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Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________ Vol.8, No.12; December 1995 Contents FEATURES 4 Knock Sensing In Cars Knock sensing is an important feature in modern cars and allows optimum performance while protecting the engine against possible damage. Here’s a rundown on how it works – by Julian Edgar 12 The Pros & Cons Of Toroidal Power Transformers Toroidal transformers have a number of advantages compared to conventional units. We examine their pros & cons – by Michael Larkin 92 Index To Volume 8 KNOCK SENSING IN CARS: HOW IT WORKS – PAGE 4 All the articles, projects and features for 1995 PROJECTS TO BUILD 8 Build An Engine Immobiliser For Your Car This simple circuit will repeatedly stall your car’s engine if a thief tries to start it and drive away – by John Clarke 22 Five Band Equaliser Uses Two Low-Cost ICs Build this circuit and customise the sound from your keyboard or guitar. It’s easy to assemble and has low noise and distortion – by John Clarke 28 CB Transverter For The 80M Amateur Band, Pt.2 The final wiring details plus the test and alignment procedure – by Leon Williams 39 Build A Subwoofer Controller Team this unit with a subwoofer loudspeaker for lots a low-down bass – by Leo Simpson BUILD AN ENGINE IMMOBILISER FOR YOUR CAR – PAGE 8 70 Dolby Pro Logic Surround Sound Decoder, Mk.2 Build this unit for big-theatre movie sound in your own home. This second and final article has the assembly and test details – by John Clarke SPECIAL COLUMNS 54 Serviceman’s Log Stop me if you’ve heard this one – by the TV Serviceman 64 Computer Bits Ram Doubler: extra sauce without the chips – by Geoff Cohen 81 Remote Control The mysteries of mixing –­by Bob Young FIVE BAND EQUALISER USING TWO LOW-COST ICs – PAGE 22 86 Vintage Radio Back to “original” – the Radiola 34E – by John Hill DEPARTMENTS 2 Publisher’s Letter 15 Bookshelf 16 Circuit Notebook 53 Order Form 60 Product Showcase 84 Mailbag 90 Ask Silicon Chip 91 Notes & Errata 95 Market Centre 96 Advertising Index SUBWOOFER CONTROLLER FOR LOTS OF BASS – PAGE 39 December 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA 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: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Electronics servicing is changing Recently, a longtime reader rang to say how much he en­joyed reading the “Serviceman” stories each month. A TV service­man himself, he went on to wonder aloud how long he would be able to keep going in the industry. Indeed, he had a very pessimistic view and said that there was little point in anyone training to do electronics servicing. From one point of view, he was absolutely correct. As time goes on, there will be less and less servicing done on TVs and other consumer electronic equipment. There are several continuing developments which are combining to bring this about. First, most consumer electronic equipment is now extremely reliable. Most purchasers of new TV sets could count themselves quite unlucky if they needed any service within the first five years; most would go 10 years or more before a visit to the serviceman became necessary. Second, in real terms, TV sets are still becoming cheaper, in spite of the trend to larger screen sizes, stereo and Dolby surround sound, multi-system capability (PAL & NTSC) and picture-in-picture. Combined with the gradual increase in labour and other costs involved in servicing, this means that the older a set is, the more likely that it won’t be worth fixing when it finally does fail. The accelerating trend to surface mount com­ponents is not helping in this regard because equipment with lots of SMDs can be virtually impossible to service at board level. Indeed, many servicemen would be out of business today if it were not for their bread-and-butter work with VCRs and mi­crowave ovens. Being largely mechanical and subject to plenty of wear and tear, VCRs can be expected to be an oft-serviced item for many years to come. And microwave ovens, because they operate under stringent conditions (high voltage and high temperature in grease and moisture-laden conditions), can also be expected to need service frequently. But even with these appliances, the cost squeeze is apparent. Some smaller microwave ovens are now very keenly priced and when they fail it is almost certain that it will be cheaper to dispose of them than to have them fixed. Fortunately, there is a raft of new equipment which does need servicing: computers with their disc drives, power supplies, monitors, printers and other peripherals, and in the business environment there are photocopiers, fax machines and so on. True, like all electronic equipment, these are becoming cheaper and more reliable. In fact, servicing has always been an evolving business. At one time, servicemen had all the work they could do with valve radios. In the fifties and sixties, they had the boon of TVs with lots of valves. With the advent of colour TV they got another boost. In the meantime, all the stuff they used to fix, such as irons, toasters and electric jugs, fell by the wayside. In the future, there will still be lots of gear to be fixed and people will be employed to do it. But whether there will be a friendly TV/video serviceman in your area could be open to doubt. 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 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. Macservice Pty Ltd High performance unleaded vehicles like these Holden Special Vehicles Commodores use knock sensing feedback loops to prevent potential engine damage caused through detonation. Knock Sensing Many cars with engine management systems have knock sensors. These are used to retard the ignition timing if knocking is occurring. As a result, most cars with knock sensors will provide increased performance if premium unleaded fuel is used because they can then employ optimum ignition advance. By JULIAN EDGAR 4  Silicon Chip Sensing when engine knocking is occurring has become in­ creasingly important in recent years. This is so for two reasons: (1) in older cars, the ongoing reduction in the lead content of fuel has meant that knocking is more likely; and (2) in cars using electronic engine management, knock sensing is used to allow the engine to run almost constantly on the threshold of knock. But while sensing knock initially looks to be a straight­forward task, it becomes much more complex when the subject is examined in depth. Engine knock occurs when the air/ fuel mixture ignites within the combustion chamber in an uncontrolled manner, rather than by the progressive action of a moving flame front. The Knock resonant frequency = 900/(πr) where the resonant frequency is measured in Hertz and “r” is the cylinder radius in metres. Electronic sensors Engine knocking can be sensed by any of the following means: (1) a pressure sensor installed flush with the combustion chamber; (2) a pressure sensor connected to the spark plug; (3) temperature measurement at the cylinder wall; (4) acceleration sensor, frequency tuned; (5) acceleration sensor, not frequency tuned; (6) force measurement at the cylinder head bolt by the use of a special washer; NUT CONNECTOR WEIGHT RESISTOR HOUSING PIEZO ELEMENT Fig.1: a typical knock sensor uses a piezoelectric element to generate a voltage output. This sensor is fitted to a turbocharged Subaru Liberty RS. Knock sensing is of particular importance in turbo cars. (Subaru). WITHOUT KNOCK AMPLITUDE terms “ping­ing” (a light, barely observable knock) and “pre-detonation” (knock caused by the ignition of the charge slightly before the full ignition of the flame front by the spark plug) are also commonly used. One definition of knock is “an undesirable mode of combus­ t ion that originates spontaneously and sporadically in the en­gine, producing sharp pressure pulses associated with a vibratory movement of the charge and the characteristic sound from which the phenomenon derives its name”. If allowed to occur in an unchecked manner, the very sudden pressure change within the cylinder can damage the engine. At worse, pistons, rings and even the head itself can suffer catastrophic damage. Obviously, heavy knocking is something to be avoided! In everyday driving, knock is most likely to be heard when using too high a gear for the engine speed and load conditions – like labouring up a steep hill with your foot flat to the floor, in third gear and travelling at 40km/h. Depending on the engine, knock can sound like a ‘ting, ting’ noise, or even a little like coins rattling in a coin tray. In some engines, the audible note is much deeper. In turbocharged cars, or cars where the compression ratio has been substantially increased, knocking can occur at high engine speed and high loads, making it very difficult for the driver to hear it above the general noise level. The frequencies generated by knock generally lie between 2kHz and 12kHz. The following equation can be used to estimate the knock resonant frequency for a specific engine: FK Y NC QUE FK = KNOCKING FREQUENCY IN THE COMBUSION CHAMBER FRE CRANK ANGLE KNOCKING FK 45° AFTER TDC Fig.2: The output of a knock sensor with and without knocking. Note that the amplitude of the knock frequency (FK) is substan­tially less than that of other frequencies also being transmitted by the block, making knock detection difficult. (Bosch). ENGINE SPEED = 2500 RPM (7) deformation measurement of the cylinder head bolt; (8) using a spark plug with a ring made of piezo ceramic material; and (9) the ionic current measuring method. The most commonly used are the acceleration sensors, which make use of piezo ceramics. These sensors consist of a piezoelec­tric disc and an associated seismic mass, with the latter either cast in plastic or formed by the body of the sensor itself. When a piezoelectric material is subjected to deformation, a propor­ tional voltage is generated. The sensor is mounted directly on the engine and so ‘lis­tens’ for sounds transmitted through the head and block. The fact that numerous components other than typical knock frequencies are contained within this noise signal is the major disadvantage of this technique. However, it has proven to be the most practical December 1995  5 FR EQ U EN CY AMPLITUDE CRANK ANGLE FK FK FK = KNOCKING FREQUENCY IN THE COMBUSION CHAMBER TDC ENGINE SPEED = 4500 RPM FK 90° AFTER TDC method of detecting knock. Fig.1 shows the components inside a typical knock sensor. Signal analysis Separating the sound of engine knock from the noise of valves opening and closing, pistons rising and falling, cam chains clanking and the general under-bonnet hubbub has proved to be the hardest part of detecting when knock is occurring. One way to reduce the problem has Fig.3: the structure-borne noise generated by knocking in the same cylinder for three successive combustions can be seen here. While the amplitudes of the knocking frequency are almost the same in all three cases, their positions change radically with respect to the frequency and time of occurrence. (Bosch). been to decrease the time for which the sensor is actually “listening”. The major compon­ents of knocking for a specific cylinder occur during a time “window” which extends from shortly after the piston reaches top dead centre to between 60-90 crankshaft degrees later. If the knock signal is averaged only when the engine is in these time windows, then the task is made slightly easier. Crankshaft position sensing is therefore required for this technique. INTERPRETIVE CIRCUIT Signal processing CONTROL CIRCUIT IGNITION MODULE KNOCK SENSOR GATE REFERENCE ACTUATOR ELECTRONIC CONTROL UNIT Fig.4: in this knock control system the analog sensor signal is processed by a 10kHz wide bandpass filter. The signal is then split, with one branch becoming the conditioned reference signal, against which the other signal is compared. A gate relates the test signal to crankshaft position, to determine whether or not it is in fact indicative of engine knock. If it is, the ignition advance is reduced. (Bosch). 6  Silicon Chip However, even examining the knock signal only within rela­tively narrow time windows doesn’t greatly ease the task! The upper part of Fig.2 shows the frequency spectrum of the struc­tureborne noise in the crankshaft angle range between TDC and 45° after TDC for one combustion, while the lower part of the diagram shows a knocking combustion over the same time period. The dark line, “FK”, is the knocking frequency and it is notable that other frequencies appear with substantially higher am­ plitudes than that of the knocking. In other words, it’s not enough to listen for the loudest noises. Instead, the specific frequencies within that noise must be pinpointed. Furthermore, when successive com­ bust­ ions are examined for the same cylinder, the patterns of noise, frequency and crank angle can vary substantially. Fig.3 shows the noise generated by knocking in the same cylinder for three successive combust­ ions. While the amplitudes are almost the same in all three cases, their positions change radically each time with respect to the frequency and time of occurrence during the combustion. In addi­tion, large differences occur between individual cylinders and from engine to engine in the same series! With a sensor tuned to a specific frequency, it can be difficult to always sense the largest amplitude in the frequency spectrum produced through knocking. Wideband sensors are there­fore more generally used, although extensive signal processing is then required to achieve good results. Unless the vehicle driver is to be an active participant in the engine management process, it is pointless letting him or her know that knocking is occurring. This means that all but one (aftermarket) knock sensing system is part of a wider automatic engine control strategy, with ignition timing retard and/or turbocharger boost reduction occurring as a result of knock detection. Fig.4 shows an example of a knock sensor control system. The analog sensor signal is processed so that signals irrelevant to knocking are filtered out; this is achieved by means of an ap­proximately 10kHz wide bandpass filter. Beyond the bandpass filter, the To reduce or eliminate these problems, some manufacturers have adopt­ed a self-learning system. Typically, this consists of five elements: a Pre-programmed Spark Advance Memory (PAM); a Gener­ ated Spark Retard Memory (GRM); an Updating History Memory (UHM); a Gain Function; and a Learning Function. PAM is a programmed spark advance map which gives the best fuel economy within the constraints of legal exhaust gas emis­sions. It has three dimensions: spark advance, engine speed and engine load, and the data is stored in read-only memory (ROM). GRM holds the spark retard map, which is updated every engine cycle. This data is held in random access memory (RAM) which is smaller than the PAM ROM because knock occurs only in a limited area of engine operating conditions. UHM holds the number of updating times of each combination of engine speed and load in GRM. The data in this memory repre­ sents the control history of GRM and has the same construction as the GRM. The Gain Function determines the retard or re-advance value of the ignition timing in proportion to the knock intensi­ty. Because direct measurement of the severity of knocking is difficult, the time between successive knock signals is used as an alternative value of knock intensity. Finally, the learning function defines the learning coefficient as a function of the UHM data. Results Using an adaptive approach such as that discussed above can give impressive results. Fig.5 shows the test results of the knock level during 10-40km/h wide-open throttle acceleration runs in third gear, with and without the Learning Control System (LCS). It can be seen that the LCS approach reduced the number of times the engine knocked in each acceleration test from eight times to only twice. Note also that without LCS, the propensity of the engine to knock actually increased over time – probably as a result of the engine increasing in temperature. Acceleration, though, was better with some knocking present – although probably at the expense of SC engine longevity! WITHOUT LCS x10-2G WITHOUT LCS 5 WITH LCS ACCELERATION Self-learning systems Turbocharged engines like this Subaru Liberty RS unit have very high cylinder combustion pressures, and so knocking can easily occur. Knock sensing in this car is used to retard only ignition timing but in some turbo cars, the boost is also reduced. NUMBER OF KNOCK TIMES signal is split, with one branch being conditioned to become the reference signal which is compared with the ‘useful’ signal. Further comparison with a test window related to crankshaft position determines whether or not the signal is in fact indica­tive of engine knock. As already stated, a “knocking” outcome leads to a retard in ignition timing in most engine management systems. However, depending on how well-developed the system is, the following problems can occur with this approach: (1) Harsh knock sounds in a steady control condition, caused by the difficulty in detecting engine knock; (2) Initial hard knock during abrupt acceleration, caused by the poor response time of the knock sensing system; (3) Unstable operation of the engine, caused by fluctuations in spark timing; (4) False alarming of the knock sensing system, causing the “limp home” engine mode to be adopted. 11 10 WITH LCS 9 0 1 2 3 4 1 5 ACCELERATION RUN NUMBER 2 3 4 5 Fig.5: the reduction in knock level that can be achieved by self-learning control systems can be seen here. The knock level during 10-40km/h wide-open throttle acceleration runs in third gear was reduced by about 80% with the implementation of the Learning Control System (LCS), although acceleration was slowed somewhat. (Toyota). December 1995  7 Protect your car with this Engine Immobiliser This circuit will immobilise your car if a thief tries to start it. Fit it to your car as cheap insurance. If a thief tries to steal your car, the engine will repeatedly stall and he will move on to easier pickings. By JOHN CLARKE There are many ways to prevent someone pinching your pride and joy. Poison gas, electrocution and automatic garrotting are some options that have been suggested by victims of car theft but sadly, these are illegal. Disabling the ignition is one of the better methods, because it prevents the thief from starting the car and driving off –unless he is keen to take your particular vehicle, he won’t want to bother finding out why the engine will not start. While simply disabling the ignition is effective, the fact that the thief may realise that the ignition has been disabled still places the car at risk. If the thief is inclined to undo the relevant wiring, the car can be started and driven away. 8  Silicon Chip On the other hand, if the thief has hot-wired your car and leaves the jumper in place, and if the coil has been permanently shorted by a hidden switch, there is another big risk –the coil could burn out. A better method is to have the ignition disabled on an intermittent basis. This is where our Engine Immobiliser comes in. Initially, the Engine Immobiliser allows the engine to be started but stops it after about 3.5 seconds. The car can then be restarted, only to stop again. After several more tries, the thief is likely to decide that the car has an intermittent problem and leave it. In the event that the thief persists, the job will get no easier. If he tries to pump the gas pedal, he is likely to flood the engine which will compound the problem. Note that there are many possible faults which will cause this sort of engine misbehaviour. They can range from dirt in the fuel causing blockages to an intermittent ignition which is exactly what it is. If the thief decides to lift the bonnet to investigate further, it is important that the single disabling wire be well hidden. Naturally, the switch to turn the Immobiliser on and off must be well concealed or camouflaged to look like one of the accessory switches, otherwise this subterfuge will be for nothing. Disabling the ignition The principle of this Engine Immobiliser is quite simple. In effect, a switch is placed in parallel with the car’s points or the ignition switching transistor, as shown in Fig.1 and Fig.2. Each time the Engine Immobiliser switch is on, it effectively shorts out the points or the switching transistor and prevents the coil from producing any sparks. By shorting out the points or ignition transistor and diverting the coil current for just a brief period, no Warning!! Don’t be caught out yourself and have the car stall just as you pull out into traffic. Always check that the Immobiliser switch is off before you start the car. For safety, it is wise to wait a few seconds before moving off, just to be sure that the Engine Immobiliser is not in effect. damage results to the coil as it possibly could if the ignition was disabled permanently. Now have a look at the circuit for the Engine Immobiliser in Fig.3. This circuit uses a high voltage Darlington transistor (Q1) which is connected in parallel with the points or the ignition transistor. IC1, a 555 timer, is connected to operate as an astable oscillator. It is powered from the ignition circuit of the vehicle via enable switch S1. Initially, when power is first applied, pin 3 of IC1 goes high. This holds transistor Q2 off and so Q1’s base is not driven. Thus the ignition system operates normally and the engine will start. Four 75V 1W zener diodes (ZD2ZD5) protect Q1 from high voltage transients generated each time the ignition coil fires. The 10µF capacitor at pins 2 and 6 of IC1 then begins charging via the 100kΩ and 220kΩ resistors. When the capacitor’s voltage reaches about +8V, the output at pin 3 goes low. This occurs some 3.5 seconds after switch-on. Pin 3 turns Q2 on via base current through the 1kΩ resistor and this turns on Q1 via its 82Ω base resistor. With Q1 on, any opening of the points or ignition transistor will not fire the coil. At the same time that the pin 3 output goes low, pin 7 also goes low to discharge the 10µF capacitor at pin 2 via the 100kΩ resistor. When the capacitor voltage drops to about +4V, pin 3 will go high and pin 7 will go open circuit to allow the capacitor to charge again via the 220kΩ and 100kΩ resistors. Since the 10µF capacitor now only has to charge from +4V to +8V, it only takes about 2.2 seconds before it begins discharging again. Hence, Q1 will be off for 2.2 seconds and on for about 0.7 seconds. So the car can be repeatedly started and will Fig.1: when fitted to a car with conventional ignition, the Immobiliser effectively shorts out the points and thereby stops the coil from producing spark voltage. Fig.2: when fitted to a car with electronic ignition, the Engine Immobiliser shorts out the main switching transistor. This does no damage because the coil current is intermittently shunted through the Immobiliser. ENABLE S1 4. 7W 470  220k 7 100k 4 8 3 1k Q2 BC327 E B IC1 555 6 2 C 1 100 16VW Q1 MJ10012 C 82 5W B 10 16VW E B E C VIEWED FROM BELOW C E B ENGINE IMMOBILISER +12V FROM IGNITION ZD1 16V 5W TO POINTS OR IGNITION TRANSISTOR ZD2 75V 5W ZD3 75V 5W ZD4 75V 5W ZD5 75V 5W Fig.3: the Engine Immobiliser is basically a 555 oscillator with a short duty cycle. It turns on high voltage transistor Q1 every 2.2 seconds to disable the car’s ignition system. just as surely stall before it can begin to move off. The process repeats itself until the ignition is turned off or switch S1 is turned off, to allow the car to run normally. IC1 is protected from transients December 1995  9 Fig.4: use this diagram when you install the parts on the PC board. by zener diode ZD1 which limits the supply voltage to +16V. A 4.7Ω resistor limits the zener current while the 100µF capacitor across the supply provides filtering of noise. Construction The Engine Immobiliser is made on a small PC board coded 05310951 and measuring just 47 x 61mm. The board is designed to clip into a plastic case measuring 82 x 54 x 31mm. Alternatively, the case could be dispensed with and the board protected by a length of large heatshrink tubing or wrapped in gaffer tape and mounted under the dashboard. Begin construction by inserting the three PC stakes for the external wiring Fig.5: this is the full-size etching pattern for the PC board. connections, as shown on the wiring diagram of Fig.4. This done, insert and solder the low profile components such as IC1, various zener diodes and resistors. Note that the zener diodes are mounted with a loop in the leads as shown in the photographs. This is to provide stress relief for the component. Make sure that the diodes are installed the right way around, as shown in Fig.4, otherwise the circuit may not work. Use the accompanying resistor colour code table to help you in identifying the correct resistor value for each position. The 5W resistor can be mounted against the PC board since it will not run hot. Now solder in the capacitors, taking care that the electrolytic capacitors are installed the right way around. Transistor Q2 is inserted and pushed down firmly so that its body is about 4mm above the PC board. Q1, the high voltage Darlington transistor, is mounted directly onto the PC board. It is secured with 3mm screws and nuts which make the collector to PC board track connection. Solder the nut nearest ZD2 to the copper pad to ensure a permanent connection and use a star washer under the screw head. Testing The circuit board can be initially tested using a 12V battery or DC power supply and a multimeter. Connect power to the board between the GND and “ignition via S1” terminals. Now set your multimeter to check that +12V is present at pins 4 & 8, then measure the voltage at pin 3. It should switch high (ie, +12V) for about two seconds and low (close to 0V) for about 0.7 seconds. If that checks out, turn off the power and connect a resistor between the collector of Q1 and positive supply (any value from 1kΩ to 10kΩ will do). Now re-apply power and check that the collector voltage goes high for approximately two seconds and low for 0.7s. If it checks out correctly, the board is ready for installation. Installation The zener diodes are mounted with a loop in one of their leads as shown here. This is to provide stress relief for these components. Make sure that all polarised parts are correctly oriented. 10  Silicon Chip As previously mentioned, the Engine Immobiliser must have all its wiring and the unit itself well concealed. We recommend that the unit be installed under the dashboard. The only wire passing through the firewall Above: installed in a plastic case or sheathed in heatshrink plastic, the unit should be concealed underneath your car’s dashboard. Left: solder the nut near ZD2 that’s used to secure Q1 to ensure a good connection to the copper track of the PC board. will be the connection to the ignition coil’s negative terminal. Note that the collector of Q1 and its associated zener diodes can have up to 300V on them when the coil fires. Consequently, they must be well isolated from contact with any under-dash wiring or metalwork. Mounting the board in a plastic case or sheathing it with heatshrink sleeving will do the job. The GND connection can be made directly to a nearby chassis point already used for existing wiring. Use a crimp eyelet for this termination. The enable switch S1 must be mounted in a concealed position where it can be easily reached from the driver’s seat but its purpose should not be obvious to anyone but yourself. Be sure also to install this switch in a location where it cannot be accidentally bumped. You might also have two such switches in series so that they have to be in the right setting before the car can be started. Now connect the “ignition via S1” terminal on the PC board to the wiper of S1. The contact terminal of the switch is wired to the fused side of the ignition switch. Use a “quick connect” spade connector to make the connection into the ignition wire or use whatever matches the harness connections in the car. The wire from Q1’s collector to the coil negative terminal should pass through the firewall via an existing grommet. Where the wire connects to the coil, make sure that it is well disguised so that it is not obvious that there is an extra wire installed. If possible, conceal it within the existing harness plastic sheathing. Does it immobilise? Now for the big test: enable the Engine Immobiliser by switching S1 to the on position and start your car. It should stall within about three seconds after you first turn the key. Try again and the engine should stall again. If it doesn’t stop the engine – you haven’t wired it in correctly. Once you have it operating correctly, switch off S1, start the car again and take it for a run. This is to check that the Engine Immobiliser does not affect normal operation in any way. Now provided you remember to switch on the Immobiliser each time you leave your car, you can enjoy extra peace of mind knowing that no-one SC can take it for a joy-ride. PARTS LIST 1 PC board, code 05310951, 47 x 61mm 1 SPST switch (S1) 3 PC stakes 2 3mm screws, nuts and star washers Semiconductors 1 555 timer (IC1) 1 MJ10012 500V NPN Darlington (Q1) 1 BC327 PNP transistor (Q2) 1 16V 5W zener diode (ZD1) 4 75V 5W zener diodes (ZD2ZD5) Capacitors 1 100µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic Resistors (0.25W 1%) 1 220kΩ 1 470Ω 1 100kΩ 1 82Ω 5W 1 1kΩ 1 4.7Ω Miscellaneous Automotive hook-up wire, eyelet lugs, self tapping screws, plastic case 82 x 54 x 31mm or heatshrink tubing. