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Vol.8, No.3; March 1995 Contents FEATURES 4 Electronics In The New EF Falcon, Pt.1 New engine management system has triple coil ignition – by Julian Edgar 11 Protection For Toroidal Power Transformers Fuse selection for short circuit & overload protection – by Michael Larkin 16 The Latest Trends In Car Sound, Pt.3 Building a Tube Sub-Woofer – by Julian Edgar 58 A Look At The 68000 Microprocessor Interface buses & registers – by Elmo Jansz 85 Tektronix TDS 784A TruCapture Oscilloscope TUNE SUB-WOOFER FOR CAR HIFI SYSTEM – PAGE 16 Can display up to 400,000 acquisitions per second – by Leo Simpson PROJECTS TO BUILD 20 Subcarrier Decoder For FM Receivers Tune into hidden FM transmissions – by John Clarke 32 50W/Channel Stereo Amplifier, Pt.1 Easy-to-build, no setting-up adjustments – by Leo Simpson & Bob Flynn 40 Build a Lightning Distance Meter It measures flash distances up to 19km – by Darren Yates 52 Wide-Range Electrostatic Loudspeakers, Pt.2 Building the treble & bass panels – by Rob McKinlay 69 IR Illuminator For CCD Cameras & Night Viewers Use it for security or wildlife observations – by Branco Justic TUNE INTO HIDDEN FM TRANSMISSIONS – PAGE 20 SPECIAL COLUMNS 46 Serviceman’s Log Doing the rounds with remote control – by the TV Serviceman 63 Remote Control Building a remote control system for models; Pt.3 – by Bob Young 72 Computer Bits Record real-time video with the Video Blaster FS200 – by Darren Yates BUILD THIS 50W/CHANNEL STEREO AMPLIFIER – PAGE 32 74 Vintage Radio The innaugural vintage radio swap meet – by John Hill 80 Amateur Radio Build a simple 2-transistor CW filter – by Darren Yates DEPARTMENTS 2 Publisher’s Letter 9 Mailbag 10 Circuit Notebook 50 Order Form 82 Product Showcase 90 Ask Silicon Chip 93 Notes & Errata 94 Market Centre 96 Advertising Index REMOTE CONTROL RECEIVER FOR MODELS – PAGE 63 March 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER NSW's new truck monitoring system Most people love to see the introduction of new technology. It usually brings improvements in the way that things are done and in the long run, usually produces economic advantages, both to those directly using the new technology and to the community at large. But there are times when the introduction of new technology gives cause for alarm and perhaps, concerted opposition. What prompts this thought is the introduction by the Road Transport Authority in New South Wales of a new computer linked monitoring system for trucks and buses. The idea is that there will be 20 speed cameras throughout the state that will be linked to a central bureau at Flemington in Sydney. Four of these cameras are now operating, at Bargo, Gundagai, Wyong and Deepwater, near Tenterfield. Not only will this system's cameras be able record any truck or bus travelling at excess speeds but by calculating the time of transit between any two monitoring cameras, it will be able to tell whether the vehicle has been speeding at other times along the way. By subsequently examining the vehicle's logbooks, the bureaucrats will also be able to tell if the driver has taken the regulation breaks. Now, given that there have been a number of very serious accidents involving trucks and buses in New South Wales and other states, you might think that this is desirable innovation by a government bureaucracy. Well, I don't think it is. In order to be able to work, the system will not just photograph those vehicles which are speeding - it will have to photograph every truck and bus which passes by. I reckon that this constitutes a gross invasion of privacy. In the past, if you exceeded the speed limit, you might expect to be caught by a speed camera operated by the police. But now, if you are a truck or bus driver, you will be photographed whether or not you are speeding! And why should the system be confined to trucks and buses? Obviously, with the capabilities of a modern computer network, there is no reason why it could not be used to track all cars travelling along the highways. Now you might be fairly relaxed about trucks and buses being continually monitored but think it through. This means that all trucking operations along major highways can be monitored by the State. The possibilities for abuse and corruption of this system are hair-raising. And when it is extended, as it surely will, to private cars, the police state will have finally arrived. If you're happy with that, fine. But if you're not, take a photocopy of this editorial and send it to your local politician along with a covering note that you want it stopped! 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 Electronics in the The XR6 is a factory-produced, high-performance version of the EF Falcon. Its 4-litre engine produces 164kW under the control of the newly-introduced EEC-V engine management system. The latest EF Falcon has a new engine management module with 88Kb of onboard memory. In addition, the system now features sequential fuel injector operation & triple-coil ignition. Pt.1: the engine management system 4  Silicon Chip The EEC-V Ford engine management system (pronounced ‘Eck-5’) replaces the EEC-IV system introduced on the Falcon in 1985. Initially used for controlling ignition and fuel delivery only, the system was subsequently upgraded in 1992 to also control automatic transmission and air-conditioner compressor operation. However, with these additional demands, the system was at its limits in terms of both input/output (I/O) and microprocessor throughput. The new EEC-V system now allows the incorporation of knock detection and control, as well as a multi-coil distributorless ignition system. In addition, the system’s greater pro- e new EF Falcon By JULIAN EDGAR Above: the EF Falcon 6-cylinder engine uses a new engine management system & a triple-coil ignition system to eliminate the distributor. cessor speed has translated directly to improvements in vehicle perfor­ mance, drivability, fuel economy and emissions. Microcontroller I/O The microprocessor in an engine management system must be able to sense physical parameters in the form of electrical signals. Two different types of sensors are used: analog and digital. Analog sensors provide a varying output voltage and measure factors such as throttle position, engine coolant temperature and intake air temperature. Digital sensors, on the other hand, provide either an “on” (logic 1) or “off” (logic 0) signal, or can deliver a variable frequency digital pulse train. The square-wave output from a speed sensor is a good example of this latter type. Analog sensors are read via analog to digital (A/D) conver­tors, while on/ off binary signals can be read by a low speed digital input port. The micro­ controller software reads the input port periodically to determine the state of the switch but this approach is appropriate only for inputs which change state at a frequency of less than 2Hz. For signals which change more rapidly than this, a high speed digital input is used. This allows an event to be captured closer to the time at which the transition took place. Output ports must also be suited to their specific applica­ tions. A low speed digital output (LSDO) is appropriate for the control of an air-conditioning compressor clutch, for example. On the other hand, a high speed digital output (HSDO) is necessary for a function that requires accurate timing control (such as fuel injector operation). For an output which repeats at a fixed time interval, it would be possible to use an HSDO and continually schedule the output events to generate an appropriate signal. However the software requirement makes this undesirable. Instead, circuitry which is activated once and then “forgotten” until a change in periodicity is required is used. These outputs use pulse width modulation (PWM) and are referred to as “Duty Cycle Outputs”. The 8065 microprocessor The 8065 microprocessor is based on the previous system’s 8061 but March 1995  5 MISSING TOOTH 6.5 AMP COIL PRIMARY CURRENT (WITH DWELL) Vp-p 6.5 AMP Fig.2: the coil primary current ramp is controlled so that it reaches its target value at the point where it will be fired. This reduc­es the load on the car’s electrical system. TOOTH CENTRE Fig.1: the crankshaft position sensor output waveform is used by the ECU to time the ignition and fuel injection systems. with several enhancements. The 8061 was a reasonably powerful 16bit chip which was optimised for high-speed, real-time applications. However, depending on which I/O mode it is oper­ated in, the 8065 can offer substantially more input and output channels. Table 1 shows the configuration chosen for the EF Falcon EEC-V system. A/D conversion The 20 channels of A/D conversion offer 10 bits of accuracy over the range from 0-5V. The time required for conversion is less than 30 microseconds, while events on HSDI ports have a capture resolution of 2 microseconds. HSDO’s are also accurate to within 2 microseconds. In addition, the 32Kb PROM of the previous system has been replaced with an 88Kb memo­ry, which Fig.3: the electronic ignition system uses a knock sensor to help determine the ignition timing advance. The sensor is screwed into the engine block. 6  Silicon Chip EDIS COIL PRIMARY CURRENT WAVEFORM allows for much greater software design flexibility. Ignition system design The EEC-V system uses a new distributorless ignition system on the 6-cylinder engine. Previously, most of the ignition-related activities were controlled by the EEC-IV’s 8061 micropro­ cessor, whereas the new system uses its own CPU. The ignition system, termed the Electronic Distributorless Ignition System (or “EDIS” in Ford parlance), replaces the con­ventional distributor with three individually controlled ignition coils. Each of these coils fires two spark plugs (in two cylin­ders) at once, with one cylinder fired on its compression stroke and the other on its exhaust stroke. The spark plug fired on the compression stroke uses far more of the available energy than the other simultaneously fired plug. The engine crankshaft position is sensed by a variable reluctance pick-up which is excited by a rotating sprocket with teeth spaced at 10° intervals. A KNOCK missing tooth SENSOR is posi­tioned at 60° before top dead centre for No.1 cylinder and this results in a distorted waveform (see Fig.1) which the EDIS CPU can sense. The EDIS CPU also calculates engine rpm from this sensor and this is then passed on to the 8065 CPU. The 8065 takes this speed information and, along with other information such as throttle position and intake air temperature, uses it to calculate the desired spark advance angle. This infor­ mation is then passed back to the EDIS CPU which carries out the necessary calculations to provide a spark at the desired angle of advance. The EDIS system also energises the coil primary in a way different to conventional ignition systems. Generally, the prim­ary side of the coil is energised well in advance of the required firing point. By contrast, EDIS uses a method of dwell control which predicts when a given coil should be turned on so that it reaches its target primary current at the point where it will be fired – see Fig.2. This not only reduces the load on the car’s electrical system but also reduces the need for current-limiting circuitry in the ignition system. Knock detection Spark timing has a major influence when it comes to obtain­ing the best fuel economy and performance. At the same time, engine knock (detonation) must be avoided to prevent engine damage. Detonation can occur due to variables in engine build, the fuel octane rating, the air/fuel ratio and internal carbon build-up. In fact, the need for a safety margin between engine-damaging detonation and optimal outcomes has seen the ignition timing retarded by as much as 6° in some cars, with a consequent reduction in performance. To overcome this problem, EDIS uses a knock detector to sense engine detonation. The sensor is attached to the engine block and is used to measure vibration within a specific frequen­cy range. This frequency range was chosen by analysing the fre­quency of engine block vibration both with and without percepti­ ble knock and then selecting the range in which there was the most noticeable change. Specifically, a band about 600Hz wide and centred on 7.5kHz is used. Detonation occurs only during the firing stroke, hence the background noise of the valve train, crankshaft rotation and so on can be measured separately and used as a reference value. During firing, the knock sensor signal is constantly compared to this reference signal. If the threshold is exceeded, knock is deemed to have occurred and the EEC-V processor retards the timing for the next cylinder by 1°. If knock continues to occur, the spark advance is then retarded by either an additional one or two degrees for each cylinder, depending on speed and load conditions. When knocking is no longer detected, the spark timing for each cylinder is advanced in 0.25° increments until knock is again detected. As a result, the spark advance hovers just below the level at which audible detonation occurs. Fuel injection Two different systems of fuel injection are used in the EF Falcon range, one for the V8 engine and the other for the 6-cylinder engine. The V8 uses sequential injection with airflow measured by a hotwire mass airflow meter. The 6-cylinder engine, on the other hand, uses a combination of manifold absolute pres­ sure (MAP) sensing, intake air temperature sensing and an rpm signal to calculate the airflow mass. In the case of the 6-cylinder engine, the fuel injection system uses a heated exhaust gas oxygen sensor to provide con­stant feedback of the air/ SPARK PLUG LEADS DOUBLE-ENDED IGNITION COILS Fig.5: the 6-cylinder engine is fitted with triple double-ended ignition coils, with each coil used to fire two spark plugs simultaneously. In this system, one cylinder is fired on its compression stroke & the other on its exhaust stroke. TABLE 1: I/O Channels For EEC-V ECM fuel ratio to the Number of Channels ECU. This oxyType of I/O EEC-V (8065) EEC-IV (8061) gen sensor is also used to provide A/D Conversion 20 13 information to an Low-speed digital input 13 0 adaptive learn­­ing mechanism. High-speed digital input 8 8 This works as Low-speed digital output 24 8 follows. The sensor output values High-speed digital output 16 10 during closed loop operation are com­ Duty cycle output 9 0 pared with those predicted by the ECU as needed un- mixtures, then the correction values der the current operating conditions. are stored and applied when the enIf there is a difference between the gine is later being driven in open-loop amount of fuel the ECU predicted mode. This occurs under full throttle, would be required and the amount during cold conditions and when the being used to provide the appropriate engine is in lean cruise mode. ADVANCE (ø) KNOCK IDENTIFIED, TIMING RETARDED IN STEPS KNOCK AGAIN IDENTIFIED 1-2ø, DEPENDANT ON SPEED/LOAD TIMING RAMPS UP IN STEPS UNTIL KNOCK AGAIN IDENTIFIED 0.25ø KNOCK STOPS TIME (PIP SIGNALS) Fig.4: when knock (or detonation) is detected by the knock sen­sor, the ignition timing is initially retarded in steps of either 1 or 2 degrees (depending on the engine speed & load) & then re-advanced in 0.25 degree increments. March 1995  7 This photo shows the new EEC-V electronic control unit (ECU) on the left, while the older EEC-IV ECU is on the right. The EEC-V uses an 8065 microprocessor capable of over a million operations per second & has 88Kb of memory. Fig.6: a heated exhaust gas oxygen sensor is used to provide vital feedback on the air/fuel mixtures. The fuel injectors are fired in two banks, with cylinders 1, 3 and 5 operating as one bank and cylinders 2, 4 and 6 as the other. The banks are fired in response to the ignition signal pulses derived from the EDIS, with the injectors in each bank opening on every third pulse (ie, once per rev). During cranking, the firing frequency is increased to give better starting. Operating modes A number of different modes of operation are employed by the ECU: (1). Closed Loop Mode. This is where the oxygen sensor input is used to determine the air/fuel ratio being used. This will nor­mally occur after the first few minutes of engine operation, when the sensor has reached its operating temperature. (2). Open Loop Mode. The input from the oxygen sensor is disre­garded in this mode. This occurs for two reasons: (a) either the sensor has not reached its operating temperature; or (b) it is necessary to run the engine at air/ fuel ratios other than stoichio­metric (that is, other than at a 14.64:1 air/ fuel ratio). (3). Crank Mode. This occurs during engine starting. In this mode, the ignition advance is set at 10° BTDC, the idle speed control bypass valve is fully open, and the evaporated fuel canister purge is closed. The injector pulse width (and thus fuel flow) is dependent on engine coolant temperature. (4). Run Mode. Once the car has started (and if it doesn’t there is an Under­speed Mode to cater for this), the ECU switches to Run Mode. In this condition, the throttle position has a large con­trolling influence on fuel injection behaviour. (5). Cruise Mode. When the throttle position sensor output is within a certain range, the ECU selects this mode. The ignition timing is now calculated as a function of RPM, load and the coolant and intake air temperatures. The fuel flow is derived from the calculated airflow and then made richer or leaner to suit the coolant temperature. (6). Wide Open Throttle Mode. This mode is selected when the throttle position sensor exceeds a prescribed value. It selects a richer mixture than in other running modes to increase engine power. Note that the ignition timing remains the same, as it is already at optimal levels. (7). Limp Home Mode. If an electronic malfunction occurs, the system reverts to the following settings: the ignition timing is fixed at 0° BTDC; the canister purge is locked out; the injector pulse width is fixed at 3ms; the injectors are fired on the rising edge of each ignition signal; and the idle speed control valve duty cycle is set to 75%. A very rich mixture which is characterised by black exhaust smoke results, although the car can still be driven at speeds of up to 100km/h in this mode. SC Acknowledgement Fig.7: the injector firing modes for the 6-cylinder engine show that the injectors are operated in two banks of three. During normal running, they operate alternately on the rising edge of each third ignition pulse. During cranking, however, the firing frequency is increased (ie, each bank operates briefly on each ignition pulse) to give better starting. 8  Silicon Chip Thanks to Ford Australia and the Society of Automotive Engineers for permission to use material from the “SAE Australa­sia” journal of October/November 1994. MAILBAG Fax/modems can cause problems Your editorial of October 1994 mentions difficulties with sending facsimiles to people who don’t know how to operate their facsimile machine. I would like to whinge about the generally unsatisfactory way many people are using their facsimile machines. Amongst my pet hates are those who think they have sent me a facsimile, then ring a week later: “Didn’t you get my fax?” These people have their machine set so that it does not print a “satisfactorily sent” report. OK that is a waste of paper but most machines allow printing of an “inability to send” slip. To turn off all report­ing is irresponsible. On a humorous note, with a happy ending, I recently re­ceived a sequence of facsimiles from a person who on several occasions sent me two blank sheets from a machine he was not familiar with. It turns out that the machine was a recent in­stallation. Eventually, someone set the firm’s name and number in the facsimile’s handshake routine. Armed with this information I was able to send a facsimile which read “please stop sending blank pages, they are too hard to read”. He rang me and we worked out that he was sending facsimiles to everyone with the pages in wrong side up and was wondering why he had got no answers! Then there is the problem you refer to, caused by those who use a common line for voice and facsimile. They answer the phone and usually there is only one person in the establishment who knows how to handle the call if it is other than a speech call. I sometimes get up in the middle of the night to handle matters that may have been nagging my mind. Have you ever acci­dentally sent a facsimile to someone with a combined line at 1.00am? I have. My effort was not well received. Some machine-phone combinations handle this problem by answering the call, listening for a facsimile tone, then connecting to the facsimile machine, or ringing a handset, if it is a voice call. However, if the call has been launched through STD, the caller is being charged from when the ringing tone stops. This is exacerbated where a voice answering machine is used too. Then there is the unsolicited and inappropriate junk mail, pages of useless information – these go straight into the bin and a mental note is made not to deal with that firm. Courteous firms ring first and ask “will you give us your fax number and accept our regular transmissions?” A conversation usually follows, establishing our mutual interest or not and consequent cost saving for both of us. I may be old-fashioned but courteous treatment by a firm is usually an indication of how they are likely to do business with me. How about the person who sends a full A4-size page with one or two lines on it? – usually accompanied by a “Fax Cover Sheet” with fancy graphics and information that would have been better received as a 2-line header! Why not use a pair of scissors to cut the sheet short and save costs at both ends? Many problems are caused by facsimile cards in a PC. I tried one a long time ago, on a line common with my normal phone, and although the idea seemed to be working from my end, I soon realised that there were problems out in the real world I was trying to talk to. The cost of these “cheap” units is deceptive. I found out that a separate line cost me no more to install, with the ongoing rental costs being worth the convenience the separate line gave me. Another not so obvious point is that some firms seem to think that separate voice and facsimile numbers are an indication of how serious one is about one’s business. If you have separate numbers, you will be treated with more care and respect. Bob Nicol, Armidale, NSW. Solar tracker could be a hot box I would like to offer some comments about the Solar Tracker in the January 1995 issue. In full sun, the temperature in that electronics box will exceed 100°C, which may prove to be destructive. I suggest it be placed under SILICON CHIP, PO Box 139, Collaroy, NSW 2097. the panel or fitted with a sun screen so that only the sensors are exposed. It seems to me that a sun-tracker only needs to operate when there is a sun to track; at other times the panel should centre. The mercury switches could be arranged to do that. The night sensor could face south and operate a comparator which would switch from the centre position mode to the tracking mode whenev­ er the direct sunlight exceeded the average reflected southlight. B. Jolly, Tranmere, SA. Sun tracker circuit query I have waited for some time for a construction article on a sun-tracker. Now you have published one which is very good but I am puzzled by a couple of things about the circuit. Why is pin 4 of the 555 not connected to pin 8 as recommended in the National Semiconductor application notes for this device? And why is there no bypass capaci­tor on pin 5? I also believe it would be normal practice to provide separate gate resistors for the FET switches. Finally, why are there no power supply filter capacitors across the 12V supply?. Other than this I intend to build the unit as soon as I can get my hands on a PC board from RCS Radio. Cliff Wylie, Leumeah, NSW. Comment: while National Semiconductor do recommend that pin 4 is tied high, it is not mandatory for it to be so. Nor is a capacitor at pin 5 mandatory. Individual gate resistors for the Mosfets would normally be used in a switching circuit but since the voltages in this circuit are so static, they are not re­quired. Bypass capacitors for the supply are also not mandatory since the circuit is powered directly from a lead-acid battery. Having said that, there is no reason why you should not change the