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Simple In-Circuit Transistor Tester $4.50 SEPTEMBER 1993 NZ $5.50 INCL GST REGISTERED BY AUSTRALIA POST – PUBLICATION NO. NBP9047 SERVICING — VINTAGE RADIO — COMPUTERS — AMATEUR RADIO — PROJECTS TO BUILD : s i h t Build Stereo Preamplifier With Infrared Remote Control • Servicing An R/C Transmitter – The Basics • Build A +5V To ±12V DC Converter • Remote-Controlled Electronic Cockroach • Amateur Radio: The Emtron Noise Bridge Intellige nt Charger/ Nicad Battery Discharg er Vol.6, No.9; September 1993 FEATURES FEATURES THIS INTELLIGENT charger does everything a nicad battery charger should. It automatically discharges the battery & then charges it & checks its condition. Details page 16.   4 Swiss Railways’ Fast New Locomotives by Leo Simpson New designs have electronic control & diagnostics 53 Test Equipment Review: The Handyscope by Darren Yates A spectrum analyser, scope & multimeter all in one PROJECTSTO TOBUILD BUILD PROJECTS 16 Automatic Nicad Battery Charger by Warren Buckingham It correctly discharges & recharges nicad batteries 24 Stereo Preamplifier With IR Remote Control by John Clarke BUILD THIS exciting new preamplifier for your hifi system. It features infrared remote control & has excellent specifications – see page 24. Add this exciting new project to your hifi system 34 Build a +5V to ±12V DC Converter by Darren Yates Can be easily adapted to provide other output voltages 56 An In-Circuit Transistor Tester by Darren Yates Tests both small signal & power transistors 72 Remote-Controlled Electronic Cockroach by John Clarke An infrared link controls the steering SPECIALCOLUMNS COLUMNS SPECIAL 40 Serviceman’s Log by the TV Serviceman We have good news & we have bad news 60 Amateur Radio by Garry Cratt, VK2YBX Emtron’s ENB-2 noise bridge YOU CAN TROUBLESHOOT transistor circuits quickly & easily with this simple tester. It can indicate whether a transistor is working or not & tell you whether it is an NPN or PNP type. Turn to page 56. 82 Remote Control by Bob Young Servicing your R/C transmitter – the basics 86 Vintage Radio by John Hill Restoring an old valve tester DEPARTMENTS DEPARTMENTS   2 10 33 62 90 Publisher’s Letter Circuit Notebook Order Form Product Showcase Back Issues 92 94 95 96 Ask Silicon Chip Notes & Errata Market Centre Advertising Index THIS PROJECT IS just for fun. It’s a remote-controlled car that’s steered by pressing two buttons on a hand-held infrared transmitter. Construction begins on page 72. September 1993  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $42 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 1a/77-79 Bassett Street, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Remote control security is suspect Over the last month or so, there have been reports in the media about the security of UHF remote controlled burglar alarms as used in cars. It is now possible for car thieves to obtain a specially designed UHF receiver which can record the pulse coded signal from a remote handpiece and then transmit it again to open the car, after the owner is out of sight. As you might expect, this has caused consternation amongst car owners because in effect, if they use one of these UHF remote controlled burglar alarms, they are leaving their cars unlocked and with the burglar alarm disabled. The only solution, for owners of these existing burglar alarms, is to use an additional steering wheel lock, which rather defeats the convenience feature of UHF remote control. For car and burglar alarm manufacturers, their alarms need to be modified so that they use a “rolling code” whereby the code transmitted is changed each time the handpiece is used. Some cars already have this feature. Alternatively, UHF transmission could be dispensed with and infrared remote control used instead, albeit with less range available. It was only a matter of time before this clandestine UHF receiver/transmitter was used by car thieves in Australia. In fact, some car burglar alarm manufacturers have known about this device for several years and surprisingly, have done nothing about it. But even if the device had not become available, the necessary equipment is already available to someone who is devi­ous enough to want to do it. What do you need? A scanner receiver that can pick up 304MHz, a recorder to record the detected pulse modulation and then a UHF remote handpiece which can be modulated with the recorded signal. Simple. Alternatively, you could dispense with the scanner receiver and just use the UHF receiver section of a car burglar alarm. Lest readers think that I should not outline this information, let me state that you don’t have to be too clever to think of it. The security problem is not just confined to cars either. What about remote controlled garage doors? They use the same principles of operation and so anyone who has one of these doors that gives access to their home should be aware of the risk. And if I’ve thought of it, you can be sure that burglars are way ahead of me. The solutions are the same – use a rolling pulse code or infrared remote control, or possibly an inductive loop receiver buried in the driveway. Or just lock the door with a key. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Interfacing projects to Macs I very much enjoy reading SILICON CHIP. I have two re­quests. First, please publish details of how Mac computer users can interface their computers with the range of external gadgets described in your magazine. All computer interfacing gadgets that I have seen described in SILICON CHIP presume that the printer port of an IBM (or clone) will be used. Many of us, however, believe and operate on the principle that “computer equals Mac”. For that reason, please be sure and explain in the future how we need to modify your instructions to enable the gadgets you de­scribe to interface with a Mac. V. Robertson, Address witheld. Haywire digit on voltmeter I just noticed on the cover of your June edition that the LED display of the Car Voltmeter shows the least significant digit as a mirror image of a 6 (six)! Since I am going to build this voltmeter, I was wondering if there’s a possible wiring error in this design or just a malfunction of the f segment actually showing an 8 (eight)! Or did you use too slow a shutter speed when taking the picture while the display was changing ? Either way, please could you clarify this before I proceed with building the project. My worries were triggered by a different and simpler design pub­lished in another magazine in which the display constantly switched (flickered) between two values when the input voltage varied slightly. To my knowledge, this can be caused by an inconsistent up count when the display is blanked. Is your design also prone to this? Another request concerns the contents of your magazine or better what’s missing from it! I’d really like to see a series of articles about “simple building blocks in electronics”; eg, each article describes a specific popular chip, like a Schmitt trigger NAND 4093, and shows an extensive variety of circuits using only one or two IC packages such as oscillators, decoders, signal shapers, level detectors and filters. These circuit files can then be collected by the reader each month to obtain eventually a complete encyclopaedia. Manfred Schmidt, Edgewater, WA. PS: I almost forgot to ask you if the V/F converter in the Car Voltmeter can be used outside the specified range of 8-17V? Could you tell me how to modify the design to read down to at least 4V without major surgery? SILICON CHIP, PO Box 139, Collaroy Beach 2097. Comment: your second guess is the correct one. The backward “6” shown on the last digit of the Car Voltmeter is simply a photo­graphic artifact. To get the digits to show up, a photographic exposure of several seconds is necessary and the effect is a result of the least significant digit switching between a “2” and “3” during this time. The circuit can not easily be modified to read down to 4V. That’s because the circuit is powered by the battery it is meas­uring and needs a regulated rail of at least 5V. Solution to do-it-yourself PC boards I note the complaint about too many tracks under ICs on PC boards by G. Donaldson (Mailbag, page 11, March 1993). I make my boards with a Dalo pen and when tracks are too close I usually fit in as many as possible and for the rest I leave a round copper “land” and solder a short piece of insulated wire across, as per the drawing. I realise there could be “ground loop” or other problems with this in RF circuits but have yet to encounter any faults in any boards I have made using this method. A. McKeon, Browns Plains, Qld. September 1993  3 Swiss Railways’ fast new locomotives Recently, the Swiss Railways introduced a new series of locomotives which are compact, very powerful and equally suited to pulling fast passenger trains or heavy freights. This was made possible by comprehensive use of electronics in the drive system. By LEO SIMPSON Intended mainly for use on the Gotthard line, the new locomotive, designated Re4/4 460, has 3-phase induction motors, very efficient regenerative braking and produces minimal wear and tear on its equipment. Locomotives designed for a variety of duties clearly offer advantages over locomotives built for just one type of duty. The work schedule for multi-pur4  Silicon Chip pose units can be drawn up to take advantage of their versatility, making down-times shorter. Also, the training of the drivers and maintenance staff is easier and spare parts inventories can be kept smaller. The Re4/4 460 locomotive is designed to operate from a single-phase 15kV AC catenary at 162/3Hz. It has a BoBo wheel arrangement (ie, two bogies with two motors each) and its adhesion mass is 84 tonnes. The maximum power at the wheel rim is 6100 kilowatts. This is a very high power for any locomotive, regardless of its design, and amounts to over 2000 horsepower per axle. In typical locomotives with series DC motors, tractive effort drops off at high speed. But in these new locos, high speed and high tractive effort are both achieved. This is made possible by the variable frequency drive system for the induction motors. The starting tractive effort is 275kN (27.5 tonnes) which is very high considering the mass of the locomotive. This maximum tractive effort is available up to a speed of 80km/h. Even at its maximum speed of 230km/h, the locomotive can still develop a tractive effort of 83kN. At the top operational speed of 200km/h, a tractive effort of about 110kN is available. This is enough to pull an inter-city train with seven passenger cars over relatively flat routes with gradients of up to 1% at a speed of 200km/h. Because of the locomotive’s tractive power and the permitted temperature rise in the traction motors, two of these locos can accelerate a train weighing 1300 tonnes to 80km/h on a 2.7% (1 in 37) gradient and then maintain this speed, at which the draw-bar power limit on the Gotthard line is reached. The experience gained with the propulsion system and the control electronics on previous Swiss locomotives (Re 4/4 and Re 4/4 450 series) proved to be very valuable. However, the higher power output and top speed called for the very latest technology. The maximum loco speed of 230km/h means that aerodynamic design is most important even though the unit is quite boxy to look at. The fact that the locomotive is used to push or pull trains made a symmetrical design necessary, with a driver’s cab at each end. Furthermore, it was important that the slipstream over the roof did not cause underpressure, especially when the train passed through tunnels, as this could impair cooling of the traction motors and converters. New bogie design The special bogie suspension allows the locomotive to travel through curves 30 percent faster than before without exceeding structural clearances. Since at this speed the lateral acceleration can reach 1.8m/ s2, passenger comfort then depends on carriages having active tilting. These are not yet in use but are being considered in Switzerland. The complete bogie weighs just 16 tonnes, including the two motors. Forces are transmitted between the body and bogie by push/pull rods, which enable the transmission point Facing page: One of Swiss Railways’ Re4/4 460 locomotives crosses the ‘Kander’ viaduct in the Bernese Overland on the occasion of the inauguration of the Berne-LotschbergSimplon Railway’s double track. The bogies for the Re4/4 460 locomotive employ two high speed 3-phase induction motors each continuously rated at 1200 kilowatts. The very short wheelbase of the bogies is made possible by the small size of the motors. on the bogie to be kept as low as possible. The load difference between each bogie’s wheelsets are therefore small. Lateral forces acting between the wheels and rails are reduced by ‘soft’ suspension of the wheelsets in the bogie frame, allowing the wheelsets to adjust radially when the train runs through curves. Another factor promoting good running in curves is the short wheelbase of only 2.8 metres. This was made possible mainly by the compact traction motors. In any electric locomotive such as this, operating from a high voltage catenary supply (ie, 15kV AC), the heaviest item of equipment is the main transformer which has to supply the full load power of more than 6 megawatts. In this case the designers have gone to special lengths to get the weight down. For example, they replaced the metal core clamps by a far lighter, non-metallic material, plywood, which also has the benefit of eliminating eddy-current losses. The aluminium transformer tank also saves weight and damps stray magnetic fields occurring at harmonic frequencies. The traction motors are four-pole, high-speed squirrel cage induction motors with a maximum speed of 4180 rev/min for an input frequency of 143Hz, and a continuous rating of 1200kW. Their short term capacity is 1560kW, equivalent to 2090 horsepower. High speed squirrel cage induction motors are used because they are lighter and more compact than equivalent series DC motors used for traction. As well, they have no brushes, commutator or slip rings and thus their long term maintenance is minimal. But the really big advantage of these induction motors is their excellent speed control and resistance to wheel slip. This comes about because of the drive system. Induction motors operating from a fixed frequency AC supply are notoriously difficult to speed control. In fact, their more or less constant speed regardless of load is normally a virtue but for traction, where trains need to run over a wide range of speeds, it is a big drawback. This is why series DC motors have been “king” for traction for so long. However, by providing a continuously variable frequency AC supply to the induction motors, speed control is achieved. Not only that, wheel slip under acceleration is virtually eliminated and full regenerative braking, almost down to a complete stop, is achieved. The two motors of each bogie are connected electrically in parallel and September 1993  5 The driver’s cab has the speedo in the centre and a diagnostics screen to the right. as in the Re4/4 and Re4/4 450 locomotives, the two bogie drive units operate completely independently of each other. Even if a fault occurs in one of the drive systems or its control units and auxiliaries, the train can continue its journey on half power. Fig.1 shows the schematic circuit of the new Re 4/4 460 locomotive and remember that this operates at powers up to 6 megawatts and beyond. At the top of the circuit is the 15kV AC catenary wire and this is fed down to the main transformer which has seven secondary windings. Three of these, marked A, B and C provide auxiliary supplies for the loco. The other four each drive four quadrant controllers. These employ gate turn-off (GTO) thyristors with an off-state voltage rating of 4.5kV and turn-off current of 2500 amps. The output of the four quadrant controllers is the so-called converter’s DC link which has a nominal voltage of 3.5kV. Such a high DC link voltage is desirable as it keeps the currents at acceptable levels. In addition, it allows the same circuit to be used in dual-voltage locomotives which are designed to run on the rail networks of neighbouring countries operating with a 3000V DC catenary. 6  Silicon Chip The DC link then supplies the variable frequency inverters which drive the three phase induction motors. These inverters are based on the same GTO thyristors as used in the four quadrant controllers. The frequency output of the inverters ranges from below 1Hz to 143Hz, at which the motors run at 4180 RPM. Regenerative braking An induction motor can be used as a powerful regenerative brake. All that needs to be done is to drive it at faster than its “synchronous speed”. With a variable frequency drive in a locomotive, this is easily achieved simply by reducing the frequency. The motor then acts as a generator and the power is then fed back via the four quadrant controllers of the inverters and DC link to the transformer and thence back to the 15kV AC catenary supply. This brake is applied continuously on downhill runs and is also used to brake the trains almost to a standstill. On the Gotthard route, for example, the locomotive’s electrical brake has to be capable of braking loads of up to 650 tonnes to a constant speed of 80km/h on gradients of about 1 in 40. GTO thyristor-controlled resistors built into the DC link provide protection from transient over-voltages caused by unexpected disconnections of the catenary supply. The resistors are connected into circuit whenever there is a power supply failure or system disturbance. The regenerative brake’s large range of action allowed a reduction in the power of the locomotive’s mechanical brakes (ie, the shoe brakes and the magnetic rail brake), despite the fact that the locomotive’s speed has been increased. The magnetic rail brake, equipped with permanent magnets, performs safety functions and serves as the parking brake. Microprocessor control The MICAS S2 traction control system used in the Re4/4 460 locomotive uses a fibre optics serial bus with data signalling rate of 1.1 Mbit/s. It can be used to link up to 256 unit addresses. Commands entered by the driver in his cab are transmitted via the locomotive bus to the locomotive control unit in the electronics cabinet. After processing, the signals are transmitted over the bus to the relevant stations. Fibre optics has special advantages for locomotives with converter-fed propulsion because of 15kV 16.66Hz 1 3 2 5 4 29 21 6 13 M 3 17 30 25 DG1 7 26 8 35 15 31 18 36 M 3 22 9 32 23 10 14 M 3 19 33 27 DG2 11 28 12 37 16 34 20 A B C RAIL 38 M 3 24 DG1 DG2 A B C 1 2 3 4 5-12 13,14 15,16 17-20 21-24 25-28 29-34 35-38 Bogie 1 Bogie 2 Converter for auxiliaries 220VAC for auxiliaries 1000VAC train busbar Pantograph (catenary) Grounding switch Main circuit breaker Main transformer Four quadrant controllers Series resonant reactors Series resonant capacitors DC link capacitors Voltage limiters Voltage limiter resistors AC drive inverter 3-phase induction motors Fig.1: schematic diagram of the Re4/4 460 locomotive. All the circuitry is controlled by a complex microprocessor system employing fibre optic links to avoid problems of electromagnetic interference. its immunity to the strong electromagnetic interference throughout the locomotive. It is anticipated that multiple control will be used very often, particularly on the Gotthard route. It is possible to operate up to four locomotives in this mode. In such cases, the locomotive bus systems will be linked to the train bus, over which the commands and messages to and from the leading locomotive are transmitted. Since the locomotive bus is a fibre optic link and the train bus uses copper conductors (two cores of the electropneumatic brake control cable) operating in TDM mode (with telegram exchange), each locomotive is coupled to the train bus by a time multiplexer multiple-control coupler. It is due to this system that locomotives can September 1993  7 regulation in the case of motors. The power is provided by four identical converters which also feature GTO thyristors. Two converter modules supply power to the traction motor and oil-cooler blowers, the third to the compressor motor, and the fourth to the oil circulation pumps of the main transformer and converter, the air-conditioning system in the driver’s cab, and the battery charging system. Mounted in the same frame is the electronics equipment for controlling the onboard system converters and auxiliaries. Driver’s cab This photo shows the four quadrant controller and other equipment asseociated with the frequency converter for a bogie drive. All the power electronics are housed in oil-filled tanks for efficient cooling. The main transformer is situated underneath the locomotive. also be placed at some intermediate position in the train, the only proviso being that the cars have to be equipped with the electropneumatic brake control cable. Diagnostics No microprocessor control system for a locomotive would be complete without a diagnostics facility and the one in the Re4/4 460 locomotive is comprehensive. Its task is to collect information needed by the train driver and the maintenance crew, without intervening itself in the process sequences. Automatic measures are initiated at the locomotive control level as they become necessary. All failure symptoms and their corresponding signals are programmed in the distributed microprocessors of the control system. These detect deviations from the setpoint behaviour in their respective areas, and transmit the information to the locomotive’s central diagnostics processor. This has a non-volatile memory with a capacity for storing up to 2500 events. The evaluation of the fault signals takes place at three levels. At level 1, a fault is announced by an alarm lamp lighting up within the driver’s field of vision, followed by short messages 8  Silicon Chip being displayed on the diagnostics screen. These messages give the nature of the fault and instructions on how to proceed. Under fault-free conditions, nothing is displayed. The driver can isolate failed equipment by pressing a fault-clearing button on his console. Level 2 is for minor maintenance. The driver can request a list of the stored faults from the diagnostics messages on the monitor. Level 3 is for detailed investigation of the failure and for obtaining a statistical evaluation of the relevant events. The diagnostic data is transferred, with all related data and fault-clearing instructions, to a portable personal computer, from where they are loaded into a central database. Although with multiple control the individual diagnostics systems represent stand-alone units, fault data is transmitted over the train bus to the driver’s cab. Provision has also been made for diagnostics data from the passenger cars to be displayed in the driver’s cab. Auxiliaries All the locomotive’s auxiliaries are fed with three-phase AC, at variable frequency and voltage to allow speed The driver’s cab incorporates basic ergonomic features which are to be found in all modern Swiss locomotives: • Controls and instruments for traction and electrical braking are on the right. • Controls and instruments for pneumatic braking are placed on the left. • The speedometer is in the centre of the driver’s field of vision. The driver’s cabs are soundproofed and fully air-conditioned. The design of the air-conditioning system overcomes the problem of presssure changes in the cabs when trains cross in tunnels. Fresh air enters from the roof chamber, above the machine compartment. All 99 of these locomotives for the Swiss Railways will have been delivered by mid-1994, as planned. They represent the very latest in traction technology and they illustrate the fact that electronics and computerisation is now vital to the efficient functioning of locomotives. In fact, without electronics and computers, today’s modern electric locomotives would simply be a dream. SC Acknowledgement The background material and photographs for this article came from the October 1992 issue of ABB Review. Other articles on modern electric locos and 3-phase propulsion were published in the series entitled “The Evolution of Electric Railways”, in the June 1989 and August 1989 issues of Silicon Chip. 8MM VIDEO CASSETES These 120-minute 8mm metal oxide video cassettes were recorded on once for a commercial application and then bulk erased. They are in new condition but don’t have the record protect tabs fitted. The hole in the upper right corner will have to be taped over. $9 Ea. or 5 for $38 LARGE NIGHT VIEWERS One of a kind! A very large complete viewer for long range observation. Based on a 3-stage fibre optically coupled 40mm first generation image intensifier, with a low light 200mm objec­tive mirror lens. Designed for tripod mounting. Probably the highest gain-resolution night viewer ever made. ONE ONLY at an incredible price of: $3990 BINOCULAR EHT POWER SUPPLY This low current EHT power supply was originally used to power the IR binoculars advertised elsewhere in this listing. It is powered by a single 1.5V “C” cell and produces a negative voltage output of approximately 12kV. Can be used for powering prefocussed IR tubes etc. $20 IR BINOCULARS High quality helmet mount, ex-military binocular viewer. Self-powered by one 1.5V “C” size battery. Focus adjustable from 1 metre to infinity. Requires IR illumination. Original carry case provided. Limited stocks, ON SPECIAL AT: $500 IR FILTERS A high quality military grade, deep infrared filter. Used to filter the IR spectrum from medium-high powered spotlights. Its glass construction makes it capable of withstanding high temper­atures. Approx. 130mm diameter and 6mm thick. For use with IR viewers and IR responsive CCD cameras: ON SPECIAL $45 12V OPERATED LASERS WITH KIT SUPPLY Save by making your own laser inverter kit. This combination includes a new HeNe visible red laser tube and one of our 12V Universal Laser Power Supply MkIII kits. This inverter is easy to construct as the transformer is assembled. The supply powers HeNe tubes with powers of 0.2-15mW. $130 with 1mW TUBE $180 with 5mW TUBE $280 with 10mW TUBE MAINS OPERATED LASER Supplied with a new visible red HeNe laser tube with its matching encapsulated (240V) supply. $179 with 1mW TUBE $240 with 5mW TUBE $390 with 10mW TUBE GREEN LASER HEADS We have a limited quantity of some brand new 2mW+ laser heads that produce a brillant green output beam. Because of the relative response of the human eye, these appear about as bright as 5-8mW red helium neon tubes. Approximately 500mm long by 40mm diameter, with very low divergence. Priced at a small fraction of their real value $599 A 12V universal laser inverter kit is provided for free with each head. ARGON HEADS These low-voltage air-cooled Argon lon Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nm) and a power output in the 10-100mW range. Depends on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply and can provide some of the major components for this supply. Limited supplies at a fraction of their real cost. $450-$800 ARGON OPTIC SETS If you intend to make an Argon laser tube, the most expen­sive parts you will need are the two mirrors contained in this ARGON LASER OPTIC SET. Includes one high reflector and one output coupler at a fraction of their real value. LIMITED SUPPLY $200 for the two Argon LASER mirrors. LASER POINTER Improve and enhance all your presentations. Not a kit but a complete commercial 5mW/670nm pen sized pointer at ONLY: $149 LARGE LENSES Two pairs of these new precision ground AR coated lenses were originally used to make up one large symmetrical lens for use in IBM equipment. Made in Japan by TOMINON. The larger lens has a diameter of 80mm and weighs 0.5kg. Experimenters delight at only: $15 for the pair. EHT GENERATOR KIT A low cost EHT generator kit for experimenting with HT-EHT voltages: DANGER – HIGH VOLTAGE! The kit also doubles as a very inexpensive power supply for laser tubes: See EL-CHEAPO LASER. Powered from a 12V DC supply, the EHT generator delivers a pulsed DC output with peak output voltage of approximately 11kV. By adding a capacitor (.001uF/15kV $4), the kit will deliver an 11kV DC output. By using two of the lower voltage taps available on the transformer, it is possible to obtain other voltages: 400V and 1300V by simply adding a suitable diode and a capacitor: 200mA - 3kV diode and 0.01uF 5kV capacitor: $3 extra for the pair. Possible uses include EHT experiments, replacement supplies in servicing (Old radios/CRO’s), plasma balls etc. The EHT generator kit now includes the PCB and is priced at a low: $23 LED DISPLAYS National Seminconductor 7-segment common cathode 12 digit multiplexed LED displays with 12 decimal points. Overall size is 60 x 18mm and pinout diagram is provided. 