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 Value 220kΩ 100kΩ 1kΩ 470Ω 4.7Ω 4-Band Code (1%) red red yellow brown brown black yellow brown brown black red brown yellow violet brown brown yellow violet gold brown 5-Band Code (1%) red red black orange brown brown black black orange brown brown black black brown brown yellow violet black black brown yellow violet black silver brown December 1995  11 The pros & cons of toroidal power transformers This article describes how toroidal power transformers can yield lower hum, less weight and size, and improved efficiency compared with conventional E-I laminated transformers. The disadvantages include slightly higher cost and greater inrush currents at switch on. By MICHAEL LARKIN* Why choose a linear power supply? Since most digital/analog circuits cannot operate from rectified, filtered, power line voltage, a step-down conversion unit must be used. Electronic equipment designers have two main methods for powering their equipment: switching and linear supplies. If the product’s operational and environmental constraints permit high levels of radiated and conducted EMI (electro­magnetic interference), slower closed-loop response to load variations and reduced reliability, then the cost, power density and efficiency of a switching supply becomes attractive. By many designs cannot tolerate the characteristics of switching supplies, making linear supplies the only viable alter­native. Examples of these products include high quality audio mixers and amplifiers, lighted matrix displays, and video processing and display equipment. Toroidal transformers are inherently time-consuming and tedious to make. The total length of wire for each winding must first be loaded onto a bobbin which is then wound onto the core, together with inter-layer insulation. 12  Silicon Chip A transformer is required to step down the AC voltage from that of the power line to the rectification, filtering and regu­lation circuits in a linear supply. The inherent advantages of the toroidal (donut-shaped core) transformer, relative to other core configurations, may be summarised generally as a nearly ideal magnetic circuit, which results in lower stray magnetic field, smaller volume and weight, less audible hum and higher efficiency. Which benefits are of interest in a particular appli­cation depend on the type of product and sensitivity of other circuitry to stray magnetic fields. Ideal magnetic circuit The toroidal transformer has a nearly ideal magnetic cir­cuit. In an E-I laminated transformer it is not possible to align the grain structure of the stamped laminations with the flux path over the entire magnetic path. This inability leads to higher core losses and less efficient operation when compared to tor­oids. Fig.1 shows a comparison of grain alignment with flux path for a toroidal and an E-I transformer. Conventional laminated transformer designs employ a bobbin-wound coil placed over a stack of “E” shaped laminations. An “I” shaped stack is butted onto the “E” , completing the magnetic path. The connection between the “E” and “I” is never a perfect junction, causing a discontinuity or air gap in the magnetic flux path. This gap has higher reluctance and so causes a greater radiated magnetic field. Similarly, in “C” cores, where strip steel is wound into an oblong shape then cut into two identical “C” shapes, air gaps are present at the junctions where the cut faces of the “C” pieces meet to complete the magnetic circuit. In any core with a gap, the properties of the gap are unpredictable and depend on pressure and the quality of the mating surfaces. A second feature which gives rise to leakage flux in E-I and C-core transformers is the discontinuity in the windings which surround the flux path. The windings are concentrated in short regions of the laminates, which leaves large portions of the flux path exposed. The abrupt transition from windings to bare laminates creates opportunities for the flux to escape the confinement of the core and form linkage paths outside the trans­former. The transitions in the windings can also lead to high leakage inductances for the device. By contrast, there is no air gap in the core of a toroidal transformer. The core is tightly wound onto a mandrel, like a clock spring, from a continuous strip of grain-oriented steel. Spot welding at the beginning and ends prevents loosening. The stresses introduced by de-reeling and winding, which could result in unacceptable core losses, are relieved by annealing the wound core in a dry nitrogen atmosphere. The result is a stable, pre­dictable core, free from discontin­ uities, holes, clamps and gaps. Fig.2 compares the stray magnetic field at 100mm from E-I laminated and toroidal transformers of equal power rating. If shielding with a copper strap and careful orientation of the E-I power transformer and sensitive devices can improve stray field immunity sufficiently, without undue expense, then a toroidal transformer may not be justified. However, the toroid’s substan­ tially lower stray field may mean the difference between accept­ able and unacceptable operation of sensitive circuitry. Reduced weight and size In the E-I core structure, the magnetic flux is not aligned with the grain of the steel for approximately 25% of the flux path (see Fig.1). This misalignment causes higher magnetisation losses and reduces the maximum flux density that can be utilised in the core. Higher efficiencies have been made possible by using high grades of grain-oriented steel which increases flux densi­ties while minimising loss- Fig.1: comparison of grain alignment with flux path for a toroidal and an E-I transformer. In the toroidal transformer, the grain alignment is always optimum. Fig.2: this graph compares the stray magnetic field at 100mm from E-I laminated and toroidal transformers of equal power rating. If the E-I transformer has a single section bobbin (or no bobbin) it may be possible to fit a copper shielding strap to greatly reduce the stray field. es. However, maximum utilisation of these properties occurs only when the flux in the steel is paral­lel to the grain direction. It can be seen in Fig.1 that the flux in a toroidal core is 100% aligned with the grain of the steel. The typical working flux density of E-I laminates is from 1.2 to 1.4 Tesla, whereas toroids typically operate from 1.6 to 1.8 Tesla. For a given core cross-section, the voltage induced in a winding is directly proportional to the flux density and the number of turns. The higher allowable flux density of a toroid thus requires fewer turns of wire in all windings to achieve the same result. Comparison of a conventional 960VA transformer with an equivalent toroid shows the weight and volume of the toroid to be only half. In an existing product which uses an E-I transformer, it is often possible to fit a toroid which has close to the same footprint but is only 60% as tall. In the case where it is desir­able to increase the power supply power rating without increasing its size, the E-I transformer might be replaced with a toroid which is the same size but has 1.5 to 2-times the power rating. It is true that the empty centre hole in a toroidal trans­ former, which is needed to enable winding, occupies some wasted volume. This wasted volume deficit is overcome by the toroid’s December 1995  13 Fig.3: this circuit can be used to substantially reduce the inrush current for a toroidal transformer. The relay coil is energised by the AC input voltage and the delay in the relay operation, which switches R1 out of circuit, is sufficient to reduce the inrush current to a safe value. volume advantage at roughly 50VA and above. So, in transformers rated less than 50VA, the size is not reduced but the other advantages remain. Audible hum Audible hum in transformers is caused by vibration of the windings and core layers due to forces between the coil turns and core laminations and due to magnetostriction in the core itself, which is manifest at any gaps in the core. Clamps, bands, rivets and welds cannot bind the entire structure and varnish penetrates the laminations only partially. As a result, laminations tend to loosen over time and produce increasing noise. On the other hand, the nature of the toroidal transformers’s construction helps to dampen acoustic noise. The core is tightly wound in clock spring fashion, spot welded, annealed and coated with epoxy resin. Audible hum, heard immediately after application of power, may be noticeable in the toroid and then die down to a quieter level a few seconds after power is applied. This is a result of the toroid’s greater inrush current, which is discussed below. Efficiency The efficiency of a transformer is stated as: E = Pout/Pin where Pout is the power delivered to the load and Pin is the power input to the transformer. The difference between Pin and Pout is represented by the losses in the core and windings. The ideal magnetic circuit of the toroid and its ability to run at higher flux density than E-I laminates reduces the number of turns of wire required and/ or the core cross-sectional area. Both benefits reduce the losses. Toroidal transformers are typically 90-95% 14  Silicon Chip efficient, whereas E-I laminated types are typically less than 90% efficient. Inrush current The characteristics which give the toroidal transformer advantages also contribute to a disadvantage: high inrush current with the initial application of power. The absence of a gap in the toroidal core means that the maximum possible remanence (residual magnetisation of the core in a particular direction and magnitude) can be substantially more pronounced in a toroid than in an E-I type. The core “stores” the static bias when the power is switched off. If the removal of power occurs at an unfavourable time, the strongest magnetic remanence will be stored in the core. When power is again applied to the primary , the peak inrush current may be as great as Vpk divided by Rp, where Vpk is the peak primary voltage and Rp is the primary resistance, depending on the power capability of the transformer and how strongly the core was magnetised. To cope with these very high surge currents, a fuse or circuit breaker with an appropriate time delay is needed; a fast blow fuse will not last for more than a few off-on power cycles. In high power applications, more exotic means may be re­ quired to ensure protection that will survive inrush, yet still protect in fault situations. One method involves a relay with its coil across the switched power line. Prior to application of power, a resistance is present in series with the transformer primary. After power is applied to the relay coil and transform­ er, the electromechanical relay begins to move from the deener­ gised to the energised contact position. If the relay takes long enough to operate, then the inrush current has been limited by the series resistor and the core’s magnetic bias has been elimi­nated. An example of this circuit is shown in Fig.3. Higher cost Toroidal transformers are manufactured individually and have a high labour content. Conversely, the plastic bobbins of small E-I laminated transformers can be wound on machines which handle several bobbins at once and operate nearly unattended. The process of applying inter-winding insulation is also more labour intensive in toroidals. E-I laminate insulation consists of one wrap of adhesive tape or Kraft paper, whereas insulation in toroids is applied in an overlapping spiral fash­ ion. This conforms best to the curved surfaces. The difference in labour content is reduced for power rat­ings of 500VA and above. Large transformers are usually made in small quantities and become more difficult to wind as the core becomes larger and the wire gauges thicker. 3-phase toroidal transformers Employing toroidal construction for 3-phase transform­ers does not offer a volume advantage over the E-I laminated type. The E-I configuration is more suited to 3-phase transform­ers, since the three legs of the E portion of the core can be used for the a-b-c phase windings and flux is then efficiently (except for the aforementioned non-alignment of flux to steel grain) linked a to b, b to c and c to a. Providing a 3-phase transformer using standard toroidal cores and winding techniques requires three separate transformers. This is inefficient use of volume. In some applications, where a very low profile transform­er is required and the real estate for 3-phase transformers is available, a toroidal 3-phase transformer set is bene­fi­cial. Summary The choice between toroidal and E-I laminated transformers depends on the application. Toroidal transformers offer low stray fields, smaller size and weight and higher efficiency, which may be required or desirable in many products. *Michael Larkin is the Managing DiSC rector of Tortech Pty Ltd. BOOKSHELF Radio Frequency Transistors Radio Frequency Transistors: Principles and Practical Applications, by Norm Dye & Helge Granberg. Published 1993 by ButterworthHeinemann. Hard covers, 235 pages, 260 x 178mm, ISBN 0-7506-9059-3. Price $85.00. This book with its 13 chapters covers the subject of RF (radio frequency) transistors in great detail. It begins in chapter one by detailing RF data sheet parameters. Items covered include DC specifications, maximum ratings, high power and low power transistor characteristics, linear modules and suggestions on the additional data which will be provided for RF transistors in the future. Chapter two, titled RF Transistor Fundamentals, starts out by describing the differences between low frequency and high frequency transistors, even though they are manufactured using similar processes. In particular, RF transistors are designed with “small” horizontal and vertical structures to allow opera­tion at higher frequencies. The authors go on to detail how, at RF, components are not the same as at lower frequencies. Resis­tors take on the properties of inductors, capacitors look like resistors and inductors appear as capacitors. They explain that RF transistors are manufactured for use at 7.5, 12.5, 28 and 50 volts but that a 50V device should not be used with lower voltag- es as it will not deliver its maximum power, or operate as efficiently as it would at its rated voltage. Bandwidth considerations in low frequency circuits are normally due to the circuit design. At HF and higher powers, the input impedance of the device becomes too low to be practical for circuit designers. To alleviate this problem, manufacturers have plac­­ ed impedance matching networks inside the device package. In general, bipolar transistors designed for VHF and rated 40-50 watts will have this feature. The chapter concludes with a brief run down on other factors involved in the selection of suitable RF power transistors. Chapter three compares parameters and circuitry of FETs (field effect transistors) and BJTs (bipolar junction transis­tors). There are still some areas where the junction transistor excels, although the lower drive requirements and better stabili­ty of FETs makes them attractive in many applications. The need for handling precautions with MOSFETs (metal oxide silicon FET) are discussed, along with a comparison of thermal runaway exhib­ited by BJTs and FETs. The three BJT circuit configurations (common emitter, common base and common collector), along with the FET equivalents, are then covered. Chapter four covers the classes of operation for power amplifiers. The usual class A, AB, B and C are detailed, along with class D and E. The latter two are switching amplifiers, class D being driven with a sine or square wave. Class E is similar except an LC network is added in the output circuit to compensate in part for the FET output capacitance and also to help reduce switching overlap. This chapter goes on to discuss forms of modulation, bias­ing and the operation of devices in pulse mode (radar, etc). Chapter five covers the procedures involved in ensuring device reliability, the main one being die temperature. Die temperatures around 150°C are considered the maximum for longterm reliability. Other potential problems under the designer’s con­trol are supply voltage, base drive voltage and load mismatch. The chapter concludes with details of gate-source breakdown in FETs and a method of zener diode protection. Construction techniques are probably the area of greatest difficulty for the newcomer to RF. Printed circuit board layouts that work well at audio frequencies may refuse to amplify, or on the other hand, may amplify too well (oscillate). Most expertise comes with experience and the details of PC board layout and the tips given in chapter six will assist the new RF designer. The correct methods for mounting RF devices for optimum efficiency and reliability are also discussed. Chapter seven covers power amplifier design, discussing the merits of single ended, parallel and push pull designs. Four pages are then devoted to impedance matching networks followed by a practical design example. continued on page 27 December 1995  15 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. Camper van inverter controller This circuit is used to switch a 12VDC to 240VAC inverter for a camper van. The inverter is located close to the battery to minimise voltage drop on the DC side and is remotely switched by the relay. Using the relay avoids having the inverter on stand-by during which it pulls 250mA. The circuit works as follows. Capacitor C1 charges while switch S1 is open. When S1 is closed, to operate the inverter, C1 discharges and transistor Q3 saturates to provide high current Simple LED chaser using transistors This LED chaser circuit uses only three transistors and no ICs. The circuit causes 15 LEDs to chase each Optical tachometer has digital readout This circuit shows how to combine the optical tachometer published in the May 1988 issue with the digital display of the LED stroboscope from the December 1993 issue. The two ranges shown (x1 and x10) will give maximum readings of 1000 (999 + 1 = 000) and 10,000 RPM. A further range of x30 could be added by using another contact on the range switch as well as another resistor and trimpot. 16  Silicon Chip (about 180mA) to close the relay contacts (RLY1). Q3 then turns off and Q1 and Q2 provide a low constant hold current – around 63-66mA to keep the relay closed. Diode D2 protects the transistors against back-EMF from the relay coil. Switch S2 and LP1 provide low level light without waiting for the inverter to fire up. C. Mooney, Seaford, SA. ($25) other, with five on at any one time. The 15 lights can be arranged to provide a convincing “chase” effect. The three transistors, capacitors and resistors are an extension of a conventional cross-coupled multivibrator with the switching rate determined by the 22µF capacitors and 33kΩ resis­tors. The 330Ω resistors limit the current through the LEDs. S. Isreb, Traralgon, Vic. ($25) The complete circuit works as follows: IC1 is a 555 timer operat­ing at 20kHz to drive Q1 and infrared LED 1 as the light source. LED 1 is pulsed on for about 4.6% of the time, with peak currents in excess of 100mA. This 20kHz pulsed light source is reflected or chopped by the rotating device being measured. The reflected light is detected by infrared photodiode ID1 and transistors Q2-Q4 which function as a high gain amplifier. Its output consists of 20kHz signal bursts which are fed to Schmitt trigger IC2a which drives diode D2 and a .022µF filter capacitor. This removes the 20kHz modulation from the pulses which can then be counted. The filtered pulses are fed to the counter via Schmitt trigger IC2b which also drives IC2c and the detect LED (LED 2). IC4 is a 3-digit counter which drives IC5, a 7-segment decoder/driver. Together, IC4, IC5 and transistors Q5-Q10 provide multiplexed drive to the three 7-segment displays. IC3 is a hex inverter which provides the latch enable and reset signals for IC4 so that it can count correctly. Calibration adjustments are provided by VR1 & VR2. The circuit can be powered by a 9-12V DC plugpack. SILICON CHIP December 1995  17 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 Five band equaliser uses two low cost ICs Liven up your keyboard, guitar or music system with this 5-band equaliser. It only uses a few low cost parts and will enable you to “customise” the sound of your system just by twiddling a few knobs. By JOHN CLARKE These days, many home music systems have equalisers and so do the more expensive car sound systems. They can be used to tailor the sound quality by removing unwanted frequency peaks and boosting frequency troughs, to flatten or enhance the overall frequency response. They are also used during recording sessions to enhance the sound of particular instruments or even to change the sound of vocalists. An equaliser can be thought of as an expanded tone control where the audio spectrum is divided up into several sections or frequency bands. 22  Silicon Chip Each of these bands can be boosted or cut independently. Some equalisers can control 30 or more bands but this design is more modest with just five frequency bands. These bands are centred on 63Hz, 250Hz, 1kHz, 4kHz and 16kHz. A potentiometer is used to boost or cut the signals in each frequency band and so the PC board has five pots but no other controls. These are standard rotary pots and not the linear sliders which are often used on equalisers. However, you can substitute slider types if you wish. This equaliser does not use fancy hard-to-get ICs but its performance is quite respectable, as detailed in the accompanying spec panel. Its overall boost and cut performance is detailed in the composite graphs of Fig.1. This shows the response of each band separately as it is set to the extremes of boost and cut. As can be seen from Fig.1, the maximum boost and cut is ±12dB. Also shown on the graphs is the frequency “ripple effect” when all controls are set to boost and cut. This is an unrealistic setting but it indicates what happens to the frequency response when two adjacent bands are set for boost or cut – you get a dip or a peak between the bands. The circuit is very quiet at better than -94dB with respect to 1V and has very low distortion, typically less than .001%. Equaliser principles Typical equalisers do not work the same way as tone controls which boost or cut frequencies above or be- low a certain frequency. As already indicated, an equaliser boosts or cuts defined frequency bands which have particular “centre” frequencies. Thus, we have the notion that each band is tuned on a particular centre frequency and that requires a circuit which is tuned or resonates, as defined by an LC (inductor-capacitor) network. This can be seen in Fig.2 which can be thought of as a one-band equaliser. In essence, we have an op amp (IC1a) connected as a non-inverting amplifier and a feedback network with a potentiometer (VR1) with its wiper connected to ground via an LC network. This LC network sets the centre frequency of the band. With VR1 centred, the op amp has unity gain and the tuned series LC circuit has no effect on the frequency response. In other words, an input signal passes through the circuit unchanged and with a flat frequency response. This is the “flat” setting for the equaliser. When VR1 is rotated to its boost setting, the LC network is connected directly to the inverting (-) input of the op amp, shunting the negative feedback to ground. At the resonant frequency, the impedance of the LC network is at a minimum. Thus, the feedback will be reduced and the gain will be at maximum, at the resonant frequency. Conversely, when potentiometer VR1 is rotated to the maximum cut setting, the LC network is connected to the non-inverting (+) input, and tends to shunt the input signal to ground. This results in a reduction (cut) in gain at the resonant frequency. Naturally, at intermediate settings of the potentiometer, the boost or cut is reduced in proportion. The centre frequency of the circuit can be obtained from the formula: f = 1/2π√(LC) We could design an equaliser using inductors and capacitors as shown in Fig.2 and that is exactly how equalisers were made more than 20 years ago. However, inductors for audio circuits tend to be quite heavy and bulky and they have tendency to pick up hum which we don’t want. So instead of using inductors we use gyrators. A “gyrator” is a pseudo inductor using an op amp and a capacitor. This circuit is shown in Fig.3. In an inductor, the current lags or is delayed by 90° with respect to the AUDIO PRECISION FREQRESP AMPL(dBr) vs FREQ(Hz) 20.000 25 OCT 95 10:59:54 15.000 10.000 5.0000 0.0 -5.000 -10.00 -15.00 -20.00 20 100 1k 10k 20k Fig.1: this composite graph shows the boost and cut performance of the equaliser at the five centre frequencies. Maximum boost and cut is ±12dB. Also shown is the frequency “ripple effect” when all controls are set to boost and cut. Fig.2: this is the essence of a graphic equaliser. A series resonant LC network and potentiometer is connected into the op amp feedback network for each frequency band. Fig.3: the circuit of a gyrator. The op amp simulates an inductor by a vector transformation of the current through the capacitor C. The resulting inductor is equal to the product of R1, R2 and C. Fig.4: these waveforms show the phase differences between current and voltage for the various points on the circuit of Fig.3. Notice that the output current IOUT lags the input voltage VIN by 90 degrees. Thus, as far as the signal source is concerned, the circuit behaves as an inductor. December 1995  23 +15V 0.47 INPUT 12 100k 13 4 IC1b TL074 10k 14 10 33pF 11 1k 8 IC1a 9 10 OUTPUT 22k -15V 10k 47  33pF 47 250Hz VR2 50k LIN 63Hz VR1 50k LIN 0.22 0.82 3 2 1 220k 6 7 220k IC2a 2 TL074 4 2k 270pF 68pF 11 3 IC1d 1.8k -15V .001 5 IC1c .0033 1.8k .0047 16kHz VR5 50k LIN .015 2k .018 4kHz VR4 50k LIN .056 2k 220k 1kHz VR3 50k LIN 10 5 1 220k 6 IC2b 7 220k 9 IC2c 8 +15V REG1 BR1 1B04 REG2 15V 240VAC 0V 15V I GO IN 470 25VW GND 5-BAND EQUALISER Fig.5: the final circuit uses five gyrators (IC1c,d & IC2a,b,c) to give centre frequencies of 63Hz, 250Hz, 1kHz, 4kHz and 16kHz. Note that the fourth op amp in IC2 is not used. voltage waveform. With a capacitor, however, the voltage lags the current by 90°. To simulate the inductor, the voltage lag of the capacitor must be converted to a leading voltage compared to the current. Consider an AC signal applied to the input of the circuit (Vin) of Fig.3. Current will flow through capacitor C and resistor R1. Because it is connected as a voltage follower, the op amp will reproduce the voltage across R1 at its output. This voltage will now cause a current to flow in R2 and it adds vectorially with the input current and the resulting total current lags the input voltage. The waveforms in Fig.4 show the phase differences between current and voltage for the various points on the circuit. Notice that the output current IOUT lags the input voltage VIN by OUT +15V 10 16VW 0.1 GIO 470 25VW 24  Silicon Chip REG1 7815 90°. Thus, as far as the signal source is concerned, the circuit behaves as an inductor. The value of simulated inductance is given by the equation: L = R1 x R2 x C where L is in Henries, R is in Ohms and C is in Farads. By substituting the gyrator for the inductor in the circuit of Fig.2, we have the basis for a complete equaliser. In our circuit, we need five gyrators and their accompanying potent­ iometers and capacitors. The complete circuit is shown in Fig.5. It comprises two quad op amps and associated potentiometers and gyrator components. The gyrator op amps are IC1c, IC1d, IC2a, IC2b and IC2c. Note that the fourth op amp in IC2 is not used. IC1b is a unity-gain buffer for the input signals. These are AC-coupled GND IN REG2 7915 10 16VW OUT -15V via a 0.47µF capacitor to the non-inverting input at pin 12. The output of IC1b is applied to the equaliser circuit via a 10kΩ resistor. The 33pF capacitor provides high frequency rolloff and prevents instability in the circuit. Similarly, the 33pF capacitor in the negative feedback path for IC1a provides some high frequency rolloff. The five potentiometers are connected between the inputs of op amp IC1a and the overall boost and cut range for each frequency band is restricted to about ±12dB with the 47Ω resistors at pins 9 & 10. As you can see, the capacitor values used in the resonant networks are large for the low frequency bands and small for the high frequency bands. The output of IC1a is AC-coupled via a 10µF capacitor and a 1kΩ resistor. The resistor is there to prevent instability in the op amp if it is connected to long lengths of cable. The op amps are run from ±15V This 5-band mono equaliser operates at line levels (ie, CD, tape and tuner levels) and gives a maximum boost and cut of 12dB at the centre frequencies of 63Hz, 250Hz, 1kHz, 4kHz and 16kHz. Fig.6: the parts layout for the PC board. Note that the pot cases must be earthed via a length of tinned copper wire. TABLE 1: RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 5 1 1 2 3 2 1 2 Value 220kΩ 100kΩ 22kΩ 10kΩ 2kΩ 1.8kΩ 1kΩ 47Ω 4-Band Code (1%) red red yellow brown brown black yellow brown red red orange brown brown black orange brown red black red brown brown grey red brown brown black red brown yellow violet black brown 5-Band Code (1%) red red black orange brown brown black black orange brown red red black red brown brown black black red brown red black black brown brown brown grey black brown brown brown black black brown brown yellow violet black gold brown December 1995  25 Fig.7: this is the actual size artwork for the PC board. Check the board carefully for etching defects before mounting any of the parts. supply rails and these are provided by the 3-terminal regulators REG1 and REG2. The input voltage can be a centre tapped 30V AC supply or a DC centre tapped source which is greater than ±18V but less than ±35V. The AC input is applied to the bridge rectifier BR1 and two 470µF capacitors to provide plus and minus DC rails for the 3-terminal regulators. PC board assembly The PC board is coded 01309951 and measures 167 x 65mm. The component overlay diagram is shown in Fig.6. Begin assembly by checking the PC board against the published pattern in Fig.7. Look for possible broken TABLE 2: CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value 0.82µF 0.47µF 0.22µF 0.1µF .056µF .018µF .015µF .0047µF .0033µF .001µF 270pF 68pF 33pF IEC Code EIA code 820n 824 470n 474 220n 224 100n 104 56n 563 18n 183 15n 153 4n7 472 3n3 332 1n0 102 270p 271 68p   68 33p   33 Specifications Frequency Response All controls centred ....................... 