heatsink preferably on the outsideof the box. The wiring diagram is givenin Fig. 3.

Peanuts sy Charles Schulz

FEBRUARY IS HEART MONTH.WELCOME YOUR HEARTFUND VOLUNTEER

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R8R9R10R11R12

5k60.22 ohm 5W3k31k

10056k2708k23k3

POTENTIOMETERSRV1 1k trim

CAPACITORSC1 4700µ 35VC2,3 100µ 25V

SEMICONDUCTORSQ1 2N390502 2N305503 2N3905Q4 2N3904Q5 2N3905

D1,2 1N5404ZD1 5.1V 300mW

MISCELLANEOUSTransformer 115V/30Vct @2APC boardHeatsinkCase, line cord and plug

F

+13.5V

0 OV


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NOTES FOR READERS OF "TOP PROJECTS" AND "CIRCUITS"For readers of our special publications "Top Projects" and "Circuits" we present here some usefulconversions. We will in future be including this information with the books.

DIODES0A91 Germanium 1N340A95 Germanium 1 N380A200 Silicon 1N4148BA100 Silicon 1N4148

GERMANIUM TRANSISTORS

BC169CBC177BC178BC179BC182LBC184BC209

MPSA18'2N39052N39052N39052N3904'MPS6515'MPS6515

AC127 2N2430 BC212 2N3905AC128 2N2706 BC214 MPS6523AC132 2N2706 BC258 2N3905AC176 2 N 2430 BC327 2N5819AC187 2N2430 BC328 2N5819AC188 2N2706 BC337 2N5818; 2N2222AACY22 2N1188 BC441 TIP31A'AD161 2N4077 BC461 TIP32A'AD162 2N2835 BC548 2N39040072 2N2706 BC549 MPS6515

BC558 2N3905BCX 31 2N5858SILICON TRANSISTORS BCX 35 2N5857

BC107 2N3904 BCY54 2N3905BC108 2N3904 BCY71 2N3905BC109 MPS6514; MPS6515 BD135 TIP29ABC109C T1597; MPSA18 BD136 TIP30ABC148 2N3904 BD137 TIP29BBC153 2 N 3904 BD138 TIP3OBBC158 2N3905 BD139 TIP29C

BD140BD266BD267BDY20BF224BFR40BFR80BFX30BFX84BFX85BFX88BFY50BFY51BSS15ZTX300ZTX500

TIP30CTIP145TIP1402N30552N3904'TIP31ATIP32A2N2905A2N22972N40012N2905A2N2297; 2N2222A2N2297; 2N2222A2N53202N2222A2N2907A

*These transistors may have different leadconfigurations. Check carefully before use.

ORP12: This light dependent resistor has adark resistance of 10M, which decreases to300R In bright sunlight.

PP3 battery: This is our 9V "transistor"battery.


Project

Freezer AlarmAn economical ETI Project Team design that provides warning of freezerfailure.

THE INCREASE IN popularity of thedomestic home freezer over the pastfew years can be attributed to anumber of factors.

One of the major attractions of thefreezer is that by buying in bulk, mostgoods can be purchased at pricesthat are significantly less than thoseobtained by purchasing the itemsone off from the supermarket shelf.

Large savings can also be made ifseasonal produce is bought inquantity while cheap, then frozen toprovide an all year round supply ofthose transient fruits of nature.

Yet another reason for the appealof the home freezer is that it is farmore convenient and economical,both in terms of time and (expensive)energy, than making continual tripsto the local shops.

The completed Freezer Alarm showing how we mounted the audio warning device on our prototype.

IC1, an LM3911, forms the temperaturesensitive element of the freezer alarm. Thedevice. described in detail in a data sheetpublished in October's ETI, produces avoltage output that is related to thetemperature at which the sensor is held.

This output voltage is given by theformula:

VOUT = 10(T + 273) mVwhere T is the sensor's temperature in

degrees centigrade.In this application we do not require the

linear output of the chip when used in itsstandard configuration, preferring an outputthat is either "on" or "off".

To achieve this two state output, and toprovide a positive switching action, we haveintroduced hysteresis.

Hysteresis is a desirable feature in manyswitching circuits and means, in this case,that the voltage level at which the output

HOW IT WORKS

KEEPING YOUR COOL

All the above advantages would,however, be negated if the freezerwere to fail. It is often the case thatthe contents of a freezer are worthmore than the thing itself, somehundreds of dollars, and failurewould prove very costly.

The design presented here willprovide warning of any such failure,allowing prompt action to be taken inorder to prevent disaster.

A warning of this sort isparticularly valuable in the case of afreezer as, unlike a fridge, manypeople pay only occasional visits totheir freezer and failure is likely to gounnoticed until its too late to takeaction.

FROZEN DESIGN

We opted to use the LM3911temperature controller chip, ratherthan the more conventional diode orthermistor, as the temperaturesensing element.

At first sight this may seem anunnecessary expense, the LM3911costing somewhat more than the 10C

stage changes state, to activate the warningdevice, is higher than the level at which itreverts to its quiescent state.

The hysteresis is provided by applyingpositive feedback from the collector of Q I tothe feedback input of IC1 via R5. Thisfeedback input is also connected to the sliderof RV1. This preset potentiometer, togetherwith R2 and R3, provides the means by whichthe unit is calibrated.

In operation, with the sensor maintained atthe working temperature of the freezer, RV1will be adjusted so that the voltage output ofthe LM3911 is just above the OV7 or so voltsrequired to turn Q1 on.

If now the sensor chip's temperature isallowed to rise, the voltage at Q1's base willfall with respect to the 0 V rail.

(The chip's output is usually takenbetween the output and the positive raii -this explains the absence of a minus sign in

the above formula.)This voltage is applied to Q1's base and, as

it falls, the voltage at Q1's collector whichuntil now has been low, will begin to rise.

The increasing positive voltage at Q1'scollector is fed back via R5 to the LM3911 andthis will cause the output to fall still further -positive feedback. This gives the requiredon/off switching action.

Once triggered, the feedback via R5 willhave the effect of keeping the device inthis state until the sensor's temperature fallsto well below the original triggering level.

RI is a current limit resistor required by theLM3911.

Q2 is a straightforward transistor switchthat energises the warning device when Q1'scollector goes high.

The power supply is provided by T1, theencapsulated bridge (BR1) and C1 whichprovides some smoothing.


or so charged fora 1N914. Uponlooking at the situation, however, theLM391 1 does however, have anumber of advantages. These includenot having to bother with stabilisedsupply rails (the LM391 1 has its owninternal regulator), and not having touse op -amps with their split supplyrails and temperature drift problems.

When these considerations areborne in mind, the temperaturecontroller chip is an attractive choicein this type of circuit - we would nothave used it otherwise.

BUY LINESNo special components are used inthis project. I he LM3911 is obtainablefrom Radio Shack or National dis-tributors.

4

3

"i0 IC12

1

TOAUDIBLEWARNINGDEVICE

Fig 3 The full circuit diagram of the Freezer Alarm.

Ti120V -9 V

50 mA

120VBR1100 V900 mA

Freezer Alarm

Fig 1 The full size (60 x 40mm)PCB foil pattern is shown left.

PARTS LISTRESISTORS all 'AW 5% CAPACITOR

R1 3k3 C1 1000u 25VR2 33k electrolyticR3 47kR4 22kR5 1M POTENTIOMETERR6 2k2R7 1k RV1 22k Vertical trim type

Fig 2. The component overlay forthe Freezer Alarm is shown above.

SEMICONDUCTORS

IC1 LM3911Q1 2N3904Q2 2N2222ABR 1 0.9A 100V

TRANSFORMER

T1 120V -9 V 50mA

TRANSDUCER

Audible Warning Device, Sonalertor similar

MISCELLANEOUS

Bo:: to suit, 5 pin DIN plug and socket,cable and plug, thin wire for sensor.

NOTE;1C1 IS LM391101 IS 2N390402 IS 2N2222A

1000u25 V

R1

3k3

R233k

R347k

RV'22k IC1

3 2

1

R4

01SENSOR

R51M

AUDIBLEWARNINGDEVICE

02


Project

ALARMING REACTIONWe also decided to use an audiowarning device, as the method ofindicating failure of the freezer.

This little fellow emits a piercingtone which should not fail to alertyou, your neighbour, yourneighbour's neighbour . . .

Just hope it does not go off in thesmall hours.

CONSTRUCTIONConstruction of the alarm is unlikelyto pose any problems. The majorityof components are mounted on thePCB and this should be assembledaccording to our overlay.

We used a fairly small box for ouralarm and this resulted in a nicecompact layout that can be seen inthe photographs of the finished unit.

The warning indicator wasmounted on the outside of our boxbut could easily be installed at alocation remote to the main circuitryif the freezer is tucked well out of theway.

The alarm is provided with anadjustment to allow the point at

Freezer Alarm

An internal view of our prototype showing the compact layout achieved

which the alarm triggers to be set atany temperature within the rangelikely to be found in a freezer.

To set up the unit, place thesensor in the freezer and leave it for afew minutes.

Apply power, and adjust RV1 untilthe alarm triggers. A setting justbefore this point should provesuitable.

If the alarm triggers spuriously,the control is probably set at toosensitive a level. "Backing off" thecontrol should put matters right.

FROZEN ASSETS

Insuring the contents of your freezermust be a good idea, but as with allinsurance, is a rather negativeapproach designed to soften the blowwhen something nasty happens.Installing the alarm should enableyou to take positive action to preventthe untoward occurring.

A final thought - a defrostedfreezer, full of food, is not a prettysight.

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A power transformer is often the single most expensive item in a project -H.E. Clayton of Reading Windings takes a close look at this often neglected item.

TRANSFORMERS ARE USED toincrease or decrease either an ACvoltage or an AC current level.

All transformers change both ACcurrent and voltage levels simultan-eously, but no transformer sig-nificantly changes power levels, asthe input power equals the outputpower plus losses which are ingeneral, negligible. Transformers canalso be used to transform impedancefrom one level (in the primary circuit)to another level in the secondarycircuit, the impedance transfer ratiobeing the square of the transformerturns ratio.

It is often possible to usetransformers in the opposite mode tothat for which they were designede.g. by feeding into the secondary of,a step down transformer and using itto step up in voltage. This will,however, usually give an outputvoltage below the rated valuebecause the turns ratio is normallymade less than the rated transforma-tion ratio to compensate for voltagedrops in the windings.