2.50 Ea. or 5 for $10 BATTERIES Brand new industrial grade PANASONIC 12V-6.5AHr sealed gel batteries at a reduced price.Yes, 6.5 AHr batteries for use in alarms, solar lighting systems, etc. Dimensions: 100 x 954 x 65mm. Weight of one battery is 2.2kG. The SPECIAL price? $38 PIR DETECTORS What are the expensive parts in a passive movement dector as per EA May 89? A high quality dual element PIR sensor, plus a fresnel lens, plus a white filter. We include these and a copy of PIR movement detector circuit diagram for: $9 MASTHEAD AMPLIFIER KIT Based on an IC with 20dB of gain, a bandwidth of 2GHz and a noise figure of 2.8dB, this amplifier kit outperforms most other similar ICs and is priced at a fraction of their cost. The cost of the complete kit of parts for the masthead amplifier PCB and components and the power and signal combiner PCB and components is AN INCREDIBLE: $18 For more information see a novel and extremely popular antenna design which employs this amplifier: MIRACLE TV ANTENNA - EA May 1992: Box, balun, and wire for this antenna: $5 extra SODIUM VAPOUR LAMPS Brand new 140W low pressure sodium vapour lamps. Overall length 520mm, 65mm diameter, GEC type SO1/H. We supply data for a very similar lamp (135W). CLEARANCE AT: $15 Ea. STEPPER MOTORS These are brand new units. Main body has a diameter of 58mm and a height of 25mm. Will operate from 5V, has 7.5deg. steps, coil resistance of 6.6 ohms, and it is a 2-phase type. Six wires. ONLY: $12 PROJECTION LENS Brand new large precison projection lens which was original­ly intended for big screen TV projection systems. Will project images at close proximity onto walls and screens and it has adjustable focussing. Main body has a diameter of 117mm and is 107mm long. The whole assembly can be easily unscrewed to obtain three very large lenses: two plastic and one glass. The basis of a high quality magnifier, or projection system? Experimenters’ delight! $30 CRYSTAL OSCILLATOR MODULES These small TTL Quartz Crystal Oscillators are hermetically sealed. Similar to units used in computers. Operate from 5V and draw approximately 30mA. TTL logic level clock output. Available in 4MHz, 4.032MHz, 5.0688MHz, 20MHz, 20.2752MHz, 24.74MHz, 40MHz and 50MHz. $7 Ea. or 5 for $25 FLUORESCENT BACKLIGHT These are new units supplied in their original packing. They were an option for backlighting Citizen LCD colour TVs. The screen glows a brilliant white colour when the unit is powered by a 6V battery. Draws approximately 50mA. The screen and the in­verter PCB can be separated. Effective screen size is 38 x 50mm. $12 MAINS FILTER BARGAIN A complete mains filter employing two inductors and three capacitors fitted in a shielded metal IEC socket. We include a 40 joule varistor with each filter. $5 Note that we also have some IEC extension leads that are two metres long at $4 Ea. WEATHER TRANSMITTERS These brand new units were originally intended to monitor weather conditions at high altitudes: attached to balloons. Contain a transmitter (12GHz?) humidity sensor, temperature sensor, barometric altitude sensor, and a 24V battery which is activated by submersing in water. The precision all mechanical altitude sensor appears similar to a barometer and has a mechani­cal encoder and is supplied with calibration chart. Great for experimentation. $16 Ea. SOLAR CHARGER Use it to charge and or maintain batteries on BOATS, for solar LIGHTING, solar powered ELECTRIC FENCES etc. Make your own 12V 4 Watt solar panel. We provide four 6V 1-Watt solar panels with terminating clips, and a PCB and components kit for a 12V battery charging regulator and a three LED charging indicator: see March 93 SC. Incredible value! $42 6.5Ahr. PANASONIC gel Battery $35, ELECTRIC FENCE PCB and all onboard components kit $40. See SC April 93. For two displays - one yellow green and one silver grey. SOME DIFFERENT COMPONENTS 1000pF/15kV disc ceramic capacitors ..............$5 20kV PIV - 5mA Av/1A Pk fast diodes .........$1.50 3kV PIV - 300mA / 30A Pk fast diodes ........... 60c 0.01uF /5kV disc ceramic capacitors ...........$1.80 680pF / 3kV disc ceramic capacitors .............. 30c Who said that power MOSFETS are expensive?? MTP3055 N-channel MOSFETS as used in many SC projects ............................$2 Ea. or 10 for $15 MTP2955 P-channel MOSFETS (complementary to MTP3055) ..........................$2 Ea. or 10 for $15 BUZ11 N-channel MOSFETS $3 Ea. or 10 for $25 Brief DATA and application sheet for above MOSFETS free with any of their purchases (ask) Flexible DECIMAL KEYPADS with PCB connectors to suit ...........................................................$1.50 1-inch CRO TUBES with basic X-Y monitor circuit CLEARANCE <at>..............................................$20 Schottky Barrier diodes 30V PIV - 1A/25A Pk. 45c 100 LED BARGRAPH DISPLAY Yes 100 LEDs plus IC control circuitry, all surface mounted on a long strip of PCB. SIMPLE - a 4-bit binary code selects which one out of the 10 LED groups will be on, whilst another 4-bit binary code selects which one of each group of 10 LEDs will be ON. Latching inputs are also provided. We include a circuit and a connecting diagram. VERY LIMITED QUANTITY $7Ea. FM TRANSMITTER KIT - MKll This low cost FM transmitter features pre-emphasis, high audio sensitivity as it can easily pick up normal conversation in a large room, a range of well over 100 metres, etc. It also has excellent frequency stability. The resultant frequency shift due to waving the antenna away and close to a human body and/or changing the supply voltage by +/-1V at 9V will not produce more than 30kHz deviation at 100MHz! That represents a frequency deviation of less than 0.03%, which simply means that the fre­quency stays within the tuned position on the receiver. Specifications: tuning range: 88-101MHz, supply voltage 6-12V, current consumption <at>9V 3.5mA, pre-emphasis 50µs or 75µs, frequency response 40Hz to greater than 15kHz, S/N ratio greater than 60dB, sensitivity for full deviation 20mV, frequency stabil­ity (see notes) 0.03%, PCB dimensions 1-inch x 1.7inch. Construction is easy and no coil winding is necessary. The coil is preassembled in a shielded metal can. The double sided, solder masked and screened PCB also makes for easy construction. The kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $11 Ea. or 3 for $30 LARGE LCD DISPLAY MODULE - HITACHI These are Hitachi LM215XB, 400 x 128 dot displays. Some are silver grey and some are yellow green reflective types. These were removed from unused laptop computers. We sold out of similar displays that were brand new at $39 each but are offering these units at about half price. VERY LIMITED STOCK. $40 OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 September 1993  9 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Wide range phase control This circuit will help to eliminate the snap-on effect and asymmetry associated with Triac phase control circuits. It will give smooth and stable control from virtually zero to full power with an inductive load. It may be more expensive than the Triac version (four SCRs) but the benefits outweigh the initial cost. The four SCRs act as a single Triac but able to be con­trolled over a wider phase angle range, and therefore giving a greater range of power control. Diodes D1-D4 are connected as a bridge rectifier across the mains supply. The current through the bridge rectifier is limited by the two paral­lel-connected 100kΩ 1W resistors and the DC voltage developed at the output of the bridge rectifier is limited by the 13V zener diode. The result is a 13V DC supply which drops to zero at the end of each mains half-cycle. The pulsed DC supply feeds uni­ junction transistor UJT1 which is connected as a trigger pulse generator. The pulse timing with respect to each mains half-cycle is set by a 20kΩ potentiometer (VR1). Regulator for solar panels This circuit regulates the output from a solar panel so that the voltage across a 12V battery is limited to 13.8V. In effect, the panel is disconnected once the battery voltage reaches 13.8V. The panel is then connected again when the battery voltage falls to 13.2V. D1 prevents current flowing back out of the battery to the solar panel at night. The heart of the circuit is an LM10 IC voltage reference and op amp. IC1a is the voltage reference section. It is used to control transistor Q1 which functions as a 10  Silicon Chip 100k 1W 240VAC LOAD 750W MAX 100k 1W D1-D4 4x1N4004 4xC122E SCR1 3.9k ZD1 13V VR1 20k UJT1 2N2646 T1 SCR4 SCR2 0.1 SCR3 Pulses from UJT1 are coupled via an isolating transformer to the gates of SCR2 and SCR4 which are each triggered into conduc­tion simultaneously. These SCRs drive the gates of SCR1 and SCR3 which then drive the load. The 1:1:1 diminutive trigger transformer is unlikely to be readily available but can be obtained by rewinding a small audio transformer from a tran- constant current source. Q1 thereby produces a constant voltage across resistor R1 and this becomes the reference voltage for IC1b which is used as a comparator. It drives Mosfet Q2 which simply acts as a switch to connect or disconnect the solar panel from the battery. Resistor R3 provides positive feedback to give a degree of hysteresis to stop the circuit hunting, ie, continually switching on and off over a very small voltage range. If the battery voltage is less than, say, 13.2V, Q2 will be turned on, charging the battery. When the battery charges to 13.8V, Q2 will turn off. No further charging will take sistor radio. The transformer requires three windings each of 200 turns using a fine gauge enamelled copper wire. Two layers of electrical tape are used for insulation between the three windings. Note that the whole circuit floats at mains potential and is potentially lethal. K. J. Benic, Forestville, NSW. ($25) place until the battery voltage falls below 13.2V again. This charac­ teristic should suit batteries designed for deep cycle perfor­mance and provides better efficiency than obtainable from a linear regulator. Current limiting is not provided as it is assumed that this would be unnecessary with a solar panel. The parameters for the circuit are: Nominal battery voltage – 12V; Regulation – on/off with hysteresis; Nominal switching levels – off at 13.8V, on at 13.2V; Current consumption – less than 1mA; Maximum output current –10A. Herman Nacinovich, Gulgong, NSW. ($25) VR1 LM2936Z-5 IN 9V OUT GND C2 10 +5V C3 0.1 R1 4.7k 1 RESET 4 13 3 A S1 TRO VCC 6 PA1 4 13 7 12 6 11 4 IC2 10 CD14511 d 2 9 e C 1 15 f B 7 14 A g LE 2 LT BI a B S2 PA0 2 C1 100pF R2 27k 16 PA7 PB1 PA6 OSC1 IC1 PA5 68HC705K1 PA4 b 5 12 6 11 10 9 c D 5 R3 9.1k 15 PA3 OSC2 VSS PB0 14 Microcontroller timer PA2 8 8 R4 4.7k 12V R1 750k Q2 MTP3055 3 7 1 2 IC1b R3 1M 200mV 8 R2 10k VR1 2.2k f g e R7 100  6 a 4 b c 2 1 9 d 10 3 3 Q1 BC547 B1 BUZZER Q2 R5 BC547 4.7k R6 4.7k R4 39k Q1 BC547 LD2 CM1-5615 7 10 3 TO SUIT CURRENT 4 9 7 D1 IC1a LM10 1 last four seconds and then restart again. It can all be done with the two programming switches, A and B. The power supply for the circuit is based on the LM2936 which is an ultra-low quiescent current 5V regulator. It works in essentially the same way as a conventional 3-terminal regula­tor but it draws less current and has a lower dropout voltage. Since the total current drain of the circuit is so low, there is no hardware off/ on switch. The current drain of the circuit is around 25µA when the K1 is in STOP mode and around 19mA when running. The off/on switch is This circuit was designed to provide the functions of a timer. While it would possibly be cheaper to provide the same function with discrete logic circuitry, this circuit has been designed to offer programming experience with the 68HC705K1 micro­ controller. It contains all the software to drive a buzzer and a 2-digit 7-segment LED display. As an example of its flexibility, it could be programmed to start at 60 seconds, beep every eight seconds and then give a different beep for the SOLAR PANEL LD1 CM1-5615 16 6 Q3 BC547 in the software. Four port lines from the micro­ controller drive IC2, a 4511 BCD to 7-segment decoder. Two additional ports drive transis­ tors Q1 and Q2 to provide the multiplexed 2-digit display. The buzzer is driven by Q3 which is controlled by port PB0. The processor runs at 262kHz as set by the components at pins 2, 15 and 16. Thus, the time counts in nominal 1-second steps. If more accuracy was required, a crystal could be connect­ed between pin 15 and 16 and then appropriate changes would be required to the software. A complete kit for this timer including the PC board, K1 programmed microcontroller and a floppy disc with software, is available from Alpine Technologies, PO Box 934, Mt Waver­ley, Vic 3149. The cost is $37.25, including postage and packing. Wanted: your circuit & design ideas Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation and send it to us. We’ll pay up to $60 for a really good circuit but don’t make them too big please. Send your idea to Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097. September 1993  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Microprocessor-controlled nicad battery charger This intelligent charger does everything a nicad charger should. It automatically checks the condition of the battery, then discharges it or charges it at 500mA or 1A. Design by WARREN BUCKINGHAM This is the first intelligent battery charger that we have presented. Previously, we have featured units which discharge nicads down to 1.1V per cell but then you have to recharge them with your own charger. By contrast, the “Nicad Battery Service Module” is an automatic microprocessor controlled unit which combines the functions of discharging and charging, together with an analysis of battery condition. 16  Silicon Chip Furthermore, you can power it from an AC plugpack or from the cigarette lighter socket in your car. Most users of nicad batteries have experienced poor battery performance at some time and generally this is brought about by incorrect charging. The most common fault is what is called “memory effect” and is brought about because the cells in the battery pack have not been correctly dis- charged before they are recharged. In effect, nicad batteries cannot be used in shallow discharge cycles otherwise their capacity is reduced. They must be discharged to the “end-point” voltage which is typically 1.1V per cell. On the other hand, if the battery is discharged too far, damage can be done to the cells and in fact can reverse the polarity of the cells, thereafter making it virtually impossible to charge the battery with a conventional charger. A few chargers on the market have a discharge button to discharge the battery while others simply discharge every time the battery is connected to the charger. This works but every time the battery is dis­charged it reduces the life of the battery. Another major problem is overcharging. When a near fully charged +V1 RLYA +5V D5 1N4004 10k 10k 10k 1. 2  5W RLY1 A LED1 RED 0.1 10k 4DIP SWITCH Q3 BC547 B 5 18 4.7k 3 17 K 16 +5V 330  4.7k 2.2k 1% 3k 1% TEST VR1 5k 10T 2 8 3 IC2 LM358 2 30k 1% Q5 BC557 1 B X1 3.579MHz E 18pF 0.27  K COND. LED3 RED RLYB  1k 1% 100  1% 10k 1% 0.1 ZD1 18V 400mW BATTERY 2.2k 1% Q4 BC547 B D6 1N4004 C K 10 C C A 10 25VW 18pF Q1 TIP32C E 9 7 13 1k 12 11 E 16VAC 1.5A A CHARGE LED4 RED 6 C 4 IC1 Z8 4 470W 1W Q2 BC547 B 430  430  E B 1 100 25VW 1. 2  5W HIGH LOW C E 15 CURRENT S1  8 430  14 FAULT LED6 OR D1-D4 4x1N4004 +V1 430  A  K READY LED5 GRN A  K B 7805 1000 25VW 2.7k POWER LED2 RED 1000 25VW +5V E C VIEWED FROM BELOW 100 25VW B CE I GO  NICAD BATTERY SERVICE MODULE battery is put on charge, it becomes hot which again reduces its life. In effect, no simple charger is ideal as far as nicad batteries are concerned. Table 1 indicates some of the problems which can occur with different modes of charging nicad batteries. This intelligent charger, or “Nicad Battery Service Module”, actually checks the condition of the battery when it is first connected. First, it places a load on the battery and then checks the slope of the discharge curve. This indicates two aspects of the battery’s condition: (1) it gives an indication of its capacity and state of charge; and (2) it indicates whether the battery is showing symptoms of memory effect. These show up as very Fig.1: the circuit for the Nicad Battery Service Module is based on IC1, a Z8 microprocessor. When the battery is first connected, it is load tested at either a 500mA or 1A rate via Q1, D6 & the associated 1.2Ω 5W resistors. Depending on the battery condition, the processor then either continues to discharge the battery to its end-point voltage or switches straight over to the charge mode. Table 1: Common Problems Function Problem Trickle charge Overcharging. Timed charge Overcharging. Delta V Under or overcharging possible. Most units switch off after the Delta V point reached, or switch off before this, due to battery chemical action. Temperature sensing Overcharging possible; not suitable for most batteries unless they have a heat sensor built in or are charged in a special housing. Manual discharge & charge If not required, time wasted and battery life reduced. Note: overcharging causes the battery to become hot and reduces its life. September 1993  17 All the parts except for transistor Q1 are mounted on a single PC board & this mounts inside a standard plastic case. Q1 is mounted on a U-shaped aluminium heatsink which fits under the board. slight fluctuations on the discharge curve. This load test lasts for up to 30 seconds after which the processor decides either to discharge the battery to the end-point voltage or switch straight over to charging. For a charger with such fancy functions, the Nicad Battery Service Module does not have a fancy appearance. Table 2: Charger Functions Discharge Remove memory. Charge To max. capacity. Flash fault LED Wrong battery, reversed cell, unable to charge. Table 3: Fault Light Indications Steady Below maximum capacity, shorted cell, charged on wrong setting, set too high. Flashing Charge cycle taking too long, battery already charged, reversed cell in battery. 18  Silicon Chip It is housed in a small black plastic instrument case measuring 93 x 56 x 135mm. On the front panel it has a single toggle switch to select the charging rate and on the top of the case are five LEDs which indicate the following: Power, Conditioning, Charging, Ready and Fault. On the rear panel are two sockets, one for AC or DC input and one for connection to the battery to be charged. The unit comes with a 16VAC 1.5A plugpack for charging from the mains supply and a cigarette lighter socket for battery charging in a car. Now let’s have a look at the circuit which is shown in Fig.1. Circuit description The heart of the circuit is the Z86EO (IC1), a member of the Z8 micro­controller family. It is clocked at 3.579MHz, as set by the crystal connected between pins 6 and 7. The Z86EO has an OTP (one time programmable) ROM, a RAM and a couple of inbuilt comparators which are used in this circuit. The ROM holds the algorithms for analysis, discharging and charging of nicad cells, as well as providing all the control functions to drive the LEDs and external circuitry. The two internal comparators of the Z86EO have been config­ured to build a 12-bit A/D converter. With an 8-bit processor such as the Z8, this is done by storing eight bits of the con­ verter output in one register and the remaining four bits in another register. The converter uses a time relationship to convert the battery voltage into a digital code. The battery voltage is applied via a voltage divider to pin 9 of IC1. This voltage is fed to the internal comparators which use it to gener­ate a sawtooth voltage at pin 10. This sawtooth is developed in the following way. Op amp IC2, in conjunction with transistor Q5, forms a con­stant current source which charges the 0.27µF capacitor at pin 10 of IC12. When the voltage at pin 10 rises above the voltage at pin 9, the comparator output at pin 11 goes high. This turns on transistor Q4 which then discharges the capacitor at pin 10, whereupon Specifications Input........................................ 12V to 16V DC or AC, 1.5 amps Output..................................... 500mA or 1A switchable Cells........................................ 1-10 selectable by DIP switch Discharge................................ Voltage end-point. Charging.................................. Switches off when Delta Peak reached. Battery Condition.................... Determined by discharge curve method. Fault Indication........................ Battery below approx. 90% of capacity. Charging Times....................... 500mAh battery, 60 minutes from dead flat; ................................................ 1000mAh battery, 60 minutes from dead flat; ................................................ 1400mAh battery, 84 minutes from dead flat. the cycle repeats itself. In effect, the circuit works as a voltage to frequency converter with an inverse frequency relationship – the higher the battery voltage, the lower the frequency. Typically, when a 7.2V battery pack is being charged, the sawtooth voltage at pin 10 will be about 2.2kHz. The processor then converts the frequency at pin 10, repre­senting the battery voltage, to a digital value. This value is compared to an algorithm selected by the DIP switch at pins 15, 16, 17 & 18. Initially, when the battery is first connected, it is sensed by the processor which sends pin 1 high. This turns on Q2 and Q1. Q1 and LED 1 form a constant current circuit that con­trols both the discharge and charging currents. LED 1 is biased on when Q2 turns on and it provides a reference voltage of about 2V to the base of Q1. Q1 then acts as an emitter follower and pro­duces a voltage of close to 1.2V at its emitter (ie, the base-emitter Where to buy the kit The complete kit for the Nicad Battery Service Module is available only from Cessnock Instru­ men­ tation and Electronics. They own the copyright for the design.The kit contains all com­ponents in­cluding the 16VAC plugpack and the silk screened and drilled plastic case. The cost is $135 plus $10 for packing and postage. Adapters to suit various batteries are available from $25 each. Send orders to CIE, 524 Abernethy St, Kitchener, NSW 2325. voltage of Q1 will be close to 0.8V). This 1.2V is ap­plied to the emitter resistors of Q1 which will be 1.2Ω or 2.4Ω, depending on the setting of switch S1. Thus, Q1 is forced to carry a current of 500mA or 1A, as selected by switch S1. So Q1 operates at this current setting, both when the charger is in charge or discharge mode. OK, so far we’ve connect­ed the battery and it has been sensed by the processor which has turned on the constant current source. This starts sucking cur­rent out of the battery which is monitored all the time by the processor. After the initial discharge test, during which time the conditioning LED (LED 3) will be on, the processor will either decide to continue discharging the battery down to its end-point voltage of about 1V per cell or it will decide to charge the battery. When the latter occurs, pin 3 of IC1 will go high and turn on Q3 which controls DPDT relay RLY1. This changeover relay connects Q1 to the incoming supply so that it now charges the battery at the current selected by S1. Charge cycle Depending on the size of battery and its initial state of discharge, the time to fully charge it can range from less than 15 minutes for the full cycle to several hours. During the charge cycle, the battery is monitored constantly and the processor detects the slight dip in voltage that each cell gives when it reaches full charge. This is the so-called “Delta V” charging method but here there is a refinement. Instead of looking for a dip in the total battery voltage, the processor actually detects the voltage dip for each cell. Since it knows how PARTS LIST 1 plastic case, 135 x 95 x 45mm 1 PC board, 110 x 75mm 1 16V AC 1.5A plugpack with 2.5mm plug 1 cigarette lighter plug & lead with 2.5mm plug 1 DPST toggle switch with cranked leads (S1) 1 3.5mm jack socket 1 2.1mm DC socket 1 4-way DIP switch 1 miniature DPDT switch 1 3.579MHz crystal 1 multi-turn 5kΩ trimpot (VR1) 1 18-pin IC socket Semiconductors 1 Z86EO microcontroller (IC1) 1 LM358 dual op amp (IC2) 1 7805 5V regulator 3 BC547 NPN transistors (Q2,Q3,Q4) 1 BC557 PNP transistor (Q5) 1 TIP32C NPN transistor (Q1) (see text) 4 red LEDs (LED1, LED2, LED3, LED4) 1 green LED (LED5) 1 orange LED (LED6) 1 18V 400mW zener diode (ZD1) 6 1N4004 silicon diodes (D1-D6) Capacitors 2 1000µF 25VW electrolytic 2 100µF 25VW electrolytic 1 10µF 25VW electrolytic 1 0.27µF 63VW MKT polyester 2 0.1µF 63VW MKT polyester 2 18pF ceramic Resistors (0.25W, 1%) 1 30kΩ 2 1kΩ 6 10kΩ 1 470Ω 2 4.7kΩ 4 430Ω 1 3kΩ 1 330Ω 1 2.7kΩ 1 100Ω 1 2.2kΩ 2 1.2Ω 5W wirewound many cells are connected, by virtue of the DIP switch settings, it knows how many voltage dips to look for. Consequently, each battery will end up being charged to a different voltage. For example, we charged three 7.2V 1200mAH nicad racing packs. Two of these were ultimately charged to just over 9V while one was charged to September 1993  19 AC INPUT D1-D4 1000uF O G 100uF I 1000uF 7805 1k 10k 10k 10k 10k 4DIP SWITCH 1. 2  5W RELAY 2.7k 1 430  D6 4.7k D5 0.1 X1 330 A A LED1 K 18pF 18pF 430  10uF K A VR1 1. 2  5W 1k LED2 K LED3 B E 470  5W Q2 Q4 LED4 A .027 K 10k 2.2k 100  2.2k 1 100uF K LED5 A 30k 3k TO Q1 MOUNTED ON HEATSINK C IC1 Z82 4.7k Q3 Q5 IC2 LM358 430  ZD1 430  0.1 S1 LED6 A K Fig.2: install the parts on the board as shown here. The parts shown dotted (link, DIP switch & 0.1µF capacitor) mount on the underside of the board. Note that the two 1.2Ω 5W resistors should be mounted clear of the board, to aid heat dissipation. 10.4V. By the way, while the nominal cell voltage for nicads in 1.2V, it can go substantially higher than this while on charge. This is quite normal. It can happen that one or more cells in a battery pack may have almost identical voltage dips at the end of charge and this can make it difficult for the processor to detect the individual cell voltage dips. This is overcome by having the processor look at the total battery voltage for an overall decline in value at the end of charge, while also taking into account the elapsed time. When the processor decides that charging is complete, it pulls pins 1 and 3 low. This de-energises the relay and turns off the current source involving Q1. At the same time, pin 13 goes high to light the green Ready LED (LED 5). It can also happen that batteries will not charge properly due to internal open or shorted cells or perhaps due to wrong settings of the DIP switches for a particular battery. These cases are indicated by the orange fault LED (LED 6). It indicates the conditions shown in Table 3. Note that if a battery is connected the wrong way around, the charger will not work. Only the Power LED will light. Let’s now recap the sequence of a charging cycle. When power is applied, LED 2 (red) lights and when a battery is connected, the charger goes into the load test phase and the red Conditioning LED lights. When the unit subsequently goes over to charge mode, the red Charge LED lights as well. Finally, when it has finished RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 6 2 1 1 1 2 1 4 1 1 2 20  Silicon Chip Value 30kΩ 10kΩ 4.7kΩ 3kΩ 2.7kΩ 2.2kΩ 1kΩ 470Ω 430Ω 330Ω 100Ω 1.2Ω 4-Band Code (1%) orange black orange brown brown black orange brown yellow violet red brown orange black red brown red violet red brown red red red brown brown black red brown yellow violet brown brown yellow orange brown brown orange orange brown brown brown black brown brown not applicable 5-Band Code (1%) orange black black red brown brown black black red brown yellow violet black brown brown orange black black brown brown red violet black brown brown red red black brown brown brown black black brown brown yellow violet black black brown yellow orange black black brown orange orange black black brown brown black black black brown not applicable The power transistor (Q1) is supplied mounted on the heatsink with three wires connected: green for the emitter, blue for the base & white for the collector. These are connected to the underside of the board, as shown in Fig.2. power dissipation of transistor Q1, otherwise it will become very hot. Construction charging, the green Ready LED lights and if a fault occurs, the orange Fault LED lights. If power is disconnected and then reconnected while a bat­tery is being charged, the charger takes 60 seconds to reset itself and then it beings the cycle again with a conditioning test before flicking into charge mode. Power for the circuit comes either from an AC plugpack or from a 12V battery via a cigarette lighter socket in a car. The AC or DC is fed via a bridge rectifier comprising diodes D1-D4 and filtered with two 1000µF capacitors before being fed to a 7805 3-terminal 5V regulator. When supplied with 12V DC, the charger can charge batteries consisting of up to eight cells (ie, 9.6V nominal). When powered by a 16VAC plugpack, the unit can charge batteries with up to 10 cells. Ideally, if the charger is to be used to charge batteries of 7.2V or less at the 1A rate, it should be used with a 12VAC 1.5A plugpack to reduce the Table 2 Switch Number of Cells Battery Voltage 1 2 3 4 1 1.2 1 0 0 0 2 2.4 0 1 0 0 3 3.6 1 1 0 0 4 4.8 0 0 1 0 5 6.0 1 0 1 0 6 7.2 0 1 1 0 7 8.4 1 1 1 0 8 9.6 0 0 0 1 9 10.8 1 0 0 1 10 12.0 0 1 0 1 0 = OFF, 1 = ON. Note: always turn the power off and wait 60 seconds before adjusting the DIP switches. The charger is housed in a standard plastic case. This has two halves which clip together. Inside is a single-sided PC board which measures 110 x 75mm. This has all the components mounted on it apart from transistor Q1 which is mounted on a U-shaped alu­minium heatsink in the base of the case. All the components will be available in a complete kit which will include a 16VAC plug­pack adapter, a cigarette lighter plug lead and a battery output lead fitted with a 3.5mm jack. The component wiring diagram for the charger is shown in Fig.2. Assembly can begin with the 0.25 watt resistors, small capacitors and the transistors. The four 10kΩ resistors associat­ed with the DIP switch are mounted “end-on” while the DIP switch mounts under the board, on the copper side. There is a long link installed on top of the board and four contacts on one side of the DIP switch are actually soldered to this link. Next, fit the diodes, the electrolytic capacitors, the LM358 (IC2), multiturn trimpot VR1 and the 3-terminal regulator. In each case, make sure that the component is correctly oriented on the board. The two 1.2Ω 5W resistors should be mounted so that they stand September 1993  21 the base. The TIP32C transistor and heatsink assembly is sandwiched between the PC board and the base with the aid of two 5/16-inch nuts which act as spacers.The method of assembly is as follows: (1) place a nut over the central pillar in the base of the case, then fit the transistor heatsink over it. (2) Place another nut over the central pillar and then an insu­lating spacer. (3) Place an insulating spacer over the other pillar and then secure the board with the two self tapping screws. Do not over-tighten the screws and fit the front and rear panels of the case before they are fully driven home. Now comes setting up and calibration. Before fitting IC1 into its socket, connect the AC plugpack to the charger and measure the voltage at pin 5 (of the socket). It should be +5V DC. Check also that +5V is present at pin 8 of IC2 and at the collector of Q3. If not, check that the 5V regula­tor is OK. This done, turn the power off and wait at least 60 seconds before inserting IC1 into its socket. Make sure you get it the right way around. The pin 1 end should face the regulator end of the board. Next, set all the DIP switches to off before turning the power on again. Apply +7V from a power supply to the battery output and adjust trimpot VR1 until both pins 2 and 4 of IC1 are high; ie, +5V. The charger is now ready for use. Battery voltage selection A nut is fitted over the central pillar on the bottom of the case before the heatsink assembly is fitted. A second nut & an insulating spacer are then fitted to the pillar & an insulating spacer also fitted to the other pillar before the PC board is secured in position. about 6mm clear of the board, to aid heat dissipation. LED 1 can be mounted with short leads but the five indica­tor LEDs need to be mounted with long leads, so that their bodies are 20mm above the PC board. This is done so that they will protrude slightly through the lid of the case when it is clipped together. An 18-pin IC carrier is used for the Z8 (IC1) but this chip should not be installed until later. A 0.1µF capacitor is con­nected underneath the processor socket (on the copper side of the board) between pins 5 and 14. Also connected 22  Silicon Chip to the underside of the board are the leads to the 3.5mm battery socket. The input power socket and the DPST toggle switch S1 are mounted on the top of the PC board. The power transistor Q1 is supplied mounted on the heatsink with three wires connected: green for the emitter, blue for the base and white for the collector. These are connected to the underside of the board, as shown in Fig.2. The PC board is assembled into the case and secured by two self tapping screws with go into integral pillars in Always turn off the power and wait 60 seconds before ad­justing the DIP switches which are accessed via a hole on the underside of the case. The settings are shown in Table 4. Charge rate selection Select 500mA or 1A, which ever is the value closest to the rating of your battery. It is not recommended to charge at a rate higher than 1.2 times the battery capacity. For example, if you have a 500mAh AA cell, choose the 500mA rate. If you have a 7.2V 1200mAh racing pack, choose the 1A rate. If you wish to charge at a lower rate, then replace the 1.2Ω 5W resistor across switch S1 with a 10Ω 0.25W resistor. This will result in a charging current of 100mA instead of 500mA. This makes it suitable for charging 9V SC 100mAh batteries. AUSTRALIAN MADE TV TEST EQUIPMENT 12 Months Warranty on Parts & Labour SHORTED TURNS TESTER Built-in meter to check EHT transformers including split diode type, yokes and drive transformers. $95.00 + $4.00 p&p HIGH-VOLTAGE PROBE Built-in meter reads positive or negative 0-50kV. For checking EHT & focus as well as many other high tension voltages. $120.00 + $5.00 p&p DEGAUSSING WAND Great for computer mon­­­it­ors. Strong magnetic field. Double insulated, momentary switch operation. Demagnetises colour picture tubes, colour computer monitors, poker machines video and audio tapes. 