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PLA CEH OLD ER 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.7, No.11; November 1994 FEATURES FEATURES DON’T THROW AWAY those AA-size dry battery! Rejuvenate them instead with this Dry-Cell Rejuvenator. You could get up to 10 times their rated life & save money – details page 14.   6 Anti-Lock Braking Systems: How They Work by Julian Edgar Electronic circuitry does the job 80 How To Plot Patterns Directly To PC Boards by John Clarke A new way to make one-off prototypes PROJECTS PROJECTS TO TO BUILD BUILD 14 Build A Dry-Cell Battery Rejuvenator by Darren Yates Recharges dry cells up to 10 times 20 A Novel Alphanumeric Clock by Anthony Nixon An old-fashioned clock using newfangled technology THIS NOVEL CLOCK tells the time just the way we say & think it. You can build one for yourself by following the article starting on page 20. 36 UHF Radio Alarm Pager by Branco Justic Ideal for keeping tabs on cars & boats 53 80-Metre DSB Amateur Transmitter by Leon Williams, VK2DOB It’s easy to build & uses readily available parts 66 Twin-Cell Nicad Discharger by Darren Yates Modifying the May 1993 discharger to do the job SPECIAL SPECIAL COLUMNS COLUMNS 32 Serviceman’s Log by the TV Serviceman Tread carefully with a new brand name 70 Vintage Radio by John Hill Resurrecting a pair of old AWA C79 chassis KEEP TABS ON YOUR CAR or boat with this UHF Alarm Pager. When triggered, it transmits a signal that activates a buzzer in a small receiver unit –­ see page 36. 77 Computer Bits by Darren Yates Review: Visual BASIC for DOS 83 Modellers With Dedication, Pt.3 by Bob Young Progress in model racing car technology DEPARTMENTS DEPARTMENTS   2 4 60 64 86 Publisher’s Letter Mailbag Order Form Circuit Notebook Product Showcase 90 92 94 96 Back Issues Ask Silicon Chip Market Centre Advertising Index IF YOU HAVE JUST obtained your novice licence, this little 80-metre transceiver will get you on the air as cheaply as possible. It uses no ICs & the parts are all easy to obtain. Details page 53. Cover concept: Marque Crozman November 1994  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $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) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Tiny electronic components can be hard to see Do you enjoy electronics as a hobby? I know I do. For my part, there is a constant stream of new devices and circuits to think about and many of these end up being presented in the magazine. I suppose I am fortunate in being able to work at one of my hobbies. This is not to say that I have a lot of opportuni­ties to work on electronic projects personally. And until recent­ly, it was just as well, because I have trouble seeing those teensy components. Yes, I have to admit it: I need to wear glasses. Years ago my close-up vision was as good as anybody’s but the passage of time has caught up with me and a couple of years ago I had to start wearing glasses for reading. But while this relieved the problem of having to hold books or magazines at arm’s length to read them, it did not help when work on circuit boards was re­quired. In particular, I found great difficulty reading the labelling on some small plastic transistors – no matter how good the light, the silver printing on the grey plastic bodies was unreadable as far as I was concerned. And those tiny resistors with their colour codes were also a big problem, particularly some brands sourced from Asia. The solution was suddenly presented to me when I happened to be in a hardware store recently. They were selling magnifying spectacles branded “Extra Eyes”. I selected a pair with a mag­nification of 2.5 and found that they suited me. The range in which I can use them is quite restricted but that is OK because I only use them at close range. It has made an enormous difference because I can now work at my hobbies in the evenings where pre­viously I could not. Now these magnifying spectacles, available from many hard­ware stores and newsagents, will not suit everyone but give them a try. They are cheap at $19.95. And if they don’t suit you, think seriously about getting prescription glasses especially for close-up work. After all, everyone needs some sort of a hobby to make their leisure time satisfying and if you can’t work at your chosen hobby, it can be pretty frustrating. As a final point, some of the keenest enthusiasts reading this magazine are retired people in their 70s and 80s. Virtual­ly all of them need glasses to pursue their hobby. So don’t be backward; if you have trouble seeing today’s teensy electronic components, don’t get frustrated, get a pair of specs. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG TV timer should be pay as you watch In the Ask SILICON CHIP pages in the June issue, a reader in Tasmania asked about a television timer that could be used to ration TV viewing to, say, 10 hours a week. If you have the timer this should be easy; a LED at the front of the set comes on when the time is up. Nothing else happens, the set remains on, but you know you are over the time you have given yourself. And if child­ ren have sole use of one set, anyone can see if they are over the time that has been allotted to them. Nicer for children would be a timer with a coin in a slot; pay for each hour, with no more coins accepted after the allowed time. They get this many each week and are free to use it as they like, so may choose to watch less than the full time that’s been allowed. J. P. Kaemmeren, Euroa, Vic. Transistors rule supreme Your response to D. Haddock’s letter in the September issue was a masterpiece of restraint. My opinion is that the last line of your July Publisher’s Letter was the perfect summation of the position today. Way back in 1968, when silicon transistors had made their appearance, I was persuaded by an engineer friend to build a transistor amplifier to replace my Williamson valve amplifier which was pretty much state of the art for valve amplifiers then. The transistor amplifier was, by today’s standards, a pretty crude affair but the reduction in cross modulation distor­tion alone, as compared to the valve amplifier, was immediately apparent. Transistor amplifier design has made significant progress since then but valve amplifiers are forever restricted by the need for an impedance matching output transformer. The prob­lem with transformer design is that every aim for good re­sponse at one end of the frequency range conflicts with that for the other end and this problem cannot be overcome. 4  Silicon Chip Your correspondent’s argument is weakened by the admission that serious music listening is seldom undertaken. In the casual listening program outlined, a fair approximation of the revered “valve sound” could be attained with a capacitor to roll off the top end a bit, giving the same result much more economically. While I do a fair bit of casual listening, I still like to have a serious listening session when I can. My current setup would be almost impossible to duplicate with valves as it is a 4-way active crossover system. The necessary valve amplifiers would consume about 2kW of power (and produce the same quantity of heat) and take up a good deal of space just to produce my average listening level of rather less than a watt. Valves are interest­ing to remind us where we have come from but let’s leave them in the museum where they now belong. Give me transistors any day! A. March, North Turramurra, NSW. Gas detectors & nicad zapping Recently, I phoned your offices for some information re­ garding suppliers of gas detectors. I did not catch the name of the person with whom I spoke, but they asked if I had tried Radio­Spares. After I rang off, I was banging my head against the wall when I was struck by an amazing thought, a veritable revela­tion. Maybe RadioSpares stocked them. And lo! they did, recently introduced! They stock four different types, one for flammable gases, one for nitrogen oxides, one for carbon monoxide and one for household odours. I saw in the August issue of SILICON CHIP a circuit for a Nicad Zapper. I have used the technique in the past, usually by applying 15V briefly until the short clears. However, I wonder at the efficacy of the process, because I usually found that zapped cells would short again a few months, maybe a year, later. I figure this is because dendrites do SILICON CHIP, PO Box 139, Collaroy, NSW 2097. not often grow sing­ly, but only one (or perhaps a few) is needed to short a cell. When you zap a cell, you only blow the dendrites that are actual­ly shorting the cell, leaving smaller ones intact to grow further and short the cell at a later date. In the end, I just replaced shorted cells with new ones, since I would probably have to do it some time anyhow. But there are times when you need the gear to work now and replacements are not on hand, and there is the consideration of the budgetary constraints of the average household. The device has its place but people should not expect too much from the process. One should always remember the golden rule of battery powered equip­ment: when you want to use battery powered equipment, the batter­ies will be almost flat and replacements are not available. Well, it seems that way to me! On another matter, a friend at work built the Steam Whis­tle/Diesel Horn Simulator published in the July 1994 issue. He said he wanted to use it as a door chime. Anyway the unit did not produce enough volume for the task, so I suggested he change the output capacitor to a 47µF electro and the 22Ω output resistor to 2.2Ω. I am not sure if the output series resistor was really needed but I thought it would not hurt and might provide a meas­ure of protection in the event of ... err, a comet strike? Anway, he was happy with the extra volume but complained that there was some residual noise when the buttons were not pressed. I first thought that maybe the transistor switch (Q2) was not providing a good enough short, so I suggested he try a big meaty Mosfet – well a VN88. The only difference was that the attack characteristic was slowed somewhat, not too surprisingly. I finally identified the problem as being due to the 2.2µF capacitor at Q2’s emitter. The CRO showed about 30mV peak to peak at Q2’s collector with the sound “off”. I added a 68µF tantalum and this significantly reduced the problem with no noticeable affect on the unit. I thought other readers might find this modification helpful, although I suspect that the problem would not arise when the unit is used as intended. P. Denniss, Dept of Plasma Physics, University of Sydney, NSW. Long distance CB via repeaters I am writing regarding the query from G. C. Corinda, Qld, published on page 92 of your August issue (of an August publica­ tion – what an awful pun) under the heading “long distance commu­nication via CB”. I am surprised that your answer made no mention of repeaters. As an amateur operator I regularly communicate with a friend who lives over 200km north, on the 2-metre (VHF) band via a repeater near Gosford. If your correspondent was to consult page 221 of the latest DSE catalog or a recent issue of “CB Action”, he should be able to find a suitable repeater somewhere along or near the path between the two locations (maybe even atop the offending mountain). Access to the repeater can be checked by transmitting (with the set on duplex mode) for a few seconds and then listening for the “tail”, a short continuation of the carrier transmitted by the repeater. Also, the height of the antennas, co-phasing of Yagis and the use of low loss cable such as RG-213 are considerations. Other possible means of communications include “Packet Radio” by “digipeating” (although currently restricted to Amateurs), HF radios such as “Codan” (quite expensive) and Cellular Mobile, especially as the network expands. A 3W portable (or in-car type) phone could be connected to an elevated outside antenna. Be sure to use low loss (RG-213, etc) coax. These phones can be purchased quite inexpensively these days, probably for very little more than he would recover from the sale of the CBs, and there are a range of cost effective “Flexiplans”. Also ask the Digital Cellular network providers about their coverage, but do make sure the deals they are offering really do make economic sense. The other benefit over CB is that you can call and be called by almost anyone you wish, no matter where in the world they happen to be at the time! It would also be useful for safety communications while travelling. Moon bounce, meteor scatter, aircraft (and their vapour trails) are basically means used by amateurs to get rare DX on VHF and above, and to set distance records, although a practical meteor scatter device has been developed, I think in North Ameri­ca, and featured on one of the technology shows on TV some time ago. The handheld keyboard device evidently detects the presence of a meteor trail and sends packets of data during the few sec­onds propagation is possible. “Sharp Edge” propagation is another method where radio waves are bent by a sharp edged ridge. Finally, radio propagation is a pretty amazing subject. For instance, along the road north of Port Stephens, the Tamworth 2-metre repeater cannot be accessed even with 45 watts and a 5/8 wave­length antenna, yet at one specific spot a few watts and a 1/4 wave will trigger it easily. Julian Sortland, Hornsby Heights, NSW. Valves and quasi-compliments How can you say that valve amplifiers do not have a place in today’s technology? I am sure you haven’t even heard one recently or even compared one with another everyday amplifier or even a high-quality one. You do have some valid points though. It is difficult/expensive to get high power out of a valve amplifier. Solution: use a separate transistor amplifier (quasi comple­mentary NOT complementary – I shall explain) for the bass driver and a valve amplifier for the mid-treble. You don’t have to use an active preamp (it would be highly beneficial if you did). I must assure you that a setup such as this would be hard to beat for P, R+T (pace, rhythm, timing and warmth) and distortion (I don’t care what your figures say)! You would also remove a lot of phase shifts caused by passive crossovers (these are very audible). I have built and bought several amplifiers over the last 10 years (I am now 25 and an electronics technician) and I still believe that newer is not always the best. Sorry Leo! I must point out that I do not like the sound that is reproduced by amplifiers that use complementary output stages (eg, 2N3055/MJ2955) and this also includ­es all IC power amplifiers that I have heard. I have researched and auditioned this quite thoroughly and even common commercial units from the USA, UK, Australia and Japan that follow this design all have the same mushy, poor slew rate, distorted sound. If you compare these amplifiers with others that use the high speed quasi-complementary pair (eg, NPN/NPN) in the output stage then you will notice a much more pleasing sound from the latter. Incidentally, the quasi-complementary design was quite popular in the 60s and 70s but seems to have been dropped, possi­bly because there are more PNP transistors available. But I assure you that the earlier configuration (NPN-NPN) has a much better pace, rhythm and timing. I also wish to make the point that I have never heard a nice Mosfet amplifier and would never recommend them. Alex Scott, New Plymouth, NZ. Comment: what’s pace, rhythm and timing? Don’t you get them at an aerobics class? Most monolithic power amplifiers use a quasi-complementary configuration. From our recollection, most fully complementary solid state amplifiers these days have a better slew rate than the older quasi-complementary designs. Coolant alarm is a winner I wish to congratulate you on the presentation of the cool­ant level alarm in the June 1994 issue of SILICON CHIP. Having already experienced the cost of $2000 plus because of an over­heated engine, due to a leaking by-pass hose, I can truly appre­ciate this marvellous protective warning device. As a newcomer to electronics, I have tried unsuccessfully for several months to design such a warning device. Well done! Les Agostini, Winnellie, NT. November 1994  5 The Landrover Discovery has ABS as an option. ABS calibration for dirt surfaces & constant 4-wheel drive is quite complicated. Anti-lock braking systems: how they work Now commonplace on family cars, anti-lock braking systems require fancy electronic control circuitry to do their job. Here’s a rundown on how they work. By JULIAN EDGAR An anti-lock braking system (commonly known as ABS) prev­ ents a car’s wheels from locking during panic braking. This has two distinct advantages: (1) it gives shorter stopping distances; and (2) it allows the car to be steered during hard braking. A car with locked wheels cannot be controlled by steering input and will also take much longer to stop than one with the wheels still turning while it is being braked. 6  Silicon Chip Anti-lock braking systems have been used in automotive applications for around 25 years but have only recently found widespread use in mass-produced family cars. This has been made possible by a reduction in the cost of the electronic circuitry required and by increased public awareness of safety issues. Unlike airbags, which protect the car’s occupants after the car has hit something, ABS gives a car greater primary safety – meaning that it is less likely to be involved in an accident in the first place. In the vast majority of situations, an ABS-equipp­ ed car will have a braking advantage over a conventionally-braked car, although it should be noted that in some (rare) situations, an ABS will actually give longer stopping distances. The task An anti-lock braking system has an apparently simple role – to stop individual wheel lockup while still providing maximum braking efficiency. In stable situations where the frictional coefficient between the tyres and the road is constant, where vehicle mass is unchanging, and where the road surface is smooth, appropriate ABS behaviour is relatively easy to organise. However, in the real world, CONTROL ZONE BY ABS the driver pull the car fully back onto the bitumen, this lateral difference in braking effort could result in the car yawing rapidly. An optimal anti-lock braking system would thus give the following charac­ teristics during operation: (1). Driving stability maintained through the retention of suffi­cient lateral guiding forces at the rear wheels; (2). Steering ability retained through the provision of suffi­cient lateral guiding forces at the front wheels; (3). Reduced stopping distances; and (4). Rapid matching of the braking force to different adhesion coefficients. FRICTIONAL COEFFICIENT BETWE E N T YRE AN D ROAD S URF ACE,  ASPHALT ROAD ICE-SNO W ROAD 0 SLIP RATIO 100% Fig.1: the maximum braking effort is obtained when there is a certain amount of wheel slippage. While it depends on the road surface, best braking is usually obtained with a wheel slippage ratio of between 8% & 30% (Subaru). a large number of variables means that anti-lock braking systems need to be very sophisticated in the way they operate. An ABS control system must take into account: (1). Variations in the amount of adhesion between the tyres and road due to changes in the road surface and in wheel loads (especially during cornering); (2). Irregularities in the road surface which cause the wheels and suspension members to vibrate; (3). Out-of-round tyres and brake hysteresis characteristics; and (4). Different friction coefficients which might exist between the left and right-hand wheels, and a possible subsequent transi­tion to a homogeneous surface. Taking the last point as an example, if a car is heavily braked while the right-hand wheels are on dry bitumen and the left-hand wheels are on the dirt verge, then the ABS would obviously reduce the braking effort in the left-hand wheels. However, should Braking behaviour Obtaining the optimal braking force is more complicated than it first appears, with brake slippage actually necessary for best results. The brake slip ratio is defined as follows: Slip Ratio = (Vehicle speed - Wheel speed)/Vehicle speed x 100% When the slip ratio equals zero the wheel is travelling at the same speed as the car (ie, there is no slippage). Conversely, when the slip ratio is 100%, the wheel is locked and does not rotate at all. The relationship between the longitudinal fric­tional force of the wheel and the slip ratio depends on the road surface. Fig.1 shows this relationship for as- Fig.2: this diagram shows the main components of a typical anti-lock braking system, in this case for the Subaru Liberty (Subaru). November 1994  7 TOOTHED WHEEL +V FULL SPEED POLE PIECE 0 S N PERMANENT MAGNET -V SLOW SPEED Fig.3: inductive sensors are used to signal wheel speed to the electronic control unit & this then calculates the vehicle speed &the slippage for each wheel. phalt and ice-snow surfaces. It can be seen that in both cases the maximum frictional coefficient between the road and the tyre is achieved when in fact there is some slip. In other words, allowing the wheel to continue to rotate at the same forward speed as the car – that is, not skidding at all – will not give maximum retardation. The slip ratio at which the maximum friction exists is generally 8-30%, depending on the road surface. While an 8-30% slip ratio works well on dry and wet bitu­ men, ice and many other road surfaces, it does not hold true for fresh snow and gravel. In Australia, the latter road surface is especially important Operation Fig.4: the toothed wheel (tone wheel) is located on the inner hub of each wheel to excite the pick-up sensor. In some cars, the same sensors are also used for traction control (Subaru). Even cheap compact cars like this Holden Barina can now be supplied with ABS as an optional extra. 8  Silicon Chip and on gravel a slip ratio of 100% gives maximum retardation. In other words, locked wheels stop the car in a shorter distance on gravel than any other technique. This is because a small dam of gravel (or snow) builds up in front of the locked wheel and helps to slow the vehicle. The skidding wheel can also gouge its way down to a firmer surface beneath the gravel. Of course, while this is happening there will not be any steering control available! Some manufacturers provide a dash-mounted switch which allows the driver to switch off an anti-lock braking system while driving on surfaces for which it is not compatible. However, most manufac­turers avoid doing this, mostly because of potential driver confusion and the fact that the anti-lock braking system might be left deacti­vated just when it’s needed. An anti-lock braking system comprises a series of input sensors which read the wheel speeds, an electronic control unit (ECU), and a hydraulic control unit (HCU). Fig.2 shows the essential elements of a typical ABS. The wheel speed input sensors are typically inductive pick­ups and these use a permanent magnet and a coil. A toothed ring attached to the inner part of the wheel’s hub rotates past this sensor. As it does so, the teeth change the magnetic coupling into the coil and so the sensor generates an AC waveform whose frequency depends on the wheel speed. Fig.3 shows an example of a sensor and its output, while Fig.4 shows its location on the car. Note that in this Subaru system, the toothed ring is called a “tone wheel”. A typical ABS electronic control unit is shown in Fig.5. As well as the sensor amplification and shaping circuitry, it com­prises the ABS comparison and control circuitry, plus a number of output transistors which control the solenoids and pump within the HCU (hydraulic control unit). A self-diagnosis circuit is included to allow easy fault-finding and self-check circuits monitor the electrical condition of the input sensors and output actuators. If a fault is detected, a dash-mounted warning light is illuminated and the brakes then operate conventionally. In sophisticated 4-channel systems, Fig.5: block diagram of a Bosch ABS. Note the safety moni­toring & the self-diagnosis circuits (Subaru). the ECU uses the input signals from two diagonally opposite wheels to derive a vehicle reference speed. Using this speed and the individual wheel speeds, it then calculates the brake slip for each wheel. When a wheel’s deceleration exceeds a preset value, the ECU transmits a “hold” signal to the HCU. At the same time, the ECU computes a dummy vehicle speed, and – should the wheel speed drop below this – the ECU decreases the brake fluid pressure to prevent lockup. However, with the decrease in brake fluid pressure the wheel accelerates. When this acceleration passes a preset value, another “hold” signal is transmitted to the HCU; should wheel acceleration continue then the brake fluid pressure is increased. The frequency of this brake fluid pressure cycling varies from 4-10Hz. The HCU consists of solenoid valves, a hydraulic pump and accumulator chambers. Fig.6 shows an external view of an HCU. Depending upon the switching state, the brake cylinder is con­ nected to the corresponding circuit of the brake master cylinder, the return pump, or is isolated. When pressure is reduced, the return pump moves the fluid flowing out of the wheel brake cylin­ ders back to the master cylinder via the accumulators. The accu­mulators are pres­ent to absorb any temporary brake fluid surplus that may be produced when the pressure suddenly drops. Other systems Fig.6: external view of a Bosch hydraulic control unit (Subaru). Not all anti-lock braking systems use four input sensors and three or four control channels – indeed not all anti-lock braking systems are even electronic. Teves, Lucas Girling and individual vehicle manufac­turers use variations on the theme. Some, for example, set the hydraulic pressure applied to both rear wheels according to the wheel with the highest slippage (ie, the same pressure is applied to both wheels). Others may do the same for the front. Some anti-lock braking systems also use an acceleration sensor which measures the rate of vehicle slowing. For example, on the Subaru Liberty, a G-sensor is used when ABS is installed on manual constant 4-wheel SC drive cars. November 1994  9 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 Build a dry-cell battery rejuvenator Are you sick of throwing away those AAsize dry batter­ies? Well, don’t – rejuvenate them instead with this Dry-Cell Rejuvenator. Depending on the state of the cells, you could get up to 10 times their rated life & save big money! By DARREN YATES That’s right – this circuit allows you to rejuvenate dry-batteries. Of course, you’ve read the warnings printed on dry battery cases quite a few times. While the exact wording may differ from brand to brand, they all say much the same thing: “do not charge this cell”. It’s true that placing a dry cell into 14  Silicon Chip an ordinary nicad charger will create serious problems. These constant current chargers cause heat which produces steam and pressure, and this can easily burst the battery casing. This Dry-Cell Rejuvenator overcomes that problem by using a charging technique that results in very little heat production, thereby greatly reducing internal stress. It can recharge dry cells up to 10 times and save your hard-earned dollars in the process. In addition, this circuit helps our environment. We cur­rently throw away millions of dry cells each year –cells that eventually rust out and release their chemical cocktail of elec­trolytes. So reducing the number of cells we throw away provides definite environmental benefits. Both alkaline and conventional carbon-zinc batteries can be recharged by the Dry-Cell Rejuvenator. And because it employs two independent (and identical) charging circuits, it can charge either a single cell or two cells at the same time. The circuit runs off a standard 12VDC 300mA plug- +9V 4.7k D2 1N914 1M 100k 10k 4 IC1a 2 LM324 15k 100k 1 1k 11 100k 6 10k 7 IC1b A LED1 CHARGE 10k  K E 10k 5 10k Q3 BC547 B 2x1N914 D3 D4 C 1.5V CELL 100  Q4 BC547 C B E 10k E 10k .01 Q2 BC327 C 4.7k Q1  100 BC547 C 1W B 68k 3 E B 100k 2.2 25VW +9V 4.7k D5 1N914 1M 100k 15k 13 IC1c 100k 14 1k 10k 100k 9 10k 8 IC1d A LED2 CHARGE 10k  K E 10k 10 10k 10k .01 Q6 BC327 C 4.7k Q5 100  BC547 C 1W B 68k 12 E B Q7 BC547 B 2x1N914 D6 D7 C 100  Q8 BC547 C B 1.5V CELL E 10k E 100k 2.2 25VW D1 1N4004 B E C E B C VIEWED FROM BELOW I GO IN 12VDC 300mA PLUG-PACK 100 16VW 7809 GND OUT +9V 100 16VW DRY-CELL REJUVENATOR Fig.1: the circuit employs two identical sections to individually charge two 1.5V cells. IC1a is a Schmitt trigger – when the battery voltage is low, its output is high & Schmitt oscillator IC1b drives Q1 & Q3. These transistors in turn switch complementary pair Q2 & Q4 to provide the charge/discharge cycles. pack and will recharge an alkaline cell in about 18 hours. Conventional zinc-based cells are recharged in around 12 hours. Note however, that a recharged cell will not have “as-new” capacity. Provided the cell is in good condition, it will typically recharge to about 60% of the new capacity, at least for the first 7-8 cycles for an alkaline cell and 3-5 cycles for a zinc-carbon cell. After that, its perfor­mance will begin to deteriorate quite markedly. As a point of interest, a recharged alkaline cell will have greater capacity than an equivalent-size nicad cell, with the added benefit that it charges up to 1.6V. This figure is equival­ent to new cell voltage and is much higher than a nicad’s 1.2V rating. A feature of the unit is that it is very easy to use – you simply switch it on, slip the battery into its holder and, after about a second, the circuit will decide if that battery can be charged. If so, an indicator LED on the front panel will light up and the battery will be charged until its voltage rises above 1.65V. At this point, the circuit automatically switches into trickle mode and the indicator LED goes out to signal the end of the charging cycle. Faulty cells What happens if you attempt to charge a cell that has gone open circuit November 1994  15 PARTS LIST 1 PC board, code RAT002, 102 x 57mm 1 zippy box, 130 x 68 x 41mm 1 front panel artwork 1 12VDC 300mA plugpack 2 “AA” size cell holders 1 2.5mm DC panel mount socket 1 Mini-U heatsink Semiconductors 1 LM324 quad op amp (IC1) 6 BC547 NPN transistors (Q1,Q3,Q4,Q5,Q7,Q8) 2 BC327 PNP transistors (Q2,Q6) 1 7809 9VDC regulator (REG1) 1 1N4004 rectifier diode (D1) 6 1N914 signal diodes (D2-D7) 2 red 5mm LEDs (LED1,LED2) Capacitors 2 100µF 16VW electrolytics 2 2.2µF 25VW electrolytics 2 .01µF 63VW MKT polyesters Resistors (0.25W, 1%) 2 1MΩ 14 10kΩ 8 100kΩ 4 4.7kΩ 2 68kΩ 2 1kΩ 2 15kΩ 4 100Ω 1W Miscellaneous Light-duty hookup wire, machine screws & nuts, washers, solder. 