Power transformers can usually beoperated at frequencies higher thanthat for which they were designed,e.g. a 50Hz transformer can be usedat 60Hz, but not vice versa.

WHAT WE WANT IS . . .

Before deciding on a transformerfor a particular application, it ishelpful to list one's requirements andto have some idea of what optionsthere are it is hoped that thefollowing outline will help.

RMS input voltages and supplyfrequency: In addition to the nominalinput voltage the maximum value towhich this can rise should also beconsidered. Most transformers willoperate satisfactorily at about 6%overvoltage for short periods of timebut if it expected to exceed this figureit is advisable to increase the ratedinput voltage. Primary windings canbe tapped to cater for several voltagesbut this adds considerably to the costof the transformer and may detractfrom performance. Twin series -parallel windings on the other hand,although adding a little to the cost, donot substantially interfere withefficiency as all of the winding is inuse for both series and parallelconnections. They are howeverlimited to dual input voltage applica-tions where one voltage is twice theother e.g. 240/120V.Output Currents and Voltages:Unless otherwise agreed, the nominalor rated output voltage is that at fullload output current based on resistiveload. Again, several voltages can beprovided by tapping and, unlike theprimary taps, several secondarytappings can be used simultaneouslyto supply a number of loads. If,however, there is a significantdifference between the load currentsat different tappings, it may bepreferable to have separate windings.NB: The information above is theminimum which must be decided bythe user, all the following require-ments may remain unspecified unlesscircumstances demand otherwise,always remembering that special

features can add considerably to atransformer's cost.Regulation (usually MaximumValue): The regulation is defined asthe difference between a secondaryterminal voltage on open circuit andthe secondary terminal voltage atrated full load current.

Maximum permissible Temperat-ure rise: This is often decided by themanufacturer rather than the user asit may depend on the materials used.Higher standard temperature risesare associated with lower ambienttemperatures.

4,1 TAMA

HMS E '<CITATION CURRENT

Fig. 1. Plot of excitation currents vs. RMS inputvoltage for typical transformer. The transformershould not be operated for long periods abovethe.knee" of this curve.

Input Current (or Excitation orMagnetising Current): The no loadinput characteristic is shaped as inFig. 1 and care should be taken not touse the transformer for long periods


with voltages much higher than the"knee- of the curve.Electrical requirements: Limitationsto distortion of secondary waveform,any special phasing requirements etc.Insulation requirements: The basicstandard requirement is for a 2kVRMS test between the input andoutput windings and between anywinding and the core if accessible.Impregnation etc: Transformerswithout hygroscopic materials (thosethat absorb moisture) are oftenvarnish dipped while those usingabsorbent materials such as paper arevarnish impregnated. Both of theseprocesses are effective for minimisinglamination vibration and sealingagainst ingress of moisture.Dimensions: Any limiting dimen-sions and /or fixing centres.Construction: Some of the commonalternatives are described below.

WHAT COREInterleaved laminations are widely

used for small power transformers,the most common shape being theno -waste 'E' and 'I' in which the 'I'sare cut from the 'E's (see Fig. 2) andthe coils assembled over the centrelimb (shell type construction). Theseare available in .50mm and .355mmthickness in various grades of hotrolled silicon iron and in 0.355 mmgrain -orientated silicon iron.

I

41,

Fig 2. No -waste E and l construction oftransformer laminations

Toroids and 'C' cores are madeof 0.355 and 0.10 mm thickness, thethicker material being used in the50-60Hz devices. Toroids have ahighly efficient magnetic circuit andby virtue of their circular shape, lowleakage flux. They are sometimeschosen because they can be used tomake a "low profile'' i.e. low heighttransformer.

Because the cost of toroidaltransformers can be three times thatof an E and I laminated transformer, acompromise between the two whichis sometimes used for low profileunits uses U and I laminations withthe coils on the long limbs of the(Core type construction).

WINDING THINGS UPMoulded bobbins are widely used

for smaller transformers. They havethe advantage that they can bewound on high speed machines.Insulation thickness between wind-ings and core and between windingscan be assured. The winding spacefactor (ratio of area occupied byactive copper and total winding area)is high and terminal tags can bemounted on the bobbin cheeks.Certain bobbins may be fitted withshrouds encasing the windings andgiving good mechanical and electricalprotection.

ENDING IT ALLThe cheapest terminations are solder

tags on the bobbin cheeks. Forapplications where solder connec-tions are not convenient terminalblocks can be mounted on thetransformer. For larger transformersterminal panels with turret lugs orbolted connections are used.

MOUNTING UPMounting brackets are available

for the range of standard no -waste Eand I laminations. They take the formof 'U' clamps with two hole fixingwhich are crimpled on to the smallersizes (up to about 50VA) and flangedand frames secured to the largertransformers with core bolts andproviding four fixing slots or each oftheir four sides (universal mounting).At the small end of the range (up toabout 5VA) pin terminations can beused for PCB mounting.

ELECTRICALPERFORMANCE

In its simplest form a transformerconsists of an input and outputwinding magnetically coupled withan iron core. The windings representan impedance in series with the load

and the core can be considered to bean impedance shunting the load. Thewinding impedances cause voltagedrops proportional to the load currentand a watts (copper) loss proportionalto the square of the load current. Thecore impedance does not directlyproduce a voltage drop but isassoc ated with an energy (iron) lossapproximately proportional to thesquare of the volts per turn for a fixedsupply frequency. The total losses(coppe' and iron) determine theoperating temperature rise of thetransformer which is usually the mostimportant factor limiting the use ofthe transformer.

WATTS A VAAlthough the transformer total

losses depend on both voltage andcurrent, they are independent of thephase factor. For this reason trans-formers are rated in maximum VAand not in watts although withresistive loads VA = watts.

Transformer windings also have"self inductance- which can bethought of as a reactance in serieswith the winding resistance andthe load and is usually referred to asthe "leakage reactance-. This doesnot usually effect the performance ofsmall power transformers (belowabout 100 VA size) particularly whenused with resistive loads.

PHYSICAL PERFORMANCEAs transformers increase in VA

rating and physical size, the workingflux density and the winding currentdensity are reduced, but even over arelatively large range of sizes, thevariation is small enough to assumethat they are constant.

With this premise, it is interestingto consider the effect on variousparameters of change in physical sizefor the same overall shape.

Fig 3 A collection of some of the more common transformer types Some of the wide varietyof constructions and terminations available can be seer in this photograph

I.

ETI CANADA - FEBRUARY 19785.3

TRANSFORMERS

We can show that1) The regulation of small trans-

formers with resistive loadsdecreases in inverse ratio to theincrease in any linear dimensionand

2) The reactive voltage dropincreases while the resistive dropdecreases linearly with dimen-sions.

Figure 4 shows the relationshipbetween transformer VA rating,volume (or weight) and regulation.The volume here is the length Xwidth X height, not the displace-ment. This is based on mainstransformers using E and I no wastelaminations and operating at 60 Hz.It is often possible to increase theoutput current of a power transformerbeyond the rated value if one canaccept a temperature rise higher thanthe designed value. Overloading thetransformer in this way will, however,cause the output voltage to fallbecause of the increased voltagedrops in the windings.

TRYING TIMEThe following tests can be used to

establish basic transformer charac-teristics.

Turns Ratio: Apply a known voltage,less than the rated value, to theprimary winding and measure thesecondary voltage. Care should betaken, especially with transformersbelow about 20VA rating, that theinstrument used does not impose asignificant load on the transformer.

Excitation Characteristic Connectas in Fig. 5 and apply the ratedinput voltage to primary terminalsand measure input current andvoltage.

Fig. 5. Connections for the excitation oropen -circuit test. The rated input voltage isapplied to the primary and the excitation currentis shown by A.

Winding Resistance Measure theprimary and secondary DC windingresistances with a multimeter orWheatstone bridge.

VOLUME WEIGHTCCs KG

REGULATION 't.

501300

Fig. 4. Graph1100 - showing relation -

1000-1c ship between

transformer VA

4.0

90G - 4' rating and both- 25 volume (or800

sc-.'s° 0Q,N,,,c,

weight) and regu-- 3 0

700 - "'4 . . -0°('

20lation. These cur -yes are based on E

600 -0

.eand I no -waste

5002- (-' O -. 15 laminations ope-

40C - rating at 60Hz.

- 10100 -200 - -REGULATION

55°C TEMP5

100RISE

I III I I II i I.0 20 40 60 80 100 120 14D 160 180 20C OUTPUT VA

Phasing. Where windings can beinterconnected e.g. with series/pa-rallel designs, it is important toestablish the relative polarity ofterminations. This can be done byconnecting the windings concerned inseries, applying an alternating voltageto one and measuring the overallvoltage (Fig. 6). If this measuredvoltage is greater than the appliedvoltage, then the windings are inphase. Conversely, if the measuredvoltage represents the difference ofthe two winding voltages the connec-tion is in anti -phase.

Fig. 6. Connections for the relative polarity test

IT TAKES ALL SORTSTransformers Feeding Rectifiers.

A common application for smalltransformers is to supply full waverectifier circuits including capacitorinput filters. The most common arethe bridge amd bi-phase circuitsshown in Fig. 7.

For the same power rating, thetransformer for the bi-phase circuitwill be larger than that for the bridgecircuit because produ-ces twice the voltage and carriescurrent during each half cycle only.Ideally the secondary winding for thebi phase transformer occupies 1 -2 -

times the space of the primarywinding. Although transformer costis higher, rectifier costs are lower forthe bi-phase circuit.

The relationship between theaverage DC voltage and the RMSsecondary voltage is complex and isdependent on the smoothing capacit-ance, the supply frequency, thetransformer series impedance and theload impedance. Curves illustratingthis and other relevant relationshipsare published by rectifier manufactu-rers but neglect the effect of

FULL WAVECAPACITIVE INPUT FILTEP

LOAD

81 PHASE CIRCUIT

FULL WAVE BRIDGECAPACITIVE INPUT FILTER

BRIDGE CIRCUIT

Fig. 7. Two of the most common rectifier circuits for use with capacitive input filters.

LOAD


transformer leakage reactance whichmay be significant on some largertransformers. Because the waveformof the transformer current is very'peaky' the effective reactive volt dropis greater than may be expected byconsidering RMS values.