circuit to tie pin 4 high, add a capacitor to pin 5 and so on. We understand that RCS Radio Pty Ltd has produced a PC board with these modifications included. March 1995  9 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Pump control system uses LDT Most country households get their water supply from tanks via an automatic pump. This cycles on and off if the demand is less than the supply capacity of the pump. The result­ing pressure variations can be mildly annoying when under the shower and extended periods of cycling leads to premature pump failure. This control system overcomes both problems by returning the surplus output of the pump to its inlet whenever the flow sensor detects a demand on the system. The flow sensor uses a linear differential transformer to detect flow. This device has a central primary winding to magnet­ise a core and two identical secondary windings, one each side of the primary, connected in series but in opposite phase. With the core positioned equally in both secondary windings there is no output. Displacement of the core by the flow sensor valve produc­es a nett output from the secondaries and when this reaches 2 volts the Triac will fire on each half cycle. The Triac turns on a solenoid valve which then returns unwanted flow from the pump back to its inlet. The solenoid valve used is the 24VAC type commonly found in garden irrigation systems and this is rated for both inrush (at switch on) and steady currents. As the interrupted current from the Triac makes the solenoid just rattle, it is rectified and smoothed by the 470µF 25VW capacitor. To provide the required inrush current, Adjusting pulse-train mark-space ratio This circuit adjusts the mark-to-space ratio of an incoming pulse train with­ o ut affecting the fin frequency. Hex Schmitt 15Hz-150kHz trigger IC1 is connected SQUARE WAVE to buffer the incoming signal and the paralleled inverters drive C1 and the associated constant current source, Q1. What happens is that the output of IC1 pulls C1 and the collector of Q1 low on each negative transition of the input signal. Q1 then recharges C1, ready for the next negative transi­tion of the input signal. If trimpot VR1 is set for its highest resistance condition, Q1 is unable to turn on and therefore the waveform 10  Silicon Chip 4x1N4001 15VAC IC1 74C14 3 24VAC SOLENOID TR1 SC141D DIFFERENTIAL TRANSFORMER 8VAC 1500T 500T 1500T 0V PUMP OUTLET FLOW SENSOR VALVE BACKPRESSURE VALVE SOLENOID VALVE PUMP INLET TO HOUSE a non-linear resistor in the form of a lamp is used. This has a cold resistance of 3Ω and hot resistance of 20Ω. For construction details of the flow sensor and back pres­sure valves, send a stamped self-addressed envelope to the de­signer. W. Jolly, 2 Hextall Ave, Tranmere, SA 5073. ($40) 4 6 IC1a 2 470 25VW +5V 14 5 1 LAMP 6.2V 0.3A 12 13 11 10 470  D1 1N914 C1 .001 150  68k Q1 BC557 1k 2 MARK/SPACE VR1 10k 12 13 IC2a 8 3 1 7 passes through unchanged. VR1 controls the amount of current available to re­charge C1 during the space period. The effect is to vary the space period from about 100ns minimum to the maximum stipulated by the incoming waveform. IC2a, a quad exclusive-OR gate, buffers the output 10 OUTPUT 9 5 8 9 IC2 4030 14 11 N S1 6 4 7 INVERT signal and also provides the facility to invert the output waveform. This means that the mark-space ratio can be varied over the full range, by use of the invert switch and VR1. The maximum input frequency is 150kHz. G. Freeman, Nairne, SA. ($40) Protection for toroidal power transformers Toroidal power transformers are well known for the advantages of compact size, low hum radiation & good efficien­cy. However, they also draw heavy surge currents at switch-on & this can cause problems. This short article discusses fuse selec­tion for short circuit and overload protection. By MICHAEL LARKIN* Simple fuses in the secondary leg of a transformer may only provide short circuit protection. Such fuses may not provide adequate overload protection in many cases. Australian Standard AS3108-1990 calls for both short circuit and overload protection for transformers (refer clause 14). It is required by Australian Standard AS3000 wiring rules that one leg of an extra low voltage transformer secondary winding be fused. This is a minimum but it may not be the whole answer. For example, consider a 240V 300VA toroidal transformer supplying a 12V track lighting system. Normally, this track would take six 50W lamps but because the track may be physically quite long, the user may have seven, eight or more lamps plugged in. Hence, we now have a situation where the fuse, due to its lack of sensitivity, does not act and the transformer will overheat. There are several possible answers to this problem: (a) put a fuse in the primary; (b) put a thermal cutout in the trans­former; (c) put a thermal protective device in lieu of a fuse in the secondary leg of the AC circuit; and (d) fit a one shot fuse in the primary winding. Table 1 below is a summary of the recommended mains fuses to be placed in the primary toroidal transformer circuit. The fuse should be a slow-blow or anti-surge type to avoid being blown by the inrush current at switch-on. This switch-on surge is much higher than the inrush cur­ rent for typical conventional transformers. If too low a fuse rating is chosen, intermittent fuse operation will occur during “switch on” of the transformer. This is the nub of the problem. It is a matter of discriminating between genuine fault Table 1: Fuse Ratings Toroid Rating Fuse Type 625VA Slow Blow or Anti-Surge 500VA Slow Blow or Anti-Surge 300VA Slow Blow or Anti-Surge 225VA Slow Blow or Anti-Surge 160VA Slow Blow or Anti-Surge 120VA Slow Blow or Anti-Surge 80VA Slow Blow or Anti-Surge 50VA Slow Blow or Anti-Surge 30VA Slow Blow or Anti-Surge 15VA Slow Blow or Anti-Surge conditions and large inrush currents. The best options are (b) or (c), from a technical point of view. Option (c) may also be the best option from an economical viewpoint. Option (d) is not really a practical approach because once the primary fuse is blown the transformer is useless. Table 1 should be regarded as a guide only and is based on a standard 3AG fuse size 5mm diameter by 20mm long. These fuses are for the 240VAC side of the toroidal transformer. Ratings should be tested in the practical circuit. This is most important. Table 2 shows the characteristics of typical slow-blow fuses. Note that with a current equal to 50% over the rating, the fuse will take a minimum of 60 minutes to blow, or in other words, it takes virtually forever. This is an essential charac­teristic for the fuse in the primary of a toroidal power trans­former. However, while a correctly specified slow-blow fuse will protect a toroidal power transformer against a short circuit in the secondary it will not protect it against overheating where the overload is, say, 33%. This is equivalent to the overload quoted for the 300VA tor­oid in Current Rating the example above. To cope with this 8.0A situation, designers 5.0A need to specify a 3.0A thermal cutout in the primary wind2.5A ing. This will be 2.0A sensitive to any over-temperature 1.0A situation with­in the 0.8A primary win­­d ing of the trans­­former. 0.315A The normal tem0.25A perature setting is 0.125A 110°C but for high ambient situations, 130°C devices may be used. * Michael Larkin is the managing director of Tortech Pty Ltd, manufacturers of toroidal and conventional transformers. Their address is 24/31 Wentworth Street, Green­ acre, NSW 2190. Phone (02) 642 6003. Fax (02) 642 6127. Table 2: Slow Blow Fuse Duration Rated Current In 1.5 2.1 x In 2.75 x In 4 x In 10 x In Min Max Min Max Min Max Min Max 125mA-10A 60 min 2 min 200ms 10s 40ms 3s 10ms 300ms March 1995  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Car Sound, Pt.3: Building A Tube Sub-Woofer Car sub-woofers are now very widely used by those who wish to listen to music containing sub-100Hz frequencies. In this article, we show you how to build a car sub-woofer capable of reproducing frequencies down to 25Hz. By JULIAN EDGAR The vented tube-type sub-woofer design shown here has several advantages over a conventional, built-in box design. These advantages are as follows: (1). compact size compared to many sub-woofer installations; (2). portability – the sub-woofer can be easily removed when more boot space is required; (3). can be used in cars with folddown rear seats, hatchbacks, station wagons, and mid-engine cars; (4). low cost (around $200 each); (5). effectiveness, with response down to 25Hz; and 16  Silicon Chip (6). good power handling capability, allowing the use of high-pow­ ered bridged amplifiers. Subwoofer design A large diameter, suitably enclosed woofer will generate good bass. However the problem is in fitting the required large enclosure into a car. As an example, the recommended vented box size for a typical 15-inch sub-woofer is 222 litres. That’s equivalent to a box size of 100 x 50 x 44.4cm, which means good­bye to the back seat or boot! On the other hand, a 10-inch driver with suitable specifi­ cations can be accommodated in a vented enclosure of just 50 li­tres. That’s less than one quarter the size required for a 15-inch driver! If two such 10-inch sub-woofers are used, their en­closures occupy less than half the volume of the 15-inch unit with only a slight reduction in effective cone area. Consequently, I decided to use two 10-inch sub-woofers, each with an enclosure volume of about 50 litres in my own car. However, the in-car results were so good that only one unit is really required – unless you want to shake the rear vision mirror so much that it is impossible to use! But how do you build-in two enclosures of about 50 litres each and still leave room to carry luggage if required? The answer is to build the sub-woofers into two 12-inch diameter tubes, one running down each side of the boot. The accompanying photos show how the tubes were fitted into the boot of my Subaru Liberty. The tubes are held in place by aluminium straps and, when bulky loads need to be carried, can be easily removed in just a few minutes. Plastic storm-water pipe (78cm long) is used for the main body of the enclosure. The end-pieces are cut from 16mm MDF & the speaker end-piece is shown here being trialfitted before being finally attached. Make sure that the end pieces are not undersized – it’s better to have to sand them back to ensure a tight fit. A sealant/glue such as “Liquid Nails” should be used to form an airtight seal & at least 16 countersunk screws (see text) should be installed around the periphery of the tube. The drivers are mounted at the front of the tubes and nor­mally pump bass through the back of the rear seat. Alternatively, if the rear seat is folded, the sub-woofers pump bass straight into the cabin. Building the unit The bass tubes are made from heavywalled (5mm thick) 32cm diameter plastic stormwater pipe. The cost from a plumbing supply house was $55 a metre. Note that this material The vents were made from 50mm-diameter plastic pipe fitted with an outside ring cut from a plumbing adapter fitting. Each vent was cut to a length of 54mm & sprayed with black paint before being fitted to the end-piece opposite the driver. is also available in sewer pipe form with a slightly thicker wall but the cost escalates to almost $80 a metre! The bass tubes were each cut to 78cm long, giving an inter­nal volume of about 60 litres with the end pieces in place. Once these pieces had been cut, the two 32cm-diameter end pieces for each tube were cut from 16mm-thick medium-density fibreboard (MDF). One end-piece has a hole cut into it to accommodate the driver, while the other has This view shows the completed enclosure, before the installation of the driver. The inside of the enclosure was lined with acous­tic material to damp out reflections. This material is actually dressmaker’s quilt wadding, which is about a quarter of the price of Innerbond. In addition, a thin layer of car carpet has been used to cover the outside of the tube & this was glued into place using contact adhesive. Parts List & Costs 1 10-inch sub-woofer, Jaycar Electronics Cat. CW-2166, $109 1 1-metre length of 32cm-dia. stormwater pipe, $55 1 10-inch speaker grille, Jaycar Electronics Cat. AX-3522, $14 1 1-metre length of 150cm-wide quilt wadding, $5 1 1-metre length of car carpet, $5 Miscellaneous: screws, “Liquid Nails” glue, scrap 16mm-thick medium-density fibreboard (MDF) for tube end pieces, loudspeaker terminal, speaker cable, $20 Total Cost: $208 each a 50mm-diameter hole to accept the vent tube. An electric jig-saw was used to make these cutouts. The end pieces are held in place by countersunk wood screws inserted from the periphery of the pipe, with 16 screws and a sealant/adhesive (eg, “Liquid Nails”) used to ensure an airtight seal at each end. Note that screws with parallel sides (not tradition­ al woodscrews) should be used to get maximum purchase when screw­ ing March 1995  17 The two bass tubes are held in position inside the boot using brushed aluminium straps. On the left is the amplifier which drives both the bass tubes & also the rear deck-mounted 3-way loudspeakers. into MDF. The large number of screws (16) proved necessary to ensure an airtight seal. Even tiny leaks can allow whistles and buzzes. Each tube was lined with a soft acrylic filling. This prevents reflections within the tube, which colour the sound and give the bass a hollow timbre. Innerbond speaker-box filling is available for about $9 a metre but very similar material can be bought from dressmaking shops under the name of quilt wadding. In this form, it’s about a quarter of the price. After testing various drivers, it was decided that the Jaycar CW-2166 had the right mix of low cost ($109) and perfor­mance. This woofer uses a rigid cast frame and has a polypropy­lene cone. Its free air resonance is 31Hz, while its power han­dling capability is quoted as 120 watts RMS and the sensitivity as 91dB. In addition, its Qts is a low 0.33, allowing it to be used in compact enclosures. In fact, the enclosure design recommended by Jaycar is perfect for use as a bass tube – a volume of 45 litres (with the acrylic filling, the tube I used would be very close to this figure), coupled with a vent 50mm in diameter and 54mm long. The speaker’s impedance is 6 ohms. Testing Testing was initially done using an Akai 45W RMS/channel home stereo amplifier and a standard graphic equalizer. Also used was a frequency generator. By feeding the frequency generator output to the sub-woofer via the amplifier, the frequency re­ Fig.1: this graph plots the performance of the author’s system. With the +12dB at 45Hz amplifier equalization switch activated, there is a peak in the frequency response of about 12dB at 31.5Hz. 18  Silicon Chip This is the view from the inside of the cabin when the rear seat is folded down. The sub-woofers are reasily removed when the full volume of the boot is needed by undoing eight wing-nuts & un­plugging two cables. Even with the seat back in its normal posi­tion, the bass is sufficient for most people! sponse (and any peaks or troughs) could be roughly determined by ear. In a domestic situation, the response sounded smooth but with plenty of punch. The next step was to mount one of the tubes in a car. My car sound system uses a mix of original and aftermarket equipment. The original Subaru front-end comprising a radio-cassette player and single CD player has been retained. The two front channels of this original system are used to drive the original dual-cone 6-inch speakers mounted in the front doors, along with a pair of Jaycar Super Tweeters which have been added to the front door sail areas (the triangular areas where the rear vision mirrors are). The two rear channels are used to drive the speaker-level inputs of a Coustic AMP-268 4 x 45W car amplifier and two of its outputs in turn drive rear deck-mounted Jaycar 6 x 9 3-way speak­ers. The other two channels of this amplifier were used to drive the twin sub-woofers via a built-in variable low-pass crossover network. With just one of the bass tubes connected, the bass was superb. The driver A steel mesh grille costing $14 was used to protect the driver. It is held in place using brackets & roundhead screws. showed no signs of being overloaded, even when driven by the amplifier in high-power bridged mono mode. In fact, my reaction was that if the bass was this good with just one bass tube, what would it be like with two? The answer is even better. Frequency response plot A visit to Adelaide car sound dealer Cartronics was made so that a Coustic Real Time Analyser could be used to check the system. This is effectively a spectrum analyser which records and prints the system’s in-car response. With the system being driven by a CD-recorded pink noise signal, and with the +12dB at 45Hz amplifier equal­ ization switch activated, the graph showed a peak in the frequency response of about 12dB at 31.5Hz. Being the sort of person who likes lots of bass, I am happy to leave the system with this boosted low-frequency response. On the other hand, purists could simply reduce the switched amplifi­ er bass boost to achieve a flatter response. Either way, the sub-woofers showed that they were capable of reproducing low SC frequen­cies with ease. March 1995  19 This photo shows the prototype ACS decoder installed in an old Harman Kardon AM/FM stereo receiver. Two aluminium brackets were used to suspend the decoder above the tuner board. A subcarrier decoder for FM receivers Many FM stations are now radiating piggyback signals with their normal stereo transmission. You can’t decipher these “hidden” signals using a standard FM receiver but you can by adding this low-cost ACS decoder. By JOHN CLARKE The jargon doesn’t sound very enlightening but ACS stands for Ancillary Communication Service. This is a technique whereby a normal FM broadcast transmitter carries one or two extra subcar­rier signals that ride “piggyback” along with the normal FM stereo transmission. These hidden transmissions have no affect on standard FM mono and 20  Silicon Chip stereo receivers. Only the main signal can be detected by such receivers, so most people are unaware that ACS signals are even being broadcast. To listen to these extra signals, you need to fit an ACS decoder such as the unit described here to your FM receiver. Despite this, you’ve probably already heard ACS broadcasts. Many department stores and shopping cen- tres now use this service to provide background music for their customers. And the program content is usually just straight music, with no voiceovers or advertising. Other ACS services include foreign language, news and spe­cial interest programs. Signal transmission Before we describe how our ACS decoder works, let’s take a look at how the ACS signals are added to the FM signal. A normal FM stereo transmission is made up of three compon­ents: (1) an L+R mono signal modulated from 0-15kHz; a stereo pilot tone at 19kHz; and a multiplexed L-R difference signal centred on 38kHz. These com- Fig.1: the ACS signals are produced by modulating subcarriers centred on 67kHz & 92kHz. These subcarriers are then mixed with the normal FM stereo compon­ents & used to modulate the main carrier. % MODULATION CARRIER STEREO CHANNEL STEREO PILOT 0 15 19 67kHz ACS CHANNEL 23 38 53 59 67 92kHz ACS CHANNEL 75 84 92 100 FREQUENCY (kHz) ponents are mixed together and used to modulate the main carrier out to 53kHz – see Fig.1. By contrast, the ACS signals are produced by modulating subcarriers centred on 67kHz and 92kHz. These two frequencies are well above the upper limit of the L-R difference signal to avoid interference. As a further precaution against interference, the ACS signal bandwidths are limited to just 6kHz. They are mixed at low level with the existing stereo components before being used to modulate the main carrier. ACS decoding At the receiving end, these ACS subcarrier signals are ignored by a standard FM receiver since they fall well outside the passband. In fact, the detected 67kHz and 92kHz subcarriers are effectively removed by the 50µs de-emphasis filtering. So, to detect ACS signals, we need to modify the receiver by fitting an ACS decoder immediately following the FM de­ modulator, before any filtering takes place. The ACS decoder described here can be switched to decode either ACS subcarrier (ie, either 67kHz or 92kHz). This is done using a single toggle switch; there are no other controls to worry about. The recovered audio 67kHz AND 92kHz INPUTS FROM FM DEMODULATOR decoder inside a separate case and run it from a suitable DC plugpack supply. We’ll have more to say about the installation later on. Block diagram Fig.2 shows the block diagram of the ACS Decoder. Its input signal is extracted from the FM demodulator in the receiver and is fed to two bandpass filter stages centred on the ACS subcarri­ er frequencies. These filters separate the ACS subcarriers from each other and from the other components of the normal FM stereo signal. S1a selects between the filter outputs, after which the selected sub­ carrier is boosted by amplifier stages IC2a-IC2c. The boosted signal is then fed into a phase lock loop (PLL) de­ modulator to recover the audio. Immediately following the PLL stage is a 150µs de-emphasis stage. This rolls off frequencies above 1061Hz, thereby reducing noise in the audio signal and compensating for the 150µs boost (pre-emphasis) given to the audio signal before transmission. Finally, the recovered audio is fed to the output via a low pass filter which removes the original subcarrier plus any other un­ w anted components above 6kHz. In summary then, the 67kHz and 92kHz subcarriers are first separated S1b 67kHZ BANDPASS FILTER IC1a,IC1b output is fed into an auxiliary input of an amplifier. Once fitted, the unit is very easy to use. All you have to do is tune your receiver to an FM station and select the appro­priate auxiliary input on the amplifier. An ACS signal will now be heard (provided, of course, that the station is transmitting ACS signals). If the station is transmitting two ACS signals, the alternative signal can then be selected using the toggle switch. Provided you live in a good signal area and have a reason­able antenna, the ACS signal should be quite clean. But don’t expect it to sound as good as a regular FM stereo signal. That’s because of the restricted bandwidth (6kHz) and the fact that the signal is mono only. In addition, an ACS signal has only rela­tively low deviation, so you’ll need a strong signal to avoid hiss. It should be possible to fit the ACS Decoder to most FM tuners and receivers, and even to many portable FM receivers. Basically, there are a couple of ways you can go about this. First, if there is sufficient room, the unit can be fitted inside the receiver itself and powered from an existing supply rail. In fact, the prototype was fitted inside an old Harman Kardon re­ceiver – see photos. Alternatively, you could mount the S1a 6kHz 12dB/OCTAVE LOWPASS FILTER AMPLIFIERS IC2a-IC2c PHASE LOCK LOOP DEMODULATOR 150us DE-EMPHASIS ACS AUDIO OUTPUT 92kHz BANDPASS FILTER IC1c,IC1d Fig.2: block diagram of the ACS decoder. The 67kHz & 92kHz subcarriers are separated out using bandpass filters & the selected subcarrier then amplified & fed to a PLL demodulator to recover the audio. Finally, the recovered audio is filtered & fed to the output. March 1995  21 22  Silicon Chip DEMODULATED FM 560pF INPUT 10k .0033 .0015 1.1k 9 10 10k 10k 1k .0047 B C VIEWED FROM BELOW E 10k 1.1k 13 12 .0033 .0015 VCC/2 I GO 92kHz TWIN TEE FILTERS 560  .0015 1.1k 8 2 3 .0027 VCC/2 67kHz TWIN TEE FILTERS 430  1k .0047 IC1c 10k 7 .0027 1k 4 IC1a 6 TLO74 11 5 .0027 VCC/2 10k VCC/2 10 +12V 10k IC1d 10k IC1b 560  .0015 1.1k 14 430  .0027 1k 1 .01 10k S1a 2 4 12 5 0V +15-30V PHASE LOCK LOOP DEMODULATOR 22k COMP OUT VCO IN 9 VCO OUT IC3 4046 7 VCO 16 1 B 150us DE-EMPHASIS .015 10k GND 10 16VW 1k Q1 BC548 POWER SUPPLY VR1 10k 10k 11 IC2b AMPLIFIERS 5 6 100k 10pF REG1 IN 7812 OUT 10k 10k 10 10 10 35VW 8 DEMOD IC2a 3 TLO74 2 92kHz .0015 10k 6 VCO 14 INPUT 3 COMP IN 67kHz S1b .0027 VCC/2 220pF ACS DECODER 92kHz 67kHz 100k 10pF 4.7k 4.7k E 0.68 C 7 220pF 10 16VW 10 9 VCC/2 +12V 6kHz FILTER 12 13 IC2c 0.1 .0033 3k VCC/2 .012 6.2k 6.2k 10k 8 4 14 +12V .01 ACS AUDIO OUT 1 11 100  IC2d 100k 100k 10pF PARTS LIST 1 PC board, code 06303951, 137 x 80mm 1 DPDT toggle switch (S1) 11 PC stakes 1 10kΩ 5mm horizontal trimpot (VR1) Semiconductors 2 TL074 quad op amps (IC1,IC2) 1 4046 CMOS phase-lock loop (IC3) 1 7812 12V regulator (REG1) 1 BC548 NPN transistor (Q1) This close-up view shows the completed ACS decoder board. It should fit inside most FM tuners & receivers & can be powered from an existing 15-30V DC supply rail. Note that the decoder will not interfere with the reception of normal FM stereo transmissions. out using bandpass filters. The selected subcarrier is then amplified and fed to a PLL demodulator to recover the audio. Finally, the recovered audio is filtered and fed to the output. Circuit details Refer now to Fig.3 for the circuit details. This can be directly related back to the block diagram. IC1a & IC1b form the 67kHz bandpass filter, IC1c & IC1d form the 92kHz bandpass filt­er, IC2a-IC2c are the amplifier stages, IC3 is the PLL demodula­tor, and IC2d is the 6kHz low pass filter. In greater detail, the input signal is picked off from the FM demodulator via a 560pF capacitor and coupled to pin 6 of IC1a via a 10kΩ resistor. IC1a and IC1b together function as cascaded twin-T filter stages centred on 67kHz. In the case of IC1a, the two 1kΩ feedback resistors and the .0047µF Fig.3 (left): the final circuit is based on two quad op amps (IC1 & IC2) & a 4046 PLL (IC3). Twin-T filter stages IC1a & IC1b form the 67kHz bandpass filter, while IC1c & IC1d form the 92kHz bandpass filt­er. The selected signal is then amplified by IC2a-IC2c & demodulated by the PLL. Q1 buffers the demodulated signal, while IC2d rolls off the response above 6kHz to reduce noise. capacitor to ground form one half of the twin-T filter, while the two .0027µF capaci­tors and the 430Ω resistor form the second half of the filter. Because the twin-T filter network has a high impedance at 67kHz, IC1a essentially functions with a gain of one at this frequency due to the 10kΩ feedback resistor. At the same time, frequencies on either side of the 67kHz centre frequency are heavily attenuated by the filter action. So IC1a allows the 67kHz subcarrier to pass through while drastically curtailing frequen­cies that are outside the pass­band. The output of IC1a appears at pin 7 and is fed to a second twin-T filter stage based on IC1b. Note that cascaded filter stages have been used here to ensure adequate attenuation of the adjacent stereo signals and the ACS subcarrier at 92kHz. Filter stages IC1c & IC1d operate in identical fashion to IC1a & IC1b, except that their passband is centred on 92kHz. Switch S1a selects between the two subcarrier frequencies and feeds the resulting signal to IC2a via a 220pF capacitor and a 10kΩ input resistor. IC2a, IC2b and IC2c each function as inverting amplifier stages with a gain of 10 and thus provide an overall gain of 1000. The 220pF capacitors at the inputs of IC2a & IC2c roll off the response below 67kHz, while the three 10pF feedback capacitors limit Capacitors 1 10µF 35VW PC electrolytic 4 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.68µF MKT polyester 1 0.1µF MKT polyester 1 .012µF MKT polyester 2 .01µF MKT polyester 2 .0047µF MKT polyester 3 .0033µF MKT polyester 5 .0027µF MKT polyester 5 .0015µF MKT polyester 1 560pF ceramic or MKT polyester 2 220pF ceramic 3 10pF ceramic Resistors (0.25W, 1%) 4 100kΩ 4 1.1kΩ 1 22kΩ 5 1kΩ 14 10kΩ 2 560Ω 2 6.2kΩ 2 470Ω 2 4.7kΩ 1 100Ω 1 3kΩ Miscellaneous Hook-up wire, solder, mounting brackets, screws, nuts, etc. the high frequency response to reduce noise in the signal. Demodulation IC3, a 4046 phase lock loop IC, has everything we need to decode the FM signal. It contains two phase comparators, a vol­tage-controlled oscillator (VCO) and a source follower. The signal from IC2c is AC-coupled to pin 14, after which it is buffered and fed to a phase comparator. This compares the incoming frequency with the VCO frequency at pin 4 and produces an output at pin 2. This output is then filtered and applied to pin 9. It controls the VCO so that it March 1995  23 6 1 2 3 Fig.4: install the parts on the PC board as shown here, taking care to ensure that all polarised parts are correctly oriented. It is a good idea to use PC stakes at all external wiring points. 1uF 2 3 10k 10k 0.68 .012 Q1 VR1 10k .01 1k 6.2k 3k 100k 220pF 1.1k 560 1.1k 1.1k 1.1k 560  1 10uF 22k 10uF remains in lock with the input signal. The filtered VCO control voltage represents the phase dif­ ference between the incoming signal and the VCO signal and thus represents the audio modulation on the subcarrier. However, rather than extracting the demodulated audio directly from pin 9, it is taken from the output of the internal source follower at pin 10 instead. This ensures that we don’t load down the VCO control signal and create further distortion. 6 .0015 10k .0033 .0033 IC3 4046 10k 10pF 6.2k 4.7k 4.7k 10k 10k 2x.0015 0.1 100 IC2 TLO74 10uF 10k 5 1 1 IC1 TLO74 10k REG1 .0027 4 10k 560pF .0033 10uF 100k 1 10k 2x.0015 10uF 35VW 100k 10k 1k 100k 10pF 2x.0027 10k DEMODULATED FM INPUT 10pF .01 .0027 220pF 10k 10k .0027 430  1k .0047 1k 1k 430  .0047 ACS AUDIO OUT GND S1 +15-30V INPUT 5 GND 4 .015 S1b selects the free-running VCO frequency by switching in the appropriate capacitor value between pins 6 & 7. When the .0027µF capacitor is selected, the VCO free-runs at 67kHz. Alternatively, when the .0015µF capacitor is selected, the VCO free-runs at 92kHz. VR1 sets the centre frequency and the locking range. Immediately following the PLL is the 150µs de-emphasis network. This network is simply a low-pass filter and consists of a 10kΩ resistor and a .015µF capacitor. The filtered signal is then buffered by emitter-follower stage Q1 and fed to the 6kHz lowpass filter stage (IC2d). Two 6.2kΩ resistors, a .0033µF capacitor and a .012µF capacitor make up the filter components. This stage operates with a gain of -1 for frequencies below 6kHz and rolls off the response at 12dB per octave for higher frequencies. Its output appears at pin 14 and is coupled to the output terminals via a 100Ω resistor and a RESISTOR COLOUR CODES ❏ No. ❏   4 ❏   1 ❏ 14 ❏   2 ❏   2 ❏   1 ❏   4 ❏   5 ❏   2 ❏   2 ❏   1 24  Silicon Chip Value 100kΩ 22kΩ 10kΩ 6.2kΩ 4.7kΩ 3kΩ 1.1kΩ 1kΩ 560Ω 470Ω 100Ω 4-Band Code (1%) brown black yellow brown red red orange brown brown black orange brown blue red red brown yellow violet red brown orange black red brown brown brown red brown brown black red brown green blue brown brown yellow violet brown brown brown black brown brown 5-Band Code (1%) brown black black orange brown red red black red brown brown black black red brown blue red black brown brown yellow violet black brown brown orange black black brown brown brown brown black brown brown brown black black brown brown green blue black black brown yellow violet black black brown brown black black black brown ACS SUBCARRIER SIGNALS PICKED OFF HERE Fig.5: as with most FM tuners, the Sony ST-JX220A uses two ICs to do most of its FM processing. These are: (1) an IF amplifier & demodulator IC; & (2) a following multiplex (MPX) stereo decoder IC. The most convenient point to pick off the subcarrier signals is at the output of the demodulator (detector) IC. 1µF capacitor. The associated 100kΩ resistor prevents large offset voltages from appearing at the output. Power for the circuit can be derived from just about any +15-30V rail (normally from inside the receiver). This is fed to 3-terminal regulator REG1 to derive a +12V supply rail. In addi­tion, a half-supply rail (Vcc/2) is derived via a voltage divider consisting of two 4.7kΩ resistors and this biases all the non-inverting inputs of the various op amp stages. Construction All of the parts for the ACS Decoder except switch S1 are installed on a PC board coded 06303951. Fig.4 shows the assembly details. No particular order of assembly need be followed but we suggest that you start by installing PC stakes at the 11 external wiring points. The two wire links can then be installed, followed by the resistors, capacitors and ICs. Make sure that the ICs are correctly oriented and use your multimeter to check each resistor value before installing it, as some of the colours can be diffi­cult to decipher. Finally, complete the board assembly by installing VR1, transistor Q1 and REG1. Note that REG1 is mounted flat against the PC board with its leads bent at right angles and is secured using a screw and nut. Don’t bother wiring up the switch at this stage; that step comes later, when the unit is installed inside a receiver. (check the ICs and the regulator). Assuming all is well, check that the regulator output is at +12V. You should also find this voltage on pin 4 of IC1, pin 4 of IC2 and pin 16 of IC3. Finally, check that +6V is present on pins 3, 5, 10 & 12 of both IC1 and IC2. Initial tests Installation Once the board assembly has been completed, connect your multimeter in series with the +15V supply input and apply power. A 12V DC plugpack will make suitable temporary power supply, as it will have a no-load output of about 17V DC and will only be lightly loaded. Check that the quiescent current is no more than about 25mA (no input signal). If it is much more than this, switch off immediately and locate the source of the problem before proceeding The ACS Decoder can be mounted inside the receiver using suitable brackets and the toggle switch mount­ ed on the rear panel. This done, the switch can be wired to the PC board using rainbow cable – see Fig.4. The power supply connections (+15-30V & ground) can be run using hook-up wire. Ideally, you should have a circuit diagram of your receiver so that you can find a suitable supply rail. Important: make sure that the ACS Decoder and all connecting leads are kept well away from any mains wiring inside the receiver. In addition, you should run a separate earth lead between the switch body and the metal chassis if the switch is not earthed via the rear panel (eg, if the rear panel is plastic). If you are installing the decoder inside a receiver, the audio output lead can be internally connected to a spare pair of line input sockets (eg, aux). This lead can be run using light-duty hook-up wire. Note that you will have to connect the two sockets in parallel, since the decoder only has a single mono output. Alternatively, if the board is mount­ ed inside an FM tuner, the decoder’s output can be run to an additional RCA socket installed on the rear CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC EIA 0.68µF 680n 684 0.1µF 100n 104 0.012µF 12n 123 .01µF 10n 103 .0047µF 4n7 472 .0033µF 3n3 332 .0027µF 2n7 272 .0015µF 1n5 152 560pF 560p 561 220pF 220p 221 10pF   10p   10 March 1995  25 Fig.6: this is the full-size etching pattern for the PC board. Check your board carefully for possible defects before installing any of the parts. panel. This audio output can then be con­nected via a Y-adapter shielded cable to the line inputs on your stereo amplifier. You now have to find the signal at the output of the demod­ulator. In a stereo tuner, this comes before the multiplex decod­er and treble de-emphasis networks. In a mono tuner, you must tap into the demodulated output before de-emphasis has taken place. After de-emphasis, the ACS subcarriers will be non-existent as we’ve already pointed out. Fig.5 shows a typical FM tuner circuit (Sony ST-JX220A) as an example. As with most such tuners, it uses two ICs to do most of its FM processing. These are: (1) an IF amplifier & detector IC; and (2) a following multiplex (MPX) stereo decoder IC. The most convenient point to pick off the sub­ carrier signals is at the output (in this case, pin 6) of the detector IC. Alternatively, the signal can be picked up at the input to the multiplex decoder IC. A suitable power supply rail for the decoder can usually be picked up from the regulator board inside the receiver. Testing The ACS Decoder should initially be tested with S1 set to 67kHz and VR1 at mid-position. Apply power and tune in one of your regular FM stations. This done, select the ACS decoder (using the selector switch on the amplifier) and check for the presence of an ACS signal. If no signal is heard, try adjusting VR1 until a signal is heard. Failing this, retune to another station and try again. When an ACS station comes up, adjust VR1 for best signal, then switch to the 92kHz position and adjust VR1 again so that both ACS signals can be heard. If no signal is present on 92kHz, try other stations in turn until you find one that’s broadcasting ACS signals on both frequencies. Copyright The signal for the prototype ACS decoder was derived by soldering the input lead directly to the output pin of the demodulator IC in the Harman Kardon receiver. If you don't have a circuit diagram of your receiver, use a CRO to determine which pin is the demodulated output. Alternatively, you may have to test each pin of the demodulator IC on a trial & error basis until an ACS signal is heard. 26  Silicon Chip Finally, readers are warned that recording or broadcasting received ACS programs without proper authorisation may breach copyright. If you have any doubts about your obligations, check with the copyright holder. SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd Build a 50W/channel stereo amplifier Looking to upgrade your system with a new amplifier? This new stereo amplifier is easy to build & does not need setting-up adjustments. Most importantly, it will give excellent sound quality & up to 50 watts per channel into 8-ohm loads. By LEO SIMPSON & BOB FLYNN Our last integrated stereo amplifier design was presented in the March & April 1992 issues of SILICON CHIP but it is now obsolete because the power transistors specified are no longer available. This new design is based on the 50W per channel stereo amplifier module presented last month. While this new amplifier offers very similar facilities to the unit referred to above, it is a completely new design with a much wider chassis and all 32  Silicon Chip new PC boards. And while the super­ sed­ ed design had an inbuilt RIAA preamplifier for phono cartridges, in the new amplifier the RIAA preamp is an optional extra board. We took this approach because many people these days do not have any vinyl records or a turntable so they don’t want the RIAA preamp. Leaving the RIAA preamplifier out also has the advantage that you have an extra pair of line level inputs (ie, suitable for CD, tuner or other program source). The overall design approach to this amplifier has been middle of the road. We have not taken the spartan European ap­proach with virtually no controls except for the volume knob and nor have we sought to incorporate every feature found in expen­sive Japanese amplifiers. Still, it does have all the features that most people want and will use. For example, while it does include tone controls, it also has a switch to disable them, to obtain a completely flat frequency response. Let us now talk about the features in some detail. Features The new SILICON CHIP 50W Stereo Amplifier is housed in a low profile case measuring 435mm wide, 95mm high and 320mm deep, including knobs rubber feet and rear projections. Specifications Power Output 47W into 8-ohm loads, both channels driven; 57W into 8-ohm loads with one channel driven. Frequency Response High level inputs: within ±1dB from 10Hz to 50kHz Phono inputs: RIAA/IEC within ±0.5dB from 20Hz to 20kHz. Total Harmonic Distortion Typically less than .05% (see graph). Signal-to-Noise Ratio High level inputs (CD, Tuner, etc): 99dB unweighted (20Hz to 20kHz) with respect to rated output (with volume at maximum) with Tone Defeat switch in or out; 100dB A-weighted under the same conditions. Phono (moving magnet): 83dB unweighted (20Hz to 20kHz) with respect to 10mV input signal at 1kHz & rated output with 1kΩ resistive input termination; 88dB A-weighted under the same conditions. Channel Separation -78dB at 100Hz; -81dB at 1kHz; & -61dB at 10kHz with respect to rated output & with undriven channel input loaded with a 1kΩ resistor. Above: the new SILICON CHIP 50W per channel amplifier offers all the facilities expected on a modern stereo amplifier &, in addition, it has a separate headphone amplifier. Input Sensitivity Phono inputs at 1kHz: 4.3mV High level inputs: 235mV Tone Controls Bass: ±13dB at 50Hz. Treble: ±13dB at 10kHz Damping Factor >56 from 100Hz to 10kHz (for 8Ω loads) Stability Unconditional It has the usual line-up of controls found on most amplifiers: bass, treble, balance, input selector, tape monitor switch, tone defeat switch and volume control. It also has a stereo/mono switch, headphone socket and power switch. Plugging into the headphone socket disables the main power amplifiers and engages a separate high quality low power stereo amplifier to drive the headphones di­rectly. This now only gives better reproduction via headphones but it also simplifies the internal wiring. Block diagram Now let’s have a look at the circuit features which are depicted in the The new 50W Stereo amplifier uses this 50-watt/channel stereo power module, as described in the previous issue. It’s based on two monolithic power ICs to give a rugged, compact design that requires no adjustments. March 1995  33 POWER AMPLIFIER IC4 OPTIONAL RIAA PREAMPLIFIER IC5 AUX 3/ PHONO CD x23 x56 OUT SOURCE MONITOR S2 TONE S5 TAPE PREAMPLIFIER IC1 TUNER VCR AUX 1 VOLUME VR1 SOURCE S1 AUX 2 TAPE OUT TAPE IN S6 x4.2 IN TONE CONTROLS IC2 POWER AMPLIFIER HEADPHONES HEADPHONE AMPLIFIER IC3 x5.7 MONO SPEAKER HEADPHONES MODE S3 STEREO TO OTHER CHANNEL TO OTHER CHANNEL BALANCE S4 Fig.1: the circuit features of the new stereo amplifier are il­lustrated in this block diagram. To keep things simple only one channel is shown. Note the separate amplifier to drive the head­phones. TO OTHER CHANNEL block diagram of Fig.1. This shows only one channel, to keep things simple. All the circuit functions are duplicated in the second channel. S1 is the 6-position selector switch and it feeds the tape output as well as the Tape Monitor switch S2. S2 selects the signal from the input selector S1 or from a cassette deck con­nected to the Tape In inputs. The signal then goes to S3, the stereo/ mono switch which shorts the two channel signals together when in the mono setting. Following S3, the signal is fed to the 11-position balance control switch S4 and the volume control potentiometer VR1. The use of a rotary switch for the balance control is unusual but there are good reasons for this approach. In past designs we have specified a special dual ganged potentio­meter known as an M/N type. This has half the resistance track in each channel shorted out to give a good balance control action and is the same as used in most domestic stereo amplifiers. However, this type of balance control has become difficult to obtain 34  Silicon Chip and so we initially took a different approach, using a single linear potentiometer with the ends connected to the signal in either channel and the wiper connected to signal earth. This approach is cheap but does not work particularly well, for two reasons. First, it has very little apparent effect over most of the middle range of the pot – all the attenuation is cramped into the extreme ends of rotation. Second, because the resistance of the wiper itself is quite high, and this resistance is common to the signal path in both channels, the separation between channels is seriously degraded, to a figure of about 25dB. Now while -25dB separation between channels is adequate to produce a convincing stereo effect, it is far below what the circuit is otherwise capable of. One approach used by some amplifier manufacturers is to use a linear potentio­meter with a centre tap connection. This gets around the problem of the wiper resistance but it still has all its control action con­ centrated at the extremes of rotation. In any case, such poten­tiometers are also difficult to obtain. Our approach was to use an 11-position rotary switch with resistors wired around it. The resistors are arranged to progres­sively reduce the gain of the attenuated channel by about 2dB. So from the centre position, the gain of each channel can be varied by -2dB, -4dB, -6dB, -8dB and then completely off. This works reasonably well and has the advantage of giving good channel separation. Following the volume control, the signal goes to a non-inverting op amp stage with a gain of 4.2. From there, it goes to the unity gain tone control stage which can be switched out of circuit by the Tone defeat switch, S5. After the tone defeat switch, the signal goes to switch S6 which is part of the headphone socket. It normally Fig.2 (right): this diagram shows the circuit of one channel of the new amplifier & the power supply which is common to both channels. The RIAA preamplifier (not shown) is optional & can be omitted, giving another pair of line level inputs. March 1995  35 E 10k C -15V E 5.6k B 33pF C 5.6k D2 1N914 7(1) D1 1N914 47k IC3a 6(2) TLO72 5(3) TO S6a +15V VIEWED FROM BELOW B 10k TAPE IN TAPE OUT AUX2 AUX1 VCR TUNER CD AUX3/ PHONO GIO 7915 A MONO OTHER CHANNEL E N 240VAC A 1.6k F1 1A CASE S7 .01 250VAC OTHER CHANNEL 1.6k 820W 1.6k 4.7k 91k 91k 4.7k 1.6k 820W 1k HEADPHONES OTHER CHANNEL STEREO MODE S3A 82  K 1k TAPE 50W STEREO AMPLIFIER I GO 7815 E Q2 C BC327 B 15  15  E Q1 BC337 C B SOURCE S1a 1k SOURCE MONITOR S2a OPTIONAL PHONO PREAMP T1 1 25V 25V BALANCE S4 VOLUME VR1a 50k LOG 4.7k 6(2) 1k 5(3) 4700 50VW 4700 50VW BR1 KBPC10-4 11 TO HEADPHONE AMPLIFIER 100k 1 15k 7(1) 22k 1 4.7k 2x330  1W -35V 47 63VW 47 63VW IN REG2 7915 GND GND OUT 100 16VW 100 16VW +35V REG1 2x330  7815 1W OUT IN L1 : 16T 0.5mm DIAMETR ENAMELLED COPPER WIRE WOUND ON 10  1W RESISTOR 100pF IC1a LM833 22 BP 22k TREBLE VR3a 25k LIN -15V GND 8 100 16VW 4 *0.1 5.6 1W F3 2A 100 16VW 100 16VW 100 16VW 100 16VW *SEE TEXT 100 63VW 3 100 63VW 10  1W LED1 3.9k 0.5W  8W +35V 7(1) -35V L1 0.7uH F2 2A IC2a 5(3) LM833 6(2) CONTROL BOARD FILTERING 0.1 0.1 5 0.1 100 16VW 39k 22k 7 IC4 LM3886 1 22k 6.8 S6a BP 0.1 33pF TONE CONTROLS S5a IN 4.7k 22k OUT .0047 22 16VW 9 10 AMP +15V 47 16VW 1k 220pF 1k 100W PHONES .0047 22k BASS VR2a 100k LIN .01 Fig.3: this graph shows the frequency response of the tone controls at their maximum boost & cut settings & also at the flat setting. AUDIO PRECISION FREQRESP AMPL(dBr) & AMPL(dBr) vs FREQ(Hz) 5.0000 14 JAN 95 20:39:02 5.000 4.0000 4.000 3.0000 3.000 2.0000 2.000 1.0000 1.000 0.0 0.0 -1.000 -1.00 -2.000 -2.00 -3.000 -3.00 -4.000 -4.00 -5.000 -5.00 20 100 1k 10k 50k Fig.4: the frequency response of the headphone amplifier, with the right channel dotted. feeds the audio signal through to the following power amplifier but when the headphone jack is inserted, the signal is diverted to the headphone amplifier. Circuit description The complete circuit diagram, except for the optional RIAA preamplifier, is shown in Fig.2. The three 36  Silicon Chip op amps are shown as IC1a, IC2a and IC3a and each is half of a dual low noise op amp. The pin numbers for the other halves which are in the second channel, IC1b, IC2b and IC3b, are shown in brackets on the circuit. For example, the non-inverting (+) input for IC1a is pin 5 while the corresponding input for IC1b is pin 3 (shown in brackets). IC1a is the non-inverting op amp with a gain of 4.2, as set by the feedback resistors connected to pin 6. Besides providing gain and a high impedance load for the volume control pot, IC1a acts as a low impedance source for the tone control stage, IC2a. This has the tone controls connected in the negative feedback network. When the bass and treble controls are centred (ie, in their flat settings), the gain of stage is unity, up to at least 50kHz. Winding the bass or treble controls towards the input side of IC2a (ie, applying boost) increases the gain for frequencies above 2kHz for the treble control and below 300Hz for the bass control. When the tone controls are rotated in the opposite direction (applying tone cut), the gain is reduced above 2kHz and below 300Hz. This is because the negative feedback has been increased, giving a reduction in gain at these frequencies. The amount of treble boost and cut provided by IC2a is limited by the 4.7kΩ resistors on either side of the 25kΩ treble pot, VR3a. Similarly the maximum bass boost and cut is limited by the 22kΩ resistors on either side of the bass pot, VR2a. Fig.3 shows the action of the tone controls at their maximum boost and cut settings and also at the flat setting. Note how S5a, the Tone Defeat switch, bypasses the tone control circuitry. Its output feeds a 6.8µF bipolar capacitor which is there to block DC from the tone control stage from getting into the input of the headphone amplifier. Headphone amplifier Following the 6.8µF capacitor and headphone switch S6a is the head­ This prototype amplifier uses five PC boards, including the optional RIAA preamplifier which is adjacent to the selector switch. No setting up adjustments are required for the power amplifiers. phone amplifier which consists of op amp IC3a in combina­ tion with transistors Q1 and Q2. The transistors are there to boost the output current capability of the TL072 op amp. They are slightly forward-biased (to keep crossover distortion to a mini­mum) by the two diodes connected between the bases. Any distor­tion produced by the transistors is also minimised by incorporat­ing them inside the feedback network for the op amp. The output current of the head­ phone amplifier is limited by the 15Ω emitter resistors and the 82Ω output resistor. This provides short circuit protection and protects the headphones against damage in the unlikely event of the amplifier being damaged. Fig.4 shows the frequency response of the headphone amplifier, with the right channel dotted. Power amplifiers As noted above, the power amplifiers are the stereo 50W module described last month. For the sake of completeness and for those who did not see the previous article, we repeat the circuit description. IC4 is an LM3886 monolithic power amplifier module with balanced supply rails and direct coupling to the loudspeaker load. It is very similar to the LM3876 50W module featured in the March 1994 issue of SILICON CHIP. The input signal which comes via the headphone switch S6a is coupled via a 1µF MKT polyester capacitor and then via an RC network consisting of a March 1995  37 distortion versus frequency at 30 watts into 8Ω loads. Phono preamplifier Fig.5: total harmonic distortion versus frequency at 30W into 8Ω loads, for both channels. 