20Hz to 20kHz within ±0.5dB Boost and cut ............................... ±12dB (see graph of Fig.1) Centre frequencies ....................... 63Hz, 250Hz, 1kHz, 4kHz & 16kHz Signal Handling Gain .............................................. Unity Maximum input & output .............. 8V RMS (all controls centred) Input impedance ........................... 100kΩ Output impedance ........................ 1kΩ Harmonic Distortion <.005% for frequency range 20Hz to 20kHz; .0017% <at> 1kHz and 3V, typically less than .001% Signal to Noise Ratio With respect to 1V RMS ............... -94dB unweighted (20Hz-20kHz); -97dB A-weighted Power Supply ................................. ±15V at 30mA 26  Silicon Chip tracks or shorts. Fix any defects before inserting any of the components. First, insert the PC stakes located at all the external wiring points. There are seven in all. Next, do the wire links and resistors. Table 1 shows the resistor colour codes but it is always a good idea to check each value with a digital multimeter as some of the colours can be difficult to distinguish. Take care when installing the 3-terminal regulators and whatever you do, do not get them swapped around otherwise they’ll self-destruct as soon as power is applied. Each regulator is secured to the PC board using a screw and nut but no heatsinks are required. The bridge rectifier (BR1) looks like an 8-pin IC with 4 pins missing. Make sure you insert it the right way. The same remark applies to the two ICs. When installing the MKT capacitors, use Table 2 if you have any doubt about the coded values. Make sure that the electrolytic capacitors are installed the right way around, as shown on Fig.6. The five potentiometers are PC mounting types which are simply inserted and soldered into the board. When they are all soldered in, solder a length of tinned copper along the top of each pot and to the earth terminal as shown in the photo. This will prevent hum pick-up. As mentioned earlier, the circuit can be powered from a centre-tapped 30V AC supply transformer or from balanced DC rails of more than ±18V but less than ±35V. Once the board is finished, it should be checked over carefully. This done, apply power and check that +15V is present between pin 4 of IC1 and IC2 and ground. Also check for -15V BOOKSHELF – CONTINUED FROM PAGE 15 PARTS LIST 1 PC board coded, 01309951, 167 x 65mm 5 50kΩ linear PC mounting pots 5 knobs 7 PC stakes 1 320mm length of tinned copper wire 2 3mm screws, star washers and nuts Semiconductors 2 TL074 quad FET-input op amps (IC1,IC2) 1 7815 3-terminal regulator (REG1) 1 7915 3-terminal regulator (REG2) 1 1B04 1A 400V bridge rectifier (BR1) Capacitors 2 470µF 25VW PC electrolytic 3 10µF 16VW PC electrolytic 1 0.82µF MKT polyester 1 0.47µF MKT polyester 1 0.22µF MKT polyester 1 0.1µF MKT polyester 1 .056µF MKT polyester 1 .018µF MKT polyester 1 .015µF MKT polyester 1 .0047µF MKT polyester 1 .0033µF MKT polyester 1 .001µF MKT polyester 1 270pF ceramic or MKT polyester 1 68pF ceramic 2 33pF ceramic Resistors (0.25W 1%) 5 220kΩ 3 2kΩ 1 100kΩ 2 1.8kΩ 1 22kΩ 1 1kΩ 2 10kΩ 2 47Ω between pin 11 and ground of IC1 and IC2. Installation When installed into audio equipment, the input and output lines should be run in shielded cable. To avoid hum loops, the shields of these cables should normally only be connected at one end. For stereo use, two equaliser boards will be needed. Also, the ±15V power output from one equaliser can be connected to the power rails of the other SC and the regulators deleted. The Motorola Impedance Matching Program (MIMP) is discussed in chapter eight. Available free of charge from ter eight. Available free of charge from Motorola, this program provides a simple method for entering and analysing impedance matching circuitry. A standard library of passive circuit elements is provided by MIMP, including various combina­tions of capacitors, inductors and transmission lines, in both series and shunt configurations. Chapter nine, titled “After the Pow­er Amplifier Output”, discusses the protection needed for solid state amplifiers. Most failures occur due to load mismatch, which causes a high current in the output transistors. Since the temperature time constant for a typical RF transistor is 0.5-1.0 millisecond, any protec­tion must be faster than this. The most common method for load sensing is the reflectometer VSWR. This sensor is usually located in series between the output stage and the load. A voltage, proportional to the amount of mismatch, is supplied by the re­ flectometer and this is used to reduce the drive, or shut down the power amplifier, depending on the design brief. Most RF power amplifiers require a low pass filter to ensure that any harmonics generated by the amplifier will not be radiated. The various types of filter, the design procedure and the types of components constitute the balance of this chapter. The 10th chapter covers wideband impedance matching which is usually done with transformers. The transformer types covered are conventional, twisted wire and transmission line. A conven­ tional transformer is defined as one with two windings, often on a ferrite core. The twisted wire type is exemplified by the humble balun used in most TV set antenna circuits. The transmis­sion line transformer is the one most likely to be unfamiliar to many readers. In practice, it can be realised with twisted enamel wires, coaxial cables, parallel flat ribbons or a micro-strip. The main identifying feature is that the power transferred from input to output is not coupled through a magnetic core but rather through the dielectric medium separating the line conductors. Various examples of each type are detailed. “Power Splitting and Combining” is the title of chapter 11. If the power output requirements exceed the capabilities of one output device, multiple stages can be combined to produce the required power. These com­ biners are similar to wideband transformers in design and construction, the main difference being the way the windings are connected. A splitter is simply a low power combin­er used in reverse. Combiners covered include the 0° and 180° devices, the 90° hybrid and the Wilkinson combiner. Chapter 12 is titled “Frequency Compensation and Negative Feedback”. As the input impedance of a BJT or FET varies much more with frequency than the output impedance, it is usual to only compensate the input. Methods used include series chokes, series resistors shunted with small capacitors in the base drive circuit or series chokes between base and ground. Negative feedback, similar to that used in audio amplifi­ers, can be used to broaden the frequency response of HF amplifi­ers but as the impedances are so much lower, considerable power can be dissipated in the feedback network. With a 300 watt 175MHz broad-band amplifier, the power loss at 10MHz could be in the order of 10%. Various methods of feedback using R, L, C (resis­tors, inductors, capacitors) and input and output transformers are discussed. The final chapter, titled “Small Signal Amp­lifier Design”, de­scribes a straight­forward approach to this topic. The three basic ingredients are the selection of a bias point, then the use of scattering parameters and noise parameters to complete a specific circuit. The authors cover each of these points in some detail and recommend the use of one or two computer programs, should the design require controlled noise and gain performance over a band of frequencies. Fourteen pages of worked examples complete the book. In summary, in view of the dearth of good current textbooks on RF design, this book can be highly recommended. Our copy came from Butter­ worth-Heinemann Australia, PO Box 5577, West Chats­wood, NSW 2067. Copies can be obtained from SILICON CHIP. The ordering details are shown in the SILICON CHIP Bookshop adver­ tisement in this issue. (R.J.W.) SC December 1995  27 A CB transverter for the 80-metre amateur band Last month, we described the circuit of the CB Transverter For 80M and show how to build the PC boards. In Pt.2 this month, we give the final wiring details and describe the test and alignment procedure. PART 2 – By LEON WILLIAMS, VK2DOB The prototype was housed in a plastic instrument case with aluminium front and rear panels. This case measures 250 x 170 x 75mm and is called a Jaybox (from Jaycar). Other cases could be used but make sure that the rear panel at least is made of alu­minium to provide heatsinking for the two FETs. The PC boards are mounted inside the case on a 2mm-thick aluminium plate measuring 155 x 240mm. This baseplate is secured to plastic standoffs in the base using four No.4 x 12mm 28  Silicon Chip self-tappers. When the plate has been secured, drill clearance holes for the long screws that pass through from the base to hold the top of the case in place. The PC boards are mounted on the baseplate using No.4 x 12mm self-tappers and 6mm-long brass spacers. The location of each board is shown in Fig.8 and can be seen from the photo­ graphs. Before mounting the boards however, it is necessary to mark out the rear panel. To do this, first sit the mixer board on 6mm spacers, push the shield against the rear panel and mark out the holes for the SO239 input connector with a pencil or scriber. Do the same thing for the PA board to find the position for the FET mounting holes. The positions of the SO239 antenna connector and the power supply binding posts should also be marked at this point. This done, remove the rear panel from the case and drill all the holes. Ensure that the holes for the FETs are smooth and free from any burrs that could puncture the insulating washers. The front panel has only two holes, one for the Rx/Tx switch and one for the variable capacitor shaft. The position for this can be found by sitting the PLL board on 6mm spacers and making a mark on the rear of the front panel around the shaft with a pencil. This done, the baseplate can be drilled to take the self tappers that secure the PC boards. Fig.8. this wiring diagram shows the location of each PC board in the case. These boards are all mounted on an aluminium plate using No.4 x 12mm self-tappers and 6mm-long brass spacers. Note that leads that carry RF signals are run using minia­ture 50-ohm coax, while the rest of the wiring consists of medi­um-duty hook-up wire. The in-line fuseholder is wired between the positive binding post and the +13.8V pin on the power amplifier board. December 1995  29 This close-up view shows the mounting details of the two IRF510 power FETs (on the PA board). Note that these must be electrically isolated from the rear panel using TO-220 mounting kits, as shown in Fig.10. When all the holes are drilled, fit the front and rear panels in the base of the case, then mount the mixer board and secure the SO239 input socket using four 3mm x 6mm-long screws and nuts. The front of the board is secured to the base using two self-tappers and 6mm spacers. The PA board is secured to the baseplate using four self-tappers and 6mm spacers. Once this board is in position, secure the two FETs to the rear panel as shown in Fig.10. Smear all mating surfaces with heatsink compound before bolting the assem­ blies together and use a multimeter to confirm that the metal tab of each device has been correctly isolated from the rear panel. The PLL board can now be secured to the baseplate. The variable capacitor shaft extends through the matching front panel hole and is fitted with a large plastic knob. This done, mount the front panel switch, the antenna socket and the power supply binding posts. All that remains now is to complete the wiring as shown in Fig.8. Note that leads that carry RF signals are run using minia­ture 50-ohm coax, while the rest of the wiring consists of medi­umduty hook-up wire. The in-line fuse holder is wired between the positive binding post and the +13.8V pin on the power amplifier board. Testing Fig.9: here are the full-size etching patterns (top & bottom) for the power amplifier PC board. 30  Silicon Chip The transverter needs a 13.8V DC supply capable of supply­ing at least 2A. The completed unit is tested as follows: (1). Connect the CB radio to the input socket using a coax patch lead and connect a dummy load capable of dissipating 12W to the antenna socket. The rear panel of the transverter carries the antenna socket, two power supply binding posts and the input socket. The latter is connected to the antenna socket on the CB transceiver via a coax patch lead. Power for the unit can be derived from any suitable 13.8V DC source capable of supplying 2A. (2). Place the Rx/Tx switch in the Rx position and turn trimpots VR1 and VR2 fully anti-clockwise. Apply power and check that 13.8V is present on all three boards. If the fuse blows, there is obviously a fault that needs to be fixed. If the relays operate, check the wiring to the Rx/Tx switch. If the switch wiring appears to be OK, check the RF detector circuit for errors. (3). If everything is correct, check the output voltages of the regulators on the PLL board. These should be close to +5V from REG1 and +8.5V from REG2. (4). Connect the lead from a fre- quency counter to pin 10 of IC2 and check that the 10MHz oscillator is working. Now move VC1 from minimum to maximum and check that there is a change in frequency. The frequency at pin 14 of IC3 should be about 185kHz, depending on the position on VC1. (5). Connect the frequency counter to the output pins of the PLL board and note the frequency. Centre VC1 and, using a suitable tool, adjust the slug in L5 until the counter reads 23.705MHz (this should remain steady, even when L5 is moved a little either way). If the correct frequency Fig.10: the two FETs are secured to the rear panel as shown here. Smear all mating surfaces with heatsink compound before bolting the assem­blies together. cannot be obtained, decrease the turns on L5 to raise the frequency or increase the turns to lower the frequency. If the PLL will still not lock, check that the frequency at pin 3 of IC3 is about 185kHz. (6). Connect a voltmeter across the 100µF capacitor in the low pass filter (located on the board near VC1). Adjust L5 until a reading of 2.5V is obtained. When the correct position for the slug has been found, it should be locked in the former using a small piece of elastic. This should be placed between the slug and the former as it is screwed in. (7). Check that VC1 can vary the output frequency of the PLL board by at least ±5kHz. If the range is too small, change the connection from the 60pF pin to the 160pF pin on VC1. (8) Remove the dummy load and connect a 3.6MHz signal source to the antenna socket. Power up the CB radio and set it to LSB, with the RF gain control at maximum. Select channel 30 and adjust the fine tune control on the transverter until the signal can be heard from the CB. (9). Adjust the slugs in T1, T2 and T3 for maximum signal, as indicated on the CB radio’s S-meter. If you have the facilities, you can adjust the bandpass filter for a flat response across the band; if not, peaking them at the centre of the band will be adequate. If you cannot hear a signal, check that there December 1995  31 32  Silicon Chip Fig.11: this is the full-size etching pattern for the mixer PC board. Make sure that all groundplanes are correctly aligned before etching the boards. Fig.12: the full-size etching pattern for the PLL PC board. Check all PC boards carefully before installing the parts. Operating You must hold an amateur radio licence to use this trans­ verter. Basically, it’s simply a matter of applying power (13.8V DC), connecting the CB to the input connector via a coax patch lead, and connecting a 3.5MHz antenna to the antenna sock­et. The only time you need to touch the transverter is to adjust the fine tune control. This control can be calibrated if required. The front panel can be marked at the knob pointer posi­tions when the VCO frequency is 23.700MHz, 23.705MHz and 23.710MHz. The 23.705MHz position represents the 10kHz spot (eg, 3.610MHz), while 23.710MHz represents the -5kHz spot (eg, 3.605MHz) and 23.700MHz represents the +5kHz spot (eg, 3.615MHz). Due to the characteristics of the crystal oscillator, it will be found that the fine tune scale is not linear. This means that there is more control on one side of the 10kHz spot than on the other. This is a small price to pay for the advantages that it provides. With these calibration marks, it is a simple matter to find any frequency at a resolution of 5kHz in the band. Note that because both the CB radio and the transverter use a PLL which is crystal locked, the frequency stability of the system is very good. Finally, if you find that the sound of the relays operating during long overs between sentences is annoying, place the Rx/ Tx switch in the Tx position while you speak to override the automat­ic switching system. Of course, you must remember to switch back to the Rx position when you finish speaking, so SC that you can receive. Fig.13: this full-size artwork can be used as a drilling template for the two holes on the front panel. is +6.2V at pin 8 of IC1 and that the VCO signal is present at pin 6. If these check OK, look for problems with the transformers and the relays. (10). Swap the signal source for a power meter or a dummy load with an oscilloscope connected across it. Install a multimeter set to measure at least 2A in the positive supply lead. Operate the Rx/Tx switch so that the relays operate continuously and note the current drawn. Adjust trimpot VR2 slowly clockwise until the current reading is 400mA higher than the previous value – this should be about 750mA. Return the switch to the Rx position and remove the multimeter from the power supply lead. (11). Push the CB PTT button and speak into the microphone. The relays should operate and release about a second after the speech stops. (12). Switch the CB to AM and operate the PTT switch. Adjust drive control VR1 until a reading is indicated on the power meter, or on an oscilloscope if using a dummy load. (13). Adjust T5 and T6 for maximum power, as indicated on the power meter. Now move the channel selector slowly from 20 through to 40 and note the power output. If there is a peak at any point, it can be balanced out by adjusting T5 and T6 until the power output is even across the band. (14). Switch the CB back to LSB and whistle into the microphone. While monitoring the waveform on an oscilloscope, advance the drive control (VR1) until the waveform starts to compress, then back VR1 off slightly. The power meter or oscilloscope should show a power reading of at least 12 watts PEP. If you do not have these facilities, listen to yourself on another receiver or have a friend listen nearby. Advance the drive control until the signal distorts and then back it off a little. The transverter does not have an ALC (automatic loudness control) circuit, so it is important to set the drive control so that the PA is not overdriven. December 1995  33 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: 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. Please feel free to visit the advertiser’s website: 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. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd Subwoofer controller with signal limiting & automatic power-on Have you ever wanted to really feel those extra bass notes from your favourite CD? Ever felt you missed out when watching that “Top Gun” video? Well here is a project that will control an amplifier/speaker combination to give that extra grunt in the bass department! The Subwoofer Controller presented here will not only control the level and frequency passed through to the sub bass amplifier, it also provides signal limiting, auto power on and off and an out-of-phase output for bridging a stereo amplifier for even more power. There are two front panel controls (cutoff frequency and level) and two LEDs (“Standby” and “On”. The cutoff frequency control is used to match the subwoofer controller to the actu- al speaker enclosure. Some speakers have a narrow range of opera­ tion, while others can handle a much wider bass range. In effect, the frequency control acts like a tunable crossover. The range of cutoff frequencies is demonstrated in the graph of Fig.4. The level control is used to set the output audio level, from the subwoofer speaker, to match the rest of the system. The compressor-limiter is basically an automatic volume control that only works when the input level is too high. This means that in the normal signal range, the signal goes straight through. Above a certain input level though, the gain is progressively reduced to prevent the sub­woofer amplifier from being driven into over­load. A built-in power-up circuit is incorporated to sense the audio input. When an input signal is present, the controller switches on a relay, which can be used to turn on the subwoofer amplifier. The relay switches off approximately 13 minutes after the signal is removed. The reason for the long delay is so that quiet patches in the program do not cause the unit to prematurely switch off. Circuit operation The circuit diagram of Fig.1 has four distinct sections comprising: (1) VOX and timer; (2) input conditioning and filter; (3) compressor and December 1995  39 40  Silicon Chip D1 D2 Fig.2: the component overlay diagram for the PC board. Leave sufficient lead length to enable to two LEDs to protrude through the front panel. output amplifier; and (4) the power supply. Input signals from the left and right channel source (usually the preamp output signals of a stereo amplifier) are mixed by resistors R2 and R29 and then fed via R4 to op amp IC2a which is wired as a Schmitt trigger. Its gain is very high so that virtually any input signal will drive it into clipping. Its output is fed to diodes D1 & D2 to develop a DC voltage across C8, a 10µF electrolytic capacitor. Op amp IC2b amplifies and inverts the voltage from C8 and its output pulls pin 7 of IC3 low, via diodes D9 & D8. IC3, a 555 timer, normally has its output (pin 3) high, so that transistor Q2 can drive the relay. As noted above, Fig.1 (left): the circuit has four distinct sections. IC2 & IC3 function as the VOX and timer, IC4 is the adjustable low pass filter, and IC1 is the signal limiter. Op amps IC7a and 7b provide out-of-phase outputs to drive a stereo amplifier in bridge mode. the relay is used operate the external subwoofer amplifier. To this end, the relay switches 240VAC to the 3-pin panel mount socket on the rear panel. LED1 indicates that the subwoofer amplifier is on. Transistors Q4, Q5 & Q6 are also driven by pin 3 of IC3 and are used to clamp the signal outputs to ground, when the unit is switched on and off. If the audio signal stops, at the end of a CD for example, the voltage across C8 drops to zero and so pin 7 of IC3 is no longer pulled low. C1, at pin 6, can now charge up and when it reaches about +8V, the output at pin 3 goes low, turning off Q2 and the relay. As noted above, this takes about 13 minutes. The mixed input signal from R2 and R29 is also fed into a 4-pole low pass filter comprising IC4, VR1 and associated compon­ents. This circuit has a low frequency cutoff at around 15Hz but has an option for a lower frequency cutoff by inserting jumper JP2 which then changes the input coupling capacitor to C28, a 10µF electrolytic. In normal practice though, there is little point in doing this as it will only add unwanted signals such as recorded rumble. IC4’s output is fed to VR2, the 10kΩ level control and then to IC1, an NE571 variable gain amplifier. IC5 and associated components are used to derive the gain control voltage for IC1. IC5 is wired as a window comparator, where the output goes low (pins 1 & 7) when the input (fed via C35) is above or below the thresholds set by resistors connected to pins 2 & 5. When a signal exceeds the threshold levels, the comparator switches low, turning on transistor Q3 and charging C19 rapidly via R26. The voltage across C19 is the gain control for IC1 and this causes IC1’s gain to fall so that high level signals are compressed but not clipped. IC1’s output is fed to IC7, a TL072 dual op amp. IC7a provides an inphase output to be fed to the external subwoofer amplifier, while IC7b provides an out-of-phase output if you want to drive a stereo amplifier in December 1995  41 bridged mode. In bridged mode, the two channels of the external stereo amplifier drive a single speaker system, connected between the two positive terminals of the amplifier’s left and right outputs. In this case, the amplifier’s full power will be delivered to the speaker but if it is an 8Ω speaker, you must make sure that the amplifier is rated to drive 4Ω loads because that it is the load that each channel will effectively “see”. Power for the controller comes from a 12.6V transformer which feeds a bridge rectifier (D4-D7) and a 1000µF capacitor. The filtered DC is fed to IC6, a 7812 12V regulator which powers the entire circuit. Note that there is no fuse in the power supply as the transformer is internally fused. Construction All the components with the exception of the power trans­ former are mounted on the PC board which measures 160 x 90mm (code K5562. PCB). The parts layout diagram for the board is shown in Fig.2. First check the board for any defects and fix them before proceeding. Then mount all the resistors and diodes. Follow with ICs Inside the subwoofer controller virtually all the circuitry is mounted on the PC board. The AC socket is used to power the external subwoofer amplifier. and electrolytic capacitors. Make sure that the diodes and ICs are the right way around. Now the rest of the components can be inserted and soldered. Having completed the PC board, let’s look at the base plate and mains wiring. All the details of the off-board wiring and the hardware details are shown on the diagram of Fig.3. You will need to attach two tapped metal spacers to the baseplate. These support the rear of the PC board when PARTS LIST 1 PC board code, (K5562.PCB) 2 jumper shunts and pin headers 1 12V relay (S-4170) 1 screened & punched front panel 1 screened & punched rear panel 1 3-core mains cord & moulded 3-pin plug 1 plastic instrument case, 203 x 156 x 69mm 1 cordgrip grommet 2 knobs (1 spline, 1 grub-screw type) 1 steel base plate 1 flush mount GPO socket 1 M-2852 12.6V transformer 2 binding posts (1 red, 1 black) 4 RCA sockets (chassis mount type) 2 solder lugs 1 3-way insulated terminal block 1 50kΩ dual gang 16mm pot (VR1) 1 10kΩ (log) 16mm pot (VR2) 1 50kΩ horizontal trimpot (VR3) 42  Silicon Chip Semiconductors 1 NE571 compander (IC1) 1 LM358 low power op amp (IC2) 1 555 timer (IC3) 1 TL071 op amp (IC4) 1 LM393 dual comparator (IC5) 1 7812 +12V regulator (IC6) 1 TL072 dual op amp (IC7) 1 BD139 NPN transistor (Q2) 2 BC558 (Q3,Q4) PNP transistors 2 BC548 NPN transistors (Q5, Q6) 4 IN914, IN4148 diodes (D1,D2,D8,D9) 5 IN4002 diodes (D3,D4,D5,D7) 2 5mm red LEDs (LED1, LED2) Capacitors 1 1000µF 16VW electrolytic 1 470µF 16VW LL electrolytic 2 100µF 16VW electrolytic 14 10µF 35VW electrolytic 5 1µF 63VW electrolytic 3 0.1µF metallised polyester (greencap) 2 .082µF greencap 1 .039µF greencap 1 .022µF greencap 1 .01µF greencap 2 .001µF greencap 1 180pF disc ceramic Resistors (0.25W, 5%) 1 3.3MΩ 1 12kΩ 1% 1 2.2MΩ 9 10kΩ 1 1.5MΩ 3 10kΩ 1% 2 1MΩ 1 8.2kΩ 1% 1 220kΩ 1 4.7kΩ 7 100kΩ 5 1kΩ 3 47kΩ 2 680Ω 2 39kΩ 1 560Ω 1 33kΩ 3 100Ω 1 22kΩ 4 0Ω links Miscellaneous Solder, PC pins, spacers, nuts, machine screws, washers, mains rated cable (three colours – brown, blue & green/yellow), shielded cable. Fig.3: note that the cases of the two pots must be earthed with a length of tinned copper wire which connects to the solder lug at one side of the PC board. Do not forget the 0.1µF capaci­tor between the main Earth solder lug and the output shield connection on the PC board. it is mounted. Feed the power cord through the relevant hole on the back panel (later it will be anchored with a cordgrip grommet). Connect the Active and Neutral wires to the insulated terminal block and connect the Earth wire to a solder lug which will be anchored by one of the transformer mounting screws. The base plate is secured to the case with four self-tapping screws. Place a solder lug underneath the lefthand front self-tapping screw. This will be used to earth the cases of the pots, with a length of tinned copper wire. For the front panel you will need to use two pot washers on the dual pot, VR1. Secure the front panel using the nuts for both pots and attach the knobs. The two LEDs should be poked through their respective holes in the front panel. This done, attach the PC December 1995  43 board to the spacers towards the rear of the case. The rear panel requires the flush mount GPO to be attached first, after which the RCA connectors and binding post terminals can be mounted. Slide the finished rear panel into the vertical slot at the rear of the case and then insert and secure the cordgrip grommet for the power cord. Wire up the rear panel according to the wiring diagram shown in Fig.3, making the connections as short and as neat as possible. Keep the shielded leads away from the transformer to avoid hum pickup. Check all wiring carefully before proceeding to test the unit. Testing To test the subwoofer controller you will require a multi­meter, an audio program source such as a CD player, an amplifier and a speaker. Connect the power and note that the power LED comes on. If not, check that the LED is the right way around. Then connect your multimeter between the anode of LED2 and the regulator heatsink tab and switch on again. There should be 12V present. Now connect an audio source to the input. Set jumper JP1 to the appropriate position (remove for line level input). The relay should click in after a short delay and LED1 should come on. If not check pin 1 of IC2. It should be between +4V and +8V. Pin 7 of IC2 should be close to 0V, with the input source on. It should go high (+11V) when the input signal is removed, after a delay of a few seconds. The timer will then start to time out and the relay should drop out after approximately 13 minutes. If these tests all check out, connect an amplifier and speaker. Feed in a music source, from a CD player, or the tape monitor output from your main stereo amplifier and have a listen. It will sound very muffled and boomy. Why? Because you are mainly listening to bass signals below 300Hz. If this checks out, the only adjust- AUDIO PRECISION FREQRESP AMPL(dBr) vs FREQ(Hz) 10.000 0.0 -10.00 -20.00 -30.00 -40.00 -50.00 -60.00 -70.00 10 100 1k 10k Fig.4: this is the range of cutoff frequencies provided by the subwoofer controller. Note that the actual gain of the circuit is set by the output level control VR2. Performance of Prototype Signal to noise ratio: 67dB unweighted with respect to 173mV in and 1V out. Total harmonic distortion: 0.05% at 40Hz and 1V out; 0.25% at 250mV out Input impedance: 10kΩ Output impedance:1kΩ Filter slope:12dB/octave Crossover frequency range: see Fig.4 ment to be made is to VR3. This is to set the maximum level to the sub­woofer amplifier. It should be set just below the clipping level of the amplifier. If you have a signal generator, then connect this to the input and set it to around 100Hz. Rotate VR2 fully clockwise. Connect your digital multimeter (set to a low AC voltage range) across one of the RCA output sockets (either one) of the controller and adjust VR3 Where to buy a kit of parts The Subwoofer Controller was designed by Altronics and they own the copyright. The kit is available in two forms. The short form kit, comprising the PC board and all the on-board components, is $49.00 (K-5562). The full kit, including the case with screen printed and punched front and rear panels, is $99.00 (K-5563). These kits are available from Altronics in Perth (phone 1 800 999 007) or from any of their interstate resellers. 