Autotransformers have a singletapped winding to provide bothinput and output circuits. Withtransformation ratios near unity.autotransformers can be much smal-ler than similarly rated double -woundtransformers

A disadvantage of autotransfor-mers is that there is a direct electricalconnection between primary andsecondary circuits so that both circuitsshare a common relationship toground.

Isolating Transformersusually have a 1:1 transformationratio and are provided specifically toelectrically isolate the secondarycircuit from any earth connection inthe primary circuit e.g. 'line'circuits.

Inverter Transformers (.e.g forswitched mode power supplies).These usually operate in the kilohertzrange of frequencies and are suppliedwith square wave -form voltage.

High Impedance Transformers areused for a variety of purposes a fewof which are mentioned below

Short -Circuit Proof transformers aredesigned to continue in operationwithout damage when the secondaryterminals are short-circuited. Small

OUTPUTVOLTS

OUTPUTCURRENT

Fig 8 Relationship between output currentand output volts of high reactance transformerwith resistive load

A

transformers (below about 5VA size)are sometimes made with sufficientlyhigh winding resistances to restrictthe short circuit current but with largertransformers an adjacent windingstructure is used with an intermediatemagnetic shunt. This gives an outputcharacteristic as shown in figure 8when used with resistive loads.

High Frequency Transformers.The foregoing is concerned

with transformers operating only at aconstant supply frequency and withsinusoidal waveforms. Transformersused in communication circuits arerequired to handle a wide range offrequencies and waveforms, al-though any repetitive waveform canbe expressed as a series of sine wavecomponents. Such transformers areoften used in an impedance matchingrole. It is well known that to transferthe maximum amount of energy into aload from a voltage source the loadimpedance should equal the sourceimpedance.

SHIELDINGStray magnetic fields produced by

power transformers can cause hum inhigh gain amplifiers in the samelocality. Shielding around the powertransformer is not normal because alarge percentage of the stray flux,which is emitted in all directions,would strike the shield at right anglesand pass through it rather than bediverted. On the other hand input(e.g. microphone) transformers areoften enclosed in a screen of magneticmaterial to reduce pick-up.

PRODUCTION METHODSCoil winding techniques and

machinery have improved immenselyin recent years. Unfortunately it is notalways possible to make the best useof these improvements which aremainly geared to high volumeproduction of standard products.Although some degree of standardi-zation in small transformers has beenachieved equipment designers stillexpect transformers to be tailor-made,often in small quantities, to theirparticular electrical and dimensionalrequirements.

Summarizing, before seeking aspecial transformer, consider first ifreadily available standard trans-formers can be used. It is generallycheaper to use a standard transformerand make circuit modifications toaccommodate it, than to use a customone. However companies such asHammond Mfg. give surprisinglyreasonable prices on non-standardmodels in quantities of just two orthree.

BINDERSIn resporse to many requests from ourreaders we have arranged for binders to bemade so that you can keep ETI's firstCanadian volume together and protectedfrom damage. The binders are covered inattractive leather -look black plastic andare designed to hold twelve issues The ETIdesign is printed in gold letters on thespine.

The binders cost $5.00 each, which includes postage and packaging. Do not send cash - you can pay by cheque. Mastercharge. or Charge,xCredit card orders must include your account number, the expiry date, and your signature. In all cases allow six weeks for delivery.

Send your order to ETI Binders, Unit 6, 25 Overlea Blvd.. Toronto. Ontario M4H 4B1. Don't forget to include your name and address.Ontario residents add 7% PST.


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BITS, BYTES and BAUDSby Bill Johnson VE3APZ

This month's subject is memory of all shapes and sizes employed in variouscomputer systems.

AT THIS POINT in our series, we haveseen how a computer works, how itaddresses memory, and how it cansend data to and receive data from aperipheral. The program (or set ofinstructions for the computer tofollow) must reside in the memory thatis readily available to the computer sothat it has access to all it needs, simplyby sending an address on the addresslines and receiving instructions on thedata lines. If the computer in ourexample were to be doing a constant,repetitive, function such as controllingthe traffic lights at an intersection, thenit would only ever need to run oneprogram. This program would bepermanently burned into a ROM(Read -only -memory). This is thesimplest form of a computer system,and its description ends here.

Of more interest to us is the generalpurpose computer, such as may befound in an office, for example. Thistype of computer may have more thana hundred different programs forvarious day-to-day jobs, as well asdozens more that are executed onlyonce a week, once a month, or lessoften. These programs are not allneeded at the same time, and so neednot all be stored in the main memory.Main memory is very expensive (seeFig. 1) when compared to offlinememory, such as paper tape, cas-settes, and discs, and so shrewdsystem designers store as manyprograms offline as possible to reducemain memory needs.

ONLINE-OFFLINESTORAGETo get a better idea of the differencebetween online and offline storage,let's compare our computer to atheatre. The actors who are currentlyperforming occupy the stage, which isa very elaborate platform, designed tobe in full view of the audience, and

having lots of expensive accessories,such as lights, microphones, scenery,etc, to make it a very effective place forthe actors to work. When the actors arenot acting, they leave the stage andwait in the wings. The wings on thestage are very crowded places wherespace is at a premium, and so you willonly find them there immediatelybefore and after their performance onthe stage. Beyond the wings you willfind all sorts of space reserved fordressing rooms, etc, where actors cango to relax. They know that when theyare in these rooms, they will get plentyof notice before they are needed on thestage.

In a computer, the stage is the mainmemory, which is sometimes referredto as executable memory, becauseprograms must be in this type ofmemory to be executed. It is veryexpensive, like the stage, because it isvery fast, and programs are only puthere when they are needed.

The wings of the stage represent anyform of fast -access device, such as afloppy disc. where data can be storedand retrieved very quickly. Data andsub -programs that are used constantly

execution they may be brought intomemory and taken out again asrequired by the program.

The dressing rooms of our computerare devices such as a cassette systemwhere we can store programs untiltheir turn comes to go into the mainmemory. Changing of main programshappens relatively infrequently, andlots of notice can be given, so thedelays in getting programs intomemory aren't very serious.

Now that we have decided that it'ssmart to store programs and dataoffline when not using them, let's lookinto the multitude of devices that canbe used for storage.

OLD FAITHFUL - THEPAPER TAPEFor tne small system owner justbuilding his system, an obviousstarting point is a teletype machine(TTY). TTYs sometimes have a punchand reader added, capable of storingand retrieving data by punching themon paper tape. For computer purposes,an 8 level machine is needed, such asthe Teletype Corporation modelASR33 or ASR35. (ASR stands for

by a main program in memory are Automatic Send -Receive, meaningstored on such a device, because that it is a basic unit with a reader -during the course of a program's punch added, as opposed to a KSR

TYPE DEVICE MEDIA STORAGE COST/ TIME TO TRANSFERCOST COST CAPABILITY BIT FIND RATE ONCE

$ $ K Bytes C DATA FOUND

PAPER TAPE 1000 100/K N/A 01 UP TO 110 Bps1 HOUR

AUDIO 50 2.00 80 3 1-2 mins 300 BpsCASSETTE

FLOPPY 4000 10.00 250 03 500 ins 250 KBpsDISC

RAM 65K 1-2 450 ns 2 MBps

Frg. 1. - Cos' of venous types of memory and 'herr speed


which simply means Keyboard Send -Receive - i.e. no punch/reader).

In order to store all programs in amanner that can be readily reloadedinto the computer, a standard must beestablished to define what each itemon the tape means. Each part ofmemory, as it is dumped onto punchedtape, can be considered as a block.These blocks of memory can be anyconvenient length, and are stored asindividual records on the tape. Everybyte of data, when sent to the teletypemachine, will cause the eight hole -punches to pierce the paper or not,depending on whether the correspon-ding bit is a 1 (hole) or a 0 (no hole).The paper moves forward after onebyte, or frame has been punched, andat the same time the teletype machineis receiving the next character forpunching. In this way, the result ofsending a complete block of memory,one byte at a time, will be a long tapewith holes corresponding to the bitsstored in memory as ones.

HOLES ARE NOT ENOUGHHowever, just to store the contents ofmemory onto paper tape does notconstitute a complete record.Generally -accepted practice dictatesthat prior to starting a dump of somememory, the computer shall send thefollowing to the teletype: (see Fig. 2)

b) One or two frames with a code thatindicates that a new record is about tostart, and sometimes, optionally, thetype of record (data or program).c) Two frames which specify theaddress where this program starts inmemory.d) Two frames that specify theaddress to which control should begiven at the completion of loading ifthis is a self-starting program.e) One or two frames which specify thelength of this block of data, so that theloader knows when to expect the endof the data.f) A variable number of framescontaining the actual data taken frommemory, beginning at the addressspecified in part (c).g) A special frame or frames thatcontain a checksum, compiled from aprocess which is affected by every byteof data on the tape. This byte iscalculated and stored as the computeris dumping the program. When thecomputer reads in the program again,it makes the same calculation as itmade before when it dumped the data,except that this time it is basing thecalculation on the data received fromthe tape. After the computer has madethis calculation on all information readin, it then compares the answer it nowgets to the answer that is stored as thelast frame(s) on the tape. If the twoanswers disagree, then the operator is

START AND TYPE OF RECORD BYTESMEMORY START ADDRESS

ADDRESS FOR CONTROL TRANSFERLENGTH OF THIS BLOCK

00000 000 00000 0000 000 000 000 000000 0000 00000 00000 00 0 000 0000 000 000000 f: 00000 00000 00000 0000 000 0 000 000 0 0,

BLANKLEADER

Fig. 2. - Data and preamble,postamble layout onpaper tape.

DATA BLOCK CHECKSUM

a) A leader consisting of several frames(usually ten or more) of blank tape.This gives the user space to write onthe tape describing the program, andalso provides an alert to the reader(when the program is loaded into thecomputer again) that a new blockfollows.

warned that an error occurred duringthe reading of the last block, and thathe should retry that block.h) Several rubouts, or all -holes -punched frames to indicate an end -of -block.

A long program would be brokendown into many smaller blocks, so that

if an error occurs during a single block,the block itself would be retried by theoperator until it is received correctly,instead of having to wait until the entireprogram has read in before reloading itall.