1kΩ series resistor and a shunt 220pF capacitor. This is an RF suppression capacitor. The voltage gain of the power amplifier is set 23 by the 22kΩ negative feedback resistor from pin 3 to pin 9, in conjunc­tion with the 1kΩ resistor and 47µF capacitor. The output from IC4 drives the loudspeaker via an RL network consisting of a 10Ω resistor in parallel with an inductance of 0.7µH. This acts in conjunction with the Zobel network comprising the 5.6Ω resistor and 0.1µF capacitor to ensure that the LEFT INPUT amplifier is stable under varying load conditions. Power supply The power supply uses a 50V centre-tapped 160VA transformer feeding a bridge rectifier and two 4700µF 50VW capacitors. Posi­ tive and negative 3-terminal regulators fed by paralleled pairs of 330Ω resistors provide the ±15V supply rails to the preamplifier boards (ie, tone control board and optional RIAA preamplifier). Fig.5 shows another aspect of the amplifier’s performance: harmonic +15V L1 150  100k 47 BP 100k 8 3(5) IC5a 2(6) LM833 4 100pF L1 : 4T, ENCU WIRE ON PHILIPS 4330 030 3218 FERRITE BEAD 16k IC PIN NUMBERS IN BRACKETS ARE FOR RIGHT CHANNEL .0047 390 -15V 1(7) 100  10 BP LEFT OUTPUT 1M 200k .015 +15V +15V 22 BP 0.1 0V 0.1 RIAA PREAMPLIFIER (OPTIONAL) -15V RIAA/IEC equalisation -15V Fig.6: the circuit of the optional RIAA preamplifier is based on an LM833 dual low noise operational amplifier. 38  Silicon Chip As noted above, this phono preamplifier is optional. The circuit is depicted in Fig.6 and again, only one channel is shown. IC5a is one half of an LM833 low noise op amp. It takes the low level signal from a moving magnet cartridge and applies a gain of 56 at the median frequency of 1kHz. Higher frequencies get less gain while lower frequencies get considerably more, as called for in the RIAA equalisation. The preamplifier board is the same as the universal preamplifier board presented in the April 1994 issue of SILICON CHIP. The phono signal is fed directly from the input socket via inductor L1, a 150Ω resistor and a 47µF bipolar capacitor to the non-inverting input, pin 3, of IC5a. The inductor, series resis­ tor and 100pF shunt capacitor form a filter circuit to remove RF interference signals which might be picked up by the phono leads. The 100pF capacitor is also important in capacitive loading of the magnetic cartridge. Most moving magnet (MM) cartridges operate best with about 200-400pF of shunt capacitance. The 100pF capacitance in the preamp input circuit plus the usual 200pF or so of cable capacitance for the pickup leads will therefore provide about the right shunt capacitance. For its part, the 47µF bipolar cap­ acitor is far larger than it needs to be as far as bass signal coupling is concerned. If we were merely concerned with maximising the bass signal from the cartridge, then an input coupling capacitor of 0.47µF would be quite adequate. At 20Hz, a capacitor of this value would have an impedance of around 15kΩ which is considerably less than the nominal 50kΩ input impedance of the preamp. However, having a large input cap­ acitor means that the op amp “sees” a very low impedance source (ie, essentially the DC resistance of the cartridge) at low frequencies and this helps keep low fre­quency noise, generated by the input loading resistors, to a minimum. The RIAA equalisation is provided by the RC feedback compon­ents between pins 1 and 2 of IC5a. These PARTS LIST 1 steel case with aluminium front panel, 435 x 90 x 265mm 1 2-pole, 6-position rotary switch, Altronics S-3022 (S1 3 2-pole 2-position pushbutton switches, Altronics S-1410 (S2,S3,S5) 1 single pole 12-position rotary switch, Altronics S-3021 (S4) 1 SPST 250VAC rocker switch, Altronics S-3210 (S7) 1 dual-gang 50kΩ log potentiometer (VR1) 1 dual-gang 100kΩ linear potentiometer (VR2) 1 dual-gang 25kΩ linear potentiometer (VR3) 1 PC mounting 6.5mm switching stereo socket, Altronics P-0076 3 3 x 2-way RCA socket panels, Altronics P-0213 1 black binding post terminal, Altronics P-0264 3 22mm diameter black aluminium knobs, Altronics H-6213 2 30mm diameter black aluminium knobs, Altronics H-6224 1 3-way mains terminal strip 2 solder lugs 1 toroidal power transformer, 2 x 25V, 160VA 1 M205 panel mount fuse holder 1 2A M205 20mm fuse 8 20mm fuse clips 4 2.5A M205 20mm fuses 2 single sided heatsinks, 72mm high, Altronics H-0522 2 TA11B IC mounting kits 3 3-way PC terminal blocks, Altronics P-2035 23 PC pins 7 15mm tapped standoffs 4 3mm x 6mm untapped standoffs 4 4M x 10mm screws 11 3M x 10mm screws 2 3M x 15mm screws 10 3M x 6mm screws 9 3M nuts 6 black No.6 x 10mm self-tapping screws 1 1-metre length 0.5mm enamelled copper wire 1 1-metre length twin shielded audio cable 3 1-metre lengths 32 x 0.2mm hookup wire (three different colours) 1 3-core mains cord & moulded 3-pin plug 1 cordgrip grommet (to suit mains cord) 4 rubber feet 1 6.4mm shaft coupler 1 6.4mm dia. x 144mm long extension shaft 1 LED bezel equalisation components provide the standard time constants of 3180µs (50Hz), 318µs (500Hz) and 75µs (2122Hz). The preamplifier also adds in the IEC recommendation for a rolloff below 20Hz (7950µs). This is pro- vided by the 22µF bipolar capacitor in series with the 390Ω resis­tor. The 390Ω resistor sets the maximum AC gain at very low frequencies while the 22µF capacitor ensures that the gain for DC is unity. This means that any input offset voltages are not ampli­ PC boards 1 power amplifier board, code 01102951, 247 x 58.5mm 1 input selector board, code 01103951, 132 x 58mm 1 selector switch board, code 01103952, 55 x 37mm 1 tone control board, code 01103953, 277 x 86mm 1 RIAA preamp board (optional), code 01103954, 76 x 78mm Semiconductors 2 LM833 operational amplifiers (IC1,IC2) 1 TLO72 operational amplifier (IC3) 2 LM3886 audio power amplifiers (IC4) 4 1N914 signal diodes (D1,D2) 2 BC337 NPN transistors (Q1) 2 BC327 PNP transistors (Q2) 1 KBPC10-04 bridge rectifier (BR1) 1 LM7815T 3-terminal regulator (REG1) 1 LM7915T 3-terminal regulator (REG2) 1 red LED (LED1) Capacitors 2 4700µF 50VW electrolytics 4 100µF 63VW electrolytics 2 47µF 63VW electrolytics 8 100µF 16VW electrolytics 2 47µF 16VW electrolytics 2 22µF 16VW electrolytics 2 22µF 50VW bipolar electrolytics 2 6.8µF 50VW bipolar electrolytics 4 1µF 63V MKT polyester 10 0.1µF 63V MKT polyester 1 .01µF 250VAC metallised paper 2 .01µF 63V MKT polyester 4 .0047µF 63V MKT polyester 2 220pF 50V ceramic 2 100pF 50V ceramic 4 33pF 50V ceramic Resistors (0.25W, 1%) 2 100kΩ 4 1.6kΩ 2 91kΩ 12 1kΩ 2 47kΩ 2 820Ω 2 39kΩ 4 330Ω 1W 12 22kΩ 2 100Ω 2 15kΩ 2 82Ω 4 10kΩ 4 15Ω 4 5.6kΩ 2 10Ω 1W 8 4.7kΩ 2 5.6Ω 1W 1 3.9kΩ 0.5W Optional RIAA Preamplifier 1 RIAA preamp board, code 01103954, 76 x 78mm 11 PC pins 1 LM833 operational amplifier (IC5) 2 Philips ferrite beads, 4330 030 3218 Capacitors 2 47µF 50VW bipolar electrolytics 2 22µF 50VW bipolar electrolytics 2 10µF 50VW bipolar electrolytics 2 0.1µF 63V MKT polyester 2 .015µF 63V MKT polyester 2 .0047µF 63V MKT polyester 2 100pF 50V ceramic Resistors (0.25W, 1%) 2 1MΩ 2 390Ω 2 200kΩ 2 150Ω 4 100kΩ 2 100Ω 2 16kΩ fied, which would inevitably cause trouble with asymmetrical clipping and premature overload in the preamplifier. Next month, we shall continue with the construction details for the new SC 50W Stereo Amplifier. March 1995  39 LIGHTNING DISTANCE METER Have you ever wondered just how close that bolt of lightning was? Well, don’t wonder about it; check it out with this Lightning Distance Meter instead. The device uses common components & measures flash distances up to 19 kilometres. By DARREN YATES There are many situations where it can be useful to know the distance to an approaching thunderstorm. Perhaps you’re just the curious type who likes to keep an eye on the weather or maybe you have a far more practical reason for wanting to know, such as when you’re ploughing a field or you’re out on the footy oval or golf course. Being caught out in the open in the middle of a thunderstorm is not a pleasant experience. Of course, you could always abandon the game when the first lightning flash appears or you could use the old “1001” rule that you learnt as a kid. 40  Silicon Chip Whenever you saw a flash of lightning, you would count 1001, 1002, 1003 and so on, and when you heard the thunder you divided the last digit by five to determine how many miles away the “bolt” was. Armed with this information, you could then elect to do a runner when the lightning got too close for comfort – five miles if you were chicken or five feet if you were more adventurous! Unfortunately, in this metricated age, most youngsters don’t know what a mile is! So unless we apply a metric conversion to the 1001 rule, we either run the risk of getting zapped or abandoning a perfectly good game for nothing. Alternatively, we could apply a more scientific approach to the problem. The answer is this Lightning Distance Meter. With a bit of eye, ear and hand coordination, you can work out the dis­tance to a lightning flash within a kilometre of so. There’s nothing complicated about using the unit. Apart from the power switch, there are just three pushbutton controls and these are labelled Start, Reset and Stop. In addition, the front panel carries a row of LEDs and these are numbered from 1-10. The principle of operation is quite simple. The speed of sound in air is about 1207km/h, which is equivalent to 1km every 3 seconds. So all the circuit does is light each LED in turn at 3-second intervals when the Start button is pressed. To use the unit, you simply press the Start button when you see the lightn­ing flash and then press the Stop button when you hear the thun­der. The LED that’s lit then gives the distance to the flash (eg, if LED 6 is lit, then the distance is 6km). D1 1N4004 S4 +6V RESET S3 680k IC1 555 2 2.2 16VW VR1 500k 8 6 1 14 CLK 4 IC2 4017 1 2 1k    6 5   7 6   100k 1k A A   K 6 S C IC3a 5 4013 2 D Q R 4 1k A K 13 8 6V 3 9 11 1k A A K K 8 9 1k 1k A A K K CE 5 1 1k 1k A A K 4 10 1k 1k A LEDS 1-9 3 7 2 4 100 16VW 15 RST 12 CO 16 3 .01  LED 10 K K K +6V 14 13 Q IC3b 7 S R START S1 8 STOP S2 D2 1N4148 .01 10 A 100k K 100k LIGHTNING DISTANCE METER Fig.1: the circuit uses 555 timer IC1 to clock decade counter IC2. IC2's decoded 1-9 outputs go high in turn & drive the indicator LEDs. On the 10th count, the CO output goes high & this toggles flipflop IC3a to light LED 10. IC3b controls IC1 to start & stop the count. If the distance is greater than 10km, the circuit first counts to 10 in the usual manner. LED 10 then remains lit while the circuit cycles through the first nine LEDs again. In this way, the circuit can effectively count up to a maximum value of 19. Thus, if both LED 4 and LED 10 are alight when the Stop button is pressed, for example, the distance to the flash is 14km. When a count of 20 is reached, LED 10 goes out and the count starts all over again from zero (ie, the count continually cycles). So, for all practical purposes, the maximum count is 19. This is not really a problem however, since it is unlikely that you will be able to hear individual thunderclaps at distances greater than 19km. The Reset button clears the counter used in the circuit and effectively “freezes” the circuit so that all LEDs are off. This reduces the current consumption to a bare minimum and is useful for maximising battery life if there is a substantial delay bet­ween each measurement. However, the circuit is also automatically reset each time the Start button is pressed. This feature is handy if you are taking a number of measurements in quick succession, since you don’t have to continually press the Reset switch. How it works Refer now to Fig.1 for the circuit details. IC1 is a 555 timer which operates as an astable oscillator. It is wired here in a somewhat unconventional manner, however. Normally, the timing capacitor charges from the positive supply rail via a resistive network and discharges (via part of that network) into pin 7. In this circuit though, the timing capacitor (2.2µF) charges when IC1’s pin 3 output goes high and discharges when pin 3 goes low. PARTS LIST 1 PC board, code 08103951, 102 x 54mm 1 plastic case, 130 x 68 x 41mm 3 momentary normally-off pushbutton switches (S1-S3) 1 SPDT toggle switch (S4) 1 front panel label, 125 x 63mm 4 AA alkaline cells 1 long 4 x AA cell holder 1 500kΩ miniature horizontal trimpot (VR1) 4 15mm-long spacers 4 3mm x 25mm machine screws 4 3mm hex nuts Semiconductors 1 NE555 timer (IC1) 1 4017 CMOS decade counter/ decoder (IC2) 1 4013 dual D flipflop (IC3) 1 1N4004 silicon diode (D1) 1 1N4148 signal diode (D2) 5 5mm red LEDs (LED1-5) 5 5mm green LEDs (LED6-10) Capacitors 1 100µF 16VW electrolytic 1 2.2µF 16VW electrolytic 2 .01µF MKT polyester Resistors (0.25W, 1%) 1 680kΩ 3 100kΩ 10 1kΩ Miscellaneous Light duty hook-up wire, tinned copper wire for links March 1995  41 START S1 POWER S4 1 STOP S2 1 3 2 4 .01 IC1 555 680k 100uF RESET S3 VR1 IC2 4017 IC3 4013 1 2.2uF D2 1 D1 LED3 LED5 LED6 LED7 1k 1k 1k 1k 1k 1k 1k 1k LED4 LED8 LED9 100k LED1 LED2 1k 1k 100k 100k 1 2 3 4 .01 LED10 6V BATTERY PACK Fig.2: make sure that all polarised parts, including the LEDs, are correctly oriented during the PC board assembly. VR1 is used to adjust the 555 timer so that the circuit counts to 10 in 30 seconds. The circuit works like this: at switch-on, pin 3 of IC1 goes high and the 2.2µF timing capacitor charges via VR1 and a 680kΩ resistor. When the capacitor voltage reaches 2/3Vcc (ie, 2/3 the supply rail voltage), pin 3 switches low and the capaci­ tor discharges until it reaches 1/3Vcc. At this point, pin 3 switches high again and so the cycle is repeated indefinitely. As a result, IC1 produces a square wave pulse train at its pin 3 output. VR1 is adjusted so that oscillator operates at a nominal 0.33Hz, which is equivalent to one positive going pulse every 3 seconds. This signal is used to clock IC2, which is a 4017 decade counter. Its decoded 1-9 outputs are normally low but sequential­ly switch high in response to the clocking signal (ie, Fig.3: this is the full-size etching pattern for the PC board. 42  Silicon Chip one output goes high at a time for the duration of each clock cycle). These outputs, in turn, drive LEDs 1-9 via 1kΩ current limiting resis­tors. The tenth LED in the sequence (LED 10) is driven from the CO (carry out) output of IC2 via flipflop IC3a (4013). In opera­tion, the CO output goes high once every 10 clock cycles and this in turn clocks IC3a which operates in toggle mode. This ensures that LED 10 remains lit as the counter cycles back through again after first counting to 10. When power is first applied, both IC2 and IC3a are reset by virtue of the 0.01µF capacitor across the Reset switch (S3). This briefly pulls pin 15 (reset) of IC2 and pin 6 (set) of IC3 high. As a result, outputs 1-9 of IC2 and Q-bar of IC3a are all ini­tially low and so the LEDs are all off. Only the decoded ‘0’ output of IC2 is high but, as this output is unused, this is of no consequence. IC3b, along with switches S1 & S2, provides the start\stop control function. When power is applied, its reset input (pin 10) is briefly pulled high via the .01µF capacitor across S2 and this ensures that the Q output (pin 13) is initially low. This, in turn, holds pin 4 (reset) of IC1 low and prevents IC1 from oper­ating. Pressing the Start button (S1) now pulls the set input of IC3b high and this toggles pin 13 high and releases the reset on IC1. IC1 now oscillates and clocks IC2 at 3-second intervals to light the LEDs in sequence. The count continues until the Stop button is pressed, at which point the Q output of IC3 goes high again and stops IC1. The count is now effectively frozen until either the Start button is pressed again or the Reset button is pressed. Diode D2 is necessary to make the circuit start counting correctly. Without this diode, IC2 would be clocked by a high going pulse from IC1 as soon as the Start button was pressed and so the first LED would light immediately instead of after the required 3-second delay. By including D2, IC2 and IC3 are reset when the Start button is pressed, which means that IC2 ignores the initial high-going pulse from IC1 and thus counts correctly. There’s one important point to note here, though. IC2 and IC3 are held reset for as long as the Start button is held down. This means that the circuit will not start counting until the Start button is released, so it should only be pressed briefly when you see a lightning flash. Power for the circuit comes from a 6V battery (4 x 1.5V AA cells) and this is applied via power switch S4 and reverse polar­ity protection diode D1. A 100µF capacitor is used to provide supply decoupling. Construction The prototype Lightning Distance Meter was built on a small PC board coded 08103951 and is housed in a plastic utility case. Fig.2 shows the assembly details. Before starting construction, check the board carefully for any shorts or breaks in the copper tracks by comparing it with the published artwork. Repair any defects that you do find (generally, there will be none), then install PC stakes at the eight external wiring points. This done, install the six wire links, followed by the resistors, diodes, capacitors and the ICs. Take care to ensure that the polarised components are correctly oriented and be sure to use the correct type numbers for D1 and D2. Trimpot VR1 can now be installed, followed by the 10 LEDs. Just load the LEDs into the board as shown on Fig.2 but don’t solder or trim their leads at this stage. That step comes later, after the front panel has been attached. Take care to ensure that each LED is correctly oriented – the anode lead is the longer of the two. We used red LEDs for LEDs 1-5 and green LEDs for LEDs 6-10, since we reckoned that any flashes within 5km were too close for comfort. The plastic utility case can now be drilled to accept the PC board, the four switches and the LEDs. The first step is to attach the front panel artwork to the lid. This can then be used as a template for drilling out the LED mounting holes. It’s best to drill small pilot holes first and then carefully enlarge them using a tapered reamer until the LEDs are a good fit. Once this has been done, use the PC board as a template for marking out its four mounting holes on the lid. Drill these holes to 3mm, then fasten the PC board to the back of the lid using 15mm spacers and machine screws and nuts. The 10 LEDs can This view shows the completed PC board assembly, before it is mounted on the lid of the case. Note that the final version differs slightly from this prototype (ie, D2 & the two .01µF capacitors were added after this photo was taken). The completed PC board is mounted on the lid on 15mm spacers & secured using machine screws & nuts. Arrange the LEDs so that they just protrude above the surface of the front panel. now be pushed into their respective front panel holes and their leads soldered. Adjust each LED so that it just protrudes above the surface of the front panel. The front panel can now be used as a guide for marking out the holes for the switches. The three pushbutton switches are mounted on the top of the case, while the power switch is mounted on the lefthand side. They must all be posi­ tioned towards the back of the case so that they clear the PC board when the lid is fitted. Once the holes have been drilled, mount the switches in position, then March 1995  43 Start Reset On Lightning Distance Meter Power Off Stop 1 2 3 4 5 6 7 8 9 10 Pressing the Start button again should now clear the display and restart the count. Finally, check the operation of the Reset button. It should only be pressed after the Stop button has been pressed and should clear the display. Do not use the Reset button to restart the count if a count is already in progress, as this will give inaccurate results. Calibration Kilometres Assuming that everything works correctly, the unit can now be calibrated so that its counts at Fig.4: this full-size artwork can be used as a drilling template for the front panel. It the correct rate. As mentioned should also be used as a guide for marking out the switch mounting positions. earlier, the sound from a lightning flash travels about 1km in 3 remove the PC board from the lid and on after a brief delay, followed by each seconds. So, to calibrate the unit, simcomplete the wiring. You can use light of the remaining LEDs in turn. Check ply adjust VR1 so that the unit takes duty hook-up wire for this job. that the unit counts correctly to 10 30 seconds to count up to 10km. This and that LED 10 then remains on as will have to be done on a trial and erSmoke test the count cycles through the first nine ror basis. Rotating VR1 anticlockwise The test procedure simply involves LEDs again. If any of the LEDs fail to increases the time, while rotating VR1 switching the unit on and checking light, it has probably been installed clockwise reduces it. Once thus has been done, you can that everything works correctly. First, the wrong way around. Now press the Stop button and complete the final assem­bly and wait check that all the LEDs are out immediately after switch-on, then press the check that the display “freezes”, with for that next southerly-buster to blow SC Start button. LED 1 should now come the current LED(s) remaining on. up. 20MHz Dual Trace Scope $795 100MHz Kikusui 5-Channel, 12-Trace 50MHz Dual trace Scope $1300 COS6100M Oscilloscope $990 These excellent units are the best value “near brand new” scopes we have ever offered. In fact, we are so confident that you’ll be happy, we will give you a 7-day right of refusal. Only Macservice can offer such a great deal on this oscilloscope . . . and you are the winners! 