16  Silicon Chip 5 1 VOLTAGE or high impedance? In the first case, the circuit will remain in trickle mode and the indicator LED will stay out. The same goes for a cell that’s already fully charged. So if the circuit refuses to start when you install a cell, check its output voltage. If the voltage is close to 0V, that cell has passed the point on no return and should be discarded. On the other hand, the circuit will attempt to charge cells that have discharged to a low voltage (ie, below 1V) and, as a result, have a high internal impedance. Cells in this condition will charge to 1.6V very quickly however, typically in less than five minutes, after which the circuit switches to trickle mode. The cell then quickly loses its charge so that, after a few minutes more, the circuit reverts to the full charging mode again. Any cell which causes the circuit to exhibit this behaviour should also be discarded, since it is obviously Fig.2: the charge/discharge waveform used by Hollows in 1955. The charge/ discharge ratio was about 5:1. incapable of holding any worthwhile charge. General guidelines In order to get the most out of the Dry-Cell Rejuvenator, there are several important guidelines that must be followed. Let’s take a look at these. First, never let the cell voltage fall below 1.0V. This is basically a cell’s “point of no return”. If its output voltage falls below this figure, it will generally not hold a sufficient charge to make recharging worthwhile. Second, recharge the cells as soon as possible when they go “flat”. The longer they are left lying around, the harder it is for the Rejuvenator to recharge them. Similarly, use them again as soon as possible after recharging, otherwise they will begin to deteriorate. This fast recycling technique will allow you to get the most out of your batteries. Third, don’t leave a battery on charge for more than two days (48 hours). If a battery hasn’t charged up in this time, it can be considered a lost cause and should be discarded. If you persist for longer than this, heat will slowly build up and some lesser-quality batteries may begin to leak. Finally, if a cell does begin to leak as a result of charg­ing or was already leaky, it should be discarded at once. The fluid discharge from a leaky cell is highly corrosive and can damage valuable equipment. Note that the Dry-Cell Rejuvenator works best on alkaline and heavy-duty (or super heavy-duty) zinc-carbon cells, so you are definitely better off spending a little extra for these types. Warning: under no circumstances should you try to recharge lithium batteries. Charging principle The charging principle relies on the chemistry inside the cell. If a carbon-zinc cell is charged with plain DC, the zinc is returned to the negative electrode in spongy blobs. Although this results in a cell with reasonable output voltage, it will also have a high internal impedance. Hence, it will be unable to deliver the expected power to the load. Much of the initial study into dry cell recharging was done nearly 40 years ago by R. Hollows and the results published in a 1955 edition of “Wireless World”. Hollows found that if the cell was charged using “dirty DC”, the zinc was distributed more evenly and compacted on the casing. The result was a cell which resembled its original charged state. A similar process occurs in alkaline cells. In this case, the term “dirty DC”, refers to a half-wave rectified DC voltage with a small negative offset. Fig.2 shows the details. When applied to a battery, this resulted in a 5:1 charge/ discharge ratio; ie, the battery was charged during the positive half cycle of the waveform and discharged during the much shallower negative half cycle. In effect, the principle could be called “five steps for­wards and one step back”. Hollow’s work was based on a circuit which used a 3VAC transformer, an item not commonly found these days. In addition, Hollow’s circuit would not have been the most efficient way of recharging a dry cell, due to the low frequency of the charging waveform (50Hz). This circuit overcomes those problems by using a square-wave oscillator to generate the charging waveform and by operating at a much higher frequency (4.5kHz). Circuit details Fig.1 shows the circuit details for the Dry Cell Rejuvena­tor. As already mentioned, it consists mainly of two identical charging circuits, one for each cell. These two circuit sections are powered from the plugpack via reverse polarity protection diode D1 and a 3-terminal regulator which delivers a 9V rail. IC1a is one-quarter of an LM324 quad op amp and is connect­ed as a Schmitt trigger. The 68kΩ, 15kΩ and 1MΩ resistors set the reference voltage on pin 3 to approximately 1.6V, while the in­verting input (pin 2) monitors the battery voltage via a 100kΩ resistor and a 2.2µF filter capacitor. If the cell voltage is less than the LED1 CELL 1 LED2 CELL 2 Fig.3: install the parts on the PC board & complete the wiring as shown here. Be sure to use the correct transistor at each location & note that a small finned heatsink is bolted to the metal tab of the 7809 3-terminal regulator. Q5 reference voltage, pin 1 of IC1a switches high and lights LED 1 to show that charging has begun. At the same time, pin 5 of op amp IC5b is biased to about half supply via a voltage divider consisting of two 100kΩ resistors. This op amp is connected as a Schmitt trigger oscilla­tor. When pin 1 of IC1a switches high, IC1b oscillates at a fre­quency of about 4.5kHz and with a 50% duty cycle. The square-wave output from IC1b appears at pin 7 and drives transistor inverter stages Q1 and Q3. These transistors, in turn, switch the main output devices (Q2 and Q4) on and off. In effect, Q2 and Q4 function as a complementary output pair. When pin 7 of IC1b goes high, Q1 and Q3 turn on, Q4 turns off and Q2 turns 100  100  10k .01 .01 D3 Q3 4.7k 4.7k 10k Q4 10k 100k 68k D2 100k 100k 10k 10k Q2 15k 1M 10k 100uF 1k 2.2uF 100k D7 10k 100k 100k 100k 100  Q7 10k 1 1M 68k 7809 100k 10k 10k D6 4.7k 1k 15k D5 Q8 12VDC PLUG-PACK 100uF 2.2uF IC1 LM324 4.7k Q6 100  D1 D4 Q1 10k 10k 10k 10k on and supplies charging current to the cell. Subsequently, when pin 7 of IC1b goes low, Q1 and Q3 turn off and so Q2 also turns off to end the charging pulse. At the same time Q4 turns on, since diodes D3 and D4 are now forward biased via a 10kΩ pullup resistor (more on these in a moment). The cell now discharges through Q4 and its associated 100Ω collector resistor. Because oscillator IC1b has a 50% duty cycle, Q2 and Q4 also operate with a 50% duty cycle. This means that the cell is charged for half the time and is discharged for the other half of the time. However, when Q2 turns on, its 100Ω collector resistor has about 7.5V across it, whereas when Q4 turns on its 100Ω collector resistor only has about 1.5V (ie, the cell voltage) across it. As a result, about 75mA flows through Q2 to charge the cell, while only about 15mA flows through Q4 to discharge it. This means that the charge-discharge ratio works out to be about 5:1, although this will vary somewhat according to the cell voltage. Trickle mode As the battery charges, its voltage is monitored by pin 2 of IC1a. When it exceeds 1.6V (the reference set on pin 3), pin 1 of IC1a switches low to about 0.7V and this set the bias applied to pin 5 of IC1b to about 0.35V. As a result, IC1b changes its output to a low-duty (1:10) square-wave with a frequency to about 2.2kHz. This change in frequency (from 4.5kHz to 2.2kHz) is due to the different bias, while the lower duty cycle is partly due to the Schmitt trigger action and partly due to asymmetry in the output of IC1b. In operation, IC1b’s output (pin 7) swings closer to RESISTOR COLOUR CODES ❏ No. ❏   2 ❏   8 ❏   2 ❏   2 ❏ 14 ❏   4 ❏   2 ❏   4 Value 1MΩ 100kΩ 68kΩ 15kΩ 10kΩ 4.7kΩ 1kΩ 100Ω (5%) 4-Band Code (1%) brown black green brown brown black yellow brown blue grey orange brown brown green orange brown brown black orange brown yellow violet red brown brown black red brown brown black brown gold 5-Band Code (1%) brown black black yellow brown brown black black orange brown blue grey black red brown brown green black red brown brown black black red brown yellow violet black brown brown brown black black brown brown not applicable November 1994  17 Take care to ensure that the DC socket is wired to suit the plugpack, so that the correct supply polarity is applied to the board. The external wiring connections to the board can be made via PC stakes. ground than to the positive supply rail and this situation is exaggerated when the input threshold is pulled low. What happens now is that IC1b delivers a train of narrow positive-going pulses and these briefly pulse Q1 and Q2 on to trickle charge the battery. Q4 remains off in this mode, however. That’s because D2 now clamps Q3’s collector to a maximum of 1.4V (remember that pin 1 of IC1a in now at 0.7V) and this, coupled with the voltage across D3 and D4, means that there will be insufficient bias to turn Q4 on. This means that the battery is not discharged for part of the time when the circuit in trickle mode. If the battery voltage now subsequently falls below the reference voltage, pin 1 of IC1a switches high again and the circuit reverts to its full 18  Silicon Chip charge/discharge mode of operation. In this mode, D2 is reverse biased and so Q3 is now able to turn Q4 on and off to provide the discharge cycle, as described pre­viously. Note that because IC1a is connected as a Schmitt trigger with about 100mV of hysteresis, the circuit is effectively pre­vented from oscillating when the cell voltage reaches the refer­ence voltage on pin 3. Instead, the cell voltage must fall from 1.6V to 1.5V before the circuit will revert to full charging mode and must then reach 1.6V again before reverting to trickle mode. If the cell is removed, the circuit behaves as if a fully charged cell is in position; ie, it switches to trickle mode and the LED goes out. That’s because the 2.2µF capacitor on pin 2 of IC1a is charged almost to +9V (via the 100kΩ feedback resistor) by the current pulses generated each time Q2 turns on. The second charging circuit, based on op amps IC1c and IC1d and transistors Q5-Q8, functions in exactly the same manner. Construction Most of the parts are in­stalled on a PC board measuring 102 x 57mm and coded RAT002. Begin construction by fitting PC stakes to the external wiring points, then install the various parts as shown on Fig.3. The resistor colour codes are shown in the accompanying table but we also recommend that you check each value using a DMM, as some colours can be difficult to decipher. Take care to ensure that all semiconductors are correctly oriented and don’t get the transistors mixed up – Q2 and Q6 are BC327 PNP types, while the rest are BC547 NPN types. The 7809 regulator must be installed with its metal tab adjacent to the edge of the board – see photo. It is fitted with a TO-220 Mini-U heatsink to aid heat dissipation. Once the board has been completed, it can be installed in a plastic zippy case measuring 130 x 68 x 41mm. Use the board as a template to mark out its mounting holes, then drill the holes to 3mm along with a hole in one end of the case to accept the power socket. This done, attach the front panel label to the lid and drill out the mounting holes for the battery holder and the two LEDs. The latter should be made just large enough so that the LEDs are a push fit. Finally, mount the various items in position and complete the wiring as shown in Fig.3. The PC board is se­cured using machine screws and nuts, with additional nuts used as spacers. Take care to ensure that the LEDs are wired with the cor­rect polarity. The anode lead of each LED is the longer of the two. Testing Before switching on, temporarily disconnect one of the leads to the DC power socket and connect a multimeter set to milliamps across the break. This done, apply power and check Where to buy a kit of parts The Dry-Cell Rejuvenator is only available from RAT Elec­tronics. Complete kits, including all specified components, instructions, case, front panel and 12V DC plugpack, are available for $44.95 ($39.95 without plugpack). Please add $5.05 for post­age and packaging for delivery within two weeks. To place your order, phone or fax RAT Electronics on (047) 77 4745 or send your cheque/money order to: RAT Electronics, PO Box 641, Penrith, NSW 2750. Note: copyright (c) 1994 RAT Electronics. Copyright of the cir­cuit and PC board art associated with this project is owned by RAT Electronics. that the current drawn by the circuit is about 10mA with no cells in place. Note that both LEDs should flash briefly when power is applied. If you now install a single “flat” cell, the circuit should switch to charge mode – the appropriate LED should light to indicate that charging it taking place and the current drain should rise to about 50mA. This should increase to about 90mA if a second “flat” cell is installed. Check also that the second LED is now lit. If you don’t get the correct current readings, switch off immediately and check the board carefully for incorrect parts placement or orientation. Check also that the 7809 3-terminal regulator is delivering +9V and that this voltage appears at pin 4 of IC1 and on the emitters of Q2 and Q6. Finally, remember that a dry cell should not be discharged below 1V if it is to be successfully recharged and don’t leave any cell on full charge for more than 48 hours – if it hasn’t charged up in this time, it can be considered defunct. That’s it – you are now ready to start recharging those expensive dry batteries and do your bit for the enviSC ronment as well. AC/DC digital clamp meter with 4000 count display and bargraph! ● High speed auto-or manual ranging ● High speed sampling for 40 segment bargraph display ● Average, Temperature test, Max hold, Peak hold functions ● Sleep mode to reduce battery con- sumption ● Continuity beeper, Data hold, Diode test and analog signal output ● Battery or AC adaptor operation Brief Specifications Functions : AC/DC current, AC/DC voltage, Ohms, Continuity, Diode test, Frequency, Temp, Data/ Peak/Max hold, Average., Analog signal output Display : LCD 3.5 digits, 4000 (Hz: 9999) count Bar Graph Display : 40 segments Ranges : Auto or manual ranging Aac, Adc : 400, 1000A Vac, Vdc : 40, 400, 650V Frequency : 10.0-999.9Hz Temperature : -50.0 to +150°C Jaw Opening : 55 mm ø or 65 x 18mm busbar Withstand Voltage: 2.5kVac, 1 minute Lloyd’s Register Quality Assurance to ISO-9001 2343 – one of the NEW Generation of Multimeters from Centrecourt D3, 25-27 Paul Street North, North Ryde Call Robyn for more information on (02) 805 0699 or fax : (02) 888 1844 November 1994  19 The Ol’ Timer: an alphanumeric clock with old-fashioned time Are you tired of looking at those boring digital clocks or at those drab looking old tickers hang­ ing on the wall? Then grab onto this old-time clock using newfan­gled technology. By ANTHONY NIXON There have been all sorts of clocks designed over the years but none actually show you the time in its most basic form – the way you think it. But now you can build the Ol’ Timer. It shows you the time just the way we all used to say it and think it and no doubt still do. It’s easy to read and can be used 20  Silicon Chip as a teach­ing aid for those people who find it difficult to understand the usual types of clocks. To show how different this clock is, let’s give a few exam­ ples of its time displays. At 12.00 AM it displays “MIDNIGHT”; at 1:15, it shows “1/4 PAST 1”; at 12.00 PM, it shows “NOON”; at 3:35, it shows “25 TO 4” and so on. In other words, it displays the time in more or less the same way as you would think it or say it. Some of the photos in this article give further examples of its time displays. Note that it will also display time in stan­dard digital format if you want it to. To provide this alphanumeric display of time, the circuit uses eight LED dot matrix (5 dots across by 7 dots vertically) displays. These displays are driven in multiplex fashion by a microcontroller to keep the circuit complexity to a minimum. Apart from ol’ time telling, this R13 220  R14 10k B D2 1N914 E 1 RTCC Q2 BC557 C 28 MCLR RA0 RB7 17 2 8 SB CLK BUZZER RA3 9 R8 10k C Q3 BC548 B R5 10k A S2 20 RC2 19 RC1 18 RC0 RB2 12 RB3 13 RB4 14 RB5 15 R11 150k R12 39k R9 100k RB6 16 3 4 LDR1 2 13 5 IC6 2003 6 7 11 DISPLAYS 10 15 2 1 16 +5V 7 D1 1N4001 6 24 RC6 4 RC7 27 X1 8MHz C1 18pF 12 8 IC8 741 R10 100k 7 14 +5V 3 2 8 SB CLK 14 1 IC5 SA 74HC164 9 CLR A B C D E F G H C8 3 4 5 6 10 11 12 13 0.1 R17-56 40x130W RB0 10 RB1 11 R7 10k FROM PIN13 IC4 TO PIN2 IC2 9 1 SA CLR A B C D E F G H 3 4 5 6 10 11 12 13 IC7 PIC16C57 B S3 R6 10k 14 IC1 74HC164 7 E MODE S1 +5V 6 R15 33k ZD1 3.3V C4 0.1 C3 0.1 2 R3 2.2k 26 C2 18pF LED1 ALARM  R16 10k B 21 RC3 22 R1 RC4 470k 23 RC5 RA1 SP1 BZW04P13B 7 OSC1 OSC2 RA2 8 R2 2.2k 25 RELAY1 4 R4 2.2k LED2 PM OL' TIMER B C Q1 BC548 E Circuit description The circuit is based on the PIC 16C57 microcontroller which has 2Kb of ROM, 72 bytes of usable RAM and 20 I/O ports. It takes care of all of the clock functions which include display multi­plexing, key scans, display dimming, timing, LED indication and relay and buzzer control. The chip is clocked using an 8MHz crystal which is divided by four internally to provide an instruction E B VIEWED FROM BELOW E C A K I GO A 7.5V WO4 240VAC  N IN 7V E Fig.1: the heart of the circuit is the PIC57 microcontroller which is programmed to drive the LED dot matrix displays. Serial data is fed from pin 17 of IC7 & converted to 40-bit wide words (ie, parallel data) by shift registers IC1-IC5. Note that IC2, IC3 & IC4 are not shown since they are cascaded between IC1 & IC5. clock features date, alarm, 99 minute timer, buzzer or relay control, daylight saving, digital format, sleep timer, leap year indicator, display dimming and power failure indication. C cycle time of 500 nanoseconds. This is further divided by 64 with a programmable prescaler to give a clock of 31.25kHz. This is used to increment an internal Real Time Clock Counter (RTCC) which, when initialised to 206, will overflow to 0 in 1.6ms. This is used as a timebase to update the display. This frequency is further divided by four for key scanning and other timing functions. Every 1.6ms, serial information from the display buffer inside the micro­ controller is sent from pin 17 of IC7 to the serial input of IC1, the first of five 8-bit serial to parallel converters which are cascaded to receive 40 bits of information. These ICs are actually C9 470 25VW REG1 7805 GND OUT +5V C10 47 16VW 74HC164 serial in/parallel out shift registers. Note that only IC1 and IC5 of this 40-bit converter string are shown on the circuit diagram but you will see that pin 13 of IC1 goes to pin 2 of IC2 and hence pin 13 of IC2 goes to pin 2 of IC3 and so on. What happens is that a 40-bit serial data stream is sent out from pin 17 of IC7 and as it is being sent out, it is clocked through the registers by a clock signal from pin 6 of IC7 to the register clock inputs (pin 8). Thus, the 40-bit serial data stream is converted to a 40-bit wide word which appears on the Q outputs of the registers. These drive the column inputs of the eight dot-matrix displays via 130Ω resistors. The seven row inputs of the dot matrix displays are driven by IC6, a November 1994  21 RELAY 1 10k BROWN BLUE D1 Q1 SP1 TERMINAL BLOCK ACTIVE BROWN NEUTRAL BLUE EARTH GREENYELLOW 1 2.2k 1 MAINS CORD 2.2k 1 2.2k MAINS CABLE CLAMP 1 40x130W X1 18pF 18pF 10k DISPLAY6 470k IC7 16C57 0.1 10k IC4 74HC164 10k 1 Q2 10k 10k 0.1 S1 DISPLAY7 IC6 2003 DISPLAY1 IC1 74HC164 7.5VAC 1 DISPLAY2 0.1 0.1 IC3 74HC164 33k POWER TRANSFORMER DISPLAY3 IC2 74HC164 DISPLAY5 220  0.1 100k D2 ZD1 Fig.2: the wiring diagram shows both patterns for the PC board. The dark grey pattern is on the underside while the light grey pattern is on top of the board. Take care to ensure that all parts are correctly oriented. 1 K LDR1 K Q3 A 39k BUZZER 7VAC 470uF REG1 O G 1 WO4 LED2 A LED1 47uF 100k IC8 741 S2 0.1 DISPLAY8 IC5 74HC164 150k 22  Silicon Chip DISPLAY4 S3 This is the view inside the clock with the rear panel (case lid) removed. Make sure that the mains cord is securely clamped & note that the Earth lead (green/ yellow) must be soldered to a solder lug that’s secured by one of the transformer mounting screws. The Active & Neutral leads go to a 2-way terminal block. 7-way Darlington array which is driven in turn by seven output lines from the microcontroller. The displays are multi­plexed in such a way that each time a row is enabled via IC6, the column lines from ICs 1-5 are updated. Thus, the LEDs are driven with a duty cycle of 14%; ie, 1.6ms on and 9.6ms off. By way of further explanation, the LED dot matrix displays are common cathode types with the cathodes of each row being pulled to 0V by Darlington transistors in IC6 and the anodes driven by the registers, IC1-IC5. In other words, the registers “source” current into the displays while IC6 sinks the current. Actual clock timing is derived from the 50Hz AC mains sup­ply. This is supplied from the 7.5V winding of the transformer via a 470kΩ resistor. A transient suppressor is connected across the output from this winding to shunt any spike voltages and thus protect IC7. The AC signal is clamped to the positive and 0V rails because of the internal protection diodes fitted to all I/O pins on the chip. These are capable of withstanding several milli­ amps of current, much more than can be supplied via the 470kΩ resistor. Transistor Q2 forms a “Brown Out” protection circuit. When the supply voltage falls below about 4V, this transistor will cease to conduct and the master clear (MCLR), pin 28, will be pulled low via the 33kΩ resistor, causing the chip to reset. The chip has internal circuitry which controls all of its resetting functions. Display dimming is achieved using IC8, a 741 op amp which has a light dependent resistor connected to its pin 3. When the ambient light level drops below a certain level, IC8’s RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   1 ❏   2 ❏   1 ❏   1 ❏   6 ❏   3 ❏   1 ❏ 40 Value 470kΩ 150kΩ 100kΩ 39kΩ 33kΩ 10kΩ 2.2kΩ 220Ω 130Ω 4-Band Code (1%) yellow violet yellow brown brown green yellow brown brown black yellow brown orange white orange brown orange orange orange brown brown black orange brown red red red brown red red brown brown brown orange brown brown 5-Band Code (1%) yellow violet black orange brown brown green black orange brown brown black black orange brown orange white black red brown orange orange black red brown brown black black red brown red red black brown brown red red black black brown brown orange black black brown November 1994  23 depending on the display requirements and ranges from around 30mA to 200mA. Mechanical details The displays are mounted on the underside of the PC board & are attached to it using individual pin sockets (see text). The LDR enables dimming of the display at night while the two LEDs in­dicate the alarm mode & PM. output swings high. When the micro­ controller detects this high, it cuts the duty cycle of the displays to 50% of their normal operation, thus dimming the display. The 150kΩ resistor from pin 6 to pin 3 provides some hysteresis and stops IC8’s output from oscillating when the light level is at the changeover point. The three pushbutton switches are read via inputs RC0-RC2 (pins 18, 19 & 20) and are debounced using software delays. IC7’s outputs RA1 and RA2 drive the PM and ALARM LEDs directly, while outputs RA3 and RC7 drive the buzzer and relay via Q3 and Q1 respectively. Average current consumption varies The Ol’ Timer clock is housed in a standard black plastic jiffy box measuring 196 x 112 x 65mm. The box is stood on its side and has a red Perspex window for the dot matrix displays. All the circuitry is mounted on a double-sided PC board measuring 145 x 90mm. The PC board doesn’t have plated through holes but uses IC pin sockets soldered to the board to complete the connections. These are used to mount the eight dot matrix displays on the underside of the board. The easiest way to solder these pins neatly is to place them on a 6-pin IC strip, then place them into the board holes and solder them. When the strip is removed, the pins are left looking tidy and with the correct spacing. These pins can be knocked out from 2 x 64 machine pin IC sockets. Some pins on the IC sockets don’t pass through the circuit board but are bent at right angles and soldered to the component side of the board. The track layout has been designed for this purpose. A quick method of knocking these PARTS LIST 1 double-sided PC board, 181 x 112mm 1 plastic Jiffy case with plastic lid, 196 x 113 x 65mm 1 transformer 7V CT + 7.5V; DSE Cat. M-2824 1 5V SPDT relay; Ritronics Cat. S-14100 1 piezoelectric buzzer; Jaycar Cat. AB-3460 3 momentary contact pushbutton switches; Jaycar Cat. SP-0710 1 8MHz crystal 1 piece of red Perspex, 180 x 95mm 2 rubber feet 1 3-core mains cord & plug 1 2 way insulated terminal block 1 cable clamp to suit mains cord 1 solder lug 2 10mm PCB spacers 13 PC stakes 96 IC pins (from 2 x 64 machine pin IC sockets) 24  Silicon Chip IC sockets 5 14-pin 1 16-pin 1 8-pin 1 28-pin Semiconductors 5 74HC164 8-bit shift registers (IC1-5) 1 2003 Darlington array (IC6) 1 16C57 preprogrammed microcontroller (IC7) 1 741 op amp (IC8) 1 7805 5V regulator (REG1) 2 BC548 transistors (Q1,Q3) 1 BC557 transistor (Q2) 1 3.3V 400mW zener diode (ZD1) 1 1N4001 diode (D1) 1 1N914 diode (D2) 1 WO4 bridge rectifier 8 7 x 5 Sun MUR18A dot-matrix column anode LED displays; C & K Elec­tronics 1 light dependent resistor; Jaycar Cat. RD-3480 (LDR1) 1 BZW04P13B transient suppressor; Farnell Electronics (SP1) 2 3mm red LEDs (LED1,2) Capacitors 1 470µF 25VW PC electrolytic 1 47µF 16VW PC electrolytic 6 0.1µF 63VW MKT polyester 2 18pF ceramic Resistors (0.25W 1%) 1 470kΩ 6 10kΩ 1 150kΩ 3 2.2kΩ 2 100kΩ 1 220Ω 1 39kΩ 40 130Ω 1 33kΩ Miscellaneous Tinned copper wire, insulated hookup wire, machine screws, nuts & washers, right-angle mounting bracket for piezo buzzer, heatshrink tubing. The three pushbuttons on the rear of the case allow selection of the various operating modes, time setting, alarm setting & so on. This close-up view shows the method of mounting the LED matrix displays. Each display is plugged into 12 machined IC pins. Take care to ensure that the displays are correctly oriented (the pins are polarised) The piezo buzzer is mounted on a small L-shaped metal bracket on the side of the case. The OL’ TIMER is an old-fashioned clock in the way it shows the time, although old-fashioned clocks never did it like this. It uses LED dot matrix displays driven by a PIC57 microcon­troller. pins out of the socket carrier is as follows. First, a piece of round steel, 3mm in diameter, is cut to a length of 25mm or so. This done, drill a 1mm hole into one end, 5mm deep. This tool is then placed over the pin and tapped lightly with a small hammer. No pins are damaged in this way. It’s a neat idea to create a pseudo through-plated hole when a socket is required. Board assembly In other respects, the PC board is quite straightforward to assemble. Sockets for the ICs are listed in the parts list and are recommended. Note that six 0.1µF capacitors are shown in the parts list but only three are shown on the circuit. The other three are associated with shift registers IC2, IC3 and IC4 which are also not on the circuit, as noted above. Note that in most cases the resistors are soldered only on the underside of the board. The 40 130Ω resistors associated with the five shift register These are just three more displays from the OL’ TIMER. It can display the date & conventional digital time as well. November 1994  25 Operating Instructions Using the Ol’ Timer clock is fairly straight­forward. Just use the MODE key to select a function and then use either the A or B keys to change the settings. After changing a setting or a function, the clock will revert back to the selected time display if no keys are pressed for three seconds. It can also be cycled back using the MODE key. If button A or B is held down, that button’s function will be repeated slowly at first and then at a faster rate. Setting the time & alarm: use the MODE key to select the time setting function. Then by pressing either A or B, the hours or minutes will be incremented respectively. Setting the alarm time is accomplished in the same manner. Setting the date: use the MODE key to select the date display and press A to select either the day, month or year. Then press B to increment the selection. If the year is a leap year, the LED at the lower right-hand corner of the display will light when the complete date is being displayed. Using the 99 minute timer: select ICs are stood on end to save space. Take careful note of the orientation and polarity of the ICs, diodes, transistors and electrolytic capacitors. PC pins should be installed for all the off-board connections. Once the board is complete, you will need to make a cutout in the base of the box for the display and drill other holes that are required. The rectangular hole for the display measures 115 x 20mm and will need to be positioned precisely to line up with the dot matrix displays. The circuit board is secured using two 10mm tapper spacers fas- the timer display with the MODE switch. The number displayed indicates the time in minutes for the timer to count down from, after which the buzzer will sound or the relay will operate. This time can be increased by pressing B or decreased by pressing A. Use MODE to set the output configuration for the timer. If BUZZER is selected, then it will sound for five seconds after the timer counts down to zero. If the relay is selected, it can either operate ‘While’ (indicated by “RELAY=W”) the timer is counting down or ‘After’ (indicated by “RELAY=A”) it has finished. Press A to select either BUZZER or RELAY. If RELAY is selected, press B to chose the ‘While’ or ‘After’ option. The relay can be turned off at any time by pressing B while the display is showing normal time. Using the alarm: after the alarm time has been set and the dis­play is showing normal time, pushing button B sets the alarm. The ALARM LED now lights. When the normal time equals the alarm time the buzzer will beep for 1 hour. If the A button tened to the base of the jiffy box by two countersunk screws. These screws are concealed by the red Perspex which becomes the front panel of the clock. The Perspex was attached to the box by a pin in each corner and these are secured inside the box with 5-minute epoxy adhesive. Note the details for connection of the mains cord. This should be anchored to the side of the case as shown in the wiring diagram and the Active and Neutral wires terminated to a 2-way insulated terminal block which Where to buy the microcontroller The programmed PIC57 microcontroller is only available from the author, Anthony Nixon, who can also supply the double-sided PC board and a set of machine pins (see text). Pricing is as follows: (1). PIC57 programmed microcontroller, $30.00 including p&p; (2). PIC57 plus PC board and set of machine pins, $47.00 including p&p. Send cheque or postal money orders to Anthony Nixon, 20 Eramosa Road East, Somerville, Vic 3912. 