The above program tape descriptiondoes not necessarily represent anactual format used by any particularmanufacturer, but rather a general ideaof how most of them operate.

This method is similar to the mainform of program loading in the earlydays of small minicomputer andmicrocomputer systems. It is largelyobsolete now in the minicomputerfield, except for small, dedicatedsystems such as industrial controllerswhose program is changed very rarely.It is still used, however, as a last-ditchmethod of getting diagnostic pro-grams into a computer system when afield engineer cannot get a majorsystem device, such as a disc, to loadprograms. For this reason, most mini-computer manufacturers still shipdiagnostics on paper tape with theirproducts.BUT EVERYBODY HAS ACASSETTEA natural development from paper tapewas the cassette, although this methodhas failed to fulfil the expectations ofcommercial users, since cassettetransports designed for home enter-tainment use are not accurate enoughfor high-speed data use, and thedevelopment of purely digital systemswas largely overshadowed by IBM'sintroduction of the floppy disc. Acassette can be viewed in exactly thesame manner as paper tape, includingthe way that blocks are formatted asdescribed above. The only differenceis that instead of parallel holes beingused to represent the ones and zeroes,tones are used in pure serial fashion onthe cassette, i.e. one after the other.The simplest method of recording dataon a cassette would be to send the datato an asynchronous line, just as if itwere going to be punched on a teletypemachine, but replacing the teletypemachine with a modem and recordingthe tones from the modem on tape.This method is rarely used, moremodern and efficient methods such asCUTS and Kansas City standardshaving been developed by computerhobbyists for better reliability.

One major disadvantage of both thepaper tape and cassette systems is thatthey are both sequential accesssystems. This means that if you storefifty programs, and later want to


retrieve the fiftieth one, you have toread through the preceeding forty-nine programs until you get to the oneyou want. With paper tape, thisheadache is almost eliminated byputting every program on a separatepiece of paper tape, but this has thedisadvantage of requiring operatorintervention to find the correct tapeand load it into the reader. Cassettesystems can sometimes have a betterapproach to this problem. This type ofsystem can turn off the tonescompletely for a distance between thedata blocks, so that there is a quiet spoton the tape. The program puts aprogram name or identifier at thebeginning of every block. (see Fig. 3)When the cassette controller isinstructed to find a particular blocknumber or program name, it reads thefirst few frames of a block, checks tosee if the identifier matches that whichit is looking for, and if so, reads thewhole block. If it does not match, itthen fast -forwards the tape untilanother silent gap is detected, at whichtime the controller slows down the tapeto read the first few frames, and so onuntil the whole program is loaded.

SILENCE

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without having to read all data beforeit.

The floppy disc is made up of aflexible, circular piece of mylar, aboutthe size of a 45 rpm gramophonerecord. (see Fig. 4) One side of the"diskette" is covered with metal oxide,just as is one side of a cassette tape. Onthis surface, all data are recorded, inthe following manner:

As the diskette spins around at 360rpm, the head can move in and outalong a line joining the centre of thehub of the diskette and a fixed point onthe perimeter of the diske:te. Theactual diskette is enclosed in anenvelope to protect it, and a slot is cutin the envelope along the line of travelof the magnetic recording head, on theside of the diskette containing theoxide. The inside of this envelopecontains a felt -like material that cleansthe diskette and traps any foreignparticles as the diskette spins.

The head can be moved in and outover the surface of the diskette inincrements of 1/48 inch. Every 1/48inch is defined as being a track,starting at a predetermined distance infrom the edge of the diskette. Each

P

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ENTER THE FLOPPY DISCWhen IBM introduced the floppy disc,it was designed to be a quick, reliablemethod of reloading the microprogramof their big mainframes, quickly andeffectively after a power failure or othercause of loss of control memory. As aresult of the availability of the floppydisc it is not worth the trouble andexpense for anyone to develop ageneral-purpose, commercial -gradecassette system, since cassettes areinherently unsuited for data purposesand a floppy disc system is onlymarginally more expensive. Also, thefloppy disc wins hands down over allsequential -access devices, because itis a random-access device.

Random access simply means thatany part of a file can be accessed

track forms a circle, centred on thecentre of the disc. Thus all data arewritten on the 77 concentric tracks.

At a specified spot on the mylar, ahole is punched so that light can passthrough it. This point is defined asbeing the start point of all the tracks. Asthe disc spins past this point, no matterwhich track the head is over, it will be atthe beginning of that track.

Each track is further divided into 26sectors. In some diskettes, a hole ispunched in the mylar to signal thebeginning of each sector. These areknown as hard -sectored diskettes,since the hardware (photocell)actually gives a signal to the interfaceto tell it when a new sector is starting.The IBM 3740 standard diskette is a so-called soft -sectored diskette, since the

Bits Bytes and Baudsstart position of each sector isdetermined by a calculation based onthe time interval after the main indexhole has passed.

INDEX HOLE

HUB CONTACTAREA

HEADCON FACAHEA

Fig. 4. - IBM 3740 Diskette.

At the beginning of each sector arewritten a series of identifying markstelling the controller the track andsector it has found. It compares thesewhen it has read them with where it hascalculated the head to be and sees ifthere has been an error. Also found atthis point at the beginning of eachsector is a series of check marksspecially encoded to test that the headis decoding the magnetic flux changesproperly. Following the above (calledpreamble) there are 128 bytes of data,followed by some more checkingmarks called postamble.

Thus the floppy disc controller canrandomly retrieve any 128 byte recordfrom the 2002 such blocks on thediskette. All the user has to do isspecify the track and sector numberwhere he stored the data, and he canretrieve it years later.

In most actual operating systems,the track and sector numbers are notused by the system user, but files arereferenced by a name that is given tothem at creation. At the beginning ofthe diskette there is a cross-referencefile which contains the file names andtheir corresponding track and sectornumbers. This file is known as thedirectory, and is manipulated by theprograms of the manufacturer -supplied operating system software tostore and later retrieve all files requiredby the user.


Sinclair CambridgeProgrammableDon't be fooled by the tiny size this is really a programmable calculator,and a useful one at that! - Les Bell reports.

MOST OF OUR READERS are involvedwith circuit design or other vaguelymathematical problems from time totime. In fact some may actually useBesse! functions, Chebyshev polynom-ials and other frightening beasts fromthe mathematical night.

A common requirement is to solvea problem repetitively; for example,a filter design may have to be optimisedand values recalculated - a long andtedious job. This is where the prog-rammable pocket calculator comesinto its own - you can load in thekeystroke sequence required to do thejob and then run that program as oftenas you want.

The problem is that programmablepocket calculators are expensive; true,they're getting cheaper, but not fastenough for most of us. But at last,the programmable is down in price tothe stage where even schoolkids canafford to use one. One companybehind this move is Sinclair Radionics.

PROGRAMMABLESinclair have been producing theCambridge range of pocket calculatorsfor a good few years now and the designhas stood the test of time pretty well.There have been a few minor changes,both internal and external, since theoriginal models, but none so big as withthe introduction of the CambridgeProgrammable.

Sinclair have had an earlier attemptat a programmable calculator as anextension of their Oxford series, butthe machine was not very successfulfrom the design point of view - itabused Reverse Polish Notation (nostack!) and could best be described asquirky in its operation. Fortunately,Sinclair have sorted out the goodpoints from the bad and used thebest ideas in producing the Cambridgeversion.

The Cambridge format is tiny -only 110 x 50 x 17 mm with 19 keys,and this makes for a very busy keyboardindeed. All the numeral keys have threefunctions, i.e. digit entry, and up -shift

60

and down -shift functions. Because thereis little space between the keys, thelegends are a little cramped and con-fusing, but with practice you soonget to know your way around.

NEAT TRICKVery neat trick No. 1: when in theprogram -entry mode all the numeralkeys are automatically interpreted asupshifted functions, unless preceded

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This is the animal slightly larger than life;you can see how crowded the keyboard is.

by a 'hash' symbol. This saves a fairnumber of keystrokes, but if you'renot used to it, you forget that symboland your program goes berserk. Back

to square one, and more practice.Apart from the mere ability to

parrot -fashion execute sequences ofkeystrokes an important facilityoffered by many programmables is

that of decision -taking. This enablesthe calculator to act differently ondifferent input values, or more imp-ortantly, to loop around, performingan iterative calculation until an accurateenough result has been achieved. Agood example of the need for decision -making capabilities occurs in games suchas 'Lunar Lander', where the calculatorhas to decide whether you're at a heightof less than zero feet, in which caseyou've landed, and the calculator nowworks out your terminal velocity.

The Cambridge Programmable doeshave rudimentary conditional branching,in the form of a 'go if neg' instruction,which jumps to a specified line numberif the result is negative, or continuesotherwise.

The calculator is a little bit awkwardto use at first, for a variety of reasons:just to get into the program mode youhave to press seven keys, and every timeyou reset it to step 0 to run a program,it displays the first step.

HANDY WRINKLERather than reset the machine to thebeginning of your program by hand,insert the sequence 'downshift/goto/0/0' at the end (if you have room) andwhen the machine halts at the end ofthe program, pressing 'RUN' will auto-matically reset the machine to step 0.Clever stuff, eh?

There is a wide variety of scientificfunctions on the C.P. including all thetrig functions, which operate in radians.

In addition, there are all the standardtechnical functions, (except log andantilog to base ten), and degree/radianconversions. On top of all that there arethe usual exponent entry, sign change,memory functions, etc., and also theprogram control and editing keys.This makes for a crowded keyboard,but after a little practice, this is noproblem. Cont'd on p 64


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The major failing with this calculatoris, we feel, the lack of accuracy on thelog and trig functions. While these areprobably good enough for everydayuse, there is considerably more impor-tance attached to accuracy in a prog-rammable calculator. The reason for thisis simple: if one is using an iterativetechnique to, tor example, find a rootof an equation, then the calculator isgoing round a loop, using the resultof the last run through the loop as theinput for the next. It is possible to goround a loop of this nature hundreds,or even thousands, of times.

Now, if the loop includes a log or trigfunction, the first time round the loopan error will be introduced into thecalculation, which may not be very large;but the second time round the loopthe error is compounded, the third timeit is still greater, and so the error is

multiplied through the calculation,possibly reaching the same order ofmagnitude as the correct result.