1. Power switch 2. LED 3. Graticule illumination switch 4. Trace rotation 5. Trace focus 6. Trace intensity for B sweep mode 7. Brightness control for spot/trace 8. Trace position 9/10/11. Select input coupling & sensitivity of CH3 12. Vertical input terminal for CH3 13. AC-GND-DC switch for selecting connection mode 14. Vertical input terminal for CH2 15/22. Fine adjustment of sensitivity 16/23. Select vertical axis sensitivity 17/24. Vertical positioning control 18/25/38. Uncal lamp 19. Internal trigger source CH1,CH2,CH3,ALT 20. AC-GND-DC switch for selecting connection mode 21. Vertical input terminal for CH1 26. Select vertical axis operation 27. Bezel 28. Blue filter 29. Display selects A & B sweep mode 30. Selects auto/norm/single sweep modes 31. Holdoff time adjustment 32/51. Trigger level adjustment 33/50. Triggering slope 34/49. Select coupling mode AC/HF REJ/LF REJ/DC 35. Select trigger signal source Int/Line/Ext/Ext÷10 MACSERVICE PTY LTD 36. Vertical input terminal for CH4 37. Trigger level LED 39. A time/div & delay time knob 40. B time/div knob 41. Variable adj of A sweep rate & x10 mag 42. Ready lamp Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 562 9500; Fax: (03) 562 9590 44  Silicon Chip 43. Calibration voltage terminals 44. Horizontal positioning of trace 45. Fine adjustment 46. Vertical input terminal for CH5 47. Delay time MULT switch 48. Selects between continuous & triggered delay 52. Trace separation adjustment 53. Ground terminal 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 SERVICEMAN'S LOG Doing the rounds with remote control This month’s notes have turned out to be a continuation of last month’s. It wasn’t planned that way; it just happened. As readers will recall, they were about remote control units & this month’s notes describe two more faults. One of last month’s stories was about some funny goings on with the infrared LEDs in a particular model remote control unit (NEC RD-309E). They would work when the unit was upside down but not when it was right way up. And it wasn’t just a one-off; I had two with identical symptoms, which was enough to suggest that it involved an inher­ ent weakness in the LEDs themselves. Replacing them was all that was required to cure the fault but the exact failure mechanism remained a mystery. Which was where we left things last month. But hardly had the presses begun to roll, than there was another episode. It was the same model unit and it came in with a familiar complaint: “it doesn’t work.” And with very good reason, as I found when I opened the case. It was another case of a broken crystal lead, only this time the break was so close to the case that there was no chance of salvaging it. Fortunately, a scrabble through the junk box produced another such unit from which I was able to retrieve a perfectly good crystal. So it all looked like plain sailing. I fitted the substi­ tute crystal, put everything back together, and gave it a try. No joy. For a moment I wondered whether I had tricked myself and fitted another dud crystal. But then I remembered the upside down behaviour. Surely not another one? But it was; I turned it over and it worked, and when I turned it back again it was dead. I could hardly believe it. I fitted another LED and that was it; its behaviour was back to normal. So there it is – mystery fault number three. And that means there must be some inherent fault in those LEDs. I had hoped to make some attempt to find out what it is but, as I mentioned last month, the LEDs involved are coated with an infrared filter which excludes visible light and makes them appear black. My idea was to try to break one open, with a minimum of force, in an effort to preserve the electrodes and, hopefully, reveal the fault. No such luck. These things are not hollow, as I had thought, but solid plastic. But one final thought. With two Fig.1: Der Fernbedienungstester RCT 5502 (ie, the remote control tester). It carries a microphone (marked “US”), an in­frared sensor (marked “IR”), two LEDs (shown on the top of the case), & a 3.5mm socket on one side. 46  Silicon Chip faults in this last unit, which came first; which one prompted the customer to call me? We shall never know. The main event So much for that little preliminary bout. The main event this month concerns a Philips colour TV set, a 63cm model using the KL9A chassis. This chassis first appeared about 1012 years ago and was used in a whole range of sets. In many sets, it was used in its basic form, without any frills, but in this case it came with the works: remote control, stereo sound and Teletext. The customer’s complaint came in the form of a phone call along the now familiar lines, “the remote control doesn’t work.” So I said, “bring it in and we’ll test it”. At this stage, it may help the reader to follow the story if I describe the test unit I use for situations like this. It is a commercial unit of German manufacture and carries the Konig brand name (type number RCT 5502). As a matter of interest, the German term for remote control transmitter appears to be “Fernbe­dienung”, so the name of this device becomes “Fernbedienungs­ tester” (I wonder if they play scrabble in Germany!). I understand that there is also at least one locally made unit available. This is carried by J. V. Tuners, 216 Canter­bury Rd, Revesby, NSW 2212. Phone (02) 774 1154. The unit I have is basically a remote control receiver, similar to that used in TV sets but, for reasons which will become apparent, is a good deal simpler. It is designed for use with both infrared transmitters and the older ultrasonic transmitters, being fitted with both an IR photocell and a small microphone. It is housed in a small plastic case about 35mm wide, 25mm thick and 120mm long. There is an on/ off switch on one side of the case, two LEDs (one red & one green) on the top, and a 3.5mm socket on the other side. The red LED indicates that the power is on, while the green LED indicates when pulses are being received from the remote control. The 3.5mm socket may be used to bring the pulses out for checking on a frequency counter or CRO. Power is supplied by a 9V alkaline battery, while the internal circuit consists of just four transistors and a few minor components. It’s all quite simple really but it works very well. Howev­er, it is not infallible. Anyway, the customer brought in his control unit and I put it through its paces on the tester. This initially involves setting up the remote control transmitter and the tester so that they are about 150mm apart on a flat surface. The tester is then switched on and each of the transmitter buttons pressed in turn. It is important to test every button because only one or two may be faulty. Many customers don’t bother with such subtle points; to them it is all summed up in the phrase, “it doesn’t work.” There were no such problems in this case. Each button pro­duced a response from the green LED and I pronounced the unit OK. Unfortunately, this wasn’t the good news one might imagine because it meant that the fault was in the TV set. This would now have to be brought in for service. Fortunately, the customer had a second set and he duly organised delivery of the Philips set to the workshop. So, at the first opportunity, I put it up on the bench for a preliminary check. And this produced a surprise; there were no channels programmed into it. This was rather strange, particularly as the customer had not mentioned it, but I considered that it might be a byproduct of whatever fault there was in the remote control section. Anyway, I programmed the local channels into it, just to get it working, and this caused no problems. Nor did there appear to be any problems with the set’s overall behaviour; it was first class. But, as the customer had indicated, it would not respond to the remote control. No circuit At this point, I fished out my circuit of the KL9A but very quickly realised that it was for the basic chassis only; there was no remote control circuitry in it. And that was about it for then; there was little point in wasting time working blind and so I rang Philips and placed a manual on order. But I left the set running on the bench for the rest of the day, until I shut down and pulled the main switch for the night. Next morning, when I pushed in the main switch, everything came up as normal except for the Philips set. All it produced was snow and noise. It didn’t take long to confirm that all the channels I had programmed into its memory the day before had been lost. Fortunately, the reason wasn’t hard to find. This set uses a nicad battery backup for the memory, designated as part No. 1675. And since it was the original, it was not surprising that it had failed after about 12 years. I rang the customer and explained that I would have to wait on a manual before I could fix the remote control problem. At the same time, I took the opportunity to point out the additional problem with the channel memory system. He was quite understanding about any delay caused by the manual. And when I mentioned the memory loss his reaction was immediate. “Oh yes, I forgot to mention that – it’s all right as long as I leave the power point on but it loses it if I turn it off”. Well, that figured; the channels had been lost when he unplugged the set to bring it in. But at least I could go ahead with this problem. In greater detail, the battery is a 2.4V 110mAh type, about 7mm in diameter and 30mm long. It was readily available from one of my regular parts suppliers and, after fit­ting it, we had no more memory problems. With luck, it might last another 12 years. I now had to solve the problem with the remote control. Eventually, the manual arrived and, after some confusion due to the fact that it contains two different versions of the cir­cuit, I was finally able to tackle the job. The relevant part of the circuit is reproduced here – see Fig.2. It shows the IR receiver (part 1725) and a couple of vol­tages and waveforms. I decided to start by checking the voltages. The two points involved were 3C1 March 1995  47 Fig.2: the IR receiver circuitry in the Philips KL9A. The incom­ing pulses from the transmitter are processed by the IR receiver at extreme left & then fed to the base of a BC548 transistor via a 1µF capacitor. The resulting signal on the emitter of this transistor in then fed via a 10kΩ resistor to pin 13 of the data processor IC at right. and 2C1 on the IR receiv­er. And, in a moment of carelessness, I neglected to observe the polarity signs at these two points, assuming instead that the 5V marking indicated two separate rails, each at 5V with respect to chassis. The habit of measuring all voltages to chassis is strongly ingrained but it is not always the right thing to do. I woke up to this very quickly but, by a strange twist of fate, both points measured very close to 5V with respect to chassis. In practice, of course, the 5V is supposed to be read between 2C1 and 3C1, with 2C1 being at 5V with respect to chassis and 3C1 being at 10V with respect to chassis. Or that was how it was supposed to be. But 3C1 was not at 10V; instead, it was almost exactly at 5V, so there was virtually no voltage between the two points. By now, having re­alised my mistake and analysed the circuit correctly, I realised that there was something amiss around 3C1. The easiest thing to do was to pull the 3-pin plug to the IR receiver, whereupon the 3C1 supply line from the main part of the circuit jumped to 10V. Pushing the plug back in again Especially For Model Railway Enthusiasts Order direct from SILICON CHIP Price: $7.95 plus $3 for postage. Order today by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or send a cheque, money order or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 48  Silicon Chip pulled it back down to around 5V, which suggested a fault in the IR receiver module. The IR receiver I pulled the entire IR receiver out for a closer look. It is housed in a small but substantial aluminium box and consists of a PC board carrying a 16-pin IC, an IR photodiode, a couple of coils, and a few other components. I quickly concluded that there was little point in thinking about repairs. There was no circuit available and, as far as I could determine, the IC wasn’t This photo shows the IR receiver board after it has been slid out of its metal case. The IR photodiode is on the board at right, while the 3-pin socket is at left. Note the IR lens on the end of the case. avail­able as a separate item. Trying to troubleshoot a problem in these circumstances can be very risky. One can waste hours, only to finish up being unable to repair it anyway. The only logical answer was a new receiver. And that posed a whole new set of questions. Was a replace­ment readily available? What would it cost? And, most important­ly, would the customer want to incur such cost? While I was fairly confident that a replacement would be available, the cost was another matter. Receivers for other brands retail from $25 to $50 and I had a gut feeling that the higher figure would be the place to start from. I rang the customer and explained the situation. Naturally, he wanted some idea as to what it was all going to cost. I went over the cost of the work already done, added my estimate of the receiver price plus labour, and we came up with a guesstimate of between $150 and $200. Did he consider it worthwhile to go this far? Yes, he did – I should go ahead. And so I contacted Philips. Yes, the receiver was avail­ able and my gut feeling was not far out; the retail price I should charge my customer was $75. Since this kept the overall cost within my guesstimate, I went ahead and ordered it. It duly arrived and, at the first opportunity, I set about fitting it. This took no more than a few minutes work but when I gave it a trial run, it simply would not respond to the remote unit. So much for my optimistic “she’ll be right now mate” attitude! She wasn’t right at all. All kinds of horrible possibilities raced through my mind. Had I fouled up the receiver installation, which seemed so straightforward? Was it a modified receiver design, unsuitable for a set of this age? Was it a much more subtle fault, somewhere in the bowels of the set itself? Was the fault really in the transmitter, in spite of my previous tests? And had I invested unnecessarily in a replacement receiver, which would sit in my stock for years to come? When the panic subsided, I decided that the first two thoughts were the least likely, so I concentrated on the possibility of a fault in the set. The first step was to check the rail voltages at 2C1 and 3C1. These now measured 5V and 10V respectively, exactly as marked on the circuit. Next I turned to the CRO. The circuit shows a waveform coming out of the receiver at terminal 1C1. The circuit depicts square wave pulses with an amplitude of 5V but, unfortunately, there is no indication as to the frequency of these pulses, nor is there any other data on the coding used. Anyway, this was the first check point. And on the basis of the limited information in the manual, everything appeared to be OK at this point. From there, the signal goes via a 1µF electro­ lytic capacitor to the base of a BC548 transistor. The resulting signal on the emitter of this transistor is then fed via a 10kΩ resistor to pin 13 of the data processor IC, where another wave­form is shown. This is similar to the first but with a slightly lower (4V) amplitude. I traced the signal along this path and finished up with the correct waveform at pin 13, as shown on the circuit. So pulses were coming out of the remote transmitter, being picked March 1995  49 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 50  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 up by the receiver, processed, and passed to the data processor IC. So why wouldn’t it work? The most logical suggestion seemed to be a fault in the data processor IC, which wasn’t a very happy thought. From previous experience, I tipped that it would be quite expensive and that, in turn, meant that the cost situation would be getting out of hand. But there were other factors to be considered. How could I be absolutely sure it was that IC? Granted, the evidence was strong but if I was wrong, I would be down the drain for an expensive IC. What else could it be? One slim possibility was the trans­ mitter, in spite of the tests I’d already made. Remember that I said earlier that the transmitter tester was not infallible. Its weakness is that it can only confirm that pulses are being trans­mitted; it has no way of confirming that they have the correct coding sequence for a particular set. No gambling So although the risk appeared to be slight, I wasn’t pre­pared to gamble the cost of an IC until I was absolutely sure that the transmitter was clean. Ideally, this could be confirmed by acquiring another transmitter, perhaps borrowed from a col­league if I was lucky enough. But first I decided to have a look inside the transmitter for any clues or obvious faults. A general once over didn’t show up anything obvious, such as dry joints or obviously faulty components, and the voltages seemed to be at least sensible, which was the best I could do. Next, I connected the CRO across the crystal oscillator circuit and confirmed that this was working correctly. Its fre­quency was around 4MHz, which is similar to many other systems. So it looked as though I had drawn a blank. And then the system suddenly came good. Acting on an im­pulse, I pressed one of the control buttons, whereupon the re­ceiver immediately responded. I went through the whole range of control functions and they all worked perfectly. The trouble was, I hadn’t a clue as to why this had hap­pened. I could only assume that there was faulty connection in the transmitter somewhere (perhaps the battery contacts), which had come good as a result of my prodding and probing. But, try as I might, I couldn’t recreate the fault. So I simply went over the board with a hot iron and resol­dered all the joints, with particular attention to those around the crystal oscillator circuit. I didn’t find anything suspicious in the process and the unit still functioned in all modes after­wards. By now, I imagine, some readers are querying whether I goofed over the receiver; was it really faulty, or had it been a transmitter fault all the time? Well, the same thought occurred to me and I couldn’t rest until I had plugged the old receiver back in. No question; it pulled the 10V rail down as before and simply wouldn’t work, so that was the end of that theory. Finally, after putting the system through a week’s hard yakka, I returned the set to the customer with a warning to contact me immediately if the fault recurred. That all happened nearly 12 months ago and the system hasn’t missed a beat since. And what did it cost? It all added up to $149, so my initial estimate of $150-200 wasn’t SC too far out. March 1995  51 In this second article, we give the details on how to build this set of wide range electrostatic speakers which have been developed in Australia. They can be built using simple materials & readily available tools. By ROB McKINLAY Wide range electrostatic loudspeakers; Pt.2 To build these loudspeakers, you will need the following equipment: (1) a table or bench with a work surface of at least 700 x 1400mm, preferably coated with melamine, Laminex or a similar material. It must be flat and able to take heavy weights. (2) One 1220 x 605mm sheet of 18mm chipboard or MDF (medium density fibreboard). This will need to be cut into three strips, two measuring 240 x 1220mm and one measuring 120 x 1220mm. These are used as the pressure pads when gluing down the air gap spacers. Subsequently, the MDF strips will need to be cut down again, to be used as grid pressure pads. (3) 70mm disposable foam paint roller covers. One frame and two roller covers are supplied in the kit. More may be necessary depending on how you proceed. This photo shows one treble and two bass panel matrix panels laid out with their respective air spacers ready to be glued. Note the crosses marked on the matrix panels. 52  Silicon Chip (4) A soldering iron. This is needed to assemble the EHT supply boards and make the various connections from the supply to the panels. (5) A heat gun such as the unit made by Black & Decker. This will be used to tension the film after it has been applied to the panels. Don’t bother trying to use a hair drier. They are not hot enough and deliver too much air. (6) Digital multimeter with a 200 After glue has been applied to the top of the matrix panels, the air gap spacers are placed around the periphery, as shown here. PLASTIC MATRIX AIR-GAP SPACERS GRID (NODE POINTS ONLY ON ONE HALF PANEL) DIAPHRAGM GRID AIR-GAP SPACERS PLASTIC MATRIX AUDIO CONNECTION Fig.1: this diagram shows how the plastic matrix pan­els, air spacers, perforated steel grids and the central dia­phragm are sandwiched together to make a complete panel. The central diaphragm is glued to the air spacers of one half panel and, after tensioning, is painted with a conductive coating. megohm resistance range, to be used for checking out the individual panels. (7) Tools such as wire cutters/strippers, pliers, screwdrivers, electric drill and bits. As noted last month, the kits for these speakers include all the materials you will need, including adhesives. The en­closures are not included but are available fully finished. Having seen the excellent finish of the enclosures and having in mind their very reasonable cost ($499 for the pair), few people would wish to build their own enclosures from scratch. Handy hints The adhesives used in this project are very strong and durable. There are no solvents for them that are kind to your skin. Always wear the gloves supplied during the gluing opera­tions and when applying the conductive coating to the diaphragms. To ensure a good understanding of how this project goes together, it is a good idea to do a “dry run” with one panel half. Fig.1 shows an exploded view of the panels which are all the March 1995  53 After the air gap spacers have been attached, pressure pads are applied while the adhesive sets. In this case, plate glass sheets are being placed and these will be weighted down with bricks. Adhesive is applied to the perforated grid with the aid of a smaller paint roller, before the grid is attached to its matrix panel. the 10mm disc node points. These are the half panels that the diaphragm is attached to. Plastic support panels This photo shows the perforated steel grid ready to be glued into the matrix panel which has air gap spacers glued to it. same in principle although the central treble panel is nar­rower than the two bass panels. Essentially, each side of the panel is a plastic matrix to which air gap supports are glued. Then a perforated steel grid is fitted into the frame formed by the air gap supports. Then the plastic diaphragm is placed over one of the matrix/grid assembles and attached with adhesive. It is then ten­ sion­ ed with a hot air gun and sprayed with the conductive layer. Finally, the mating matrix/grid assembly is attached and the panel is com­plete. The dry run should be as follows. Place a white plastic support matrix 54  Silicon Chip on the work surface with the black crosses facing up. Place two long air gap spacers on top of the matrix covering the edge square segments. Place a medium length air gap spacer at each end on top of the matrix, forming a rectangle with the two long spacers. Place a perforated steel grid centrally within the rectangle with the screw terminal protruding into the matrix; ie, facing the work surface. The black crosses should be visible through the holes in the grid. This is where the node points are attached. This forms the basis on which the 12 half panels are assembled. Note that only six of these half panels carry The first operation is to bond the air gap spacers around the outside section of each plastic support matrix. Six of the panels are marked with a series of crosses running vertically down the centre line and six have a cross in each corner. During all assembly procedures place these faces up on the work surface. The white PVC spacers are to be bonded around the outside section of the plastic matrix. One side of the PVC strip will have a clear protective covering stuck to it; this face is to be kept up on the assembled half panel. Before applying adhesive to any components, check that they fit in their intended positions. The long spacers may overhang the matrix slightly but this excess can be sanded off after gluing. It is best to start work on a maximum of three half panels at first, until you have some experience with the process. There­fore, you can start with two bass half panels and one treble half panel. Place the three half panels on the work surface with the black crosses up. Select six long, four medium and two short air gap spacers. Lay these on the work surface next to each other with the non-covered side facing up. This will allow you to roll a coat of adhesive, first over the long spacers, then the medium and short spacers, in one operation. Note: it is essential to place a plastic sheet) under the plastic matrix before gluing, in case the adhesive runs down and sticks to the work surface, making removal of the matrix diffi­cult. The clear plastic covering on the spacers will prevent adhesion to the pressure pad. This covering should be not be removed until all gluing