240V AC 2.2 amps, 7700AT. $85.00 + $10.00 p&p TUNER REPAIRS From $22. Repair or exchange plus p&p. Cheque, Money Order, Visa, Bankcard or Mastercard TUNERS 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone for free product list Phone (02) 774 1154 Fax (02) 774 1154 September 1993  23 Stereo preamplifier with infrared remote control This new stereo preamplifier incorporates the very latest trends in audio design technology. It has excellent speci­fications for noise & distortion & includes infrared remote control for input & mode selection, volume & balance. All control settings are indicated on LED displays. By JOHN CLARKE Sit back and relax with your Studio Remote Control Pream­plifier. You can adjust the volume and balance from your armchair or select the program from six signal sources (Phono, CD, Tuner, VCR, Aux 1 and Aux 2) plus a Tape deck (Tape Mon). The green LED display on the front panel shows the settings made via the infrared remote control. Volume level is displayed directly in dBs, while the balance setting is indicated with discrete LEDs as a bargraph. Separate 24  Silicon Chip green LEDs show the select­ed program source. We know that you will be impressed with the action of the remote volume control. It provides volume changes in steps of 1.5dB over a huge 88.5dB range with perfect tracking between channels. The balance display is a 9-LED bargraph which simulates the setting of a horizontal slider control. When the balance is centred, the centre LED lights. When the balance is shifted to the right, the LEDs to the right will be successively lit and vice versa. Balance adjustment is made in 1.5dB steps from 0dB to -9dB and then fully off. The three LEDs either side of centre indicate 3dB balance steps (-3, -6 and -9dB), while when two adjacent LEDs are lit they indicate the in-between settings (-1.5, -4.5 and -7.5dB). When the extreme left LED is on, the right channel is fully off. Similarly, when the extreme right LED is on, the left channel is off. For temporary interruptions such as phone calls you can instantly reduce the volume setting by 21dB using the Mute con­trol. This is indicated by seven of the nine LEDs being on. Mono and stereo selection can also be made via the remote control. Knobs are provided on the front panel for the bass and treble controls and there is a tone defeat switch which can be used to bypass the tone circuitry for a ruler-flat frequency response. The front panel also carries a headphone socket for private listening and duplicate volume control switches so that you can change the volume setting without having to use the remote control. While the remote volume control is very convenient, it also solves the limitations found on conventional dual-ganged volume controls. All normal potentiometers become noisy with use and since the volume control is the one we use the most it is the first control to have problems. A second problem with volume control potentiometers is their poor tracking between channels, particularly at low volume settings. This means that as you turn the volume down, the bal­ance between channels shifts and requires adjustment with the balance control. With this new remote control preamplifier, no noise can develop because there are no moving parts in the volume control and the channel tracking is excellent, even at low volume settings. The new Studio Remote Control Preamplifier is housed in a black 1-unit high rack case with a screen printed front panel. The volume LED and balance LED displays are located behind a neutral Perspex filter in the front panel and there are nine green LEDs for program and mode selection. The front panel is relatively uncluttered, with only a few controls. This has been made possible because most functions are accessed via the remote control which has 15 pushbuttons. Inside the unit there is a large single PC board which accommodates most of the components, including the tone control potentiometers, the tone defeat switch and the headphone socket. A small front board is used for the front Most of the parts are mounted on a large PC board, while a second smaller board accommodates the LED displays & three click-action pushbutton switches (Volume Up, Volume Down & Mute). panel displays and switches. Inputs and outputs As noted above, the Studio Remote Control Preamplifier caters for six pairs of inputs and has a tape monitor loop. This means that you can connect up to seven stereo program sources, all of which can be selected via the remote control. When select­ing Tape Monitor or Source via the remote control, you have the choice of either mono or stereo modes. Having a mono tape monitor mode means that a mono tape deck can • • • • • • • • • • • • • drive both channels or alternatively, the stereo program being fed through the preamplifier will be converted to a mono signal if you wish to make a monaural tape recording. When listening via headphones, the preamplifier’s output signal to the power amplifier is disconnected. This prevents you from inadvertently overdriving your loudspeakers when listening with headphones. The headphone amplifier has the potential to deliver more than adequate drive for even insensitive headphones. This will allow listening Main Features Infrared remote control of all functions except power on/off, tone controls & tone defeat switch Very low noise on phono & line inputs Very low harmonic & intermodulation distortion Up to seven program sources can be connected Tape monitor loop Separate high quality headphone amplifier Headphone socket disables output signal to power amplifier Tone defeat switch 88.5dB volume control range in 1.5dB steps with 3-digit display 21dB mute Balance control in 1.5dB steps to -9dB then fully off Initial settings of -48dB volume and CD stereo signal source Excellent left and right channel tracking for volume setting September 1993  25 26  Silicon Chip CMOS SWITCH IC11 VCR AUX1 AUX2 PHONO CD TUNER TAPE IN x1 LATCH IC10 5 CONTROL INPUTS AUX2 TAPE OUT 4 AUX1 IC8 3 VCR CMOS SWITCH IC2 2 OUT TUNER 1 0 IC1 CD PHONO RIAA PREAMPLIFIER A ACK. MONO TAPE MON. DECODER AND LATCH IC12 CONTROL INPUTS By Bx C MONO Cy CMOS SWITCH IC3 TAPE Ay MON. Ax INFRARED RECEIVER AND DECODERS IC22, IC23 DOWN DUAL LOG D-A CONVERTER IC15 MUTE MON. UP RIGHT MONO STEREO SOURCE TAPE IC16 x2.5 IC5 INFRARED TRANSMITTER BALANCE DISPLAY (dB) h 9 6 3 0 3 6 9 h L BALANCE R MICROPROCESSOR IC14 ATTENUATION DISPLAY (dB) BALANCE AUX2 TUNER LEFT AUX1 VCR x1 IC4 CD PHONO TO RIGHT CHANNEL UP, DOWN MUTE SWITCHES TO RIGHT CHANNEL 330k 4.7k BASS AND TREBLE CONTROLS IC6 IN TONE S5 HEADPHONE OPERATED S6 OUT x4.7 IC7 TO RIGHT CHANNEL RELAY PHONES OUTPUT VDD R Vin 2R R 2R S1 2R S2 Vin A R RFB A 2R S3 2R OUT A 17 BIT DAC A S17 RFB OUT A GND OPAMP 17 BIT LATCH Vout DB0 Fig.2: the arrangement for a standard 17-bit R-2R D/A converter. In this application, the D/A converter is used as a programmable resistance to control the gain of an op amp & thus the audio level at the output. at ear-deafening levels should the need arise. When the preamplifier is turned on, it always has the CD source selected, the volume set at -48dB and the Mute on (-21dB) This prevents the speakers from blasting if the CD player goes straight into play at switch-on. Omissions To keep the unit simple, we have omitted some features that are found on some stereo amplifiers. First, there is no loud­ speaker switching which is rather unwieldy when you have a sepa­rate control unit. Second, we have not provided for moving coil cartridges in the RIAA phono preamplifier. And third, there is no dubbing and monitoring facility between two tape decks. Dubbing is possible however, if the outputs of one deck are fed into a pair of auxiliary inputs. Block diagram ▲ Fig.1 shows the main features of the unit. To keep the block diagram simple, we have shown only one channel. The second channel has identical circuit functions. The six inputs (Phono, CD, Tuner, VCR, Aux 1 & Aux 2) are selected using CMOS analog switch IC2. It Fig.1 (left): this block diagram shows the general layout of the Remote Control Preamplifier. Incoming signals are routed via CMOS switches IC2 & IC3 & fed to a D-A converter (IC15). This D-A converter is controlled by microprocessor IC14 & in turn controls the gain of op amp stage IC16. The signals from IC16 are then further amplified & fed to the tone control stage. 8 BIT BUFFER DB7 DAC A DAC B CONTROL LOGIC DECODE LOGIC 17 BIT LATCH RFB B operates as a single-pole OUT B 6-way switch. For stereo 17 BIT DAC B operation, a second IC is required. The input selected depends on the code at the CS Vin B D GND A GND WR control inputs. Fig.3: block diagram of the AD7112 D/A Note that the Phono input converter IC. It has eight data inputs & these are buffered & decoded to control two 17-bit is fed via RIAA pre­amplifier D/A converters (DACs), thus making it ideal stage IC1 before passing to for use in a stereo system. IC2. The output of IC2 connects to the Ax input of IC3 and is muting when the preamplifier is powalso fed to amplifier IC8. IC8 provides ered up and down. a buffered signal for the tape monitor Microprocessor control output. IC3 provides for tape monitoring The heart of the preamplifier is a and mono/stereo mode selection. This Motorola 68HC705C8P microprocesIC contains three separate single-pole sor. This is used to drive the digital double-throw switches. The “A” readout and the LED balance display, switch provides switching between and to monitor the signal from the the tape monitor or source signals from infrared remote control receiver. It IC2. The “B” switch provides identical also controls the dual D-A converter, switching for the other channel. IC15, which in turn controls the volThe A output of IC3 is fed via a ume level. 4.7kΩ resistor to amplifi­er IC4. The Control signals from infrared rereason for the 4.7kΩ resistor is to avoid ceiver IC22 and decoder IC23 are undue signal loading when the “C” monitored by the microprocessor, switch in IC3 is turned on to mix the decoder and latch stage IC12, and by signal with that from the other channel latch IC10. IC10’s logic outputs confor mono listening. trol IC2 while logic data from IC12 IC4’s output connects to a dual log- controls IC3. IC12 also drives the tape arithmic D-A converter. This device, monitor and mono LEDs, as well as the in conjunction with op amp IC16, acknowledge LED which lights whe­n controls the level of the audio signal. a valid transmission from the remote The signal then passes on to op amp control transmitter is detected. IC5 which has a gain of 2.5. From IC11 is a CMOS switch identical there, the signal goes to the unity gain to IC2 and it decodes and drives the feedback tone control stage IC6 which source display LEDs. can be bypassed using the tone defeat One problem that can occur when switch S5. using a microprocessor in audio A jack-operated switch diverts the equipment is noise injection due to signal to amplifier IC7 when head- the high speed switch­ing of its internal phones are in use. When headphones circuitry. This can be minimised by are not in use, the signal passes careful circuit board layout but the through the relay contact and then to only really effective solution is to shut the output. The relay provides signal down the microprocessor whenever it September 1993  27 Specifications Frequency response Phono inputs: RIAA/IEC ±0.3dB from 20Hz to 20kHz High level inputs: -0.2dB at 20Hz, -0.2dB at 20kHz Total Harmonic Distortion Better than .005%, 20Hz-20kHz with respect to 1V output and 0dB volume setting. Signal-to-Noise Ratio Phono (moving magnet): 92dB unweighted (20Hz-20kHz) with respect to 10mV input signal at 1kHz and rated output with 1kΩ resistive input termination; 97dB A-weighted with respect to 10mV input signal at 1kHz and rated output with 1kΩ resistive termination. High level inputs (CD, Tuner, VCR and AUX1 & 2): 100dB unweighted (20Hz-20kHz) with respect to rated output (volume at maximum) with Tone Defeat switch in or out; 102dB A-weighted with respect to rated output (with volume at maximum) with Tone Defeat switch in or out. Separation Between Channels -67dB at 10kHz; -82dB at 1kHz and -88dB at 10Hz with respect to rated output and with undriven channel input loaded with a 1kΩ resistor. Crosstalk (between input sources) -93dB at 10kHz; -100dB at 1kHz and -100dB at 10Hz with respect to rated output and undriven inputs loaded with 1kΩ resistors. Input Sensitivity Phono inputs at 1kHz: 9mV High level inputs: 400mV Input impedance (phono): 50kΩ shunted by 100pF Input impedance (CD, etc): 47kΩ Overload capacity (phono) 300mV at 1kHz Output Level Rated output, 1VRMS; maximum output, 8V RMS; output impedance, 600Ω Tone Controls Bass: ±11dB at 100Hz; Treble: ±12.5dB at 10kHz Attenuation Accuracy (1kHz, <at> 25°C) <1dB to -54dB; <2dB to -66dB; <2.5dB to -88.5dB Channel Tracking within ±0.25dB Phase Non-inverting (ie, zero phase shift) from Phono to output and from high level inputs to output. Non-inverting from all inputs to Tape Out. With tone controls defeated: inverting (ie, 180° phase shift) from phono and high level inputs to output. is not needed and that is most of the time. This technique is called “static idle” and it means that the microprocessor only becomes active when a signal from either the remote control 28  Silicon Chip or a front-panel volume control switch is received. Volume control system As previously mentioned, a dual logarithmic D-A converter (IC15) is used to control the volume of the audio signal. Howev­er, analog to digital conversion and back again does not occur. All audio signals remain in analog form. Instead, IC15 is used as a programmable resistance to change the audio signal level ap­plied to op amp IC16. Fig.2 shows the concept. This diagram depicts the arrange­ ment for a standard R-2R D-A converter. The voltage at Vin is applied to the inverting input of an op amp via a series string of resistors of value R which are shunted with resistors of value 2R. The 2R value resistors can be connected independently either to the inverting input of the op amp or to ground via switches S1-S17. Note that we are using a 17-bit D-A converter (ie, with 17 switches) but only four of these are shown here. When all switches (S1-S17) connect to the OUT position, the signal at Vin passes directly to the op amp output with no atten­uation. If all the switches are connected to ground, then the signal is attenuated by a factor of 217. Other settings of the switches provide attenuation levels which are between these two values. The D-A converter we have selected is the AD7112 from Analog Devices. Its internal block diagram is shown in Fig.3. It has eight data inputs (DB0DB7) which are buffered and then decoded with an 8-bit to 17-bit decoder. The 8-bit inputs provide 256 volume settings in 0.375dB steps. Our circuit only requires volume setting steps of 1.5dB, so we only need to use the most significant 6-bits (DB2DB7). For this reason, the DB0 and DB1 inputs are permanently tied low. Actually, the AD7112 provides two 17-bit D-A converters, one for each channel, and both are controlled by the DB0-DB7 inputs. This facility allows us to provide the balance facility whereby the left and right channels can be individually adjusted. Transmitter Circuit Fig.4 shows the circuit for the infrared remote control transmitter. It comprises a single IC, a ceramic resonator, two infrared LEDs, a Mosfet and several resistors and capacitors. IC1 is a Plessey MV500 IC which provides PPM (pulse position modulation) signals suitable for driving a transistor and infrared LEDs. In stand- XXX00 ▲ Fig.4 (right): the transmitter circuit is based on an MV500 IC. Each time one of the switches is pressed, a unique code appears at the pin 1 output & this drives Q1 & two infrared LEDs. 10k XXX10 9V A UP S1 SOURCE STEREO S2 11 2 BAL-R S3 VCR S4 12 LED1 13 111XX A 3 BAL-L S5 AUX2 S6 ON S7 PHONO S8 4 SOURCE MONO S9 5 TAPE MON STEREO S11 MUT1 S10 6 TUNER S12 7 AUX1 S13 8 CD S14  K 2x CQY89A A 15  LED2 B by mode the IC draws 2µA and so the circuit does not require an on/off switch. The MV500 operates with an oscillator frequency of 500kHz as set by its ceramic resonator. This matches the receiver frequency of IC23. Fifteen switches are connected between the row pins (pins 2-9) and the column pins (pins 11-13). Note that the connection to pin 13, which is actually the positive supply pin, is via a 10kΩ resistor. When a switch is pressed, a unique code for that switch is delivered from the output at pin 1 and this drives the gate of Mosfet Q1 via a 10Ω stopper resistor. Q1 then drives two infrared LEDs (LED 1 and LED 2) via a 2.2Ω current limiting resistor. The LEDs are driven by 15µs duration 1.3A pulses at a 20% duty cycle in order to obtain a good range from the remote control. The 220µF capacitor across the battery supplies the peak current required for the LEDs. Next month we will describe the full circuit of the pream­plifier and present SC the parts list. 220 16VW 0.1 XXX01 TAPE MON. MONO S15 9 14 K 110XX 101XX 2.2 Q1 MTP3055E IC1 MV500 OUT 10  1 D G S 100XX 011XX 010XX 001XX GDS A K 000XX 16 100pF X1 500kHz 17 18 100pF IR REMOTE CONTROL FOR PREAMPLIFIER September 1993  29 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A84 ❏ $A42 ❏ $A105 ❏ $A53 ❏ $A130 ❏ $A65 ❏ $A130 ❏ $A65 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia September 1993  33 Build this +5V to ±12V DC converter This low-cost project uses only junkbox components to convert a +5V DC supply to ±12V DC rails (24V total) capable of supplying up to 100mA. What’s more, you can easily change it to provide other output voltages. By DARREN YATES The most convenient way to power most projects is to use a DC plugpack supply. These little “black boxes” provide a single fixed DC rail and they usually have quite a bit of grunt as well. Most plugpacks can supply 300mA or more which is more than ade­quate for most projects. But what if your project requires dual (ie, positive and negative) supply rails? These are unavailable from plugpack sup­plies and you have to resort to using an AC supply, a bridge rectifier, filter capacitors and positive and negative voltage regulators instead. This approach can sometimes be inconvenient and causes unnecessary expense if you already have a DC plugpack or some other DC supply; eg, a car battery or solar panel. Fortunately, there is a way around this problem and that’s where this project will be of use. It’s a simple converter that can produce ±12V supply rails (100mA max.) from any 5-10V DC supply. In addition, you can easily adjust the circuit to produce lower output voltages and each supply rail can be adjusted inde­pendently of the other. The only proviso is that the input vol­tage must be lower than the output voltage. You can also use the circuit to stepup the DC input vol­tage to a much larger single supply rail. For example, you can derive a 24V rail simply by connecting across the ±12V rail, or you can connect between either supply rail and ground. Block diagram Fig.1 shows the block diagram of the ±12V Converter. As you can see, it uses a master oscillator and this produces two anti-phase pulse waveforms. Each anti-phase waveform is then fed to a switching inductor driver circuit. These switching driver circuits step up the input voltage to produce the positive and negative output rails. In addition, each driver circuit is fitted with a supply regulator so that the master oscillator is not disturbed while it is running. Circuit diagram Let’s now take a look at the complete circuit diagram – see Fig.2. Transistors Q1 and Q2 are connected as a standard astable multivibrator and this forms the anti-phase pulse waveform generator. The associated 470pF and .0022µF capacitors determine the duty cycle of the waveform and set the frequency of oscill­ation to approximately 13.3kHz. In practice, the frequency is not all that important, as long as it is somewhere in the vicinity of 1215kHz. The two output sig- The converter uses only low-cost parts & can be powered from any 5-10V DC source. It provides both positive & negative supply rails up to ±15V & the output voltages can be varied by changing two zener diodes. 34  Silicon Chip nals are taken from the collectors of Q1 and Q2 and fed to the supply driver circuits via 22kΩ resistors. The positive supply driver circuit is based on transistors Q3-Q5, while the negative driver circuit uses transistors Q6-Q8. Since these two driver circuits are different, we’ll go through them one at a time. Starting with the positive rail, Q4, Q5 and their associat­ed parts function as a step-up voltage converter. In operation, the pulse waveform from Q1’s collector is fed to the base of Q4. This signal has a duty cycle of approximately 20%; ie, the output is high for 20% of the time and low for the remaining 80%. Q4 acts as an inverter and thus drives Q5 with a high-duty pulse waveform. However, as we’ll see later, this part of the circuit can be disabled by the voltage regulation circuitry. Q5 is a TIP122 Darlington NPN transistor and this switches inductor L1 on and off. When Q5 is on, current flows through L1 and energy is stored in the inductor. During this time, diode D1 is reverse biased since its anode is effectively connected to ground. When Q5 subsequently switches off, the collapsing magnetic field asso­ciated with the inductor tries to maintain the current through it and so the voltage across the inductor rises. D1 now becomes forward biased and so the inductor dumps its stored energy into a 470µF reservoir capacitor. This capacitor is used to smooth the DC output to the load. Voltage regulation As well as supplying the load, the output voltage is also applied to zener diode ZD1 via a 4.7kΩ resistor. This part of the circuit, in conjunction with Q3, forms the voltage regulator for the positive rail step-up converter. The voltage regulation works like this: as the voltage across the 470µF output capacitor rises from 0V, Q3 will initial­ ly be off and ZD1 will be non-conducting. This allows the signal from Q1 to operate the step-up circuitry as normal. However, as the output voltage rises, ZD1 eventually breaks down and clamps Q3’s base to 12V. Q3’s emitter continues to rise though, which it does for about another 0.6V (ie, it rises to about 12.6V). At this point, Q3 turns on and pulls Q4’s base high, thus turning SUPPLY REGULATOR POSITIVE SUPPLY DRIVER SUPPLY INPUT MASTER OSCILLATOR GND NEGATIVE SUPPLY DRIVER Fig.1: block diagram of the ±12V converter. It uses a master oscillator to drive positive & negative step-up converter circuits. SUPPLY REGULATOR +5-10V 4.7k Q3 BC558 10k B 2x1N4004 E Q4 BC558 B C ZD1 12V 400mW 47k D1 FR104 E Q5 TIP122 C 470  47k +12V OUT C B 470 16VW E 1k +5-10V 4.7k L1 D5 D4 4.7k 470pF .0022 22k GND Q2 C BC548 B Q1 BC548 B E C +5-10V 470 16VW E 1k Q7 BC548 22k B B 10k E C VIEWED FROM BELOW B C D3 1N4004 470  B D2 FR104 C E E C L2 -12V OUT 470 16VW E 4.7k ZD2 12V 400mW B CE Q6 BC548 Q8 TIP127 L1-L2 : 60T, 0.4mm DIA ECW ON NEOSID 17-732-22 ñ12VCONVERTER CONVERTER ±12V Fig.2: Q1 & Q2 form the master oscillator, while Q4, Q5 & inductor L1 function as a switching converter to step up the supply for the positive output. Similarly, Q7, Q8 & L2 function as a switching regulator which provides the negative output. Zener diodes ZD1 & ZD2 set the output voltages. Brief Specifications Input supply ............................................................ +5 to +10V DC Maximum output ..................................................... ±15V DC Maximum output current......................................... 100mA at ±12V Efficiency................................................................. 50% (approx). Quiescent current.................................................... 50mA (5V DC supply) September 1993  35 Semiconductors 4 BC548 NPN transistors (Q1,Q2,Q6,Q7) 2 BC558 PNP transistors (Q3,Q4) 1 TIP122 (or BD679, BD681) NPN Darlington transistor (Q5) – see text 1 TIP127 (or BD680, BD682) PNP Darlington transistor (Q8) – see text 2 FR104 fast-recovery 1A diodes (D1-D2) 3 1N4004 silicon diodes (D3-D5) 2 12V 400mW zener diodes (ZD1-ZD2) Capacitors 3 470µF 16VW electrolytics 1 .0022µF MKT polyester 1 470pF MKT polyester Resistors (0.25W, 1%) 2 47kΩ 4 4.7kΩ 2 22kΩ 2 1kΩ 2 10kΩ 2 470Ω GND +OUT -OUT 470uF L1 470  1k Q4 ZD1 4.7k Q3 D1 L2 Q5 D2 Q8 1k 22k .0022 4.7k 47k 4.7k 47k Q2 Q1 470pF 470  Q7 Q6 10k 4.7k 1 PC board, code 11109931, 102 x 57mm 2 14.8mm OD Neosid 17-732-22 toroidal cores 1 3-metre length of 0.5mm diameter enamelled copper wire 5 PC stakes The negative rail is derived in a similar fashion, the main difference being that everything is reversed; ie, NPN transistors are swapped for PNP devices and vice versa. In this case, the drive signal appears at the collector of Q2 and is fed to the base of Q7. Unlike the signal fed to Q4, this signal has a duty cycle of 80%. Q7 in turn drives PNP Dar­lington transistor Q8, while the associated inductor (L2) is connected between Q8’s collector and ground. As before, the inductor tries to maintain the current through it when its associated switching transistor (Q8 in this case) turns off. The difference here is that the voltage on the collector goes negative instead of positive, which is why fast-recovery diode D2 and the 470µF filter capacitor are connected the other way around. Zener diode ZD2 and transistor Q6 make up the voltage regu­lator for the negative rail. Q6 remains off until the output voltage drops below about -12.6V. At this point, Q6 turns on and pulls the base of Q7 to -0.6V, thus turning Q7 and Q8 off. The voltage on the negative rail now rises towards 0V and when it rises above -12.6V, Q6 turns off again and the converter circuit restarts. Diode D3 protects Q7 by preventing its base from going any lower than -0.6V when Q6 turns on. If it wasn’t for 470uF D5 D4 Negative rail PARTS LIST GND +IN 470uF 10k This process is repeated indefinitely while ever power is applied and thus keeps the output regulated to +12.6V, as set by ZD1. Diode D4 protects Q4 by clamping its base to the supply rail when Q3 switches on. Thus, if the supply rail is +5V, Q4’s base will be clamped to +5.6V when Q3 turns on, regardless of the output voltage. D5 ensures that Q4 turns off completely when its base is pulled high. 22k Q4 off and disabling the voltage stepup circuit. The output voltage across the 470µF capacitor now decreases due to the load current. However, as soon as it drops below about 12.6V, Q3 turns off again and releases the high on Q4’s base. This allows the voltage step-up circuit to restart and so the output voltage increases until Q3 turns on again. D3 ZD2 Fig.3: install the parts on the PC board as shown in this diagram. The two inductors are made by winding 60 turns of 0.5mm diameter enamelled copper wire onto a toriodal core. this diode, Q7’s base would be pulled almost to the negative output rail when Q6 turned on and this would destroy the transistor. Construction Building the +5V to ±12V Converter is quite straightfor­ward, since all the parts are mounted on a small PC board. This board is coded 11109931 and measures 102 x 57mm. Before you start any construction work, check the board carefully for any shorts or breaks in the copper tracks. Faults of this kind will be quite rare but it pays to make sure before mounting any of the parts. Fig.3 shows how to install the parts on the PC board. Begin by installing the five PC stakes at the external wiring points, then install the wire link, resistors and diodes. The accompany­ ing table lists the colour codes for the resistors but it’s also a good idea to RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 2 2 4 2 2 36  Silicon Chip Value 47kΩ 22kΩ 10kΩ 4.7kΩ 1kΩ 470Ω 4-Band Code (1%) yellow violet orange brown red red orange brown brown black orange brown yellow violet red brown brown black red brown yellow violet brown brown 5-Band Code (1%) yellow violet black red brown red red black red brown brown black black red brown yellow violet black brown brown brown black black brown brown yellow violet black black brown Protect your valuable issues Silicon Chip Binders Fig.4: check your PC board for defects by comparing it with this full size etching pattern before mounting any of the parts. The two inductors can be secured in position by gluing them to the board using epoxy resin or by pouring a little hot wax over them. To test the unit, you will need a power supply with an output of 5-10V DC and this should be connected to the board via your multimeter. Set the meter to the 2A range and make sure that you have the supply polarity correct before switching on. With no load connected, the current should be about 50mA for a 5V supply and about 30mA for a 10V supply. If the current drain is appreciably more than this, switch off immediately and check the board carefully for assembly errors. If everything is OK, disconnect your multimeter, select a suitable voltage range and check the output voltages. You should get a reading of about +12.6V for the positive rail and -12.6V for the negative rail. Changing the output The output voltage for each rail is set by its correspond­ing zener diode. You can alter these as you wish to give voltages other than ±12V, with the proviso that the input voltage must always be less than the desired output voltages. The output voltage is approximately equal to the zener diode voltage plus 0.6V for the positive rail, or the zener diode voltage minus 0.6V for the negative rail. For example, if ZD1 is rated at 13V and ZD2 at 15V, you will end up with +13.6V and -15.6V rails. Footnote: we would like to thank Adilam Electronics for supplying the FR104 fast-recovery diodes used in SC this project. These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. Use this handy form ➦ check them on a digital multimeter, as some of the colours can be difficult to decipher. The diodes and transistors can be installed next. Make sure that you install these parts correctly. The FR104 fast-recovery diodes and the standard 1N4004 rectifier diodes look very simi­ lar, so make sure that you don’t get them mixed up. Similarly, be sure to use the correct transistor type at each location. Some of the transistors are NPN types while others are PNP types and they don’t take too kindly to being transposed. The TIP122 and TIP127 Darlington transistors (Q5 & Q8) come in TO-220 packages and must be oriented with their metal tabs as shown in Fig.3. The alternative BD679-BD682 Darl­ing­ton power transistors come in TO-126 packages. Take care with the lead connections for these transistors – they must be mounted with their metal surfac­es facing in the opposite direction to the TO-220 types. You have been warned! Finally, install the capacitors and the two inductors (L1 & L2) on the board. The two inductors are identical and are made by winding 60 turns of 0.5mm diameter enamelled copper wire on a 14.8mm outside-diameter Neosid toroidal core. Begin with a 1.5-metre length of wire and thread it half-way through the centre of the core. Now, using one half of the wire, wind on 30 turns as tightly and as neatly as possible. The other half of the wire is then used to wind on the remaining 30 turns. Once each inductor has been wound, strip and tin the wire ends, then solder the leads to the board. Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ September 1993  37 SERVICEMAN'S LOG We have good news & we have bad news First, the good news. It’s not often that these stories relate a complete win; a puzzling problem, a neat technical solution & financial satisfaction for all concerned. The hard ones seldom make much profit, so this is an exception. The set concerned was an Akai CTK-107, a 34cm set which is very similar to a Samsung CB-349F. And one of the hardest parts of the job was getting a clear description of the fault from the owner. About the only thing he was definite about was that it was intermittent in operation. But intermittent what? Complete failure? Loss of picture? Loss of colour? Loss of sound? No – it was none of these. Eventu­ally, after putting him through the third degree, I formed the opinion that it was a form of horizontal tearing, sometimes accompanied by streaking. So we left it that. When I put it on the bench and turned it on I was lucky for once; it put on a display immediately and was almost exactly along the lines I had envisaged. Unfortunately, the symptoms didn’t tell me much; they could have been due to a hundred dif­ferent faults. And of course, it came and went as it saw fit, lasting anything from a few seconds to a few minutes. I let it run on the end of the bench while I attended to other jobs, glancing at it from time to time, hoping it might display some other symptom. And it did – for one fleeting second, during a particularly bad bout of tearing, the picture suddenly changed shape. This new shape could best be described as a wedge shape, or keystone. In short, it had normal scan width at the top but tapered to a much narrower scan at the bottom. And, naturally, the colour convergence went completely haywire. Then, in a flash, all the symptoms disappeared and the set was back to normal. Mental block Now I should have known what it meant and I knew I should know. But, for the life of me, I couldn’t pick it. So I simply let it run. And it ran day after day without any sign of the fault. I was on the point of giving it back to the customer until some more drastic or permanent symptom appeared. Fortunately, he had another set and he indicated that I should keep it for as long as necessary. In fact, the set had to be put aside for a couple of days. When I set it up again, it came up with a perfect picture and so I let it run. 40  Silicon Chip Then, suddenly, I looked at it and there was a perfect keystone, this time apparently permanent. And that’s when the penny dropped. Of course –a deflection coil fault or, more precisely, a shorted turn in the horizontal section. I had seen one way back in the early days of monochrome TV and even remem­bered a reference to it in the textbook of the time: “Basic Television”, by Bernard Grob. (Some textbooks, including Grob’s, describe this shape as a trapezoid but all my references describe a trapezoid as having no parallel sides, which does not fit this effect. My best referenc­es suggest that it would be better called a trapezium, although there appears to be some confusion here too). Anyway, I unplugged the neck board, removed the convergence adjustment rings, and eased off the scan coils. And one glance was enough (see photo). The wonder was not that there was a fault; the wonder was that the set had worked as well as it had for as long as it had. OK, so I’d found the fault, But what to do about it? Both cost and availability were problems. Akai replacement parts can sometimes be hard to get and a new scan coil was going to cost around $100 or more. Combined with labour, the repair could well be uneconomical. What about a Samsung unit? Well, it should be available but might still be too costly. More importantly, would it be totally compatible? The two sets were similar but not identical. While musing thus, I suddenly remembered that I had a junked Sam­ sung tucked away somewhere and, if I remembered cor­rectly, the scan coil assembly looked very similar. In fact, the set turned out to be a Samsung CB-515F, a much larger 51cm model. On the other hand, the scan coils were visually identical, even down to the plug on the cable. But were they identical? Would they So that’s the good news for the month. The bad news is in the form of a letter from a reader, Mr K. E. of the ACT. It details his problems finding competent service organisations. This is what he writes. Tale of woe work on the smaller set? Well, it was worth a try, even though I wasn’t very confid­ent. So I fitted the coils back on the tube (rather roughly), followed by the convergence rings and the neck board. With everything back in place, I switched on and, to my complete amazement, the picture came up almost spot on. There was some static and dynamic convergence error but no more than one would expect from a proper replacement coil. It looked like a goer. And so it was. After a full convergence routine, I had a picture which was every bit as good as the original. So it was a win all round. It was a rare fault, with symp­toms that initially looked as though they could be due to almost anything. And then came a breakthrough when the fault obligingly identified itself. So half the job was done with almost no man-hours expended. Finally, a I had a suitable replacement part right to hand which made the repair economical. I charged the customer a modest fee, made a reasonable profit, and everyone was happy. I also learnt (or re-learnt) a couple of important points. First, I re-learnt the symptoms of a faulty scan coil and second, I learnt that a scan coil from one set could be used successfully on a completely different make and model. It is a point worth remembering, both in terms of these particular devices and as general rule. If two scan coils look similar, don’t be put off because they come from different sets. It is worth a try. I read R. Pankiv’s letter in the March edition and it imme­diately reminded me of a couple of odd problems I have had with two different electronic units. The first was with a VCR, the second with a Commodore computer. The recorder is a Teac MV-400. It was bought in a secondhand shop, where I saw it working, both recording and playing back. It was then about 18 months old and the shopkeeper gave it a month’s guarantee. The machine must have heard him because, guess what, the problem appeared six weeks later. It’s now over five years old and probably not worth fixing. It works perfectly well most of the time. In the fault condition, no matter what is done with the remote control or panel buttons, the tape will not run forward. There is no fast forward in play mode, no play function and no fast forward without the head engaged. Turning it off and on again, even at the power point, made no difference. But it would work after the mains power was off for a day or so! I put up with it for a while, then took it down to a nearby TV and VCR serviceman. I explained minutely what the problem was and he said: “OK, give us a couple of days.” A few afternoons later, he came back with the statement: “Well we cleaned the head. $25 please”. “What, was it dirty?” “Nah, not very. In fact it was pretty clean”. “What about the refusal to run forward?” He blinked. “That didn’t happen. I didn’t see that at all”. “That’s why I brought it here. I told you all about it. I explained at length; I told you the fault was intermittent”. What followed was a long spiel about sunlight and/or room lights shining into the cabinet and confusing the infrared sen­sors. Or it could be weak batteries in the remote control causing it to send out wrong signals, without being touched. It sounded like nonsense but I couldn’t be sure. He was the bloke who was supposed to know. September 1993  41 SERVICEMAN'S LOG – CTD One glance at the scan coil was enough to identify the fault in an Akai CTK-107 34cm colour TV set. The wonder was not that there was a fault; the wonder was that the set worked as well as it did for so long. I bought new batteries for the remote control and took the thing home. A few days later it was playing up again – same fault. I took it to another serviceman, told him not to clean the heads because that had been done, and told him exactly what was wrong. After a few days he said that there was nothing wrong with it. Eventually, I ran a Teac service agent to earth (no; not in the ACT). This time I took a big luggage label and wrote the fault details on it. This was attached to the mains cord so that it could not easily be ignored. I handed the same details on a sheet over the counter. After a week I phoned. It was clear that they hadn’t even looked at it. After another week I tried again. Guess what, they had cleaned the head. Three days later I called in. The spiel this time made more sense. In the digital control area, 5% tolerance resistors have been used and this can result in one which is 42  Silicon Chip just slightly too high. It’s no problem if the resistor is at the lower end of its tolerance range. But if you happen to have a slightly high one, sometimes it’s a bit too high. This makes the control circuit think it sees the end of the tape. The resistor is buried so far in the depths that it would be a major job just to get at it. Which resistor is it? That I never found out but a tempo­rary cure is to disconnect the sensor just to the left of the tape carriage. The VCR will then play but not record. I decided that enough was enough. I took the damn thing home and it’s been playing up on and off ever since. It hasn’t been near any serviceman either. Well, that’s E. K.’s tale of woe – a little edited – about the Teac recorder. I don’t propose to deal with the computer problem. I am not “into” computers and would not do it justice. But what a tale of woe about the recorder. I think it best if I deal with it at two levels: (a) the treatment by the various service organisations, and (b) any thoughts of my own on the purely technical aspect. In regard to the service organisations, it is a tale of ineptitude, technical gobbledegook fob-offs and, overall, straight-out dishonesty. And all three organisations had one thing in common: they did not observe the fault or, more importantly, make any real attempt to observe it. It is virtually impossible to tackle a fault which cannot be observed and intermittent faults often call for a lot of patience, just to reach this point. But none of them was prepared to exercise such patience. They displayed what I regard as an “intermittent block”; a fai­lure to recognise the word, at least insofar as it applies to technical problems. The word is brushed aside, or totally ig­nored, and the equipment serviced solely on the basis of what is observed when first turned on. Which is just another way of saying that the customer’s comments are totally ignored. Granted, these can be rather weird at times and often largely irrelevant, but seldom totally so. Somewhere in their dissertation there will be some useful snippets of information, often quite vital. It is the serviceman’s job to sift the wheat from the chaff. But never ignore the customer’s story; you do so at your peril. Of course, sometimes the customer won’t talk, but that’s another story. Unfortunately, this attitude is encountered all too often, and is responsible for the many complaints by customers that a service organisation, “... charged me (so many) dollars and didn’t fix the fault”. The explanations As for the explanations offered, they are also typical of this approach; pure technical gobbledegook, designed to blind the customer with pseudo-science. The first one, about light confusing the sensors, is a partial truth. It has happened to me but only when the recorder is out of its case on the bench. When it is back in its case, it would be a strange lighting arrangement indeed which could cause such an effect. The suggestion that it was weak batteries in the remote control unit was, as K. E. suspected, pure nonsense. It is not worthy of comment. The service agent’s explanation Fig.1: this diagram, from a Panasonic training manual, illustrates the various transport control and safety functions normally found in a video recorder. While the unit discussed would differ in detail, this will help the reader follow the story. was more refined, at least to the point where, initially, it seemed to make some sense. But it doesn’t stand up to close examination. If the idea was anything more that spontaneous guesswork, then it should have been at least possible to nominate the resistor or, at least, the ones most likely to be involved. As K. E. himself asked, which resistor? And as for them being too hard to get at – well, there are many components which are hard to reach but I don’t believe there are any which are too hard. And it wouldn’t be the first time I have had to pull something apart to get at a suspect component; and then found that it wasn’t the culprit after all! All of which adds up to a situation where the three organi­ sations have performed a gross disservice – to both the customer and the industry as a whole. What more can one say? Technical aspects And what are my thoughts on the technicalities of the prob­ lem? Not very much, I’m afraid. Unfortunately, it is a make and model which I know little about. I don’t recall ever having handled one and I have no service manuals or even a circuit. I flogged the problem to a number of colleagues, hoping to score either some literature or a comment based on experience. Unfor­tunately, I drew a blank on both. And since servicing by remote control is hard enough at any time, these limitations make it almost impossible. I can only comment on the broad basis of all such machines, although the details vary considerably between makes. To help in this regard I am reproducing a drawing from a training manual put out by Panasonic, covering the NVG-20 and NVG-21 series recorders. While undoubtedly differing in detail from the Teac, the information is basic and should help the reader to follow the story. It gives a skeletal portrayal of the microprocessor, with the associated control and safety functions likely to involved in a fault of this kind. At top left are the two end-of-reel phototran­sistor sensors (take-up and supply) and their LED light source. Below this is the safety tab switch, the dew sensor, the cassette switch, and the reel movement sensor. This latter is another photosensor device, September 1993  43 SERVICEMAN'S LOG – CTD provided to shut the system down if a reel is not rotating when it should. On the right is a rotary switch, called the mode select switch. We will have more to say about this later. One of the significant aspects of this case is the fact that the failure involves tape movement in one direction only: forward. This might suggest an end-ofreel sensing failure; the only seemingly sensible suggestion hinted at by the first serv­iceman but in a nonsensical context. So let’s assume that an end-of-reel sensor fails; ie, goes open circuit. Normally, with a tape loaded and in mid-reel, neither end sensor photo­ 44  Silicon Chip tran­s­istor will see the sensing light source; they will see it only through the clear tape at one end or the other (some tapes do not even have this refinement). So, failure of the phototrans­istor, or associated circuit, to “see” the light source, would not halt the tape movement; it would have contrary effect. Now let’s consider the reverse possibility; a leakage or short circuit in or around one of the phototransistors –par­ticularly the supply reel one – such that it thinks it is seeing a light continuously. As a result, it tells the microprocessor that the system has reached the end of the tape and inhibits all forward movement. But it wouldn’t inhibit reverse movement, because this is what would have to happen in this condition; the tape would have to be rewound. And K. E. provides a clue to support this theory. He says that “... a temporary cure is to disconnect the sensor just to the left of the tape carriage. The VCR will then play, but not record”. Assuming that he has identified the supply reel sensor, then this theory would seem to fit, at least as far as the transport problem is concerned. On that basis I would suggest that replacing the phototransistor would be the first thing to do. They are worth only a few cents and it would quickly settle this point. But this still leaves the mystery as to why it won’t record with this improvised cure. One might hope that replacing the phototransistor would cure this problem also but I very much doubt it. I cannot see any connection bet­ween this part of the circuit and the recording function. So do we have two separate faults and if so, why hasn’t the recording fault been observed before? Or is the whole theory of a faulty phototrans­ istor wrong, in spite of K. E.’s observa­ tions? All right, if the theory is wrong, what else do we have? The most likely culprit – and at least one colleague plumps most strongly for this – is the mode select switch. This is a mechani­ cal switch, sometimes a rotary type, sometimes a slide type, activated by the recorder mechanism, according to the function selected by the user: play, fast forward, rewind, etc. A major reason for suspecting this is that it is a known source of trouble – not frequently but often enough to put one on guard. And when it does play up, it can produce some weird faults. So this would be the next thing to check. With a few excep­tions, they are not particularly expensive and are relatively simple to fit. But one or two are a mite pricey and at least one is quite critical to fit, creating its own weird effects if it is not precisely mounted. So there it is E. K. It’s the best advice we can offer at this distance. Maybe it will help but if it doesn’t, at least I didn’t charge anything – not even for SC clean­ing the heads! SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Test Equipment Review Handyscope: a spectrum analyser, scope & multimeter all in one If you’re looking for a low-cost entry into PC-based test equipment, then you should have a look at the Handyscope. It contains a 2-channel oscilloscope, a digital multimeter & a spectrum analyser with a frequency response from DC to 50kHz. By DARREN YATES There’s been quite a bit of noise made over the last year or so about PCbased test equipment and if you look through the engineering magazines, you’ll find that the number of plug-in cards is on the increase. Some of them claim to be able to re­place dedicated instruments although, as you might expect, if you want top performance, you’ll pay a lot of money. But when we recently saw the Handyscope in action, we were quite surprised by its performance. It doesn’t claim to beat specialised test gear but it’s extremely flexible at what it can do – and that’s quite a bit! The Handyscope originates from TiePie Engineering in Hol­ land, is distributed in Australia by Applied Electro Systems from Queensland and is available in either single or two-channel form. The first thing we noticed was that there is no plug-in card and this is great – you don’t need to open up your computer and look for a slot. In fact, it comes in a small box measuring 145 x 84 x 37mm, with a nice long cable at the rear which con­ nects to your printer port. If you have more than one port, you can connect your print­er to one and the Handyscope to the other. It doesn’t matter which goes where because the software automatically searches for the Handyscope itself. One intriguing thing we noticed was that there are no power supply cables for the Handyscope. Many of you may know that the printer port doesn’t have any supply rails on the pins, so the question is where do they get power from? The clever trick used is that they have set five of the data output lines of the printer port high and then pull 4mA out of each line. Because the outputs are TTL, this is quite OK and inside the Handyscope box is a step-up converter which converts this supply into ±5V DC. Specifications The Handyscope uses a 12-bit A/D converter which has a conversion time of 10µs, giving a sampling frequency of 100kHz and a maximum possible Left: the 2-channel digital voltmeter measures AC & DC voltag­es with true RMS values. Other modes offered are peak-to-peak, mean value, min-max, power, dBms & frequency. DC voltages are read automatically if DC coupling is selected by the switch on the front of the box. September 1993  53 Initially, it comes up in oscilloscope mode and it produces a normal scope display with graticule and trace. But there are lots of other little tricks. If you connect a signal to the input, you’ll see it appear on the screen but the interesting thing is that if you wind the signal amplitude up or down, the volts/div will follow it by auto-scaling to give an optimum display on the screen. The timebase ranges from 0.5ms/div to 2 seconds/div with the option to magnify this up to 20 times. (If running on an XT, the 0.5 and 1ms/ div ranges are not available). The accuracy of the timebase is only fair at ±5% but this is adequate for many applications. The Y-axis can also be changed to either linear or dB modes. All the usual scope features are available, including trig­ ger settings for channel and slope. You can also select the hysteresis level for the triggering as well. If you have the two-channel model, you can add or subtract one waveform from another. You can also zoom in on one part of the screen waveform and examine it in expanded format. Spectrum analyser The Handyscope hooks up to your PC & uses the monitor as the readout. It contains a 2-channel oscilloscope, a digital multimeter & a spectrum analyser with a frequency response from DC to 50kHz. input frequency of 50kHz. The 12 bits give a maximum resolution of about 0.025% (ie, 1/4096=LSB). Linearity is good to 10 bits over a frequency range of DC to 50kHz. The input impedance of each channel is 1MΩ with 20pF ca­pacitance, which is the same as for standard oscilloscopes. Two switchable 1:1/10:1 probes are supplied. Software As with all PC-based equipment, there’s software to consid­er as well. And in this case, it’s quite well done. The software comes on single 3.5-inch and 5.25-inch discs for both drive types. There’s no installation procedure – you can either run the pro­gram straight from the floppy or copy the disc’s contents to a directory on your hard disc drive. The program isn’t all that big either –you’ll need only about 350Kb of disc 54  Silicon Chip space to copy everything over. The good news is that it runs in DOS so you don’t have to slow it down by running it in Windows. However, if you wish to take some screen snapshots, you can run Windows in the background and when you have the shot on the screen you want, you just type [ALT][PRINT SCREEN] and the screen will be copied to the Windows clipboard. As far as I’m concerned, this gives the best of both worlds. In fact, the screen shots shown in this article were produced by this method. To start the Handyscope, you plug the cable into the print­ er port and then type HS[enter]. The program then looks and announces that it has found the Handyscope on whatever printer port you’ve connected it to. You can then select all modes and settings using your mouse which makes it quite attractive to use. The spectrum analyser is a very handy tool and is quite speedy on a 386DX-40 considering the number of computations it must do. You can select to average over a choice of samples from 1 to 200 as well as changing the frequency response and volt/div settings of the screen. Another good point is that the Handyscope system even runs on an old XT and although the spectrum analyser mode works up to 36kHz on an AT, it only goes to 12kHz on an XT. There are 12 ranges covering the frequency band of 0.025Hz to 36kHz for ATs and above and 10 covering 0.025Hz to 12kHz for XTs. You can multiply these ranges up to a maximum of 20 times as well for a more detailed view of the display. The analyser uses the Fast-Fourier-transform (FFT) method and takes 1024 samples. From these samples, it produces 512 spectral components which are then displayed on the screen. It also has the ability to calculate total harmonic distor­tion based on the fundamental frequency you select by dragging the crosshairs on the screen to any spectral line you wish. It pro- Since the Handyscope works as an AC multimeter, you can make more accurate measurements by centring the frequency. For example, by setting the centre frequency to 50Hz, signals with frequency components from 10Hz to 500Hz will be correctly calcu­lated. The maximum input voltage is 200V peak-to-peak and 600Vpp with the probe set to 1:10. Transient recorder The spectrum analyser is a very handy tool. You can select to average over a choice of samples from 1-200 & you can change the frequency response & volt/ div settings. There are 12 ranges covering the frequency band of 0.025Hz to 36kHz for ATs & 10 ranges covering 0.025Hz to 12kHz for XTs. The transient recorder can be used to measure a system over long periods. The time between measurements can be set from 0.01 seconds up to 300 seconds, while the maximum number of readings taken is 30,000. Measuring methods using this recorder can be true RMS, mean, minimum, maximum or momentary pulses. The unit comes with a comprehensive instruction manual, which includes details on the pinouts for the printer port as well as data output format. This is to allow users to write their own software to control the Handyscope. Example code is given in the manual for TurboPascal but by following the layout and form of the code, it can be easily translated into QuickBASIC. Disc operation All the usual scope features are available, including trig­ger settings for channel & slope. You can also select the hysteresis level for the triggering & if you have the 2-channel model, you can add or subtract one waveform from another. vides a reading of the amplitude of the fundamental frequency as well as that of the first 10 harmonics and then the THD in decibels (dB). Digital voltmeter The digital voltmeter measures AC and DC voltag­es with true RMS values. Other modes offered are peak-to-peak, mean value, min-max, power, dBms and frequency. You can even set the thickness of the digit displays as well. DC voltages are read automatically once DC coupling is selected by the switch on the front of the box. You can also operate it as a comparator by setting an input reference level and if the signal is higher or lower, the display indicates HI or LO approp­ riately. Alternatively, you can use this feature to compare one channel against another. As you would expect, you can save any waveforms to disc for storage and later retrieval or you can print the screen to a printer. You can use either the method we mentioned earlier or you can print direct to the printer using a spare printer port. The printout can be in either dot matrix or laser form. Each set of data is stored in two separate files: the data is stored in filename.DAT, while the settings of the instrument are stored in file­name. GEG. Overall, the Handyscope is a well thought out unit. It may not be ideal if you’re looking for extremely accurate results but for schools and TAFE colleges where you need to be able to display waveforms quickly and easily, this will be an ideal and a relatively low-cost addition. The two-channel model sells for $960 ex tax and the single channel version for $550 ex tax. For more details, contact Ap­plied Electro Systems Pty Ltd, PO Box 319, Woodridge, Qld SC 4114. Phone (07) 208 6911. September 1993  55 Do you have a boxful of unknown transistors or a transistor circuit that’s not working properly? This simple tester will indicate whether a transistor is working or not & tell you whether it is an NPN or PNP type. By DARREN YATES Build an in-circuit transistor tester I F YOU’VE built a few projects, then the odds are that you’ll have a fair collection of transistors in your junk­box. You will probably have a good range of types as well, ranging from small signal to high power devices. After a while, it’s easy to forget which ones are good and which are suspect. And if you’ve bought one of the semiconduc­ tor “grab bags” that some retailers offer, you’ll undoubtedly have trouble determining which are NPN and which are PNP types –unless, of course, you have the appropriate data books. That’s where this simple Transistor Tester comes in handy. It can test both 56  Silicon Chip small signal and power transistors and will indicate whether the device is an NPN or PNP type. Basically, it tells you whether a device is “go” or “no-go” and can indicate the nature of a fault – it cannot determine the lead configura­tion or tell you anything about the gain. In addition, the project can be used to test transistors that are already in circuit. So if you have an AM radio, an amplifier or some other device that’s not working, this project will prove invaluable for troubleshooting. You don’t even have to bother pulling the transistors out of circuit to test them. The test results are indicated by two LEDs mounted side-by-side on the front panel. If nothing is connected to the test leads, both LEDs flash rapidly. However, if a working device is connected, then one of the LEDs will go out, depending on whether the device is an NPN or a PNP type. If the transistor is faulty, the result will depend on the nature of the fault. Both LEDs will flash if there is a base-emitter short, while both LEDs will go out if there is a short between collector and emitter. A chart on the front panel shows what the results mean. Circuit diagram Let’s now take a look at the circuit diagram - see Fig.1. It’s based on tran- S1 1k C 100k 1 16VW 100k 1 16VW Q1 BC548 B signals on the collectors of these two transistors are complementary, their voltage levels will be out-of-phase; ie, when one is high, the other is low. This causes both LEDs to flash alternately when power is applied, provided no TUT is connected. 