We found that the ex (or exp)function was a bit hairy; for example,exp (1) gave a result of 2.7179766,as opposed to the correct answer ofthe transcendental number e, whichequals 2.718281828.... This is an errorof 0.012% (!). The trig functions hadlower errors - compare these resultswith the correct answers in brackets:sin tr/2 = 0.9998814 (1), cos ir/2 =0.0154012 (0), tan rr/2 = 64.95699(infinity), sin n =0.0814007 (0),cos n = 0.9966814 (-1), tan it =

0.0816717 (0). In each of these casesthe error symbol lit on the display.For mid -range values: sin tr/3 =

0.8658722 (0.8660254034), cos n/3=0.5002651 (0.5), tan it/3 = 1.730829(1.732050806).

These results are not stunninglyaccurate. The accuracy is adequatefor most everyday applications, but hasto be watched in iterative programs.Who needs 12 -digit accuracy anyway -there is virtually nothing in the universethat can be measured that closely,so that five or six digits suffice formost calculations. We shall qualify ourcomments later when discussing theinnards of the machine.

Other minor moans: the 'powerbulge' in the back of the machine is

not very elegant, and there is no yxfunction. Both of these are only minorquibbles.

INNARDSVery neat trick No. 2: when you openup the back of the calculator you willbe pleasantly surprised to discover thatthere is nothing inside to go wrong(well almost). There is one calculatorchip, one digit driver chip, a capacitor,and a display and keyboard. The key-board is Sinclair's standard design, the

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1-C) press RUNdigit driver is National Semiconductor'sstandard design, the capacitor is ITT's,and the display, although made byNational, is not standard, and is pre-sumably specially made for Sinclair.

But the calculator chip is the realbelle of the ball. It is National's MME799Controller Oriented Processor (COPS),a MOS/LSI device which can scan up to56 keyboard switches, can outputBCD or 7 -segment data, and has serialI/O ports for expansion to externalmemory and peripherals such as printers.On the chip are 384 bits (96 digits)of RAM, and 1536 bytes of ROM, anALU (Arithmetic and Logic Unit), andan on -chip clock plus lots of otherbits of logic. The ROM is mask -pro-grammed, which is an expensive op-eration and only economical for quan-tities in the tens of thousands, so don'tgo out and try to buy one! This deviceis really an 8 -bit microcomputerorganised to do BCD arithmetic.

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is not too hot accuracy dept.With only 1.5 Kbytes available for theircalculator microcode, just getting ina reasonable number of scientificfunctions would be very tricky, andmaking it programmable would be verytricky indeed. Now, for a calculatorapplication, the COPS processor seemsto have rather more RAM than is

required for the amount of ROM; andso we suspect that Sinclair's designersfound themselves stuck with a trickydecision. They could either provide acomprehensive and accurate straightscientific, which would fully utilisethe ROM but leave a lot of spare RAM,or they could omit some of the functionsand/or compromise on the accuracy,thereby releasing some ROM toimplement programmability - theprogram could then be stored in the40 -odd spare nybbles of RAM.

Well, they went for the programmable;I would have, too. The loss of accuracyis easily tolerable in exchange for prog-rammability. The problem with iterativeloops is not a serious one - perhaps oneof our readers who has time to sparemay like to do a study of this, as wejust haven't had the time. Iteration isa useful technique for solving equationsof the form x = fix), e.g. x = //x + 4,but this is only one application forprogrammable calculators, and most willnot be troubled by accuracy consider-ations.


Sinclair Cambridge ProgrammableNow that Sinclair's engineers are fully

aquainted with the COPS processor, itis quite probable that they will produceother calculators using it - a financialmachine is particularly appealing, sinceanother standard COPS chip providesa complete interface to a Seiko printer.

PROGRAM LIBRARYHere is very neat trick No. 3: due to thefact that the calculator is algebraic,strange and very non -obvious keystrokesequences can be used to perform usefulfunctions - the most obvious one isthat pressing x twice performs squaring.These tricks considerably expand thepower of the calculator, but unfortu-nately they are not explained in themanual (which we reckon gives you allthe information you need, but onlyjust).

The main source of information is

Sinclair's Program Library. Seeing thata major attraction of the machine would

be a large amount of readily -availablesoftware for people who do not wishto write their own programs, they havecompiled a collection of 294 programsrelevant to a wide variety of disciplines.Their application programmer obviouslyunderstands the machine fully and usesevery trick in the book to maximisethe power of his programs. The 4-

volume Program Library is worth everypenny, even if you never use half theprograms, but also for what you canlearn from it.

zOr, summing up (sorry, I couldn'tresist it!). The Sinclair CambridgeProgrammable is an enthusiast'smachine. Experimenting with it will payoff handsomely, especially if you takethe time to work through some of theprograms in the Library and figure outjust what the calculator is doing. If

you're not very enthusiastic aboutcalculators, and don't really need a

programmable, forget about this one,you'll get fed up with the fiddlinessof the key sequences, and probablygive up.

Although we have been pretty critical,we reckon we have covered just aboutall the failings of this calculator, and ifthese are all there are, then it standshead and shoulders above similarlypriced calculators. It offers superbvalue for money, virtually unlimitedcapability, and a lot of fun. We con-fidently predict that it will be popularwith our readers, so if you write anyinteresting programs let us know aboutthem and we'll pass them on.Beginning with our March issue we willbe publishing interesting software inour SOFTSPOT department. We willwelcome programs for this or otherprogrammable calculators -- see theannouncement elsewhere in this issue.

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tech -tipsTech -Tips is an ideas forum and is not aimed at the beginner.

ETI is prepared to consider circuits or ideas submitted byreaders for this page. All items used will be paid for. Draw-ings should be as clear as possible and the text should prefer-ably be typed. Circuits must not be subject to copyright.Items for consideration should be sent to ETI TECH -TIPS,Electronics Today International, Unit 6, 25 Overlea Blvd.,Toronto, Ontario, M4H 1B1.

CHEAPO DOWN COUNTERAF Bush

This circuit, when presented with a 4 bitbinary number in the range 0000-1001will present the nines complement ofthat number at the output.

Connecting the circuit between a

7490 and a 7447, will, instead of theusual up count, provide a display whichcounts down from nine.

This provides a useful alternative tothe 74192 when only a down count isrequ i red.

NPN-PNP INDICATORF Read

The first 2 inverters IC1a and IC1b forma multivibrator running at approximate--1y 2 kHz. The next two inverters buff--er the multivibrator outputs, whichthen go to the collector and emitter ofthe transistor under test.The signal applied to the base of the

transistor is always in phase with thecollector so the transistor, whether PNPor NPN, will always be turned fully onevery half cycle.

When an NPN transistor is being testedthe collector will always be near OV andwhen a PNP transistor is being testedthe emitter will always be near OV.The last two inverters detect which

terminal is held at OV and drive theappropriate LED via the current limit--ing resistors R4 and R5.The six inverters needed are all con-

tained in a single IC package - theSN7404.

13

C1

R1 100n2k2

TO PIN 7, ICI -VeNo.

R22k2 C2

100n

AO

IC1a-d

IC1fD6

BCDCOUNT

INPJTS OUTPUTS COMPL-EMENTDC BA 0 QC 013 QA

0 0 0 0 0 1 0 0 1 9

1 0 0 0 1 1 0 0 0 8

2 0 0 1 0 0 1 1 1 7

3 0 0 1 1 0 1 1 0 6

4 0 1 0 0 0 1 0 1 5

5 0 1 0 1 0 1 0 0 4

6 0 1 1 0 0 0 1 1 3

7 0 1 1 1 0 0 1 0 2

8 1 0 0 0 0 0 0 1 1

9 1 0 0 1 0 0 0 0 0

0 CIA

IC1=SN7404D1 -9=1N4148

°A-4QB=BClc=1BCUB:C)QD=B.CD

12 11

3

10

R31k

9

5

NOTE:IC1 ISSN7404

R4330 R

PNP

bk

LED1

TO PIN 14, IC1 +Ve

NPN

R5330R LED2


ALARMS

Contents

Basic AlarmPhoto Intruder AlarmIntruder AlarmPhoto Electric RelayLow Temperature Lights outTemperature SensorCoolant levelWater LevelElectronic LockCar Battery WatchdogSimple Car AlarmSimple Lock

AMPLIFIERS &PREAMPLIFIERSHigh Input impedanceHigh Impedance BufferLow Output ImpedanceHigh Input ImpedanceLow Frequency ExtenderVirtual Earth PreampIC Tape Head PreampSimple Stereo Tape Player2 5 Watt20 Watt Slave10 WattLoudspeaker MicrophoneVoltage Controlled AmpWide Band AmplifierVideo Power AmpBroadband Amp

SIGNAL PROCESSORS

Fuzz BoxGuitar FuzzFuzz BoxWaa WaaDisco AutofadeSimple AutofadeInformation TransferOptical Pulse ConditionerTV Sound PickoffCrackletree PotentiometerVoltage to FrequencySine to Square WavePrecision AC to DCVoltage ProcessorUniversal MeterDouble PrecisionFast Half WaveSimple ChopperNoise Rejecting SCR TriggerPhase Shifter

SIGNAL GENERATORS

SimpleVariable Duty cycleFast EdgeFETImproved MultivibratorVariable Duty cycleStable R CCheap (CMOS)Simple TTL XTALUncritical XTALPulseZero CrossingSimple PulseNeedle PulseStable Linear SawtoothZenerNoisePink

The first in a new seriesof 'ideas books' for the experimenter

Simple RelaxationTriangle with independent slopeExponentialWiderange MultivibratorMultiple WaveformLinear SweepStep FrequencyBeeper7400 SirenSimple SirenShip SirenTwo ToneToy SirenKojak, Startrek. Z CarsSound EffectsSound Effects

FILTERS

BandpassLow & High PassRejection NotchBandpassCartridge EC/ A /RumbleHum StopperTape Hiss ReductionSimple Crossover

DIGITALThermometerHeads or TailsBinary CalculatorVoltmeterSeven Segment to DecimalDieRandom BinaryCMOS DieMultiplexer HintsLearning MemoryCMOS Clock