26  Silicon Chip is pushed, the buzzer will be silenced for 10 minutes and then resound. The ALARM LED flashes while the ‘Sleep’ function is operating. This function can be continued for 1 hour. If A is pressed while the sleep function is operating, then the buzzer will stop until the two times match again. If B is pressed, the buzzer will stop, the alarm will be disabled and the ALARM LED will extinguish. Setting daylight saving time: press MODE until ‘DLS = ’ is displayed. Daylight saving is enabled if ‘DLS = Y’ is displayed, or disabled if ‘DLS = N’ is displayed. When enabled, the normal time is increased by one hour and decreased by one hour when disabled. All dates are updated in the process. Use A to en­able/disable. Display format: the last function selects the display format. Press A to alternate between OL’ TIME and DIGITAL formats. Power failure indication: when the clock is first turned on or if there has been a power failure, the display will flash “OL’ TIMER” on and off. You then must reset all time and alarm settings. also terminates the primary wind­ings of the transformer. The Earth wire of the mains cord is terminated at a solder lug which is secured to one of the transformer’s mounting lugs. A small bracket will need to be made up to mount the piezo buzzer, as shown in the photos. Ventilation holes should be drilled in the rear panel, as well as the holes for the three pushbutton switches and the cord entry. Initial tests When all assembly work is complete, carefully check your work and then apply power. The display should flash ‘OL TIMER’ on and off. Check the 5V supply rail from the regulator. If any LEDs fail to light , it is quite easy to determine which row and column they are in and then check for open circuits in the board connections. Assuming that all is well, the correct time can now be set as detail­ed in the SC operating instructions. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SERVICEMAN'S LOG Tread carefully with a new brand name How does one cope with a set of unknown brand? Is it an orphan brought in by an overseas traveller, or is there a local importer? If so, what backup service in the way of technical data & spare parts is available? In an extreme case, where the set is an orphan or nothing can be found out about it, there is often little option but to bow out right at the start. It may not do much for one’s reputa­tion in the short term but the alternative is to risk much great­er damage. If lack of data and replacement parts means that 32  Silicon Chip the job ultimately has to be abandoned anyway, the customer is no better off and the serviceman in down the drain for his time. Of course, all this is leading up to the fact that some time ago I encountered a set carrying a brand name I had never heard of and had to go through the above mental gyrations in order to decide how to handle the situation. While that is now history, what followed is technically interesting and I thought it worthwhile to point out the need to investigate the background in all such cases. Unknown to me at the time, the story really started a couple of years earlier when a local motel changed hands. The new owner had come from Victoria – a point of some importance as it turned out – and one of the first decisions he made when taking over was to replace all the TV sets. It was a logical decision. From what I knew of the original setup, the sets were approaching the end of their commercial life anyway (life in a motel can be pretty rugged at times) and were all VHF-only models. With a significant number of guests now wanting to watch SBS, the lack of UHF was a serious shortcoming. So, after carefully studying what was available in his state of origin, he settled for 12 Contec 51cm colour TV sets, model MSVR-5383. And this was what I was presented with when he approached me sometime later to undertake the service of these sets. From a business point of view, of course, it was an attrac­tive offer. But, initially, I hesitated to be become involved. I had never heard of the Contec brand and needed to be reassured along the lines already discussed, before committing myself. As it transpired, the owner had done his homework pretty well. The sets had been purchased from a Melbourne firm, Freecor International and, yes, he had investigated the service and backup situation and was able to give me the name and phone number of the manager of their service organisation. Which wasn’t a bad effort. But he’d gone one further; he had secured some circuits. And as circuits go these days, they are quite good for the most part. The only snag is that, in the original, -31V 5V 4 F 3 F 12V 1 F 2 F 1 E 2 E 8 1 D510 C514 47 7 6 240V D511 3 4 2 5 R519 1k IC 510 IC502 330 C515 470 0.1 Q506 T501 Q505 T502 114.9V C 5 6 Fig.1: the power supply circuitry for the Contec MSVR-5383 (note: primary side of the switchmode supply not shown). some parts have been shaded, leaving a dot pattern which can make some values hard to read. However, with all that information to hand, I felt reason­ably confident about tackling these sets. And, initially, most of the faults turned out to be fairly routine. But then, about 12 months ago, I encountered the first difficult one, which I am about to relate, followed by a couple of real weirdos. More about those in notes to come. Lost stations So what was this one? The customer’s complaint was that if the set was turned off at the power point, as can easily happen when motel rooms are being serviced, then all the channels pro­ grammed into it would be lost. To get it working again, it had to be reprogrammed. But this only occurred if the power point was turned off; it did not occur if the set was turned off into the standby mode. With the set on the bench, I found the owner’s description quite accurate; the only additional factor, which the owner himself added, was that the power point had to be off for someth­ing like half an hour before the memory D516 C C523 C 1 2 3 Q508 Q509 was lost (the exact reason for this is still a mystery). And so, having confirmed the situation, I was faced with the problem of where to start look­ing. I had never encountered such a fault or anything remotely like it at that time. Nor had I encountered any literature ex­plaining in detail how these systems worked. I turned to the circuit for inspiration but it didn’t help a great deal. All I learned was that it was most likely in or around one of three ICs: IC801, IC802 and IC804. IC801 was the 42-pin central processing unit (CPU); IC802 was a 14-pin unit with internal boxes captioned “memory transistor array”, “address register”, “address decoder”, etc; and IC804 was a 16-pin unit that contained an oscillator, a display timing generator and various other circuits. Both these latter ICs were closely asso­ciated with IC801 (the CPU). Of those three, IC802 looked the most likely possibility. But that was – at best – little more than an educated guess. I needed more than that; I needed some real help. I decided it was time to put the owner’s backup research to the test. I rang the service organisation and was put through to the service manager. And that was a real bonus, because he turned out to be most co-operative and was familiar with many of the firms and personnel that I dealt with in Sydney. More importantly, he was a mine of information about the set. As soon as I described the symptoms, he was onto them. And I was right about one thing; it did involve IC802. He drew my attention to pin 2, which is marked as -31.65V. This voltage is derived from a small 50Hz power supply, based on transformer T501, on the main power supply board. This is the standby supply, which means that it is activated while ever the power point is turned on. It provides the -31V rail from pin 8 of T501 via a diode (D510), a 47µF filter capacitor (C512), a 1kΩ resistor (R519) and a zener diode (IC501). This goes out on pin 4 of plug/socket F. Subsequent analysis revealed that this supply also provides a regulated 5V rail for the CPU and the remote control receiver, from pin 7 of T501, via IC502 and a simple filter network. This goes out on pin 3 of plug/socket F. And there is a 12V supply for IC904 (the audio output stage) from pins 3 & November 1994  33 SERVICEMAN’S LOG – CTD 4 of T501, via a full-wave rectifier and regulator transistor Q506. This goes out on pin 1 of plug/socket E. Having pinpointed pin 2, the service manager came straight to the point. “Check that 31V rail. You’ll probably find it either zero or very low. We have had cases where IC802 has failed internally and taken out the 1kΩ resistor in the power supply”. Well, that was about the most succinct diagnosis I can remember. I thanked the gentleman and went back to the bench. And he was dead right; the voltage on pin 2 was down to a couple of volts and the cause was R519, which had gone very high. But there was more; diode D510 was also faulty. Not completely open cir­cuit; more partially broken down. It may still have been provid­ing some rectification. After that, the job was pretty much routine. I replaced R519 and D510 and fitted a new IC for IC802, and we were back in business. Of course, the set had to be reprogrammed but once that was done, it would hold the program regardless of the condi­tion of the power point. So the set went back to the customer and 12 months later it is still behaving itself. But it was a valuable experience, and I learned a great deal from it. And the experience was to prove invaluable more recently when, as I have already hinted, there were more problems in this area but with quite different symptoms and different causes. More about those in future notes. Another motel set My next story concerns a Samsung 34cm colour set, model CB-349F, one of several belonging to another local motel. In fact, these sets have featured in these notes before. The complaint – or rather the problem – was lack of bright­ ness. And I make this distinction because the complaint was poor colour; they claimed they couldn’t adjust the colour properly. Taken at its face value, such a complaint would suggest lack of colour saturation. Unfortunately, some people have diffi­culty in differentiating between colour and brightness – it’s 34  Silicon Chip all the same to them. In fact, there was no colour problem; it was simple loss of brightness. Where the loss is only slight, one might be tempted to adjust sub-brightness control VR203 – a 2kΩ pot. Another pos­sibility is to increase the setting of the “screen” or G2 voltage control, or even try adjusting both. However, these tricks smack of a quick fix approach and are best avoided in most cases. But it is wise to check these two controls, in case someone has had a fiddle (it does happen) – they should be in about mid-position. In any case, unless the G2 voltage is significantly below normal, it is best left alone. There was no temptation in this case. The brightness loss was considerable, which clearly indicated a fault of some kind. And I had a pretty good idea where it would be. The most frequent cause of this problem in these sets is resistor R208, which has a nasty habit of going high. It is part of the beam limiting circuit and is connected between the 125V HT rail and pin 4 (pedestal clamp) of the main IC, IC501. (It’s a swine of a thing to find on the circuit, being tucked away down below the horizontal output transformer). Its value is not given directly on the circuit but in a table on the side. For 14-inch and 16-inch tubes – which covers this one – it is given as 127kΩ 0.5W. For 18-inch or 20-inch tubes, the value is 110kΩ 0.5W. And it has something of a history. Back in May 1990, this resistor was mentioned in a Samsung service note, advising that it be checked for an increase in value. In fact, several such cases were found. At the same time, there was some initial confu­sion as to what value these resistors were supposed to be, since they carried a colour coding which didn’t seem to make sense with the values in the table. However, that’s all by way of background because, in this case, the resistor measured spot on. From there, I checked the G2 voltage and found that it was down significantly. And I seemed to recall that there was another common fault which produced these symptoms but, for the moment, I couldn’t remember the details. A caffeine fix helped and the memory suddenly clicked. Of course, a capacitor on the neck board – in particular, capacitor C519, a 330pF 1kV disc ceramic which bypasses the G2 line to chassis. As soon as I saw it, I was even more convinced that I was on the right track; it was a blue disc ceramic and I recalled encountering these in the power supply on several previous occa­ sions, where their tendency to leak caused some nasty problems. And I had mentioned their unreliability in these notes at the time. Well, that was it. I pulled it out, confirmed the leakage, and fitted a new one. And that was it; normal brightness returned and I had another satisfied customer. Naturally, the new capaci­tor was a different brand to the original – one about which I feel a lot more confident. It hadn’t been any big deal but it did make me think about some of those previous faults which I had temporarily forgotten. One’s memory needs to be jolted from time to time. The HMV portable To finish off, here is another story which in itself was no big deal. In fact, it was little more than routine but I decided to tell it because it presents an opportunity to discuss a couple of important points. The set involved was an HMV portable TV set, model 8010501, a 34cm unit actually made by JVC. It’s getting a mite long in the tooth now, being some 15 years old at least, but is still a goer for all that. The customer’s complaint was straight to the point; no picture and no sound. When I set it up on the bench this proved to be literally true. But there was a raster and some white noise from the speaker; it wasn’t much use to the customer but was quite valuable as far as I was concerned. Even more valuable was a very prominent hum pattern on the raster and the fact that this was also shrunken on all four sides. So it didn’t take a genius to deduce that we had a power supply problem. And finally, there was the HT rail. This should have been around 110V but was actually only about 80V. Likely causes? The first thought is almost automatically to blame the main filter capacitor but there are other possibili­ties. For example, failure of the voltage regulator transistor I had measured it proper­ly, or whether there was a fault in the tester. A few quick checks soon ruled out those ideas, so I patched it back into circuit and gave it another try. I could have saved my time; it simply would not work. Well, it’s not the first time I’ve struck such contradic­tions. And it emphasises the old rule that the final test for any component is whether it will work where it is supposed to work. So what was wrong with the capacitor? It could be one of several faults that show up in electrolytics but my guess is that it was suffering from high internal resistance. It is a known fault and it means that, even if the capacitance value is cor­rect, it cannot charge or discharge fast enough to provide the required function. Capacitor compatibility can produce a variety of symptoms, including those listed above, this depending on the exact nature of the fault. Another possibility is a faulty bridge rectifier. Failure of one diode will result in only half-wave rectification, with reduced voltage and lots of hum. But these thoughts were quickly put on hold. Time enough to worry about them if the most likely culprit was cleared. So I went straight to the main filter capacitor, a 600µF 180V electro­lytic. The easiest way to check this is simply to clip another one across it. But hold on – not while the set is turned on. A large value discharged capacitor is, in effect, a short circuit and connecting it across a HT supply with another capacitor already in circuit will create an almighty splat. And the spikes such a splat can generate on the HT rail can produce some unpleasant surprises – like defunct ICs and transistors. And so I switched the set off, fished out an appropriate capacitor and patched it into circuit via a couple of clip leads. And that was it; when I switched the set back on, we had 110V on the HT rail, normal picture and normal sound. But while I considered the point proved, there was one surprise. When I pulled the old capacitor out, I put it on the capacitance tester. And according to that it was OK; it measured just a whisker under its rated 600µF. For a moment, I wondered whether So that clarified the diagnosis. But it was not quite the end of the job; there were some practical problems still to be solved. The test capacitor I had used was physically incompat­ible, as were all the others of suitable value which I had in stock. The closest would fit in the space OK but its leads did not match the mounting holes in the board. And considering the age of the set, finding an exact replacement would, at best, call for considerable time and effort; time which would cost money and inconvenience the customer. In these circumstances, I felt that a certain amount of improvisation would be justified. In fact, it wasn’t all that difficult. There was enough space around the mounting area, on the underside of the board, to permit drilling a couple of new mounting holes to suit the replacement capacitor. The copper pattern was cleaned around these and the new lugs soldered to them. It made a perfectly satisfactory job, with a minimum of delay. But there was a rather interesting aftermath. A couple of weeks after I had finished the job, I came across the faulty capacitor on the bench and I hooked it up to the capacitance meter again. And this time it read about 200µF. Later again, when I came to write these notes, I tested it again and it measured virtually zero. Well, it had taken a long time to completely die but it had finally given up the ghost. And good riddance. SC November 1994  35 Keep tabs on your car or boat with this UHF RADIO ALARM PAGER This UHF alarm pager is ideal for keeping tabs on a boat that’s moored near your home, or on a car parked in your driveway or in a nearby carpark. When triggered, it transmits a signal that activates a buzzer in a small receiver unit. By BRANCO JUSTIC Car and boat theft is a common problem but unfortunately conventional alarm systems are not always the complete answer. You don’t have to be too far away from the vehicle to be out of earshot and, of course, most people ignore alarms due to the high incidence of false triggering. That’s the main problem with conventional alarms. Despite the fact that the car (or boat) is not far away, it’s quite possible to miss the alarm if it goes off. This particularly applies if the car is parked in the street and you live at the back of a block of units, or 36  Silicon Chip if you visit an office block or shopping centre and the car is in an adjacent car­park. This unit overcomes that problem by paging you if it de­tects an intrusion, although any such incident should always be investigated with due discretion. It has a range of about 300 metres in open air and about 150 metres in a built-up area or if you are inside a building. Note that these figures were obtained with the transmitter placed on the dashboard of a car and will vary depending on the individual installation. As can be seen from the photos, the Alarm Pager consists of two separate units: (1) a PC board which carries the sensor/transmitter circuitry; and (2) a compact receiver unit built into a plastic case with a keypad. The transmitter board mounts inside the car (or boat) and is powered by the existing 12V supply. It’s designed to be au­tomatically armed when the ignition is switched off, which means that you cannot forget to switch the unit on. It has two sensor input channels and can be triggered using vibration detectors (ie, piezoelectric transducers), high or low-going alarm sensors (eg, reed switches), or a combination of both. The receiver circuit is built into a small plastic case which is fitted with a clip so that the unit can be worn on a belt. It is controlled by a keypad which has the following func­ tions: Off, On, Battery Test (Batt.), Test and Reset. This unit is powered from a 9V alkaline battery which should have a life of about 400 hours. When a valid paging signal is received from the transmit­ter, a buzzer inside the receiver briefly “beeps” every five seconds or so and continues until the receiver is manually reset (by pushing the Reset button). This internal buzzer also provides audible feedback when the other keys are pressed. For example, pressing the On key gives a short “beep”, while pressing the Off key gives a much longer “beep”. Pressing the Test key gives the paging sequence (ie, a brief beep every five seconds), while a continuous “beep” results if the Batt key is held down (provided of course that the battery is OK). By making some simple decisions during construction, you can customise the alarm pager to suit your requirements. One option is to use the unit with an existing alarm system, so that it is triggered by an existing sensor. It could even be switched on and off using the existing alarm’s remote control. However, for the purposes of this article, we’ll assume that you intend arming it via the ignition switch. Vibration sensor Ideally, we recommend that you trigger the unit using sen­sors mounted inside the front doors or adjacent to the door pillars. A vibration detector consists of a piezoelectric disc with a threaded rod and nut assembly soldered close to the rim – see photo. This arrangement provides excellent sensitivity to bumps and knocks but, since the resonant frequency is set to about 70Hz, avoids false triggering due to low-frequency vibra­tions (eg, from wind gusts). By using this arrangement, the unit pages you each time you get out of the car and shut the door (assuming that you are using the ignition to activate the unit). The resulting sequence of beeps from the receiver assures you that the unit is working correctly and is a useful test feature. Similarly, the unit will page you when you enter the car but will be disarmed as soon as the ignition is turned on. How it works: transmitter Fig.1 shows a block diagram of the alarm/transmitter cir­ cuit. It’s really several circuits all rolled into one. Starting at the left, the alarm in- ENABLE/ DISABLE (IGNITION SWITCH) ANTENNA SWITCHED MODE +15V TRANSMITTER +15V SUPPLY IC4, Q8 IC2 SENSOR INPUT 1 SENSOR INPUT 2 P1 ALARM INPUTS 8-SECOND MONOSTABLE Q1-Q3 IC1c IC1d Q7 PT VIBRATION SENSORS Fig.1: block diagram of the UHF Alarm Pager. When an input is detected, an 8-second monostable turns on Q7 via IC1d & starts a switched mode power supply (IC2). This in turn “fires” up the transmitter circuit (IC4 & Q8). puts can be triggered by the above­ mentioned vibration detectors or by some other sensor with a pulsed output (either positive or negative-going). When triggered, the input circuit (Q1-Q3) triggers an 8-second mono­ stable and Q7 turns on (via IC1d) for the duration of the mono­stable period. When Q7 turns on, a switched mode power supply (IC2) “fires up” and supplies power to the transmitter circuit (IC4 & Q8). As a result, the transmitter broadcasts a pulse-coded RF signal for eight seconds and this signal is picked by the receiver and processed to pulse the internal buzzer on and off. Fig.2 shows the complete circuit details for the alarm/transmitter. It uses two virtually identical input chan­nels, one for low-going sensors (Input 1) and one for high-going sensors (Input 2). The only real difference between the two channels is that Input 1 includes inverter stage IC1a to invert the low-going input • pulse. Associated with this is an extra clamping diode to protect the inverter inputs (pins 1 & 2) plus a 47kΩ pullup resistor. Let’s take a closer look at how this input operates. Normally, no signal is applied to the input and so pins 1 & 2 of IC1a are pulled high. Pin 3 of IC1a will thus be low and FET Q1 and transistors Q2 & Q3 will all be off. However, when a low-going pulse is applied to the input, pin 3 of IC1a switches high and forward biases D4. As a result, a voltage of about 0.6V appears across D4 and a sample of this is applied to the gate of FET Q1 via VR1. Alternatively, the signal for FET Q1 can come from piezo transducer P1. When this vibrates (eg, when a door closes), it generates an AC output voltage. This voltage is clipped to about 0.6V p-p by back-to-back diodes D4 & D5 and applied to the gate of Q1 via VR1 as before. Features Function: detects intrusion into parked vehicles, moored boats or a building and transmits a paging signal to a receiver. • Range: approximately 300 metres in open air, reliable 150-metre range in normal building locations. Note: these figures were obtained with the transmitter placed on top of a plastic car dashboard. • Transmitter power supply: 9-14V DC operation from a car bat­tery, a plugpack supply or from a battery pack (eg, about 800 hours from eight series C-size alkaline batteries). Current consump­tion is 3.5mA quiescent or 50mA during transmission. • Receiver power supply: 9V battery (about 100 hours from a zinc-carbon battery or 400 hours from an alkaline type). Current consumption negligible when “off” or about 2.5mA when “on”. • Battery test: battery checks as OK if above 5.4V. During this test, the battery is continuously loaded by the buzzer. November 1994  37 38  Silicon Chip R11 10k D8 1N914 D2 1N914 R1 10k D1 1N914 ZD1 15V 1 2 7 R12 10k P2 PIEZO TRANSDUCER D9 1N914 OUT C13 .0033 D10 D5 D3 1N914 R3 10k +8V GND IC1a 4093 14 3 P1 PIEZO TRANSDUCER R2 47k C12 470 16VW IN IC3 7808 D11 2x1N914 D4 2x1N914 C14 10 VR2 1M VR1 1M C9 0.47 R30 220  5 C4 10 C3 680pF C2 10 C1 680pF +8V C7 100 UHF ALARM PAGER-TRANSMITTER SENSOR INPUT 2 SENSOR INPUT 1 GND FROM BATTERY +12V R31 D20 1N4007 22  1W G G 6 R14 680k R13 39k S D S Q4 2N5484 D12 1N914 D6 1N914 Q1 2N5484 C8 .0015 2.2k R28 D R4 39k 2 R5 680k 4 7 R27 470  IC2 MC34063 R26 1 3 8 1 E C11 0.47 R9 22k R10 100k R35 10k 13 R34 10k 12 R33 10k 11 R32 10k 10 R17 100k R16 2.2k R15 470  R8 100k C E B Q5 BC558 R18 22k E Q6 BC548 C R19 100k D13 1N914 E Q2 D7 BC558 1N914 C Q3 R7 BC548 C 2.2k B B R6 470  C10 100 D19 SR103 L1 +15V 5 6 A12 15 16 17 R36 1M 4 E R20 100k D14 1N914 I GO +8V IC1b R25 1k B 12 13 C5 11 10 D18 1N914 D15 1N914 C G S D VIEWED FROM BELOW C E BC--B R24 10k ICId C E B A 10 +8V C18 6.8pF C16 4.7pF 2SC3355 8 9 Q8 2SC3355 VC1 2-7pF R22 1M E C R21 10k R40 82  B * L2 *ETCHED ON PC BOARD C6 100 IC1c D16 1N914 C15 .001 C17 .001 * ANTENNA D17 1N914 R39 2.2k R37 6.8k D47 1N4148 LED1  K ENABLE/DISABLE VIA IGNITION SWITCH 9 IC4 AX5026 A11 A10 A9 18 A R38 120  K Q7 2N2219 R23 1k B R29 10  304MHz SAW FILTER E C The FET amplifier stage (Q1) is normally biased at close to its cutoff point due to the high value of source resistance used (R5 = 680kΩ). Similarly, transistor Q2 is normally biased off by R4 and so Q2’s collector normally sits at 0V. However, when a sensor is triggered (or vibrations are detected), Q1 conducts and charges capacitor C2. While C2 charg­es, sufficient base current flows to turn Q2 on and this, in turn, switches Q3 on and pulls pin 6 of IC1b low via D7 (note: pin 6 of IC1b is normally held high via R10). Q2 then switches off again as soon as C2 is charged, since the voltage across R4 is now too low to provide sufficient forward bias. IC1c and its associated parts form the 8-second mono­stable. Normally, pins 12 & 13 of IC1c are held low via R20 and so both sides of C5 are high, pin 10 of IC1d is low and Q7 is off. However, when pin 6 of IC1b goes low, its output at pin 4 switches high and pulls pins 12 & 13 of IC1c high via D14 Pin 11 of IC1c now switches low and so the positive side of C5 also goes low. Pin 10 of IC1d thus switches high and this turns on Q7 and the transmitter (by switching on its power sup­ply), as described previously. At the same time, D15 latches pins 12 & 13 of IC1c high to ensure the correct monostable timing period. C5 now charges via R22 and R21 and, after about eight sec­onds, pulls the inputs of IC1d high again. Pin 10 of IC1d thus switches low again and Q7 turns off. At the same time, the high on pins 12 & 13 of IC1c is released and so the monostable is ready for a new timing cycle. Note that when pin 10 of IC1d switches high (to turn on Q7), C6 charges via R24 and D18 and the voltage across C2 is pulled high via D6. Similarly, the voltage across C4 Fig.2 (left): this diagram shows the complete circuit details for the alarm/ transmitter. It uses two virtually identical input chan­nels, one for low-going sensors (Input 1) and one for high-going sensors (Input 2). When triggered, Q7 turns on & the transmitter section (IC4 & Q8) broadcasts a coded RF signal, as set by address lines A9-A12. The pre-built UHF front-end module in the receiver