44  Silicon Chip 18 SEP 95 15:02:59 to the rated sensitivity of the amplifier, typically 1V RMS. Note: do not do this adjustment with the external sub­woofer amplifier connected as it will drive it to full power or beyond. If you do not have a signal generator, you can do the ad­justment with your subwoofer amplifier connected but you will need to limit the power delivered to the subwoofer itself. To do this, connect a 100W 240VAC lamp in series with your speaker. The cold resistance of the lamp will be around 50Ω or thereabouts and this will safely limit the power although it will still be more than adequately loud while you are driving the subwoofer amplifi­er to full power. Now connect a CD player and select a disc with plenty of bass present. Adjust VR3 until clipping is heard from the speaker. This will sound like a buzzing or high distor­tion of the bass signal. Back off VR3 slightly until the clipping is no longer present. The best signal source for the controller is a line level output, derived from just after the volume control in your stereo amplifier. Note that “Tape Out” and similar outputs are unsuit­ able, as they are not volume dependent; ie, the signal from these points does not vary with the volume control. Alternatively, take the signal from one of the speaker outputs on SC your stereo ampli­fier. 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 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. 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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 December 1995  53 SERVICEMAN'S LOG Stop me if you’ve heard this one This month’s notes are on a slightly different tack than usual. Almost by accident, they finished up as a resume of all the dreadful things that happen to, or are done to, video recorders. Take note; it might happen to you. It all started with the story in the October notes, about the ballpoint pen pushed into a Philips VR6448/75 video recorder – presumably by one of the owner’s children. That incident caused considerable trauma all round. Inevitably, this story came up at an informal gathering with a couple of colleagues, who are aware that I write these notes. And just as inevitably, it prompted memories of all the strange things that had been found in video recorders, some of which I have listed in previous notes. One I recall was a 20c piece, which caused a lot of trou­ ble. And then there was the machine which had 54  Silicon Chip been stored in a garden shed and had become home for a family of ants. Between us, we came up with quite a list. Toys being “post­ed” are common. And there was another ants’ nest story, from a colleague this time. The owner of that machine lived in a bush­ land setting in what might be described as a rather elementary dwelling. Fortunately, the infestation wasn’t very severe and the machine was salvaged without much trouble. But it could have been a lot worse. Cockroaches are another common foreign body. They don’t do much damage as long as they keep clear of the moving parts. But when they do tangle with them, they can make an awful mess. Some of the more unusual items found in video recorders have been wedding and diamond engagement rings, false finger nails (the mind boggles), fruit cake and sweets! The wedding and engagement rings were found by a colleague in two separate machines. There must have been a couple of inter­ esting stories about them but we will never know. My colleague was working on a subcontract basis for another firm and he never heard anything more about them. Another frequent offender is the cassette label which has lost its glue and fallen off, jamming the reel and loading mechanisms. And then there was the VCR that came in with no less than three tapes jammed inside! The owner was under the fond impression – I never did find out why – that as each tape was played, the machine automatically ejected it from the rear. How do you get three cassettes into one machine? With great difficulty, might be smart answer. But this owner managed it. Granted, this particular machine lent itself to such abuse more readily than most. As it came in, there was one cassette correct­ly loaded, another which had been forced in on top of it, and a third which was protruding from the loading opening. It was the latter that apparently alerted the owner to the fact that someth­ing was wrong! That story just about exhausted the “foreign bodies” theme but led quite logically to other common VCR faults. And I re­alised that many of the common faults we tend to take for granted had not found their way into these notes, either at all or for a very long time. So here are a few; some from me and some from my colleagues. A common complaint One common complaint in some machines is caused by attempt­ing to load a cassette upside down or the wrong way around, which bends or breaks the cassette door unlock lever. This lever en­ gages a small square plastic pin immediately behind the cassette door flap, on the right-hand side. (Pushing this pin allows the door to be opened manually, exposing the tape – a common trick where damaged tape is suspected). So, if the unlock lever is damaged, the cassette door will not open, preventing the set from accepting a cassette. It goes in, but only the left side goes down; the right side cannot, as the door is still closed. One machine that I encountered quite recently was a varia­tion on this theme. The customer brought in his machine, a Na­tional NV-370-A, along with a cassette, an NEC HDx E-240 made in Korea. And it was a virgin tape, just removed from its plastic wrapping. His problem was that the machine would not accept it. It could be pushed in and, initially, everything would appear to be normal. But then, after a few seconds, the machine would eject it. On closer examination, he realised that the entrance flap had not closed completely but he had no idea what this meant. However, he had another machine available – an older Sharp – and this accepted the cassette without hesitation. Ergo, the fault must be in the National. Had he tried any other cassettes? No – he had not wanted to force the situation for fear of causing further damage. It was a commendable attitude, even if it turned out to be an overreaction – which in fact it was. I tried the suspect cassette in the National and it behaved exactly as the owner had said. Then I pushed in one of my own tapes and it loaded immediately, as did a second and a third. This removed any lingering doubts; the fault was in the cassette, not the machine. But why? And should the cassette go back to where it was bought? This presented problems. It had been bought some time ago and the purchase docket had long since been lost. And, in any case, there might be some difficulty proving that the cassette was faulty. Then I had an idea. I had another customer’s machine on hand, an older, top loading type. I tried the cassette in this and it baulked also, but in a different way; the loading cradle would not go right down. However, the top loading arrangement made it possible to see more clearly what was happening and it was obvious that the cassette door was not opening. And I was able to get a small probe down the side of the cradle where there was an intermediate lever, used to engage the door opening pin, and exert slight pressure. And that did it – the door opened and the cradle could be pressed home. I took the cassette out and tried another trick. There was a small amount of lateral slack between the cassette and the cradle and I loaded it again with the cassette pressed hard to the right. Success again; the cradle went down quite readily. I then tried the same trick with the National, pressing the cassette hard right as I pushed it into the opening. Once again, it loaded normally. So what was causing this problem? Apart from the obvious fact that the door release pin was not being fully activated, the basic cause remains a mystery. I suspect that it is a plastic moulding problem. Either the die was faulty – unlikely – or the plastic was sufficiently unstable as to permit some shrinkage – which seems more likely. More importantly, what to do about it? We mulled over various ideas aimed at ensuring that the cassette was held hard right on entry but they all had disadvantages. In the end, the customer decided that the easiest way was simply to remember to push it hard right on loading – and to mark it in some way as a reminder. Dirty video heads Another common problem is dirty video heads. I find it almost impossible to convince people that dirty heads are almost always due to faulty tapes and that, after I have cleaned them, it is essential that they locate and discard the tape that caused it, otherwise the same thing will happen again. It should not be that hard to understand that the heads protrude above the drum surface, are in contact with the tape, and spin at 1500 RPM. Nor should it be hard to understand that there will be an awful mess if the tape surface isn’t perfect. But it’s no good; within days they are back saying it is doing exactly the same thing – and you both know the same tape was tried again. Nowadays, I try to be philosophical about it and just clean it again, if possible in front of them. I always advise December 1995  55 clients to buy quality tapes and play them in the “standard play” mode. After all, you get what you pay for, and expecting cheap tapes to perform well in “long play” mode is pushing the system to its limits. Normally, I clean the heads by very gently rubbing them with oil-free acetone (available from the local hardware store) and a lint-free cloth. If you have ever seen what acetone can do to tape, you will appreciate how powerful it is. However, there have been times when the dirt is so compacted in the video head gap that even this would not shift it. On one occasion, many years ago, I had an Akai VS2 come in with no picture on play, the snow effect being muted by the set’s circuits. I tried cleaning it with acetone very aggressively but to no avail. I was about to condemn the heads when I remembered a Maxell tape cleaner in the waste bin, one that I had fished out another machine earlier. I had never been very keen on these gadgets – I’m still not for that matter – but, with nothing to lose, I tried it on the Akai. Amazingly it worked. So 56  Silicon Chip now, as well as the acetone treat­ment, I resort to a tape cleaner in the most severe cases. And I found quite by accident that two abrasive tape cleaners have a very useful capability – Maxell T-CL and TDK TCL-11 tape cleaners have the ability to record a video signal. The picture quality isn’t the best but a video image on the tape can provide a very useful guide. It means that, when you are cleaning dirty heads, you need only play the tape until the picture reappears; you don’t have to flog it until it has cut its way right through the heads. Unfortunately, I haven’t seen Maxell tape cleaners avail­able anywhere recently. Also, the T-CL version has been replaced by the E-CL type, which doesn’t record nearly so well, which is a great pity. Similar symptoms One problem with servicing VCRs is that many of the symp­toms are very similar, particularly snow and lines, and those involving tracking. And, because most people don’t see these somewhat similar symptoms very often, they are not good at de­scribing them. As a rule of thumb, lines and tracking faults are normally confined to mechanical tape path and servo electrical areas, while snow is indicative of head and head amplifier failures. But occasionally it can be other areas, such as power supplies, that give strange effects. One clue for these less common faults can be the time taken before the symptom occurs. If it takes some time for the fault to either come good or go bad, it implies that heat can be affecting a vital component. The Sharp VC488X, Philips VR6940/75, and Marantz 740A early series of hifi video recorders are a case in point. These ma­chines are packed with electronics, with at least three or four PC boards stacked one above the other, resulting in poor air circu­lation. The power supply, in particular, is the cause of most of the heat, and the power regulator board (PWB) is one the victims. More particularly, it is the electrolytic capacitors which dry out and upset the various rails. Two 1µF 63V capacitors, C962 and C963, and sometimes C970 (100µF), can cause the machine to perform as though the heads are dirty or very worn, with snow and smearing video. Not only is it sometimes difficult to be sure about these components but, when they are suspected, it is just as tricky to replace them, as access to this board is appalling. The power supply PWB-P is tucked away deep down in the left rear corner of the chassis and, even after removing about umpteen screws and removing the two head amplifier modules, it is still very diffi­cult to pull the circuit board away from the wiring harness. In fact, it is necessary to bend part of the metal board support, if you want to complete the job in a reasonable time. When the board is finally extracted and all the connections unplugged, one is then faced with about 20 electrolytic capaci­ tors (C952-C972). So how many should be replaced? The main cost of the repair is the labour involved in removing and replacing this module and it is false economy to risk doing this again in a hurry. I normally replace all the physically smaller sized capaci­tors (about 15) up to about 220µF with higher temper- ature (105°C types, such as the TKR series). I also rework all the solder joints before reassembling the beast. Note: care must be taken to properly refit the chassis screw at the rear of the head amplifi­er board, otherwise there is a risk of losing the 9V rail, marked +PB 9V on the board. Other head type problems, like snow, can be attributed to drum/cylinder motors which lock out of phase, usually intermit­tently. This generally means that replacement motors are re­quired. Early Akai video recorders often had these problems due to lack of heatsinking on the control IC. The best quick confirmation of head performance and align­ment is probably displaying the output from the head amplifier on the CRO, but it doesn’t necessarily indicate precisely where the problem is. Some early Sharp models had a feature built in that would automatically put the deck into the search mode from the play position when a blank part of the tape was reached. It appears that the system monitors the video signal sync pulses and, if these are not present, goes into the search mode. The result is snow on the screen and no sound, until a video signal is encountered, whereupon the systems reverts to the play mode. However, if some defect, such as dirty or damaged heads, prevents the system from sensing a video signal of ade­ quate amplitude, it will assume there is no video, and go into the search mode permanently. What appears on the screen depends on the exact nature and degree of the fault, and may vary from snow to some attempt at a picture but with no sound. And significantly, the makers point out in the instruction manual that the system may not work cor­rectly with poorly recorded tapes. So when I am told that the problem is that the tape goes into fast forward, it is usually due to the machine having dirty heads. Last week, I was faced with just such a situation but one with a sting in its tail. The machine was a model VC-583X, which features this facility. It is owned by an elderly lady customer who complained of exactly the symptoms I would expect from such a problem. A check on the bench confirmed that the lady had described the fault quite accurately; the system was quite Fig.1: the power supply circuitry in the Sharp VC488X, Philips VR6940/75 and Marantz 740A VCRs. Two 1µF electrolytic capacitors labelled C962 and C963 (upper centre) and a 100µF capacitor labelled C970 (lower right) are always prime suspects in this circuit but a mass replacement may save future problems. definitely in the search mode and was producing a grotty speeded up version of the video on the tape, but with no sound. I fixed the problem by simply cleaning the heads. I then gave it a thorough test and made a few other routine service adjustments, such as aligning the audio erase and control heads to track correctly, and cleaning the lower drum assembly to prevent tape stiction, etc. The set bounces Anyway, I was satisfied that it was working correctly in all respects and she took it away. Then, one week later, it bounced. She brought it back complaining, initially, of the same fault. I thought, “Here we go again – a crook tape”, and prepared to clean the heads again. But, as before, she had described the fault very accurately and, ironically, is was this accurate description which alerted me to the fact that it was not the same fault. True, the tape was running fast but, as well as a picture, there was sound. The system was not in the fast search mode at all. Obviously, the problem was more complex than before and she had to leave it with me. The fault turned out to be due to the pinch roller not making firm enough contact with the capstan shaft, resulting in the reel motor pulling the tape through faster than the capstan motor. When I removed the bottom covers and checked the loading motor timing marks I found that indeed they were out. And on removing the mode select switch, I found the gear had cracks, due to age, in the plastic on the axle collar to the switch shaft, and it was slipping. I realigned it with the internal switch mark and glued it in place before reassembling it and setting it all up properly. Once again, it all worked properly, with plenty of pressure on the capstan motor shaft. But when the lady picked it up she neither thanked me or even offered to pay for the considerable additional labour it had taken to repair this second fault ... she just considered I hadn’t fixed it properly the first time! I wasn’t prepared to argue; you win some and you lose some. SC December 1995  57 NICS O R T 2223 LEC PC CONTROLLED PROGRAMMABLE POWER SWITCH MODULE This module is a four channel programmable W 0 S 1 N 9 , driver for high power relays. It can be used in 7 y le 70 any application which requires algorithm control 9, Oat Fax (02) 5 rd 8 a x C o for high power switching. This module can work Visa PO B 579 4985 as a programmable power on/off switch to limit fax a rd , ) & C 2 0 e ( r unauthorised access to equipment where the n e e o t n s h : o s a p r h P access to use or change parameters is critical. , M ith rde d o w r a d d c e This module can also be used as a universal B a n k x accepte most mix 0. Orders timer. The timer software application is ine r 1 o m $ f A ) cluded with the module. Using this software l i P a & & m r the operator can program the on/off status (ai s. P t r Z e e N n d . r ; of four independent devices in a period of o rld $10 o w 4 $ <at> a week within an accuracy of 10 minutes. . tley a Aust o : The module can be controlled through L I A M the Centronics or RS232 port. The computer is opto by E isolated from the unit, to ensure no damage can occur to the computer. Although the relays included are designed for 240V operation, they have not been approved by the electrical LEARNING - UNIVERSAL REMOTE CONTROL authorities for attachment to the mains. Power consumption These Learning IR Remote Controls can be used to replace is 7W. Main module: 146 x 53 x 40mm. Display panel: 146 up to eight dedicated IR Remote Controls: $45 x 15mm. We supply: two fully assembled and tested PCBs (main plus control panel), four relays (each with 3 x 10A / NEW CATALOGUE AT OUR WEB SITE 240V AC relay contacts), and software on 3.5" disk. We do We have combined efforts with DIY ELECTRONICS (a Hong not supply a casing or front panels. Kong based company) in producing a WEB SITE on the $92 (Cat G20) INTERNET. At this site you can view and download a text version of both of our latest catalogues and other up to date 3.5 DIGIT LCD PANEL METER information. Email orders can also be placed through here. 200mV full scale input sensitivity, “1999” count, 9 to 12V The combined effort means that you get offered an extensive <at> 1mA operation, decimal point selectable (with jumper range of over 200 high quality, good value kits, and many wire), 13mm figure height, auto polarity indicator, overrange more interesting components and items. The range of kits indication, 100Mohm input resistance, 0.5% accuracy, 2 to offered includes simple to more advanced kits, and they cover 3 readings per second. With bezel and faceplate. Dimensions: a very wide field of applications: educational, experimental, 68 x 44mm. Use in instrumentation projects. EPROM, microprocessor, computer, remote control, high $27 (Cat D01) voltage, gas and diode lasers, night vision etc. We’ll leave it to you to do the exploring at: CCD CAMERA-VCR SECURITY SYSTEM http://www.hk.super.net/~diykit This kit plus ready made PIR detector module and “learning You can also request us to send you a copy of our FREE remote control” combination can trigger any domestic IR catalogue with your next order. remote controlled VCR to RECORD human activity within a 6M range and with an 180 deg. angle of view!. Starts HELIUM-NEON LASER BARGAIN VCR recording at first movement and ceases recording Helium neon 633nM red laser heads (ie tubes sealed in a few minutes after the last movement has stopped; just a tubular metal case with an inbuilt ballast resistor) that like commercial CCD-VIDEO RECORDING systems costing were removed from equipment that is less than 5 years thousands of dollars!! CCD camera not supplied. No conold. These are suitable for light shows. Output power is in nection is required to your existing domestic VCR as the the range of 2.5-7.5mW. Heads are grouped according to system employs an “IR learning remote control”: $90 for output power range. Dimensions of the head are 380mm an PIR detector module, plus control kit, plus a suitable long and 45mm diameter. Weight: 0.6kg. A special high “lR learning remote” control and instructions: $65 when voltage supply is required to operate these heads. With purchased in conjunction with our CCD camera. Previous each tube we will include our 12V universal laser power CCD camera purchasers may claim the reduced price with supply kit MkIV (our new transformers don’t fail). Warning: proof of purchase. involves high voltage operation at a very dangerous energy level. SUPER SPECIAL: FLUORESCENT LIGHTING SPECIAL $80 for a 2.5-4.0mW tube and supply. (Cat L01) A 12V-350V DC-DC converter (with larger MOSFETS) plus a $130 for a 4.0-6.5mW tube and supply. (Cat L02) dimmable mains operated HF ballast. This pair will operate a This combination will require a source of 12V <at> at least 32-40W fluorescent tube from a 12V battery: very efficient. 2.0A. A 12V gel battery or car battery is suitable, or if 240V See June 95 EA: $36 for the kit plus the ballast. operation is required our Wang computer power supply (cat number P01) is ideal. Our SPECIAL PRICE for the Wang power STEREO SPEAKER SETS supply when purchased with matching laser head/inverter A total of four speakers to suit the making of two 2-way kit is an additional $10. speakers (stereo). The bass-midrange speakers are of good quality, European made, with cloth surround, as used in LASER WARNINGS: upmarket stereo televisions, rectangular, 80 x 200mm. The 1. Do not stare into laser beams; eye damage will result. tweeters are good quality cone types, square, 85 x 85mm. 2. Laser tubes use high voltage at dangerous energy levels; Two woofers and two tweeters: $16. be aware of the dangers. 3. Some lasers may require licensing. NEW: PHOTOGRAPHIC KITS SLAVE FLASH: very small, very simple, very effective. ARGON-ION HEADS Triggers remote flashes from camera’s own flash to fill in Used Argon-Ion heads with 30-100mW output in the blueshadows. Does not false trigger and it is very sensitive. Can green spectrum. Head only supplied. Needs 3Vac <at> 15A even be used in large rooms. PCB and components kit: $7. for the filament and approx 100Vdc <at> 10A into the driver SOUND ACTIVATED FLASH: adapted from ETI Project circuitry that is built into the head. We provide a circuit for a 514. Adjustable sensitivity & delay enable the creation suitable power supply the main cost of which is for the large of some fascinating photographs. Has LED indicator that transformer required: $170 from the mentioned supplier. makes setting up much easier. PCB, components, plus Basic information on power supply provided. Dimensions: microphone: $13. 35 x 16 x 16cm. Weight: 5.9kg. 1 year guarantee on head. Price graded according to hours on the hour meter. SINGLE CHANNEL UHF WITH CENTRAL LOCKING Argon heads only, 4-8 thousand hours: $350 (Cat L04) Our single channel UHF receiver kit has been updated to Argon heads only, 8-13 thousand hours: $250 (Cat L05) provide provision for central locking!! Key chain Tx has SAW resonator locked, see SC Dec 92. Compact receiver GEIGER COUNTER AND GEIGER TUBES has prebuilt UHF receiver module, and has provision for two These ready made Geiger counters detect dangerous Beta and extra relays for vehicle central locking function. Kit comes Gamma rays, with energy levels between 30keV and 1.2MeV. with two relays. $36. Additional relays for central locking $3 Audible counts output, also a red LED flashes. Geiger tube ea. Single ch transmitter kit $18. unplugs from main unit. To measure and record the value of nuclear radiation level the operator may employ a PC which is MASTHEAD AMPLIFIER SPECIAL connected to the detector through the RS232 interface. This High performance low noise masthead amplifier covers gives a readout, after every 8 counts, of the time between each VHF-FM UHF and is based on a MAR-6 IC. Includes two count. Main unit is 70 x 52 x 35 mm. Geiger tube housing PCBs, all on-board components. For a limited time we will unit is 135mm long and is 20mm diameter. Power from 12 also include a suitable plugpack to power the amplifier from to 14V AC or DC. mains for a total price of: $75 (Cat G17) $25 EY OATL E 58  Silicon Chip CCD CAMERA Very small PCB CCD Camera including auto iris lens: 0.1Lux, 320K pixels, IR responsive, has 6 IR LEDs on PCB. Slightly bigger than a box of matches!: $180 VISIBLE LASER DIODE KIT A 5mW/670nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept 94 EA). UNBELIEVABLE PRICE: $40 Suitable case and battery holder to make pointer as in EA Nov 95 $5 extra. 12V-2.5 WATT SOLAR PANEL KITS These US made amorphous glass solar panels only need terminating and weather proofing. We provide clips and backing glass. Very easy to complete. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: $20 ea. or 4 for $60 A very efficient switching regulator kit is available: Suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. SOLID STATE “PELTIER EFFECT” DEVICES We have reduced the price of our peltiers! These can be used to make a solid state thermoelectric cooler/heater. Basic information supplied: 12V-4.4A PELTIER: $25 We can also provide two thermal cut-out switches, and a 12V DC fan to suit either of the above, for an additional price of $10. BATTERY CHARGER Simple kit which is based on a commercial 12 hour mechanical timer switch which sets the battery charging period from 0 to 12 hrs. Timer clock mechanism is wound-up and started by turning the knob to the desired time setting. Linear dial with 2 hrs timing per 45 degrees of rotation, eg, 270 deg. rotation for 12 hr. setting. The contacts on the timer are used to switch on a simple constant current source. Employs a power transistor and 5 additional components. Can easily be “hard wired”. We supply a circuit, a wiring diagram, and tables showing how to select the charging current: changing one resistor value. Ideal for most rechargeable batteries. As an example most gel cells can be charged at a current which is equal to the battery capacity rating divided by 5-10. Therefore if you have a discharged gel cell that has 5Ah capacity and are using a charge current of 0.5A, the timer should be set for about 10 hours: Or 5hrs. <at> 500mA. This circuit is suitable for up to approximately 5A, but additional heatsinking would be required at currents greater than 2A. Parts and instructions only are supplied in this kit. Includes a T-03 mini fin heatsink, timer switch, power transistor and a few other small components to give you a limited selection of charge current. You will also need a DC supply with an output voltage which is greater by about 2V than the highest battery voltage you need to charge. As an example a cheap standard car battery charger could be used as the power source to charge any chargeable battery with a voltage range of 0-15V: $12 (K72) COMPUTER CONTROLLED STEPPER MOTOR DRIVER KIT This kit will drive two 4, 5, 6 or 8 wire stepper motors from an IBM computer parallel port. The motors require a separate power supply (not included). A detailed manual on the computer control of motors plus circuit diagrams and descriptions are provided. Software is also supplied, on a 3.5" disk. PCB: 153 x 45mm. Great low cost educational kit. We provide the PCB and all on-board components kit, manual, disk with software, plus two stepper motors of your choice for a special price. Choose motors from M17/M18/M35. $44 (K21) Kit without motors is also available: $32 MOTOR SPEED CONTROLLER PCB Simple circuit controls small DC powered motors which take up to around 2 amps. Uses variable duty cycle oscillator controlled by trimpot. Duty cycle is adjustable from almost 0-100%. Oscillator switches P222 MOSFET. PCB: 46 x 28mm. $11 (K67) For larger power motors use a BUZ11A MOSFET: $3. FM TX MK 3 This kit has the most range of our kits (to around 200m). Uses a pre-wound RF coil. The design limits the deviation, so the volume control on the receiver will have to be set higher than normal. 6V operation only, at approx 20mA. PCB: 46 x 33mm: $18 (K33) LOW COST IR ILLUMINATOR Illuminates night viewers or CCD cameras using 42 of our 880nm/30mW/12 degrees IR LEDs. Power output (and power consumption) is variable, using a trimpotentiometer. Operates from 10 to 15V and consumes from 5mA up to 0.6A (at maximum power). The LEDs are arranged into 6 strings of 7 series LEDs with each string controlled by an adjustable constant current source. PCB: 83 x 52mm: $40 (K36) VHF MODULATOR FOR B/W CAMERAS (To be published, EA) Simple modulator which can be adjusted to operate between about channels 7 and 11 in the VHF TV band. This is designed for use in conjunction with monochrome CCD cameras to give adequate results with a cheap TV. The incoming video simply directly modulates the VHF oscillator. This allows operation with a TV without the necessity of connecting up wires, if not desired, by simply placing the modulator within about 50cm from the TV antenna. Suits PAL and NTSC systems. PCB: 63 x 37mm: $12 (K63) SOUND FOR CCD CAMERAS/UNIVERSAL AMPLIFIER (To be published, EA). Uses an LM386 audio amplifier IC and a BC548 pre-amp. Signals picked up from an electret microphone are amplified and drives a speaker. Intended for use for listening to sound in the location of a CCD camera installation, but this kit could be used as a simple utility amplifier. Very high audio gain (adjustable) makes this unit suitable for use with directional parabolic reflectors etc. PCB: 63 x 37mm: $10 (K64) LOW COST 1 to 2 CHANNEL UHF REMOTE CONTROL (To be published, SC) A single channel 304MHz UHF remote control with over 1/2 million code combinations, which also makes provision for a second channel expansion. The low cost design has a 2A relay contact output. The 1ch transmitter (K41) can be used to control one channel of the receiver. To access the second channel when another transmitter is purchased, the other transmitter is coded differently. Alternatively, the 3ch transmitter kit (K40) as used with the 4ch receiver kit is compatible with this receiver and allows access to both channels from the one transmitter. Note that the receiver uses two separate decoder ICs. This receiver operates from 10 to 15Vdc. Range is up to about 40m. 1ch Rx kit: $22 (K26) Expansion components (to convert the receiver to 2 channel operation; extra decoder IC and relay): $6 ONE CHANNEL UHF TRANSMITTER AX5326 encoder. Transmit frequency adjustable by trimcap. Centred around 304MHz. Powered from 12V lighter battery. LED flashes when transmitting. Size of transmitter case: 67 x 30 x 13 mm. This kit is trickier to assemble than the 3ch UHF transmitter: $11 (K41) THREE CHANNEL UHF TRANSMITTER The same basic circuit as the 1ch transmitter. Two buttons, allows up to 3 channel operation. Easier to assemble than the 1ch transmitter and has slightly greater range. Size of transmitter case: 54 x 36 x 15mm: $18 (K40) ULTRASONIC RADAR Ref: EA Oct 94. This unit is designed to sound a buzzer and/or operate a relay when there is an object at a preset distance (or less) away. The distance is adjustable from 200mm to around 2.5 metres. Intended as a parking aid in a car or truck, also may be used as an aid for the sight impaired, warning device when someone approaches a danger zone, door entry sensor. PCB: 92 x 52mm. PCB, all on-board components kit plus ultrasonic transducers (relay included): $22 (K25) Optional: buzzer $3, plastic box $4. SIREN USING SPEAKER Uses the same siren driver circuit as in the “Protect anything alarm kit”, kit number K18. 4" cone/8 ohm speaker is included. Generates a really irritating sound at a sound pressure level of 95dB <at> 1m. Based around a 40106 hex Schmitt trigger inverter IC. One oscillator modulates at 1Hz another oscillator, between 500Hz and 4KHz. Current consumption is about 0.5A at 12V. PCB: 46 x 40mm. As a bonus, we include all the extra PCBs as used in the “Protect anything alarm kit”. $12 (K71) PLASMA BALL Ref: EA Jan 94. 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 to 15V supply and draws a low 0.7A. Output is about 10kV AC peak. PCB: 130 x 32mm. PCB and all the on-board components (flyback transformer included), and the instructions: $28 (K16) 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. Hint: connect the AC output to one of the pins on a fluorescent tube or a non-functional but gassed laser tube. Large non-functional laser tube or tube head: $10 ELECTROCARDIOGRAM PCB + DISK The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 (K47) TOMINON HIGH POWER LENS These 230mm (1:4.5) lens have never been used. They contain six coated glass lenses, symmetric, housed in a black aluminium case. Scale range is from 1:10 through to 1:1 to 10:1. Weight: 1.6kg. Applications include high quality image projection at macro scales, and portrait photography in large formats: $45 (Cat O14) PROJECTION LENS Brand new, precision angled projection lens. Overall size is 210 x 136mm. Weight: 1.3kg. High-impact lexan housing with focal length adjustment lever. When disassembled, this lens assembly yields three 4" diameter lenses (concave, convex-concave, convex-convex). Limited quantity: $35 (Cat O15) INTENSIFIED NIGHT VIEWER KIT Reference article: Silicon Chip Sept 94. See in the dark! Make your own 3 stage first generation night scope that will produce good vision in starlight illumination! Uses 3 of the above fibre optic tubes bonded together. These tubes have superior gain and resolution to Russian viewers. 25mm size tube only weighs 390g. 40mm size tube only weighs 1.1kg. We supply a three stage fibre optically coupled image intensifier tube, EHT power supply kit which operates from 6 to 12V, and sufficient plastics to make a monocular scope. The three tubes are already bonded together: $270 for the 25mm version (Cat N04) $300 for the 40mm version (Cat N05) We can also supply a quality Peak brand 10x “plalupe” for use as an eyepiece which suits all the above 25 and 40mm windowed tubes well: $18 35mm camera lenses or either of the Russian objective lenses detailed under “Optical” suit these tubes quite well. IR “TANK” TUBE/SUPPLY KIT These components can be the basis of a very responsive infra red night viewer; the exact construction of which we leave up to you. The new IR tube is as used in older style military tank viewers. The tube employed is probably the most sensitive IR responsive tube we have ever supplied. Responds well even to 940nm LED illumination. The resultant viewer requires IR illumination, as without this it will otherwise only “see” a little bit better than the naked eye. Single tube, first generation. Screen diameter: 18mm. Tube length 95mm. Diameter: 55mm. Weight: 100g. Tube can be operated up to about 15kV. Our miniature night viewer power supply (kit number K52) is supplied with its instructions included. Only very basic ideas for construction of viewer is provided. Tube and the power supply kit only: $80 (Cat N06) RUSSIAN SCOPE KIT Our hybrid Russian/Oatley kit design makes this the pick of the Russian scopes in this price range! We supply a fully assembled Russian compact scope housing containing the intensifier tube, adjustable eyepiece and objective lens. Housing is made from aluminium. The objective lens is fixed in focus, but it is adjustable after loosening a grub screw. We also include the night viewer power supply kit (kit number K52) and a small (84 x 55 x 32mm) jiffy box to house the supply in. The box must be attached by you to the scope housing. Operates from a 9V battery. This scope has a useful visible gain but is difficult to IR illuminate satisfactorily. Length of scope is 155mm: $290 (Cat N07) LASER POINTER A complete brand new 5mW/670nM pointer in a compact plastic case (75 x 42 x 18mm) with a key chain. Features an automatic power control circuit (APC) which is similar to our kit number K35 & our laser diode module’s circuit. Battery life: 10 hours of operation. Powered by two 1.5V N type batteries (included). This item may require licensing: $80 (Cat L08) MAGNETIC CARD READER Commercial cased unit that will read some information from most plastic cards, needs 8 to 12V DC supply such as a plugpack. Draws about 400mA. Power input socket is 2.5mm DC power type. Weight: 850g. 220 x 160 x 45mm: $70 (Cat G05) 400 x 128 LCD DISPLAY MODULE - HITACHI These are silver grey Hitachi LM215 dot matrix displays. They are installed in an attractive housing. Housing dimensions: 340 x 125 x 30mm. Weight: 1.3kg. Effective display size is 65 x 235mm. Basic data for the display is provided. Driver ICs are fitted but require an external controller. New, unused units. $25 ea. (Cat D02) 3 for $60 VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nM laser diode modules. Consists of a visible laser diode, diode housing, driver circuit, and collimation lens all factory assembled in one small module. Features an automatic power control circuit (APC) driver, so brightness varies little with changes in supply voltage or temperature. Requires 3 to 5V to operate and consumes approx 50mA. Note: 5V must not be exceeded and there must be no ripple on the power supply, or the module may be instantly destroyed. These items may require licensing. We have two types: 1. Overall dimensions: 11mm diameter by 40mm long. Driver board is heatshrinked onto the laser housing assembly. Collimating lens is the same as used in the above laser pointer, and our visible laser diode kit: $55 (Cat L09) 2. Overall dimensions: 12mm diameter by 43mm long. Assembled into an anodised aluminium casing. This module has a superior collimating optic. Divergence angle is less than 1milliradian. Spot size is typically 20mm in diameter at 30 metres: $65 (Cat L10) This unit may also be available with a 635nm Laser Diode fitted. FLUORESCENT LIGHT HIGH FREQUENCY BALLASTS European made, new, “slim line” cased, high frequency (HF) electronic ballasts. They feature flicker free starting, extended tube life, improved efficiency, no visual flicker during operation (as high frequency operation), reduced chance of strobing with rotating machinery, generate no audible noise and generate much reduced radio frequency interference compared to conventional ballasts. The design of these appears to be similar to the one published in the October 1994 issue of Silicon Chip magazine, in that a high frequency sine wave is used, although these are much more complex. Some models include a dimming option which requires either an external 100K potentiometer or a 0-10V DC source. Some models require the use of a separate filter choke (with dimensions of 16 x 4 x 3.2cm); this is supplied where required. We have a limited stock of these and are offering them at fraction of the cost of the parts used in them! Type A: 1 x 16W tube, not dimmable, no filter, 44 x 4 x 3.5cm: $20 Type B: 1 x 16W tube, dimmable, filter used, 43 x 4 x 3cm: $26 Type C: 1 x 18W tube, not dimmable, no filter, 28 x 4 x 3cm: $20 Type D: 2 x 32W or 36W tubes, dimmable, no filter, 43 x 4 x 3cm: $26 Type E: 2 x 32W tubes, not dimmable, no filter, 44 x 4 x 3.5cm: $22 Type F: 1 x 32W or 36W tube, not dimmable, no filter, 34 x 4 x 3cm: $20 Type G: 1 x 36W tube, not dimmable, filter used, 28 x 4 x 3cm: $20 Type H: 1 x 32W or 36W tube, dimmable, filter used, 44 x 4 x 3.5cm: $20 (Cat G09, specify type). CYCLE/VEHICLE COMPUTERS BRAND NEW SOLAR POWERED MODEL! Intended for bicycles, but with some ingenuity these could be adapted to any moving vehicle that has a rotating wheel. Could also be used with an old bicycle wheel to make a distance measuring wheel. Top of the range model. Weather and shock resistant. Functions: speedometer, average speed, maximum speed, tripmeter, odometer, auto trip timer, scan, freeze frame memory, clock. Programmable to allow operation with almost any wheel diameter. Uses a small spoke-mounted magnet, with a Hall effect switch fixed to the forks which detects each time the magnet passes. Hall effect switch is linked to the small main unit mounted on the handlebars via a cable. Readout at main unit is via an LCD display. Main unit can be unclipped from the handlebar mounting to prevent it being stolen, and weighs only 30g. Max speed reading: 160km/h. Max odometer reading: 9999km. Maximum tripmeter reading: 999.9km. Dimensions of main unit: 64 x 50 x 19mm: $32 (Cat G16) December 1995  59 PRODUCT SHOWCASE New digital scopes from Tektronix Tektronix has moved to consolidate its position in the digital oscilloscope field, particularly at the low price end of the market. It has announced three new models of its TDS300 series with more performance and the inclusion of features which were previously costly options. Of special interest to first-time digital scope buyers, the new TDS300 series represent a doubling in their performance standard with no increase in price. The three new models are the 100MHz TDS340, 200MHz TDS360 and 400MHz TDS380. All three scopes feature the Tektronix patented Digital Real Time (DRT) over­sam­pling technology which effectively eliminates aliasing and ena­bles single shot waveform capture at the instrument’s rated bandwidth. By way of explanation, until the introduction of DRT, all digital scopes had poor performance in single shot mode. For example, a scope with 100MHz bandwidth and a sampling 60  Silicon Chip rate of 300Ms/s (megasamples/second) would be hard-pressed to provide a 3MHz bandwidth in single shot mode. The problem is the sampling process itself; a typical digital scope cannot generate enough samples to enable a single shot waveform to be accurately repro­duced. The Tektronix approach to this problem has been to essen­tially overwhelm it with huge sampling rates. Hence, the sampling rate of these new TDS300 series scopes is five times their analog bandwidth: the 100MHz TDS340 samples at 500Ms/s; the 200MHz TDS360 at 1Gs/s and the 400MHz TDS380 at 2Gs/s (Gigasamples/second). As with earlier models, the TDS300 series offer four acqui­ sition modes: sample, envelope, average and peak detect. Video and edge triggering capabilities are built-in, along with the ability to capture transients down to one nanosecond. For users to who need to capture and store many waveforms for future reference, the TDS360 and 380 models come with a 3.5 inch floppy disc drive which is PC DOS compatible. It can store waveforms in a variety of formats which can then be taken into many programs for analysis or subsequent printout. Indeed, the provision of the disc drive effectively makes the need for a printer port no longer necessary in most circumstances. As a further attraction, all three TDS300 models include Fast Fourier Transform (FFT) capability at no extra cost. Pre­ viously a costly option on high end digital scopes, FFT is useful for analysing harmonic content in waveforms, noise in mixed digital/ analog systems, line current harmonics and so on. Also available as options are a GPIB port, RS-232 serial and Centronics parallel ports, and a VGA monitor output. The new TDS300 series scopes will be available from Tektro­nix distributors from the 1st December 1995. The TDS340 has a suggested retail price of $3700; the TDS360, $5200; and the TDS380, $6800. These prices do not include sales tax. All models come with a 3-year warranty. Digital power meters from Yokogawa The recently introduced WT110/ WT130 digital power meters from Yokogawa are compact, low-cost instruments offering high performance. Capable of operating at DC or AC over a bandwidth of 10Hz to 50kHz, the meters have a basic accuracy of ±0.25%. Integrated power (Wh) and current (Ah) can be displayed continu­ ously on the instruments’ 3-line, 7-segment LED displays. This standard function allows the display of integrated power and current with positive and any negative values measured separately. The decimal point position automatically moves during integration. This enables high resolution measurements to be carried out over short periods. The instruments include GPIB and RS-232C interfaces and conform to IEC1010 safety standards, with isolation between the voltage and current terminals to 3.7kVAC/50Hz for one minute and surge resistance to 300A, 2kV/1 cycle (50Hz). For further information, contact Yokogawa Australia, 25-27 Paul St North, North Ryde, NSW 2113. Phone (02) 805 0699. 750 watt power supply The Kepco RCW series is a group of seven 750W single output switching power supplies that incorporate FET-based forward converters. The fan-cooled modular style switchers have adjust­ able outputs based around nominal voltages of 3.3, 5, 12, 15, 24, 28 & 48V DC, and are able to source currents of 15-150A, depend­ing on the mod­el. They can be operated at temperatures ranging from -10°C to +71°C, delivering full power at 50°C. With a switching frequency of 160kHz, the RCW converters provide high efficiency at either 240 or 120 VAC. The input voltage can be anywhere between 85V and 264V and is sensed au­tomatically so that no user selection is necessary. An EMI filter is built-in to ensure that conducted noise meets FCC Class A limits. In addition, an active power factor correction circuit ensures that current is drawn over the entire mains cycle so that the RCW meets the IEC’s harmonic current limit (IEC 555-2). To allow for paralleling, a current share circuit is pro­vided to equalise the outputs from as many as three RCW series units together. A square type overcurrent limiter is backed by an undervoltage detector that shuts down the RCW when an overload persists for more than 40 seconds; over­voltage shutdown is in­stant­aneous. In either case, reset is achieved by removing the mains power for about 40 seconds. Overvoltage, under­ volt­ age, fan stop and input alarm are all flagged by red LEDs on the front panel. For more information on the Kepco RCW series, contact Obiat Pty Ltd, 129 Queen St, Beaconsfield, NSW 2014. Phone (02) 698 4111 or fax (02) 699 9170. December 1995  61 Outdoor speaker from Akai Designed for both inside and outside sound reinforcement applications, Akai’s SRM-500 outdoor loudspeakers can be conveniently fitted under awnings or mounted on walls. Capable of handling up to 100 watts, the SRM-500s use a 120mm carbon poly­propylene woofer and a 32mm dome tweeter. Covered by a twelve month parts and labour warran­ty, the SRM-500s are avail- Programmer for AT89C2051 flash micro AirBorn Electronics has announced the PG2051 development programmer for the At89C2051 microprocessor. The At89C2051 is a 20-pin 8051 compatible microprocessor with 2Kb of flash memory. The PG2051 erases, programs and verifies AT89C2051 chips in six seconds. The programmer may be connected to a PC or other host by 62  Silicon Chip able at Akai dealers and selected department stores. For further information, contact Akai on (02) 763 6300. a serial cable and the data download­ed in Intel hex format. The programmer will test, erase, program, verify, write protect and security protect as it receives the file, according to the settings on its DIP switches. It also features a test switch which allows the owner to check if an AT89C2051 is blank, working, programmed or failed.. Flash memory means the micro itself can be reprogrammed quickly and easily. Previously, designers had the difficult choice of higher cost UV erasable chips or cheaper One-Time-Programmable chips. The UV chips were often several times the OTP price but could be reused if a program change was needed. The AT89C2051 is priced even more attractively than most of the OTP chips and erases in milliseconds. The At89C2051 executes all of the 8051 instructions and has all the peripherals and registers. This means the large quantity of development software and library and applications code already available for the 8051 can be used with this new microprocessor. AirBorn Electronics is selling the PG2051 program with a datasheet and plugpack for an introductory price of $188 (ex tax). A complete evaluation kit is also available, for $233 (ex tax). It includes the programmer and plugpack, two At89C2051 devices, a small prototype board to get an At89C2051 up and running and a diskette with some example ASM code, a shareware assembler and a dis-assembler. For further information, contact AirBorn Electronics, Suite 201, 19-21 Berry St, North Sydney 2060. Phone (02) 9925 0325. Boundary microphone from Amber Technology Amber Technology has announced the new Beyerdynamic MPC 65 acoustic boundary microphone. Measuring just 86 x 61 x 31mm, the small and unobtrusive MPC 65 is ideal for recording and sound reinforcement applications requiring high quality reproduction of speech, including tele­ phone and video conferencing systems, boardrooms, courtrooms and churches. Beyer claim the MPC 65 provides higher gain before feedback than typical boundary microphone designs. It has a semi-cardioid response and an integral low-cut filter to remove low frequency rumble and unwanted surface-bound noise. The microphone requires 12-48VDC phantom power and may be used free standing or surface-mounted via an integrated connector in its base. The Beyer MPC 65 is available with a built-in or external preamplifier, terminated with a captive cable, XLR or jack con­nector and in matte black or off-white finishes. Recommended retail prices start at $599. For further information, contact Amber Technology, Unit B, 5 Skyline Place, Frenchs Forest, NSW 2086. Phone (02) 9975 1211 or fax (02) 9975 1368. AUDIO TRANSFORMERS Mini pistol grip driver Released by Scope Laboratories of Melbourne under their Cadik brand (code SD-CCC-811), this 5-in-1 pistol Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 grip driver combines small size for the tool box, good ergonomic design and a ratchet/reversible func­ tion. Three slotted and two Phillips bits are stored in the handle. For further information, contact Scope Laboratories, 3 Walton Street, Airport West, Vic 3042. Phone (03) SC 9338 1566. ANOTHER GREAT DEAL FROM MACSERVICE 100MHz Tektronix 465M Oscilloscope 2-Channel, Delayed Timebase VERTICAL SYSTEM Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or less for DC coupling and -15°C to +55°C. Bandwidth Limit Mode: Bandwidth limited to 20MHz. Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C. Uncalibrated, continuously variable between settings, and to at least 12.5V/div. Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from 10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.) Display Modes: Ch 1, Ch 2 (normal or inverted), alternate, chopped (250kHz rate), added, X-Y. Input R and C: 1MΩ ±2%; approx 20pF. Max Input Voltage: DC or AC coupled ±250VDC + peak AC at 50kHz, derated above 50KHz. HORIZONTAL DEFLECTION Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-2-5 sequence). X10 mag extends fastest sweep rate to 5ns/div. Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div. Horizontal Display Modes: A, A Intensified by B, B delayed by A, and mixed. CALIBRATED SWEEP DELAY Calibrated Delay Time: Continuous from 0.1µs to at least 5s after the start of the delaying A sweep. Differential Time Measurement Accuracy: for measurements $900 of two or more major dial divisions: +15°C to +35°C 1% + 0.1% of full scale; 0°C to +55°C additional 1% allowed. TRIGGERING A & B A Trigger Modes: Normal Sweep is triggered by an internal vertical amplifier signal, external signal, or internal power line signal. A bright baseline is provided only in presence of trigger signal. Automatic: a bright baseline is displayed in the absence of input signals. Triggering is the same as normal-mode above 40Hz. Single (main time base only). The sweep occurs once with the same triggering as normal. The capability to re-arm the sweep and illuminate the reset lamp is provided. The sweep activates when the next trigger is applied for rearming. A Trigger Holdoff: Increases A sweep holdoff time to at least 10X the TIME/DIV settings, except at 0.2s and 0.5s. Trigger View: View external and internal trigger signals; Ext X1, 100mV/div, Ext -: 10, 1V/div. Level and Slope: Internal, permits triggering at any point on the positive or negative slopes of the displayed waveform. External, permits continuously variable triggering on any level between +1.0V and -1.0V on either slope of the trigger signal. A Sources: Ch 1, Ch 2, NORM (all display modes triggered by the combined waveforms from Ch 1 and 2), LINE, EXT, EXT :-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM, EXT, EXT :-10. Optional cover for CRT screen – $35 through the vertical system. Continuously variable between steps and to at least 12.5V/div. X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth: DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz. DISPLAY CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosX-Y OPERATION phor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence) markings with horizontal and vertical centerlines further marked in 0.2cm increments. 10% and 90% for rise time measurements. Australia’s Largest Remarketer of markings Graticule Illumination: variable. Beam Test & Measurement Equipment Finder: Limits the display to within the graticule area and provides a visible 3167. Tel: (03) 9562 9500; Fax: (03) 9562 9590 display when pushed. MACSERVICE PTY LTD 20 Fulton Street, Oakleigh Sth, Vic., **Illustrations are representative only. Products listed are refurbished unless otherwise stated. December 1995  63 COMPUTER BITS BY GEOFF COHEN gcohen<at>pcug.org.au Ram Doubler: extra sauce without the chips This program can effectively double your PC’s memory and dramatically increase system resources as well. It’s easy to install and is much cheaper than adding real RAM. We all want more memory for our PCs but, of course, we don’t always have the money available to buy the extra RAM. Currently, RAM costs about $270 per 4Mb. Fortunately, there are several software solutions available to correct low memory problems, the most well-known being “Magna RAM” and “RAM Doubler”. They use proprietary memory compression techniques to effectively double the RAM available to Windows. The program reviewed here (ie, the one we played with) is RAM Doubler, which does seem to significantly reduce low memory problems with Windows 3.1 or Windows 3.11 and allow many more programs to run simultaneously. On the machine used, the available System Resources in­ creased from 9% to 39% free after Ram Doubler was installed and the same programs loaded. After loading several more programs, I still had 14% free but without Ram Doubler I would have never been able to load them all. Indeed, according to RAM Doubler, I would have had -31% free without it running! System requirements RAM Doubler will work on any 386, 486 or Pentium PC running Windows 3.1 or 3.11 in enhanced mode. A minimum of 4Mb of RAM is required but 8Mb is recommended. I was also pleaded to see that RAM Doubler will work with either QEMM, 386Max or Netroom DOS memory managers, as Fig.1 (above): because Windows only allocates a limited amount of memory to manage system resources, its all too easy to get the dreaded low resources message when running lots of applications. RAM Doubler can correct this by dramatically increasing system resources, as shown in Fig.2 at right. 