POWER SUPPLIES

ConstantTemperature StableConstantVoltage ControlledPrecision Voltage DividerDual PolaritySimple BalancedVoltage DividerLow RegulatedShort Circuit ProtectedSimple TTL SupplyZN414 SupplyStable ReferenceTransformerless Invert°,DC to DC ACVoltage MultiplierAutomobile ConvertorShaver AdaptorDC -DCHigh Voltage From BatteryVariable ve or -ye outputSimplet2V from Battery ChargerBucket RegulatorAdjusting Zener VoltageVariable ZenerZener Boosting of RegulatorsHigh PowerElectronic FuseBetter FuseRegulator E. FuseFes, ActingSCR CrowbarVoltage PolarityNI CAD DischargeCurrent Limiting

TEST

Diode CheckerGO NO GO Diode TesterZener CheckGO NO GO Transistor TesterQuick JFET TestCurrent Gain TesterBasic Transistor TesterSimple Transistor SCRSCR TesterCrystal CheckCrystal CheckerGood Bad Battery TesterBattery TesterOp -Amp TesterOp -Amp CheckerCheap Logic Probekudible TTL ProbeAudible Slow PulsesLogic ProbeLogic AnalyserI and 0 Display ProbeSimple High ImpedanceVoltmeterAuclio,RF TracerThermocouple ThermometerMetering Stabilised suppliesSimple Frequency Meter

TIMERS & DELAYS

Low Standby Drain741 TimerSelf Triggering TimerPulse TimerPulse DelayVoltage Controlled MonostableSequential RelaysDoor Chime Delay

SWITCHING

Touch Triggered BistableTouch Sensitive SwitchElectronic SwitchSound Operated 2 WaySPST Switch Flip FlopTwo Signals on one Wire

INDICATORS

Line -o -Light3 Step LevelLight LevelBargraph DisplayFuse FailureBlown FuseBack Up LampDC Lamp FailureFM Tuner StationCurrent FlowDisco Cue

FLASHERS

Dancing LightsLow Frequency Strobe

FlasherUltra Simple

POWER CONTROL

LDR Mains ControlFloodlamp ControlZero Crossing SyncTrain ControllerLow Differential ThermostatSimple Temperature ControlFull Wave SCR Control

AUTOMOBILE

Brake Lamp FailureCourtesy Light DelaySimple Hazard LightLight Extender & RemincerFour Way FlasherHeadlamp DipperWiper DelaySuppressed Zero VoltmeterRev CounteriTachometerAuxiliary Battery

DETECTORS &COMPARATORS

Peak Detect & holdWindow DetectorPeak ProgramPositive PeakReaction Comparator

RADIO FREQUENCY

Crystal Marker100 kHz MarkerRF VoltmeterRF DetectorLED RF IndicatorRF Amplifier ProtectionFET-RadioOp -Amp Radio

MISCELLANEA

Phase Locked LoopTouch DoorbellPhase Lock ControlAudio MixerVirtual Earth MixerPlop EliminatorLoudspeaker ProtectionDigital Capacitance ProbeDigital Tape Reorder AdaptorBreakdown Diode Subsitution

0 i4S4

Dual Function ChargerDual Mode Amp

$S°°

1

Capacitor SubstitutionElectronic CapacitorSpeeding Up DarlingtonsShutter SaverThristor SensitivitySound Operated FlashStrength TesterLogic Noise Immunity

TIPS

Identifying 74 SeriesSupply PinsSoldering IC'sTinning With Solder WickPCB StencilsFront Panel FinishDIL DrillingFluorescent StartingAvoiding Insulated Heat SinksTTL Mains InterfaceBoost Your MainsHigh Resistance on Low MetersHigh Voltage ElectrolyticsTransistor IdentificationTemplate & Heat Sink forPower TransistorsTransistor SocketSolder Flow ProblemsOdd Resistor ValuesResistors in parallelCMOS OIL HandlingIdentifying Surplus ICSExtending Battery LifeBattery SnapsPower Supply or BatteryBattery CheckingMuck RemoverTransformers in reverseLoudspeaker CheckingImproving UJT LinearitySignal TracerCrystal EarpiecesCheap VaricapsZener Lifts Capacitor Rating

DATA

741 Op -Amp DataBC 107-109 DataBC 177-179 DataCMOS & TTL Data2N3055 DataM.)2955 DataBipolar Data TablesBipolar FETs RectifiersDiodes Pinouts Zener Misc


tech -tipsONE CHANNEL ONLY SHOWN

C14u7

RV1100k

C210u

n 77

741

RI10k

R35k6 01

2N3904

R2100k

1-25 035k6

2N3905

0+9

02 042N1893

0

Headphone AmplifierJ Macaulay

The circuit will deliver full'orchestral' levels to four pairs ofstereo headphones connected inparallel across the output.

Input signals are coupled to thenon inverting input of a 741 op ampvia the volume control RV1.

This IC is used to drive a

quasi -complementary output stageconsisting of Q1-4.

Quiescent current in the outputtransistors is provided by the voltagedrop across R7 and local feedbackprovided by R6 in Q2's emittercircuit.

R6 is included to render thewhole amplifier short circuit proof(to protect Q2 and Q4). Overallfeedback is applied from theload end of R7 so this component hasnegligible effect on the dampingfactor of the amplifier.

With the components shown thefrequency response is -3dB at 4Hzand 100KHz, distortion below 0.1%at 1 KHz (50mW out, 80 load), andsensitivity 60mV.

ETI MARKET PLACEWe will allow you up to twenty-five words to advertise items you want to buy or sell, or to publicise meetings of clubs, etc.Advertising will be accepted at our discretion - we will not accept commercial or any form of company advertising.

Please type, or clearly print, your message on the back of a sealed empty envelope - as shown below.Our tentative plan is to run ads up to two consecutive issues as space permits.

For more insertions mail in again.

PLEASE SEND IN YOURADVERTISEMENT IN THIS FORMUSE A POSTCARD OR ANEMPTY SEALED ENVELOPE,WITH YOUR MESSAGE ONTHE BACK.

ETI MARKETPLACEUNIT 6 2-5 oVERLEp. BLVD,TORONTO , ONTARIO,

151

When this issue went to press readers' advertising

THE FIRST ADS

had just started

WANTED: PLANS FOR A TRANSISTORIZED HI -SENSITIVITY AMP,NAME YOUR PRICE ALSO WANT CIRCUIT FOR UNIJUNCTIONTRANSISTOR ELECTRONIC ORGAN. WILL BE WILLING TOEXCHANGE CIRCUIT DESIGNS INSTEAD OF MONEY. ANYBODYINTERESTED? PLEASE SEND CORRESPONDENCE TO: STEPHENKAWAMOTO, BOX 165, ALDERGROVE, B.C. VOX 1A0

FOR SALE. TRANSISTORIZED MULTI -METER WITH FIVE POPULARSCALES. ALSO 5" OSCILLOSCOPE - NEVER BEEN USED.DETAILS/OFFERS - OTTO A WEINKAUF, BOX 400, MACKLIN,SASK. SOL 2C0.

to come

FoR SALE ETI REACTION TESTER,

$30 415-, bi".1 S.1.44- FA614T MS

DELIVERY. ALSO mope,: cwrs-wuiskok LiittEt-es5,411.49.lIpT. nog/ EARTH taLvo, VANOWER 4571K6

in. Here are the first items .

FOR SALE: CPU 8080A, NEW AND UNUSED. $10' @ COMPLETEWITH SPECS AND TROUBLESHOOTING CHARTS. M. JESSOME,P.O. BOX 78, DARTMOUTH. NOVA SCOTIA B2Y 3Y2

JE DEMANDE LIVRES ET PERIODIQUES ELECTRONIQUE DETOUTES SORTES. WANTED: ELECTRONIC BOOKS ANDMAGAZINES OF ALL SORTS. J.C. LACHAPELLE. 3924 MENTANA,MONTREAL H2L 3R8.

FOR SALE BEARCAT 101 SCANNING MONITOR RECEIVER.COVERS 3 VHF AND UHF BANDS. REQUIRES NO CRYSTALS. $250.WRITE G. PERRY, 121 PRESLEY AVE., SCARBOROUGH ONT M1L3P9. PHONE 416-599-4127.


Cfsc0-

LONG

MEDSHORT

FOR THE LONG, MEDOR SHORT HAUL...

ifs thenew

ADJUSTABLEVACUUM STROKE

lEIKEIVIEn@nlk,

IbqedieNtieW;Compact tool for convenient toolbox storage. Precision moldedplastic barrel and low -massplunger creates rapid vacuumimpulse with negligible recoil.Three position plunger adjustsloading span to fit large or smallhands. Ample vacuum for mostcircuit board desoldering require-ments.

Write for completeEdsyn catalogue

len finkler ltd25 Toro Road, Downsview, Ontario M3J 2A6telephone 630-9103 telex 065-24010

for the Science, Photography and

Technology mindedTWO NEW GREAT CATALOGUES!EDMUND SCIENTIFIC PRODUCTS

ANDNATIONAL CAMERA PRODUCTSEdmund Catalogue ContainsOpcs. MicroscopesElectronics Fiber OpticsLase. Light ShowTelescopesOver 4.000 items is all

National Camera 'FLASHER'An extensive line of finequality small tools andshop aids for the electronicsand technically orientedindividual

YCU CAN NOW OBTA N BOTH CATALOGUES

E-3 r EFSTONLINE INC.

Name

AddressCit/ Pro,

Postal Code


A BURNING NEED!Protect Your Family by Installing an

Early Warning

DICON SMOKE DETECTOROver 80% of fire victims are not burned to death. They are ASPHYXIATED.The major killer is smoke, especially when you are asleep.

LOUD 85 DECIBEL ALARMOur DUAL IONIZATION CHAMBER senses invisible combustion particles,even before there is visible smoke at the beginning of a fire. This providesvaluable, often crucial TIME TO ESCAPE.

only

$33.95each

Uses inexpensive,easy to obtain,

DURACELL Battery

BATTERY OPERATED:Keeps working even if house power fails.Uses INEXPENSIVE, easy to obtain, Mallory 9 volt MN -1604 Duracell battery.

DUAL IONIZATION CHAMBER:Responds to fires in their earliest stages of development.Compensates for changes in humidity and temperature toVIRTUALLY ELIMINATE "NUISANCE ALARMS"caused by normal atmospheric changes in the home.

LOW BATTERY WARNING:Unit gives audible "click" every sixty seconds for a mini.mum of seven days when battery needs replacing.