must be installed with its component side towards the AX528 decoder IC, as shown here. Sockets were used to mount the ICs in the prototype but these can be considered optional. in the other channel is held high via D12. This effectively disables the two input channels during the 8-second monostable period and for some time afterwards since FETs Q1 & Q2 are biased off. When pin 10 of IC1d switches low, it takes about 30 seconds for C6 to discharge via R5 & R14. This means that the 8-second monostable can only be retriggered some 30 seconds after the previous cycle has ended. This prevents false triggering at the end of the monostable period. The other sensor input channel accepts signals from sensor 2 and/or piezo transducer P2. As mentioned previously, it works in virtually identical fashion. When triggered, Q6 pulls pin 5 of IC1b low and so pin 4 swit­ ches high and triggers the 8-second monostable as before. IC2 and its associated parts forms the switched mode power supply. This is enabled whenever Q7 is on (ie, during the 8-second monostable period) and supplies power to the transmitter circuit. IC2 is an MC34063A DC-DC converter IC and is wired here in standard step-up configuration. It accepts an 8V input from 3-terminal regulator IC3 and steps this up to provide an output of 15V across C10. R28 & R30 set the output voltage, while C8 sets the frequency of the internal switching oscillator. This arrangement is used to provide a stable +15V supply rail for the transmitter. It ensures frequency stability with varying input supply voltages and also ensures that the transmit­ter board can be used with supply voltages from 10-14V. Transmitter circuit The transmitter circuit is based on an AX-5026 trinary encoder IC. When power is applied, this IC generates a sequence of pulses at its output (pin 17). The rate at which these pulses are generated is set by a 1MΩ timing resistor (R36), while the code sequence is set by resistors R32-R35. These resistors pull the A9-A12 address lines low, while the remaining address lines are left open circuit. The coded output from IC1 appears at pin 17 and drives RF transistor Q8. This transistor is connected as a Hartley oscilla­tor operating at 304MHz, as set by a tank circuit consisting of L2 (etched on the PC board), VC1, C16 and C18. In addition, a SAW resonator is used to provide a narrow-band feedback path. Its lowest impedance is at its resonant frequency of 304MHz and thus the tuned collector load must be set to this frequency in order for Q8 to oscillate. The SAW resonator ensures frequency stability and makes the transmitter easy to align. It ensures that the oscillator will only start and pulse LED 1 when the tuned circuit is virtually dead on frequency. November 1994  39 ON S5 7 IC3d K BATTERY TEST S3 R15 27k K  R8 47k D1 1N914 R7 470k 11 C3 22 8 10 1,3,6,8 10,11,12 UHF ALARM PAGER-RECEIVER TEST E S1 A12 12 A11 A10 A9 11 10 9 R4 4.7k 2 Q1 BC548 C B UHF RECEIVER MODULE 2 7 5 R2 1M 16 13 IC1 AX5028 17 R3 10k C1 0.47 18 14 15 R1 220  1 11 RESET S2 13 IC3b 12 9 11 4 3 CONNECTION NUMBERS ON SWITCHES REFER TO KEYPAD HEADER SOCKET LED2 R11 4.7k A BUZZER 7 R10 14 4.7k 10 IC2d 4093 9 IC3a 4093 8 R6 4.7k R5 4.7k IC2c IC2a 1 Fig.3: the coded signal from the transmitter is processed by the UHF front-end module & decoded by IC1. When a valid signal is received, Q1 turns on & oscillator stage IC2a drives Q2, the buzzer & LED 2 to deliver the paging signal. C E 7 R14 10k R13 10k A Q2 BC558 E LED1  R12 B 22k K E C Q3 B BC558 C R9 10k C4 0.47 C2 22 13 6 12 5 2 IC2b 4093 ANTENNA 40  Silicon Chip VIEWED FROM BELOW B D5 1N914 D4 1N914 D3 1N914 D2 1N914 +9V R17 1k R16 1k A C5 22 C6 100 4 IC3c 4093 3 How it works – receiver 6 12 0FF S4 5 2 1 14 R18 4.7k R19 4.7k 4 B1 9V VC1 is used to adjust the centre frequency of the tuned circuit. This point corresponds to maximum current consumption and is found by adjusting VC1 to obtain peak brightness from the LED 1. Fig.3 shows the circuit details of the receiver. This is based on a factory-built “front-end” module that’s accurately aligned to the transmitter frequency (304MHz). It uses surface mount components to give a compact assembly and is fitted with a pin connector along one edge so that it can be plugged into a PC board. In operation, the front-end module picks up the coded RF pulses from the transmitter via a short antenna. The received signal is then processed via an internal bandpass filter, an RF preamplifier, a regenerative detector, an amplifier and a Schmitt trigger. When a valid signal is received, a digital pulse train appears at pin 5 and this is fed to pin 14 of IC1. IC1 is an AX-528 Tristate decoder and is used to decode the signal generated by the transmitter. As with the AX-5026 encoder, this device has 12 address lines (A1-A12) and these are connected to match the transmitter code (ie, pins 10-13 are all pulled low). If the code sequence on pin 14 of IC1 matches its address lines, the valid transmission output at pin 17 switches high and turns on transistor Q1. This in turn triggers an S-R flipflop based on gates IC3a & IC3b. Normally, the flipflop is in the reset state and so pin 10 of IC3a is low. However, when Q1 turns on, pin 8 of IC3a is pulled low and so pin 10 goes high. This high enables a Schmitt trigger oscillator stage based on IC2d. Its timing capacitor (C3) is charged via R7 each time pin 10 goes high and discharges via D1 and R8 when pin 10 goes low. This arrangement means that IC2d operates with a duty cycle of about 10:1. As a result, a pulse train that’s high for about five seconds and low for 0.5 seconds appears at pin 10 of IC2d. This pulse train is applied to the base of PNP transistor Q2 and this in turn drives the buzzer (B1) to produce a brief sound every five seconds. It also flashes LED 2 which is wired in parallel with the buzzer. Test switch S1 bypasses transistor Q1 and is used to check that the buzzer circuit is working correctly. Once the buzzer is activated, the circuit can only be reset by pressing S2. This pulls pin 13 of IC3b low and resets the S-R flipflop. The receiver circuit is turned on and off by switching power to the UHF front-end module and to decoder IC1. This is done by pressing switches S4 & S5 and these in turn toggle a second S-R flipflop based on IC3c & IC3d. When S5 (ON) is pressed, pin 6 of IC3d is pulled low and the output at pin 4 goes high and pulls pin 2 of IC3c high. Pin 3 of IC3c thus switches low and this low is inverted by parallelled inverter stages IC2a-IC2c to supply power to the UHF front-end module and to IC1. INPUT 1 ENABLEDISABLE 10uF 22k D13 100k 470  D12 2.2k 100k 39k 82  IC4 AX5026 1M Q6 Q5 1 10k .0033 100uF .001 2.2k D47 6.8k A K 120 10k D18 Q8 SAW LED1 10k D19 D6 .001 4.7pF 1 .0015 0.47 10k 2.2k 22k D7 100k 680pF 100k Q2 Q4 10k 470uF IC3 7808 D20 +12V 22  1W GND 10k D8 D9 470  39k 680 k 10uF 680k D4 D5 D11 D10 VR2 Q3 6.8pF 100uF 10k 10W 1k 1k 1M 680pF 10uF INPUT 2 D16 D17 10k D15 IC2 34063 VR1 P2 220  1 470  L1 2.2k 1 Q1 P1 VC1 Q7 D14 IC1 4093 10k 47k D2 D1 10k D3 0.47 10uF 100k ZD1 Fig.4: install the parts on the transmitter PC board as shown here, taking care to keep all component leads in the UHF transmitter section (around IC4 & Q8) as short as possible. The enable/disable input is wired to the ignition switch. Pressing S4 (OFF) has the opposite effect. This pulls pin 1 of IC3c low and so the output at pin 3 goes high. The outputs of inverters IC2a-IC2c thus switch low and remove power from the front end of the circuit. The remainder of the circuit draws negligible current in the quiescent state and so is permanently powered from the 9V battery. The RC timing circuits connected to the outputs of IC3c & IC3d set the on and off indication periods. When S5 (ON) is pressed, pin 3 of IC3c goes low and this takes the negative side of C5 low. C5 now immediately begins charging via LED 1, the base-emitter junction of Q3, R13, D3 & R16. As a result, Q3 turns on while C5 charges and briefly flashes LEDs 1 & 2 and sounds the buzzer. A similar sequence of events occurs when S4 is pressed except that this time C6 charges via R14, D5 & R17. Diodes D2 & D4 ensure that the positive sides of C5 & C6 can not rise more than 0.6V above the positive supply rail. Finally, the circuit includes a battery test feature based on S3, R12 & R15. Because of the values chosen for R12 & R15, Q3 will only be biased on when S3 is pressed if the battery voltage is greater than about 5.5V. This means TABLE 1: RESISTOR COLOUR CODES (TRANSMITTER BOARD) ❏ No. ❏   2 ❏   2 ❏   5 ❏   1 ❏   2 ❏   2 ❏ 10 ❏   1 ❏   3 ❏   3 ❏   3 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 ❏   1 Value 1MΩ 680kΩ 100kΩ 47kΩ 39kΩ 22kΩ 10kΩ 6.8kΩ 2.2kΩ 1kΩ 470Ω 220Ω 120Ω 82Ω 10Ω 1Ω 22Ω 4-Band Code (1%) brown black green brown blue grey yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red red orange brown brown black orange brown blue grey red brown red red red brown brown black red brown yellow violet brown brown red red brown brown brown red brown brown grey red black brown brown black black brown brown black gold gold red red black brown 5-Band Code (1%) brown black black yellow brown blue grey black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red red black red brown brown black black red brown blue grey black brown brown red red black brown brown brown black black brown brown yellow violet black black brown red red black black brown brown red black black brown grey red black gold brown brown black black gold brown brown black black silver brown red red black gold brown November 1994  41 No particular order need be followed for the transmitter board assembly but make sure RECEIVER 0.47 that all polarised parts are cor­ FRONT END 1 rectly oriented. In addition, 22uF 220  be sure to keep all component 1M leads as short as possible in the Q1 1 transmitter circuit (top right­ 0.47 IC1 AX528 hand corner of the board). 1 Note that the flat side of trimmer capacitor VC1 should go 4.7k LED1 towards Q8. The SAW resonator K A Q2 Q3 IC3 should be mounted flat against 470k 4093 47k the board, while transistor Q8 K A 1100uF 22uF D1 should only stand about 1mm LED2 22UF proud of the board. Be careful BUZZER with the orientation of the LED – its anode lead is the longer D2 D4 of the two. It can be mounted close to the PC board since it is 27k only used during the setting-up 10k procedure. 10k The large inductor (L1) is KEYPAD SOCKET B1 supplied pre-wound and can 1 be left until last. Clean and Fig.5: this is the layout for the receiver tin the ends of its leads with PC board. Note that pins 10-13 must be solder before mounting it on connected to the 0V rail via short wire the board. When this is done, links to match the address code in the check the board carefully to transmitter (see text). ensure that the assembly is correct – it only takes one wrong that the buzzer will sound and the component value to upset the circuit two LEDs will light only if the battery operation. is OK. The receiver board is equally straightforward to assemble but again Construction keep all leads as short as possible. Fig.4 shows the wiring details for Install the parts exactly as shown in the transmitter board, while Fig.5 Fig.5, leaving the receiver module till last. This component must be installed shows the receiver layout. 4.7k 22k D3 D5 1k 1k 4.7k 4.7k 4.7k 10k 4.7k IC2 4093 10k 4.7k 250mm ANTENNA The completed receiver can be fitted with a clip so that it can be worn on a belt. Note that the keys on the keypad must be labelled exactly as shown here; ie, key 1 = Reset, key 3 = Test, key 5 = Battery Test, key 7 = Off & key 9 = On. with its component side towards the 1MΩ resistor. The 13-pin keyboard connector is mounted at the other end of the board – see photo. It’s optional as to whether the two LEDs are hidden inside the case (in which case there will be no visible paging or on/off indication) or mount­ed on the end of the case near the keypad. If you elect to hide them inside the case, they can be mounted directly on the The keypad is connected into circuit by plugging it into a keypad socket at one end of the receiver PC board. Take care to ensure that the buzzer is oriented correctly & don’t forget to fit a 250mm-long antenna to the designated pad near the front-end module. 42  Silicon Chip PC board and all indication will be via the buzzer. On the other hand, you might wish to have a silent pager, with indication via the LEDs only (just leave the buzzer out). The antenna consists of a length of insulated hook-up wire about 250mm long. This is soldered to a pad which connects to pin 2 of the front end module. The A9-A12 address line of AX528 decoder IC must now be tied low to match the address programmed into the AX5026 encoder in the transmitter. This simply involves connecting pins 10-13 to the adjacent earth track that runs along the outside edge of these pins. Note: if you wish, you can alter the coding in both the transmitter and the receiver by tying selected address pins high or low or leaving them open circuit. That way you can have your own unique code, although it is not really necessary for this project. For example, you might tie A9 high, leave A10 open circuit, and tie A11 & A12 low. Short wire links can be used to make these connections in the receiver but note that you will have to scrape away the solder mask from the adjacent rails at each connection point so that the track can be soldered (the positive rail runs adjacent to the inside edge of the address pins in the receiver). What ever you do, make sure that the transmitter code exactly matches the receiver code otherwise the remote control won’t work. Once completed, the receiver board can be installed in the bottom of the case and secured to the integral standoffs using a couple of self-tapping screws. This done, plug the keypad into its connector and secure it by A piezo disc is turned into a vibration detector by soldering a threaded rod & nut assembly (made of brass) close to its rim to give a resonant frequency of about 70Hz. The opposite edge of the disc is then soldered to a piece of scrap PCB material as shown here. The wiring connection should be run using shielded cable (centre conductor to the centre of the piezo disc, shield to the PC board). peeling away its backing paper and carefully affixing it to the top of the case. The keys on the keypad should be labelled exactly as shown in the photograph; ie, key 1 = Reset, key 3 = Test, key 5 = Battery Test, key 7 = off and key 9 = on. Test & alignment To test the receiver, connect a 9V battery and carry out the following checks: (1). Press Test and check that the buzzer beeps and LED 2 flashes every five seconds or so. Check that the circuit can be reset by pressing Reset. (2). Press On and check that the buzzer briefly sounds and that both LEDs briefly light. If so, press Off and check that the buzzer sounds and both LEDs light for about three seconds. (3). Press Batt and check that the buzzer sounds and that both LEDs light for as long as the key is held down. If all these checks are OK, then most of the receiver cir­cuit is working correctly and the case assembly can be completed. Before doing this, however, a small channel must be filed in the end of the case adjacent to the battery compartment to serve as an exit point for the antenna. The case can then be clipped together and secured using two self-tapping screws at the battery compartment end. We now come to the transmitter TABLE 2: RESISTOR COLOUR CODES (RECEIVER BOARD) ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 4 7 2 1 Value 1MΩ 470kΩ 47kΩ 27kΩ 10kΩ 4.7kΩ 1kΩ 220Ω 4-Band Code (1%) brown black green brown yellow violet yellow brown yellow violet orange brown red violet orange brown brown black orange brown yellow violet red brown brown black red brown red red brown brown 5-Band Code (1%) brown black black yellow brown yellow violet black orange brown yellow violet black red brown red violet black red brown brown black black red brown yellow violet black brown brown brown black black brown brown red red black black brown November 1994  43 PARTS LIST Transmitter Board 1 PC board, code OE93/ PAGERTX 1 304MHz SAW filter 1 prewound inductor (L1) 2 piezo discs 2 1MΩ trimpots Semiconductors 1 4093 quad Schmitt NAND gate (IC1) 1 MC34063 switched mode supply IC (IC2) 1 7808 3-terminal regulator (IC3) 1 AX-5026 trinary encoder (IC4) 2 2N5484 FETs (Q1,Q2) 2 BC558 PNP transistors (Q2,Q3) 2 BC548 NPN transistors (Q3,Q4) 1 2N2219 NPN transistor (Q7) 1 2SC3355 NPN RF transistor (Q8) 1 15V 1W zener diode (ZD1) 1 SR103 Shottky power diode (D19) 1 1N4007 power diode (D20) 19 1N4148 or 1N914 signal diodes (D1-D18, D47) 1 red LED (LED1) Capacitors 1 470µF 16V electrolytic 3 100µF 16V electrolytic 4 10µF 16V electrolytic 2 0.47µF monolithic 1 .0033µF ceramic (3n3) 1 .0015µF ceramic (1n5) 2 .001µF ceramic (1n) 2 680pF ceramic 1 6.8pF ceramic 1 4.7pF ceramic 1 2.7pF trimmer capacitor (VC1) Resistors (0.25W, 5%) 2 1MΩ 2 1kΩ 2 680kΩ 3 470Ω 5 100kΩ 1 220Ω 1 47kΩ 1 120Ω 2 39kΩ 1 82Ω 2 22kΩ 1 10Ω 10 10kΩ 1 1Ω 1 6.8kΩ 1 22Ω 1W 4 2.2kΩ Receiver 1 PC board, code OE/93/PAGER 1 case with battery compartment 1 keypad 1 PC-mounting keypad socket 1 304MHz front-end module 1 9V buzzer Semiconductors 1 AX-528 Tristate decoder (IC1) 2 4093 quad Schmitt NAND gates (IC2,IC3) 5 1N4148 signal diodes (D1-D5) 2 red LEDs (LED1, LED2) 1 BC548 transistor (Q1) 2 BC558 transistors (Q2,Q3) Capacitors 1 100µF 16V electrolytic 3 22µF 16V electrolytic 2 0.47µF monolithic Resistors (0.25W 5%) 1 1MΩ 4 10kΩ 1 470kΩ 7 4.7kΩ 1 47kΩ 2 1kΩ 1 27kΩ 1 220Ω Where To Buy The Parts A kit of parts for the UHF Alarm Pager is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Prices are as follows: Transmitter (includes PC board plus on-board components): $49.00. Receiver (includes PC board, on-board components, case & keypad): $52.00. Please add $4 for postage with each order. Note: copyright © of the PC boards associated with this project is retained by Oatley Electronics. alignment. To do this, temporarily solder a link between the collector and emitter of Q7 and apply power (12V to +12V & GND). This will start the switch­mode supply based on IC2 44  Silicon Chip and “fire up” the transmitter for as long as the link is in place. All you have to do now is adjust VC1 using a plastic tool until LED 1 begins to flash. When this happens, the oscillator is working and you can tweak VC1 for maximum transmitter output (ie, maximum LED brightness). Finally, the completed transmitter board can be tested by removing the link across Q7, then re-applying power and pull­ing sensor input 1 low (ie, by connecting the input to ground). When you do this, the transmitter LED should flash for about three seconds. If the receiver is on, it should immediately begin paging you (ie, you should hear a brief beep every five seconds). Sensor input 2 can be checked in a similar manner by con­necting it to the positive supply rail. Just remember that after each transmission, you will have to wait at least 30 seconds before the transmitter can be reactivated (this is the time it takes for C6 to discharge, as described earlier). In fact, it’s best to wait for about 60 seconds after the transmitter LED goes out before attempting to retrigger the unit. Installation Finding a convenient location to mount the module is prob­ably the greatest challenge in installing the unit. On top of the rear parcel shelf is probably the best location in a car, with power derived from the supply to the boot lamp. The enable/dis­able input should be connected to the switched side of the igni­tion switch and this will involve running a lead back to the front of the vehicle (eg, you can tap into a suitable point in the fusebox). If you elect to switch the unit using a UHF remote control (eg, as part of an existing alarm), just remember that pulling the enable/disable input high (ie, to +8V) disarms the circuit. The vibration detectors can be installed inside small plastic cases and these can be mounted next to the door pillars. Finally, note that this unit can be easily adapted for use as a 12-channel paging system and that is why provision has been made on the transmitter board for diodes D21-D42 (bottom right­ hand corner). When combined with suitable switches, these diodes change the coding of the transmitter and you can build individual receivers with unique matching codes. Full details on how to convert the unit to a 12-channel pager will be supplied with a kit from Oatley Electronics and this kit will also include SC the extra diodes (D21-D42). 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 80 metre DSB amateur g Ri If you are studying for your novice licence, you will want to get on the air as cheaply & easily as possible. This little 80-metre transceiver is the way to do it. It uses no integrated circuits & all the parts are cheap & readily available. By LEON WILLIAMS, VK2DOB There’s a certain fascination and challenge in extracting the most performance from the least number of components and this project is the outcome of a desire to do just that. The 3.5MHz to 3.7MHz, or 80-metre Amateur band, is ideal for the experimenter. The relatively low frequencies allow the use of semiconductors generally meant for audio applications. As well, construction techniques are not as critical as for VHF or UHF circuits. At night, signals can be quite strong and therefore receiv­ers do not need November 1994  53 54  Silicon Chip 100pF 220pF 470  Q1 470  E .001 0.1 Q7 BC549 B MIC GAIN VR2 500  2.2M 10k .0056 .012 10k 10 16VW 150  220  B Q8 BC549 E .01 Q2 BC337 C B 1 E 16VW C 100  10 16VW 1M 0.1 .01 .01 D2 1N4148 CARRIER 6T NULL VR1 200  56  T1 D1 1N4148 470  +RX .022 220W 16VW 1 1M 100 16VW 1k B 4.7k 4T VOLUME 10 16VW E C 6T Q6 BC549 4T T2 100  1 Q9 BC549 C 16VW B VR3 E 50k LOG 5.6k 0.1 56  0.1 80 METRE DSB TRANSCEIVER 10 16VW 100pF Q1 BC549 C 68k B OPTIONAL OSCILLATOR 330pF 100pF 330pF 33k F1 3.58MHz ZD1 15V 1W MICROPHONE TUNE VR4 20k LIN 0.1 100 F1 3.58MHz 10k 0.1 56  470  E Q10 BC549 C B 5.6k 100  0.1 220  1k 0.1 0.1 0.1 22  10  D5 68pF 10 16VW D6 1N4148 +TX E L1 6T D4 PLASTIC SIDE 4.7k B 470 25VW E 2. 2W 330  0.5W E C C L4 2.2uH 100pF Q5 BD139 0.1 0.1 C B E E TX RX 560pF L2 2.2uH 220pF 820pF 13.8V +V 820pF L3 2.2uH 100pF B C HEADPHONES S1 VIEWED FROM BELOW B C +RX 560pF 100 E 16VW C Q12 BC549 220  E 1k B Q11 BC337 820pF 2. 2  E B Q4 BD139 C B 2x1N4148 0.1 Q3 D3 BD139 C 1N4004 B 6T T3 820  0.5W 10  +TX +V ANTENNA to be extremely sensitive and it is possible to work long distances (DX) with low power. From my location near Canberra I have easily worked New Zealand with just a few watts of output power when conditions were favourable. This transceiver is about as simple as can be. The trans­mitter and receiver share a balanced mixer; in transmit mode it operates as a balanced modulator and in receive mode as a product detector. The carrier oscillator is also common to both transmit and receive modes and for simplicity, can be crystal controlled. Also delightfully simple is the method of using a ceramic resona­tor to form a simple variable oscillator. The main feature of this transceiver is the use of cheap and common components. Other features include a power output of about 1.5 watts PEP and easy single PC board construction. There are no expensive and hard to get integrated circuits and no difficult alignment procedures to undertake. The transmis­sions are Double Side­ band or DSB. This means that the carrier is nulled out and only the two sidebands (upper and lower) are transmitted. This is much more efficient than conventional AM (amplitude modulation) because there is no RF output when there is no modulation. This means the output stage is not wasting power and heating up while you are not talking. While single sideband (SSB) is the most used mode on the Amateur bands, an SSB transceiver is a lot more complex than a DSB type. In any case, a DSB signal is compatible with an SSB receiver and has the advantage that the receiving station can choose either USB or LSB mode. The receiver is a direct conver­sion type where the incoming signal is mixed directly with the carrier frequency to produce an Fig.1 (left): this transceiver is about as simple as can be. The trans­mitter and receiver share a balanced mixer (T1); in transmit mode it operates as a balanced modulator and in receive mode as a product detector. The carrier oscillator is also common to both transmit and receive modes and, as an option, it can be crystal controlled. PARTS LIST 1 PC board, code 06110941, 143 x 71mm 1 Jiffy box, 196 x 112 x 60mm 1 black binding post 1 red binding post 1 3.58MHz ceramic resonator (F1) 1 SPDT toggle switch (S1) 1 4-pin microphone panel socket 1 square mount S0239 panel socket 1 6.5mm stereo jack socket 1 200Ω horizontal trimpot (VR1) 1 500Ω horizontal trimpot (VR2) 1 50kΩ log potentiometer (VR3) 1 20kΩ linear potentiometer (VR4) 2 knobs 15 PC stakes 4 F14 balun formers (L1,T1,T2,T3) 3 2.2µH RF inductors (L2,L3,L4) Semiconductors 7 BC549 NPN transistors (Q1,Q6-Q10,Q12) 2 BC337 NPN transistors (Q2,Q11) 3 BD139 NPN transistors (Q3-Q5) 5 1N4148 diodes (D1,D2,D4,D5,D6) 1 1N4004 diode (D3) 1 15V 1W zener diode (ZD1) Capacitors 1 470µF 25VW electrolytic audio signal. Once again, an SSB signal is compatible, the only disadvantage being that there is equal response to both the lower and upper sidebands. Now let’s have a look at the circuit diagram of Fig.1. Carrier oscillator The carrier oscillator is formed around Q1. It is config­ured as a Colpitts oscillator with feedback provided by the capacitors connected to the base and emitter. The oscillator frequency is set by F1, a 3.58MHz ceramic resonator. This is used in preference to a crystal because it can be pulled in frequency quite easily by altering the circuit capacitance around it. This is achieved by using a variable capacitance diode, which is in fact a 15V 1W zener diode, ZD1. These are cheaper and easier to get than a dedicated Varicap. A variable resistor and a 10kΩ series resistor provide a means of varying the frequency. 3 100µF 16VW electrolytic 5 10µF 16VW electrolytic 3 1µF 16VW electrolytic 13 0.1µF monolithic 1 .022µF MKT polyester or greencap 1 .012µF greencap 3 .01µF ceramic 1 .0056µF greencap 1 .001µF ceramic 3 820pF ceramic 2 560pF ceramic 1 330pF ceramic 1 220pF ceramic 4 100pF ceramic 1 68pF ceramic Resistors (0.25W, 1%) 1 2.2MΩ 3 470Ω 2 1MΩ 1 330Ω 0.5W 5% 1 68kΩ 4 220Ω 1 33kΩ 1 150Ω 3 10kΩ 3 100Ω 2 5.6kΩ 3 56Ω 2 4.7kΩ 1 22Ω 3 1kΩ 2 10Ω 1 820Ω 0.5W 5% 2 2.2Ω Miscellaneous Screws, nuts, spacers, medium-duty hook-up wire, shielded cable, scrap aluminium. A 0.1µF capacitor is included as protection against noise on the supply rail modulating the oscillator. The prototype tuned from 3.568MHz to 3.583MHz and while this is not a big range, it allows greater flexibility than when a crystal is used. Note that the oscillator does not have any voltage regulation and it is important to use a regulated power supply to stop the oscillator changing frequency while transmitting. The small value capacitors around the oscillator are speci­fied as ceramics in the parts list. This was satisfactory in the prototype, however if excessive frequency drift is experienced, polystyrene capacitors may need to be substituted. Q2 operates as a buffer stage and provides a low impedance drive for the balanced mixer. As an alternative to a ceramic resonator, a 3.579MHz crys­tal can be used for the oscillator, to give fixed November 1994  55  10uF  470   100pF Q11 560pF 560pF   820pF  0.1   100uF 10uF 330  0.1 ANTENNA SOCKET 220pF L2 10  820   1k Q10 10uF   470uF 820pF 100pF   L3  Q9 2. 2  2. 