64  Silicon Chip well as the standard EMM386 memory manager that comes with Microsoft DOS. How RAM Doubler works RAM Doubler increases your computer’s apparent memory using three methods. First, RAM Doubler moves any hardware device drivers from the lower 1Mb area, giving your applications more RAM space. These typically include network and display drivers. In addition, RAM Doubler moves any Visual Basic Extensions (VBX), as this software tends to fill up the first 1Mb of your PC’s memory. Normally, you only become aware of the problem when Windows is unable to cope and displays an “Insufficient Memory” error mes­sage. Typically, you may have installed a new video card or installed new software, and then find that you can’t load Wind­ows. Ram Doubler can fix this sort of problem. Second, RAM Doubler restructures several critical “System Heap” Installing RAM Doubler Installing RAM Doubler is simple. As a welcome change from the bloat­ ed software that’s become the trend these days, RAM Doubler comes on one 3.5-inch floppy disc. After starting Wind­ows, from the Program Manager click on File, Run and enter will then give you the option of registering on-line (see Fig.4). I tend to avoid this, unless it is an Australian program, as it usually tries to dial ISD, which can be a smidgen expensive from Oz. To ignore this option, just click “Do Not Register”, then click “OK” at subsequent screens. The Installation Successful mess­­age then pops up. You now simply remove the RAM Doubler disc and exit and restart Windows. When Windows restarts, you will see Fig.3: installing RAM Doubler is easy & it a message at the bottom even comes with an uninstall option. of the screen (see Fig.5), letting you know that RAM A:SETUP on the command line. Doubler has been successfully RAM Doubler will search for any installed. earlier versions that may be on your Another nice feature is that if, for hard disc and then ask if you want some reason, you don’t want RAM to install the program (see Fig.3). Doubler to load, you just press There is also an uninstall option, Escape when Windows is starting. which is a very useful feature that During this time, the message “RAM many Windows 3.x programs lack Doubler disabled by user request” (of course, this isn’t a problem with will appear on the screen. I can’t acWindows 95 software). tually think of a reason why anyone Assuming that you click “Install” would want to do this but it does show (it being rather difficult to install the that the program’s developers have software if you don’t), the program tried to cope with any eventuality. YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. Fig.4: RAM Doubler gives you have the option of registering on line during installation. To ignore this option, just click “Do Not Register”, then click “OK” at subsequent screens. mem­ ory resources. These are used by Windows to keep track of all the icons, menus, windows and many other items. Unfor­tunately, they can quickly fill up, as the heap size is fixed and relatively small. The heap space available at any one time de­pends on what program you are running (some use more heap space than others) and how many programs are running simultaneously. The problems that Windows may develop depends on exactly what programs you are using. Sometimes you will only notice that Windows “loses” some icons. At other times, a program will hang or you will get the dreaded continued on page 69 PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 December 1995  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. 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 Fig.5: each time Windows starts, this message appears at the bottom of the screen, to let you know that RAM Doubler has been successfully installed. Computer Bits – from page 65 “Low Resources” message (see Fig.1). When that happens, Windows can become unpredictable and the application or the whole system can “hang”, with the probability of lost data. Even if your PC has 16Mb or 32Mb of RAM, Windows will usually run out of system resources before running out of memory. RAM Doubler will normally correct this deficiency. Finally, RAM Doubler compresses memory by looking for memory blocks that Windows has used but probably will not need again soon; eg, programs that only run at start-up. The compres­ sion technique uses proprietary algorithms to reduce virtual memory disc accesses and only reduces the PC’s speed slightly (usually by 2-5%). However, the fact that RAM is many orders of magnitude faster than physical disc access (80ns versus 10ms) makes the speed difference negligible and, in the case of a slow hard disc, RAM Doubler may even speed up your PC. RAM Doubler testing I tested RAM Doubler on a typical Windows 3.x system, with a 386DX40 processor, 4Mb RAM, a 130Mb hard disc and VGA screen. Before installing RAM Doubler, I started a lot of SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. Now you can search through all the articles ever published for the one you want. The index comes as an ASCII file on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers and you can use any word processor or our special file viewer to search for keywords. Simply enter in the keyword(s) and the index will quickly find all the relevant entries. All commands are listed on the screen, so you’ll always know what to do next. Price $7.00 + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. programs, including several copies of Word 2, Excel and Thumbs Plus, until the PC was nearly out of resources, with only a few percent free. After installing RAM Doubler, the system was slightly slower to load Windows but applications loaded and ran with no appreciable speed reduction. And with the same set of programs loaded as before, system resources increased significantly, going from 9% to 39% free (see Fig.2). On this basis, RAM Doubler does seem to offer a worthwhile increase in available resources and is a lot cheaper than adding more physical RAM. How much will you save by using Ram Doubler? Well, the more RAM you have, the greater the apparent saving. Using RAM Doubler to make 4Mb of RAM look like 8Mb will save you around $120, while using it to make 8Mb look like 16Mb saves $440. Of course, the savings are even greater if you have more than 8Mb of RAM. Price & availability At the time of writing, RAM Doubler has a recommended retail price is $139.00. The product is distributed by Firm­ ware Design (047 21 7211) and is available from most computer retailers. A Windows 95 version of RAM Doubler was due to be released SC in early November. December 1995  69 Dolby Pro Logic Surround Sound Decoder, Pt.2 In this second and final article, we describe construc­tion and testing which involves assembly of the PC boards and a fair amount of interconnecting wiring. By JOHN CLARKE The Prologic Surround Sound Decoder and Effects Unit is housed in a low-profile metal case measuring 430mm wide, 59mm high and 307mm deep, including knobs, rubber feet and the rear heatsink. Virtually all of the components, with the exception of the power transformer, switches and potentiometers, are mounted on PC boards. There are five boards in all: the main decoder board, labelled “Pro Logic Main”, 70  Silicon Chip code 01409951, 160 x 165mm; the power supply, code 01409952, 105 x 140mm; the power amplifier board, code 01409953, 200 x 50mm; the microprocessor board, labelled “Pro Logic Micro”, code 01409954, 76 x 90mm; and the display board, code 01409955, 26 x 115mm. Begin construction by checking the PC boards for any de­fects. Check particularly for any breaks or shorts between tracks. There should be 3mm holes on all boards for the mounting screws and a 3mm hole is required to accommodate the regulator mounting screw for REG5 on the power supply board. Start assembly of the main decoder PC board (see Fig.4) by inserting all the PC stakes required for external wiring and then the links, using tinned copper wire. To produce a neat job with the links, we recommend that the wire be slightly stretched: grip one end of a length of wire (say 30cm long) in a vise and then pull the other end with a pair of pliers. Pull just hard enough to make the wire “give” slightly and then it will become straight. Cut the wire to lengths suitable for each link and bend the ends of each link using pliers so that they fit neatly into the required positions. Next, install the ICs. Take care with their orientation, noting that IC1 and IC2 face in different directions, while R OUT 100k 100  EFFECTS AMP IN GND EFFECTS AMP OUT GND L OUT 100k 100 GND 100 SURR OUT SURR OUT C OUT 100k GND GND 100 RELAY +25V 180pF 4.7k 4.7k VR3 D11 RLY2 RLY4 RLY1 0.33 33k RLY3 1 100 IC5 LF347 47k 0.1 7.5k 1 IC4 LF347 -15V 47k 47k 47k 47k 100k Q1 180pF 0.1 VR2 100 4.7k 470 10uF PC0 +15V .068 100pF 47uF 15k 18k 470pF 10uF LL 680pF .0033 .047 0.68 680pF 0.22 0.22 1 2x.022 0.22 0.22 4.7uF VR4 1uF 470pF 0.1 15k 1uF 4.7uF +4V 10M 0.1 .047 IC1 M69032P 0.1 .0056 15k 330k 0.1 0.1 10  15k .068 .0022 100uF 10  E 0.1 1M X1 22k 100k 22k 22k A 8.2k 100k 15k IC2 M65830P 470pF B +12V 7.5k 18k 5.6k 30  1 .0047 22uF 47k 7.5k 0.1 15k 15k 68k 68k 22k 100uF 0.1 10uF 10uF 47k 7.5k 0.1 1uF 1uF .0056 .0056 100uF 22k 1uF 10uF 25VW GND .056 L IN G R IN 0.1 1uF GND 2.7k 22k 1uF 1uF LP OUT 22k .047 1k 0.1 1uF IC3 TDA1074A +20V 100pF 100  10uF 100uF 10uF 0.18 1 R S P 15k 22k 100uF 1uF 0.1 1uF VR1 150k 0.22 15k 68k 180pF 68k 180pF 7.5k 7.5k 15k 15k GND 0.1 15k +5V 15k 15k GND Fig.4: the component overlay diagram for the main decoder board. Take care to avoid solder bridges between the closely spaced pins of IC1 and check that all polarised parts are correctly oriented. IC3, IC4 & IC5 all face in the same direction. When soldering the closely spaced pins of IC1, be sure that solder does not bridge between pins. When installing the resistors, check the colour code for each value against Table 1. It is also a good idea to check each value with a digital multimeter. When inserting the capacitors, use Table 2 to check the values. For example, a .047µF capacitor could be labelled 47n or 473. Once the capacitors are in, mount the four reed relays, diode D11, transistor Q1 and the 2MHz crystal, X1. Take care with the orientation of D11 and Q1. Amplifier board assembly Refer now to Fig.5 for the component overlay of the power amplifier board. Again, start with the PC stakes and the link (one only), then insert the resistors and capacitors. The fuse holder clips are inserted with their locating tabs oriented toward the ends of the fuse. If the tabs are located incorrectly, you will not be able to fit the fuses. The power ICs (IC7, IC8 and IC9) come with preformed leads. When inserted and soldered, the mounting hole in each metal tab should be located 16mm above the PC board, to line up with the holes in the rear of the chassis. The power supply board is equally straightforward (see Fig.6) and you can start with the PC stakes and links. This done, install the diodes, taking care with the orientation of each. Note that D1-D4 are larger than D5-D10. The small bridge, BR1, must be located with its notched end adjacent to the 470µF capacitor. The three 0.25W resistors can be mounted next, followed by the four 3-terminal regulators, REG1-4. Make sure that you don’t mix December 1995  71 47uF 25VW Surround Sound Decoder – ctd D5 +25V TO RELAYS D6 18VAC GND 0V D1-D4 GND GND 1k 22uF F3 CENTRE IN 18VAC 22k 2.2uF 100uF 10k 10000uF 25VW +25V GND 10000uF 25VW -25V IC7 18k 0.1 0.1 100uF D10 D9 D8 D7 680W 5W 0.22 1 4700uF 25VW TO CENTRE SPEAKER F2 +20V 1000uF +12V SURR L IN GND 2.2uF 100  5W REG5 7805 18k 0.1 0.1 +5V +5V SURR R IN 1k X2 1M 2.2uF B A E R S D PC0 2x39pF 10k IC6 MC68HC705C8P 18k 0.1 1k 0.1 IC9 0.1 47k 47k 47k 22k 100uF DIP1 ON 47k 0.1 GND 10uF Fig.6: the component overlay for the power supply board Note that the diodes for D1-D4 are larger than those for D5-D10. TO SURR L SPEAKER 10uF 100uF 0.22 F6 1 10k GND 1 Fig.5: the component overlay diagram for the power amplifier board. No setting-up adjustments are required for the power amplifiers. +5V S4b +5V 330 330 330 330 330 330 330 330 330 330 GND 330 330 330 TO SURR R SPEAKER 72  Silicon Chip +15V 3x10uF 0.22 10uF F7 470uF 1.8k 1 22uF 470uF BR1 100uF F4 REG3 -15V 330  GND REG4 2x 10uF IC8 -25V +25V REG1 120  22k 100uF F5 REG2 1k 22uF Fig.7: the component overlay for the microprocessor board. We used a 6-way pin header for the B, A, E, R, S and D output lines. TABLE 1: RESISTOR COLOUR CODES 4-Band Code (1%) brown black blue brown brown black green brown orange orange yellow brown brown green yellow brown brown black yellow brown blue grey orange brown yellow violet orange brown orange orange orange brown red red orange brown brown grey orange brown brown green orange brown brown black orange brown grey red red brown violet green red brown green blue red brown yellow violet red brown red violet red brown brown grey red brown brown black red brown yellow violet brown brown orange orange brown brown brown red brown brown brown black brown brown orange black black brown brown black black brown brown black gold gold D13 D12 S5 LED1 10k S6 D14 10k DISP2 HDSP5301 10k DISP1 HDSP5301 Value 10MΩ 1MΩ 330kΩ 150kΩ 100kΩ 68kΩ 47kΩ 33kΩ 22kΩ 18kΩ 15kΩ 10kΩ 8.2kΩ 7.5kΩ 5.6kΩ 4.7kΩ 2.7kΩ 1.8kΩ 1kΩ 470Ω 330Ω 120Ω 100Ω 30Ω 10Ω 1Ω 10k ❏ No. ❏   3 ❏   2 ❏   1 ❏   1 ❏   6 ❏   4 ❏ 11 ❏   1 ❏ 12 ❏   5 ❏ 14 ❏ 11 ❏   1 ❏   6 ❏   1 ❏   3 ❏   1 ❏   1 ❏   5 ❏   1 ❏ 14 ❏   1 ❏   7 ❏   1 ❏   2 ❏   3 A K S7 Fig.8: the display board. The two 7-segment displays are oriented with the decimal points to the lower righthand side, while the switches (S5-S7) all have their flat side towards the top of the board. LED1 should initially have only one lead soldered to the board to allow for easy adjustment later on. them up. REG1 is a 7815 type, REG2 is a 7915, REG3 is a 7812 and REG4 is an LM317. REG5 is mounted on a small heatsink using a screw and nut to secure it to the PC board. The capacitors are next. The two 10,000µF and 4700µF electrolyt­ics are mounted on their side and can be secured to the PC board using a small amount of silicone sealant. The remaining capacitors are mount­ ed vertically, with the polarity shown. The 100Ω and 680Ω 5W resistors are mounted 1mm proud of the PC board to allow cooling. Microprocessor board The microprocessor board has only a few parts, as shown in Fig.7. We used a 6-way pin header for the B, A, E, R, S and D output lines. Make sure you orient IC6 correctly. Its notched end is adjacent to the 10µF capacitor. The DIP switch, DIP1, is oriented with the “on” label adjacent to the edge of the PC board. The display PC board is next – see Fig.8. Solder in the resistors and diodes, taking care with the orientation of D12-D14. The two 7-segment displays are oriented with the decimal point to the lower righthand side, while the switches, S5-S7, have the flat side toward the top of the PC board. Finally, install LED1 and solder only one lead to 5-Band Code (1%) brown black black green brown brown black black yellow brown orange orange black orange brown brown green black orange brown brown black black orange brown blue grey black red brown yellow violet black red brown orange orange black red brown red red black red brown brown grey black red brown brown green black red brown brown black black red brown grey red black brown brown violet green black brown brown green blue black brown brown yellow violet black brown brown red violet black brown brown brown grey black brown brown brown black black brown brown yellow violet black black brown orange orange black black brown brown red black black brown brown black black black brown orange black black gold brown brown black black gold brown brown black black silver brown TABLE 2: CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.68µF   680n   684 0.33µF   330n   334 0.22µF   220n   224 0.18µF   180n   184 0.1µF   100n   104 .068µF   68n  683 .056µF   56n  563 .047µF   47n  473 .022µF   22n  223 .0056µF   5n6  562 .0047F   4n7  472 .0033µF   3n3  332 .0022µF   2n2  222 680pF   680p   681 470pF   470p   471 180pF   180p   181 100pF   100p   101 39pF   39p   39 the PC board. This will allow easy adjustment later on. The display and microprocessor boards are soldered together at right angles after aligning the track buses together. At this stage only tack solder December 1995  73 CENTRE SURR L SURR R IEC PLUG F1 BROWN (ACTIVE) GND NEUTRAL (BLUE) EARTH GREEN/ YELLOW EARTH LUG GND 2 1 MOV POWER AMPLIFIERS ORANGE ORANGE WHITE PINK YELLOW T1 RED 26 25 B E S A R D POWER SUPPLY 26 MICROPROCESSOR CONTROL DISPLAY .01 3kV S7 6 10M S1 S6 10M S5 74  Silicon Chip 8 9 S4 S3 7 VR1 SUBWOOFER L OUT OUT L IN 0.47 R IN Fig.9: this diagram shows the general disposition of all the PC boards. Be sure to run shielded audio cable in the locations indicated and use mainsrated cable for all mains wiring to the IEC plug, transformer, power switch and fuseholder. R OUT at two locations so that the boards can be adjusted when installed in the case. GND GND 3 Chassis assembly GND +25V -25V 4 5 1 MAIN 2 25 10 23 24 9 12 14 7 6 8 11 13 16 15 17 20 22 19 21 18 B A E S R D 24 23 VR2 VR3 13 15 16 21 22 20 14 10 12 11 3 19 17 18 5 4 S2 VR4 Work can now begin on the case. The general disposition of all the boards and the interconnecting wiring is shown in Fig.9. First, secure the sides to the baseplate using the self- tapping screws supplied. This done, cut the pot shafts and rotary switch shaft to a length suitable for the knobs supplied. Install these and switches S1, S3 and S4 on the front panel. Also insert the red Perspex window for the 2-digit display. Next, affix the Dynamark labels in position on the rear panel and fit the RCA sockets, fuseholder, IEC mains socket and loudspeak­ er terminals. This done, attach the front and rear panels to the chas­sis with the screws supplied. You can now mount the amplifier PC board against the back of the case on seven 6mm standoffs, using 3mm screws and nuts. The three power amplifier ICs are secured to the rear panel with TO-220 insulating washers and insulating bushes. The screws also hold the heatsink in place. Apply a smear of heatsink compound between the mating surfaces of the heatsink and rear of the case before assembly. The Dolby licensing label can now be affixed to the top of the heatsink. Mount the decoder and power supply PC boards on the base of the case as shown on the wiring diagram of Fig.9 using 9mm tapped spacers and short 3mm screws. The microprocessor PC board is mounted on 12mm spacers. Initially, secure the spacers to the PC board so that it can be positioned in the base of the case. Now check that the pushbutton switches are centred in the front panel holes. If necessary, adjust the height by re­soldering the front panel display board. The remaining connections between the two boards can now be soldered. December 1995  75 This photo shows the general layout inside the chassis. Note the use of plastic cable ties to bind the shielded cable runs between the PC boards and the front panel controls. The large heatsink on the rear panel dissipates the heat generated by the three LM1875 power amplifier ICs (IC7-IC9). Next, the micro/display board can be mounted in place. Secure the standoffs to the baseplate and adjust the LED so that it just protrudes through the front panel. Solder both leads to the display PC board. Transformer wiring Bolt the toroidal transformer to the base of the case using the two rubber washers and the large washer. Secure the mains terminal block to the case 76  Silicon Chip as shown in Fig.9. The earth lug is secured to the chassis with screw, nut and star washer. Scrape away the paint or anodising around this screw hole to ensure a good earth contact. Use mains-rated wire for all 240VAC connections. Solder a green/yellow striped earth wire to the earth terminal of the IEC socket and solder it to the earth lug. Using a blue mains rated wire, solder one end to the Neutral side of the plug. This con­nection must be insulated with heatshrink tubing, so slip a length over the wire before securing into the terminal block. Similarly, the brown mains wire secures to the Active terminal of the socket with heatshrink tubing over its terminal. Solder the Active lead to the fuse after slipping a length of heatshrink tubing over the wire, Solder another brown wire to the second terminal of the fuse holder and insulate the fuse terminals with the tubing. Again, switch S1 is insulated with heatshrink tubing after soldering the wires to the terminals. These wires connect to the fuse and terminal block TABLE 3: DIP SWITCH SETTINGS as shown. Do not forget the .01 3kV capacitor across the switch and the varistor (MOV) across the terminal block. The fuseholder, IEC plug and switch insulating tubing can now be shrunk down with a hot air gun. Connect the orange primary transformer wires to the termi­ nal block and solder the secondary wires to the power supply board. You should now carefully check all your work before moving to the test procedure. Testing Insert the fuse into the rear panel holder, fit an IEC mains lead and apply power. Use your multimeter to check that the voltages on the power supply board are correct. These are shown on the board overlay diagram of Fig.6. Note that the +25V rail can be as high as +28V. The regulator output voltages should be within ±5% of their nominal values. If it all checks out, remove the power so that you can continue the wiring for the DC rail connections. We used green hook-up wire for the GND wiring, red for +5V, blue for -15V and yellow for +15V. There is nothing sacred about this but you should use consistent colours for all the wiring. Delay 1 2 3 4 15ms on on on on 16ms on on on off 17ms on on off on 18ms on on off off 19ms on off on on 20ms on off on off 21ms on off off on 22ms on off off off 23ms off on on on 24ms off on on off 25ms off on off on 26ms off on off off 27ms off off on on 28ms off off on off 29ms off off off on 30ms off off off off Other wiring using hook-up wire should be completed now. Note that the wiring between the B, A, E and R, S, D terminals on the microprocessor PC board and the decoder board is done using the two separate 3-way rainbow cables. Terminate the microproces­ sor wire ends into the header socket pins. The wires then pass under the power supply PC board to connect into the R-D termi­nals. The B-E terminal wires also pass under the decoder board. The RCA sockets require a short length of tinned copper wire soldered between each earth connection. A 0.47µF capacitor solders between this wire and a solder lug which is secured to the chassis. Use a multimeter on the Ohms range to check that this lug is properly earthed. The remaining wiring is run using shielded cable. Try to keep these wires as short as possible and use cable ties to bundle them into neat looms. There are two holes in the decoder board to secure a cable tie near switch S2. Do not forget to solder the two 10MΩ resistors across the terminals of switch S3. When the wiring is complete, check your work thoroughly, then apply power and recheck the voltages on the power supply board. If these are now incorrect, switch off immediately and check for wiring errors. If the voltages are correct, observe December 1995  77 TABLE 4: PERFORMANCE OF PROTOTYPE Dolby Requirement Prototype -3dB <at> 50Hz & 15kHz; R & L channels -3dB <at> 50Hz & 6-8kHz; S channel -3dB <at> 50Hz & 15kHz; wideband C channel -3dB <at> 90-140Hz & 15kHz; normal C channel -3dB <at> 15Hz & 40kHz -3dB <at> 24Hz & 7kHz -3dB <at> 20Hz & 40kHz with C trim centred -3dB <at> 120Hz & 40kHz with C trim centred -65dB CCIR/ARM L, C & R channels -71dB unweighted Distortion <1% <at> 300mV input & 1kHz 0.05% R, L & C outputs; 0.15% S output Headroom +15dB above reference; all channels 17dB S ouput; 15.5dB R, C & L outputs <350mV RMS 300mV RMS 25dB minimum between channels >31dB between channels Volume Tracking <3dB over top 40dB range for all outputs <0.2dB to -70dB level; <1dB to -80dB S Channel Delay 20ms fixed or 15-30ms 15-30ms adjustable Noise Sequencer 10-15db below reference -11.3dB <at> 2s/channel 2V RMS 5.6V RMS ±10dB for C & S channel outputs ±10dB -3dB <at> 90-140Hz -3dB <at> 130Hz Frequency Response S/N Ratio (wrt to 100mV or 1W into 8W) Input Sensitivity Crosstalk Output Clipping Gain Trim Subwoofer Output Power Output 20W RMS per channel into 8W load Note: reference level is 300mV/1kHz at pin 30 of IC1 (C out) the LED display. At switch-on, the display will show two dashes (- -), then after about five seconds the display will show a delay time between 15 and 30 seconds. The actual time will depend on the settings of DIP switch DIP1. Table 3 shows how to set DIP1. Delay values can be altered using the UP and DOWN switches. Pressing the Noise switch will change the display to show L, C, r and S in sequence. The LED will also light. Note that the Mode switch must be in the surround position for all four display indications. The 3-stereo and stereo settings will truncate the display settings to L, C and r and L and r accordingly. Check that the relays switch on at the instant the LED display changes from the dashes to the delay time at switch on. They produce a slight clicking sound when closing. Check that +12V is present at pin The microprocessor and display boards are butted together at rightangles to form a single assembly before mounting in the chassis. 78  Silicon Chip 37 of IC1 and +20V is at pin 11 of IC3. Pin 4 of IC4 and IC5 should have +15V while pin 11 of these ICs should have -15V. IC7, IC8 and IC9 should have +25V on pin 5 and -25V on pin 3. There should be +5V at pins 1 and 24 of IC2 and pins 40, 37, 34 and 3 of IC4. Check also for +4V at pins 43 and 44 of IC1. A +10V reference should be at pin 8 of IC3. Connect a stereo amplifier to the left and right channel outputs and This photo shows how the leads to the fuseholder and IEC socket are fitted with heatshrink sleeving to prevent accidental contact with the mains. loudspeakers to the centre, surround left and sur­round right amplifier outputs. Switch on the noise sequencer with the Mode switch in Surround mode. Check that there is a noise signal in each channel. Adjust the surround and centre trim controls so that there is equal volume in all channels. Check the volume control operation from minimum to maximum rotation. At minimum volume, nothing should be heard from the loudspeakers while at maximum volume it should be loud. If all is well, you can connect up to your stereo TV or stereo VCR. The left and right channel outputs from your VCR or TV connect to the left and right channel inputs of the Surround Sound Decoder. It is important not to cross-connect the left and right channels otherwise the decoder cannot operate correctly. For the centre loudspeaker, there are several options available. Firstly, no loudspeaker is required if the phantom mode is selected. The centre channel signal will be diverted equally into the left and right channels. The second approach is to use a centre channel speaker which does not have bass response below 100Hz. When the normal selection for the centre channel is selected, signals below 100Hz are rolled off in the centre channel and added to the left and right The LM1875T power amplifiers (IC7,8,9) are each secured to the rear panel with a TO-220 mounting kit, to isolate them from chassis. The three screws also secure the heatsink to the rear of the chassis. *Trademarks & Program Requirements Note 1: “Dolby”, “Pro Logic” and the Double-D symbols are trademarks of Dolby Laboratories Licensing Corporation, San Francisco CA94103-4813 USA.) Note 2: this Dolby Pro Logic surround sound decoder requires a program source such as a stereo TV set or hifi stereo VCR. The program must be Dolby Surround encoded as depicted in the movie credits by the Dolby double-D surround symbol. For unencoded stereo signals, the Dolby 3-stereo selection will provide the centre front channel. Effects selection will provide surround sound from any stereo signal source. The decoder will not operate from a mono signal. December 1995  79 The rear of the chassis has a large single-sided heatsink for the power amplifiers, RCA sockets for the inputs and front chan­nel outputs, three pairs of terminals for the centre and rear speakers, and an IEC power socket. AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 12 OCT 95 11:41:12 1 0.1 0.010 0.001 T .0005 20 T T 100 1k AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 10k LEVEL(W) 20k 12 OCT 95 11:37:41 1 channels. As a consequence, the centre bass information is not lost. Warning! If a centre loudspeaker is used, it must have magnetic shielding if it is to be placed on top of or underneath your TV set. Severe colour distortions and loss of purity could result from placement of a normal speaker near a television screen or monitor. The third alternative is to use a full range loudspeaker in the centre channel. In this case, the wideband selection is chosen for the centre channel. The subwoofer output can be connected to an amplifier and loudspeaker which can provide a low frequency bass response. Note that this option is available only for the phantom and normal settings for the centre loudspeaker. When listening to Dolby encoded video tapes, the Dolby Prologic setting should be used. Adjust the delay time for best results. For unencoded music, the Effects setting will provide a rear channel ambience. The effects control sets the amount of rear channel level, while the delay can be adjusted to provide the required amount of echo. Errata Two errors have appeared in the parts list published last month. First, the capacitor across the mains switch should be .01µF/3kV, not 0.1µF. Second, there are eight 22kΩ resisSC tors, not seven. 