1k 9V Q2 BC548 B C B E E E C VIEWED FROM ABOVE LED1 A  K NPN test transistor Let’s now see what happens when we connect a working K A K NPN transistor as the TUT. A  There are two conditions to D1 D3 consider. The first is when 4x1N4148 Q1’s collector is low and Q2’s 1k D2 D4 collector is high. In this case, the NPN TUT is biased on and so current flows through D3, D4 and the collector-emitter juncE B C tion of the TUT. This means that TO T.U.T there will be about 1.2V across IN-CIRCUIT TRANSISTOR TESTER D3 and D4, which is too low to Fig.1: transistors Q1 & Q2 form a 5Hz keep LED 2 on. multivibrator which alternately switches Thus, LED 2 will go out when the collector & emitter terminals of the the test transistor is con­ducting. TUT high & low. If the device is good, one LED 1 will also be off during of the LEDs will alternately flash on & off. this time, since it will be reverse biased. sistors Q1 and Q2 which are wired to Now let’s consider what happens operate as a standard astable multi­ when Q1’s collector goes high and vibrator. The frequency of oscillation Q2’s collector goes low. In this case, is set to about 5Hz by the associated the TUT will be biased off and so LED 100kΩ resistors and 1µF capacitors. 1 will be on. At the same time, LED As a result, a 5Hz square-wave is 2 will be reverse biased and so will produced at Q1’s collec­tor while a sec- remain off. ond 5Hz waveform of opposite phase Thus, if a working NPN transistor appears at Q2’s collector. Q1 drives is used as the TUT, LED 1 will flash the emitter of the transistor under test on and off at a 5Hz rate, while LED 2 (TUT), while Q2 drives the base of the will be off at all times. TUT via a 1kΩ resistor. The collector of the TUT is driven via diode array PNP test transistor D1-D4. For a working PNP transistor, the Note that these are universal inputs; opposite occurs. When Q1’s collector ie, both NPN and PNP devices connect is low and Q2’s collector is high, the to the same EBC test points without TUT will be biased off and LED 2 will any need for switching. light. LED 1 will be reverse biased The two LEDs are connected in re- during this time and will be off. verse-parallel between the collectors When the collectors subsequently of Q1 and Q2. Because the 5Hz output change state, the TUT will be biased LED2 S1 1k 1uF 1k K Q2 D4 LED2 D2 C 100k 1k 100k 1uF TO 9V BATTERY Q1 LED1 A D1 D3 TO B TEST CLIPS E Fig.2: install the parts on the PC board as shown here. The LEDs are mounted about 15mm proud of the board & clip into two bezels on the front panel. PARTS LIST 1 plastic case, 82 x 54 x 30mm 1 PC board, code 04109931, 51 x 37mm 1 self-adhesive front panel label, 49 x 79mm 1 SPDT toggle switch (S1) 1 9V battery 1 9V battery clip lead 2 LED bezels 1 150mm length of black hookup wire 1 150mm length of yellow hookup wire 1 150mm length of blue hook-up wire 3 small hook clips Semiconductors 2 BC548 NPN transistors (Q1,Q2) 2 5mm green LEDs (LED1,LED2) 4 1N4148, 1N914 diodes (D1-D4) Capacitors 2 1µF 16VW PC electrolytic Resistors (0.25W, 1%) 2 100kΩ 3 1kΩ on and current will flow through the transistor, this time via diodes D1 and D2. LED 2 will now be biased off, while LED 1 will remain off due to the low voltage across it. This voltage will be equal to the voltage across the two diodes plus the saturation voltage of the transistor (ie, a little over 1.2V). Thus, when a good PNP device is used as the TUT, LED 1 goes out and LED 2 flashes. Crook devices What if you connect a TUT with a collector-emitter short? Regardless of whether it’s an NPN or a PNP device, neither LED will light because the current will alternately flow through each of the series diode pair. This means that only about 1.2V will be developed across the LEDs, which is insufficient to turn them on. If the base-emitter junction of the TUT is shorted, then the transistor will be unable to turn on and current will flow through the 1kΩ base resistor. Both LEDs will continue to flash since the voltage developed across this 1kΩ resistor is suffi­cient to allow them to operate. September 1993  57 C B E + + TRANSISTOR TESTER + + NPN PNP CE SHORT BE SHORT ● ● ● ● ● ● ● ● LEDON LEDOFF ● ● + OFF + ON + Fig.4: this full-size artwork can be used as a drilling template for the front panel. Make sure that all polarised parts are correctly oriented & note particularly that D1 & D2 face in the opposite direction to D3 & D4. The battery clip must be modified slightly to allow the battery assembly to fit inside the case – see text. Power for the circuit is derived from a 9V battery. Construction Since there are only a few devices in the In-Circuit Tran­ sistor Tester, the construction is a breeze. All the components are installed on a single PC board measuring 51 x 37mm and coded 04109931. Fig.2 shows where the parts go on the PC board. You can mount the parts in any order but make sure that the diodes, LEDs, transistors and electrolytic capacitors are the right way around. The two LEDs should be mounted so that their tops are about 15mm above the surface of the board, so that they later protrude through two bezels mounted on the front panel. You can easily identify the LED leads since the anode lead will be the longer of the two. The board can now be mounted inside a small plastic utility case. First, attach the adhesive label to the lid, then use it as a template to drill out the 58  Silicon Chip holes for the LED bezels and the on/off switch. In each case, it’s best to drill a small pilot hole first and then carefully ream the hole out to the correct size. Three small holes are also drilled in one end of the case to take the flying Base, Emitter and Collector leads for the TUT. This done, the on/off switch and LED bezels can be mounted and the Fig.3: this is the full-size etching pattern for the PC board. wiring to the PC board completed. Use different colours for the test leads and feed them through the holes in the end of the case before making the connections to the PC board. The PC board is held in position by clipping the two LEDs into the bezels. The battery clip will have to be modified to allow the battery assembly to fit inside the case. This involves removing the plastic cover from the clip and soldering the leads onto the sides of the clip eyelets. Finally, the three test leads must be fitted with hook-type test clips or alligator clips. Alligator clips were fitted to the prototype but you will find that small hook clips are easier to use. As soon as you switch on, you should find that both LEDs flash at a rapid rate. To test the circuit, you’ll need two working transistors – one an NPN device and the other a PNP. Check that only the lefthand LED flashes when you connect the NPN device and that the righthand LED flashes for the PNP device. If both LEDs stay on or both go out and you are certain that the transistors are OK, check that the two LEDs are correctly oriented. Finally, we should mention that the In-Circuit Transistor Tester does not work well with Darlington transistors. This is because they have a higher saturation voltage than normal transistors and so both LEDs will simply go dim SC for a working device. LED BRAKE LIGHT INDICATOR This “brilliant” brake light indicator employs 60 high intensity LEDs (550-1000mCd) to produce a display that is highly visible, even in bright sunlight. The intensity produced is equal to or better than the LED brake indicators which are now included in some late model “upmarket” vehicles. The LED displays used in most of these cars simply make all the LEDs turn on every time the brakes are applied. The circuit used in this unit can perform in this manner and, for non-automotive applications, it can be customised to produce a number of sweeps (110) starting at the centre of the display and with a variable sweep rate. It not only looks spectacular but also attracts more attention. All the necessary “electronics” is assempled on two identical PCBs and the resulting overall length of the twin bargraph dis­play is 460mm. It’s simple to install into a car since only two connections are required: Earth and the brake­ LASER SCANNER ASSEMBLIES These are complete laser scanners as used in laser printers. Include IR laser diode optics and a very useful polygon scanner ( motor-mirror). Produces a “fan” of light (approx. 30 deg) in one plane from any laser beam. We provide information on polygon scanner only. Clearance: $60 400 x 128 LCD DISPLAY MODULE – HITACHI These are silver grey Hitachi LM215XB dot matrix displays. They are installed in an attractive housing and a connector is provided. Data for the display is provided. BRAND NEW units at a low: $40 LASER OPTICS The collimating lens set is used to improve the beam (focus) divergence. The 1/4-wave plate and the beam splitter are used in holography and experimentation. All are priced at a fraction of their real value: 1/4 wave plate (633nM) ..............................$20 Collimating lens sets ..................................$45 Polarizing cube beam splitters ....................$65 GREEN LASER TUBES We have a limited supply of some 0.5mW GREEN ( 560nm) HeNe laser tubes. Because of the relative response of the human eye, these appear as bright as about a 2mW red tube: Very bright. We will supply this tube and a suitable 12V laser power supply kit for a low: $299 CCD ELEMENT BRAND NEW high sensitivity monolythic single line 2048 element image sensors as used in fax machines, optical charachter recognition and other high resolution imaging applications: Fairchild CCD122. Have usable response in the visible and IR spectrum. Supplied with 21 pages of data and a typical application circuit. $30 INFRARED TUBE AND SUPPLY These are the key components needed for making an INFRARED NIGHT VIEWER. The tubes will convert infrared light into visible light on the phosphor screen. These are prefocussed tubes similar to type 6929. They do not require a focus voltage. Very small: 34mm diameter, 68mm long. All that is needed to make the tube light connecting wire. The case for the prototype unit which would be suitable for mounting on the rear parcel shelf, was mainly made from two aluminium “L” brackets that were screwed together to make a “U” section. A metal rod and its matching holders (commonly available from hardware shops) are used for the supporting leg. $60 for both the PCBs, all the onboard components & instruc­tions: the 60 LEDs are included! We also have available a similar kit that does not have the sweeping feature. It produces similar results to the commercial units installed in cars: all the LEDs light up when power is applied. $40 for both the PCBs and all the onboard components. This kit is also supplied with the 60 LEDs and it uses different PCBs, that have identical dimensions to the ones supplied in the above­ mentioned kit. operational is a low current EHT power supply, which we provide ready made or in kit form: powered by a 9V battery and typically draws 20mA. INCREDIBLE PRICING: $90 For the image converter tube and an EHT power supply kit! All that is needed to make a complete IR night viewer is a lens an eyeiece and a case: See EA May and Sept. 1990. ALUMINIUM TORCHES – INFRARED LIGHTS These are high quality heavy-duty black anodised aluminium torches that are powered by four “D” cells. Their focussing is adjustable from a spot to a flood. They are water resistant and shock proof. Powered by a krypton bulb – spare bulb included in cap. $42 Note that we have available a very high quality INFRARED FILTER and a RUBBER lens cover that would convert this torch to a good source of IR: $15 extra for the pair. PASSIVE NIGHT VIEWER BARGAIN This kit is based on an BRAND NEW passive night vision scope, which is completely assembled and has an EHT coaxial cable connected. This assembly employs a high gain passive tube which is made in Russia. It has a very high luminous gain and the resultant viewer will produce useful pictures in sub-moonlight illumination. The viewer can also be assisted with infrared illumination in more difficult situations. It needs an EHT power supply to make it functional and we supply a suitable supply and its casing in kit form. This would probably represent the best value passive night viewer that we ever offered! BECAUSE OF A SPECIAL PURCHASE OF THE RUSSIAN-MADE SCOPES, WE HAVE REDUCED THE PRICE OF THIS PREVIOUSLY ADVERTISED ITEM FROM $550 TO A RIDICULOUS: $399 This combination will be soon published as a project in EA. NOTE THE REDUCED PRICE: LIMITED SUPPLY. Previous purchasers of the above kit please contact us. 24VDC TO MAINS VOLTAGE INVERTERS In the form of UNINTERRUPTABLE POWER SUPPLIES (UPS’s).These units contain a 300W, 24V DC to 240V 50Hz mains inverter. Can be used in solar power systems etc. or for their original intended purpose as UPS’s. THESE ARE VERY COMPACT, HIGH QUALITY UPS’s. They feature a 300W - 450W (50Hz) SINEWAVE INVERTER. The inverter is powered by two series 12V 6.5Ahr (24V). batteries that are built into the unit. There is only one catch: because these NEW units have been in storage for a while, we can not guarantee the two batteries for any period of time but we will guarantee that the batteries will perform in the UPS’s when these are supplied. We will provide a 3-month warranty on the UPS’s but not the batteries. A circuit will also be provided. PRICED AT A FRACTION OF THEIR REAL VALUE: BE QUICK! LIMITED STOCK! $239 ATTENTION ALL MOTOROLA MICROPROCESSOR PROGRAMMERS We have advanced information about two new STATE OF THE ART microprocessors to be released by Motorola: 68C705K1 and 68HC705J1. The chips are fully functional micros containing EPROM/OTPROM and RAM. Some of the features of these new LOW COST chips include: *16 pin DIL for the 68HC705K1 chip * 20 pin DIL for the 68HC705J1 chip * 10 fully programmable bi-directional I/O lines * EPROM and RAM on chip * Fully static operation with over 4MHz operating speed. These two chips should become very popular. We have put together a SPECIAL PACKAGE that includes a number of components that enable “playing” with the abovementioned new chips, and also some of the older chips. IN THIS PACKAGE YOU WILL GET: * One very large (330 x 220mm) PCB for the Computer/Trainer published in EA Sept. 93; one 16x2 LCD character display to suit; and one adaptor PCB to suit the 68HC705C8. * One small adaptor PCB that mates the programmer in EA Mar. 93 to the “J” chip, plus circuit. * One standalone programmer PCB for programming the “K” chip plus the circuit and a special transformer to suit. THE ABOVE PACKAGE IS ON SPECIAL AT A RIDICULOUS PRICE OF: $99 Note that the four PCBs supplied are all silk screened and solder masked, and have plated through holes. Their value alone would be in excess of $200! A demonstration disc for the COMPUTER/TRAINER is available for $10. No additional software is currently available. Previous purchasers of the COMPUTER/ TRAINER PCB can get a special credit towards the purchase of the rest of the above package. PLASMA BALL KIT This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. The EHT circuit is powered from a 12V supply and draws a low 0.7A. We provide a solder masked and screened PCB, all the onboard components (flyback transformer included), and the instructions at a SPECIAL introductory price of: $ 25 We do not supply the standard light bulb or any casing. The prototype supply was housed in a large coffee jar, with the lamp mounted on the lid – a very attractive low-cost housing! Diagrams included. LASER DIODE KIT – 5mW/670nm Our best visible laser diode kit ever! This one is supplied with a 5mW 670nm diode and the lens, already mounted in a small brass assembly, which has the three connecting wires attached. The lens used is the most efficient we have seen and its focus can be adjusted. We also provide a PCB and all on-board components for a driver kit that features Automatic Power Control (APC). Head has a diameter of 11mm and is 22mm long, APC driver PCB is 20 X 23mm, 4.5-12V operation at approx 80mA. $85 PRECISION STEPPER MOTORS This precision 4-wire Japanese stepper motor has 1.8 degree steps – that is 200 steps per revolution! 56mm diameter, 40mm high, drive shaft has a diameter of 6mm and is 20mm long, 7.2V 0.6A DC. We have a good but LIMITED supply of these brand new motors: $20 HIGH INTENSITY LEDs Narrow angle 5mm red LED’s in a clear housing. Have a luminous power output of 550-1000mCd <at> 20mA. That’s about 1000 times brighter than normal red LED’s. Similar in brightness SPECIAL REDUCED PRICE: 50c Ea or 10 for $4, or 100 for $30. IR VIEWER “TANK SET” ON SPECIAL is a set of components that can be used to make a complete first generation infrared night viewer. These matching lenses, tubes and eyepieces were removed from working tank viewers, and we also supply a suitable EHT power supply for the particular tube supplied. The power supply may be ready made or in kit form: basic instructions provided. The resultant viewer requires IR illumination. $180 We can also supply the complete monocular “Tank Viewer” for the same price, or a binocular viewer for $280: Ring. MINI EL-CHEAPO LASER A very small kit inverter that employs a switchmode power supply: Very efficient! Will power a 1mW tube from a 12V battery whilst consuming about 600 mA! Excellent for high-brightness laser sights, laser pointers, etc. Comes with a compact 1mW laser tube with a maximum dimension of 25mm diameter and an overall length of 150mm. The power supply will have overall dimensions of 40 x 40 x 140mm, making for a very compact combination. $59 For a used 1mW tube plus the kit inverter. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 September 1993  59 AMATEUR RADIO BY GARRY CRATT, VK2YBX Emtron’s ENB-2 Noise Bridge One of the most underrated yet valuable pieces of test equipment available to amateur radio operators is the RF noise bridge. It can help optimise your antenna installation This ingenious device, when used with a monitor receiver, is capable of not only locating the resonant frequency of an antenna but is also ca­pable of determining if an existing anten­na is the correct length for the frequency at which resonance is desired. Basically, the bridge consists of a wideband noise genera­tor and an RF impedance bridge. Fig.1 shows the basic test set-up when using a noise bridge. The most commonly used configuration for the noise generator is to use either a zener diode, or re­ verse biased base-emitter junction of a silicon transistor, under low current conditions. This circuit arrangement generates wideband noise. Commonly used designs modulate the noise with a square wave generator at a 50% duty cycle and a frequency of 1kHz. This NOISE SOURCE REFERENCE LOAD has the affect of making a null in the noise generated more noticeable in the monitor receiver. The modulated noise is then followed by two or three stages of amplification using AC coupling, until a level sufficient to produce an S9 signal on the monitor receiver is achiev­ed. This normally equates to several millivolts of output. Fig.2 shows the complete circuit of a typical noise bridge design, as originally published in the ARRL Handbook. It uses a zener diode as the noise source and the 555 time generates the modulating square wave. The bridge part of the circuit consists of a trifilar wound transformer, a potentiometer, variable capacitor, and a fixed value capacitor, arranged as a Wheatstone bridge. One winding of the transformer is used to couple noise BRIDGE MONITOR RECEIVER Fig.1: this diagram shows the test set-up involving a noise bridge. It allows you to check the resonance of an antenna. into the bridge, while the remaining two windings are arranged so that they each form one arm of the bridge circuit. The potentiometer and variable capacitor form the third leg of the bridge, in effect the resist­ance and reactance tuning controls. The antenna under measurement and a fixed capacitor (selected according to the frequency bands of operation) form the fourth, “unknown” leg of the bridge. The entire arrangement is normally S1 .01 7 4 3 6.8k D2 1N914 D1 1N914 60  Silicon Chip 1.8k Q1 2N2222A Q2 2N2222A .01 .01 5 6 1 .01 3 .01 6 5 2 1 ZD1 6.8V 1W IC1 555 2 0.1 22k 8 J2 UNKNOWN T1 10k 6.8k C2 120pF SM U 680  1.2k 9V 4 B T1 : 9 TRIFILAR TURNS, 26 B&S ENCU WOUND ON AMIDON FT-37-43 TOROID ANTENNA UNDER TEST VR1 250  VC1 250pF R J1 RECEIVER Fig.2: the circuit uses a zener diode as the noise source & a 555 timer to generate the modulating square wave. The bridge part of the circuit consists of a trifilar wound transformer, a potentiometer, a variable capacitor, & a fixed value capacitor. built into a metal box, having two coax connection sockets on the rear panel, one for the monitor receiver, the other for the antenna under test. The two reactance controls are mounted on the front panel. The circuit is easily powered by a 9V battery and as the current drain is only around 20mA or so, battery life is quite reasonable, considering the intermittent use of such a device. The two front panel controls are “resistance” and “reac­ tance”. The resistance control has a range of 0 to 250Ω in most designs, whilst the “reactance” range runs from -j150Ω (capaci­tive reactance) to +j150Ω (inductive reactance). Tuning an antenna To tune an antenna, the operator connects the antenna of unknown resonant frequency to the “unknown” socket, and the monitor receiver to the “receiver” socket through any length of coaxial cable. The monitor receiver is then tuned to the frequen­ cy at which antenna resonance is desired. By adjusting both controls for minimum signal in the moni­tor receiver, it can be determined from the position of the reactance control on the front panel of the noise bridge if the antenna requires inductive or capacitive reactance to tune it to resonance. If the reactance control tunes to the “XL” side of the scale, the antenna is too long. If the reactance control indi­ cates “XC”, the antenna is too short to resonate at the nominated frequency. The “R” control indicates the feed­ point resistance. Since it gives this detailed information, the RF noise bridge is a more versatile device than an SWR meter for checking antennas. An SWR meter can show a ratio of 2:1 but an RF noise bridge can tell the amateur operator that the impedance causing the SWR is 25Ω or 100Ω. The SWR meter cannot tell if an antenna is above or below resonance, but the noise bridge can be used to determine this parameter. So this is the basic theory and operation of an RF noise bridge. But where can this magic device be purchased? Fortunately, we have a manufacturer right in our own back­ yard. Local company Emona Electronics Pty Ltd, based in Sydney, produce a Although the Emtron ENB-1 noise bridge is a simple instrument, it can be a great help in tuning & measuring antennas. unit capable of operation on the HF bands from 10m to 160m, the ENB-2 noise bridge. The unit is housed in a sturdy box with an aluminium base and a steel lid finished in hammertone enamel. Both resistance and reactance controls are located symmetrically on the front panel, whilst SO-239 coax sockets are used for the “unknown” and “re­ceiver” connections. The unit is powered by an internal 9 volt battery, the ON/OFF switch function being provided by the switched “resistance” control. Unlike designs seen in amateur mag­azines, this unit does not modulate the zener noise source, and has an additional “expand” pushbutton control. This function gives greater reso­lution in the lower HF band. The unit is accompanied by a 12-page booklet, which explains the versatility of the unit. Apart from instructions on how to tune a random length antenna, the booklet also covers detailed theory behind measuring quarter wavlength feedlines (useful when making stub filters), measuring unknown inductors and capacitors, checking trap dipole antennas, testing a balun, correctly setting the controls of an antenna tuner without RF excitation, and checking Yagi antennas. In order to check the ease of operation of the bridge, we connected it to our lab monitor receiver, a Yaesu FRG-7700. The “unknown” terminal was connected to a halfwave dipole, originally designed for listening to the 8.8MHz HF aviation frequency as used by international aircraft inbound to Australia from the USA. When this was measured, the bridge produced a null in the monitor receiver at 7.8MHz, and the reactance control showed inductive reactance at 8.8MHz, indicating that the antenna was too long for the original desired frequency. No doubt if I had climbed up on the roof and trimmed the antenna, better results could then have been obtained at 8.8MHz. The whole point of the exercise was to demonstrate the ability of the noise bridge to do in practice what was claimed in theory. Apart from the somewhat unique mounting arrangement for the internal battery (glued to the chassis!), the ENB-2 noise bridge is well made and performed exactly as claimed. The mathematical information supplied with the unit, explaining some of the more complex operations of the unit, indicate that the designer has firm ideas about the needs of the market, and as such he has gone to extreme pains to explain all possible applications in detail. Considering that the price of the bridge is only $129 in­cluding sales tax, it is no wonder the unit enjoys strong popu­larity amongst HF operators. Emona Electronics has a range of equipment for the amateur including the matching ETP-1 receiver antenna tuner and amplifier. It sells for $179 includ­ing tax. You can see the full range at Emona Electronics Pty Ltd, 94 Wentworth Ave, Haymarket, NSW SC 2000. Phone (02) 211 0988. September 1993  61 PRODUCT SHOWCASE Sadelta TC402D field strength meter Strictly speaking this is not a field strength meter since it does not measure field strength as such. What it does do is measure RF signals fed to its front panel BNC socket. It measures the signals in terms of microvolts or millivolts or dBµV. If it was used with an adjustable calibrated dipole, it could then be used to measure field strength which would be calculated in term of millivolts or microvolts per metre. Having made that qualification, we can state that its main application will be with TV antenna installers who want to measure the signal they are receiving from their standard test antenna or from an already installed antenna. Some installers make do with a portable TV set but having an instrument such as the Sadelta TC402D makes the whole job much more professional – you can measure the signal precisely, allow for cable and splitter losses and then select the correct masthead or distribution amplifier, if needed. The Sadelta TC402D is a nicely presented instrument in a plastic case measuring 222 x 92 x 235mm. It has a 4 digit liquid crystal display to show the measured frequency and an analog meter to display the signal strength. There are seven measurement ranges with full scale deflection ranging from 100µV to 100mV. In practice, signals can be measured down to 20µV. By use of the correction graphs (individually printed for each instrument), the signal measurement accuracy can be within ±2dB. In-car charger for nicad batteries Premier Batteries has announced the release of a new in-car charger for nickel cadmium batteries used in cellular phones and camcorders. The unit is designed to operate directly from the 12V lighter socket of your car or from an approved 240VAC plugpack adaptor. The “Master Charger” is available with interchangeable plug-in battery pockets. By simply switching the plug-in cups the unit will charge most batteries for Motorola, Kenwood, Icom, Standard and Shinwa cellular phones. Pockets are also available for professional video camera batteries such as 62  Silicon Chip NP1A/NP1B and NP22. Depending on the capacity, the charger charge any battery in 1/2 hour to 3 hours and then automatically switch to a trickle charge mode. For further information, contact Premier Batteries Pty Ltd, 9/15 Childs Road, Chipping Norton, NSW 2170. Phone (02) 755 1845. There are three overlapping frequency ranges: low VHF (41 to 170MHz), high VHF (140 to 460MHz) and UHF (430 to 864MHz). The unit is tuned by means of a tenturn pot and the frequency is displayed with an accuracy of ±0.1% ±1 digit. The unit also has an audio output via an internal loudspeaker so you can listen to the signal if needed. Power comes from