2   L1 1k 220  4.7k 100  D6 1uF 1uF D4 13.8V B C E 0.1 L4 220  470  10uF 220    0.01  0.1 D5  .001 VR2  68pF 100  0.1 Q9 10 22 820PF 1uF 2 B C E 220   .022 0.1 1 0.1 100uF  Q5  Q3 5.6k   0.1 Q4 T3 4.7k .012   D3 0.1 1k  .01 100  .0056 Q8 Q6 T1 1M 10k 10k  Q7    2.2M 0.1 100pF  D1 5.6k 10uF  D2 .01 150  470  10k  Q2 100pF ZD1 0.1 Q1 VR1  0.1  1M F1   56   330pF T2 56W 56W 68k 33k 0.1 100uF   CONNECTIONS MADE TO GROUND PLANE 1 HEADPHONES 2 S1 MICROPHONE VR3 VR4 frequency operation. This alternative is shown on the circuit diagram of Fig.1. Microphone input Transistor Q7 is the microphone amplifier and its gain is variable by adjusting the emitter degeneration with potentiometer VR2. The circuit should provide enough gain for most microphones, however low output microphones may need an extra external ampli­fier. A .001µF capacitor is wired across the input of the ampli­fier to filter out any RF that may make its way in via the micro­phone lead. Q8 performs the dual role of buffer stage and low pass filter. The buffer stage provides a high impedance load to Q7 and provides a low output impedance drive for the balanced modulator. The low pass filter has a cutoff frequency of about 2kHz. A 56  Silicon Chip DSB transmitter occupies twice the bandwidth of an SSB signal and we must limit the audio response to avoid interference to adjacent stations. Balanced modulator The balanced modulator components are transformer T1, two 1N4148 diodes (D1 & D2) and a 200Ω trimpot (VR1). T1 is a trifilar wound transformer, where three lengths of wire are twisted to­gether and wound on a former as one. This provides close coupling between the windings and also aids in the balance or nulling of the carrier. Let’s look at how it works in transmit mode, firstly with no audio input from the microphone amplifier stages. The high level RF from Q2 causes current to flow in the secondary winding of T1. A .01µF capacitor effectively grounds the centre of the winding to RF. Due Fig.2: this component overlay diagram shows all the components which must have their leads soldered to the top & bottom of the PC board; all the relevant component leads are marked with a black star dot. to the phasing of the windings (shown by dots on the circuit), the two diodes conduct during the negative half of the RF cycle. Thus, equal currents will flow through the diodes and the resulting voltage at the wiper of VR1 will be zero. In the next (positive) half cycle, the diodes will be turned off and again no voltage will appear at the wiper of VR1. When an audio signal appears at the centre of the winding, depending on the instantaneous voltages, one of the diodes will conduct more than the other. The result is that the modulator is unbalanced and a vol­tage will appear at the wiper of VR1. This voltage follows the envelope of the original audio signal and is a suppressed carrier double sideband (DSB) signal. A 56Ω resistor provides a broadband resistive termination. Ideally D1 and D2 should be a matched pair, however we can get good results by adjusting VR1 to obtain the deepest carrier null (we’ll talk more about this aspect later). The output of the balanced modulator is coupled by trans­former T2 to the RF driver stage Q3. It is biased in class A, with a collector current of 50mA. The collector load for Q3 is transformer T3 with the secondary winding driving the output stage Q4 and Q5 which are two BD139 transistors in parallel except for their separate emitter resistors. These resistors stabilise the AC and DC gain, ensure that the current is shared more or less equally between the two transistors and prevent thermal runaway. The transistors are biased in class AB which means that the transistors are just conducting when there is no input signal. D3 and an 820Ω resistor provide a stabilised base voltage and the final stage draws 30mA under no-signal conditions (ie, with no speech into the microphone). L1 is the collector load and the output signal is fed from it through a low-pass filter before connection to the antenna. The 330Ω resistor in parallel with the collector coil is included to suppress a spurious signal that was noticed during develop­ ment. It is important that the low-pass filter is used because quite large harmonics can be produced in the RF amplifier. The filter is basically a double Pi filter with notch frequencies at 7MHz, set by L2 and a 220pF capacitor, and 10MHz, set by L3 and a 100pF capacitor. When the output signal was viewed on a spectrum analyser, all harmonics were at least 45dB below the signal fundamental. Receive circuit The signals from the antenna flow through the just men­tioned low-pass filter and this helps attenuate strong out-of-band signals. The signal then passes through a bandpass filter form­ ed by L4 and an 820pF capacitor. A 100pF and a 68pF capacitor match this bandpass filter to the impedances of the low-pass filter and receive preamplifier. Diodes D4 and D5 protect tran­ sistor Q6 from damage during transmit mode. Transistor Q6 is the receive preamplifier. The collector load of Q6 is one winding of transformer T2 and the output is coupled to the product detector via the 4-turn winding (of T2) All of the circuitry is on a double-sided PC board with a ground plane on the top. Note the two BD139 transistors which are bolted together with heatsink flags. These function as the RF output transistors. and potentiometer VR1. The product detector uses the same components as used for the balanced modulator in transmit, except that the signal path is now reversed. When there are no signals coming from the antenna, the balance is maintained and no audio signals are produced at the centre tap of T1. When a signal is tuned in, the balance is upset and a voltage representing the audio signal is produced and passed to the first audio stage Q9. A 56Ω resistor and two .01µF capacitors filter out any RF that may be on the audio signal. The signal level at this point is quite small and so Q9 is configured for high gain. The collector load is essentially a 5.6kΩ resistor in parallel with a .022µF capacitor. This combina­tion acts as a low-pass filter, where the gain of the stage is greatest at low frequencies and drops off rapidly at higher frequencies. This is necessary to filter out adjacent signal interference and it is in these audio stages that the adjacent channel selectivity of the receiver is determined. The output of Q9 is passed to the volume control VR3. This is the only gain control for the receiver and needs to be adjust­ ed for differing signal strengths as there is no automatic gain control. The second audio stage is Q10 and again low-pass filter­ing is accomplished by the collector combination of a 5.6kΩ resistor in parallel with a 0.1µF capacitor. The audio output stage is Q11 and provides enough power to drive a pair of low impedance headphones. Power supply decoupling is included to ensure amplifier stability. Transmit/receive switching Normally, a relay is used in a transceiver to switch the antenna and power supply between the transmit and receive cir­cuits. Relays are both bulky and expensive, so this design avoids them by using some novel techniques. The antenna and low-pass filter are permanently connected to both the transmit output stage (Q4) and the receive bandpass filter. During transmit, the receiver (ie, the input of Q6) is protected by a pair of back-to-back diodes (D4 & D5) which limit the voltage to about 1.2V peak-to-peak. The 100pF capacitor feeding the receive bandpass filter is small enough in value to avoid affecting the operation of the low-pass filter. During receive, Q4 and Q5 are turned off and the collectors exhibit a high enough impedance to avoid November 1994  57 Fig.3: here are the full size etching patterns for the double-sided PC board. attenuating the signal on its way to the receive section. Power supply switching has been simplified by using the transmit/ receive switch, S1. Power is permanently connected to the audio section, the carrier oscillator section and the RF output stage collectors. When the switch is in transmit, power is applied to the microphone amplifier, the RF driver and the RF output base bias circuit. Power is also applied to diode D6 which turns on Q12 and mutes the receive audio sections. In receive, power is switched to the receive RF preamp and the audio mute transistor Q12 is turned off. There is a small turn-off delay as the 10µF capacitor discharges via the 4.7kΩ resistor and the base of Q12. This is done to 58  Silicon Chip avoid any signal from the microphone feeding through to the audio amplifier stages while the microphone amplifier is turning off. Construction All parts except for the controls and sockets are mounted on a PC board coded 06110941. The PC board is double-sided, with the top side being a continuous groundplane with clearances for the component leads. Components which require a ground plane connection are soldered to the top and these points are marked with a black star symbol on the component overlay. The electrolytic capacitors get their earth connection through the earth leads of adjacent components which are themselves soldered on the bottom and top of the board. This can be seen on the wiring diagram of Fig.2. As with any RF project, keep the component leads as short as possible. The overlay diagram shows the variable frequency oscillator components installed. After you have checked the board for any defects, commence by soldering in the resistors, then install PC stakes for the external connections. Continue with the capacitors, diodes, ceramic resonator and the prewound 2.2µH RF chokes. Install the transistors, taking particular care with the orientation of the BD139s. The output pair need to be installed about 5mm above the board. Place a 3mm screw through the mounting holes of the two transistors while they dsb Fig.4: this full-size artwork can be used as a drilling template for the front panel. Rx phones Tx Ri 80mg allel to each other. While holding one end of the set of wires secure in a vice, twist the other end until there is about five twists per centimetre. A hand drill or a battery operated drill with variable speed con­trol would be handy for this job. Wind the wires on the former as discussed before. Cut off the excess and untwist the ends for identification with a multi­meter. The start of one and the finish of another winding need to mic All coils are wound on 2-hole F14 ferrite balun formers, using enamelled copper wire: • L1: 6 turns 22 B&S enamelled copper wire • T1: 6 trifilar turns 26 B&S enamelled copper wire • T2: primary 4 turns; secondary 4 turns; Q6 collector winding 6 turns 26 B&S enamelled copper wire • T3: primary 6 turns; secondary 4 turns 26 B&S enamelled copper wire • L2, L3 & L4 are prewound 2.2µH RF chokes. L1 is straightforward, as is T3 except that it has two windings. T2 has three windings. The winding ends can be identi­fied by scraping the enamel off the ends of the wires and check­ing for continuity with a multimeter. Ideally each winding would use a different colour wire or you could use a spot of paint; some form of identification needs to be used so that the winding polari­ties are as specified. When pulling the wire through the balun formers, try not to damage the enamel. This can happen as the wire passes over the sharp edges of the holes and could ultimately cause shorted turns. Note that T1 is wound using the trifilar method: take three 400mm lengths of wire and place them par- audio Coil winding details tune are being soldered in. The holes need to be in line, so that a small heatsink can be attached. This can be simply constructed from two pieces of scrap aluminium 16mm wide by 28mm long. These are formed into two “L” shapes with a bend at 8mm. A hole is drilled in the centre of the short leg of each piece. One is placed in between Q4 and Q5 and the other is placed against the metal surface of Q5. A screw is then passed through the assembly and tightened with a nut. Next comes the coil winding. Normally this involves cans and formers with slugs and can be an quite involved. This project makes it simple by requiring just a few turns of wire wound on 2-hole ferrite balun formers. These are sold in two sizes, the one required measures about 12 x 12 x 7mm. A turn is defined as passing a wire up through one hole, out the other end and feeding it back again down the other hole, so that both ends (start and finish) of the wire are at the same end of the former. be joined to form the centre tap of the secondary winding. The remaining winding becomes the primary. Final assembly The PC board is housed in a plastic jiffy box measuring 196 x 112 x 60mm. On the front panel are knobs for tuning (VR4) and audio volume (VR3), the transmit/receive switch, the microphone socket and the headphone socket. The PC board is mounted on November 1994  59 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. No._______________   ❏ Gift subscription ☞ RATES (please tick one) Australia Australia with binder(s)* NZ & PNG (airmail) Overseas surface mail 2 years (24 issues) 1 year (12 issues) ❏ $A90 ❏ $A49 ❏ $A114 ❏ $A61 ❏ $A135 ❏ $A72 ❏ $A135 ❏ $A72 ❏ $A240 Overseas airmail ❏ $A120 *1 binder with 1-year subscription; 2 binders with 2-year subscription GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) YOUR DETAILS Your Name_________________________________________________ (PLEASE PRINT) Address___________________________________________________ Address______________________ _____________________________ State__________Postcode_______ ______________________________________Postcode___________ Daytime Phone No.____________________Total Price $A __________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ Master Card 9am-5pm Mon-Fri. Please have your credit card details ready 60  Silicon Chip ______________________________ 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 The rear panel of the transmitter carries the SO239 antenna socket & binding posts for the power supply connections (13.8V DC). the bottom of the box with four spacers secured with 3mm screws and nuts. The square mount SO239 antenna socket is mounted in the bottom right corner of the base of the box with a solder lug under one of the retaining nuts for the earth connec­tion. The power supply binding posts are mounted on the base above the antenna socket. All wiring from the PC board is done with hook-up wire except the microphone lead which should be via shielded audio cable. Twist the wires to the antenna socket, the tune control and the volume control. Keep the wiring to the front panel as short as possible but long enough so that the PC board can be accessed when the front panel is lent forward. Note that the headphone socket is a stereo type wired for mono operation. Testing Once construction is complete, check all the wiring one more time. Place the transmit/receive switch in receive and connect a power supply to the binding posts. The transceiver is designed to be run off 13.8V DC regulated and draws about 70mA, however there should be no troubles with a voltage between 12V and 15V. A supply of 15V should be considered a maximum and 12V will give a reduced power output, compared to the nominal setting of 13.8V Plug headphones into the phones socket and advance the volume control. A hiss should be heard indicat- ing that the audio stages are working correctly. Check that the oscillator is work­ing by measuring the frequency with a frequency counter at the emitter of Q2. Failing this, listen on a receiver placed nearby which is tuned to the oscillator frequency. Inject a signal into the antenna socket at 3.58MHz and check that you can hear a tone of about 1kHz – rotate the tune control until the tone is heard. You should only need very light coupling to the antenna socket for a good, clean tone. If you fail to hear a hiss, the fault will be later in the audio sections and if you hear a hiss but no tone then look for trouble in the RF sections or around the early audio stages. Unless you have a second transmitter or a friend nearby, you will probably have to wait till late after­noon to receive off-air voice signals. Before testing the transmitter, plug a 50Ω dummy load or wattmeter into the antenna socket and place a multimeter set to the 1A range in the supply positive lead. Place the modulator balance trimpot (VR1) at halfway. Switch to transmit and without a microphone connected, check the current; it should read about 180mA. A reading far from this indicates a fault and should be looked into. The next step is to balance the modulator. This can be done by using a low power wattmeter, a dummy load and an oscilloscope or a second receiver. A dummy load can be simply two 100Ω 1W resistors in parallel wired across the antenna socket. In all the methods, the aim is to rotate balance control VR1 until minimum output power is obtained. This should be at half way, but it may need adjusting a little either way to obtain balance. If you are using a receiver be careful to avoid picking up the direct signal from the oscillator which can cause misleading S-meter readings. With the carrier nulled, plug in a microphone and either listen to yourself on a second receiver or have someone else listen while whistling into the microphone. Advance the mic gain control VR2 until the signal starts to distort and just back it off a little. Driving the transmitter too hard will cause a distorted signal and should be avoided at all times. The transmitter draws about 400mA on voice peaks. Operating Before you can transmit with this project you must hold a current amateur radio licence. To obtain the best results with any radio it is important to use an effective antenna. With a QRP or low power transmitter it is even more important, because we want as much signal radiated as possible. The most popular anten­na for the 80-metre band is the half wave dipole, which is about 40 metres long and generally fed at the centre with 50Ω coax cable. While the antenna is very important, the band conditions can also play a large part in getting good contacts. Sometimes the band can be noisy or propagation poor, so do not expect to work long distances every time. When making a CQ call, it is helpful to say that you are operating QRP. This stirs the curiosity of those listening and also explains the possibility of your low signal strength. Most stations on the air will be using commercial transceivers with much greater output powers than your 1.5W, so a little patience and skill is needed to get contacts. You will, however, be pleasantly surprised with the signal reports you get. If you intend to contact other DSB stations, it will be necessary to adjust the tune control very accurately. In fact the two carrier frequencies should be exactly the same frequency and in phase to recover the audio properly. This will generally not be possible but, with a little knob twiddling a success­ ful contact will be possible. This problem does not occur with SC SSB signals. November 1994  61 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. Super bright LED brake light array This circuit flashes 13 super bright LEDs when connected to a car’s brake circuit; ie, from the switched supply of the brake lamps to ground. Operation is controlled by a single flashing LED (LED 14) which receives its bias from the 390Ω resistor via LED 12 & LED 13. The voltage developed across this 390Ω resistor it not enough to bias on either Q1 or Q2 until LED 14 is on. When LED 14 turns on, it draws approximately 20mA and this develops a voltage across the 390Ω resistor which is limited by LED 11 to 1.8V. This acts as a reference voltage for two constant current sources based on Q1 and Q2. Hence, Q1 & Q2 drive series strings with the pulse current set to 50mA. Note: in some states, flashing brake lights are not ap­ proved. If you wish to convert the circuit to a non-flashing version, replace LED 14 with a 470Ω 1W resistor. E. Kochnieff, Lutwyche, Qld. ($20) 12-24V circuit tester for cars & trucks BRASS ROD D1-D4 4x1N4004 CLIP 470  ZD1 6.8V 100k Q2 BC548 ZD2 6.8V 15k Q1 BC548 15k Display dimmer for LED clocks This circuit automatically dims the digits of a LED clock in low light conditions. The LDR (PR1) will have a low resistance in daylight and so the pin 6 output of op amp IC1 will be low. As the ambient light reduces, the output of the op amp goes high, turning on transistor Q1. 64  Silicon Chip LED1 GREEN  LED2 RED  560  +11-15V 22  LED11 LED11 RED  390  22  Q2 BC327 Q1 BC327 LED1 RED  LED2 RED  LED3 RED  LED4 RED  LED5 RED  LED12 RED LED13 RED LED14 FLASHING LED    LED6 RED  LED7 RED  LED8 RED  LED9 RED  LED10 LED10 RED  GND This tester can be used to detect the presence of 12V or 24V in car or truck wiring. It has a bridge rectifier input so the supply polarity doesn’t matter and one of two LEDs will light to show the presence of 12V or 24V (green for 12V, red for 24V. The circuit works as follows. Zener diodes ZD1 & ZD2 do not conduct if less than about 16V is applied to the input via the bridge rectifier (D1-D4). Hence Q1 stays off and Q2 is able to turn on, biased by the 100kΩ collector resistor for Q1. When Q2 turns on, LED 1 lights, indi­cating the presence of a nominal 12V supply. If more than 16V is applied to the input via the bridge rectifier, ZD1 & ZD2 conduct and allow Q1 to turn on. This turns off Q2 and both LED 1 and LED 2 light up. A. Glover, Nanango, Qld. ($20) Both zener diodes (ZD1 & ZD2) should drop a large number of volts in daylight which allows the current flowing through R1 to turn on Q2 to almost full saturation. This allows the full current to flow through to the LED displays. When it is dark, Q1 shorts out ZD1 so that ZD2 drops a small voltage. Q2 now receives less current from R1, making Q2 less saturated. This allows less current to the LEDs, thus making the display dimmer. The 10µF filter capacitor on Q2’s base prevents momentary shadows and bright flashes from triggering the circuit. To assess the voltages required for ZD1 and ZD2, they can initially be replaced with a trimpot with the centre leg going to the collector of Q1. The voltage can then be measured and the correct voltage diodes put in place. It is not advisable to +12V 16 4 4.7M 10 100k X1 32.768kHz IC6 4016 IC1 4060 6 7 22k 12 3 2 2 4 4 1 7 TENS S2 IC3 4017 10 12 14 3 7 5-30pF IC4 4017 10 1 5 5 6 6 9 9 11 11 +12V S3 START 16 14 8 UNITS S1 8 33pF 14 9 3 16 13 .027 15 8 13 15 8 +12V A 240VAC 12V RLY1 240VAC D1 1N4002 22k IC7 IN 7812 OUT BR1 470 0.1 GND 100 +12V 1 0.1 N 2 Low cost photo timer This digital photo timer can be set in half second incre­ments from zero to 49.5 seconds. It provides a highly accurate and repeatable time interval due to its crystal timebase. When the start switch is pressed, the relay (RLY1) closes and 240VAC is supplied to the enlarger light bulb. After the set period, RLY1 is switched off. A 32.768kHz crystal is connected between pins 4 & 10 while the internal inverter is biased with the 4.7MΩ resistor. The 100kΩ resistor prevents the crystal from operating at a higher harmonic frequency. The 33pF capacitor and 5-30pF trimmer provide the correct loading for the crystal and the use resistors permanently be­cause voltage fluctuations will cause noticeable variations in the display brightness. You will also need to experiment with the value for resistor R1. This resistor should be large enough to limit the current through the two zener diodes to a safe value. Try 2.2kΩ as a start. A. Chin, Heidelberg, Vic. ($20) 3 7 IC5 4081 E 14 BULB 14 6 S 1 Q IC2 4013 R 4 7 22k 22k trimmer can be used for fine adjustment of the crystal frequency. IC1 is a 14-stage binary counter with its lowest division output at pin 3. This provides us with a 2Hz signal (32.768kHz/16,384) which is applied to the clock input (pin 14) of IC3 via CMOS analog switch IC6. IC3 and IC4 are decade counters which provide a separate output for each count. The “0” output is at pin 3, the “1” output at pin 2 and so on down to the “9” output at pin 11, as shown on the circuit. When start switch S3 is pressed, the reset pins (pin 15) of IC3 and IC4 and the set input (pin 6) of flipflop IC2 are pulled high. Q1 is now turned on to drive the relay RLY1. The Q output of IC2 also switches on IC6 so that clock pulses from IC1 are counted by IC3. The carry out from IC3 at pin 12 clocks IC4 every five seconds. IC5 is a 2-input AND gate which monitors the outputs of IC3 and IC4 as selected by S1 and S2. Available outputs from IC3 are from zero to 4.5s in 0.5s increments, while IC4 provides 5s to 45s in 5s increments. When both selected outputs go high, the output of IC5 goes high and resets IC2. The Q output goes low and this switches off Q1 and the relay. IC6 is also disconnected. Note that the relay will be activated for the length of time that the start switch S3 is held down plus the time set by S1 and S2. Gordon Boytell, Maleny, Qld. ($40) V+ Q2 BC639 R1 0V PR1  ZD2 3 VR1 20k 2 7 IC1 741 4 6 4.7k Q1 BC547 Q1 BC548 10 TO LED SUPPLY OR CATHODE TO LED ANODE OR GROUND ZD1 4.7k 6.8k November 1994  65 Modifying the Nicad Cell Discharger to discharge 2-cell packs If you’re looking for a twin-cell nicad pack discharger, this simple modification to the Nicad Cell Discharger described in the May 1993 issue will enable you to do the job. to begin discharging the battery pack. At the same time, IC2a compares the battery pack voltage with a reference voltage de­rived from ZD1 via VR1. Provided that the battery voltage is higher than the reference, IC2a’s output (pin 1) remains high and so Q1 remains on and power is applied to IC1 when the START switch is released. When the battery voltage subsequently falls below 2.2V, pin 1 of IC2a switches low and Q1 switches off and removes power to IC1. This in turn switches Q2 off and so the battery pack ceases discharging. IC2b is configured By DARREN YATES Over the last couple of years, we’ve presented a number of nicad dischargers and they’ve all been very popular. The only problem is that we haven’t catered for those people wanting to discharge two-cell (2.4V) nicad packs. Our most recent circuit for a nicad discharger was pub­lished in the September 1994 issue and this catered for battery packs with 3-10 cells. Another circuit published in May 1993 was designed to discharge single cells only, including AAA, AA, C and D types. That circuit contained a number of desirable features, including a flashing LED indicator to indicate discharging and automatic switch-off at 1.1V. Recently, we decided to take a closer look at this circuit to see if it could be converted to discharge a two-cell pack. As it turns out, the modifications are quite simple. Circuit diagram The new circuit is shown in Fig.1. We won’t go into all the details again. Briefly, IC1 is configured as a 1.5V to 9V DC step-up converter and this is used to power comparator stage IC1a and oscillator stage IC1b. When the START switch (S1) is pressed, IC1 starts and turns on Q2 START S1 D1 1N4004 STEP-UP VOLTAGE CONVERTER S D 2x NICAD CELLS 2.7k Q1 MTP3055 +2.4V L1 50uH G R 2 8.2 0.5W C 470 16VW Q2 BC328 B Fig.1: only a few modifications are required to the front end of the original circuit to convert it to a twin-cell discharger: (1) the two 1Ω resistors are deleted; (2) the positive rail from the battery is now connected to D1’s anode; & (3) the 6.8Ω resistor is changed to an 8.2Ω 1W resistor. 4 6 3 2 0.1 8 IC1 TL496 5 +8.8V 7 10k 3 15k VR1 10k ZD1 BZX79 C5V1 8 5 1 IC2a LM358 2 6 10  10 16VW EXTRA DISCHARGE L1: 33T, 0.5mm ECW ON NEOSID 17-732-22 TOROID B E TWIN CELL NICAD DISCHARGER 66  Silicon Chip VIEWED FROM BELOW C A GDS 1.5k 18k COMPARATOR REFERENCE 7 IC2b 10k 4 0.1 E  SEE TABLE 2.2k 10k 680  470 16VW R1 1.5k 6.8k 470k K A LED1 DISCHARGING DISCHARGING FLASHER  K TABLE 1 SATELLITE SUPPLIES Cell Capacity Discharge Current Q2 R1 R2 1800mAh (AAA) 125mA no - - 500mAh (AA) 125mA no - - 1.2Ah (C) 185mA yes 1.5kW - 2Ah (C,D) 185mA yes 1.5kW - Aussat systems from under $850 4Ah (D) 405mA yes 1.5kW 8.2W SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 Q1 IC1 TL496 470k 2.2k 0.1 1 0.1 680  D1 S1 1.5k IC2 LM358 10 R2 8.2  TO NICAD CELL HOLDER 1 2.7k 470uF 6.8k L1 10k 10k A 18k ZD1 K 10k 10uF VR1 Q2 470uF R1 1.5k as a Schmitt trigger oscillator and is used to flash LED 1 on and off during the discharge cycle. Note that Q2, R1 and R2 are only used for the larger cells, to increase the nominal discharge rate. These components can be left out of circuit for AAA and AA cell packs. Circuit modifications The modifications are all at the front end of the circuit. First, the two 1Ω resistors used in the reverse polarity protec­tion network have been deleted and the positive rail from the pack is now connected to D1’s anode. Next, the 6.8Ω 0.5W resistor in series with Q2’s collector is changed to an 8.2Ω 1W resistor. And that’s all there is to it. What happens now is that D1 is connected in series with the batteries and drops the voltage applied to IC1 (via Q1) to 1.8V. This is well within the parameters of IC1. As an added bonus, this modification means that no current is consumed by the circuit when the cells are accidentally connected in reverse, whereas before the consumption was almost 1A. Construction The circuit can be built on the same PC board as before (code 14305931) LED1 Fig.2: this revised parts layout diagram includes all the modifications listed in the text. Note that Q2, R1 & R2 can be left out for AAA & AA cells but may be required for larger capacity C & D cells (see table). LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 15k –just leave out the two 1Ω resistors, and con­nect the positive lead from the cell holder to D1’s anode – see Fig.2. The standard discharge rate without components R1, R2 and Q2 in circuit is approximately 100mA. This is quite adequate for discharging AAA and AA size cells but should be increased to discharge larger cells within a reasonable time. Table 1 shows the components that you need to add to suit the various battery pack capacities. For example, adding R1 and Q2 increases the discharge rate to 150mA, while adding R2 as well increases it to 330mA. Finally, a 2.2V rail is required in order to accurately set the reference voltage applied to pin 2 of IC2a. This can come from a variable power supply or can be improvised using a couple of 1.5V batteries and a trimpot. Set the output voltage to exact­ly 2.2V, then connect the supply to the circuit in place of the nicad pack and adjust VR1 until the comparator just switches off. Note that this method of adjustment is necessary to compen­ sate for the voltage drop across D1. The reference voltage cannot be set using the method SC described previously. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 November 1994  67 SPECIALS BY FAX If your fax has a polling function, dial (02) 579 3955 and press your POLLING button to get our latest specials, plus our item and kit listing. Updated at the start of each month. MEDICAL LASER One only water cooled medical laser with selectable outputs: Argon (7W multiline) or Dye laser (1W red). Large water cooled unit with a separate control box and accessories (350kg): $15,000 LEVEL RECORDER One only, Bruel & Kjaer level recorder type 2305, in good condition: $300 DIE CAST BOXES These large (187 x 120 x 56mm) aluminium die cast boxes have several holes drilled in them and have a C+K toggle switch and a 6.25mm phono socket fitted. New units from an unfinished production project: $4 Ea. WELLER SOLDERING IRON TIPS New soldering iron for low voltage Weller soldering stations and mains operated Weller irons. Mixed popular sizes and temperatures. Specify mains or soldering station type: 5 for $10. NICAD BATTERY PACKS Brand new Toshiba 7.2V - 2.2AHr Nicad Battery packs in a plastic assembly: $20 Ea. If you purchase three packs we will supply a matching fast charger (90 min.) that can charge up to three of these batteries (one at a time): modern unit that employs “delta V” voltage detection to terminate charge, needs an external 12V-2.2A unregulated supply: $60 for three battery packs and a three way charger. PLUGS/SOCKETS 3-pin chassis mounting socket and a matching covered 3-pin plug. Good quality components that will handle a few amperes at low voltage: $5 for 4 pairs. DYNAMIC MICROPHONES Low impedance dynamic microphones with seperate switch wiring, 3.5mm mic. plug, 2.5mm switch plug, as used on most cassette recorders: $4 Ea. 40mW IR LASER DIODES New famous brand 40mW - 830nm IR laser diodes, suit medical and other applications: $90 Ea. Constant current driver kit to suit: $10. LOW COST 1-2 CHANNEL UHF REMOTE CONTROL Late in October we will have available a single channel 304MHz UHF remote control with over 1/2 million code combinations 68  Silicon Chip which also make provision for a second channel expansion. The low cost design includes a complete compact keyring transmitter kit, which includes a case and battery, and a PCB and components kit for the receiver that has 2A relay contact output!. Tx kit $10, Rx kit $20 Additional components to convert the receiver to 2 channel operation (extra decoder IC and relay): $6. INCREDIBLE PRICES: Complete 1-Channel Tx-Rx Kit: $30 Complete 2-Channel Tx-Rx Kit: $36 Additional Transmitters: $10 FIBRE OPTIC TUBES These US made tubes are from used equipment but in excellent condition. Have 25/40 mm diameter, fibre-optically coupled input and output windows. The 25mm tube has an overall diameter of 57mm and is 60 mm long, the 40mm tube has an overall diameter of 80mm and is 92mm long. The gain of these is such that they would produce a good image in aproximately 1/2 moon illumination, when used with suitable “fast” lens, but they can also be IR assisted to see in total darkness. Our HIGH POWER LED IR ILLUMINATOR kit, and the IR filter are both suitable for use with these tubes. The superior resolution of these tubes would make them suitable for low light video preamplifiers, wild life observation, and astronomical use. Each of the tubes is supplied with a 9V - EHT power supply kit. INCREDIBLE PRICES: $120 for the 25mm intensifier tube and supply kit. $180 for the 40mm intensifier tube and supply kit. We also have a good supply of the same tubes that may have a small blemish which is not in the central viewing area!: $65 for a blemished 25mm intensifier tube and supply kit. $95 for the blemished 40mm intensifier tube and supply kit. HIGH POWER LED IR ILLUMINATOR This kit includes two PCBs, all on-board components plus casing: switched mode power supply plus 60 high intensity 880nm IR (invisible) LEDs. Variable output power, 6-20VDC input, suitable for illuminating IR responsive CCD cameras, IR night viewers etc. Professional performance at a fraction of the price of the commercial product: COMPLETE KIT PRICE: $60 INTENSIFIED NIGHT VIEWER KIT SC Sept. 94. See in the dark! Make your own night scope that will produce good vision in sub-starlight illumination! Has superior gain and resolution to all Russian viewers priced at under $1500. We supply a three stage fibre-optically coupled image intensifier tube, EHT power supply kit, and sufficient plastics to make a monocular scope. The three tubes are supplied already wired and bonded together. $290 for the 25mm version $390 for the 40mm version We can also supply the lens (100mm f2: $75) and the eyepiece ($18) which would be everything that is necessary to make an incredible viewer! components are required to complete this excellent stereo/twin amplifier! Incredible pricing at just: $25 For one 240V-28V (80W!) transformer, two TDA1520 monolythic hifi amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. SIEMENS VARISTORS 420VAC-20 joule varistors that are suitable for spike protection in Australian 3-phase systems: 10 for $5. CAMERA FLASH UNITS Electronic flash units out of disposable cameras. Include PCB/components and Xenon tube/reflector assembly. Requires a 1.5V battery. $2.50 TAA611C ICs TAA611C audio power amplifier ICs, no more information: 5 for $5. MAINS POWERED GAS LASER Includes a professional potted mains power supply and a new 3mW red tube to suit. One catch, this supply requires a 4-6V (TTL) enable input which is optically isolated, to make the unit switch ON: very low consumption from a 4.5V battery. $100 For a new 3mW tube plus a TTL mains power supply to suit. SUPER DIODE POINTERS - HEADS These pointers probably represent the best value when you compare them on a “brightness per dollar” basis. They are about 5 times brighter than 5mW/670nm pointers! They have an output of 2.5mW at 650nm, which is about equal in brightness to a 0.8mW HE-NE tube!! SPECIAL INTRODUCTORY PRICE: $150 We will also have available some of the 3V diode modules used in these pointers at approximately $125, and also some 2.5mW/635nm laser diode modules with special optics at approximately $280. VIDEO TRANSMITTERS Low power PAL standard UHF TV transmitters. Have audio and video inputs with adjustable levels, a power switch, and a power input socket: 10-14VDC/10mA operation. Enclosed in a small metal box with an attached telescopic antenna. Range is up to 10M with the telescopic antenna supplied, but can be increased to aproximately 30M by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25 TDA ICs/TRANSFORMERS We have a limited stock of some 20 watt TDA1520 hifi quality monolythic power amplifier ICs: less than 0.01% THD and TIM distortion, at 10W RMS output! With the transformer we supply we guarantee an output of greater than 20W RMS per channel into an 8ohm load, with both channels driven. We supply a far overated 240V-28V/80W transformer, two TDA1520 ICs, and two suitable PCBs which also include an optional preamplifier section (only one additional IC), and a circuit and layout diagram. The combination can be used as a high quality hifi Stereo/Guitar/ PA amplifier. Only a handful of additional LIGHT MOTION DETECTORS Small PCB assembly based on a ULN2232 IC. This device has a built-in light detector, filters, timer, narrow angle lens, and even a siren driver circuit that can drive an external speaker. Will detect humans crossing a narrow corridor at distances up to 3 metres. Much higher ranges are possible if the detector is illuminated by a remote visible or IR light source. Can be used at very low light levels, and even in total darkness: with IR LED. Full information provided. The IC only is worth $16! OUR SPECIAL PRICE FOR THE ASSEMBLY IS: $5 Ea. or 5 for $20 GAS LASER SPECIAL We have a good supply of some He-Ne laser heads that were removed from new or near new equipment, and have a power output of 2.5-5mW: very bright! With each head we will supply a 12V universal laser power supply kit for a ridiculous TOTAL PRICE of: $89 AA NICADS Brand new AA size Saft brand (made in France) 500mA Hr. batteries, also have solder connections (can be removed): $2 Ea. or 10 for $16 TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8 eight wire stepper motors from an IBM computer parallel port. Motors require separate power supply. A detailed manual on the COMPUTER CONTROL OF MOTORS plus circuit diagrams/ descriptions are provided. We also provide the necessary software on a 5.25" disc. Great “low cost” educational kit. We provide the kit, manual, disc, plus TWO 5V/6 WIRE/7.5 Deg. STEPPER MOTORS FOR A SPECIAL PRICE OF: $42 IR LASER DIODE KIT BRAND NEW 780nm LASER DIODES (barely visible), mounted in a professional adjustable collimator-heatsink assembly. Each of these assemblies is supplied with a CONSTANT CURRENT DRIVER kit and a suitable PIN DIODE that can serve as a detector, plus some INSTRUCTIONS. Suitable for medical use, perimeter protection, data transmission, IR illumination, etc. Bargain at $40 5mW VISIBLE LASER DIODE KIT Includes a Hitachi 6711G 5mW-670nm visible laser diode, an APC driver kit, a collimating lens, heatsink assembly, a case and battery holder. That’s a complete 3mW collimated laser diode kit for a TOTAL PRICE OF: $75 BIGGER LASER We have a good, but LIMITED QUANTITY of some “as new” red 6mW+ laser heads that were removed from new equipment. Head dimensions: 45mm diameter by 380mm long. With each of the heads we will include our 12V Universal Laser power supply. BARGAIN AT: $170 6mW+ head/supply. ITEM No. 0225B We can also supply a 240V-12V/4A5V/4A switched mode power supply to suit for $30. 12V - 2.5 WATT SOLAR PANEL SPECIAL These US made amophorous glass solar panels only need terminating and weather proofing. We provide terminating clips and a slightly larger sheet of glass. The terminated panel is glued to the backing glass, around the edges only. To make the final weatherproof panel look very attractive some inexpensive plastic “L” angles could also be glued to the edges with some silicone. Very easy to make. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE until the end of 94!: $20Ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminatig clips, an isolating diode, and the instructions. A very efficient switching regulator kit is available: suits 1224V batteries, 0.1 - 16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. CCD CAMERA A monochrome CCD camera which is totally assembled on a small PCB and includes an auto iris lens. It can work with illumination of as little as 0.1Lux and it is IR responsive. Can be used in total darkness with infrared illumination. Overall dimensions of camera are 24 x 46 x 70mm and it weighs less than 40 grams! Can be connected to any standard monitor, or the video input on a video cassette recorder. NEW LOW PRICE: $199 IR “TANK SET” A set of components that can be used to make a a very responsive infrared night viewer. The matching lens tube and eyepiece sets were removed from working military quality tank viewers. We also supply a very small EHT power supply kit that enables the tube to be operated from a small 9V battery. The tube employed is probably the most sensitive IR responsive tube we ever supplied. The resultant viewer requires low level IR illumination. Basic instructions provided. $140 For the tube, lens, eyepiece and the power supply kit. SOLID STATE “PELTIER EFFECT” COOLER - HEATER These are the major parts needed to make a solid state thermoelectric coolerheater. We can provide a large 12V-4.5A Peltier effect semiconductor, two thermal cut-out switches, and a 12V DC fan for a total price of. $45. ITEM No. 0231 We include a basic diagram/circuit showing how to make a small refrigerator/heater. The major additional items required will be an insulated container such as an old “Esky”, two heatsinks, and a small block of aluminium. RUSSIAN NIGHT VIEWER We have a limited quantity of some passive monocular Russian made night viewers that employ a 1st generation image intensifier tube, and are prefocussed to infinity. CLEARANCE: $180 INFRA RED FILTER A very high quality IR filter and a RUBBER lens cover that would fit over most torches including MAGLITEs, and convert them to a good source of IR. The filter material withstands high temperatures and produces an output which would not be visible from a few metres away and in total darkness. Suitable for use with passive and active viewers. The filter and a rubber lens cover is priced at: $11 DOME TWEETERS Small (70mm diam., 15mm deep) dynamic 8-ohm twetters, as used in very compact high quality speaker systems: $5 Ea. We also have some 4" woofers: $5 Ea. VIDEO ZOOM LENSES Two only 10:1 video zoom lenses, f=15150mm, 1:1.8, have provision for remote focus aperture and zoom control; three motors, one has a “C” mount adaptor, 150mm diam. by 180mm long: $390 Ea. MINIATURE FM TRANSMITTER Not a kit, but a very small ready made self contained FM transmitter enclosed in a small black metal case. It is powered by a single small 1.5V silver oxide battery, and has an an in-built electret microphone. SPECIFICATIONS: Tuning range: 88 108MHz. Antenna: Wire antenna - attached. Microphone: Electret condenser. Battery: One 1.5V silver oxide LR44/G13. Battery life: 60 hours. Weight: 15g. Dimensions: 1.3" x 0.9" x 0.4". $25 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 Ea. MORE KITS-ITEMS Single Channel UHF Remote Control, SC Dec. 92 1 x Tx plus 1 x Rx $45, extra Tx $15. 4 Channel UHF Remote Control Kit: two transmitters and one receiver, $96. Garage/Door/Gate Remote Control Kit: Tx $18, Rx $79. 1.5-9V Converter Kit: $6 Ea. or 3 for $15. Laser Beam Communicator Kit: Tx, Rx, plus IR Laser, $60. Magnetic Card Reader: professional assembled and cased unit that will read information from plastic cards, needs low current 12VDC supply-plugpack, $70. Switched Mode Power Supplies: mains in (240V), new assembled units with 12V-4A and 5V-4ADC outputs, $32. Electric Fence Kit: PCB and components, includes prewound transformer, $28 High Power IR LEDs: 880nm/30mW/12deg. <at> 100mA, 10 for $9. Plasma Ball Kit: PCB and components kit, needs any bulb, $25. Masthead Amplifier Kit: two PCBs plus all on board components: low noise (uses MAR-6 IC), covers VHF-UHF, $18. Inductive Proximity Switches: detect ferrous and non-ferrous metals at close proximity, AC or DC powered types, 3-wire connection for connecting into circuitry: two for the supply, and one for switching the load. These also make excellent sensors for rotating shafts etc. $22 each or 6 for $100. Brake Light Indicator Kit: 60 LEDs, two PCBs and 10 resistors, makes for a very bright 600mm long high intensity red display, $30. IEC Leads: heavy duty 3-core (10A) 3m leads with IEC plug on one end and an European plug at the other, $1.50 Ea. or 10 for $10. IEC Extension Leads: 2m long, IEC plug at one end, IEC socket at other end, $5. Motor Special: these motors can also double up as generators. Type M9: 12V, I No load = 0.52A-15,800 RPM at 12V, 36mm Diam.-67mm long, $5. Type M14: made for slot cars, 4-8V, I No load = 0.84A at 6V, at max efficiency I = 5.7A-7500 RPM, 30mm dia, 57mm long, $5. EPROMS: 27C512, 512K (64K x 8), 150ns access CMOS EPROMS. Removed from new equipment, need to be erased, guaranteed, $4. Green Laser Tubes: Back in stock! The luminous output of these 1-1.5mW GREEN laser diode heads compares with a 5mW red tube!: $490 for a 1-1.5mW green head and a 12V operated universal laser inverter kit. 40 x 2 LCD Display: brand new 40 character by 2-line LCD displays with built in driver circuitry that uses Hitachi ICs, easy to drive “standard” displays, brief information provided, $30 Ea. or 4 for $100. RS232 Interface PCB: brand new PCB assembly, amongst many parts contains two INTERSIL ICL232 ICs: RS232 Tx - Rx ICs, $8. Modular Telephone Cables: 4-way modular curled cable with plugs fitted at each end, also a 4m long 8-way modular flat cable with plugs fitted at each end, one of each for $2. 12V Fans: brand new 80mm 12V-1.6W DC fans. These are IC controlled and have four different approval stamps, $10 Ea. or 5 for $40. Lenses: a pair of lens assemblies that were removed from brand new laser printers. They contain a total of 4 lenses which by different combinations - placement in a laser beam can diverge, collimate, make a small line, make an elipse etc., $ 8. Polygon Scanners: precision motor with 8-sided mirror, plus a matching PCB driver assembly. Will deflect a laser beam and generate a line. Needs a clock pulse and DC supply to operate, information supplied, $25. PCB With AD7581LN IC: PCB assembly that amongst many other components contains a MAXIM AD7581LN IC: 8-bit, 8-channel memory buffered data acquisition system designed to interface with microprocessors, $29. EHT Power Supply: out of new laser printers, deliver -600V, -7.5kV and +7kV when powered from a 24V-800mA DC supply, enclosed in a plastic case, $16. Mains Contactor Relay: has a 24V 250ohm relay coil, and four separate SPST switch outputs, 2 x 10A and 2 x 20A, new Omron brand, mounting bracket and spade connectors provided, $8. FM Transmitter KIt - Mk.II: high quality high stability, suit radio microphones and instruments, 9V operation, the kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip, $11. FM Transmitter Kit - Mk.I: this complete transmitter kit (miniature microphone included) is the size of a “AA” battery, and it is powered by a single “AA” battery. We use a two “AA” battery holder (provided) for the case, and a battery clip (shorted) for the switch. Estimated battery life is over 500 hours!!: $11. High Power Argons: the real thing! Draw pictures on clouds, big buildings etc., with a multiline watercooled Argon laser with a few watts of output. “Ring” for further details. Argon-Ion Heads: used Argon-Ion heads with 30-100mW output in the blue-green spectrum will be back in stock soon. Priced at around $400 for the “head” only, power supply circuit and information supplied. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 Bankcard, Master Card, Visa Card & Amex accepted with phone & fax orders. P & P for most mixed orders: Aust. $6; NZ (airmail) $10. November 1994  69 VINTAGE RADIO By JOHN HILL A pair of old AWA C79 chassis Fixing vintage radio receivers for other collectors can be quite a challenge. This is the story of how a couple of old 5-valve TRF console receivers were resurrected. other had been recently worked on by someone else. For the purpose of this article I will refer mostly to the near original set. This one was worked on first so that I could become familiar with it before moving onto the modified one. I recently met a vintage radio collector by the name of Dick Howarth. Never have I come across a collector with Dick’s enthusiasm. In a time span of less than nine months (at the time of writing), Dick has collected no fewer than 15 early console radios with turned legs. This style of receiver is about the only type he is interested in. There is little doubt that consoles from the late 1920s and early 1930s are very collectable items and to obtain more than a dozen such receivers is evidence of Dick’s enthusiasm. It is not unusual for him to drive interstate just on the off-chance of finding an interesting old radio. Capacitor blocks Personally, I don’t care how many radios Dick finds or where he finds them. In fact, I hope that he keeps on finding them. Why am I so supportive? Because Dick wants me to do his repairs – that’s why! Not only is it paying work, it also helps extend my repair knowledge and supplies me with interesting material for my monthly column, as is the case this month. Two of Dick’s radios share similar chassis. They are a 1930 AGE 44A and a 1931 AWA 45E. Both use the AWA C79 chassis and I had these to repair at the same time. One was almost completely original while the The C79 chassis uses a considerable amount of paper capacitors. The capacitor block on the right contains many individual units, wired together internally, & has no less than 10 colour-coded lead-out wires. 70  Silicon Chip The chassis that had recently been worked on had already cost Dick $150 and yet no attempt had been made to replace the numerous paper capacitors throughout the set. The only capacitors replaced were three 15µF electrolytics. Now some of these old receivers are a bit daunting to work on if one is unaccustomed to sets of this vintage. Although the C79 is a relatively simple 5-valve TRF type receiver, it does not look at all simple when you are working on it. One of the main problems is the use of capacitor blocks which contain multiple units of bulky paper capacitors. Along the front of the chassis there are three metal cans, each containing three 0.25µF 1000V capacitors, while a much larger block capacitor is housed under a pressed steel cover mounted on top of the chassis. This cover also houses a tapped high-tension choke. The big block capacitor is a bit of a nightmare because there are 10 coloured leads coming from it that go to various connection points throughout the circuit. One has to be careful when disconnecting this block capacitor because it has to be duplicated with modern capacitors and reconnected as it was originally. It is necessary to make an accurate sketch showing which coloured wires go where. As there are two black, two light brown and three blue leads, one must be attentive. The fact that This large pressed steel can houses the tapped high tension filter choke (still in the can) & a huge block capacitor. the colours have faded doesn’t help either. Block capacitors have been dealt with in a previous story. It should be sufficient to say that, in the case of these two C79 chassis, the capacitors were more than 60 years old and it is unreasonable to expect them to still be in working order. They were replaced without hesitation! Tuning setup These two old radios from the early 1930s have other odd characteristics apart from the huge wad of paper capacitors. Following is a brief description of some other notable aspects of the C79. The tuning setup is unusual in that it uses three single tuning capacitors which are interconnected (ganged) by a network of steel belts and pulleys. To find mechanically coupled independent tuning capacitors in 1930-31 receivers was a surprise. I had been under the impres­sion that that idea had gone out of fashion several years before. The valve line up for the C79 is fairly standard for the era and consists of three 24As, a 45 output and the usual 80 rectifier. The 24A is a radio frequency (RF) tetrode, while the 45 is a directly heated output triode. The volume is controlled by a This metal can contains three 0.25µF paper capacitors. After 64 years, the wax that sealed the capacitors from at­ mospheric moisture had shrunk away from the can & had become useless. wirewound potentiometer which varies the screen voltage on the RF valves. This technique differs from the more usual cathode bias arrangement. The volume control was in good condition. Another oddity is the electrodynamic loudspeaker. First the speaker cone has a soft leather outer rim suspension to give it flexibility. And second, the field coil has a fairly high im­pedance of 7500 ohms and is placed directly across the high tension supply. It is unusual items such as the C79’s speaker that makes repairs to these early AC receivers fairly difficult –especially if the set is to remain reasonably original. As far as I’m concerned, hard to find spare parts are Dick’s problem. He has to chase around and locate these out-of-the-ordinary bits and pieces – not me. While both C79 chassis are driving speakers of the original type, one of them came from Queensland and it was possibly sheer good luck that it was found when it was needed. Usable spares in good condition are becoming quite difficult to find. The tapped high-tension choke has been previously mentioned and, as luck would have it, both chassis had their chokes intact. There is also a much smaller choke mounted at one end of the chassis in a pressed steel can. There are two such cans actually; one houses the choke while the other The paper capacitors have been replaced with modern polyester types. Faulty capacitors cause many problems and their replace­ment is a logical step in the restoration of old radio receivers. November 1994  71 This front view of chassis shows the dial & one of the two drive belts & pulleys used to interconnect the three separate tuning capacitors. The tone switch is in the foreground. popularity, prior to the universal acceptance of re­sistance-capacitance coupling. The aim was to provide the highest practical plate voltage for the driving valve, while still pro­viding a high value plate load. This would be particularly im­portant considering the high drive requirements of the type 45 valve. Subsequently, higher gain output valves made the more economical resistance coupled system a better proposition). The open circuit output transformer could not be repaired and a replacement was installed. As the new unit was a little smaller than the original, the 3-piece steel can that housed it had to be held together with an epoxy resin adhesive (Araldite®), otherwise it would have fallen apart. The original output trans­former filled the can and held the three pieces in place. Switching on The 80 rectifier valve sits between the coupling choke on the left & the output transformer on the right. Both these units were open circuit. The transformer was replaced, while a 0.5MΩ resistor was connected across the choke terminals. contains the output trans­ former. In one chassis, both units were open circuit while in the other chassis they were OK. Incidentally, this small chassis-mounted choke is used as a coupling device (in conjunction with a capacitor) to couple the detector valve to the output valve. It serves as a plate load for the detector. A previous repairer had inserted a 100kΩ resistor across the open choke connections which seems a logical and easy way out of the problem. However, it was discovered later, when the set was working, that a 0.5MΩ resistor gave much better results. 72  Silicon Chip It seems to me that many of these early AC-powered receiv­ers were more complicated than they really needed to be. In later years, all these elaborate and expensive chokes were removed from radio circuits. The field coil alone served the dual role of a high tension choke and an electromagnet for the loudspeaker – without the need for additional chokes in the high tension. As previously stated, a 0.5MΩ resistor was an adequate replacement for the open circuit coupling choke; so there wasn’t much need for that particular component! (Editorial note: choke-capacitance coupling enjoyed a brief period of After many hours of work, the receiver was finally ready for a tryout. Two seconds after switch on, it was apparent that all was not well. A dreadful loud buzzing sound was all that could be heard through the loudspeaker – not the sound I expected to hear. Now this speaker was the one that came from Queensland and I had been told that it was in good working order. It had been plugged into another working set and it functioned quite OK, so I had no reason to doubt it. But what I wasn’t told was that the speaker plug had been removed and the pin connections resoldered but not checked. As a result, the plug leads had been inserted into the wrong pins, resulting in the voice coil being wired across the high tension supply. No wonder it made such a noise! It took quite some time to work out what the problem was, for the simple reason that I had been told that the speaker was OK. It was only after trying another loudspeaker that I realised what was wrong. There is a good lesson to be learnt there. Don’t believe anything anyone tells you until you have checked it yourself! After a tune-up to align the three tuning capacitors, both sets were working really well. They are not brilliant performers by superhet standards but give the sort of performance one would expect from a 5-valve TRF type receiver. RESURRECTION RADIO Valve Equipment Specialists Repairs – Restoration – Sales This rear view of chassis shows the power transformer cover (left) & the high tension choke & capacitor block cover (right). Also shown is the type 45 output valve at the end of the chassis. The pair of C79s consumed a fair amount of time and there were a few worrying moments. However, they are now back inside their elegant cabinets and they look and sound really good. Cabinet restoration My favourite is the AWA 45E. It is an attractive looking set and Dick has put a lot of time into restoring the cabinet. In this instance, an entirely new front panel has been made to replace the original, which had a broken fretwork. The replacement panel has a lighter coloured veneer than the original and the two toned effect is most pleasing. Dick does his own cabinet refinishing and they get better with each one he does. So next time you’re at an auction VALVES – 1200 types in stock    EL34/BCA7 matched $30 ea.    6L6GC matched $28 ea. Parts are available for the enthusiast, including over 900 valve types, high voltage cap­a citors, transformers, dial glasses, knobs, grille cloth etc. Circuit diagrams for most Australian makes and models. Send SAE for our catalog. WANTED: Valves, Radios, etc. Purchased for CASH Call in to our NEW showroom at: 242 Chapel Street (PO Box 2029), Prahran, Vic 3181. Phone: (03) 510 4486; Fax (03) 529 5639 where there are a few old radios going under the hammer, say “Hello!” to SC Dick – he’s bound to be there! Above: this massive old electrodynamic loudspeaker works surprising­ly well for its age. The 7.5kΩ field coil is wired across the high tension, not in series with it, as was the case in later years. Left: the Radiola 45E in all its glory. This particular cabinet had badly damaged fretwork & a new front panel has been made to replace it. The lighter tone of the new panel looks even better in real life than it does in a black & white photograph. November 1994  73 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 COMPUTER BITS BY DARREN YATES Visual BASIC for DOS provides Windows-like user interfaces The Visual BASIC package includes two large manuals – one a programmer’s guide & the other a command reference manual. The program also supports an extensive on-line help system. Designed to replace Quick BASIC 4.5, this DOS version of the popular Windows program will run all QB4.5 & DOS’s QBasic programs & allows you to produce Windowslike user interfaces. But is it that much of an improvement? Visual BASIC has certainly renewed interest in a language which many purists (read “C programmers”) had previously dis­ missed as a toy. It’s certainly now the easiest way to create Windows programs that run, look and feel just like those expen­sive big-company applications. However, reading through the reference manual and looking at all the financial commands that are available, you quickly get the feeling that it was designed mainly with the economist in mind. The lack of almost all hardware control commands certainly hasn’t endeared it to those of us who like to plug bits and pieces into the back of our PCs. Many of you have read our “Computer Bits” series where we have made use of Quick BASIC 4.5. Although it may be a good language and used by many small businesses, Microsoft’s decision to no longer support it probably means that its life span is coming to an end. Or is it? We recently upgraded our software to the new Visual BASIC for DOS in the hope that it would contain enough hardware control commands to make it worthwhile. All over the packaging, they make the claim that it will run all QBasic and QuickBASIC 4.5 pro­ grams. In fact, if you look through the November 1994  77 The programming environment displays the code editor as soon as you boot up. It has quite a few similarities to the old QuickBASIC 4.5. The menu box on the right is used to change between the code & form editors. monochrome monitors with no graphics facility, we can only hazard a guess that this may be the reason why text-only screen windows are available. For a language created in 1992, this does seem a bit archaic, particu­larly when you consider that the soon-to-be released Windows 4 won’t even run on a 286 machine, let alone on an XT! Memory requirements are at least 640Kb of RAM but it will support XMS (extended) and EMS (expanded) memory if your PC has it – sort of. So long as you’re prepared to run your application from the programming environment – that is, from within Visual BASIC – you’ll be able to use the upper memory. However, if you prefer to run compiled applications from the DOS prompt, then you’re stuck with the 640Kb limit. In this respect, it hardly seems much of an improvement on QB4.5. Of course, by running DOS 5 or later, you can push most of