TEST BUTTON:Pressing the button virtually duplicates the effect of smokein the sensing chamber. Alarm sounds when button is

pressed to test unit.

OPERATING LIGHT:This Light Emitting Diode (LED) flashes once every minuteto confirm that the unit is receiving power from the battery

SUPERVISED SENSING SEMICONDUCTOR:Continually on .. should electrical continuity to this vitalcomponent break, the alarm will sound immediately.

EASY INSTALLATION:Two screws and anchors (supplied) provide mountingsimplicity. Nothing else to connect.

ALARM:85 DECIBEL ALARM to alert sleeping occupants AUTO-MATICALLY RESETS when the hazardous condition haspassed.

tit

Suggested retail price $49.95

RKG Hospitality Services direct mail price only $33.95

plus $1.95 shipping and handling.

Underwriters Laboratories of Canadalisted and labelled

Clip and mail to:RKG Hospitality Services, Dept. 27A, P.O. Box 144Postal Station "R", 2 Laird Dr., Toronto, Ontario M40 3T0Please send me my Dicon Smoke/Fire Detector for only $33.95 plus $1.95 shippingand handling. Ontario residents please add 7°/a P.S.T.Total cheque/money order enclosedNameAddressCity Prov. P C

Please print clearlyEl Chargex. 0 Master Charge. Expiry dateCredit card no

Signature0 COD orders. Please include $1.50 (Non refundable)

15 DAYMONEY BACKGUARANTEE

TWO YEARWarranty

against defectsin workmanship

and materials


SO

intimateWant power?

The kind of power that onlyour new compact PhilipsDeForest ADK 40 can give you.The clear highs...definitivemid-range...lowest octaves...at a price to fit your budget.Our ADK 40 competes intonal quality with many of thecostlier high power three-wayhigh fidelity speaker systems.

The tweeter is the latestdevelopment of the extremelysensitive Philips dome tweeter.It has one of the widestdispersion patterns and lowestdistortion characteristics.Magnet is 10 oz., among the

ADK 40 shown without removable grille

7Z i1171101

AN NI WWII I-..w 11111WAIF1ff I/ipr .1111 ..4111/

10

60

5010

'U--,AN IIA

.01MP `MI IM

lor AbINII I011 I NI,

AN

20 tO 100

largest size used for tweeters.Level control (located on theback panel) gives up to 10 dBattenuation of the upper fre-quencies. Tweeter never shutsoff, even in the minimumposition of level control. Atmaximum, sparkle of the highend is rarely matched.

7" woofer has 16 oz. magnet.An 8" passive radiatoris used to lift the lower bass.In effect, it acts as amotional port to give you the"North American Sound".

Crossover network has twoclose tolerance copper -woundinductors. Woofer coil is air-

cored for very low losses.Tweeter crossover capacitor is+ 10 percent polyester filmcomponent that will never driftin value or dry up as is possiblewith electrolytic capacitors.

Our new ADK 40 looksgood too. Finished in matchedoiled American walnut veneer,the solid 3/4" top, front, back,bottom and sides are structur-ally solid. The grille frame isremovable, and enclosurefront in its smooth matte blackfinish is esthetically pleasing.

200 500 Hz 1 2 5 10 alit 20

Settle in and enjoy theintimate Philips DeForestADK 40. Size: 25" H.,111/2" W, 9" D., only $150.00(suggested retail price).

Other Philips DeForeststate-of-the-art speakers

Look into the PhilipsDeForest ADK 40 today. Askyour dealer about preassem-bled kits. For the location ofyour nearest dealer, look inthe Yellow Pages under "stereo-phonic", or get in touch withus: Gayle Quintilian, PhilipsElectronics Ltd., ElectronDevices Division, 601 MilnerAve.,Scarborough, Ont. M1B 1M8.

DeForest6-LoudQuspeaakerslitr

ElectronDevicesDivision PHILIPS


Classified Advertising RatesMinimum charge $27.00 per insertionMinimum size One inch depth by one column wide (21/4").Allow 36 letters and/ or spaces per line.Bold face Heading and Signature $3.00 extra.Otherwise only FIRST word and NAME set in bold caps.

Nine lines of thissize of type toone inch depth.

Nine lines ofthis size oftype to one inchdepth, includingHeading andSignatureand whitespace ifused.

Advance payment required except for classified ads placed by recognizedadsertising agencies. 1 .0. Box not accepted unless advertisers providespermanent address and phone number. 10, discount on consecutiseinsertions without copy change. Copy must he reeeked 8 weeks preccedingmonth of issue.

Semi -Display Advertising RateCamera reads cop\ must he supplied or work a ill he billed hack to client. 11Ndiscount on repeat insertions without change. Payment in advance. except forrecognized agencies. Deadline 8 weeks preceedint. month of issue.

0:7" Led Clock q Digits Alarm ClockModule LT70IE, 60Hz

EACH L1701G, 60 Hz12 hr. display$1350

24 hr. displayPower Supply 12V AC

Ideal for panel clock, deckclock, or auto clock kit

COMPANY NAME AND ADDRESS HERE

One size onlyOne column, 2" wideby I" inch depthCost $40.00per insertion

Send copy and cheque or money order toETI Magazine; Classified Advertising Dept.,

25 Overlea Blvd, Unit 6,TORONTO, Ontario, M4H I BI

Rapitype * New from ET!

eti PitliffiLsFERsTT.;

Rub -down panelmarkings

nol

A really high quality system sheets (a full-sized one cut infor finishing off your pro- half for easy postage) andjects. The sheets include a contain sufficient lettering

for dozens of projects.Send $3.50 (including post-age) to ETI PANEL TRANS-FERS. Unit Six. 25 OverleaBlvd.. Toronto. Ontario. M4H161. Ontario Residents add 7%PST.

mass of lettering and controlscales for both rotary andlinear pots.

The lettering is trans-ferred simply by laying on tothe panel and rubbing down- it's strong and permanent.

The markings are on two

This is easy -anyone can solder -

WITH

KESTER SOLDER

11

Handymen! Hobbyists!DO-IT-YOURSELFERS!Let Kester Solder aid you in your home repairs or hobbies. For that householditem that needs repairing -a radio, TV, model train, jewelry, appliances, minorelectrical repairs, plumbing, etc. - Save money - repair it yourself. Solderingwith Kester is a simple, inexpensive way to permanently join two metals.When you Solder go "First Class" - use Kester Solder.

For valuable soldering information send self-addressed stamped envelope toKester for a FREE Copy of "Soldering Simplified".

KESTER SOLDER COMPANY OF CANADA, LTD.Litton P.O. BOX 474 / BRANTFORD, ONTARIO, CANADA N3T 5N9

4

IYou Can Write, Draw or Advertise

Anything You Like in ThisSpace, for Only

FOR MORE DETAILS CALL

Peter Priest416 423 3262

72 ETI CANADA FEBRUARY 1978

HOW TO BUILD A LOW COST LASER by RonaldM. Benrey - This book is structured to presentthe basic theory, experimental techniques andprovides practical information. Written especiallyfor the hobbyist, this book shows how to actuallybuild a low cost gas laser. #5934-5 $5.95

REPAIRING TRANSISTOR RADIOS - 2nd Edition,revised, by Sol Libes. Information on the operationand servicing of transistorized equipment includ-ing portable AM receivers. Provides up to datecoverage on hybrid and all transistor auto radios,PA and hi-fi amplifiers. FM and multiband re-ceivers. #5057-7 $7.15

HOW TO MAKE ELECTRONIC TESTS WITHOUTSPECIALIZED EQUIPMENT by Rufus P. Turner -Designed to aid the reader in finding ways ofmaking tests for voltage, current, etc. Describesa number of tests that can be made withoutspecialized instruments. #5868-3 $5.95

ATTENTIONDealers and Distributors!

Walgram Publishing Limited have been appointedNational Canadian Distributors for the complete Hay-den line of technical books including Rider, Ahernsand Sparton. Inquire on your official stationary if youwish to stock these or any of the total line ofelectronics and communications books at regulardiscount prices. Write for complete listing.

HAYDENhave a complete line of educational and "do-it-yourself" books covering every aspect of electro-nics from the beginner/hobbyist level right on upto the Electronic Technician who wants to be keptup to date on the latest advances in electronicsservicing. The following is but a brief samplingof the total line.

For the ElectronicianCOLOR TELEVISION - Principles and Servicingby Howard & Marvin Bierman -A practical guideto understanding color television receivers. Dis-cusses tube circuits, transistor circuits and ICs,with special sections on test equipment andtrouble -shooting. #5929-9 $7.15SIMPLIFIED TRANSISTOR THEORY by TrainingSystems Inc. and Stanley L. Levine - Planned forthose who have little or no previous knowledgeof transistors, this book presents the basic theoryof transistor operation by the use of detailedprogrammed instruction. #0705-1 $7.15

For the Hobbyists

50 IC PROJECTS YOU CAN BUILD by Ronald M.Benrey - The project selection ranges from asimple IC crystal set to an automotive tachometerand TV commercial killer. Comes complete withparts list and instructions. #0723X $6.55

103 SIMPLE TRANSISTOR PROJECTS by Tom Knei-tel - For the beginner and advanced experimenter,this book contains a number of projects from anaudio amplifier to a geiger counter. Many hoursof fun for everyone. An ideal gift!#0313-7 $5.95

Other exciting "how to" books for everyone . . .

25 SOLID STATE PROJECTS by Rudolph F. Grafand George J. Whalen-Projects include an inter-com, electronic timer, two metal detectors andmuch, much more with detailed information oncircuit theory, construction, trouble shooting anduse. #0134-7 $5.95

John F. Rider #0146-0 $5.10All books are paper back and you canorder them directly, adding 50* to allprices for handling and mailing. Allow 4to 6 weeks delivery.

WALGRAM PUBLISHING LIMITED2175 Sheppard Ave. East, Suite 106

Willowdale, Ont. M2J 1W8 (416) 496-1203

To WALGRAM PUBLISHING LIMITED,Box 569, Don Mills,Ont. M3C 2T6

Please rush the following book(s) # (s)I have included a cheque or money order for the fullamount plus 500 each for handling and mailing.