0.1 0.010 Kit Availability 0.001 .0005 0.1 1 10 50 Figs.10 & 11: these two diagrams show the performance of the three power amplifiers. At top is the harmonic distortion versus frequency at a power level of 10 watts while immediately above is the harmonic distor­tion versus power at 1kHz. 80  Silicon Chip Kits will be available from all Jaycar Electronics stores. Our thanks to Jaycar Electronics for their assistance in the development of this project and for their liaison with Dolby Laboratories who have approved the design. Jaycar Electronics is the licensee for the design which was developed in our labora­tory. REMOTE CONTROL BY BOB YOUNG The mysteries of mixing This article has nothing to do with the making of alco­holic drinks, about how to behave at parties or even the design of radio receivers. It is about mixing the control signals to servos in models. Mixing makes difficult models easier to fly. Now that my Mk.22 transmitter design is close to realisa­ tion, it is appropriate to consider the mysteries of mixing. Why? – because one of the most powerful features of the proposed Mk.22 transmitter is the provision for mixing any or all channels from 1 to 24. Now mixing is a little understood subject and so we will spend some time examining the interaction between elec­ tronic theory and practical application. It is the ability to mix controls on the modern transmitter that has contributed greatly to the vastly improved standards of performance and skills of the operators. Without mixing, some flying manoeuvres would be virtually impossible, particularly in helicopters and high performance gliders. Mixing is best defined as the modification of one or more control positions by inputs from one or more different control channels. In its simplest form, it consists merely of a small shift in neutral on one channel controlled by the full excursion of another channel. In its most complex form, it may require inputs from three or four channels, some with add-subtract (dif­ ferential or inversion) inputs. There are many practical reasons for using mixing and mostly they fall into the category of making it easier on the driver. A good example is the tail rotor control on a model helicopter. The prime function of the tail rotor is to hold the tail boom in the desired location against the torque of the main rotor blades. If the throttle/collective pitch control (these are usually coupled on model helicopters) is increased, there will be more torque and the tail rotor will therefore require more pitch to Fig.1: a simple mixing circuit which could be useful for easier control of a helicopter. Some of the throttle control input (CH1) is fed to the tail rotor control channel (CH2) to introduce automatic compensation for torque changes in the main rotor. VR1 is used to set the mix ratio of the feedback voltage. compensate. Likewise, if the throttle is reduced, the tail rotor will require a reduction in pitch. Now flying helicopters is a real handful at any time because all four primary controls are constantly in motion and the level of manual dexterity required from the pilot to co-ordinate all four controls simultaneously is very high. Here then is a prime application for mixing. If we take some of the throttle control input and feed it across to the tail rotor control channel, then we can effectively introduce automat­ic compensation for torque changes in the main rotor. Fig.1 shows a representative circuit for a mixer of this style. It is the most simple of the mixing circuits in that a small percentage of the main control channel is used modify the neutral of the second channel. The direction of the feedback remains constant with no inversions required. I must point out that the circuits presented here are representative of the type of mixer for use on voltage driven encoders (they will not work on the old 1/2 shot encoders). These encoders use a reference which is 1/2 of the regulated supply rails. In this manner, the control pots can be inverted for servo reversing without any neutral shift in the servos. Thus, the REF input is connected to the 1/2 regulated supply rail of the trans­mitter. Referring to Fig.1 the main control pot of Channel 1 (CP1) supplies a feedback voltage to the control input of Channel 2 (CP2) via the gain set control pot VR1. This pot is used to set the mix ratio of the feedback voltage. The values will vary depending on which encoder you are hooking the mixer into. Typi­cally, pots CP1 and CP2 are 5kΩ, VR1 is 50kΩ and all fixed resis­tors are about 100kΩ. In the practical example of our helicopter model, CP1 is the control December 1995  81 Fig.2(a): mixed elevators/flaps are used for aerobatics or com­ pensation for trim shift induced by large angles of takeoff/landing flaps. It is desirable to arrange for the mixing to be switched in or out very quickly and easily during normal flight. Fig.2(b) shows elevator trim compensation for the pitch change that takes place when the takeoff or landing flaps are selected. The direction of compen­sation will depend on the configuration of the aircraft Fig.3: the plan and end elevation of a typical glider wing. The outboard trailing edge panels are the ailerons and perform some unusual functions. The inboard panels are the variable camber panels and they also perform multiple tasks. pot (stick) for the Throttle/Collective pitch and is thus the primary control. CP2 is the stick control pot for the tail rotor. To set the system up, you would place the Throttle and Tail Rotor control sticks in neutral and set VR1 for an approximation of the desired mix ratio. Moving the Throttle stick will now induce a neutral shift on the Tail Rotor pitch. The amount of Tail Rotor pitch change is adjustable via potentiometer VR1 and is found by experimentation. This will vary from model to model 82  Silicon Chip due to aerodynamic influences. Model aircraft Another application is the mixing of flaps and elevators in a model aircraft. There are two basic scenarios here: (1) the use of mixed elevators/flaps for aerobatics; and (2) compensation for trim shift induced by large angles of takeoff/landing flaps. In both cases, unlike the helicopter scenario, it may be desirable to arrange for the mixing to be quickly switched in or out during flight. To do this, a switch inserted in the feedback line from VR1 is all that is required. This switch is best mounted on the front of the Tx case. In this case, the flaps work in reverse to the elevators but deflect equally about neutral (Fig.2a). The ratio of elevator movement to flap movement is again set via VR1. This is an old control-line trick and the effect of this arrangement is to tighten the radius of inside and outside loops to the point where square loops are possible. A further extension of this circuit is used for elevator trim compensation of the pitch change that takes place when the takeoff or landing flaps are selected (Fig.2b). Putting the flaps down can result in violent trim changes on full size and model aircraft. This is brought about by the large change in angle of attack on the wing and the sudden shift in the centre of drag in relation to the thrust line of the aircraft. As a result, large control inputs may be required on the elevators. The direction of compensation will depend on the configu­ration of the aircraft. As a general rule, high wing aircraft will require down elevator trim and low wing aircraft, up eleva­tor trim. Further variations are possible in that the flaps may be proportional or switched. In the first case, a further complica­ tion is introduced in that there will be a full excursion of the flap channel from the up or closed position which will be the neutral position for the elevator feedback, hence the flaps only supply a one-way correction. A more simple system is the fitting of a 3-position switch as the flap control instead of the pot. This would provide closed (0°), takeoff (15-20°) and landing (60-90°) flap positions. The same circuit could be used to control the cavitation plates on high speed model boats. Here, they could be coupled to the throttle and possibly even with some rudder mixed in to help control the turns. All of the above come under the heading of operator aids – nice touches, designed to make life easier for the driver. Glider controls A more complex situation arises in the class F5B and F5J gliders. These are required to perform a variety of tasks which include endurance, distance and pure speed runs. These tasks virtually call for three separate airframes and the design of a single airframe to achieve the best compromise is a very flap movement. Also, during the speed run, a small amount of up flap deflection may improve the aerofoil, again depending on the aerofoil selected for the model. All of the above only requires a simple mixer. Getting complicated Fig.4: this mixer provides add-subtract outputs. Thus, the two channels controlling the aileron servos are coupled together, with a reversal on one channel for normal aileron control. It may also be desirable to mix some aileron control into the flap panels to help improve turns. demand­ing exercise indeed. To get the results they require, the glider operators make extensive use of mixing. Here we find mixing being used to actually reconfigure the physical properties of the entire wing and this application falls well and truly outside the bounds of mere operator comfort. For the competition glider pilot, this is life and death stuff. One of the big problems they face is getting the model back on the ground due to the cleanness of the airframe. These models are capable of very high speeds and most enter the speed trap at speeds around 220km/h. (Yes I did say they were gliders. You know, no motor). Once these models hit ground effect, they can glide on forever and so very effective spoilers are a must. In addition, the endurance run requires a different camber on the wing aerofoil to that required for the speed run. Thus, the entire trailing edge of the wing is given over to variable camber devices which are required to carry out a variety of functions. Fig.3 shows the plan outline of a typical glider wing. The outboard trailing edge panels are the ailerons and perform some unusual functions. The inboard panels are the variable camber panels and they also perform multiple tasks. In addition to the complex wing functions, these models need aileron/ rudder coupling for the entire flight. This is largely due to the reduction in drag on the inboard wing tip and the increase in drag on the outboard wing tip screwing the aircraft in the opposite direction to the turn. The long, high aspect ratio wing (typically 13-15:1) makes this effect more pronounced on gliders, particularly during the slow speed endurance flights. To discuss the mixing required for contest gliders, we need to understand that each control surface on the wing requires a separate servo and thus four servos and four separate channels are used, all with mixing applied. In addition, there is the usual config­uration of a separate elevator and rudder servos, the only unusual feature being that the rudder and elevator servos may be buried in the fin or rear fuselage for balance. So we are talking about a very sophisticated little aeroplane capable of a wide range of tasks. To begin, let’s put the simple mixer of Fig.1 in place for a coupled aileron/ rudder. This is usually switched out during the speed run. During the high speed runs, very snappy turns are required and here the old control line trick discussed previously is of great benefit. Thus, we must add another mixer for coupled flaps/elevators, only this time we mix in both flap ser­vos. So, when the elevators go up both flap servos go down, the mix again being determined by experimentation. This must be capable of being switched in and out, as it is not desirable to use this feature in the endurance run, for example. The typical maximum deflection of the flap is about 5°. It is also desirable to use variable camber on the trailing edge of the wing to provide the best lift/drag ratio on the aerofoil for each task, so we must have normal flap control. Hence, we select a bit of flap to increase the camber during the endurance run, to improve the lift/ drag ratio of the wing. Thus, both flaps need to be able to be moved down as a normal flap, the angle of deflection depending on the aerofoil section used. In addition, during winch launch, the wing camber is in­creased for maximum lift and thus line tension. This calls for approximately 20° of down Now we get to the really complicated bit. The ailerons which control the roll axis require opposite rotation from each servo, thus any mixing applied to these controls will require an inverter with a gain of -1. The mixer in Fig.4 is typical and provides Add-Subtract outputs. Thus, the two channels controlling the aileron servos are coupled together with a reversal on one channel for normal aileron control. It may also be desirable to mix some aileron control into the flap panels to help improve the turns. The landing configuration calls for the lift to be dumped and the drag to be increased as much as possible. Here we see a remarkable configuration used on the wing which is known as “crow”. In this configuration, the ailerons which usually work in opposition are both raised up 20°. This reduces the lift across this portion of the wing and also ensures that the wing tips do not stall before the centre section. Conversely, the centre section flaps are deflected down by approximately 60° to provide the drag necessary to slow these missiles down for landing. All of this requires very complex mixing facilities and a great deal of experience on the pilot’s behalf to set up and master. All of the above combinations must be capable of being switched in and out instantly and in the heat of a turn at 220km/h, initiated up to 1km from the operator and sometimes close to the ground. This is definitely not for the fainthearted. So there you have it. It only takes a moment’s reflection to see that the development of a commercial computerised transmitter with the flexibility to handle all of the above scenarios is a serious undertaking. You can also see why the modern computer radio has become so complex and why in many instances it has outgrown the requirements of the average club modeller. The proposed Mk.22 transmitter will have a simple system which can be tailored to your own requirements. You add only the features you need. Only a handful of people require a system as SC complex as described earlier. December 1995  83 MAILBAG Doesn’t like the answers I would like to express my disappointment at the attitude to my letter that you published in the Mailbag section of the September 1995 issue of SILICON CHIP. I don’t know why your response to my letter was so negative. A number of other people that I have talked to have also questioned your attitude to what seems a useful project. If you take a look through the Dick Smith catalog you will find that the lowest rated power amplifier is the 0.5W “Champ”. The next step up in power is a guitar amplifier with a rating of 4W and was designed by “Australian Electronics Monthly” in 1988! This kit comes with a front panel label and other assorted ex­tras, which blows the cost out to $30 for one channel only. The next step, or leap, in power is to a 20W amplifier, designed by “Electronics Australia” in 1984. In the Jaycar catalog, the selec­tion starts with the “Champ” again, and the next step in power is the 25W amplifier of December 1993, that you suggested that I use instead. More bureaucracy on the way? In your October 1995 edition, you published an advertise­ ment for the Spectrum Management Authority (page 9). The advert advises all man­u­fac­turers, importers and wholesalers of new regulations governing elec­tro­magnetic interference. I have ob­ tained the information booklet published by the SMA and have some grave concerns about the extent of these regulations. Intended to be phased in from January 1997, the regulations cover all electrical, electronic and electromechanical equipment. Most of the projects described in your magazine will be affected so I think it is in your best interest to investigate for your­ self the implications of this new legislation. For myself, a small 84  Silicon Chip I did take a look at this project, and the first problem that I could see was the size of the PC board. I have been able to reduce the size of this board by about half. I have built and tested this amplifier and have found that it will ring if there is no resistor across the input. I tried a 10kΩ resistor which worked nicely. In conclusion, lighten up. I thought that my idea would be ideal as a quick project for the Christmas holidays. All you had to do was shrink the artwork and bingo there was a new project. I was quite amused with your suggestion in the November issue to use the low power FM transmitter to broadcast the sound in a church. I have built two of these kits and have found that the practical range is only 10 metres at the most, even less if there is a strong FM station in the area. I’ve built one transis­tor versions that had a lot more range. A.P. would be better off installing an inductive loop system, at least the hearing aids the parishioners would be wearing will be already designed for this purpose. M. Allen, Artarmon, NSW. Comment: we regret that you regard manufacturer of low volume electronic equipment, it is yet another log thrown in the path of getting a product to market. The new regulations are as wide ranging and prohibitive as the Austel regulations governing connection to the public tele­phone network. For SILICON CHIP, the ramifications for kit sup­pliers of your projects may be even more devastating. For in­ stance, a switchmode power supply or microprocessor controlled project kit (that’s 50% of all kits these days) will need to be submitted for testing and approval by the seller to a registered NATA testing laboratory. This obviously can’t happen! My first thoughts were that linear circuits and low speed digital circuits would not be included in any EMC (Electromagnet­ic Compatibil- our answer as negative. Look­ ing at the letter again, we can only reply that the answer we have given is eminently practical and cheap. While you have redesigned the board to make it smaller, your solution is an en­dorsement of our answer. Using a readily available, cheap power IC is practical and good design practice. We may redesign the board to make it smaller while still making it possible to use a single or dual supply amplifier but we do find that many readers do not like minuscule boards and nor do they like what many regard as “rehashes”. As far as the low power FM transmitter is concerned, it certainly has a range of much greater than 10 metres, as does the FM wireless microphone featured in our October 1993 issue. In fact, the latter design was tested extensively during our devel­opment of the Diversity FM Tuner featured in the November & December 1993 issues. These were demonstrated together in a 700 square metre warehouse (much larger than most churches!) and they performed very well. Inductive systems for such large areas are not simple or easy. ity) legislation but this appears not to be the case. Motors cause EMI; so does a linear audio amplifier driven into clipping or one with crossover distortion, plasma balls, stepper motors and drive circuits, any PC driven equipment, train controllers, drill speed controllers, dimmers, test equipment, etc. I am not against the necessity to reduce EMI; in fact, I’m all for it. However, the legislation appears to be so wide rang­ing that many businesses, products and individuals that are not significant contributors to the EMI problem will suffer at the hands of yet another bureaucratic attempt to correct a problem which they have neglected for the past 30 years. T. Morley, East Victoria Park, WA. TWO MORE UNBEATABLE OFFERS FROM MACSERVICE TEKTRONIX 100kHz to 1800MHz Spectrum Analyser System WAVETEK Signal Generator/ Deviation Meter Consisting of: 7613 Storage Mainframe Model 3000-200 incorporates a complete 1 to 520MHz FM, AM and CW Signal Generator with an FM Deviation Meter in one convenient instrument. 7L12 1.8GHz Spectrum Analyser Plug-In 7A17 Amplifier TR501 1.8GHz Tracking Generator TM503 3 Slot Mainframe $4250 Please phone or fax today for a full specification sheet incorporating all the system’s features. Frequency Range: 1-520MHz selectable in 1kHz steps; 1kHz resolution; frequency programmable via rear-panel connector. RF Output Level: +13dBm to -137dBm (1V to .03µV RMS); output level continuously adjustable in 10dB steps and with an 11dB vernier; impedance = 50 ohms. RF Output Protection: resettable RF circuit breaker; RF trip voltage = 5V RMS nominal; maximum reverse power = 50W. Specrtal Purity: harmonic output > 30dB below fundamental from 10520MHz; residual AM > 55dB below carrier in a 50Hz to 15kHz post-detection bandwidth; residual FM <200Hz in a 50Hz to 15kHz post-detection bandwidth (100Hz typical). Amplitude Modulation: internal 400Hz and 1kHz ±10%; external DC to 20kHz; range 0-90%; distortion 3% to 70% AM at 1kHz. Frequency Modulation: internal 400Hz and 1kHz (±10%); 50Hz to 25kHz; accuracy ±500Hz on x1 range, ±5kHz on x10 range; distortion 4% at 1kHz. FM Deviation Meter: frequency range 30-500MHz; input level range 10mV to 5V RMS; impedance 50 ohms; deviation range 0 to ±5kHz, 0 to ±50kHz MACSERVICE PTY LTD Australia’s Largest Remarketer of Test & Measurement Equipment $1250 20 Fulton Street, Oakleigh Sth, Vic, 3167. Tel: (03) 9562 9500; Fax: (03) 9562 9590 **Illustrations are representative only. Products listed are refurbished unless otherwise stated. KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. •• FMTX1 FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. •• FMTX2A FMTX5 $99: both FMTX2A & FMTX2B on one PCB. FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input •connector for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92KHz subcarriers. Protect your valuable issues Silicon Chip Binders • AUDIO Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being •soldDIGI-125 since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface •to Max the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with •onlyIBM3 chips and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. 19" Rack Mount PC Case: $999. •• Professional All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4mb RAM 1/2 size card. PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA •PC104 card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. These beautifully-made binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $3 p&p each (NZ $6 p&p). Just fill in & mail the order form on page 101; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. December 1995  85 VINTAGE RADIO By JOHN HILL Back to “original” – the Radiola 34E A few weeks ago, I repaired an AWA Radiola model 34E TRF receiver with a C77 chassis. Part of my job was to restore it to “original” condition. It was an odd repair for an odd receiver. This particular model Radiola can be best described as a timber cabinet, table model, 4-valve TRF type receiver with long spindly legs. That’s right –although the cabinet is basically a table model, it was originally sold with optional turned legs and can be converted into an odd looking console or “tallboy” simply by screwing in these legs. The 34E’s vintage is 1930, give or take a year. The 34E fits into a category that I have mentioned before; ie, a 4-valve TRF receiver with mediocre performance. These radios have only one radio frequency (RF) stage, a detector and a single audio output. If they were anything less, they would re­ quire headphones to listen to. Such a receiver is lacking in both sensitivity and selec­ tivity. In other words, if the set is to operate with any degree of volume, then the aerial needs to be tightly coupled, which has the undesirable side effect of broadening the tuning. This, in turn, can cause serious interstation interference. Loosening the aerial coupling improves selectivity but does so at the expense of overall operating volume. So these simple 4-valve receivers are very much a compromise and their performance levels are only mediocre. While such a comment may sound rather harsh, it is nevertheless true. This type of receiver, however, can give a reasonable ac­count of itself in a capital city situation where about half a dozen local stations are spread approximately equidistant across the dial, as is often the case. Using an indoor aerial, the receiver would work fairly well on the strong locals but little else. In many instances, that was all a receiver was required to do anyway, regardless of the number of valves or type of circuit. One could go on for quite some time about the good and bad aspects of these low-performance TRF receivers from the early 1930s but it has been said before so we will not dwell on it unnecessarily. However, to prove the point about the lowly performance of these radios, it is interesting to note that the 34E Radiola in question has had an additional audio stage added to it. This addition was the reason for the owner’s concern and it was my job to remove the extra stage and restore it to original condition, regardless of the poorer performance aspect of such a conversion. Originality This front view of chassis shows the dial and the connecting steel belt to the second tuning capacitor. AWA used this idea extensively for quite a few years, even though ganged tuning capacitors were in common use at the time. 86  Silicon Chip This 34E repair seemed like my big chance to square off with those, who in the past, have criticised me for making non-standard modifications in order to restore a set to working condition. In this rare instance, I was going to remove a non-standard modification and restore the set back to “original”. That said, removing the extra audio stage would do little to restore this particular set’s originality. Apart from the extra audio stage, there were other unorigi­nal aspects with this 34E. These included a per- Rear view of the Radiola model 34E C77 chassis. The valves, from left, are: 45, 24A, 24A and 80. Note the two single tuning capacitors on the front panel. These and other 4-valve TRF receivers were notoriously poor performers. mag loudspeaker mounted inside the frame of the old electrodynamic unit and a home-wound power transformer with an additional 6.3V winding. This 6.3V winding was used to supply the heater in the 6AV6 in the extra audio stage. In addition, the original 24A detector plate load inductance (coupling choke) was missing, as were the HT (high tension) and RF chokes. Another problem associated with the power supply was that the HT voltage was determined by a 750Ω wirewound filter resistor in place of the original electrodynamic speaker field coil. An electrodynamic speaker supplied by the owner to replace this setup had a 1500Ω field coil, which would reduce the high tension voltage to well below the nominal 250V. I might add at this stage that the 6AV6 valve and its accompanying circuitry were all mounted inside the missing cou­pling choke’s shield can. The choke had been replaced with a resistor and the whole wicked plot was all hidden from view. In terms of restoring originality to such a receiver, well it’s a bit unrealistic when you think about it, especially if one is to do the job properly. If this receiver were to be made original again it would require the correct power transformer, loudspeaker, coupling choke and RF choke, as well as a few other incidentals. What’s more, these parts would be difficult to locate and, even if found, they could cost a sizable sum of money. The cabinet, too, had some missing decorative mouldings and these have been replaced with something appropriate but certainly not original. So now you know why I used inverted commas a few paragraphs back. The word “original” simply could not apply to this particular receiver. An easy job Actually, my job was relatively easy. The 6AV6 audio stage was removed, which amounted to a few disconnect­ ions. The detector was then resistance/capacitor coupled to the output valve. Although originally choke/ capacitor coupled, experience has shown that a resistor is at least a better-than-nothing substitute for a coupling choke. It worked this time too! Wiring in the speaker with the 1500ohm field was next and the speaker socket was required to once again operate with an electrodynamic loudspeaker. This required the removal of The additional audio stage used a 6AV6 which is dwarfed by comparison with the old 45 output valve. This extra audio stage was added to help boost the set’s performance. December 1995  87 The 6AV6 addition was tucked away inside the missing coupling choke’s shield can. As the owner did not like this arrangement, the first audio stage was removed, thus converting the receiver back to “original”. This power transformer is not exactly an original looking com­ponent for an early 1930s receiver. The twisted wires at the right are the 6.3V heater supply for the 6AV6. the 750Ω wirewound resistor which acted as a HT filter with the permag speaker setup. The replacement loudspeaker need­ ed an output transformer and this unit was attached to the speaker frame. It should have been chassis mounted but it really didn’t make much difference where it went. Not in this set! The 1500Ω field resistance reduced the HT voltage consider­ably. The plate voltage on the output valve was down to 180V, which is a bit low for good 