DOS into the upper memory area and have around 600Kb left for your application. That said, we would have thought that it would­n’t have been too hard to incorporate E/XMS driver support in the compiler. The pluses? The code here is for CALC.FRM, a basic function calculator. This comes with VB for DOS & gives you an idea on how to program using this system. By clicking on the up arrow, you can make the code editor full screen size. manuals, the QB4.5 com­mand set is actually a subset of VB for DOS. This thankfully means that all QB4.5 programs can remain alive for some time yet. And more importantly for those of us who like to “tinker” and play around with our PCs, it means that all of the QuickBASIC hardware control commands have been retained in their past for­mat. However, if that’s the case, what are the new features in this Visual BASIC for DOS? Well, its main selling point is its ability to create a DOS version of the Windows user interface with command buttons, dialog boxes, directory listings and the like. While these can make it much easier for a user to run programs, the 78  Silicon Chip interface is designed to run from the text screen only – so you can’t produce any fancy graphics or company logos. This is disappointing but more on this later. Hardware requirements One of the reasons for this is probably due to the fact that VB for DOS will run on any 8088-based PC. Note that it won’t run on an 8086 machine. If you want VB to run on your old XT, you’ll have to open the lid and have a peek inside to see which processor you have. What you need to look for is a 40-pin dual in-line (DIL) IC. It will either be marked 8086 or 8088. If it’s an 8086, then you’re out of luck. As many, if not most, XTs used Well, one thing that no one can take away from Visual Basic for DOS is its mouse control command support. Now you can add mouse support to all your programs by simply adding in the appropriate commands. You don’t need to know anything about the mouse hardware or interrupts. This is one feature that everyone will agree was badly needed on QB4.5. The manuals, although a bit confusing at times (aren’t they all!), have been split into two 650-page plus volumes – one a programmer’s guide and the other a command reference man­ual. The programmer’s guide contains all the peripheral information such as converting programs from QB4.5 to VB and describes how to produce a Windows-like interface. It also includes a compatibili­ty chart between VB for DOS and Windows, Quick­BASIC, QBasic and even the old GW-BASIC. The reference manual contains detailed information on each command, as well as programming examples for most of the com­mands. Most of this is also found in the on-line help system The complier is said to be more efficient in creating code which means that your programs will run faster. One good thing they suggest is that you can load your QuickBASIC programs into Visual BASIC, compile them and they’ll run just the same as before, only faster. Product support The form editor is where your graphic screens are designed. You are limited to block graphics which is disappointing but it allows all PCs to use your programs. The menu box on the left allows you add a variety of tools, including command buttons, directory boxes and ASCII graphics. This window shows you the possible subroutines which can be modified in the code editor. The numbers to the right of each subroutine are the sizes to the nearest kilobyte, while the “cmd” before each subroutine indicates that it is based on a command button response. which will tell you almost all that you need to know. How is it to use? If you’re used to QuickBASIC 4.5 and its programming envi­ ronment, then it won’t take you too much time to get used to the new format of VB. As we mentioned in the VB for Windows review, programming is now based on what is called “object oriented programming” or OOP. Instead of writing your programs in the conventional manner, you have to take into consideration what the user could be doing. If you have a series of command buttons appearing on the screen for example, you must consider that any one of those buttons could be activated and you have to write code to handle that. When programming, you’ll find yourself swapping between the user interface editor and the programming editor. The user inter­face editor allows you to create screens called “forms” which the user will see. These are created using a process that’s similar to using a desktop publishing program. You click and drag out marques to indicate the size of the item you wish to put on the screen, whether it is a command button or a dialog box. In this respect, it is very similar to the Windows version. We had a few questions to ask Microsoft on how some aspects of the language worked. So we decided to ring up the product support division of Microsoft, just as an ordinary customer would, to get some help. After ploughing through their infuriating phone system, we were told we’d be charged $35 for each call made. When pressed, we were told that “product support is not included in the purchase price of most Microsoft products”. Come on Microsoft, can’t we have just one call? The other alternative is to look at some of the computer books from companies such as Que Corporation and others. They have produced quite a few good books on both the DOS and Windows version of VB. If you desperately need to use EMS or XMS memory in your compiled programs, you will require the professional version of Visual BASIC. With this version, you also get the ability to produce compiled code which is optimised for either 286 or 386 processors but at $765 RRP, or more than twice the cost of the standard version, the price seems a little steep. Conclusion If you have an investment in Quick BASIC and you’re looking for the upto-date product, then Visual BASIC for DOS is it. But if you don’t need to create a Windows-like interface, then you may be better off sticking with what you’ve got. We also feel that it could have been made to do a whole lot more. Had they included the option of having the windows operate in VGA mode, it would have been almost ideal and a huge leap above QuickBASIC 4.5. Instead, it’s more of an upgrade for Quick­BASIC rather than a “whole new programming system”. At the time of writing, the recommended retail price of Visual Basic for DOS is $295 but don’t expect to get any support for that price – support SC costs extra. November 1994  79 How to plot patterns directly to PC boards Making prototype PC boards is usually time consuming & is sometimes a hit-or-miss procedure. But by using an X-Y flat bed plotter & a special type of pen & ink, good quality single or doublesided PC boards can be made quite quickly. By JOHN CLARKE A necessary part of the work we do at SILICON CHIP involves making PC boards for our prototypes. Every design that we pub­lish, apart from the circuits in Circuit Notebook, must be built and tested before publication. It’s our way of checking that the design works as it should. Making one-off PC boards is an integral part of any elec­tronic design and development process. It enables a prototype to be built and tested before a large number of final production boards are made. Prototype PC boards can be sent out to be made by printed circuit board manufacturers or they 80  Silicon Chip can be made on-site where the design and development takes place. The advantage of making boards on-site is that they can be finished in a relatively short time. Sending out a PC board pattern to be made by a manufacturer may take several days. Of course, for complex multi-layered boards, a professional board manufacturer is the only place where a prototype board can be successfully made. Of the boards produced to date by SILICON CHIP, most have been single sided and, in rare cases, double sided. These can be made with relatively simple equipment. An exception was the main PC board used in the Remote Control Preamplifier pub­ lished in September and October 1993. This board was too large (350 x 230mm) to be made by us at the time and so it was made for us by RCS Radio Pty Ltd. This company can produce prototypes as well as quantity boards and they can supply the majority of PC boards featured in SILICON CHIP. While in most instances we produce our own boards, the process used has not been without its problems. Let’s describe how we have produced prototype boards for the last seven years and why we have now adopted a new process. The old process Our printed circuit boards are designed using Protel Auto­trax, from Protel Technology Pty Ltd, a Tasmanian based company. Prior to 1992 our PC board artworks were produced using Bishop Graphics tapes and pads laid onto clear film. This latter method gave us a ready made artwork but the CAD-produced artwork needs to be printed out before the PC board can be made. We use a laser printer for this task and print directly to 3M transparency film specially made for use with laser printers. Alternatively, we print to paper and then photocopy onto transparency film. In either case, we have a positive artwork. Rather than go through the process of making a negative, as required for Riston-coated boards, we use a positive photo resist material which is brushed onto the blank PC board after it has been thoroughly cleaned. The board is then baked in an oven (or electric frypan) to harden the coating. (Some other types of photo resist available in a spray can do not require baking but they are quite a bit more expensive). The positive artwork is placed over the coated PC board and exposed using UV fluorescent tubes in a light box. Once exposed, the PC board is developed in caustic soda solution to dissolve away the UV-exposed portions. It is then etched using ammonium persulphate or ferric chloride in solution. After etching, the resist is removed using methylated spirits. Finally, the board is drilled, trimmed to size and coated with a clear protective lacquer to prevent the copper from oxidising. Alternatives There are a number of variations to this basic board making process, the most popular being with “Riston” pre­coated board. The disadvantage of precoated boards is that they require “safe” light for handling and cutting and they cannot be stored indefinitely. Safe light handling means that whenever the light proof container holding the precoated board is opened, it must be done in a room where the lighting is of a type that does not affect the UV- sensitive coating. Apart from the high cost and the need to handle it in safe light, Riston precoated board is very good for prototype use. We have usually coated our own boards with positive photo resist because it is quick, cheap and you only need to coat the board needed at the time of processing. However, the particular posi­tive photo resist we used is not supplied any more due to its carcinogenic nature. Spray cans of photo resist which are not carcino- An ultrasonic bath is necessary when it comes to cleaning the pen. The main bath is filled with warm water, while the pen itself is immersed in a small quantity of methylated spirits in a small plastic container. genic are available, although these are very costly. Problems One of the main problems we experience with our PC board production involves the transparency films produced by the photo­copier or laser printer. The black areas tend to be not dense enough to block all the light during UV exposure. This causes pin spots over the copper areas of the board and in severe cases can cause open circuits in the tracks. The problem is more prevalent on larger boards. Another problem occurs when exposing the coated board in the UVlight box. Any warping in the board can mean that the artwork does not sit in close contact with the copper. This causes faulty exposure and the job has to be done again. These problems could be solved but not without considerable time and expense to improve a system which is essentially messy anyway. New method Since all our PC board patterns are produced with a CAD system, on Protel Autotrax, the computerised output could be printed out in many different formats including a dot matrix printer, laser printer, inkjet plotter or X-Y pen plotter. It is this last format that interested us. If the computer could plot out the printed circuit pattern onto paper using an X-Y plotter, it could also print the pattern directly onto the PC board. Then the board would be directly ready for etching. A printed circuit board could then be made without the need for photo resist coat­ings and UV exposure and development. While the concept sounds simple enough it needs the right pen and ink. The ink needs to be resistant to being washed off in the ammonium per­sul­ph­ate solution which is used at about 60°C. And as this story demonstrates, the right pen and ink are now available. Our first tests were done using a Roland 980A A3 flat-bed plotter. This particular plotter did not have sufficient pen height adjustment to cope with the thickness of the PC board material which is typically about 1.5mm thick. We solved the problem by placing a small washer in the pen adaptor to raise the pen tip by 0.5mm. Once we set the pen speed correctly, the plot­ting results onto the copper were excellent. There was no sign of un-inked sections nor was there any tendency to form globs of ink onto the copper surface. We tested the ink in hot (60°C) ammonium persulphate solution and etched the copper from the board. At no time was the ink removed from the copper during this etching process. The ink coating on the etched copper November 1994  81 This photograph shows a fully plotted PC board which is now ready for etching. Note that the discoloration visible in the centre of the board is due to a lighting effect when the photograph was taken – the board itself had been thoroughly cleaned with Ajax® powder & steel wool just prior to plotting. board was then easily removed with methylated spirits. The accompanying photographs show the results which are consistently good. With these initial tests proving successful, we subsequently purchased a Roland DXY-1150 A3 flat-bed plotter and have found the technique to be reliable, producing cleanly etched boards every time. Procedure These are the steps we now use to produce prototype PC boards with a flat-bed plotter. First, the copper surface is thoroughly cleaned with Ajax® powder and soapless steel wool or a Scotchbrite® scourer, to remove any traces of oxide and oil. When rinsing the surface with water, the water should flow across the copper without the tendency to “bead”. Beading means that there is still oil remaining on the copper. The copper surface is then dried with a blow dryer or a hot air gun. Avoid wiping the surface with a towel since it will leave lint on the surface and thus lead to poor plotting results. Once the board is dry, do not touch the copper surface with your fingers. If you do so, you will inevitably leave fingerprints which must be cleaned off again before plotting can proceed. Next, you need to know where to place the PC board onto the bed of the plotter. The way to check this is to make an initial plot onto paper. That done, place the PC board onto the plotter so that it is centred over the plot area and secure it at each corner with adhesive tape. The plotting speed should be set to a slow rate so that the ink has time to flow as the pen traverses the copper surface. We 82  Silicon Chip found 100mm per second (4-inches per second) suitable for our pen size. The pen was a Staedtler Mars Plot tungsten carbide 0.35mm-diameter cross cut type and the ink is a special formulation, also made by Staedtler, for this application. The ink dries quickly, so the pen must be capped immediately after plotting has been completed. The copper is etched in hot (60°C) ammonium persulphate solution. (We have not tried ferric chloride solution, although it should work just as well.) Once etched, the ink is easily washed from the PC board with methy­lated spirits. After drying, the copper is coated with a protective PC board lacquer. Cleaning the pen Since the ink dries so fast, there is a danger that it will clog the pen if it is not cleaned thoroughly, using methy­ lated spirits. Since the emphasis is on thorough cleaning, the only practical way to is use an ultrasonic cleaning • System Requirements CAD software with HPGL print format. • Flat-bed X-Y plotter, Roland DXY-1150 or equivalent. • Staedtler 757PL3CS Mars Plot Tungsten Carbide 0.35mm dia­ meter cross groove pen. • Staedtler 75PL07H2PC plotter adaptor. • Staedtler 48523SAR-9 solventbased ink. • Ultrasonic cleaning bath, Altron­ics A-0100. bath. We used an ultrasonic bath from Altronics (Cat. A-0100) which is currently priced at $219.00. It comes with a small plastic tub so that only a small quantity of methylated spirits is required to clean the disassembled pen. The procedure is to use warm water in the main bath and the tub of methy­ lated spirits is placed into this. The water couples the ultrasonic energy into the small tub and the ink just streams out of the pen. Several bursts of cleaning may be necessary to remove all the ink from the dis­assembled pen, using clean methy­ lated spirits each time. You may wish to use rubber gloves too, to stop the ink from staining your fingers. Some points should also be mentioned. The plotter must be a flat-bed type, preferably A3 size. The type of paper hold system, whether magnetic or electrostatic, is not important since the PC board will need to be held down with tape at each corner. The pen tip height must be sufficient to clear the top of the board and the pen tip should be a cross groove type to allow sufficient ink flow. A tungsten carbide tip is recommended to reduce pen tip wear. Finally, there are other possibilities which are now possi­ble with the plotter. Artwork can be drawn directly onto front panels and overlay diagrams could be plotted on the top side of PC boards. Acknowledgement Our thanks to Mike Matthews of CAD Consumables & Con­ sultancy, Suite 3/83 Hartnett Drive, Seaford, Vic 3198 (PO Box 1049, Frankston, Vic 3199). Phone (03) 782 4000 or fax (03) 782 4011. Mike kindly supplied us with a sample Staedtler tungsten carbide cross groove pen, plotter adaptor and the Staedtler 48523SAR-9 solvent-based ink. CAD Consumables also sells Roland X-Y plotters and the SC full range of Staedtler pens. REMOTE CONTROL BY BOB YOUNG Modellers with dedication; Pt.3 This month, we continue the story of John and examine his involvement in model car racing. In doing so, we will look at the development of model car racing technology over the last 20 years or so, to the high-power models of today. When I first met John, he was building and driving full-size racing cars so I guess that the progression to model racing cars was fairly natural. As we have seen from last month’s story, John’s first love seems to be model railroading and when he takes on a job he does it with great flair and energy. One striking feature of John’s workshop is the sheer volume of model car equipment hung neatly in racks and from hooks on the wall. There are chassis of all types and descriptions that effec­tively present a full history of R/C car technology over the past 20 years. In this story, we will examine the development of this technology in some detail but first a little background on model R/C racing. The International Federation of Model Auto Racers (IFMAR) is the world governing body for R/C racing. This is divided into various divisions and John is the president of the One Eight Scale division. The Pacific region, in turn, is governed by the Far East Model Car Association (FEMCA). I will give you one guess who is the president of this erstwhile body – right again, our friend John. Under this umbrella shelters the Australian Associa­tion of R/C Model Car Clubs. As you can see then, model R/C racing is well organised and there are vast numbers of people who race or enjoy running R/C models of all types. John’s own collection of wheeled vehicles ranges from model tanks to high performance race cars, with racing trucks, electric cars, scale semi-trailers and mammoth scale racers all thrown in for good measure. John’s son Stewart is a world-class one-eighth scale car driver and the pair make up what can only be described as the ultimate dynamic duo. Their showcases are loaded with trophies from all over the world and it is interesting to speculate who dragged who into the business of R/C racing in the first place. However, I think it has now settled down to the usual arrange­ment: father builds the models and the son has all the fun driving them. Talking with Stewart is fascinating as he explains the technological explosion that has taken place in model cars, as it has in all fields of human endeavour. The series of photos in this article show the progression of that technology but they do not adequately capture the actual feel of that development. When you see all of the bodies lined up side by side, the first thing that strikes you is just how complicated the newer vehicles are. More than that however, the new models are so substantial in construction, yet weigh in at not much more than their fore­ bears. This is made possible by exotic new materials such as glass-filled Nylon, carbon fibre, etc. Motor size Photo 1: the first in a line of model race cars. This is fitted with an OS .15 engine capable of about 0.3 hp. It has a rigid front axle, small tyres, no gearbox, no diff & a simple centrifugal clutch. However, the most striking feature, to me at least, is the size of the motors. Admittedly, the car in photo 1 is only fitted with an OS .15 but in those days the OS .15 (2.5cc) was only fractionally smaller than the OS .21 (3.5cc) and externally both motors looked almost identical. Incidentally, the figures .15, .21, etc refer to the November 1994  83 Photo 2: this chassis is quite capable of absorbing the 1.4hp from the K & B .21 motor fitted to it. Here we see a flex chassis fitted with a simple differential, single disc brake & independent suspension but still fitted with a simple 2-wheel drive at the rear. Photo 3: here we see the first of the 4-wheel drive cars from around 1985. This car is a P.B. X-5 & features such advanced items as a progressive locking differential & rear wheel roll steer­ing which is adjustable to provide over or understeering when cornering. It has a 2-speed automatic gearbox & 4-wheel drive. swept volume of the motor in cubic inches. This is the American system of engine sizing. The English system uses cubic centimetres (cc) and the English sizes are given in brackets. These days, the American system is the most commonly used. Compare the size of the motor in photo 1 (circa 1972) with the size of that in photo 4 (1994). The 1994 motor is still only a .21 (the maximum 84  Silicon Chip allowed under the rules) but it looks substan­ tial enough to be a modern .49 aircraft motor. This increase in size has come about because of the requirements for more cooling and stress containment, due to the very high RPM these motors are pulling. Cooling problems Cooling in model cars has always been a major problem, particularly as the original motors were mainly designed for model aircraft, where copious quantities of cooling air were available. Thus, the cooling fins of the old model aircraft motors were grossly inadequate for motors intended to spend their life locked up inside a plastic body, away from a high-speed airflow. The original fix was a bolt-on heatsink and the car in photo 1 shows a primitive bent aluminium heatsink of this type. This type gradually gave way to the bolt-on finned heatsink which in turn gave way to the dedicated replacement cylinder head. This came with a very substantial extended heatsink and replaced the original cylinder head of the model aircraft motor. While all this was going on, the motor rework boys were beavering away at squeezing out every last drop of horsepower possible. The result has seen motor power skyrocket and thus the need for more and more substantial castings in the crankcases and more heatsinking again. Likewise, cylinders, pistons and conrods have all increased in size. The results of this development are shown quite clearly in the series of photos presented with this arti­cle. For example, the OS .15 (from memory) had a rating of about 0.3hp at about 10,000 RPM. These are approximate figures only as none of us can remember that far back. In those days, a good .60 would deliver about 1hp at 10,000-12,000 RPM. Compare this to the motor shown in photo 2 (circa 1980). David Hyde won the Austra­ lian one-eighth scale sports GT championship with this car. The motor (K & B .21) gives out 1.4 hp, a remarkable increase. Compare this then to the motor shown in photo 4 and here we are looking at a Rossi .21 which develops 2.3 to 2.4hp. The results of this phenomenal increase in power are cars that are capable of 125km/h on a 90-metre straight, with acceler­ ation of 0-100km/h in under three seconds! Incidentally, Stewart tells me that from about 1980 onwards, the model car fellows have been getting good results with the newer synthetic oils. Oil such as EDL and WB have been giving excellent results with mixtures containing as low as 8% synthetic oil, 2% castor oil, 20-30% nitromethane and the rest being methanol. Photo 4: this car exhibits the rampant technology of today. It has a motor fitted with a mini-tuned pipe giving out 2.4hp, an automatic gearbox, 4-wheel drive with changeable overdrive ratios bet­ween front & rear wheels, centrifugal clutches, Sprague clutch­es in the gearbox, front wheel drive & independent suspension. It is all made from exotic materials. Stewart tells me that the castor oil is to provide the smoke which acts as a guide for obtaining the correct running mixture. I suspect however that the castor oil also provides the upper cylinder lubricant required for the extremely high head temperatures encountered in model engines. Here I must add my usual warning that these are not my recommended figures and that you use synthetics other than those mentioned above at your own peril. Personally, I have never had any luck with synthetic oils, but I have also never used the above lubricants. I certainly intend to try some of Stewart’s fuel in the near future and I will keep you posted on the results. Chassis development Returning now to the actual car chassis, it is obvious that we are now faced with a very serious problem. How do you control or absorb this amount of power, especially into a chassis as primitive as that shown in photo 1? A quick look at it reveals the inadequacies: a rigid front axle, small tyres, no gearbox, no diff, and a simple centrifugal clutch which even then was inade­quate and broke on the second run. There is no way that this chassis could absorb 2hp or more. Photo 2 shows a chassis which has been developed to a large extent. This chassis is quite capable of absorbing the 1.4hp from the K & B .21 of that day. Here we see a flex chassis fitted with a simple differential, a single disc brake and independent suspension but still fitted with a simple 2-wheel drive at the rear. John and Stewart did extensive re-manufactur­ ing on this type of car to get the performance they required. The kit manufacturers had not yet caught up with the enthusiasts. Photo 3 shows a vastly superior car, circa 1985. Here we see the first of the 4-wheel drive cars and the kit manufacturers are starting to close the gap. This car is a P.B. X-5. Still heavily remanufactured, it nevertheless represents a quantum leap in chassis design. The technology in this chassis is staggering. This car features such advanced items as a progressive locking differential, rear wheel roll steering which is adjustable to provide over or understeering when cornering, a 2-speed automatic gearbox, and the very useful (some would say essential) 4-wheel drive. The 4-wheel drive is particularly clever and features Sprague clutches, or what are commonly known as one-way bearings. Thus, when the rear wheels slip or spin, the power is transferred to the front wheels via the Sprague clutches. Now we have a chassis capable of absorbing all of the power you can cram into it. By now it is starting to become obvious that tyres are starting to become an issue, just as in full size motoring. Space does not allow a detailed examination of this problem, which could fill a column of its own. Suffice to say that the real skill of the driver is in his ability to assess a track and fit the correct tyres for that day. This is particularly difficult when visiting strange tracks where you only have one or two days prior to the competition to prepare your car. The whole business of model car racing is an intricate and detailed science and it is easy to see how the enthusiasts become wrapped up in beating the problems presented by this very demanding sport. Photo 4 shows the latest in the line of development and here we see rampant technology: a motor fitted with a mini-tuned pipe giving out 2.4hp, an automatic gearbox, 4-wheel drive with changeable overdrive ratios between front and rear wheels, cen­ trifugal clutches, Sprague clutches in the gearbox, front wheel drive and independent suspension. And it is all made from exotic mate­rials. This is virtually a full kit with little remanufact­uring and the overall finish, design and construction of the kit is immaculate. So what is left to separate the men from the boys on the race track if it is possible now to just walk into a shop and buy kits such as this? The four scales featured in these photos tell part of this story. These are used for precise balancing of the cars. I am not going to reveal just how the balance is correctly set but suffice to say that the knowledge required to set up a car correctly is not easily come by. Finally, a few words about the radio systems. Stewart uses simple 2-channel radio sets with few bells and whis­tles but is very particular about the brand and even the model number of the receivers he uses. He runs the whole radio on 7.2V but finds only certain receivers will operate satisfactorily on this voltage, hence his choice of mainly older model receivers. He is also very fussy about servos and servo transit times. He feels that some of the new servos are too fast and has settled on transit times of about 0.36 