Note: on orders of 3 or more, only 350 each book.NAME

ADDRESS

City/Town

Prov. Postal Code


INFORMATION

COMPONENT NOTATIONS AND UNITSWe normally specify components using the recentlyagreed International Standard. Many readers will be un-familiar with this but it's simple, less likely to lead to errorand will be used by everyone sooner or later. ETI hasopted for sooner!

Firstly decimal points are dropped and substituted withthe multiplier, thus 4.7uF is written 4u7. Capacitors alsouse the multiplier nano (one nanofarad is 1000pF). Thus0.1uF is 100n, 5600pF is 5n6. Other examples are 5.6pF= 5p6, 0.5pF = Op5.

Resistors are treated similarly: 1.8M ohms is 1M8,

56k ohms is 56k, 4.7k ohms is 4k7. 100 ohms is 100R,5.6ohms is 5R6.

BACK NUMBERSPrevious issues of ETI-Canada are available direct fromour office for $2.00 each. Please specify issue by themonth, not by the features you require.

EDITORIAL QUERIESWritten queries can only be answered when accompaniedby a self-addressed, stamped envelope, and the reply cantake up to three weeks. These must relate to recentarticles and not involve ETI staff in any research. Markyour letter ETI Query.

AMPLIFIER KITS,ELECTRONIC PARTS

New, expanded FREE '78 catalog,new lower competitive prices.50W/50W complete stereo kits $155.0060W low TID pow module $38.00100W low TID pow module $70.00Class -A 60W pow module $130.00Stereo low TID pre -amp $95.00Stereo Active tone -control $40.00MJ802/MJ4502 5MHz 200W $8.50/Pr.2N3055/MJ2955 2MHz 100W $3.00/Pr.1N4148 .05, 1N4003 .10, 2N5088 . 25LM -741 .30, LM -1310 1.50, LM -555 .557400N .22, 7404N .22, 7490 .60Resistor .05, capacitor .10, etc.Post. & pack. add 10%, Que.Res. add8% S.T.

COMPUTRONICSP.O. BOX 531, STAT. "H"

MONTREAL. QUEBEC H3G 1R0

HAMTRADERS INC.45 BRISBANE ROAD. UNIT 18

DOWNSVIEW. ONTARIO M3J 2K1"CANADA'S FRIENDLIESTAMATEUR RADIO STORE"

Write for FREE literatureTel (416) 661-8800

NON-FUNCTIONING PROJECTSWe cannot solve the problems faced by individual readersbuilding our projects unless they are concerning inter-pretation of our articles. When we know of any error weshall print a correction as soon as possible at the end ofNews Digest. Any useful addenda to a project will besimilarly dealt with. We cannot advise readers on modifi-cations to our projects.

COMPONENT STORESETI is available for resale by component stores. We canoffer a good discount and quite a big bonus, the chancesare customers buying the magazine will come back to youto buy their components.

PRICESAll prices quoted in the editorial of ETI are in Canadiandollars, except where stated. Advertisers in U.S. may giveU.S. dollar prices. Where we only know an overseas price,e.g. in U.K. pounds, we convert approximately to Cana-dian dollars, erring on the conservative side, where possi-ble.

COMPONENT SUPPLY

We do not supply components for our projects and areunable to supply advanced information on componentsused in any projects. However to enable readers to obtainprinted circuit boards without undue delay we will besupplying retailers and manufacturers with certain p.c.board designs. Any company interested in receiving suchdesigns should write to us on their headed note paperrequesting details.

CLASSIFIEDMA 1002 AC Clock Mod $14.95, +TR &SWS $19.95MA 1003 12 VDC Car Clock mod +3SWS $24.95Strong Stn Wagon Tailgate Mtr 12VDC

$ 4.95IC SOCKETS 8-25d, 14-25d, 16-30d, 24-25d

40-$ 1.00FM -1 FM wireless Mike Kit 100 FT Range

$ 2.95FM -2 Ditto with 1 Trans Mike Preamp

$ 4.95MG -1 Mag Stereo Preamp Kit High Sens

$ 5.95MG -2 Mag Stereo Preamp & Control Kit

$14.95CPO -1 Code OSC Kit . . $2.95, Brass Key

$ 3.95LO -1 Light Organ Kit 200 W per than (3)

$12.9514V -h 5A Trans . . $5.95, 100V -25ABridge $ 3.5012VCT-500MA . $1.50, 25V-200MA

$ 1.5016VCT-300MA + 21V200MA . . $1.50,50VCT-200MA . . . . . . ...... $ 1.5053VCT-2A . . . $4.95, 2200 UFD-35C .

50(1 . . 10/ $ 4.00Heavy Duty Line Cords 2 Wire. 50d, 3Wire 850C.O.D., Chargex, Mastercharge, Collectall OK

Send for our FREE 1978 CatalogueARKON ELECTRONICS LTD.,

91 QUEEN ST.E., TORONTO, ONT.M5C 1S1

(416) 868-1315

MAIL ORDER AUDIO PRODUCTSPre -amplifier and amplifier kits.Automobile stereo amplifiers availableAutomobile stereo amplifiersavailable to 100 watts.Speaker and electronic cross overs.

Send for free catalogue Audio Systems Design157 Holland Ave., Ottawa, Ontario K1Y 0Y2

J & J ELECTRONICS LTD.,P.O Box 1437 E,Winnipeg, Manitoba R3C 2Z4Semiconductor SpecialistsDo you get our bargain flyers? Send$11:210 to receive the current literatureand specials and to be placed on themailing list for the future publications.

AUDIO KITSBuild Your Own And Save

AMPLIFIER MODULE125W OCL high power parallel outputwith C.S.G. output protection S59.006UW high definition OCL circuit withC.S.G. output protection 536.0015 15W stereo complete with pre -amptone control, OTL power amp, andpower supply 536.00

FREE CATALOGUEAUDIOVISION SERVICE

P.O. Box 955. Stn. 8, Willowdale. Ont. M2K 2T6


PHILIPS

THE TELEVISIONCABLE CONVERTERFROM PHILIPS

UNIVERTER

ONLY

X4495Comes complete witheasy installationinstructions.

PHILIPS

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FOR THE FIRST TIME A COMPLETE CABLE -TO -UHF CONVERTERTHAT ALLOWS YOU TO RECEIVE ALL THE CHANNELS PROVIDEDBY YOUR CABLE COMPANY.

No leasing or renting - one time low cost.

No cords . "Hands Off" operation.

Easy to install and operate.

Reliable and stable.

C.S.A. approved AC Adapter.

Canadian designed and manufactured.

One year warranty.

Fits all makes of TV with UHF Tuner.

Installing the UNIVERTER, gives the cable customer, in effect, the ability to receive 9 midband and 7superband channels that would ordinarily only be available with an expensive set -top converter as sold byseveral manufacturers. The UNIVERTER utilizes a portion of the unused UHF Band from 36 to 68 for thispurpose.

Available from your Philips dealer or service centre. For more information write or call the centres below.

Service Branches from coast to coast: Halifax: 902-429-0260 - Quebec City: 418-681-4639 - Montreal: 515-342-2043- Ottawa: 613-829-9295 - Toronto, West: 416-781-5201 - Toronto. Central: 416-489-2022 - Toronto, East: 416-438-9822 - Hamilton: 416-547-4914 - London: 519-636-9671 - Sudbury: 705-560-4866 - Winnipeg: 204-774-1931 -Regina: 306-543-0446 - Saskatoon: 306-244-2299 - Calgary: 403-243-7737 - Edmonton: 403-452-8491 -Vancouver: 604-434-6647

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5 Major TypesThat Handle Practically AllYour Capacitor Requirements

ORANGE DROP® TWIST-LOK®

DIPPED TUBULAR CAN -TYPE

FILM ELECTROLYTIC

CAPACITORS CAPACITORS

Double -dipped in brightorange epoxy resin to beatheat and humidity.

Won't leak or drip.

Crimped radial leads forcorrect spacing whenmounted on printed wiringboards.

Marked with blackstripe to indicate outsidefoil.

Capacitance values from.001 to .5 µF.

Voltage ratings from200 to 2,000 WVDC.

Lock in place with twistof tabs.

Sealed aluminum casesfor long life.

Withstand high surgevoltages, high ripple cur-rents, high temperatures.

Single, dual, triple, andquadruple section units.

Capacitance values from2 to 5000 µF.

Voltage ratings from 6to 600 WVDC.

ATOM®

TUBULAR

ELECTROLYTIC

CAPACITORS

Dependable metal caseconstruction with plasticinsulating sleeve.

Withstand high temper-atures, high ripple currents,high surge voltages.

Low leakage currents.

Long shelf life.

Designed for operationat temperatures to 85° C.

Single, dual, triple,quadruple and quintupleunits.

Capacitance values from1 to 50,000 µF.

Voltage ratings from 1

to 600 WVDC.

VERTI-LYTIC®

SINGLE -ENDED

ELECTROLYTIC

CAPACITORS

For vertical installationon high -density printedwiring boards.

Used for coupling, de -coupling, bypass, filtering.

Excellent capacitancestability.

Low leakage current,low ESR.

Metal -encased, withplastic insulating sleeve.

Capacitance values from.47 to 3300 µF.

Voltage ratings from 6.3to 63 WVDC.

For complete listings of more than 5600 replacement componentsget Catalog CC -621 from your Sprague distributor, or write or call:

JOHN R. TILTON, LTD.1900A Eglinton Ave. East P.O. Box 117Scarborough, Ontario M1L 2M1 Dollard Des Ormeaux, Que. H9G 2H5Tel. (416) 757-4171 Tel. (514) 747-4266

CERA-MITE®

DISC

CERAMIC

CAPACITORS

Fit easily into tightspaces, even across sub-miniature tube sockets.

Low self-inductance ofsilvered flat -plate designyields very high by-passefficiency.

Designed for 85° C op-eration.

General application,High -K, frequency -stable,temperature -stable, tem-perature -compensatingtypes available.

Capacitance values from1.0 pF to .022 µF.

Voltage ratings from250 to 7500 WVDC.

SMITH-PATTERSON & ASSOCIATES1120 Hamilton St. 30 Midland St.Vancouver, B.C. R3E 2T1 Winnipeg, Manitoba R3E 2Y6Tel. (604) 681-0743 Tel. (204) 774-1855

YOUR NUMBER 1 SOURCE FOR ELECTRONIC COMPONENTS THETHE MARK OF RELIABILITY

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