eight alkaline or nicad batteries or via a 12V DC plugpack. The TC402D comes with an attractive padded Cordura carrying case which is appropriate to its intended applications. The TC402D is priced at $799 plus sales tax where applicable. For further information and price details, contact Peter C. Lacey Services Pty Ltd, 80 Dandenong Road, Frankston, Vic 3199. Phone (03) 783 2388. Panasonic launches first televideo set Panasonic has released its first Televideo, model TC-W21, which has a VHS video deck located above a 51cm television receiver. Features include audio/video in/ out terminals for hooking the TV set to other equipment, a sleep timer and on-screen indicators. For the VCR section, they include multiple search and playback functions. Subscribe now to the largest faults & remedies library in Australia ✱ ✱ 1994 manuals are now available. Our database is regularly updated with information supplied by technicians such as yourself. ✱ Exclusive backup service by qualified technicians. ✱ ✱ Over 10,000 faults and remedies on file with flow charts and diagrams. Covers Colour TVs and VCRs of all brands sold in Australia EFIL Phone or fax now for your FREE information package ELECTRONIC FAULT INFORMATION Reply Paid 4 P.O. Box 969 AIRLIE BEACH 4802 Ph 079 465690 Fax 079 467038 September 1993  63 Learning remote control from Philips does the lot No longer do you need to suffer the confusion of which remote control you should pick up to change the hifi volume or the TV channel. One “learning” remote control will do the lot! Philips have released a new multi-function “learning” remote control unit with operating functions for TV/Teletext, video, CD, tape deck, tuner/amplifier and auxiliary equipment. It also lets you transfer and store the transmission codes of any manufacturer’s remote controls into the unit. When operating the learning function, a three-colour LED indicator tells you what mode you are in, when codes have been transferred, and whether or not the codes have been stored. This LED display also warns you when the batteries need to be replaced. All memory data is retained for 30 minutes after the batteries are removed, giving plenty of time for batteries to be replaced. Priced at $269, the Philips Learning Remote (SBC 8503) comes with a fully illustrated manual. It is available from selected retailers throughout Australia. For further information, contact, phone Philips Accessories on (02) 742 8437. For easy operation, the video deck starts playing as soon as a tape is loaded and recording is a one-button operation on the remote control. World 7 system compatibility means it can record and play tapes in PAL and NTSC formats. Recommended retail price is $2,599. For further information,contact Panasonic Australia (02) 986 7400. TTL level programmable square wave generators, at low cost. Both models come with one or two synthesisers per card, with each channel being independent of the other, and crystal controlled for excellent stability. An optional external reference input is also available, with reference source then being jumper selectable between external or on board frequency source. Software supplied with the cards provides either command line or popup menu selection of output frequency. Driver software is also supplied, with source code, for writing custom programs and an example program is included. The FSC-30 has a range of 0.024Hz to 30MHz while the FSC-50 has a range of 2.98Hz to 50MHz, with resolution for both being 27,000 steps per decade. The cards have three switchable addresses, for multiple card use, and are connected via 50W coax with BNC connectors. For further information, contact Boston Technology Pty Ltd, PO Box 1750, North Sydney, NSW 2060. Phone (02) 955 4765. New Akai TV sets from Akai Low cost frequency synthesizer Capable of ultra-wide frequency synthesis, the FSC-30 and 50 are half length cards for any PC-XT/AT/386 and provide one or to two independent VIDEO & TV SERVICE PERSONNEL TV & VIDEO FAULT LIBRARIES AVAILABLE AS PRINTED MANUALS $90 EACH + $10 DELIVERY BOTH MANUALS VIDEO & TV $155 + $15 DELIVERY OR AS A PROGRAM FOR IBM COMPATIBLES $155 + $10 DELIVERY FOR MORE INFORMATION CONTACT TECHNICAL APPLICATIONS FAX / PHONE (07) 378 1064 PO BOX 137 KENMORE 4069 64  Silicon Chip Akai have released two UHF/VHF, remote control, FST, (flat Screen Tube) colour TV sets with on screen display, sleep timer and A/V and RF input facilities. The CTK-2166 51cm set has a mono tuner 40 programme memory and twin dynamic speakers. The larger 59cm set, model CTK2576, is a high resolution set with stereo tuner, Teletext and A/V, SCART, RF and S video inputs. Front panel A/V inputs for easy VCR and camcorder connection are additional features. Priced at $699 (CTK-2166) and $1499 (CTK-2576) both models are covered by a twelve month parts and labour warranty and are available at selected retailers. For further information, contact Akai on (02) 763 6300 TDK mini disc released TDK has released their new recordable Mini Disc to the Australian market. The MD-XG Mini Disc is available in both 60 and 74 minute playing times. TDK's MD-XG 2.5-inch Mini Disc is fully compatible with the MD format and is recordable and erasable. The magneto-optical disc offers similar performance to CD including playback time, frequency response, and dynamic range. Over 10 years of research has gone into the development of the new MDXG Mini Disc. It employs a specially developed magnetic layer of Terbium Ferric Cobalt (TbFeCo) alloy that has been formed into a six layer structure using a proprietary sputtering technique. (Note: Terbium is a rare earth element). Prices for the MD-XG60 and MDXG74 are $19.95 and $23.95 respectively. TDK's new Mini Discs will be available at selected dealers only. For further information, contact TDK (Australia) Pty Ltd on (02) 437 5100. Micron Sure Shot desoldering tool One of the most frustrating tasks in electronics can be the removal and replacement of ICs, transistors and other component from PC boards. There is only one way to do it. You must heat up the solder joints for each lead of the component, suck off the excess solder and then remove the component. All this must be done quickly and without applying too much heat otherwise the component may be damaged (which should be avoided if it is merely suspected of being faulty) or the tracks of the PC board can be damaged. Till now, most people would have done the job using a conventional soldering iron plus a solder sucker or solder wick. Either way, the process is risky and you may need two or more ties at each solder joint to clear it. There has to be a better way. Sure there are vacuum powered desoldering machines with special heating bits but these are very expensive units which could not be justified by service technicans and enthusiasts. This is where the Micron Sure Shot desoldering machine enters the picture. It is, as its name suggests, a self contained desoldering tool with a temperature controlled bit. You place the tool on the soldered joint just long enough to melt it and then press the trigger button while still holding the heated bit on the joint. The solder instantly is sucked off by the machine and then you can move on to the next joint. Using a self contained machine like this is a dream compared to juggling a soldering iron and a solder sucker, probably while attempting to hold the PC board too. When you press the trigger button it activates a solenoid plunger which applies instant vacuum to the solder joint. The tool is well balanced and pleasant to hold and its name describes it well, "Sure Shot" – not hit and miss. The Sure Shot comes with full instructions, a spare bit, filters and a neat plastic carrying case. It sells for $349 and is available from Altronics, 174 Roe Street, Perth WA 6000 or any Altronics reseller. September 1993  65 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd Build this fun project: Remote-controlled electronic cockroach This version of the Electronic Cockroach has its steering controlled via an infrared link. You just put it on the ground, switch it on & steer it left or right by pressing one of two buttons on a handheld transmitter. By JOHN CLARKE In February 1993, we published an Electronic Cockroach which automatically steered itself towards a dark corner. This new version - dubbed the Remote Control Cockroach - dispenses with the dark-seeking feature and has infrared remote steering instead. The Remote Control Cockroach consists of a PC board, two small motors, and a handful of cheap components to make the control circuitry and the IR transmitter. Admittedly, it's cheap72  Silicon Chip er to go out and buy a commercial remote-controlled toy but that won't teach you anything. By contrast, this project will test your electronic and mechanical skills. It's just for fun. A real cockroach has six legs but our electronic version has to make do with three wheels – two at the front and one at the back. The two wheels at the front are independently driven by separate motors while the rear wheel, which is mounted on a swivel, trails behind. Steering is accomplished by stopping one of the motors. The simple but effective drive arrangement uses rubber bands to drive the two front wheels directly from the motor spindles. In order to obtain maximum torque, each motor is driven by a pulse width modulated (PWM) control voltage rather than by a varying DC voltage. This technique ensures that the maximum peak voltage is always applied to the motor, regardless of the speed setting, and helps prevent stalling. Another worthwhile feature of the circuit is speed regulation for the motors. Speed regulation helps the vehicle maintain its speed despite changes in load; eg, due to gradient or rough terrain. Fig.1 shows the basic principle of the motor speed regulator circuit. What happens is that the circuit monitors the back-EMF generated by PARTS LIST RECEIVER Fig.1: the motor speed of the vehicle is controlled by comparing the motor’s back-EMF with a triangle waveform to derive a voltage pulse train. If the motor slows, the back-EMF falls & the pulse length increases to bring the motor back up to the correct speed. the motor (the faster the motor spins, the greater the back-EMF). This backEMF is compared against a triangle waveform generated by an oscillator and the resulting pulse waveform then drives the motor. When the motor is running at high speed (with a light load), the back-EMF is high and so the resulting pulses fed to the motor are quite narrow. However, if the motor is heavily loaded, the back-EMF voltage drops because the motor slows down. This then increases the width of the pulses applied to the motor to bring the motor back up to speed. Circuit details Fig.2 shows the circuit details. While it may look complicated at first glance, it can be readily split into two sections: (1) a remote control receiver (IC3 & IC4); and (2) the motor control circuitry (IC1 & IC2). Furthermore, the motor control circuitry can be split into two identical sections. IC1c, IC1b, IC1a and Q1 control the righthand motor, while IC1d, IC2b, IC2c and Q2 control the left motor. IC2a is the triangle waveform generator referred to earlier. This device is wired as a Schmitt trigger and operates as follows: when power is first 1 PC board, code 08307931, 84 x 238mm 2 hobby motors (M1, M2 - Jaycar Cat. YM2707) 2 42mm diameter plastic wheels (Aristo-craft or equivalent) 1 130mm-length of 1/8-inch brass tubing 1 150mm-length of 1/8-inch brass threaded rod 4 brass nuts to suit 1 22mm aluminium knob 2 12mm brass untapped spacers 2 9mm brass untapped spacers 2 6mm brass untapped spacers 4 1/8-inch steel washers 1 4-way AA square battery holder 1 battery clip for holder 4 AA 1.5V alkaline cells 4 6 x 60mm diameter rubber bands 1 SPDT toggle switch (S1) 2 10kW horizontal trimpots (VR1,VR2) 1 200mm-length 1.5mm copper wire 1 250mm-length 0.8mm tinned copper wire 1 80mm-length red hook-up wire 1 80mm-length black hook-up wire Semiconductors 2 LM339 quad comparators (IC1,IC2) 1 4049 hex CMOS inverters (IC3) 1 LM358 dual op amp (IC4) 2 BD646 PNP Darlington transistors (Q1,Q2) 1 BC548 NPN transistor (Q3) 1 3.3V 400mW zener diode (ZD1) 2 1N4004 1A diodes (D1,D2) 3 1N4148 switching diodes (D3,D4,D5) 1 BPW50 infrared photodiode (IRD1) applied, pin 1 is high and the 2.2µF capacitor at pin 6 begins to charge via the 22kW resistor. When the capacitor voltage exceeds the voltage on pin 7, pin 1 goes low and the capacitor now discharges until the voltage at pin 6 drops below the voltage on pin 7 again. Pin 1 then switches high again and so the process is repeated indefinitely while ever power is applied. The resulting triangle waveform at pin 6 is applied to the non-inverting Capacitors 1 1000µF 16VW PC electrolytic 1 470µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 3 2.2µF 16VW PC electrolytic 3 0.1µF MKT polyester 1 .047µF MKT polyester 5 .01µF MKT polyester 5 100pF ceramic Resistors (0.25W, 1%) 3 470kW 2 4.7kW 12 100kW 1 2.2kW 1 68kW 7 1kW 3 47kW 1 390W 1 22kW 1 180W 1 15kW 1 120W 10 10kW 1 47W TRANSMITTER 1 plastic case, 82 x 54 x 30mm 1 PC board code, 08307932, 47 x 45mm 2 momentary click action PC-mount switches 1 216 9V battery 1 battery clip 8 machined IC pins (from socket) Semiconductors 1 ICM7555, LMC555CN CMOS timer (IC1) 2 CQY89A infrared LEDs (LED1,LED2) 1 BC328 PNP transistor (Q1) 2 1N4004 1A diodes (D1,D2) Capacitors 1 220µF 16VW PC electrolytic 1 0.1µF MKT polyester 1 0.01µF MKT polyester Resistors (0.25W, 1%) 1 4.7MW 1 100kW 1 5.6kW 1 150W 1 5.6W inputs of IC1a, IC1b, IC2b & IC2c. IC1b compares the triangle waveform with the voltage on its pin 4 input, as set by trimpot VR1 and the back EMF developed by motor M1, to produce a pulsed waveform. IC1b's output is inverted by IC1a. Thus, each time the output of IC1b swings low, pin 1 of IC1a is pulled high (via a 10kW pull-up resistor) and Q1 is held off. Conversely, when IC1b's output swings high, IC1a's output goes September 1993  73 74  Silicon Chip IRD1 BPW50 B1 6V  A K 47k 8 1 10 1000 16VW POWER S1 B CE IC3a 4049 9 470 16VW 180  A K .01 B V+ 100 16VW 14 14 IC4b AGC +3.3V 10k 10k 100k +3.3V 5 6 .047 10k 15 2.2 16VW 7 D5 1N4148 IC3c 100k 100pF 6 7 10k 10k IC2a LM339 68k 120  .01 3 1 1k REMOTE CONTROL COCKROACH ZD1 3.3V 400mW 47  +6V 15k .01 470k +3.3V 2.2k 470k VIEWED FROM BELOW Q3 BC548 0.1 10k IC3b 12 11 100k 100pF IC3d 2 22k 100k 100pF 10k 100k 100k +3.3V 100k 100k 100k +3.3V .01 5 8 9 10 10 11 11 IC3e 100k 100pF 4 IC1d 2.2 16VW 14 2.2 16VW M2 SPEED VR2 10k IC1c 10k 13 M1 SPEED VR1 10k .01 47k 7 1k 1k 5 4 5 4 IC1b 6 10 16VW IC2b 10 16VW IC3f 100k 100pF 2 1k 0.1 D4 1N4148 10k D3 1N4148 2 10k 470k 100k 0.1 9 8 1k 7 6 390  3 V+ D2 1N4004 4.7k 8 1 10k 14 10k 4 IC4a LM358 D1 1M4004 4.7k 12 3 V+ IC2c 2 3 47k 12 IC1a LM339 10k M2 LEFT TURN Q2 BD646 M1 RIGHT TURN BACK EMF 1k +6V C E +6V C Q1 BD646 E B BACK EMF 1k 1 +3.3V Fig.2 (left): IC1b, IC1a & Q1 drive motor M1 on one side of the vehicle, while IC2b, IC2c & Q2 drive motor M2 on the other. IC2a is the triangle waveform generator – its output is compared with the back-EMFs generated by the two motors using IC1b & IC2b. Infrared diode IRD1 receives steering pulses from the transmitter. These pulses are processed by IC3a-f, IC4a & IC4b & used to switch the motor drive circuits. low and turns transistor Q1 on via a 1kW current limiting resistor. Because Q1 is a Darlington type (BD646), it requires only a small amount of base current to fully switch on. Diode D1 protects Q1 against any large voltage spikes that are generated by the motor M1 when the transistor turns off. The back EMF developed by the motor is sampled by a voltage divider consisting of a 4.7kW resistor and a 1kW resistor and the sampled voltage then applied to D3. When the motor is off, D3 will be forward biased and so a sample of the back-EMF also appears across the associated 10µF filter capacitor. This voltage is then further filtered by a 1kW resistor and 2.2µF capacitor and applied to pin 4 of IC1b. If the back EMF rises, the voltage on pin 4 also rises. As a result, the pulses from IC1b become narrower and so the motor slows down. Conversely, if the back-EMF falls, the voltage on pin 4 of IC1b also falls and the output pulses become wider to bring the motor back to the set speed. The initial speed of the motor is set by trimpot VR1. When Q1 is switched on, D3 is reverse biased and so the filtered backEMF voltage in unaffected (ie, the back-EMF is monitored only when the drive to the motor turns off). Motor M2 is controlled in exactly the same manner by IC2b, IC2c and Q2. The back-EMF of this motor is monitored via diode D4, while VR2 sets the overall speed of the motor. Infrared receiver The infrared receiver consists of linear amplifier stages IC3a-IC3f and comparators IC4a & IC4b. This section of the circuit is powered from a regulated 3.3V rail so that it will be unaffected by battery voltage fluctuations due to motor operation. Because op amps have very poor frequency response and low gains when powered from 3.3V, CMOS inverters have been used as amplifiers instead. These are biased to operate in a linear mode by connecting a 100kW feedback resistor between each input and output. IR pulses from the transmitter are picked by infrared receiver diode IRD1 which then applies voltage pulses to pin 9 of IC3a. The resulting voltage pulses on IC3a's pin 10 output are then amplified by IC3b-IC3f. Each of these amplifiers operates with a gain of 10, as set by their 100kW and 10kW This “under-the-chassis” view shows the arrangement of the front & rear wheel assemblies. A small piece of black cloth was glued to the rear wheel so that its appearance matched the other wheels. Fig.3: the left & right turn signals consist of 40µs pulses with repetition rates of 33ms & 0.7ms, respectively. The filtered signal on pin 2 of IC4a is about 0.3mV for a left turn signal & about 150mV for a right turn signal. feedback resistors. The .01µF capacitor at the input of each amplifier rolls off the frequency response below 1.6kHz to filter out 50Hz mains signals. As an additional precaution, a 100pF capacitor is connected across each feedback resistor to roll off the response above 16kHz. Note that pin 7 to IC3f is tied to the 3.3V supply rail via a 47kW resistor. This ensures that pin 6 of IC3f remains low when no IR signals are being received. When IR signals are received from the transmitter, pin 6 of IC3f delivers an amplified positive-going pulse train. The output from IC3f is split two ways. First, it drives the inverting input (pin 2) of IC4a via an RC filter circuit. And second, it drives an AGC filter consisting of a 120W resistor, diode D5 and a 0.047µF capacitor. When an IR signal is received, the positive-going pulses from IC3f charge the .047µF AGC capacitor via D5. If the voltage across the capacitor rises above 1.4V, Q3 turns on and shunts the signal at pin 11 of IC3b via a 0.1µF capacitor. This forms a crude form of automatic gain control (AGC) that prevents the amplifier stages from overloading when a strong infrared signal is received. The DC level at pin 2 of IC4a is used to discriminate between a left or right September 1993  75 ► 2x1N4004 D2 D1 LEFT TURN S1 Q1 BC328 RIGHT TURN S2 4.7M 100k 5.6k B1 9V 7 4 150  6 A LED1 CQY89A  K A LED2 CQY89A C A C 5. 6  .01 B VIEWED FROM BELOW 3 1 E B 8 IC1 7555 2 E 220 16VW 0.1 Fig.4: the transmitter circuit uses 7555 timer IC1 to drive two infrared LEDs via switching transistor Q1. The pulse repetition rate depends on whether the 4.7MW or 100kW timing resistor is selected & this in turn depends on whether S1 or S2 is pressed.  K K REMOTE COCKROACH TRANSMITTER turn signal from the infrared transmitter. Fig.3 shows how it works. As shown, both the left and right turn signals consist of a train of 40µs pulses. However, whereas the left turn pulses have a repetition rate of 33ms, the right turn pulses have a repetition rate of just 0.7ms. As a result, the filtered signal on pin 2 of IC4a will be close to 0V (0.3mV to be exact) for a left turn signal and about 150mV for a right turn signal. IC4a compares the filtered signal on it pin 2 input with a 120mV reference voltage on its non-inverting (pin 3) input, as set the 10kW and 390W divider resistors. Its output at pin 1 will thus be high for a left turn signal and low for a right turn signal. The 47kW feedback resistor provides hysteresis so that the op amp switches cleanly at the transition point. If the output from IC4a is low (for a right turn signal), pin 9 (and thus pin 14) of IC1d will also be low. The output of IC2c will thus be pulled high and so Q2 and motor M2 will be off. Motor M1 continues to run however, and so the vehicle turns right. Conversely, if a left turn signal is received, pin 1 of IC4a goes high and so motor M2 runs. Pin 10 of IC1c will now be at ½Vcc (due to the two 100kW divider resistors), while the output of IC4b will be low due to the AGC signal on pin 6. Pin 11 of IC1c will now be lower than pin 10 and so Q1 and motor M1 turn off. Motor M2 is Fig.5: the top two traces on this oscilloscope photograph show the triangle waveform at pin 5 of IC2b superimposed on the back-EMF (pin 4 of IC2b). The lower trace shows the motor drive signal at pin 14 of IC2c. (Note: The vertical sensitivity is 0.2V/div for the top two traces and 1V/div for the bottom trace). 76  Silicon Chip running, however, and so the vehicle now turns left. When no infrared signal is received, the outputs of IC4a and IC4b are both high and both motors are free to run. Power for the circuit is derived from a 6V battery pack comprising four AA cells. S1 switches power on and off and the 6V rail is used to directly power the Darlington transistors (Q1 & Q2). This rail is decoupled using a 1000µF capacitor. IC1 & IC2 are powered via a decoupling circuit consisting of a 180W resistor and 470µF capacitor, while the remainder of the circuit is powered from a regulated 3.3V rail derived using ZD1 and a 100µF capacitor. Transmitter circuit The transmitter circuit uses a 7555 timer (IC1) to drive two infrared LEDs via switching transistor Q1 - see Fig.4. IC1 is wired as an astable oscillator and delivers 40us wide negative-going pulses to transistor Q1 when power is applied. Each time a pulse is received, Q1 turns on and drives the two infrared LEDs (LED1 & LED2) via a 5.6W current limiting resistor. This results in brief 1A current pulses through the LEDs but since the average current is much lower than this, it is well within the LED ratings. The pulse repetition rate depends on which of two timing resistors is selected and this in turn depends on whether S1 or S2 is pressed. If S1 is Fig.6: this oscilloscope photograph shows the right turn signal from the transmitter. The trace shows the voltage developed across the 5.6W currect limiting resistor in series with the infrared LEDs. The 40µs pulses occur once every 0.7ms (scope settings: 1V/div vertical sensitivity & 0.1ms horizontal timebase). 1k 68k 10k IC2 LM339 1 2.2k 10k 1000uF D1 1k 10k 1k 1 10k D3 1k VR1 Fig.7: install the parts on the PC board as shown in the wiring diagram. Make sure that all polarised parts are correctly oriented (see Fig.2 for semiconductor pin-out details) & note that the metal bodies of the motors must be grounded. pressed, the 4.7MW resistor is selected and the pulses occur once every 33ms. If S2 is pressed, the 100kW timing resistor is selected and the pulses occur at 0.7ms intervals. SOLDER Power for the transmitter is derived from a single 9V battery and is applied to the circuit via D1 or D2, depending on which switch is pressed. These two diodes isolate the timing resistors from NUT WASHER 30mm PCB 9mm UNTAPPED BRASS SPACER SOLDERED IN HOLE IN PCB WASHER SOLDER NUT NUT 1/8" THREADED BRASS ROD 22mm DIA ALUMINIUM KNOB 100pF 100k 0.1 470k 47k 2.2uF 0.1 100pF 100k 100pF 47k 10k .01 47k IRD1 A K 120  0.1 1 100k 390  IC4 LM358 MOTOR 1 2.2uF IC1 LM339 100k 10uF 1 10k Q1 4.7k 100pF 10k .01 100k 100pF VR2 100k 1k S1 B1 6V D4 10k 10k 1k D2 .01 10k .01 100k 10k 100k D5 Q3 .047 470k 10k 15k 100k 1k 4.7k .01 470k 2.2k 10k 100k ZD1 IC3 4049 MOTOR 2 470uF 10uF 100k Q2 100uF 47  100k 2.2uF 180  each other. A 220µF capacitor decouples the supply rail and helps supply the peak current to the LEDs, while the 0.1µF capacitor provides supply decoupling for IC1. Construction All the parts for the Remote Control Cockroach are installed on a PC board coded 08307931 – see Fig.7. No particular order need be followed when installing the parts on the PC board but make sure that all polarised parts are correctly oriented. These include the electrolytic capacitors, diodes, transistors and ICs. Take care also with the orientation of the infrared photodiode (IRD1). After mounting, bend its leads at right angles so that its photosensitive area faces upwards (see photo). The circuit diagram (Fig.2) shows the pin details for IRD1 and the transistors. SOLDER NUT 9mm BRASS SPACER NUT 60mm SOLDER DRILL HOLE THROUGH KNOB THIS END Fig.8: the rear wheel assembly is made up using a 22mm-diameter aluminium knob, a 150mm-length of threaded brass rod, two 9mm spacers & several nuts & washers. Make sure that the knob spins freely on its spacer & that the pivot assembly rotates freely before soldering the nuts to the threaded rod. Fig.9: a convex mound of solder must be built up on each motor shaft to prevent the rubber bands from coming adrift while the motors are running. This is done by applying solder to the shaft while the motor is running (wear eye goggles) & then filing the solder to shape. September 1993  77 MOTOR SHAFT Fig.10: this plan view shows how the motor shafts are coupled to the front wheels via the rubber bands. Position the axle so that the rubber bands stretch by about 7mm when they are installed & adjust the spacers so that the wheels clear the PCB by about 2mm. MOTOR SHAFT RUBBER BAND RUBBER BAND UNDERSIDE OF PC BOARD 12mm UNTAPPED BRASS SPACERS SOLDERED TO PC BOARD 6mm UNTAPPED BRASS SPACERS WASHERS WHEEL WHEEL CRIMP END WITH PLIERS 1/8" BRASS TUBING ADJUST FOR RUBBER BAND TENSION 2mm 2mm 130mm The two motors are secured to the PC board using enamelled copper wire straps (1.5mm-thick) – see photo. In each case, one strap is soldered to the motor body to provide shielding for the receiver circuitry. You will have to scrape away some of the enamel on each of the two straps to achieve a good solder joint. Once the motors have been secured, they can be wired to the PC board as LED1 A LED2 K A 5. 6  K 5.6k .01 220uF S1 TO B1 100k Q1 S2 4.7M IC1 7555 D1 150  0.1 1 D2 Fig.11: parts layout for the remote control transmitter. The two switches are mounted on machine IC pins & must be correctly oriented (see text). 