88  Silicon Chip results. A new 80 rectifier valve lifted the voltage to about 200V, although no significant difference in performance was noted. Radiolas of this vintage have their speaker socket mounted about 12mm in from the back edge of the chassis with access to the socket being through a 30mm hole. As most standard 4-pin speaker plugs are larger than 30mm, the speaker plug had to be changed. The conversion back to four valves did little to help the set’s limited per- formance. The old 34E needs to be operated with a good aerial and earth and with the volume control full on for most stations. It’s not my idea of an interesting collectible radio and is a dismal affair to say the least. Its unusual cabi­net style is about all it has going for it – that is if you happen to like that sort of thing. Another problem with the 34E is that its fidelity left much to be desired and the level of audio distortion is quite obvious. Many of these early TRF receivers had noticeable distortion and this was mostly caused by the detection method used. Anode bend and leaky grid detectors produce distortion and this distor­ tion is quite noticeable when compared to the clarity of diode detection. As a result, diode detection became the preferred method by the mid-1930s. (Editorial note: the need to use a resistor for the detec­tor plate load could also have contributed some distortion. This would reduce the voltage on the 24A valve plate and thus reduce its signal voltage swing before overload. The type 45 valve requires a grid swing of over 100V p-p to deliver a maximum output of 2W. There would appear to be no way that the 24A could deliver such a signal with a resistor as a plate load). Although the AWA sales brochure referred to the detector as a “linear power detector”, it seems to be nothing exceptional in the fidelity department and there is not much power associated with it either! Tinkering with a few component values did little to help the distortion problem. So the 34E was eventually returned to its owner and he intends to sell or trade it to someone who might love it more than he does. Big dollars The incredible part of this story is that someone will pay or trade to the value of $600 or more for this particular old radio. Personally, I just cannot see big dollars in old radio receivers and I only collect those radios that happen to appeal to me and come my way at reasonable prices. Anyway, the 34E is a good example of just how unoriginal some old radios can become. This one has been modified extensive­ly and while the finished “restoration” looks OK at a casual glance, it is the sort of receiver K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed This close-up view shows the controls. Despite the number of control knobs, the set is a mediocre performer at best, with noticeable distortion and poor volume. that would hold little inter­est for the serious radio collector. While I often make light of the originality aspect of re­pairs, when one is confronted with such a hot-rodded piece of equipment as this 34E, then there is a good point to be made for keeping a set as original as possible. On the other hand, I sympathise with the previous repairer who had to face a repair with immense problems, including an open power transformer and field coil. In the absence of the necessary spare parts he did the best he could in the circumstances and he did get the set going again. No spares Despite the many unoriginal aspects of the old 34E, it scrubbed up fairly well. It’s not hard to see that it is a close relative to the 45E. As a vintage radio repairer, I must confess that I’m not particularly thrilled at the prospect of restoring some of these ancient receivers. I have few suitable spares to repair them in a way that even closely resembles original condition. It is bad enough working on some of these things without the added worry of genuine replacements. When repairing such sets for other people, I simply sti­pulate that they find the required parts. Often, after a fruit­ l ess search, some com­promise has to be accepted. The necessary bits and pieces are not always available. While originality is a nice ideal, in some instances it is a near impossible dream. The 34E is testimony to SC that! MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 December 1995  89 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. Query on ignition timing Thank you for the articles on automotive electronics. Just one minor point – in the September 1995 issue, about ignition systems, your graph says that the point of maximum cylinder pressure should be just after top dead centre. I was given to understand that it was best to design the cylinder head etc so the cylinder pressure gradually rose to peak when the crankshaft was at 90° after TDC; ie, at the point of maximum lever­ age. This should produce maximum power. Also, maybe as a product of the effect noted above, some engines’ ignition systems can be advanced from the manufacturer’s recommended 2° to around 10° before detonation occurs, but power will be at its peak at the manufacturer’s setting; ie, it is not necessarily a good idea to advance the ignition until detonation occurs and “back it off a bit”. I am looking forward to the subsequent articles. Keep up the good work. (J. A., Giralang, ACT). Variation on the digital water tank gauge I am interested in building the Digital Water Tank Gauge, featured in the April 1994 issue. The tank is underground and the lid is at ground level which forms part of the patio under the clothesline. For practical reasons, it is not possible to mount the main PC board in the local unit. I wish to fit the transducer assembly above the tank, as outlined in the article, and run a cable to a box a considerable distance away, which will house the main PC board. My concern is whether this distance will effect the operation of X1 and X2 by varying the resistance and capacitance of the input of IC1a and the output from Q3 respectively. If 90  Silicon Chip • As far as cylinder pressure is concerned, it would not necessarily be optimum to have it peak at 90° after TDC. After all, the power developed is a function of the integral of the cylinder pressure over the whole power stroke. Therefore it makes sense to have a higher cylinder pressure when there is less mechanical advantage from the crank and less pressure when there is more leverage, leading to a smoother and more consistent power delivery during the stroke. In practice, as noted in the October article, the maximum ignition advance can be as much as 40° before TDC. More sensitivity for the digital voltmeter I am writing in regards to the Digital Voltmeter kit de­ scribed in the June 1993 issue. Would it be possible to convert this to a meter capable of measuring 0-100mV? I have made several attempts at this without success. So far, I have disconnected the 3.3kΩ resistor from the +ve supply, using this as the input to measure the mV and this is the case, what can I do or what additional circuit can I build to solve the problem? What does Vcc stand for and what is the difference between this and the + voltage rail; eg, +12V? (A. T., Ouyen, Vic). • The operation of the circuit should not be prejudiced if the cable between the transducer board and the local unit is only a few metres. If the distance is to be greater than this it might necessary to increase the input sensitivity and the drive voltage to the transmitter. Vcc is the positive supply rail in a transistor circuit and can be thought of as the voltage that all the transistor collec­ tors are tied to. In a FET or CMOS circuit, Vdd is the positive rail while Vss is the negative rail. connected a separate supply to run the circuit (via the voltage regulator). As for the V/F converter, can you shed some light on the subject? (A. C., Clyde North, Vic). • There is no easy way of making this circuit measure the low voltage range you require. Even placing a DC preamplifier in front of it would not be simple as it would require very low drift. A much more straightforward approach would be to build or buy the $29 digital multimeter described in our June 1995 issue. Kits are available from Dick Smith Electronics, or Altronics in Perth, or you can buy an equivalent product from Jaycar Elec­ tronics. Problem with metal locator I constructed the induction balance metal detector that appeared in the May 1994 issue of SILICON CHIP. Everything ap­peared to be fine during construction. I had no problems with the electronics and when the board was complete, the test voltages were close to what they should be. I then constructed the search coils and connected them into circuit. When first switched on, the voltage from the receive coil was around 1.5V. By adjusting the coils, I brought the voltage back to around 0.5V. The detec­tor then acted as a metal locator. It would pick up a coin at around 75cm, using a 10-cent coin as the target. However, I noticed that if I adjusted the receive coil a little more, the voltage would go to zero but the pickup would increase slightly. My main problem concerns the controls. The ground, sen­sitivity and volume controls were hooked up according to the diagram and everything looks normal to me. However, the ground control appears to have no effect on the operation of the detec­ tor but the low growl that is used in operation can only be achieved with the use of the sensitivity control. Use of this control can increase or decrease I have recently built the Digital Effects Unit described in the February 1995 issue but cannot get it to function correctly. I am therefore wondering if you can shed any light on the prob­lem. The supply voltages appear OK, although the +16V rail actu­ ally reads about +17.5V at IC1 and IC2. When the unit is switched on, the two dashes are displayed OK but after that, the “delay” and “vibrato” rates are read out alternately on the display about once every second, with the “delay” LED flashing on each time the delay rate is displayed. The display values themselves are OK and correspond with the different DIP switch settings at power-up but no other switches/ the frequency of the sound, as though the roles of the ground and sensitivity controls are reversed. Yet, as I have said, I can see nothing wrong. If you can help me, I would really appreciate it. (B. D., Narooma, NSW). • We suspect that the ground control is not operating. Check that the wiper of VR3 does vary in voltage from 0.64VDC down to about 6mV as the potentiometer is rotated. A similar voltage should also be present at the pin 14 output of IC1b. The metal locator is operating correctly apart from the ground control problem. The sensitivity control will adjust the output tone since it amplifies the offset provided by the ground control. Speed regulation for model trains I have built myself a model train layout which has the tracks divided into 12 sections and incorporates a block system, preventing one train from running into the back of anoth­er. When the throttle is set, if one or more trains stop, the others speed up and this can cause derailments. After reading the September 1995 issue of SILICON CHIP on the Railpower Mk.2, I wondered if it were possible to incorporate this concept into my system. When the throttle is set, the trains functions appear to work; ie, none of the momentary switches do anything and the echo switch doesn’t do anything. Obviously, all connections and switches and switch orientations have been checked. All ICs appear to be seated correctly and in contact and all components are oriented correctly. Are you able to shed any light on the situation? (T. T., Auckland, NZ). • The vibrato switch, S7, or associated tracks leading to IC5 at pin 31, must be shorting to ground. Check the orientation of S7. The switch must be oriented with the “flat” to the bottom of the board as shown. Alternatively, the wiring between the PC boards should be tested for a short using a multimeter. Pin 31 of IC5 will be shorted to ground and show a low resistance reading. should run at the original setting. (R. W., Buderim, Qld). • If we are interpreting your letter correctly, it sounds as though your throttle circuits or your power supply have very poor regulation; ie, the voltage output varies depending on the size of the load. The simplest way to avoid this problem is to run each throttle from a separate power supply. In this way, there can be no interaction between throttle controls. Notes & Errata Railpower Mk II, September & October 1995: the component overlay diagram on page 33 shows a .0047µF MKT capacitor connect­ed to pin 10 of IC1. The capacitor’s value should be .047µF. Electric Fence Controller, July 1995: it has been brought to our attention that Australian Standard 3129-1981 for Electric Fence Controllers has been superseded by the new standard AS/NZS 3129.1:1993. This specifies a maximum fence output of 10kV com­ pared to the previous limit of 5kV. In order to increase the output of our Fence Controller to 10kV, we recommend changing the 6.8Ω 1W resistor in series with the ignition coil to 1.2Ω 0.5W. No other changes are necessary. AVICO POWER PRODUCTS APPROVED I E C CONNECTORS Avico Electronics now have available, a range of NSW Dept. of Energy approved “IEC” 3 PIN connectors. Features Include: • Rated at 240Vac 50Hz <at> 10A • 5mm wide solder or spade terminals • Clip or screw mounts • Integral fuse holder MODELS AVAILABLE IEC1 - Standard panel “clip mount” 3 pin Male socket......... RRP $1.45 IEC2 - Panel “screw mount” 3 pin Male socket............... RRP $1.45 IEC3 - Standard panel “clip mount” 3 pin male socket with fuse holder......... RRP $4.45 IEC4 - Panel “screw mount” 3 pin Male socket with fuse holder............... RRP $4.45 IEC5 - Standard panel “clip mount” 3 pin Female socket...... RRP$1.45 IEC6 - Panel “screw mount” 3 pin Female socket............ RRP $1.45 IEC7 - Dual socket panel “clip mount” 3 pin Male/Female......... RRP $4.95 IEC14 - Right angle plug screw terminating 10A 240Vac 3 pin Female plug.... RRP $2.95 IEC15 - Inline plug screw terminating 10A 240Vac 3 pin Female plug........ RRP $2.45 Imported and distributed by AVICO ELECTRONIC PTY LTD PHONE: (02) 624-7977 FAX: (02) 624-7143 Trade Enquiries Only ASK FOR AVICO PRODUCTS AT YOUR FAVOURITE ELECTRONICS RETAIL STORE Troubleshooting the Digital Effects Unit December 1995  91 Index to Volume 8: January-December 1995 Features 01/95 6 The Latest Trends In Car Sound, Pt.1 01/95 53 Volkswagen’s Golf Ecomatic 02/95 4 The Latest Trends In Car Sound, Pt.2 02/95 14 The 1994-95 CESA Sound & Image Awards 03/95 4 Electronics In The New EF Falcon, Pt.1 03/95 11 Protection For Toroidal Power Transformers 03/95 16 The Latest Trends In Car Sound, Pt.3 03/95 58 The 68000 Microprocessor 03/95 85 Tektronix TDS 784A TruCapture Oscilloscope 04/95 4 Electronics In The New EF Falcon, Pt.2 04/95 8 VW Releases An Electric Car 05/95 4 CMOS Memory Settings What To Do When The Battery Goes Flat 05/95 8 Electronics In The New EF Falcon, Pt.3 05/95 16 Introduction To Satellite TV 06/95 4 Electronically-Controlled LPG System For Fuel Injected Engines 06/95 86 Audio Precision One Analyser 07/95 4 Review: Philips’ CDI 210 Interactive CD Player 07/95 8 The Jamo Classic 4 & Classic 8 Bass Reflex Loudspeakers 07/95 16 Review: The Brymen 328 Automotive Multimeter 08/95 4 Electronic Diesel Engine Management 08/95 14 133MHz Pentium Processor 09/95 4 Automotive Ignition Timing, Pt.1 09/95 8 Review: Philips Brilliance 21A Autoscan Computer Monitor 10/95 4 Automotive Ignition Timing, Pt.2 10/95 66 Connecting To The Internet With Windows 95 11/95 4 LANsmart: A LAN For Home Or A Small Office 11/95 16 Programmable Fuel Injection Control 12/95 4 Knock Sensing In Cars 12/95 12 The Pros & Cons of Toroidal Transformers Serviceman’s Log 01/95 40 Contec MSVR-5383; Sony STR-AV1070X Amplifier 92  Silicon Chip 02/95 62 NEC RD-309E R/C; Palsonic 345 Colour TV 03/95 46 NEC RD-309E R/C; Philips Colour TV KL9A 04/95 56 AWA C3423; Kriesler 59-1; NV-470 VCR 05/95 76 Mitsubishi VS-360A Projection TV; National TC-2138 06/95 40 NEC N2092 Colour TV; Panasonic NN-9859 Microwave Oven 07/95 68 Panasonic NV-SD10A VCR; National TC-2697 TV 08/95 40 Philips KT-3 48cm; Samsung CB-515F 09/95 34 Vision VIS-146R; Sony KV2764EC; Mitsubishi CT2553EST 10/95 40 AWA-Mitsubishi SC6341 AS630; Philips VR6448/75 VCR; Panasonic NV-MS4A Video Camera 11/95 69 Sony KV-2183AS; NAD/ITTNokia 7163VT 12/95 54 Objects Found In VCRs; Power Supply Problems Computer Bits 01/95 62 A Low-Cost Emulator For Zilog’s Z8 Microcontroller 02/95 53 Adding A CD-ROM Drive To Your Computer 03/95 72 Record Real-Time Video With The Video Blaster FS200 04/95 65 Prune & Tune Your Hard Disc For Best Performance 05/95 4 CMOS Memory Settings What To Do When The Battery Goes Flat 07/95 63 Adding RAM To Your PC 08/95 72 An Easy Way To Identify IDE Hard Disc Drive Parameters 09/95 57 Running MemMaker And Avoiding Memory Conflicts 10/95 66 Connecting To The Internet With Windows 95 12/95 64 RAM Doubler: Extra Sauce Without The Chips Remote Control 01/95 72 Working With Surface Mount Components 02/95 77 Building A Remote Control System For Models, Pt.2 03/95 63 Building A Remote Control System For Models, Pt.3 04/95 70 An 8-Channel Decoder For Radio Control 05/95 53 A 16-Channel Decoder For Radio Control 06/95 72 A Multi-Channel Radio Control Transmitter For Models, Pt.1 07/95 72 Transmitter Interference: What Can Be Done About It 11/95 41 Are R/C Transmitters A Health Hazard? 12/95 81 The Mysteries Of Mixing Control Signals To Servos In Models Vintage Radio 01/95 78 Basic Tools & Test Equipment 02/95 82 Restoring A Tasma TRF Receiver 03/95 74 The Inaugural Vintage Radio Swap Meet 04/95 86 Fault Finding: There’s Always Something Different 05/95 82 A Console Receiver From Junk 06/95 76 The 5-Valve Darelle Superhet Receiver 07/95 82 The 8-Valve Apex Receiver: A Glorified Sardine Tin 08/95 80 A Couple Of Odd Radio Repairs 09/95 84 An Interesting Grid Bias Problem 10/95 86 Vibrators: A Slice Of History 11/95 86 How Good Are TRF Receivers? 12/95 86 Back To "Original" - The Radiola 34E Amateur Radio 01/95 82 Wideband Preamplifier Has Response To 950MHz 03/95 80 Build A Simple 2-Transistor CW Filter Circuit Notebook 01/95 22 Using 3-Wire Railway Crossing Lights 01/95 23 Electronic Guitar Tuning Fork 01/95 23 Level Translator For PC Games Port 02/95 38 Analog Multiplier Uses Transconductance Amp 02/95 39 Thumb Wheel Selection For Pattern Generator 03/95 10 Pump Control System 03/95 10 Adjusting Pulse-Train MarkSpace Ratio 04/95 68 48V Charger For SLA Batteries Projects To Build 01/95 14 Sun Tracker For Solar Panels 01/95 24 Battery Saver For Torches 01/95 32 Dolby Pro-Logic Surround Sound Decoder, Pt.2 01/95 56 A Dual Channel UHF Remote Control 01/95 65 Stereo Microphone Preamp 01/95 82 Wideband Preamplifier Has Response To 950MHz 02/95 18 50-Watt/Channel Stereo Amplifier Module 02/95 26 Digital Effects Unit For Musicians 02/95 40 A 6-Channel Thermometer With LCD Readout 02/95 56 Wide Range Electrostatic Loudspeakers, Pt.1 02/95 72 Oil Change Timer For Cars 02/95 77 Building A Remote Control System For Models, Pt.2 03/95 16 Building A Tube Sub-Woofer 03/95 20 Subcarrier Decoder For FM Receivers 03/95 32 50W/Channel Stereo Amplifier, Pt.1 03/95 40 Lightning Distance Meter 03/95 52 Wide Range Electrostatic Loudspeakers, Pt.2 03/95 63 Building a Remote Control System For Models, Pt.3 03/95 69 IR Illuminator For CCD Cameras & Night Viewers 03/95 80 Simple 2-Transistor CW Filter 04/95 14 FM Radio Trainer, Pt.1 04/95 25 A Photo Timer For Darkrooms 04/95 38 Balanced Microphone Preamplifier & Line Mixer 04/95 42 50W/Channel Stereo Amplifier, Pt.2 04/95 52 Wide Range Electrostatic Loudspeakers, Pt.3 04/95 70 An 8-Channel Decoder For Radio Control 05/95 32 Mains Music Transmitter & Receiver 05/95 41 Guitar Headphone Amplifier 05/95 53 A 16-Channel Decoder For Radio Remote Control 05/95 58 FM Radio Trainer, Pt.2 05/95 68 Low-Cost Transistor & Mosfet Tester For DMMs 06/95 12 Satellite TV Receiver, Pt.2 06/95 26 A Train Detector For Model Railways 06/95 34 A 1-Watt Audio Amplifier Trainer 06/95 56 Video Security System 06/95 62 Build A Digital Multimeter For Only $30 06/95 72 A Multi-Channel Radio Control Transmitter For Models, Pt.1 07/95 20 An Electric Fence Controller 07/95 32 Run Two Trains On A Single Track 07/95 40 Satellite TV Receiver, Pt.3 07/95 54 Build A Reliable Door Minder 07/95 76 A Low-Cost MIDI Adaptor For Your PC Or Amiga 08/95 18 Vifa JV-60 2-Way Bass Reflex Loudspeaker System 08/95 24 Fuel Injector Monitor For Cars 08/95 30 A Gain-Controlled Microphone Preamp 08/95 54 Audio Lab: A PC-Controlled Audio Test Instrument 08/95 60 Build The Mighty Mite Powered Loudspeaker 08/95 75 6-12V Alarm Screamer Module 09/95 16 Keypad Combination Lock 09/95 22 The Incredible Vader Voice 09/95 40 Railpower Mk.2: A WalkAround Throttle For Model Railways, Pt.1 09/95 62 Notes On The Train Detector For Model Railways 09/95 68 A Jacob’s Ladder Display 09/95 74 Audio Lab: A PC-Controlled Audio Test Instrument, Pt.2 10/95 16 A Compact Geiger Counter 10/95 22 A 3-Way Bass Reflex Loudspeaker System 10/95 32 Railpower Mk.2: A WalkAround Throttle For Model Railways, Pt.2 10/95 54 A Fast Charger For Nicad Batteries 10/95 74 Digital Speedometer & Fuel Gauge For Cars 11/95 22 A Mixture Display For Fuel Injected Cars 11/95 28 A CB Transceiver For The 80M Amateur Band 11/95 44 A Low-Cost PIR Movement Detector 11/95 60 Dolby Pro Logic Surround Sound Decoder, Mk.2 11/95 79 Digital Speedometer & Fuel Gauge For Cars, Pt.2 11/95 90 Build A PC-Controlled Robot From Surplus Parts 12/95 8 Build An Engine Immobiliser For Your Car 12/95 22 Low-Cost Five-Band Equaliser 12/95 28 A CB Transverter For The 80-Metre Amateur Band; Pt.2 12/95 39 Build A Sub-Woofer Controller 12/95 70 Dolby Pro Logic Surround Sound Decoder, Mk.2, Pt.2 04/95 68 Tachometer Pick-Up For Diesel Engines 04/95 69 Temperature Controller For Home Brewers 05/95 24 Digital Readout For A Weighbridge 05/95 25 Balanced Microphone Preamplifier (Incorporating “Phantom Power”) 05/95 25 Automatic Charger/Discharger 06/95 54 Emergency Lighting Circuit Has Charger 06/95 54 Expanded Scale Voltmeter For Cars 06/95 54 Low Cost Nicad Zapper 06/95 55 Simple Probe Detects Logic Levels & Pulse Trains 06/95 55 Stereo Signal Switcher For Testing 07/95 38 Encoder For Surround Sound Decoders 07/95 39 Coolant Alarm For Positive Earth Vehicles 08/95 38 Relay Driver Board With High Voltage Supply 08/95 39 Automatic Antenna Controller For Cars 09/95 32 Rev Limit Indicator For Rally Cars 09/95 32 Car Courtesy Light Monitor & Extender 09/95 33 Touch Sensitive Switch Uses A Single IC 10/95 10 Speed Controller For Small Motors In Models 10/95 11 Adding Tail Lamps To Guard’s Vans 10/95 11 Low-Cost Stepper Motor & Controller 11/95 8 Weekly Rubbish Reminder 11/95 8 Simple Solar Tracker 11/95 9 Multi-Way Switching For 240VAC Lighting 11/95 9 Ignition Coil/Condenser Tester 12/95 16 Camper Van Inverter Controller 12/95 16 Simple LED Chaser Using Transistors 12/95 16 Optical Tachometer Has Digital Readout Notes & Errata For Projects 02/95 93 Coolant Level Alarm, June 1994 03/95 93 25W Amplifier Module, December 1993 03/95 93 Multi-Channel Remote Control, May 1994 03/95 93 50W Stereo Amplifier Module, February 1995 03/95 93 Digital Effects Unit, February 1995 07/95 93 Mains Music Transmitter & Receiver, May 1995 08/95 92 Walkaround Throttle, Ask Silicon Chip, Page 93, May 1995 09/95 100 Fuel Injector Monitor, August 1995 12/95 91 Railpower Mk II, September & October 1995 12/95 91 Electric Fence Controller, July 1995 December 1995  93 SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. 94  Silicon Chip semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer's Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE EDUCATIONAL ELECTRONIC KITS: easy to build. Good quality. Up-to-date technology. Cheap. Guaranteed to work. Wide range selection. Send $2.00 in stamps for catalogue and price list. Or log onto our BBS FREE for full details of every kit. DIY ELECTRONICS, 22 CLASSIFIED ADVERTISING RATES 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): $25 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. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ McGregor Street, Numurkah, Vic 3636. Ph/Fax (058) 62 1915. Ph/BBS (24hr) (058) 62 3303. UK MAGAZINE ETI is currently running a series of articles on a PIC Basic Interpreter that will support 10/18 I/O lines and 2K/8K EEPROM. Larger versions under construction. Programs a micro in Basic from the serial port of your PC. To get a free copy of the *FULL* Win 3.1/95 Dev System, Manual and hardware pricing, send me a $2 coin and I’ll send it on my Promo disk to you. Don McKen­zie, 29 Ellesmere Crescent, Tullamarine 3043. (03) 9338 6286. 68HC705 DEVELOPMENT SYSTEM: Editor, assembler, In Circuit Simula­tor and Programmer board. Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 541 0310. Fax (02) 541 0734. email:OZTEC<at>OZE­MAIL.COM.AU. MicroZed are supplying BS2 upgrade kits free with purchase of BS2 and carrier, regardless of where you bought your legit BS1. Proof of purchase required. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses ‘C8 and switch mode supply. Features galore!! Contact Mantis Micro Pro­ducts, 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available in ❏ Bankcard   ❏ Visa Card   ❏ Master Card ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. 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 December 1995  95 MicroZed Computers Advertising Index Easy to use Easy to learn Low cost On-chip interpreter BASIC Stamp I and II Boards, Software, Chipsets, Books. Versa Tech Avico Electronics.........................91 NEW Micro Car Projects Book....................OBC Send 2 x 45c postage stamps for information. PO Box 634 (296 Cook’s Rd), ARMIDALE 2350. Ph (067) 722 777       Fax (067) 728 987 Mobile (014) 036 775 Scott Edwards Electronics Accessories for Stamp and second source for Stamp I TICkit – a 21 I/O PIC based controller SIMMS (Parity/No Parity) 4MB 30 PIN-70 $210 $196 4MB 72 PIN-70 $217 $193 8MB 72 PIN-70 $435 $364 16MB 72 PIN-70 $834 $728 32MB 72 PIN-70 $1663 $1428 EDO SIMMS 4MB (1Mbx32)-70ns $215 8MB (2Mbx32)-70ns $425 MAC 8MB P’BOOK $435 VIDEO MEMORY 256KX16 70ns (SOJ) $30 256KX16 70ns (ZIP) $57 LASER PRINTER MEMORY HP 2MB UPGRADE $158 CO-PROCESSORS 80387SX/DX to 40MHz $90 COMPAQ 8MB CONTURA AERO $445 TOSHIBA PORTEGE/SATELLITE 8MB / 16MB $650 / $1200 DRIVES SEAGATE 545MB EIDE 14ms 3yr $264 850MB EIDE 11ms 3yr $308 1080MB EIDE 11ms 3yr $365 2150MB SCSI 9ms 5yr $1250 MODEMS (Includes Sales Tax) 14,400 BANKSIA 5yr W $283 14,400 SPIRIT 2yr W $229 28,800 BANKSIA V.FC $385 28,800 SPIRIT V.34/V.FC $410 EX TAX PRICING AS AT NOVEMBER ‘95 Sales Tax 22%, O/Night Delivery $8. Ring For Latest Prices. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Ph: (02) 980 6988 Fax: (02) 980 6991 Suite 6, 2 Hillcrest Rd, Pennant Hills, 2120. Australia. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $149.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $410 + $6 p&h (save $139) • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h •DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 (inc label). We use and recommend the HILO ALL-07 Universal Programmer • Fixed price PCB layout & photoplots. We use and recommend PROTEL For Windows EDA tools • Credit cards accepted • Call Bob for more de­tails. MICROCRAFT, PO Box 514, Concord 2137. Phone (02) 744 5440 or Fax (02) 744 9280. HEAPS OF OLD radios, electrical stuff, transformers, valves, test equipment. Max (07) 3856 1736. 96  Silicon Chip Av-Comm.....................................65 68HC11 F1 boards with resident FORTH. Others supplied. Dick Smith Electronics........... 18-21 MEMORY * DRIVES * MODEMS SPECIAL! (Incl Tax) 1Mbx9 – 70ns Simm $52 1Mbx9 – 80ns Simm $38 Altronics ................................ 66-68 Emona.........................................61 Harbuch Electronics....................63 Instant PCBs................................96 COMPLETE WORKSHOP PROGRAM: suit IBM compatible 386 or better computer. Handles: Stock Control, Sales, Service Records, Debits, Credits, Faults, Service Manuals and Phone Directory. Full price $399.00. For demo disk, phone or fax your details to (045) 71 1640. Jack Albers Electronics & Software Development. EA & ETI MAGAZINES: EA from 2/71 to 8/95. ETI from 4/71 to 5/88. Over 490 issues in good condition. Job lot only $250. Ph Earle (03) 9336 3061 1600 hrs to 1900 hrs EST. C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140 for the set. Debug monitors: $70 for 6 CPUs. All compilers, XASMs and monitors: $400. 8051/52 or 80C320 simulator (fast): $70. Demo disk: FREE. All prices + $5 p&p. GRANTRONICS PTY LTD, PO Box 275, Wentworth­ville 2145. Ph/Fax (02) 631 1236 or Internet: lgrant<at>mpx.com.au. HC11s AND ICs - http://worf.albany­is. com.au/bobhome.html. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gorizont, Rimsat. Warehouse Sale – 4.6m Dish & Pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 482 3100 8.30-5.00 M-F. Jaycar ................................... 45-52 Kalex............................................89 Kits-R-US.....................................85 Macservice..........................3,63,85 MicroZed Computers...................96 Oatley Electronics.................. 58-59 Pelham........................................96 Railway Projects Book...............IFC RCS Radio ..................................95 Rod Irving Electronics .......... 34-38 Scan Audio..................................62 Silicon Chip Bookshop.................94 Silicon Chip Walchart.................IBC Tortech.........................................89 _________________________________ 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.