operations are finished. Apply a thin coat of adhesive to the non-covered side of the spacers with a roller. Place the spacers around the matrix outer segment as in Fig.1. It is important that the outer edge of the spacers line up with the outer edge of the support matrix. This will ensure that the grid has sufficient room to fit into and be bonded to the support matrix. When in position, place a sheet of chipboard (or plate glass) over the spacers, making sure not to disturb them. Place weights on the chipboard such as 12 bricks, etc. Allow 24 hours for the adhesive to cure. Repeat this operation on all panels. Once the perforated grids have been attached to the matrix panels, MDF pressure pads ensure they are kept flat while the adhesive cures. Grid preparation 12 perforated steel grids have been provided; eight wide (bass) and four narrow (treble). The grids are supplied in mirror matched pairs. Do not mix them up. They have been colour coded to assist in identification. Each grid has a 3mm screw connection silver-soldered to it. This screw protrudes through a segment of the plastic support matrix, enabling the signal con­nection to be made. Before proceeding to the next step, check that the grid sits in the gap created by the air gap spacers, without the screw fouling the matrix. If necessary, carefully use side cutters to break out the offending piece of matrix. Grid bonding For this operation, you need a piece of MDF 5-6mm narrower and 5-6mm shorter than the grid, to enable pres­ sure to be applied during bonding. Cut some polyethylene sheet into strips that are wider than the grids to be glued. These will stop the pressure pad from sticking to the grid. Lay Once the matrix/grid assembly is complete, blobs of silicone are applied to the grid to form nodes for the diaphragm. Teflon node buttons are placed onto the blobs of silicone (see previous photo) & pressed down using a steel ruler (see text). some polyethylene sheet on the work surface, then lay the plastic matrix on the sheet with the white PVC spacers facing up. Hold the grid vertically in one hand and roll a light coat of adhesive onto the side of the grid that is to come into con­tact with the plastic matrix; ie, the side with the threaded portion of the terminal. Avoid getting adhesive on the diaphragm side of the grid or onto the threads of the audio connection terminal. Place the grid centrally in the space created by the PVC spacers so that the glue contacts the plastic matrix. Ensure that the audio connection terminal does not foul the plastic matrix. Place a strip of polyethylene sheet over the grid and then the MDF pressure pad. Place weights on the MDF to ensure good adhe­sion to the matrix. The polyurethane glue used for the construction relies on the moisture in the air to cure. Normal curing occurs in 24 hours. On very dry days the curing cycle will be longer. If there is any doubt as to whether the glue is cured, leave for additional time. Repeat the above operation for all the grids, then remove the clear plastic covering from the air gap spacers. Diaphragm nodes Six of the plastic matrix panel halves are supplied with a series of black crosses running vertically March 1995  55 position level to the top of the air gap spacers, plus a thickness of paper, they will be level with the air gap spacer when the backing paper is removed. The diaphragm will adhere strongly to the adhesive on the disc, eliminating diaphragm rattles and the need for a matching disc on the other half panel. This method of construction greatly reduces the risk of EHT leakage from the conductive side of the diaphragm to the grid. Leakage caused by dust collecting on the node points is also eliminated. Allow the silicone adhesive to cure before attaching diaphragms to these panels. This photo shows the foil tape attached to one side of the matrix assembly. It is then drilled to take a screw connection. The clear plastic diaphragm is stretched over the panel and taped down as shown and the adhesive is activated by the heat gun. Once the diaphragm adhesive has cured, the film is tensioned on the panel by shrinking it with the heat gun. through the centre axis. These crosses are where the nodes are to be fixed and should be visible through the grid. If the centre is not visible, project where it should be and mark the grid with a felt pen at this point. The nodes are made up of small discs of 2mm thick Teflon attached to the grids with silicone adhesive. Place a blob of silicone adhesive about 5mm in diameter and 4mm high at the centre of each cross. Place a white Teflon disc with the backing paper (brown side) up, gently on top of the blob. Place an ordinary piece of A4 paper on top of the long PVC spacer on either side of the Teflon disc. Using the edge of a steel rule, press the disc into the blob of silicone until the rule is resting on top of both pieces of paper. The surface of the disc should be parallel to the surface of the air gap spacer. Now move up to the next node position. Repeat this process on all panel halves which are marked with the black crosses running down the centreline (six of them). The Teflon discs have an adhesive layer which is covered by backing paper. As the disc has been set at a 56  Silicon Chip Installing the foil tape Each panel has a wire attached to its diaphragm for the EHT. Some matrix panels do not have a fully filled-in section on one side. The side that is filled in has the foil tape attached to it. The 150mm long foil tape is placed on the air gap spacer, running towards the top of the panel. From the small roll, tear off about 150-175mm of foil tape. Peel about 50mm of the backing from the foil and apply the tape at the connection point first and run it onto the top of the PVC spacer. The tape needs to be turned through 90° toward the top of the half panel. The easiest way to do this is to fold the tape over at 90° in the opposite direction to that which is desired; ie, fold the tape towards the bottom of the panel. Peel off some more backing and fold the tape back on itself towards the top of the panel. This will make a neat turn in the tape. Peel off the backing about 50mm at a time and stick the remainder of the tape down onto the air gap spacer. Drill a 3mm hole through the foil and matrix at the connec­tion point. Don’t use too much pressure as the matrix is fragile. Crimp or solder an eye connector to 400mm of EHT wire and fix to the panel connection point with a screw and nut. It is best if the terminal is on the inside section of the matrix. This will allow the channel section to sit as close as possible to the matrix. When tightening the screw, be careful not to tear the foil tape. Diaphragm installation It is suggested that the diaphragms for the narrow treble panel should be fitted first. This will give some experience for the more difficult bass panel. Place the half panel with the Teflon node points spacer side up onto the work surface. Make sure that the clear protective covering on the air gap spacers has been removed, as mentioned earlier. Remove the backing paper from the Teflon node points. Remove the clear backing from the supplied diaphragm. “TOP” has been marked on the diaphragm surface to identify it. Tear off four pieces of masking tape about 80mm long and attach them to each corner of the diaphragm. With the help of an assistant, hold the diaphragm taut over the half panel and lower it onto it. It is important that the diaphragm overlaps the air gap spacers on all sides before coming into contact with the Teflon node points, as the adhesive bond will be difficult to break if an error is made. If an assistant is unavailable, tape down one end of the diaphragm to the work surface, keeping the other end off the panel. Lower the diaphragm down onto the panel, ensuring there is some overlap around all edges. Tape the diaphragm down to the work surface using more masking tape. Use tape in the four corners and at about seven or eight equally spaced positions along the longest edge. Tension the diaphragm as much as possible by pulling on the tape prior to sticking to the work surface. This initial tension­ing will not affect the ultimate tension achieved after the heat shrinking process. It is simply to make this process easier. The diaphragm should now be taut and wrinkle free. The node points should be visibly contacting the diaphragm all down the centre axis of the half panel. Using a heat gun on low setting, aim the hot air from about 150mm at an angle of about 45° at the PVC spacer. Keeping the heat gun moving at all times along the air gap spacer, use a small pad of folded tissue to gently push the heated diaphragm into contact with the PVC. The heat will melt the adhesive back­ing and allow a strong bond to the PVC spacer. Follow this procedure all the way around the perimeter of the panel. Small wrinkles will occur in the diaphragm during this procedure. Don’t worry about them. They will disappear when the diaphragm is fully tensioned. Conductive fluid is applied to the diaphragm film with the aid of a small sponge. After the diaphragm is stuck to the panel it will need to be tensioned. Keeping the heat gun moving at all times, direct the hot air around the edges slowly working towards the centre of the panel. Take care not to blow the diaphragm down onto the grid. If this does happen it may be released by gently heating and pushing through from underneath with a paint brush. The alternative method is to release the diaphragm from the PVC spacer nearest to the stuck down portion using gentle heat, and lifting the diaphragm clear of the grid. It can then be re-stuck to the PVC spacer. The correct tension has been reach­ ed when the diaphragm will not shrink any more. This point can be determined by passing the gun over the diaphragm and watching if any wrinkles appear as heat is applied. If none do, the diaphragm has reached its maxi­mum tension. If wrinkles appear or the diaphragm “sags” when heat is applied, continue with the shrinking process. Applying conductive coating Note: it is essential that the conductive coating is ap­plied in temperatures above 20°C. Failure to do so will lead to a poor surface cure. After the diaphragms have been tensioned they need to be made conductive. Gently wash down the surface of the diaphragm with methylated spirit and a clean tissue. Do this three times (on the same diaphragm). Ensure that the diaphragm is dry. The heat gun can be used for this. Pour a small amount of the acrylic conducting solution into a small bowl. Using a small piece of sponge, lightly swab the solution over the surface of the diaphragm. Keep the conductive coating about 5mm from the internal edge of the air gap spacers except in the area that will be contacted by the foil tape on the other half panel. The conductive coating should overlap this air gap spacer by about 10mm for the length of the foil tape. This is the only portion of air gap spacer that should have the conduc­tive coating overlapping it. The covering should be light with no evidence of puddles. Avoid air bubbles on the surface. If any foreign matter such as hair sticks to the coating, it may cause a discharge path for the bias voltage. Avoid this like the plague. Do not allow the con­ductive solution to spill over the side of the panel as this may also allow a leakage path for the EHT. Make sure that the solu­tion is applied to the diaphragm area that the foil tape will contact when the panel halves are assembled. Now put this panel aside and coat the next. The solution takes about two to three hours to cure. Check the resistivity and continuity with your multimeter. Place the two probes gently on the diaphragm surface about 100mm apart. The resistance reading should be 20 to 100 megohms. Place the probes at either end of the diaphragm on the conductive coating. A reading of over 20 megohms should be obtained. The actual value is not critical. This test just confirms that the diaphragm is conductive all over. When using probes on the diaphragm ensure that it is not punctured. Next month will give the final assemSC bly instructions. March 1995  57 A Look At The 68000 Microprocessor RO UN DE DG E 0 HB By ELMO JANSZ The 68000 microprocessor is manufactured by Motorola & made its debut in about 1979. It is a 16-bit device & was designed to supersede the earlier 8-bit 6800. It is widely used in Apple Macintosh & Atari machines. Over the years, the amount of hardware and software acces­sories available for this device has grown rapidly. From the 68000, a family of devices has now come into existence such as the 68010, 68020, 68030 and the 68040. In this article we shall confine discussion to the 68000. From this point onwards we shall refer to the microproces­ sor as the MPU. The 68000 comes in a 64-pin package which elimi­ nates the need for multi-function pins and simplifies interfacing with external hardware. It has a 32-bit internal architecture, which includes 16 internal general purpose registers, each 32 bits wide. Eight of these are data registers and the rest are address registers. The data and address registers do not have dedicated func­tions such as an accumulator, which was so with the 6800. In­structions can be written 58  Silicon Chip so that operands reside in any of the data registers or storage locations in external memory. The MPU can handle a bit, a byte, a word or a long word of data. A bit is one binary digit, a byte is eight binary digits, a word is 16 binary digits, and a long word is 32 binary digits. The MPU has 23 address lines, giving it access to a very large range of addresses in external memory. It also has access to a user/supervisor environment which provides for multi­pro­ cess­­ing and multitasking activities; ie, the ability to handle more than one task at a given time. Interface buses Fig.1 is a block diagram of the MPU showing its interface buses. Buses are groups of pins or lines and these come under the following headings: Address, Data, Asynchronous Control, Proces­sor Status, System Control Bus/ Function Codes, Interrupt Control, Arbitration Control and Synchronous Control. Let’s examine each of these in turn. The address bus: the MPU has a 23bit address bus. Lines A1 to A23 are used to address memory and input/ output devices. A0 is not shown as it is internal to the device and is used to deter­mine whether the upper or lower byte of a word is to be used when processing byte size data. The data bus: labelled D0-D15, this bus is bidirectional and can be used to read/write data. Byte size data can be transferred on either half of the bus, while word transfers use both halves. The asynchronous control bus: the MPU uses asynchronous bus control. This means that once a bus cycle (ie, a procedure) is initiated, it is not completed until a signal is returned from external memory. Five signals are available to control address and data transfers. These are: (1) Address strobe (AS-bar) (2) Read/write (R/W-bar) (3) Upper data strobe (UDS-bar) (4) Lower data strobe (LDS-bar) (5) Data transfer acknowledge (DTACK-bar) The MPU has to indicate to external devices when an address is available and whether a read or write operation is to take place. The AS-bar and R/W-bar signals perform this activity. When a valid address is placed on the address bus, the AS-bar line is pulsed low. The R/W-bar indicates whether a read or a write is to com­mence. When the MPU reads data from the data bus, R/W-bar is pulsed high. When data is written to memory or to an output device, R/W-bar is pulsed low. The asynchronous bus cycle re­quires external memory to signal the MPU when the cycle is com­pleted. The DTACKbar input provides this. During a read cycle a low on DTACK-bar indicates to the MPU that valid data is on the bus. The MPU reads, latches the data, and completes the cycle. During a write operation, DTACKbar informs the MPU that data has been written to memory or an output device. The UDS-bar and the LDS-bar are called the upper and lower data strobes respectively, and indicate whether a byte or word of data is on the data bus. A low on UDS-bar indicates a data transfer on the upper eight lines of the data bus. A low on LDS-bar indicates a transfer on the eight lower data lines. Table 1 shows the logic levels possible for each type of data transfer. Bus function codes: during a bus cycle, the MPU outputs a 3-bit status code on FCO, FC1 and FC2. These are called the bus func­tion codes and these inform external devices what type of bus cycle is in progress. They indicate whether data or program is being accessed and whether the MPU is in the user or supervisor state. The codes are output at the beginning of each read or write cycle and continue to be valid until the next read or write cycle commences. System control bus: this bus is comprised of the three lines BERR-bar, HALT-bar and RESET-bar. BERR-bar is an input to the MPU to inform it that there is a problem with the current bus cycle, while the HALT-bar signal is used to stop the MPU. An external signal applied to this line stops it at the completion of the current cycle. HALT is bidirectional and when an instruction execution is terminated, external devices are informed of the fact using this line. RESET-bar is used for initialisation with a signal from ADDRESS BUS VCC(2) A1-A23 ADDRESS/ DATA GND(2) CLK DATA BUS D0-D15 FC0 PROCESSOR STATUS MC68000 PERIPHERAL CONTROL (SYNCHRONOUS CONTROL) FC1 FC2 MC68000 MICROPROCESSOR R/W UDS E LDS VMA ASYNCHRONOUS BUS CONTROL DTACK VPA BR BG BERR SYSTEM CONTROL AS BGACK RESET HALT BUS ARBITRATION CONTROL IPL0 IPL1 IPL2 INTERRUPT CONTROL Fig.1: this block diagram of the 68000 MPU shows all the various interface buses. These fall into various groups & the function of each group is explained in the text. external hardware, generally at power up. It is bidirectional but its output is software controlled. Interrupt control bus: this bus is comprised of three lines, IPLO-bar, IPL1-bar and IPL2-bar, and is used to service inter­rupts from external devices. In an interrupt routine, the MPU discontinues its current activities and services an external device. The external device provides a 3-bit code on these lines and this is compared with a mask value in the status register. Arbitration control bus: this bus is comprised of the three lines BR-bar, BG-bar and BGACK-bar. These signals are used for hand­ shaking activities that control transfer of the MPU’s system bus between devices. Hand­ shaking is the correct communication between devices so that information can be smoothly transferred between them. The device that possesses control of the bus at any time is called the Bus Master. Synchronous operation: the MPU has facilities for transferring data over the system bus in a synchronous manner. In a synchro­nous transfer, no acknowledgment is required from the receiving device before the next piece of information is transmitted. Three control signals are available for this function: Enable (E), Valid Peripheral Address (VPA-bar) and Valid Memory Address (VMA-bar). They are used to interface the MPU to much slower devices. Enable (E) provides a free-running clock 1/10th of the MPU clock frequency. For example, it could be used to interface the 10MHz MPU Table 1: Logic Levels For Each Type of Data Transfer UDS-bar LDS-bar R/W-bar 0 0 0 Word transferred to memory or I/O 0 1 0 High byte transferred to memory or I/O 1 0 0 Low byte transferred to memory or I/O 1 1 0 Invalid data 0 0 1 Word transferred to MPU 0 1 1 High byte transferred to MPU 1 0 1 Low byte transferred to MPU 1 1 1 Invalid data Comments 31 16 15 87 16 15 31 0 0 15 87 SYSTEM BYTE USER BYTE to a 1MHz external device. VPA-bar indicates to the MPU that it is to perform a synchronous data transfer over its asyn­ chronous system bus. Valid Memory Address (VMA-bar) is a signal produced by the MPU when VPA-bar goes active. It tells external equipment that a valid address is present on the address bus and that the next data transfer will be synchronised to the enable (E) line. Clock input: the block diagram shows a single clock input la­belled CLK. This signal is externally generated and fed to the MPU at frequencies between 4MHz and 12.5MHz. Internal registers The MPU contains 18 32-bit internal registers as depicted in Fig.2. Observe that there are eight data registers, seven address registers, two stack pointers, a program counter and a status register. The status register, unlike the others, is only 16 bits wide. The eight data registers are labelled D0 - D7 and are each 32 bits wide. The least significant bit is labelled B0 and the most significant bit B31. Each can work with a byte, a word or a long word of information. This information is generally referred to as the operand. Byte data always resides in the eight least significant bits, words in the least significant 16 bits and long words occupy all 32 bits. The size of the operand is specified in the instruction. Data registers can also be used as index registers. The value in the register represents an offset, which 60  Silicon Chip EIGHT DATA REGISTERS A0 A1 A2 A3 A4 A5 A6 SEVEN ADDRESS REGISTERS A7 TWO STACK POINTERS 0 USER STACK POINTER SUPERVISOR STACK POINTER 31 D0 D1 D2 D3 D4 D5 D6 D7 0 Fig.2: the MPU contains 18 32-bit internal registers as depicted here There are eight data registers, seven address registers, two stack pointers, a program counter & a status register. PROGRAM COUNTER STATUS REGISTER can be combined with the contents of another register to point to a data location. This facility is very useful in reading blocks of information. Address registers The address registers are labelled A0 to A7 and are also 32 bits wide. They do not store data but rather address information such as base and pointer addresses. There are two stack pointers called the user stack pointer (USP) and the supervisor stack pointer (SSP). Only one of these is active at any time and for this reason they are shown as a single register, A7. USP identifies the top of the stack in the user part of system memory. This is the section in memory where return addresses, (ie, when called upon to temporarily suspend its normal activities and attend to some other demand) are stored. Register data and other parameters are also saved in the stack. When in the supervisor state the user stack pointer becomes inactive and the supervisor stack becomes active. The address contained in the supervisor stack points to the top of a second stack called the supervisor stack. The supervisor stack is used for the same purpose as the user stack but it is also used by supervisor calls such as soft­ware exceptions, interrupts and internal exceptions. Exceptions are similar to interrupts. The procedure permits the MPU to respond to certain events, external or internal, by suspending its current activities and switching to a new program sequence. At the completion of the routine, the program is switched back to the point at which it left off in the main program. (The return address is stored in the stack before commencement of the new program sequence). The program counter The program counter points to the next instruction to be executed. It is automatically incremented by two when an instruc­tion is fetched. Although the PC is shown as composed of 32 bits, only the lower 24 are used. These can access 16M bytes or 8M words; ie, the address space can be considered to hold 16M bytes or 8M words. Word addresses are even and can have values from 00000016 through to FFFFFE16. Note that 1K = 1024 bytes and 1M = 1,048,576 bytes. The status register The status register is shown in Fig.3. Two bytes called the User byte and the System byte are shown. Each byte consists of a number of flags or condition codes. The carry flag, bit 0, is set when an add operation generates a carry out or a subtract (or compare) operation requires a borrow. During shift or rotate operations (ie, the movement of the bits of a piece of informa­tion), it holds the bit that is rotated or shifted out of a reg­ister or memory location. The overflow flag is bit 1. If an arithmetic operation on signed numbers (numbers that are represented as positive or negative quantities) produces an incorrect result, then the overflow flag is set; otherwise it is cleared. The zero flag, bit 2, is set when the result of an opera­tion is zero. A non-zero result clears the z flag. The negative flag, bit 3, depends on the sign bit; ie, the most significant bit of the result of an arithmetic logic, shift or rotate opera­tion. If this bit is 1 then