78  Silicon Chip shown in Fig.7. Note that the motor terminals are not identified. If either motor subsequently runs backwards, just swap the wiring to the PC board. The 9mm spacer for the rear wheel pivot can now be soldered into place. This spacer is mounted vertically immediately to the left of IC3 and should be installed so that it protrudes about 3mm above the board surface. The circuit can now be checked for correct operation. To do this, wind both trimpots fully clockwise, apply power and check for +5V (approx.) on pin 3 of IC1 and on pin 3 of IC2. ZD1 should have a nominal 3.3V across it and this voltage should appear on pin 1 of IC3 and pin 8 of IC4. If the supply voltages are correct, rotate each trimpot until its corresponding motor runs reliably at slow speed. Check that each motor exhibits a fair amount of torque when you try to stop it by grabbing hold of its shaft. If one or both motors fails to operate, go over the board carefully and check for wiring errors. in Fig.9. This ensures that the rubber bands remain on the shafts and don't wind off when the motors start to run. To form this solder mound, run the motor at a slow speed, apply the iron and allow the solder to slowly build up on the shaft (important: wear eye goggles to avoid getting solder in your eyes). When a sufficient mound REMOTE CONTROLLED COCKROACH + + LEFT RIGHT Mechanical assembly The first step in the mechanical assembly is to apply a convex mound of solder to each motor shaft, as shown Fig.12: this is the full-size artwork for the transmitter front panel. Bend the leads of the photodiode (IRD1) through 90° so that its sensitive area faces upwards as shown in this photograph. This close-up view shows the solder mound on the shaft of one of the motors. The two motors are fastened to the PCB using straps made from 1.5mm-diameter copper wire, with at least one strap soldered to each motor body to provide shielding for the receiver front end. has built up, remove the iron and the solder to cool with the motor still running. Once the solder has cooled, it can be carefully shaped using a small file. Again, this is best done while the motor is running. The front wheel assembly is next. Temporarily fit one of the wheels to the axle, position it on the underside of the vehicle and fit the rubber band as shown in Fig.10. Position the axle so that the rubber band is just stretched by about 5mm and mark the position of the axle on the board with a pencil. The two 12mm spacers can now be soldered to the underside of the PC board (see Fig.10). Position these spacers so that additional 6mm spacers can be fitted as shown. These spacers ensure that the inside edges of the wheel clear the PC board. The wheels can now be fitted and secured by crimping the axle ends with pliers. Note that two small washers are fitted between each wheel and the crimped axle end so that the wheel turns freely. Don't just use one washer here. If you do, it may bind on the crimped end of the axle and stop the wheel from rotating freely. The pivoting rear wheel assembly is shown in Fig.8. We used an aluminium knob for the wheel and 1/8-inch threaded brass rod for the swivel. The normal shaft hole in the knob was drilled right through to accept the brass rod, while a 9mm brass spacer serves as CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.1µF   100n   104 0.047µF   47n   473 0.01µF  10n  103 100pF  100p  101 RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 3 13 1 3 1 1 10 1 2 1 7 1 2 1 1 1 Value 4.7MW 470kW 100kW 68kW 47kW 22kW 15kW 10kW 5.6kW 4.7kW 2.2kW 1kW 180W 150W 120W 47W 5.6W 4-Band Code (1%) yellow purple green brown yellow purple yellow brown brown black yellow brown blue grey orange brown yellow purple orange brown red red orange brown brown green orange brown brown black orange brown green blue red brown yellow purple red brown red red red brown brown black red brown brown grey brown brown brown green brown brown brown red brown brown yellow purple black brown green blue black gold 5-Band Code (1%) yellow purple black yellow brown yellow purple black orange brown brown black black orange brown blue grey black red brown yellow purple black red brown red red black red brown brown green black red brown brown black black red brown green blue black brown brown yellow purple black brown brown red red black brown brown brown black black brown brown brown grey black black brown brown green black black brown brown red black black brown yellow purple black black gold green blue black black silver September 1993  79 Fig.13: full-size etching pattern for the transmitter PCB. The transmitter PCB clips into a small plastic utility case, leaving enough room at one end for the 9V battery. Bend the leads of the two IR LEDs at right angles so that the devices protrude through holes drilled in one end of the case. the wheel bush. This brass spacer fits into the existing 6mm-diameter shaft hole in the knob. The wheel assembly is fitted to one end of the brass rod and secured with a nut on either side. Check that the wheel turns freely before soldering the nuts in position. This done, bend the rod into a U-shape around the wheel, taking care to ensure that it finishes up at right angles to the axle. The end of the rod is then bent upwards through 90° about 60mm from the axle, so that it fits through the vertical spacer on the PC board. Finally, the battery holder can be secured to the PC board using two more rubber bands. Transmitter assembly Fig.11 shows the assembly details for the infrared transmitter. All the parts are installed on a PC board coded 08307932 and this clips neatly into a small plastic case. Before mounting any of the parts, drill out the mounting holes for each of the two switches using a 1/16-inch drill. A machined IC pin (obtained from a machined-pin IC socket) should now be pushed into each mounting hole. Push each pin down to its top flange, so that only about 0.5mm of the pin remains above the board. This done, the two pushbutton switches can be mounted and soldered directly to the tops of the pins (see photo). Be sure to orient the switches exactly as shown in Fig.11 – ie, with the flat side of each switch towards the IR LEDs. Adjust trimpots VR1 & VR2 on the main board so that the two motors run at the same speed. This will ensure that the vehicle tracks in a straight line with no steering input. If one of the motors runs backwards, just swap its lead connections to the PCB. 80  Silicon Chip The two pushbutton switches are mounted by soldering their leads to machined IC pins that sit about 0.5mm above the surface of the PCB. This close-up view shows how the battery clip is modified so that the battery assembly fits inside the case. Part of the plastic moulding around two of the screw holes in the lid must also be cut away to provide clearance for the battery. The remaining parts can now be installed on the PC board. Mount the two infrared LEDs at full lead length and make sure that you orient them correctly (the anode lead is the longer of the two). After mounting, the two LEDs are bent over at right angles so that they protrude through two holes drilled in one end of the case. You will also have to drill two holes in the lid of the case for the pushbutton switches. This can be done by first attaching the self-adhesive label as a drilling template. Note that the battery clip must be modified to allow and the battery assembly to fit inside the case. This simply involves removing the plastic cover from the top of the clip and soldering the two leads to the sides of the eyelets instead of to the top. In addition, you will have to cut away part of the plastic moulding around two of the screw holes in the lid, to provide clearance for the battery. Test the operation of the transmitter by checking that the left and right switches stop the right turn and left turn motors respectively. Warning: do not hold the transmitter too close to the receiver diode, as this will only overload the front end of the receiver and cause incorrect operation. Finally, check the transmitter operation with the car on the ground. By walking directly behind the vehicle, you should be able to steer it left or right at will with the transmitter. Note that the range of the infrared link is limited to about three metres, due to the low supply voltage used SC for the receiver circuit. Fig.14: full-size etching pattern for the main PCB. September 1993  81 REMOTE CONTROL BY BOB YOUNG Servicing your R/C transmitter Modern R/C equipment has dramatically improved in quality & reli­ability in the past few years but still responds well to routine maintenance. This month, we will look at some of the basic servicing procedures. So your favourite toy is ailing? Range is down, one of the servos is chattering away around neutral and all in all you feel it is unwise to venture out to the flying field, race track or pond. You desperately need a relaxation fix. What to do? From the outset I must state that the best place for ailing R/C equipment is back with father (ie, the manufacturer). However in Australia 1993, father usually resides overseas. Thus, the next best is factory appointed agents. These agents usually have trained technicians, circuits, good test equipment and the cor­ rect range of spares, a vital point in equipment that is subject routinely to 100G+ de­celer­ations. Having decided to waive the above options, you are about to embark on the great adventure – finding out how your set works. Test equipment This ancient unit is an absorption wavemeter that has served the author for many years. 82  Silicon Chip For AM systems, the test equipment required is very basic and for those fortunate enough to possess an oscilloscope, even the modulation pattern is plainly visible. For FM systems, the requirements in regards to test equipment are more stringent and thus more expensive. PCM (pulse code modulation) adds a new dimension, with software analysis on top of FM to be taken into account, and is outside the scope of this article. The really basic elements for AM servicing are the usual assortment of handtools, a toothbrush, a can of CRC.226 spray cleaner and a multimeter. To this, in descending order of impor­tance, may be added the following: cycling battery charger, oscilloscope (preferably 15MHz bandwidth or better), absorption wave­meter, servo analyser and signal generator. For FM sets, you can add a modulation meter and frequency counter to the list. Finally, for tuning a modern transmitter, a spectrum ana­lyser is a must, because part of the tuning procedure involves the suppression of harmonics. The transmitter Fig.1 is the schematic of a typical Tx and recourse to the actual circuit diagrams for your make and model of set will be a great help. Fig.2 gives the typical PPM pulse train. The great difficulty with modern R/C equipment is the in-house integrated circuit. In the old days of discrete components, circuits could be traced, components were clearly labelled and substitutes could often be purchased at the local electronics store. These days, the encoder and decod­ er are usually in a single IC labelled with a house number and available only from the manufacturer’s agent. Fortunately, the RF section is usually still discrete and thus can be serviced. However, I must point out here that the most probable causes of trouble are battery or mechanical. The electronics rarely fails, so there is much that can be done by the handy modeller to keep his or her gear in good condition. One of the problems with R/C transmitters as far as testing is concerned is the measurement of power. As the ANTENNA ENCODER/ MULTIPLEXER/ MICRO MASTER CLOCK AM MODULATOR CONTROL POTS FM RF BUFFER AMPLIFIER PA RF OSCILLATOR RF METER Fig.1: block diagram of a typical radio-control transmitter. The encoding circuitry will be contained in a single IC but the RF section is usually discrete & thus can be serviced. 1-2ms 350us 50us 20ms Fig.2: typical PPM pulse train from a radio-controlled transmitter. If you have a CRO, you can check that this waveform appears at the output from the modulator. antennas are built in and do not use coax connections, it is difficult to hook up test equipment. This type of equipment is also expensive and not readily available to the average modeller. Thus, one of the most helpful instruments for transmitter testing is the absorption wavemeter. They can be built by the home constructor and provide a useful guide to transmitter output. One of the photos accompanying this article shows my origi­nal wave­ meter, much admired over the years by customers but sadly now showing its age. Built in 1955, this meter has done Trojan service. Standing in the one spot at Riverwood for 22 years, it has provided me with an instant guide to the relative field strength of all transmitters. Because it contains no batteries, it provides a stable and thus reliable indication of transmitter output. In open air, it will provide a reading from a typical Tx up to 10 metres. When using a wavemeter, it is important to remember that long extension leads or large masses of metal placed in the vicinity of the wavemeter or transmitter will influence the meter reading. Thus, the Tx test area must be kept clear of these items. While there is very little in the circuitry of an absorp­tion wavemeter, its mechanical construction can be a little tricky although the photos of my treasured unit may not demonstrate this. If possible and if parts are available, I may be able to describe the construction of an absorption wave­meter in a future issue. Battery checks To begin your analysis of your R/C system, take the back off the Tx and go straight for the batteries. Statistically, this is number one on the list of suspects. Modern rechargeable AA cells have a useful life in excess of five years if treated with respect and some of the SAFT AA cells in Silvertone sets are still working after 10 years. Personally, I recommend replacing battery packs in transmitters every three to five years and airborne packs in the same time corrosion. When the cells vent, they give off corrosive gases which can eat the legs clean off components and devour PC board tracks. “Black wire” usually appears in the black or negative bat­tery lead and is only associated with nicad batteries. This curious corrosion completely removes all traces of copper from the conductor and replaces it with some sort of black garbage. The wire then becomes dark or black in appearance, very brittle and incapable of carrying any current. Electronic problems usual­ly associated with a lack of earth will then begin to appear and ultimately the set will fail completely. It is more dangerous in the airborne battery because of the amount of current drawn by the servos. A complicating factor is the high level of engine vibration which may eventually snap the wire as it becomes more brittle as the corrosion progresses. Tin plating the conductors slows the process considerably and unplat­ ed copper conductors should not be used as battery leads. The corrosion can cross soldered joints but usually stops at the switch. So all wiring associated with the battery, switch and charging circuits should be examined regularly. This may mean removing covers or cutting off heatshrink sleeving on cables. Please do not be put off by this for the results may be well worth it. Model aircraft in particular demand preventative maintenance and even if the batteries come out of the inspection squeaky clean, you will at least have no concerns in this area. The batteries and leads should be examined once every two years and One of the most useful instruments for transmitter testing is the absorption wavemeter. They are very easily built by the home constructor & provide a useful guide to transmitter output. frame or after physical damage from a crash. Inspect the batteries for any signs of corrosion and, in particular, examine the battery leads very closely for signs of “black wire syndrome”. You should also examine the components and the PC board area above the battery for once salting of the terminals begins to appear, every six months after that. CRC-226 sprayed onto the battery termi­nals, charge socket and switch from new will slow down the black wire problem considerably. Repeat this procedure every 12 months or so. Since I last wrote about “black wire September 1993  83 freezing and vibration testing failed to produce the slightest shift in neutral at my factory but as soon as the customer took it home, the neutrals would shift. This went on for several weeks. You can imagine the havoc created in the service department. Tempers were fraying and reputations were in tatters. The owner of this particular set lived in a small flat and did all of his work on his models on the kitchen table after tea. In other words, after he had cooked his evening meal. Thus, we eventually reasoned, the kitchen would be full of steam and cooking smells. In desperation, I blew on the PC board through a piece of heatshrink sleeving which localised the airstream to a small segment of the PC board. The tube provided a venturi effect, chilling the air and leaving moisture on the PC board. Bingo! The neutrals shifted immediately I blew on the PC board just above the negative battery terminal and by quite a considerable amount. The same test on a new transmitter of the same brand and model yielded no result. The servo neutrals remained normal. The set’s history While there is very little circuitry inside an absorp­tion wavemeter, its mechanical construction can be a little tricky. A wavemeter contains no batteries & provides a reliable indication of transmitter output. syndrome” in the February 1990 issue, I still have found no clear explanation of the cause and I am more mystified than ever about this problem. I have even found several cases of “black wire” in signal leads and one in the positive lead. The red lead in question was in a portable telephone and the corrosion had eaten the tracks off the PC board. The black lead was perfectly OK, something that I have never encountered before in any nicad-powered system. Board contamination The above problem raises the spectre 84  Silicon Chip of the most serious outcome of battery corrosion – contamination of the PC board and surrounding electronics. We have a tendency at Silver­tone Electronics to call all problems by pet names and by far the most baffling service problem I have ever encountered was the “kitchen table syndrome”. The problem manifested itself in a shift of servo neutrals, something quite extraordinary in PPM systems. There was no sign of corrosion in the encoder components or PC board tracks. This shift appeared at random intervals and all attempts to pin down the cause were fruitless. Heating, An examination of the history of the transmitter revealed that the problem appeared after the customer had the original battery replaced, because it had split during charging. The original was a button cell battery pack and these were quite prone to this problem once they had aged. It appeared that the battery chemicals had vented onto the PC board and formed a substrate which, when overlaid with cook­ ing fumes and steam, provided a leakage path sufficient to alter the pulse width of the one-shot generators. Scrubbing the PC board with solvents and spraying on a liberal coating of lacquer completely eliminated the problem and the set soldiered on to a respectable retirement. As always, this problem was simple once solved. We now do the “blow test” as routine on all transmitters over a few years old. In addition, PC boards are always cleaned and lacquered after battery replacement. Modern sets incorporate the lessons learned in dealing with these problems and some transmitters now have the battery in a semi-sealed com- partment to minimise the incursion of vented battery gases into the areas containing electronics. Some gas may still find its way up into the electronics however, so always be alert for signs of corrosion, particularly where the battery wires join onto the PC board. Charging the batteries This now brings us to the problems of battery charging. No more vexing a problem exists for modellers than fighting their way through the maze of argument and counter argument surrounding the care and charging of nicad batteries. I feel that much of the above damage is the result of poor charging techniques. Yet modern nicad batteries have many built-in safeguards to prevent damage caused by overcharging and figures quoted by SAFT, for example, give a safe overcharge of 20,000 hours at the c/10 rate. Why then, does “black wire” occur, what can be done to prevent it and what is the actual chemical process involved? The battery literature main- How do you come to grips with a foe as slippery as this? (Editor’s note: the electrolyte in nickel cadmium and alka­line manganese cells is based on potassium hydroxide (ie, caustic potash) and this is released if these cells vent or leak. The vent for nicad cells is at the positive end. If the cells are leaking, the electrolyte can travel under the heat­shrink sleeving of the case and then up the battery leads by capillary action and ultimately migrate to the tracks of the PC board. Thus, it would seem that the “black wire syndrome” is essentially a product of corrosion between copper and potassium hydroxide). Storing nicads Originally, common wisdom for the storage of nicads was to fully discharge each cell and store it in the discharged state with a strap shorting out each cell. I have seen nothing since that has altered my view that this is the correct method for storing nicads. It is, however, almost impossible to do with a set of stacked cells that have been sealed in a plastic housing. Nicads are now the number one killer of model aircraft. It is safe to say that all sets fitted with nicads will be subject to corrosion to a greater or lesser degree at some stage of their lifetime. tains a stony silence on all of the above. In the absence of any official, definitive data, I can only offer the following subjective advice based on 40 years of practical experience with nicad batteries. Firstly, nothing is as it seems. Above I stated that I feel the damage is caused by overcharging yet I can quote several cases of sets which were purchased from new, charged once or twice and never used again; a very common problem in modelling. These sets some years later exhibited severe black wire corro­sion. Again, I call this problem the “black wire syndrome” be­cause I first encountered it in the black or negative battery lead and yet, as stated above, I have also encountered black wire syndrome in the signal and positive battery leads. Therefore, I recommend that after each operating session, you should use a cycling battery charger. Discharge the batteries to their safe endpoint (1V per cell) and leave them in this state until the night before the next session. At Silvertone, I use a chart recorder to trace the voltage curve on all sets we service. This uses a fixed load current of 270 milliamps (which is the industry standard for the simulation of a 4-servo system) and gives a trace of about two hours for a good set of nicads – equivalent to 8-10 15- minute flights. If the set is not used for a period in excess of six months, run a couple of discharge/charge cycles to keep the chemicals circulat­ing inside the battery. As before, it’s best to leave the cells in a discharged state. Avoid overcharging and high rate charging. If you do not agree with leaving the batteries flat, then cycle them every time before you go flying. If you do not have a cycling charger, then use a battery discharger and your regular charger. SILICON CHIP has published details of these devices, as noted at the end of this article. The No.1 killer I have spent a considerable amount of time on nicads in this issue because they are now the number one killer of model aircraft and a great source of vexation for all modellers and indeed all users of nicads. It is safe to say that all sets fitted with nicads will be subject to corrosion to a greater or lesser degree at some stage of their lifetime. Some of the latest transmitters fitted with sealed batter­ies which are housed in a moulded compartment inside the trans­mitter case may be the exception. These batteries slide into their compartment and the clips make contact with nickel plated leaf springs. Thus, there is a solid nickel barrier between the batteries and the transmitter interwiring. This type of trans­mit­ter is a pain to repair because once the back comes off, all contact is lost with the battery. However, they do represent the most logical approach to preventing battery corrosion. The principles above apply to all nicad-powered devices. They are problems we will all become more familiar with in time. This is not to say that nicads have become more unreliable. Rather quite the opposite, for they have become much more robust and reliable over the past few years, particularly in the AA cell configuration. However, the reliability of the electronics has far outstripped that of nicads and left them in the low spot on the totem pole. Next month, we will look at some of the electronic and me­chanical maintenance procedures. References (1). How to Get the Most Out of Nicad Batteries, by Garry Cratt. SILICON CHIP, August 1988. (2). Nicad Battery Discharger, SILICON CHIP, July 1992. (3). Automatic Nicad Battery Discharger, SILICON CHIP, November 1992. (4). Single Cell Nicad Discharger, SILISC CON CHIP, May 1993. September 1993  85 VINTAGE RADIO By JOHN HILL Restoring an old valve tester A valve tester is an invaluable item of test equipment for the vintage radio restorer. They are usually not too difficult to restore to full working order &, although not infallible, can give a good indication as to the serviceability of unknown valves. Recently, I acquired a valve tester, a late model Palec ET-4a which was in quite reasonable condition for its age. By “late model”, I mean that it was made sometime in the late 1950s and, therefore, is capable of testing the smaller 7 and 9-pin miniature valves in addition to the earlier pre-war types. Older valve testers can be a problem in that they will not accommodate miniature valves without the aid of an adaptor of some type. Very early testers that cannot handle octal valves have fairly limited use and make better display items than working valve testers. I paid $80 for the Palec and it was bought because the tester was accompanied by its original instruction manual. For some reason or other, instruction books for valve testers become lost over a period of time in much the same manner that antique radio receivers frequently become separated from their original loudspeakers. The interesting aspect of the Palec manual was the fact that it appeared to be almost unused. Some pages were slightly marked with a few grubby fingerprints but otherwise the book looked almost new rather than 30-plus years old. Printed on the front cover of the manual is the name of a Victorian TAFE College, which gives a clue as to why this particular valve tester has had so little use. Valve technology occupies only a very small part of any modern electronics course and no doubt the old valve tester has spent the best part of its life sitting on a shelf. But although the instruction manual looked near new, the same could not be said for the tester itself. It had been col­lecting dust for many decades and the top-mounted valve sockets were chocked full of dirt and grime from years of unprotected storage. What’s more, all of the 10 straight-line switch levers were bent to one side and a knob and the power cord plug were missing as well. One often has to take a punt with this vintage radio caper and the old valve tester looked as though it would clean up OK. Besides, coming up with something different every month for my column is no easy task and repairing a valve tester suddenly seemed like a really good idea! Restoration The valve sockets are mounted on the top of the Palec valve tester & this allows dust to accumulate in the connections. Dust-free storage is essential for trouble-free operation. 86  Silicon Chip Restoring an instrument of this nature is relatively sim­ple. A valve tester is little more than a power transformer plus a mass of switches, socket contacts and connecting wires, so it’s only a matter of getting these components to operate again. Basically, it boils down to cleaning the dust out of the switch and socket contacts and adding a little lubrication here and there so that the mechanical parts work smoothly again. Two new top cap leads had to be made for the Palec valve tester. They plug into the small socket at centre top. a little smoother. If a switch is a bit scratchy in its operation after clean­ing, then a light spray of WD40 or some similar compound may help to improve things. These contact cleaners contain a lubricant which helps the dry switch contacts slide in and out of contact more freely. Unfortunately, any oil type of lubrication will eventually collect dust, so unless the instrument is properly stored, dirty contact problems may occur again at a later date. The front control panel on the Palec has six rotary switch­es plus 10 4-position straight-line lever switches. The filament switches alone have 21 different positions and cover a range of voltages from 0.6V to 117V. A valve tester with malfunctioning switches is not only an unreliable instrument but is a frustrat­ing thing to operate. Power transformer This close-up view shows the test meter which indicates whether a valve is good, doubtful or should be replaced. The “shorts” neon is mounted in the top right-hand corner. It was evident by turning some of the rotary switches that some form of maintenance was necessary. They felt stiff and gritty and to use them in that condition would result in consid­erable damage. Dust and moving parts are a bad combination. The back of the tester was removed and with the aid of a small paint brush and a few blasts of compressed air, the dust from inside the cabinet was forcefully removed. Cleaning the valve sockets was the next item and they took quite some time to do. Pipe cleaners dipped in solvent did a good job of the larger sockets, while a tooth brush and a drill shank were used on the smaller sockets. Again, compressed air was a handy aid to the cleaning process. The sockets were also checked for contact tension and any loose ones were adjusted so that they had a firm grip on the base pins. Many of these socket connections were making poor contact and if they had not been attended to they would have given noth­ing but trouble. Switches The switches (and there are plenty of them in a valve tester) were all flushed out with contact cleaner. Spraying on the solvent while activating the switch gear soon cleaned the contacts and washed away the rubbish. A couple of drops of oil on the control shafts also helped to make switching It was at this stage of the proceedings that I thought the worst had happened. Checking out the power transformer indicated that there was a serious problem; what appeared to be an open winding. However, the problem sorted itself out when the filament voltage switches were set to their correct positions. Whew! The power transformer is the heart of any valve tester. It is not an everyday, common garden variety transformer but one with multiple tappings for a wide range of voltages. Both the primary and the secondary windings are tapped and to find a working transformer would be an almost impossible task. The power transformer of the ET-4a has no less than 33 individual connec­tions and is a transformer winder’s nightmare! If a valve tester’s transformer has an open winding, it is a repair job for a skilled tradesman because each tapping must deliver a specific voltage. One of the rotary switches had a cluster of resistors at­tached to it and a check on these indicated that they were still operative and within tolerance. However, a small paper capacitor mounted on the same switch was replaced with a modern polyester one in case it had deteriorated over the years. The bent switch levers were no trouble to straighten and the front panel looked a good deal better after the job had been done. Other incidentals included checking September 1993  87 A “ring-in” control knob (top, left) was fitted to the old valve tester to replace a knob that had gone missing & a matching knob fitted to the other side. Despite having several buckets full of knobs, a suitable match for the original knobs could not be found. and zeroing the panel meter, cleaning and checking the wire-wound range potentiometer, and fitting two new knobs to the top two controls (one to replace the missing knob and the other to match the replacement). A couple of top cap leads were also made up and the whole cabinet and front panel was polished with automotive cut and polish compound. The cut and polish treatment removed most of the lighter scratches and smeary marks and also rejuvenated the paint work. Finally, a 3-pin plug was fitted to the power cord and the resto­ration was complete. All that remained was to see if the old Palec valve tester would work. Testing No problems were encountered during the trail run and the tester functioned well. A couple of known defective valves acti­vated the “shorts neon” indicator which is build into the test meter. Known good valves were also tested and the meter needle swung over to the green “good” section of its movement. But although the tester worked normally, I was not in complete agree­ment with some of the test data. The power transformer (centre) has 33 individual tappings. A transformer breakdown would require an expensive rewind & what a job that would be. Note the surrounding switch gear & wiring. 