seconds as being ideal. He raises a serious objection to modern servo savers, stating that they are no longer powerful enough to handle the torque from the modern servo and need to be SC doctored to do so. November 1994  85 PRODUCT SHOWCASE Tektronix TSG95 Pathfinder PAL/NTSC signal generator In the past, Tektronix has been renowned for its tele­vision test equipment intended for use in broadcast stations but it has had little to offer TV maintenance and installation tech­nicians. Now, in a significant move, it has produced the TSG95 Pathfinder, a complete PAL/NTSC signal generator. The TSG95 is a handheld instrument with a two-line liquid crystal display and it can be powered from internal batteries or an external mains 12V plugpack. The generator’s outputs are 1V composite video via a BNC socket and audio left and right channels via 3-pin XLR sock­ets. For PAL, 20 different signals can be selected and for NTSC, 16 signals. For PAL, the available signals include the following: 75% & 100% colour bars, 75% & 100% bars over red, red, blue and green fields, multiburst, 5-step gray scale and conver­ gence (crosshatch). For NTSC, the available signals include: SMPTE bars, multi­burst, NTC7 composite and combination, 5-step gray scale, FCC composite and black burst. The available audio signals comprise 13 tones from 50Hz to 20kHz or a sweep signal selectable from the tone menu. Three tone levels are available (0, +4dBu & 8dBu) and an audio click sequence can be selected as an aid in identifying the left and right channels in an installation. A unique feature is character ID. Up to eight messages, each containing two 16-character lines, may be stored for later re­call. One message may be inserted into the video test signal and up to four may be cycled into the test signal in a continuous loop (displaying each message for 1-9 seconds). Creating the ID is simply a matter of typing it in using the alpha- These are two of the PAL TV patterns available. At left is the convergence (crosshatch) pattern, while at right is the 86  Silicon Chip numeric keypad; there is no need to scroll through the alphabet for each character. We’ve used the instrument and found that it works well and would 100% bars over red pattern. Note that the TSG95 identifier can be turned off if necessary. be just the ticket for anyone with a need for a selection of TV patterns and audio signals from a small handheld instru­ment. Our sample test pattern photos include the TSG95 identifier but this may be turned off if desired Fluke’s first autoranging DSO Fluke has introduced a digital storage oscilloscope (DSO) which features fully autoranging atten­ uators and timebase. The new PM3394A CombiScope oscilloscope is part of the CombiScope family of instruments that combine digital storage with an analog oscilloscope. The autoranging innovation is part of Fluke’s commitment to make test instruments easier to use. Fully autoranging attenua­tors and timebase enhance and may even supersede Autoset, a feature common on most oscilloscopes. Auto­ set operates only once when the corresponding button is pressed, while autoranging operates continuously on both the attenuators and timebase to maintain an optimal signal display even when the signal changes. A TM5320 digital signal processor running at 40MHz ensures that the PM3394A has an almost instantaneous response to signal changes. The PM3394A has three processors dedicated to different instrument functions. This means that mathematics and autoranging features, for example, do not slow down other parameters, such as the response to changes in control panel settings. Probing a circuit with the new PM3394A is easier than ever before. During troubleshooting, the – just one of the many selections available. The Tektronix TSG95 Pathfinder is priced at $1595 plus sales tax. For further information, contact Tektronix toll free on (008) 02 3342. user can probe test points while concentrating on the circuit and not on the operation of the scope. The PM3394A allows the user to keep both hands on the work without reaching for the attenuator or timebase controls every time an adjustment is necessary. Autoranging works simultaneously on more than one channel. Input and output signals are continuously tracked and displayed on screen. A special windows display mode ensures that traces remain in an allocated screen area. This gives a clear non-overlapping view of each trace while maintaining high vertical resolution for detailed measurement results. The autoranging time­­ base has two modes of operation: the traditional 1-2-5 step mode and the variable timebase mode, which maintains the same num­ ber of signal periods on screen. This is achiev­ed by a variable sample clock, not just a rescaling of the display. The new series consists of two 4-channel models with 100MHz and 200MHz bandwidths (PM­ 3384A and PM3394A), and two “2+2” channel models, again with 100MHz and 200MHz bandwidths (PM3382A and PM3392A). All models have a serial interface for hard copy and PC communications as standard. A GPIB/IEEE 488.2 interface can be specified as an option. The GPIB interface supports remote con­trol commands that conform to the new industry-standard SCPI protocols (Standard Commands for Programmable Instruments). For further information, contact Philips Scientific & Industrial, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 8222. November 1994  87 Reference with low knee current GEC has a new range of 3.3V high-precision references that have a typical knee current as low as 15µA with a typical temperature coefficient of 15ppm/°C. Using a bandgap design, the SRC330 provides a stable 3.3V reference without the need for an external stabilising capacitor. The SRC330 has an operating temperature range of -40°C to 85°C, with a current range of 20µA to 5mA. The reference is available in a low profile SOT-23 surface mount package as well as standard 2-pin and 3-pin TO92 formats with a choice of tolerance rating of ±3, ±2 and ±1%. For further information, contact GEC Electronics Division, Unit 1, 38 South St, Rydalmere, NSW 2116. Phone (02) 638 1888. Versatile stereo mixer for discos Designed for mixing stereo sources together, this unit has been tailored to meet the needs of discos and dance K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed 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 88  Silicon Chip parties. There are four stereo inputs, three for phono or line inputs (switch­ able) and one which accepts signals from a tape deck or CD player (switchable). A 7-band graphic equaliser can be switched in to tailor the sound to suit the venue. The case is a standard 19-inch rack size so that it can be easily mounted in disco consoles or racks. Illuminated stereo VU meters monitor the output levels. Headphones can be used to individually monitor inputs while cueing up, before adding the input to the mix. A crossfader allows fading between any of the stereo inputs. There are two microphone inputs, one a local input with a talk-over switch that drops the music level while the DJ is talking. The front panel has a goose-neck mounting plate to make mic placement over the console easy. The second mic input has a low-cut switch to reduce the possibility of feedback into the microphone at high volume. Connections are made via the rear panel. Microphone inputs use 6.5mm phone sockets and the stereo inputs and outputs use RCA sockets. Finished in powder coated black enamel, the mixer re­tails for $379 (Cat AM-4216). For more information, contact the Jaycar Electronics store closest you. Radio telemetry with phone/fax phone based alterna­tives, especially in remote areas. For up-market applications, the range of USA-sourced Proxim 900MHz 242Kbits/s wireless modems has been expanded to include 2.4GHz 1.6M­bit/s units and a range of OEM card level products for engineering clients wishing to integrate spread spectrum technol­ogy into their systems. For further information, contact McLean Automation, PO Box 70, Freemans Reach, NSW 2756. Phone (045) 796 365. McLean Automation has continued to expand the telemetry side of their short haul, licence exempt, radio link technology. Their Australian sourced ‘Local Knowledge’ low-speed half-duplex wireless RS232 link now has the option of an inbuilt Austel approved phone/fax modem. This makes the units more suitable for tele­servicing and data logging applications where the host or remote systems are not within cabling distance of a PSTN outlet. The internal phone/ fax card means the system can be pro­ gramm­ ed to dial out reports from a remote radio-linked site to a fax mach­ine or E-mail equipp­ ed host. This integrated solution is a cost effective alternative to cellular Removable hard disc drives Teac have a new dual docking bay that fits into a standard 5.25-inch drive slot. The kit comes with one removable drive, with a second available as an option. Drive capacities vary from 250-540Mb, giving the docking bay a total capacity of 1.08Gb, with an IDE interface. Having a removable drive means that data can now be locked away at night. While in use, the drive can be locked into the docking bay, preventing unauthorised removal. Dual slots allow a second drive to be inserted to backup data in far less time than a tape backup. The second slot can also be used with multiple discs to provide mass storage for CAD and desktop publishing packages. A carrying case lined with foam is supplied to protect the drive while in transit. Data can thereby easily be transported without fear of damage. The removable drives have no exposed circuit boards and may be inserted or removed while the machine is still running. The driver software supplied with the kit takes care of the problems asso­ciated with the operating system finding out that the hard disc has been removed. For more information, contact Rick Stanford at Southend Data Storage, PO Box 25, Menai, NSW 2234. Phone (02) 541 1006. Yokogawa’s pocket DMM Yokogawa has released a new pocket-sized digital multimeter which has a 3200 count and bargraph display. The ultra compact size and one hand operation, along with data hold, auto ranging, auto power off and a high speed sampling (12 times/sec for bar­graph), makes this meter convenient and versatile. The battery compartment is easily accessible and it uses standard button cells. Measuring functions include DC & AC volts, resistance, continuity and diode test. For further information on the Model 7536 03 Pocket Digital Multimeter, contact Yokogawa Australia, 25 Paul St North, North Ryde, NSW 2113. Phone (02) 805 0699. November 1994  89 Silicon Chip With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). June 1990: Multi-Sector Home Burglar Alarm; LowNoise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/ Square Wave Generator, Pt.2. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In HomeBrew Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance ORDER FORM Please send me a back issue for: ❏ September 1988 ❏ November 1988 ❏ April 1989 ❏ May 1989 ❏ June 1989 ❏ July 1989 ❏ September 1989 ❏ October 1989 ❏ November 1989 ❏ December 1989 ❏ January 1990 ❏ February 1990 ❏ March 1990 ❏ April 1990 ❏ June 1990 ❏ July 1990 ❏ August 1990 ❏ September 1990 ❏ October 1990 ❏ November 1990 ❏ December 1990 ❏ January 1991 ❏ February 1991 ❏ March 1991 ❏ April 1991 ❏ May 1991 ❏ June 1991 ❏ July 1991 ❏ August 1991 ❏ September 1991 ❏ October 1991 ❏ November 1991 ❏ December 1991 ❏ January 1992 ❏ February 1992 ❏ March 1992 ❏ April 1992 ❏ May 1992 ❏ June 1992 ❏ July 1992 ❏ August 1992 ❏ September 1992 ❏ October 1992 ❏ January 1993 ❏ February 1993 ❏ March 1993 ❏ April 1993 ❏ May 1993 ❏ June 1993 ❏ July 1993 ❏ August 1993 ❏ September 1993 ❏ October 1993 ❏ November 1993 ❏ December 1993 ❏ January 1994 ❏ February 1994 ❏ March 1994 ❏ April 1994 ❏ May 1994 ❏ June 1994 ❏ July 1994 ❏ August 1994 ❏ September 1994 ❏ October 1994 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PCCompatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/ VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. February 1992: Compact Digital Voice Recorder; 50Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Low-Cost March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2 July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Peripherals For The Southern Cross Computer; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags: More Than Just Bags Of Wind; Building A Simple 1-Valve Radio Receiver. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6; Switching Regulators Made Simple (Software Offer). April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/ CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 July 1994: SmallTalk – a Tiny Voice Digitiser For The PC; Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11; Philips’ Widescreen TV Set Reviewed. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Beginner’s Dual Rail Variable Power Supply (±1.25V to ±15V); Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, December 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. November 1994  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Bridging the LM3876 amplifier The LM3876T amplifier as featured in the March 1994 issue of SILICON CHIP presents many excellent qualities for such a simple circuit. Unfortunately, it does not deliver quite enough power, so I would like to bridge two of these units together. A problem arises due to the low impedance that bridging presents to an amplifier. I have been told that single chip amplifiers do not cope well with low impedances when bridged and driven with full power supply for 8Ω loads. Is this so? What is the maximum expected power from two bridged LM­3867T’s and will bridging them downgrade their performance. Will they accept a signal at an output impedance of some 2400Ω from a valve preamp? (G. F., Henley Beach, SA). • You can bridge two of LM3876T amplifiers together to deliver around 100 watts into an 8Ω load. They cannot be used to drive a 4-ohm load in bridge mode because each amplifier “sees” a load impedance which is half the actual load; ie, 2Ω. In other re­spects, the performance of the LM3876T will be little different from that of a single amplifier driving a 4-ohm load. A Suggestions for future articles I have two suggestions for future articles. First, I’d like to see plans for the building and installation of a comprehensive security system for an average household. The system should include a range of different sensors for a number of different sectors, a backup power supply, keypad controls, and whatever else a good general household security system usually includes. Second, how about an article on interfacing external devices with Macintosh computers. (V. R., no address supplied). 92  Silicon Chip low impedance signal source will not present a problem. The main challenge in obtaining the best performance from monolithic amplifiers such as these is to design the PC board to give single point earthing and to minimise interaction between supply leads and the signal paths. This latter factor can have a far greater effect on performance than is realised by the “golden ear” brigade who tend to worry more about esoteric capacitors and highly expensive signal and loudspeaker leads. Capacitor voltage ratings I was alarmed to read the last three paragraphs of the letter from D. H. of Annandale in “Ask Silicon Chip” of July this year and I’m surprised that you made no comment on it. (It con­ cerned a near-disaster resulting from operating a capacitor directly from the mains). It scared the daylights out of me because I had an exactly similar setup running 24 hours per day under my own house as part of an emergency lighting system. There must be hundreds of such things around Australia, since as D. H. said, the circuit was published every year • We have already published a microprocessor controlled bur­glar alarm in September and October 1992 and a much simpler design in June and July 1990. Both were compatible with various sensors and had backup batteries. If you require copies of the articles, we can supply the relevant back issues at $7 each, including postage. We are not able to help with articles on interfacing to the Mac­ intosh. As our recent reader survey reveals, very few of our readers have access to a Macintosh and even fewer it seems have any expertise in this area. The same applies to our own staff. for many years in at least three of the major electronics catalogs and it was very convenient way of powering a LED without having to use a special power supply. It has since disappeared from the DSE catalog and is marked “not recommended” in Jaycar’s. Now I know why, although I think they should either explain why or delete the circuit altogether, if it is actually as dangerous as it seems. And that is the point, I suppose; maybe you didn’t comment because you don’t think it is all that dangerous and that D. H. was dead unlucky. I would like to see an authoritative opinion on this because, as I said, there must be many of these things around, and probably most of the owners still aren’t aware of the possible consequenc­es. I was able to arrange an alternative supply from a trans­former belonging to an entirely separate installation, so I can now sleep soundly again! (J. K., Kenmore, Qld). • As far as the letter from D. H. was concerned, we did not feel that a comment was really necessary since his letter said it all – you got the message, after all. However, perhaps we can use your letter to emphasise the point. The real problem with such circuits is that they did not specify 250VAC-rated capacitors. Anything else is suspect. We would extend the remarks to include any circuit where DC rated capacitors have been included in high voltage AC circuits. Fast charger for nicads Congratulations to Darren Yates on the production of your simple but elegant Nicad Fast Charger (SILICON CHIP, May 1994). At last, I feel, we have a simple and versatile solution to an otherwise difficult problem, especially in a field situation – almost! On behalf of the thousands of scuba divers and ex-divers around Australia, I would like to ask you to modify your circui­try to suit their needs. We use a combination of two but most usually four 4A.h D-size nicads or an equivalent lantern pack in underwater torches and photographic equipment. The recharge time available between successive dives is usually in the order of 2.5 hours. Perhaps a simple top-up from the car battery may be all that is needed rather than a controlled and complete discharge/recharge cycle, leaving that for the next day. I’m sure that the TEA1100 circuit could be modified easily, however the design subtleties and desirability of 0.5C, C or 2C charging in these heavier duty circumstances is beyond me. I thank you in eager anticipation. Secondly, the circuit certainly solves the problem of nicad self-discharge over time. However, the quoted values raise yet more questions: (1) A quoted value elsewhere for average float charge of 0.01 to 0.05C. What is your preference? (2) The same source suggests continuous steady and even float charging of nicads over extended time is to be avoided due to damaging internal crystal growth in the cell. Is this theory or fact? (3) Your pulsed current “trickle“ charging design, LED indicat­ed, suggests this to be the preferred method. What value of pulse current, in terms of cell capacity C, do you recommend and is the duty cycle important? (4) Is pulse trickle charging, as a method of float charging nicads, suitable for long term or permanent circumstances; for example, float charging a 9V nicad clock radio backup battery? (C. O., Hoppers Crossing, Vic). • As far as we can determine, there is no difference in pulse or continuous current charging of nicads, as far as the cells themselves are concerned. The overriding reason why pulsed current designs have come into vogue is that you can use switch­mode circuitry and this largely eliminates the need for heatsinks on transistors. The comprehensive data article on the TEA1100 in the Sep­tember 1994 issue will show how other battery combinations can be charged although we do plan to publish a fast-charge design with voltage step-up from a 12V car battery. We do not have any information about float charging and the size of current although our feeling is that it should be as low as possible. Wok awound the clok I would like some more details on your Woofer Stopper. Will it work on kangaroos on the highway? There is a device called “Slo Roo” but it is about $300. Also would it affect birds as I would not like to upset them too much? All I want to do is keep the feral cats away from the ducks on our lake and the hares (I think) away from our young trees at night. I would also like to put one into the car for use on the highway if it would warn roos we were coming; for this it would have to be on all the time and I see from “Ask Silicon Chip” that somebody has had trouble leaving it on all night. Also, is it possible to direct the sound in a beam like a torch to target individual animals or have a limited range, say 10 metres? Would it be effective on cows and goats or could you give me frequen­cies for different animals and tell me where to obtain the infor­mation. I would also like to build a parabolic microphone. I have two Wok lids – one is 280mm in diameter and 55mm deep while the other is 290mm in diameter and 80mm deep but I do not know the formula for finding the focal point for the microphone. Also, should I use a normal microphone or a small electret? I would like to try recording bird calls. • It is likely that the Wok lids you have are spherical rather than parabolic in section but for this application that is of no importance. The focus of a parabolic/spherical reflector is at a distance equal to half the minimum radius, along the main axis. You can work out the radius, knowing the diameter and depth of the lids, by using the formula shown on the accompanying diagram. We suggest you use a cheap electret mic insert to try out the idea, after which you may wish to try a more expensive micro­phone. With regard to the Woofer Stopper, it will certainly work on cats and probably on kangaroos as well but it does not work on birds, as far as we have been able to ascertain. We don’t think it would be effective in avoiding collisions with kangaroos as it is not particularly powerful. We don’t know if it would work with cows or goats. November 1994  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $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. REAL TIME ICE!!! The only way to go. MOTOROLA 6805 EMULATOR and programmers. Prices and data from Graham Blowes, Mantis Micro Products, 38 Garnet Street, Niddrie 3042. Phone (03) 337 1917 (a/h), (03) 575 3349 (b/h). Fax (03) 575 3369. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ OSCILLOSCOPE: Hameg HM 205 Digital Storage CRO. As new condition with probes, comprehensive manual and case. $1100.00. Phone (065) 57 0341. HP DRAFTPRO PLOTTER: A1/A2 8 pen ink plotter with RS232 inter­face. Excellent condition. Paper, film and pens included. Price $4500 ono. Phone (02) 476 2244 BH. RACAL DANA 4003 DMM: 1uV-10V DC source, AV09, Paton PA-2 power analyser, Palec 10A shunt, Telemax insulation tester. Offers (02) 684 1729. WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & Rtty receiving program. Suitable for CGA, EGA, VGA and Hercules cards. Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip 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 TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.7, PO Box 1058, St Marys, NSW 2760. Ph: (02) 833 1146. Fax: (02) 623 5559. and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. MONITOR HARDWARE SIGNAL(S): a change takes place, a two-chip cir­cuit programmed by you in Basic uses a cheap 2400 modem to dial an alphanumeric pager and leave a numeric message. You can even “ring in” from any phone for an instant report. It’s Don’s Basic Stamp. Promo Disk $2. Don McKenzie, 29 Ellesmere Crescent, Tulla­marine 3043. Phone (03) 338 6286. CAPACITORS: Markon electrolytic 33,000µF 63V. $10ea plus postage. Phone (02) 399 9623. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” ($249 plus S/T & post), extra modules ($66 plus S/T & post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­dale, NSW 2350. Facsimile (067) 72 8987. MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. • • • • 350 Watt Power MOSFET Amplifier Module As published in the June 1994 issue of Silicon Chip. Kit price $159.00. Postage and handling $8.00. Payment by M/C, B/C, Visa, Cheque or Money Order. 3kg O/N Air Bag $10.00 Computer & Electronic Services Pty Ltd 27 Osborne Avenue, Trevallyn Launceston, Tasmania 7250 Phone 003-34 4218; Fax 003-31 4328 MEMORY & DRIVES PRICES AT SEPT. 28TH, 1994 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $58/54 4Mb 30-pin $208/198 2Mb 72-pin $125 4Mb 72-pin $230/210 8Mb 72-pin $470/420 16Mb 72-pin $815/745 32Mb 72-pin $1690/1500 MAC 6Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $395 $90 LASER PRINTER HP with 2Mb $200 COMPAQ CONTURA 8Mb $425 DRAM DIP 1Mb x 1 256 x 4 70ns 70ns $8 $8 IBM PS.2 THINKPAD L40/N33 90/95 8Mb 4Mb 4Mb $655 $280 $230 TOSHIBA 3100SX 46/1900 4Mb 4Mb $210 $260 SUN SPARC 10/20 16Mb SPARC 10/20 64Mb $965 $4080 DRIVES – SEAGATE 428Mb 14ms 3yr w 528Mb 12ms 3yr w 1052Mb 9ms 5yr w $325 $420 $995 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 INTELLIGENT INFRARED RECEIVER (ref SILICON CHIP, March 94). Now with 8 outputs. Use your TV or VCR infrared remote control trans­mitter to control your TV or hifi appliances with an intelligent infrared receiver kit. Also available infrared transmitters, preprogrammed and learning models. Coming soon: Economy Infrared Audio Control Kit. For details call BENETRON P/L (018) 20 0108. BINARY CLOCK - OCTOBER 1993: complete documentation supplied, includes introduction to binary, how it works, PLD source list­ings, conversion tables. Kit with PC board and all PELHAM components $75 plus $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 plus $5 p&p. Available from Prototype Electronics, 1/29 Stewart St, Parra­matta, NSW 2124. Phone (02) 890 2960; Fax (02) 630 3148. Pay by cheque, money order, credit card. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. 68705 DEVELOPMENT SYSTEM: In Circuit Simulator/Emulator and programmer board. Supports all 68HC705 SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. 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. November 1994  95 SmallTALK for PCs: voice digitiser for 286's and up Play speech on your PC's speaker with no sound card! 3 minute version $34.95 HDD version $39.95 Optional QLB/LIB libraries $14.00 All orders add $3.05 p+p. Send your cheque/order to: RAT Electronics AUSTRALIA PO Box 641, Penrith, NSW 2750 Ph: (047) 77 4745 Fax: (047) 77 4745 Microprocessor For Stereo Preamplifier Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). Also suits the Remote Volume Control (May & June, 1993). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9795644; Fax (02) 979 6503. SECONTRONICS Advertising Index COMPONENTS, COMPUTERS, ELECTRON TUBES S/H TEST EQUIPMENT, COMPUTER REPAIRS RECYCLED EPROMS: ALL ARE CLEANED, ERASED AND BLANK TESTED. 2716 2732 2764 27128 27256 $1.50 ea or 10 for $12 $1.50 ea or 10 for $12 $2.00 ea or 10 for $16 $3.00 ea or 10 for $26 $3.50 ea or 10 for $32 Altronics ................................ 74-76 Av-Comm..................................3,87 Computer & Elect. Services.........95 David Reid Electronics ..............19 Dick Smith Electronics........... 10-13 TRANSISTORS AND ICs 2N3440 $0.50 ea or 10 for $4 2N7000 $0.80 ea or 10 for $6 TIP122 $1.20 ea or 10 for $10 4023, 4024, 4049 $0.60 ea 10/$5 4040 $1 ea, 10/ $8; 4520 $1.50 ea, 10/$12 7406 $0.25 ea or 25 for $5 LM380N $2.50 ea or 10 for $20 DAC O8EP $5.00 ea or 10 for $45 Emona Instruments.....................89 QQV07/50 $15 6SG7 $6 1S2 $3 6AM6 $5 Macservice............................ 62-63 VALVES: 12AV7 $4 1B3GT $5 6J6WA $5 3D21 6U8A 6080WA 6X5GT $6 $6 $9 $5 Phone, mail or fax your orders. Credit cards accepted for orders $20 and over. Mail orders to PO Box 2215, Brookside, Qld 4053. Or shop sales at 143 Grays Road, Enoggera Qld. Hours: Thursday 4pm-9pm; Sat 9am-4pm. Phone (07) 353 4919, Fax (07) 855 1014. Instant PCBs................................95 Jaycar ................................... 45-52 Kalex............................................88 L & M Video.................................67 Oatley Electronics.................. 68-69 Pelham........................................95 Rat Electronics............................96 Resurrection Radio......................73 RCS Radio ..................................94 Rod Irving Electronics .......... 27-31 range including C4, C8, J2, K1, P9, C9, D9 & 68705P3, U3, R3 microcontrollers. For more information contact Oztechnics, PO Box 38, Illawong NSW 2234, Phone (02) 541 0310, Fax (02) 541 0734 Email oztec<at>ozemail.com.au. WANTED WANTED: made in USA or Western Europe audio valves, vintage audio equipment and books about valve technology. Contact Wai Kei Leung, Block B, 5th Floor, 7 Kweilin St, Shamshuipo, Kow­loon, Hong Kong. Fax: (852) 387 5560. WANTED TO BUY: Radio valves, loose, or in cartons, by keen col­lector. Will call almost anywhere. Phone (02) 759 2948. WANTED: Philips FM828 Band A mobile units, also UHF units suit­able for conversion to UHF CB repeater operations. Contact Woo­mera CFS Comm’s Officer after hours (086) 73 7306. CALLING ALL HOBBYISTS We provide the challenge and money for you to design and build as many simple, useful, economical and original kit sets as possible. We will only consider kits using lots of ICs and transistors. If you need assistance in getting samples and technical specifications while building your kits, let us know. YUGA ENTERPRISE 705 SIMS DRIVE #03-09 SHUN LI INDUSTRIAL COMPLEX SINGAPORE 1438 TEL: 65 741 0300    Fax: 65 749 1048 96  Silicon Chip Secontronics................................96 Silicon Chip Back Issues....... 90-91 Silicon Chip Binders..................IBC Silicon Chip Projects Book........IFC Silicon Chip Wallchart..............OBC Transformer Rewinds...................95 Yokogawa....................................19 Yuga Enterprise...........................96 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590.