the flag is set; otherwise it is cleared. The extend flag, bit 4, takes the same status as the C Flag, resulting from a shift or rotate operation. Let us now examine the system byte of the status register. It contains the bits that control the operational options of the MPU and the interrupt mask which was mentioned above. Bit 13 is used to distinguish between the user and super­visor states of operation. A logic 1 in this bit indicates that the MPU is operating in the supervisor state while a 0 indicates the user state. Trace Mode (T) The T bit (Trace mode) is used to enable or disable trace (Single Step) operation. It is active or not by setting or clear­ing bit 15. The entire contents of the Status Register can be read using software. Un-implemented bits are read as logic 0. The system byte can be modified only when the MPU is in the super­visor state. Addressing modes Addressing modes give information to the programmer on how to generate an address that identifies the location of the oper­and. The operand is the information being worked upon. We observed earlier that the MPU includes eight data registers and eight address registers. Data registers are used for storing usable data. Address registers, on the other hand, are used to access source or desti­nation operands residing in memory. The MPU can address a very large memory space, 16 megabytes in fact. The addressing modes available to the MPU can be classified under the following headings: (1) Immediate (2) Direct (3) Absolute (4) Address Register Indirect (5) Address Register Indirect with 16-Bit Displacement (6) Address Register Indirect with Index and 8-Bit Offset (7) Address Register Indirect with Post-Increment (8) Address Register Indirect with Pre-Decrement (9) Program Counter Relative with 16-Bit Displacement (10) Program Counter Relative with Index and 8-Bit Offset Let us examine each of these using only the MOVE instruc­tion which is available with all addressing modes. Immediate: in immediate addressing, the operand is included in the instruction. For example the operation “MOVE.W #$AABB,DO” moves the word $AABB into Data Register D0. The symbol # indi­cates that immediate addressing is to be used. The $ sign indi­cates hex-data. $AABB is the source operand. SYSTEM BYTE 15 T 13 S USER BYTE 8 10 I2 I1 I0 4 X N Z V 0 C TRACE MODE SUPERVISOR STATE INTERRUPT MASK EXTEND NEGATIVE CONDITION CODES ZERO OVERFLOW CARRY Fig.3: the status register. Two bytes called the user byte & the system byte are shown. Each byte consists of a number of flags or condition codes. For dealing only with bytes of data, a special form of immediate addressing called Quick Immediate addressing is avail­able. The instruction “MOVEQ #AA,D0” uses this form of immediate addressing to move the byte $AA into D0. Direct: Direct addressing is used only when one of the data or address registers contain the operand. If the register specified by the instruction is the data register, the addressing mode used is called Data Register direct. On the other hand, if the address register is specified, it is called Address Register direct. Consider the instruction “MOVE.W AO,DO”. The Move.W portion indicates that the word in A0 is to be moved into D0. A0 contains the source operand and D0 has the destination operand. The source operand uses address register direct addressing, while the destination operand uses data register direct address­ing. Both operands do not reside in external memory. Absolute: in the absolute addressing mode, the effective address of the operand is included in the instruction. There are two forms of absolute addressing, called absolute short and absolute long. Both forms are used to access operands residing in external memory. If absolute short addressing is used, a 16-bit address must be included as the second word of the instruction. This is the storage location of the operand in memory. Consider the instruc­tion: “MOVE.L $2345,D0”. It indicates that the long word commenc­ ing at address location $2345 is to be moved into the data reg­ister D0. The MPU does a sign extension based on the most significant bit of the absolute short address to give a 32-bit address. (Remember only 24 bits are used as the address bus is 24 bits wide). $2345 = 0010 0011 0100 0101 The most significant bit is 0. Extending it gives: 0000 0000 0010 0011 0100 0101 ie, the required address is $002345. Absolute short addressing generates an address correspond­ing to the first and last 32K bytes of the MPU’s address space. Absolute long addressing permits the use of a 32-bit number as the data address. The instruction “MOVE.L $02345, D0” has the same effect as the previous one, with the exception that the absolute address is specified with more than four digits. The source operand is now encoded by the assembler as an absolute long address using 32 bits instead of 16. Again, only 24 bits are actually used. The operand can now reside anywhere within the address space associated with the MPU. Address register indirect: in this form of addressing one of the address registers contains the address of the source or destina­tion operand. As an example, in the instruction “MOVE.L (AO), D0”, A0 contains the address of the source operand and must be enclosed in brackets. D0 is the destination operand. Execution of the instruction causes the long word at the address location pointed to by the contents of A0 to be copied into D0. Address Register Indirect With 16-Bit Displacement: this address­ ing mode uses a sign extended 16-bit displacement, which is added onto the contents of the address register to March 1995  61 generate the address of the operand. Consider the instruction “MOVE.W 10 (AO), D0”. 1010 is the 16-bit displacement. Since the displacement is 16 bits wide, the operand must be within +32K bytes of the memory contents pointed to by the address register. In Address Register Indirect addressing, the address of the operand is determined by adding the contents of an internal register and the signed 8-bit offset to the contents of the address register. The internal register serves as the index. For example, in the instruction “MOVE.W 12(A0, D0), D1” 1210 is the offset, A0 the address register and D0 the index register. These quantities are added to determine the address of the operand. Address Register Indirect With Post-Increment: this addressing mode is similar to address register indirect addressing. However, with post-increment, after the address is used, the contents of the address register are incremented by one, two or four depend­ ing on whether a byte, a word or a long word was accessed. Con­sider the instruction “MOVE.W #AABB,(A0)+”. We observe that the operand is to be placed in the address location pointed to by the address register. After the operation, the address register is automatically incre­ment­ed by 2, since the operand is a word. Address Register Indirect with Pre-Decrement: is similar to address register indirect with Post-Increment, except that the address register is first decremented by one, two or four depend­ing on whether a byte, word or long word is involved. Consider the instruction “MOVE.W #AABB, -(A0)”. The address register is first dec­ remented by 2 since a word is involved and the word $AABB is moved into the address indicated by the address reg­ister. Program Counter Relative with 16-Bit Displacement: in this mode, a displacement is used to indicate to the program counter how many bytes the data to be accessed is located away from its current position. When the instruction is executed, the MPU sign extends the 16-bit displacement to 32 bits and then adds it to the updated value of the program counter. Consider the instruction “MOVE.L Loc (PC), D0” which moves the long word starting at memory location with label Loc into D0. To do this the assembler calculates the number of bytes the updated value of the program counter is away from the address with label Loc. This value is expressed as a signed 16-bit binary number and is added onto the current value of the program coun­ter. Since 16 bits are used the operand lies within +32K bytes of the updated value of the program counter. Program Counter Relative with Index and 8-Bit Offset: this is similar to the addressing mode examined above except that both an index and an offset are used. The contents of an index register – any of the data or address registers, together with a signed 8-bit offset – are added to the updated value of the program counter to determine the address of the operand. Now consider the instruction “MOVE.W 6(Pc, D0), D1”. 610 is the 8-bit offset and D0 represents the index. Both values are added to the updated value of the program counter to obtain the address of the operand. Once located the operand is loaded SC into D1. SILICON CHIP BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers and are made from a dis­tinctive 2-tone green vinyl that will look great on your bookshelf. SUBS BUY A GET A CRIPTION ON TH DISCOUN & T E (Aust BINDER . Only ) ★ Hold up to 14 issues (12 issues plus catalogs) ★ 80mm internal width. ★ SILICON CHIP logo printed in gold-coloured lettering on the spine & cover. Yes! Please send me ________ SILICON CHIP binder(s) at $A14.95 each (incl. postage in Aust.). NZ & PNG orders please add $5 each for postage. Enclosed is my cheque/money order for $­__________ or please debit my:   ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_______________________ Card expiry date______/______ Name ___________________________________________________ PLEASE PRINT Street ___________________________________________________ Suburb/Town_____________________________ Postcode_________ 62  Silicon Chip Mail, phone or fax your order to: SILICON CHIP PUBLICATIONS PO Box 139, Collaroy Beach, NSW 2097, Australia. Phone (02) 979 5644 Fax: (02) 979 6503. REMOTE CONTROL BY BOB YOUNG Building a complete remote control system for models; Pt.3 This month, we describe the construction of the Mk.22 receiver board. The top of the board accommodates the coils, a ceramic resonator & crystal holder, while the underside is packed with surface mount components. D1 C4 ANT2 Q1 C3 R1 R9 E OUTPUT +4.8V C16 TB1 L4 CF1 L3 R11 R3 C12 Q2 Q5 Q6 L6 Q4 R13 C8 R2 C6 C1 R4 C2 C14 C9 C5 This is quite a delicate little PC board to make. Minimum track spacing is .016-inch, minimum track width is XTAL1 C10 C11 R12 C15 R5 C13 Q3 R10 C7 Construction R6 R7 R8 ANT1 ers. The decoder layout (to follow next month) allows the utmost in flexibility to overcome the problems of non standardisation of the servo plugs. The decoder also features heavy filtering to help minimise the problems of inter­ ference on long servo leads. The physical layout is that used in all Silvertone receiv­ers since 1969 and both the receiver and decoder PC boards may be used as direct replacements for earlier modules back to Mk.7. The Mk.22 is better in regard to mechanical robustness, receiver OUTPUT The receiver will be supplied as a full kit, as an assem­bled and tested PC board, or as a fully assembled receiver with decoder included. In all cases a PC board is supplied but for the those wishing to do their own PC boards, I have just one few tip which is “don’t bother. After all, it took many refinements of the basic layout before I was completely happy.” However, a little background won’t hurt. The Mk.22 is de­signed essentially as an AM receiver replacement for all brands of commercial R/C receiv- sensitivity and electric motor noise immunity. The physical layout provides the smallest frontal area, with the PC boards mounted at right angles to the direction of travel of the model. This minimises component damage in crashes. The case is very robust, being heavy gauge aluminium, and this also provides improved noise immunity. The two-board arrangement also allows the receiver to be used separately, free of the clutter of an existing decoder. Note that the board is double sided, with the ground plane on the top. The holes are plated through, so there’s no need to solder the throughhole components on both sides. L1 L2 L4 D2 Fig.1: the layout of the surface mount components, shown 50% larger than actual size. Note that the components are numbered to match those on the circuit published in last month’s issue. Fig.2: the through-hole components, such as the coils and crystal holder, shown 50% larger than actual size. Note that the coils are numbered to match those on the circuit published in last month’s issue. March 1995  63 Fig.3: repeated from last month, this scope photo shows a typical output waveform at the collector of transistor Q6. Note that the number of spikes will depend on the control settings of the transmitter. .012-inch and mini­mum component spacing is .020-inch. I have tried to keep the number of components to a minimum and the spacing as wide as possible but on a board this size spacing will always be tight. Check the etched PC board for shorts, particularly where two tracks go under one component. Now set the PC board groundplane down on a clean sheet of white paper and commence to place the surface mount components. The paper is for contrast when you drop a component. You will not find it on a dirty bench. Do not leave discarded components lying around on the bench where you are working, especially unmarked capacitors. You have been warned. Keep that sheet of paper clear of all items except the component value you are working with at the time. I would suggest that before going further, you re-read the column on the hand assembly of surface mount PC boards in the January 1995 issue. The layout of the surface mount components is depicted in Fig.1, shown 50% larger than actual size. The through-hole com­ponents, such as the coils and crystal holder, are shown in Fig.2, again 50% larger than actual size. Note that the diagrams show the components numbered to match those on the circuit pub­lished in last month’s issue. Begin by aligning the PC board with the single SOT23 pad for D2 closest to your soldering hand. Proceed to tin one pad only in each component 64  Silicon Chip This larger-than-life size photo shows the completed receiver assembly. Note the socket for the plug-in crystal. The resistors, capacitors & transistors are surface-mounted on the other side of the board. set. The best pad to tin is that closest to your soldering hand. Once one pad in every component set is tinned, you may commence component placement. To mount each component, simply pick it up with the tweezers, heat the tinned pad and slide it into position, taking care to obtain correct alignment on the centre of the pads. Now, while the component is still warm, solder the other leg(s). There is no set order of assembly but it is a good idea to place all of one value at a time. I usually start with the semi­conductors. One good tip is keep your components in a little plastic tray. The lid of a small pill bottle is ideal, but make sure it is white. Tip all of the components (one type only) into the lid. Most components, if they are marked at all, are only la­belled on one side and you should mount them with the marking visible, so that servicing is easier later. Now when you want to turn a component over you just tap the lid gently on the work­bench and the components will do a little dance and some of them will turn over. Mount those that present the markings up and then just keep tapping the lid until all components are placed. When all the surface mount devices are mounted, begin mounting the components on the topside of the board, as shown in Fig.2. Finally, solder one metre of hook-up wire to Antenna 2 (ANT 2). Plug in the receiver crystal and you now have a finished receiver. It takes me approxi- mately an hour to assemble a receiv­er with conventional components or 45 minutes for the surface mount version. A surface mount assembly machine will do the same job in approximately one minute! There is one point to note in regard to TB1, the 4-pin header. This may be mounted or left out completely. In the latter case simply insert the wires from the decoder directly into the holes. You may wonder why there are two pins connected together. The spare pin can be very useful for tuning the receiver. Even if the header pins are not mounted, solder a short piece of wire into the spare hole as a tuning point to hook oscilloscope and meter leads onto. Alternatively, if a remote antenna is used, these two pins may be separated and the spare pin used as an antenna connection. In this case, join Antenna 1 to the spare pin on TB1 with a jumper. Testing & tuning Conduct one final visual inspection to ensure all connec­tions are complete. Check for shorts and then switch your multi­ meter to its lowest resistance range and check across the power connections for a direct short. Wind the slugs in RF coils L5 & L6 well in towards the bottom of the formers and set the oscillator slug flush with the top of the coil. You must use a plastic alignment tool for this job; don’t use a small screwdriver as it is too easy to damage the slugs. Begin with the routine DC checks. Hook up a 4.8V nicad pack to the appropriate pins on TB1. If the header pins have been installed, then the pin layout is directly compatible with a J.R or Futaba battery pack connector and the battery pack may be plugged directly into this connector. Check to ensure that the DC conditions are correct on each stage. The decoupled power rail after Q5 will be about +4.1V when supplied directly from the battery and approximately 0.2V lower when supplied from the decoder which has its own decoupling. The oscillator coil tuning is not critical and the oscilla­tor should be running with the slug in the coil flush with the top of the coil former. If an oscilloscope and frequency counter are at hand, then check the waveform and frequency of the oscil­lator. The waveform should be near sinusoidal, approximately 1.5V volts peak-peak in amplitude and if Showa crystals are used, almost on frequency. The tolerance on these crystals is ±0.005% and thus a variation of ±1.5kHz is acceptable. C7 and C10 may be adjusted to trim the frequency if other brands of crystals are used and they are not close enough to the designated frequency. If all is well at this point, hook up a meter to ground (Black) and pin 4 on TB1 (red lead). It is a good idea to put a 4.7kΩ resistor in each meter lead to provide isolation for the receiver. Hook the scope to the meter side of these leads. Apply power and the meter should read approximately 3.9V and steady. The scope trace should be a straight line. You are now ready to tune the RF and IF stages. This will be achieved by tuning for the maximum no further gains are to be had. At this point the receiver is tuned. A word of warning: do not run commercial transmitters for too long with the antenna collapsed as this may damage the output transistors. If you have a scope, check the output waveshape at Q6 and compare it with the photo of Fig.3. All being well, it should be comparable. You now have a going receiver ready for connection to a decoder. Troubleshooting The finished receiver & decoder are shoe-horned into a very compact folded aluminium case. This easily comes apart for good access to the two boards inside. dip in the collector voltage of Q6. Turn on the transmitter or signal generator and set the output to maximum or fully extend the transmitter antenna. A dip should be noticeable on the meter with the RF signal present. You may have to almost touch the transmitter and receiver antennas. These may be touched together as long as the Rx antenna is insu­lated. Beginning with coil L5, tune the slug for maximum dip (minimum volts) at the collector of Q6. Move then to L6, L4, L2 and L1. By this time the voltage at Q6 should be almost zero. Now reduce the signal level, move the transmitter away or collapse the antenna and retune with the smallest comfortably detectable signal (about 0.5V). From here on, all tuning must be done with the lowest level of signal possible, otherwise the AGC action will affect the tuning on the IF coils. Continue to cycle through the coils, reducing signal and retuning until Provided you have used the components supplied in the kit, most of your problems will be assembly faults. Check for dry joints and shorts or missing or unsoldered components. A scope is very handy at this point. Begin by checking the rail voltages and then move on to the oscillator and check the DC voltages at the transistor. If the oscillator is running, the base voltage will be lower than the emitter voltage. Next, check the voltages around transistors Q1, Q2 and Q4. The base voltage will be approximately 0.6V higher than the emitter voltage (eg, base +1.1V, emitter +0.35V). The collectors will sit at the decoupled supply voltage, +4.1V. The base of Q6 will be +0.6V and the collector with no signal approximately +3.9V. If all of the DC conditions are OK, from here on it is routine RF servicing, using a signal generator (Tx) and oscillo­scope and stage by stage debugging. If all else fails, send it back to father (yours truly) and he will either repair it or replace the module at a nominal fee. Details of kit availability and prices will be given in next SC month’s issue. Protect your valuable issues with these Silicon Chip Binders These beautifully-made binders will protect your copies of SILICON CHIP.They feature heavy-board covers & are made from a distinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality with heavy board covers ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Aust). NZ & PNG orders please add $5 for postage. Not available elsewhere. Just fill in & mail the order form in this issue; or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. March 1995  65 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au An IR illuminator for cameras & night viewers What ever would you use an infrared (IR) illuminator for? To see in the infrared region, that’s what for. More precisely, an IR illuminator can be used with CCD video cameras & with IR night viewers such as the model described in the September 1994 issue of SILICON CHIP. By BRANCO JUSTIC This IR illuminator provides an output of up to 1.4 watts at 880 nano­metres. Most CCD cameras will respond, to some extent at least, to infrared light. The CCD modules themselves are quite responsive to infrared light but many cameras include an infrared filter. This is done so that pictures taken in low light condi­tions do not have unnatural highlights (to our eyes) due to the pickup of infrared light. There are two easy ways to check the IR response of your CCD video camera. First, set it up in a darkened room and then use a torch with red cellophane over the glass. The camera should then produce a useable picture of the room. Second, try the same thing but with illumination now provided by the infrared remote control for your TV, VCR or other appliance. This is also a good way of checking that your IR remote control is working. Applications Now that we have established that CCD cameras can work with IR light, why would you want to do it? The most important appli­ cation is for security. You could light a building, room, or a yard with infrared light and any miscreant would have no way of knowing that his actions were being monitored by a video camera. You could also use an IR illuminator and CCD video camera for watching wildlife. Perhaps you have possums or other nocturn­al visitors in your backyard or at your campsite. Now you can video them without any disturbance to their behaviour. March 1995  69 D1 MR856 L1 200uH 0.47 5 4 PARTS LIST +26.5-29.5V +9-12V 100k 100 47  47  A 1 100 16VW IC1 LM2577 2 4.3k 1.5k 1k 0V K A  LED40 LED20 K  LED41 K A VR1 1k A  LED21 K 3 0.47 47  A  LED1 2 PC boards (see text) 1 200µH inductor (L1) 1 1kΩ pot (VR1) A  LED60 K  K CIRCULAR PCB 1 5 A K INFRA-RED ILLUMINATOR Fig.1: the circuit uses a switched mode power supply based on IC1 to step up the battery voltage to 26.5-29.5V. This rail then drives an array of 60 IR LEDs via 47Ω current limiting resistors. Another application is for monitoring patients in sickrooms or in hospital. They can then be permanently watched without having their sleep disturbed. Some CCD camera modules intended for security applications come with inbuilt IR LEDs for illumination but generally they would only be sufficient for close-up work. The IR illuminator to be described here is much brighter. It is also an ideal IR source for most first generation IR night viewers. For example, just one single fibre optic tube from the three stage viewer design published in the September 1994 issue of SILICON CHIP would produce good results when illuminated with this IR source. One experiment involved combining the unit with a CCD camera supplied by Oatley Electronics. This setup provided good vision on a monitor of a vehicle parked about 50 metres away in very low ambient light. The circuit As you can see from the circuit diagram of Fig.1, the illu­minator is basically a closely packed array of 60 IR LEDs. There are three series strings of 20 LEDs fed via a 47Ω resistor The power supply section employs a switch­­ed mode power supply which is used to step up the voltage of the battery to a regulat­ed output voltage adjustable over a range of about 26.5-30V. The battery voltage can be 9-12V without any need to change the circuit. An economical way of obtaining a 12V battery for this unit would be to connect two 6V lantern batteries in series. These can be obtained for around $4 each, or less. Each IR LED drops a voltage of approximately 1.33V when it is conducting, thus each string of 20 LEDs requires a minimum of 26.6V. The Semiconductors 1 LM2577T-ADJ step-up voltage regulator (IC1) 1 MR856 or PL01 fast recovery diode (D1) 60 IR383 880nm IR diodes (LED1-60) Capacitors 2 100µF 35VW electrolytic 2 0.47µF 50V monolythic Resistors (0.25W 5%) 1 100kΩ 1 1kΩ 1 4.3kΩ 3 47Ω 1W 1 1.5kΩ Where to buy a kit The complete kit for this project, including the two PC boards is priced at $60 plus $4 for postage & packing. The LEDs are available separately at 10 for $9.00.The kit is available from Oatley Elec­tronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. current in each string is equal to (Vo26.6)/47Ω. The current in each string is, therefore, adjustable from about 8 to 72mA. Since there are three strings, the maximum total power delivered by the step-up inverter is approximately 6.5W. The voltage regulator employs a National Semiconductor LM2577T. This device can be used to step up input voltages in the range of 3.5-40V to output voltages up to 60V. The IR LEDs used in this project (IR383) have a very high quantum efficiency. They are specified as having an output of 30mW <at> 100mA at a wavelength of 880 nanometres. The maximum continuous current for these is 100mA but they can be pulsed at currents up to 1.2A. The diodes supplied in the kit have a radia­tion angle of 12° but they are also available in a 60° version (IR333). Construction This view shows the final version of the IR Illuminator. Note the small heatsink attached to IC1. 