88  Silicon Chip There are some peculiar discrepancies in the ET-4a’s in­struction book; eg, the range control settings for 6A7 and 6A8 valves. The book recommends a range control setting of 35 for the 6A7 and 28 for the 6A8. As far as I am aware, there is no dif­ference between these two valves apart from their base configura­tions. A 6A8 is a 6A7 with an octal base. Another example of different test settings is the 6D6 and 6U7. Again, only the bases of these two valves are different. Perhaps the later versions used a more active cathode coating material and produced different levels of emission It is interesting to note that when a number of new valves were tested in the Palec, the meter needle usually indicated a reading no higher than 85 on a 0-100 scale – about half the “GOOD” range. Why shouldn’t the meter give a reading of 100 when testing new valves? A valve needs a certain minimum level of emission to func­tion properly and additional emission above this level doesn’t make the valve work any better. While new valves may have consid­ erable variations in emission levels, there is no reason to assume that the “stronger” valves perform better or last longer than those with less –but adequate – emission. What is important is that a valve tester indicate the mini­mum effective emission level at the lower end of the “GOOD” range on the meter. Any valve that tests below this level can then be considered to be too low in emission This view shows the fully-restored Palec valve tester. A little time & effort have given the old tester a new lease of life & it is quite useful when restoring derelict receivers. Send Postage Stamp For List Of Other Items Including Valves L.E. CHAPMAN TAPE DECK OR RADIO POWER LEADS Plugs and Sockets $1.50 Test prods and leads $1.50 TOUCH MICRO SWITCHES as used on TV sets. 4 for $1 TRANSISTOR EAR PIECES plug & lead 4 for $2 PUSH BUTTON SWITCHES 4 pos 50c SPEAKER TRANSFORMERS 7000 to 15/Ohm 5W $10 7000 to 3.5Ohm 15W $10 5000 to 3.5Ohm $10 SPEAKERS 5 x 7 $5    6 x 4 $4 5" 8 Watt $5 INLINE FUSE HOLDERS 4 FOR $1 SHIELDED LEADS 7ft 3.5 to 3.5 $1 3.5 to 6.5 $1 6.5 to 7ft 75c Inline Baynet Plugs & Sockets 4 for $1 to function at its full potential. Of course, such a valve may still work but its perfor­mance will be lacking. To set the tester so that the meter reads 100 on new valves could cause suspect valves to actually read “good” when they should read “doubtful” or “replace”. One particular valve tester I have used was a bit this way inclined and just about every valve tested would whack the needle hard over on the good scale. It was a great valve tester – nearly every valve tested better than new! One interesting aspect of the Palec valve tester is its 7-pin socket. For the benefit of readers who may be SHIELDED CABLE 10m $2 The range control potentiometer is a wire-wound unit & was found to be in excellent condition. It is important that this control has clean contacts & functions smoothly. TAG STRIPS 10 for $2 mixed TWO WAY SPEAKER CROSSOVER NETWORK $2 50c 50c $1 ea 50c 10 for $1 $1 ea 3 for $1 3 for $1 $1 ea 5 for $1 3 for $1 4 for $1 10 for $1 5 for $1 4 for $1 IC SOCKETS 16 pin * 24 pin * 28 pin Four for $1 PLUGS & SOCKETS R.C.A. plugs and sockets 50c pair 2.5mm sockets 4 for $1 3.5mm sockets 4 for $1 6.5mm sockets 4 for $1 Thermistors 4 for $1 Speaker plugs and sockets 4 pin 50c pair 2 pin 50c pair POTS 1/2Meg $1.50 Dual 2 Meg Ganged Lin $2.00 1/2 Meg Switch $2.00 Dual 1 Meg Ganged Lin $2.00 1 Meg $1.50 1 Meg Dual Ganged Log $2.00 1 Meg Switch $2.00 10k Ganged Log $1.00 25k Dual Ganged $2.50 50 Ohm Single 50c ELECTROS 20UF 450V 2000UF 25V SLIDE POTS 1/2 Meg dual 1 Meg Dual 1 Meg Dual 1k Dual 25k Dual 5k Single 250k Single 10k Single $1 $2 $2 $1 $2 50c 50c 50c SPECIAL 12 Mixed Switches This old valve tester is typical of so many instruments that are now turning up. It’s dirty, no longer working & has no instruction manual or valve test data. This particular tester has sockets for Philips side contact valves which could be an advan­tage at odd times. CAPACITORS 6N8 150V 1000uF 16V 1000uF 50V 0.0039uF 1500V 0.0068 250V 47uF 63V 47uF 160V 470uF 16V 47uF 200V 0.1uF 250V 680uF 40V 0.027 250V 10uF 25V 22uF 160V 0.039uF 400V SPECIAL PICK UP ARM Includes cartridge and stylus. Plays mono or stereo $15 5 MIXED ROTARY SWITCHES 5 for $2.50 Special TUNING CAPACITOR 2 gang covers all Aust. AM bands. $10. P&P $1.80 for one or two. unfamiliar with 7-pin valves, there are two different sizes, one having the pins on a slightly larger diameter circle than the other. The 6A7 is of the smaller size and the old 59 is of the larger. The Palec will only take the smaller base size and there is no test data for the 59. Another Palec tester I have used occasionally takes only the larger base size. That minor detail doesn’t mean that there is no test data for the 6A7 and other small 7-pin valves. There is test data even if the tester will not directly accommodate them. The most likely explanation is that an adaptor was origi­nally used to cope with this situation but that this has long since gone the way of all adaptors – it has been lost. Incidentally, the 7-pin socket in my Heathkit tester will accept both base sizes because the socket connections have been made slightly elongated. The smaller base pins make contact with the inside of the socket connections, while the larger base pins contact the outside of the socket connections. My Palec valve tester has turned out to be a very useful instrument and I would hate to go back to the days when I did not have a valve tester. While they are not infallible, they do give a good indication of the serviceability of unknown valves. When restoring a derelict receiver, that is very useful SC information to have. SPECIAL Dual VU Meters $4. P&P $1.80 for one or two $1.50 $1 $4.50 200 MIXED SCREWS self-tappers, bolts, nuts etc. 200 for $2 CAR RADIO SUPPRESSORS 4 for $2 OXTAL VALVE SOCKETS $1 each Stick Rectifiers TV20SC $2 Transistors AD61-62 pair $3 AD 149 $2 each Chrome 1/4" push on knobs RRP 1.20 EA 10 for $1 Mixed capacitors fresh stock 100 for $2 Mixed resistors all handy values 100 for $2 Slide pot knobs 10 for $1 1F 455kHz for valve radios $2 ea Telsco Microphone Ceramic $2 pp $1 SPECIAL: CELLULAR HORN TWEETER Mounting specification 12.5cm x 7.1cm. Frequency range 2000-20,000Hz. Sensitivity 105dB. Maximum power 30 Watts. Impedance 8 ohms. $12. TV CRYSTALS 4.43619kHz 03061 NDK; 8.867238kHz 03122.937 $2 each. VALVES 6K7 $10 6U7 $10 6V4 $7 6BL8 $7 6SA7 $10 12AX7 $10 6BQ5 $10 6AV6 $10 6SN7 $10 EF50 $7 6K8 $12 1S5 $7 6BM8 $10 5AS4 $10 IT4 $7 6AM8 $10 6SL7 $10 205A $10 12AT7 $10 6J5 $10 6AS6 $10 6AN8 $10 6005 $10 12DL8 $10 6136 $10 12BL6 $10 6X4 $10 6SL7 $10 12X4 $10 6BE6 $12 6V4 $8 6M5 $12 EM84 $12 IR5 $10 6LEA8 $10 6N8 $12 6BV7 $10 6EM7 $10 6AU6 $10 12AU7 $10 6LM6 $10 EF86 $10 6X9 $10 6BAL6 $10 152 $5 6AQ5 $10 122 Pitt Road, North Curl Curl, NSW 2099 Phone (02) 905 1848 Send Postage Stamp For List Of Other Items Including Valves September 1993  89 Silicon Chip Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. October 1988: Build an FM Stereo Transmitter; High Performance FM Antenna; The Classic Matchbox Crystal Set; LED-Light; How To Convert A CB Radio To The 28MHz Band. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. January 1989: Line Filter For Computers; Ultrasonic Proximity Detector For Cars; 120W PA Amplifier (With Balanced Inputs) Pt.1; How to Service Car Cassette Players; Massive Diesel Electrics In The USA; Marantz LD50 Loudspeakers. February 1989: Transistor Beta Tester, Cutec Z-2000 Stereo Power Amplifier, Using Comparators To Detect & Measure, Minstrel 2-30 Loudspeaker System, VHF FM Monitor Receiver, LED Flasher For Model Railways, Jump Start Your New Car March 1989: LED Message Board, Pt.1; 32-Band Graphic Equaliser, Pt.1; Stereo Compressor For CD Players; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Map Reader For Trip Calculations; Electronics For Everyone – Resistors. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know About Capacitors; Telephone Bell Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Electronic Pools/Lotto Selector; Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2; PC Program Calculates Great Circle Bearings. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Please send me a back issue for: ❏ December 1988 ❏ January 1989 ❏ May 1989 ❏ June 1989 ❏ November 1989 ❏ December 1989 ❏ April 1990 ❏ June 1990 ❏ October 1990 ❏ November 1990 ❏ March 1991 ❏ April 1991 ❏ August 1991 ❏ September 1991 ❏ January 1992 ❏ February 1992 ❏ June 1992 ❏ July 1992 ❏ November 1992 ❏ December 1992 ❏ April 1993 ❏ May 1993 ❏ September 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 February 1989 July 1989 January 1990 July 1990 December 1990 May 1991 October 1991 March 1992 August 1992 January 1993 June 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ October 1998 March 1989 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 February 1993 July 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues November 1988 April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 March 1993 August 1993 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. On Your PC; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ r ecov­ e rable Application Error; Index To Volume 4. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ ories; Valve Substitution In Vintage Radios. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; PEP Monitor For Amateur Transceivers. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing Windows April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. November 1992: MAL-4 Microcontroller Board, Pt.1; Simple FM Radio Receiver; Infrared Night Viewer; Speed Controller For Electric Models, Pt.1; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.2; Automatic Nicad Battery Discharger. December 1992: Diesel Sound Simulator For Model Railroads; Easy-To-Build UHF Remote Switch; MAL-4 Microcontroller Board, Pt.2; Speed Controller For Electric Models, Pt.2; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.3; Index to Volume 5. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Low-Cost Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock, although stocks are low for some older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. September 1993  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. SLA charger for lead acid batteries I have a question about the SLA Battery Charger featured in the Aug­ ust 1992 issue of SILICON CHIP. I know that it is intended for sealed lead acid (SLA) batteries but I want to know if it can be used to charge conventional lead acid batteries used in cars. (J. S., Stanmore, NSW). • Yes, you can use the SLA Battery Charger to charge ordinary car batteries. In fact, we have pressed the prototype charger into service for recharging the heavy duty batteries used during the development of the 240VAC 2kW inverter. There are, however, two minor drawbacks. As presented in August 1992, the circuit has a maximum current output of 3A and this is a little slow if you want to charge large batteries in a hurry. Second, as the name suggests, the charger has been opti­ mised to suit sealed lead acid batteries and the changeover from main charge to float mode at 14.6V is probably a little higher than optimum for conventional lead acid batteries. Drill speed control not smooth I am having trouble with the Drill Speed Controller which was first featured in the September 1992 issue and then subse­quently modified in the November 1992 issue of SILICON CHIP. I am using it to control a sewing machine motor, a small hand drill and also my 30W and 60W soldering irons, as a temperature con­trol. I have blown up several of the Triacs and also find that the speed control is not smooth and there is a lot of “cogging” at even quite high speed settings. Can you suggest what is wrong? (A. K., Penshurst, NSW). • When we published this 92  Silicon Chip On the other hand, typical car battery chargers are pretty crude by comparison with the SLA battery charger and they simply rely on the rising voltage of the battery to cut back the charg­ing current to a reasonable level; there is no such nicety as a “float charge” mode on these simple chargers. Nixie tube data wanted Thanks for the refreshing digital clock project recently published is the April 1993 issue of SILICON CHIP. I found it interesting to go back to bas­ ics and build what otherwise would have been a meaningless 1-chip project. I am determined to fur­ther enhance the project by changing the display to Nixie tubes. I know that might sound crazy but I’m really bored by LEDs & LCDs and after much searching I got my hands on four matching tubes. Could you give me some advice on how these beasties work (as I don’t wish to damage them)? I know that they will need a separate high volt- heavy-duty circuit we did not envis­age that readers would want to use it for controlling flea-power appliances and that, to put it in a nutshell, is the problem. To work reliably, this circuit needs a load of at least 100 watts. And paradoxically, the fact that you are using it with small loads is the most likely the reason why you have blown up several Triacs. To solve the problem, we suggest the use of a more sensi­ tive and lower current device such as the C122E silicon con­trolled rectifier. This has the benefit of being quite a bit cheaper than the 40A Triac specified for the circuit. No other circuit modifications should be necessary. age power supply of some sort. Any advice would be appreciated. (G. G., Kensington, NSW). • Unfortunately, we do not have information about these devic­es although we do remember them (dimly). We hope some of our readers can provide the necessary information. Eliminating the ignition points I’ve been advised by my local Dick Smith store manager that your magazines of May-June-July 1988 had a CDI circuit diagram that would enable me to get rid of my points. Could you please tell me if these magazines are still available and at what cost? Also do you make kits for the CDI? If not, do you know of anyone who does? (J. L., Charters Towers, Qld). • Our May and June 1988 issues did feature a high energy ignition system but this was not a CDI design. These have fallen out of favour with designers since they present crossfire prob­ lems for car engines. However, CDIs are still favoured for motor­bike and outboard motors. The above magazines are no longer available but we can provide you with photostat copies at $6.00 each including post­age. We do not make kits but you can purchase the kit from Jaycar Electronics, phone (02) 743 6144 D61A scope needs TLC I have a Telequipment D61A portable dual trace scope which was designed/developed by Tektronix UK for field service (mainly on television equipment it appears, but it is also a good general purpose scope). Mine has developed a sweep generator fault which destroys the Miller timebase FET TR36. (A new FET is destroyed if installed and the timebase is run, but the FET remains intact if the timebase is used on “Ext X” or “Chan 2” sweep). Some of the transistors and FETs in the scope are unique to Tektronix UK. The NZ Tektronix agents have some (minimal) parts but they have no experience with the D61A. To help all this along, there are some ambiguities in the schematic and circuit description and I have been unable to clarify these. The power supply voltages to the timebase generator are within specification, the ripple looks OK, the other transistors in this part of the circuit check OK (by substitution), and all of the (many) diodes seem to be OK by circuit test with a multi­meter. All the timing capacitors are poly­ propylene or polystyrene and so are unlikely to be leaky. The only electrolytic in this part of the circuit checks OK. Does any reader have experience with servicing this scope and perhaps can recall if there were known faults which destroyed FET TR36 (or made the sweep erratic)? Are any timebase parts known to be unreliable (ie, resistors or capacitors which change value, or capacitors which leak)? I was also considering building the Infrared Remote Control for Model Railroads (SILICON CHIP April, May, June 1992) but have struck a snag with availability of the Plessey SL486 (IC5) and the MV601 remote control receiver (IC6). A local supplier who has had these devices says Plessey devices have virtually “dried up” and he has no confidence he will have them again. Can you advise a source of these devices in Sydney or elsewhere in Australia? (K. Macdonald, 68b Chats­worth Road, Silverstream, New Zealand). • The Plessey devices you require are available from Farnell Electronic Components in Sydney. There is also a Farnell repre­sentative in Auckland. His name is Chris Words­worth and his telephone numbers is (09) 537 4470. Maybe one of our readers can help supply the necessary information on your Telequipment D61A oscilloscope. 30-minute universal timer wanted I am interested in the “Universal Timer for Mains Applianc­ es” described in the August 1990 issue of SILICON CHIP. This gives nine minutes but I need a timer with a 30-minute Protective diodes for the LM317 In the Dick Smith 1993-94 catalog, a circuit is shown on page 210 for the LM317/LM350 regulator. There are two diodes shown on the circuit and it is stated that they are protection diodes in case the regulator input or output is short circuited. Because these regulators have inbuilt thermal and overload pro­ tection, I cannot see why the output needs any more protection. I find it hard to understand how they work (especially the diode connected between VOUT and ADJ and would appreciate an explanation. (D. A., Findon, SA). • The two diodes shown on the circuit are there to protect the regulator in case the input supply limit. Can the limit to this timer be altered and is there a similar timer on the market but with a 30-minute limit? (J. L., Wembley Downs, WA). • The time limit can be increased to 30 minutes by changing the .047µF capacitor at pin 2 of IC1 to 0.15µF. As far as we know, there is no equivalent timer on the market with a 30-minute limit. Electronics for anti-fouling No doubt there are many of your readers who own boats and like me, dread the yearly, or sometimes half-yearly haul out to scrape the barnacles and other marine growth from the bottom. After this is done, it is necessary to paint the bottom with anti-fouling paint which today does not seem as effective as it once was. If you have to use a crane to lift the boat out and in, it becomes expensive as well as messy. There has to be a better way and I believe there is an electronic unit overseas which keeps the pests off the hull. I have never seen one described in a magazine but I presume ultra­sonic transducers are employed. It may be possible to keep the transducers inside the boat if the hull is wooden or fibreglass. is removed or in case the output is short circuited. Diode D1, which is connected directly from VIN to VOUT of the regulator, protects it when the input supply voltage is removed but the output is still present, as could occur if you have a large capacitive or reactive load at the output. So, effectively, this diode shunts the output voltage back to the input and prevents reverse voltages from damaging the regulator. Diode D2, connected from the adjust terminal to the output terminal, protects against a short circuit load. What happens is that the capacitor at the adjust terminal tries to deliver its full current charge via the regulator if the output is short circuit. Diode D2 shunts this current to the output and again protects the regulator. As boat batteries have a hard time as it is, it would be preferred if nicads were used with perhaps a solar charger switching in as required. I hope SILICON CHIP can develop such a unit as I am sure it would be a very popular project for people who have to leave their boats in the water. (N. A., Bate­ mans Bay, NSW). • We have not heard of this idea before but we have published your letter in the hope that it triggers some information from read­ers. SLA battery charger has low ripple I have a 5A version of the SLA Battery Charger published in March 1990 and a 5A version of the SLA charger published in the June 1990 issue of SILICON CHIP. When I went to purchase a Son­nenschein A212/28AH gel cell battery, the retailer said that the charger sounds like a good unit but they would not sell the battery with replacement warranty unless the ripple content is within ±30mV per cell. Would you please advise? (G. R., Tura Beach, NSW). • This charger design delivers pure DC to the battery, not the unfiltered rectified DC of simple chargers. The actual ripple content when charging at 12V is less than 1mV peak-to-peak. September 1993  93 94  Silicon Chip POWER SOCKET EXTERNAL INPUT VIDEO IN VIDEO OUT 11 10 8  SEE TEXT 4.7k 1.5k 1.2k Q3 5.6k 10k 6.8k  7 6 100uF 680  Q6 150  2.2k 0.1 100uF 5 470W 100uF 10uF 7805 0.1 D3 4 1 270pF 75k 6 7 8 Q5 9 10 4 100uF 470 0.1 VR3 4.7k 6.8k 1M IC1 4066 1 47pF 11 IC2 4070 100pF 9 10k 100  1k 2.2k Q4 1.2k Q2 D1 1.5k 1.2k 0.1 1 2 100k 3 D2 10k 4.7k 1k Q1 82  Colour Video Fader, August 1993: there are several anoma­lies between the circuit and the wiring diagram. Also, due to spreads in the 4030/4070 XOR gates, it has been found necessary to make a number of changes. These corrections and changes are included on the revised wiring diagram reproduced here and this must be followed if you are building the project. Kitset suppli­ers have been advised of these changes. The changes are as follows: the 22kΩ resistor between the base of Q5 and the +5V supply rail should be 2.2kΩ; the 1kΩ resistor between the base of Q5 and the emitter of Q3 should be 1.2kΩ; and the 220Ω resistor at the emitter of Q4 should be 100Ω. On the wiring diagram, the connections to the video input socket are reversed. The 220pF capacitor at pin 4 of IC2b should be changed to 270pF. The 10kΩ and 12kΩ resistors connected in series between the +5V supply and ground at pin 2 of IC1a should be replaced with a 20kΩ trimpot (VR3). This trimpot should connect between the +5V and ground supply rails with the wiper connecting to pin 2 of IC1a. A hole will need to be drilled in the PC board to take the trimpot wiper. The trimpot will allow adjustment for correct sync pulse triggering by IC2a. VR3 is set up by first applying a video signal to the video input and viewing the output signal on your TV set (via your VCR). Rotate the Fade and Wipe controls fully clockwise with the wipe direction switch in the R-L position. Initially, centre VR3, then adjust anticlockwise until the picture starts to roll. Note this position. Now adjust VR3 clockwise and note the position that the picture completely loses sync. Finally, set VR3 in-between these two positions. The picture should now be in lock and the Wipe and Fade controls should operate. Having set the sync levels with VR3, the 10kΩ resistor at the base of Q3 may need to be adjusted to set the black level. You only need to do this if the wipe and fade controls do not provide a satisfactory black picture. If the picture is still visible on full fade or wipe, reduce the value of the 10kΩ resis­tor to 8.2kΩ. If this value does not provide sufficient bright­ness when the fader control is fully anticlockwise you may need to use a value between 10kΩ Fig.1: this revised wiring diagram for the Colour Video Fader includes all the changes described in the text. Note that you will have to drill an extra hole in the board to mount trimpot VR3. 470  Notes & errata 5 2 3 S1 1 VR1 and 8.2kΩ. This is achieved using paralleled values; eg, 10kΩ in parallel with 100kΩ gives 9.1kΩ. We also recommend earthing the potentiometer cases with a lead back to the video input socket as shown on the revised wiring dia­gram. Studio Twin 50 Stereo Amplifier, April, May 1992: since this amplifier was published, it has enjoyed modest popularity in the marketplace although the kit has since been discontinued. Part of the reason is that the original Darlington transistors have become virtually unobtainable. A number of kits have been supplied with TIP142/147 Dar­lingtons made by SGS-ATES and these have been found to be ther­mally unstable. If a Studio Twin 50 using these Darlingtons is left on long enough, it will most probably burn them out. The reason appears to be that the SGS transistors do not have the same bias and thermal characteristics as the Philips TIP142/147 transistors used in the original design. So as originally pre­sented, the circuit is not thermally stable with these SGS tran­sistors. Our remedy has been to modify the Vbe multiplier (Q17) and to increase VR2 the source degeneration resistors in the output stage. To be specific, the Vbe multiplier (Q7) is now a BD679 Darlington transistor and the resistor between its base and collector has been reduced from 680Ω to 330Ω. The 0.47Ω emitter resistors have been increased to 1Ω. This will slightly reduce the maximum power output. We have also reduced the quiescent current setting to around 25mA. These changes make the amplifier thermally stable but even so, its quiescent current stability is still not as good as would be the case with the originally speci­ fied Philips TIP­ 142/ TIP147 Darlington transistors. Amateur Radio, August 1993: the article on satellites requires a number of corrections. In Fig.1(a) page 73, the equations for apogee and perigee are transposed. Perigee height = a(1-e) - 6378km; apogee height = a(1+e) - 6378km. In Fig.1(b), the veloci­ ty of a low orbit satellite should be 26,000km/h not 13,000km/h. On page 74, in the paragraph beginning “AO-21 is a LEOS ... ”, the sentence referring to apogee and perigee heights should read: “Apogee and perigee heights are 1000km and 958km respectively”. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO CLASSIFIED ADVERTISING RATES _____________ _____________ _____________ _____________ _____________ ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recondensering, valve testing & mechanical refurbishment. Rejuvenation of wooden, bakelite & metal cabinets. Plenty of parts – require details for mail order. About 1200 radios within 16,000 square feet. Two-year warranty on full restoration. Open on Saturday 10am-4.30pm; Sunday 12.30-4.30pm. 109 Cann St, Bass Hill, NSW 2197 Phone (02) 645 3173 BH or (02) 726 1613 AH. _____________ _____________ _____________ _____________ _____________ FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (state which). Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 September 1993  95 TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 76 1291. Fax: (065) 76 1003. ICL 286 Board Kits All in one board with two serial, printer, IBM keyboard, high density floppy & IDE mono video interface. Up to 4Mb RAM, 80286-16cpu, MS-DOS compatible, 130 page manual, small size 170mm x 255mm. Max I/O kit for PCs, 7 relays, ADC, DAC, stepper driver, TTL inputs, with software $169 PC I/O card with 8255 chip 24 I/O lines programmable as inputs or outputs $69 1.5 watt AM broadcast transmitter XTAL locked $49 2.5 watt FM broadcast transmitter 88-108MHz. $49 Digi-125 audio power amp (over 19,000 sold since 1987) 50 watt/8 $14 125 watt/4 $19 New 200 watt/2 version $29 Infrared relay kit $9 Remote control tester $4 $299 Ampo little PC All in one NEC V40 CPU board, MS-DOS compatible, high density floppy. SCSI hard disk, 2 serial, printer, solid state hard disk, IBM keyboard interface, (4W), CMOS single +5V rail, up to 768Kb RAM, 384Kb ROM, 145mm x 250mm, 98page manual. $299 P.C. Computers SIMM 1Mb x 3 70ns 1Mb x 9 70ns 4Mb (72-pin) 4Mb x 9 70ns 4Mb x 8 80ns $80 $95 $320 $270 $250 DRAM DIP 1 x 1Mb 70ns 256 x 4 70ns 1Mb x 4 Z DRIVES SEAG 42Mb SEAG 107Mb SEAG 130Mb SEAG 214Mb SEAG 261Mb 28ms 15ms 16ms 16ms 16ms $10 $8 $35 $190 $283 $290 $343 $390 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $130 $320 $320 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 8Mb $340 $340 $680 MAC 2Mb SI & LC 4Mb P’Book $150 $330 CO-PROCESSORS 387SX to 25 $110 387DX to 33 $110 Laser PTR HP with 2Mb $203 Sales tax 21%. Overnight delivery. Credit cards welcome. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. PAY TV & SATELLITE Scrambling News Monthly, with the latest on de­ scrambling techniques & addresses, where to buy the latest descramblers. Send stamp for info. John Papp, Box 37885 Winnellie, NT 0821. ELECTRONIC COMPONENT KITS: 100s of capacitors and resistors with numerous switches, pots, transistors, clips and connectors. Limited number of kits at $120 each plus postage. COD only. Phone (07) 209 6874. INFRARED BINOCULARS: ex-NATO issue, with spare parts listing $500; American M24 tank infrared periscope, first time offered, very rare, collectors' item $600. Postage paid. Coming soon: Russian night vision gear. For more info. P. Samootin, PO Box 28, Berowra, NSW 2081. PEER TO PEER NETWORK SOFTWARE: for IBM PCs. The “$25 Network” Advertising Index Active Media Images ..................63 All Electronic Components ...........3 Altronics ................................ 30-32 Antique Radio Restorations.........95 A-One Electronics.................. 38-39 Av-Comm.....................................65 David Reid Electronics ..............23 Dick Smith Electronics........... 12-15 Ring for Latest Prices Electronic Fault Info. ...................63 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Harbuch Electronics....................23 Tel: (02) 980 6988 Fax: (02) 980 6991 PELHAM Instant PCBs................................96 Jaycar ................................... 45-52 36 Regent St, Kensington, SA. Phone (08) 332 6513. THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. 96  Silicon Chip MEMORY & DRIVES PRICES AT OCTOBER 2ND, 1993 JV Tuners.....................................23 L. E. Chapman.............................89 Oatley Electronics....................9, 59 links 2 or 3 PCs via serial ports at up to 115K bps. Uses only 15K RAM. Only $40. “Little Big LAN” offers multi-user record locking, linking via serial, parallel and/or Arcnet cards, up to 250 nodes and print spooling. Only $95. Both support printer re-direction. Prices are for a whole network. Add $3 for postage in Australia. For more information, send SASE to GRANTRONICS, PO Box 275, Wentworthville 2145. Phone A/H (02) 631 1236. PC Computers.............................96 RADIOTRON DESIGNERS HANDBOOK: 4th Edition (Langford-Smith) 1498pp (see EA, July 93, p99). A few only, secondhand, complete, fair condition, $100 ea plus $10 p&p. Hurley POB 245/R, Blackburn, Vic. 3130. Phone (03) 899 6337. Silicon Chip Binders............IBC, 63 NICAD BATTERY Charger Conditioner Analyser. As featured in SILICON CHIP. September 1993. Complete kit $135.00. Built and tested $185. P&P $10. C.I.E., 524 Abernethy St, Kitchener, NSW 2165. Phone (049) 91 1389. A WORD IS ONLY worth a micro-picture. Need the full picture? Send $2 in stamps, cash or Jelly Beans for Don's MS-DOS Demo/Promo disk. Covers all of my hardware kit projects. Don McKenzie, 29 Ellsmere Crescent, Tullamarine 3043. Phone (03) 338 6286. Pelham........................................96 Peter C. Lacey Services..............40 Philips Test & Measurement....OBC RCS Radio ..................................95 Rockby Electronics .......................7 Rod Irving Electronics .......... 66-71 Silicon Chip Back Issues....... 90-91 Silicon Chip Order Form..............33 Technical Applications.................64 Tektronix....................................IFC Transformer Rewinds...................96 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590.