70  Silicon Chip Two PC boards are required for this project. There is a small board for the step-up circuit and one for the 60-LED array. The photos accompanying this LED1-60 100uF 0V 0.47 0.47 200uH +9-12V D1 100k IC1 LM2577 (ON HEATSINK) 1.5k Fig.2: install the parts on the two PC boards as shown in this wiring diagram. The 200µH inductor is supplied ready-wound. 100uF A A A A A A A A A A A A 47  A A A A A 47  A A A A A 47  1k 4.3k A A A A A A A A A A A A A A A A A VR1 article show the two boards neatly mount­ ed in a short length of PVC tubing but while this is quite an attractive package, we found it doesn’t work well in practice because both the LM2577T switching regulator and the LEDs themselves dissipate quite a respectable amount of heat. However, provided the regulator is fitted with a small heatsink and is not mounted in the same housing as the LEDs, the circuit will function satisfactorily. On the other hand, if the whole unit is packed into a short length of tubing as shown, and no heatsink is fitted, the current drawn from the battery will gradually rise and the regulator’s temperature will rise to the point where it switches itself off. So you have been warned – don’t pack it tightly into a small space and make sure both the regulator and the LEDs are reason­ably well ventilated. Assembly of the boards is quite straightforward. Install all the components on the regulator board first. Note that a 100µF electrolytic capacitor must be connected across the battery inputs to the board. This capacitor is not shown on the screen print overlay on this board alA though it is shown on Fig.2. A A When the reguA A A lator board is complete, power it up A A A and check the DC A A A output voltage. The voltage should be A A A able to be varied from about 29.3V to A A A 26.6V. The LM­2577 A A IC runs at close to 50kHz and if you A are able to examine the switching waveform on an oscilloscope, you will find that the duty cycle varies depending on the input voltage and the setting of the pot, VR1. Now assemble the LED board and make sure you connect each LED in the right way around. The longer lead on each LED is the cathode, marked “K” on the PC board. When complete, connect both PC boards together and power up. Unfortunately, you can’t immediately tell whether the LEDs are emitting but after a short while you can easily tell –they radiate heat! As a final check, fire up your video camera in a com­plete­ly dark room – it will show the illuminator lighting it up SC brightly. The prototype PC boards were built into a short length of PVC tubing but note that this will lead to overheating problems unless the unit is used only in brief bursts (see text). A heatsink should also be fitted to IC1. March 1995  71 COMPUTER BITS BY DARREN YATES Record real-time video with the Video Blaster FS200 Creative Labs have released the second version of their popular video package. We take a look at the improvements which include real-time video recording & playback. These days with movies such as Jurassic Park, as much work is done on the computer (in this case Silicon Graphics) as there is on the actual set. While these computer systems can cost beyond the million dollar mark, Creative Labs, the makers of the Sound Blaster, have made some big improvements in their graphics package, the Video Blaster. The original version (see our review in the April 1994 issue) could display real-time video on screen but the only manipulation you could do was to grab a frame and edit it or save it to disc. The FS200 provides a pretty dramatic improvement by allowing you to record and replay full-motion video at up to 30 frames per second – not at full VGA resolution but good enough to make watching video on your PC worthwhile. What you’ll need As you can imagine, capturing video signals is a pretty time consuming task so don’t expect an XT to do the job. In fact, you’ll need a minimum of an 386SX-25 (25MHz) processor with 4Mb of RAM and at least 4Mb of spare The Video Blaster FS200 lets you display full-motion video in a moveable window. It comes bundled with a comprehensive range of software, including Aldus PhotoStyler & Aldus Gallery Effects so that you can edit captured video. 72  Silicon Chip hard disc space. The manual quotes 2Mb but by the time you’ve installed the Video Blaster software, as well as the Microsoft Video for Windows software, plus some space to work with, you’ll need at least 4Mb. The Video Blaster software itself only allows capturing of a video frame for editing but it does allow you to do some spe­cial effects with a live video feed such as chroma keying and rotation. To record and replay full motion video, you’ll need to install the Video for Windows software. Here, the user’s guide suggests a minimum of a 386 processor and 2Mb of RAM, or 4Mb of RAM if you wish to capture video. As with most software, the more RAM you have, the faster it will run. Both packages require a VGA card with at least 16-colours and 640 x 480 pixels resolution. You’ll also need a CD-ROM drive to access the video images located on the CD-ROM that accompanies the package. Microsoft suggest also that you have at least 100Mb of hard disc space free to store your captured video and your drive will need a write speed of at least 320Kb/second. Any of the Sound Blaster audio cards can also be used to record and replay audio with your video as well. Note that you’ll need this just to get the audio/video signals into your computer. You’ll need the TVCoder to export the video to your VCR if you wish to store it on tape. If you use one of the 16-bit stereo sound cards, then you’ll need a hifi VCR to record the sound at the same quality. Video accelerator card One aspect that is a little disappointing is the fact that to get full Software The software for both packages comes in both DOS and Wind­ ows versions. Also bundled in with the FS200 are a couple of Aldus packages – a special edition of PhotoStyler and the first volume of Gallery Effects. Both of these are designed for single-frame editing and for creating special effects. PhotoStyler allows you to alter the screen image by remov­ing unwanted objects from a picture as well as allowing you to convert a captured image to CYMK colours. You can also produce colour separations if need be. One of the more stunning effects is the ability to cut out a portion of an image and paste it directly onto another, called “merging”. This is similar to an effect that can be done with Windows Paintbrush but with much greater control. Gallery Effects allows you to change the texture of a captured image. Some of the textures you can use are chrome, emboss, mosaic, watercolour and spatter. These can give your images a more artificial, “painted” look. System requirements for these packages are the same as for the Video Blaster except for hard disc space. The Gallery Effects manual suggest that a scanned 8 x 10-inch image can require up to 7Mb of space so we recommend that you have at least a 200Mb drive if you wish to use this for serious work. Overall, the Video Blaster FS200 system is a very desirable improvement over the original version but you’ll need to have a few extras such as the video accelerator card and others men­tioned previously to get the maximum benefit. The package comes complete with a video card, software and manuals, plus connection cables for your PC and video equipment. At $599, it has to be one of the cheapest solutions for editing full frame rate video. For further information, contact your nearest SC Rod Irving Electronics store. SILICON CHIP SOFTWARE 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. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ motion replay on your VGA screen, you need a video accelerator card. The only place I saw this mentioned was at the beginning of Chapter 2 of the Video for Windows user manual. I would have thought that this was a pretty crucial point consider­ing that the major selling point of the FS200 is its full motion record and replay. March 1995  73 VINTAGE RADIO By JOHN HILL The inaugural vintage radio swap meet This month, we begin by taking a look at the Inaugural Vintage Radio Swap Meet. We then review a new & interesting book on crystal sets by Australian author, Bob Young. Swap meets are common these days and one of the biggest and longest running is the Bendigo Swap Meet, which is held annually in mid-Nov­ ember. While the Bendigo Swap Meet is pre-dominantly a vintage car meeting, the Historical Radio Society of Australia (HRSA) has a site there each year and encourages members who wish to sell their wares to come along. Dick Howarth is a Bendigo radio collector who has somewhat more go than most. He has just organised Aus­tralia's first Vintage Radio Swap Meet which was held on 23rd October 1994 at the Glenroy Technical School As­sembly Hall in Melbourne. The meet was not confined to vintage radio. It was more of a vintage sound affair and included phonographs and some amateur radio equip­ment as well, although most of the items offered were vintage radio re­ceivers. Dick is a relative newcomer to ra­ dio collecting. He is a fairly impatient type who wants his repairs done yes­ terday, works on his radio cabinets until 2am, and is prepared to travel interstate on the off-chance of finding an interesting old radio. He always seems to be thinking about vintage radio and he probably dreams vintage radio as well. Anyway, things weren't happening fast enough for Dick and he felt that more could be done to promote inter­est in vintage radio. A radio swap meet seemed like a good idea and he set the wheels in motion some six months before the actual meeting. Dick always does what he says he is going to do and he is prepared to put his money where his mouth is. The highly successful Inaugural Vintage Radio Swap Meet was a good example of Dick Howarth doing what he said he would do. What's more, the meet was well organised, properly run, and a credit to Dick and his wife Raeleene, who put as much work into the day as anyone. The HRSA were approached and they added their support to the project. Some of the Melbourne members arranged a display of vintage equipment which was neatly laid out on the stage of the hall. Dick added to the stage display by including some of his con­sole radios. Only a console with turned legs will attract Dick's attention and his radios are really first class. Dick does his own cabinet refurbishing and few, if any, could do a better job. Unwanted items HRSA President Bruce DeLacy with some of the HRSA receivers on display. These are, from left: a Dutch Philips multi-band radio, a mid-1930s Radiolette, a Healing mantel model, a Little Nipper all transistor radio, and the top of a late 1930s Airzone console. 74  Silicon Chip Unfortunately, driving to Melbourne is something I loathe and will do just about anything to avoid. But as Glen­ roy is on the right side of Melbourne for me, I decided to take a site at the meet to help off-load some of my unwanted bits and pieces, and to sup­port Dick's venture. Apart from being a profitable day, the swap allowed me to catch up with some old friends and meet a few new ones. My wife and I took turns at our site while the other walked around, looking and talking. I suspect I may have scored the better deal there, as I knew a lot more people to talk to. This site had a large range of early radios, radiograms & phonographs. The STC console radio (centre) was priced at $645. Author Bob Young spent more than 12 months on his book “Crystal Sets ‘n’ Such”. The book is a remarkably informative publication & should be of interest to most vintage radio enthusiasts. Pride of place on this table was taken by a fully-restored Edison "Fireside" cylindrical phonograph. Immediately behind it are an Airzone mantel radio & a Celestion loudspeaker. According to some old avertisements, the tone of a Celestion loudspeaker improved with age! The difference in prices from site to site was considerable and one example was lightning arresters. Mine were priced at $5 while those at another site were $15. Neither of us sold any! Items for sale As the accompanying photographs show, there were a lot more items for sale apart from lightning arresters. There was an impressive array of vin­ tage equipment and just about every­one who came to the meet went away with something they wanted or could use. At the end of the day, my trading table was just about bare. Four 807 valves, two 1950s mantel receivers, two books, a valve tester and the lightning arresters were the only things left. If prices are realistic, just about any item will sell. In most instances, people were happy to pay the marked price.· Only a few haggled for a better deal. Looking back on the day, I'm glad I decided to take a site at the swap meet. Fortunately, this year's site hold­ ers have first preference for next year and I have already indicated my in­tention to be there. One different aspect to the swap meet was the launching of a new book. As mentioned in my October 1994 column, Bob Young (no, not Remote Control's Bob Young) has been writ­ing a book on crystal sets and now it has finally reached completion. It was my pleasure to help launch the book at the swap meet. Of course, this is a difficult task when one is presented with the book only a cou­ple of hours beforehand, with no time to read it. I'm sure that the ink was still wet! Fortunately, I had previously read some of the earlier chapters and had a good idea of the direction Bob's book was heading. In my opinion, “Crystal Sets ‘n’ Such” is a brilliant piece of work! It is in all probability the first really com­ plete work on crystal sets that has been written and it should be of inter­est to any vintage radio enthusiast, whether he is a new recruit or some­one who thinks he knows it all. There is something in it for just about every­one. A number of the early chapters are interesting from a historical view­point alone. Keep it simple The secret to good technical writing March 1995  75 is to keep things as elementary as possible and never assume that your reader knows everything about the subject being covered. If this basic rule is ignored, then the text may be­ come quite meaningless to many read­ ers and they will soon lose interest and look for something else to read. That's not the case with “Crystal Sets ‘n’ Such”. Every concept pre­sented to the reader is carefully ex­plained in simple terms, along with the appropriate illustrations, charts, diagrams and analogies. It is a very informative book and is directed at those with an interest in radio and particularly those who like to dabble around building their own receivers. Pick a meter, any meter – there's lots to choose from amongst this collection! As far as a vintage radio enthusiast is concerned, these's no such thing as a digital meter. Just about every site had vintage radios on display. In the front row here, from left, are two Philips receivers and a Mullard, while in the back row are a Breville, an Aristone, a "don't know", and a Stromberg-Carlson. This RCA Model 60 cabinet (circa 1928) was refurbished by Dick Howarth. It was just about a total wreck before he started and has been restored to "betterthan-new" condition. 76  Silicon Chip Crystal detectors The chapter on crystal detectors is interesting and delves into the many and varied types that have been used over the years. A comparison between the various detectors is very well dealt with. This comparison is not done using a headphone performance test but on an oscilloscope screen. There are also instructions for setting up similar tests if you wish to do so your­self. This book on crystal sets is a whole new approach to building these sim­ ple receivers and the theories and practices involved. “Crystal Sets ‘n’ Such” includes, as one would expect, a wide range of crystal set circuits. These cover everything from basic single-coil types to several three-coil sets which are quite elaborate affairs for a supposedly sim­ple radio receiver. When a crystal set ends up with half a dozen or more controls (which all interact with each other), it is starting to get fairly com­plicated - for a crystal set, that is! I was particularly pleased to see my “Classic Crystal Set” (Vintage Radio, September 1994) amongst the more complex designs (circuit number 7). It is a very good performer – not that I can lay claim to its good design. The chapter on coil winding is also well covered. The “Q” factor of a tuned circuit makes interesting reading when it is presented simply with explanations and appropriate diagrams. Al­though a mathematical formula is given relating to the Q factor, complex calculations do not enter into the text of the book to any great extent. But the odd formula is there for those who may require them. RESURRECTION RADIO VALVE EQUIPMENT SPECIALISTS Repairs – Restoration – Sales for RADIO & AUDIO Equipment S VE L VA These three consoles are from Dick Howarth’s collection. They are, from left, a 1932 AWA 55E, a 1932 Raycophone, and a 1934 Airzone. Dick mostly collects console receivers with legs. BOUGHT SOLD   TRADED Send SSAE for Catalogue Visit our Showroom at 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel: (03) 9510 4486; Fax (03) 9529 5639 Silicon Chip Binders This table carried an old Palec valve tester and what appears to be an early Stromberg-Carlson communications receiver. A “Resonant Circuit Component Value Calculator” is also included in the book and this could be of some assistance when coil winding. The calculator is a chart with three scales: (1) inductance in microhenries; (2) frequency in kilohertz; and (3) capacitance in picofarads. By placing a straight edge through any two known quantities, the unknown value can be read off the third scale. Perhaps the most refreshing aspect of “Crystal Sets ‘n’ Such” is the way in which it is written. Bob Young’s sense of humour really shows through and his book is a fun thing to read. He has a way of expressing himself that is, at times, quite light-hearted, which is one of the best ways there is of getting a message across. “Crystal Sets ‘n’ Such” is a good book. It covers the subject well, I enjoyed reading it and I learnt from it too! It is available from: Mr R. Young, RMB 1561, Benalla, 3673. Phone (057) 68 2418. Fax (057) 68 2508.’’The cost is $19.95, including postage. Yes, the Inaugural Vintage Radio Swap Meet (including the book launch) was a great day and was enjoyed by all who attended. I for one will be there again next year for what will, no doubt, be an even bigger and SC better event. These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 979 6503; or ring (02) 979 5644 & quote your credit card number. March 1995  77 NICS O R T 2223 LEC 7910 y, NSW EY E OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd KITS & BITS i 9 PO 579 4 r C a rd , V e & fax ) 2 0 ( n e e Phon rd , M a s t with pho orders: a d c ed B a n k x accepte most mix 0. Orders $3; 50 x 72 x 3mm: $3. LINE GENERATING e r 1 OPTIC: makes a line out of a laser beam: & Am . P & P fo (airmail) $ s $5. LASER DIODE COLLIMATING LENS: order 4-$10; NZ world.net $4. PORRO 90 deg. PRISM: makes a $ <at> . y t e s l t u rainbow from white light: $10. PRECISION ROTATING a A AIL: o MIRROR ASSEMBLY: as used in levelling equipment, by EM needs small motor/belt, plus a laser beam, will draw a HIGH INTENSITY RED LEDs 550-1000mCd <at> 20mA, 100mA max, 5mm housing: 10 for $4, or 100 for $30. LOW COST IR ILLUMINATOR Employs 42 high output 880nM IR LEDs (30mW <at> 100mA ea.) & a seven transistor adjustable constant current driver circuit. Designed to be powered from 10-14V DC, current depends on power level setting: 5 - 600mA. The compact PCB is designed to replace the lid on a standard small 82 x 53 x 28mm plastic box. Good for illuminating IR responsive CCD cameras, IR & passive night viewers & medical use. The complete kit even includes the plastic box & is priced at a low: $40 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 inbuilt 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". $32. COLOUR MONITORS Used but guaranteed 12" colour computer monitors: $40 REEL TO REEL TAPES New studio quality 13cm-5" “Agfa” (German) 1/4" reel to reel tapes in original box, 180m-600ft: $8 ea. ARGON HEADS These low voltage air cooled Argon Ion Laser Heads are priced according to their hours of operation. They produce a bright BLUE BEAM (488nM) and a power output in the 10-100mW range - depending on the tube current. The head includes power meter circuitry, and starting circuitry. We provide a simple circuit for the supply. Limited supplies at a fraction of their real cost: $300 - $500. AC MOTOR Small but very powerful GEARED AC motor. 1 RPM/60Hz/24V/5watt. We supply a circuit diagram that shows how to power this motor from 12V DC: Variable speed/full power (bridge output). Bargain priced: $9 PCB and all on-board components kit for the 12V driver kit will be available late in May: $8 OPTICS BEAM SPLITTER for 633nM: $45. PRECISION FRONT SURFACE ALUMINIUM MIRRORS 200 x 15 x 3mm: 78  Silicon Chip line right around a room (360 deg.) with a laser beam: $45. LARGE LENS: out of a night viewer, can easily be pulled apart: $18. ARGON MIRRORS: high reflector and output coupler used to make an Argon tube: $50. POWER SUPPLIES Used but very clean non standard computer power supplies, enclosed in metal casing with perforated ends for air circulation, built in fan, IEC input connector and OFF-ON switch, “flying” DC output leads, overall dimensions: 87 x 130 x 328mm, 110-220V input, +5V/8A, +12V/3A, and -12V/0.25A DC outputs. BARGAIN PRICED: $18 ea. or 4 for $60. Used IEC lead with Australian plug $2.50 extra. TWO STEPPER MOTORS PLUS A DRIVER KIT This kit will drive two stepper motors: 4, 5, 6 or 8-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. MAINS LASER SPECIAL Includes a compact potted US made power supply which can be powered from 110/220-240V AC, a 2-3mW He-Ne tube, a ballast resistor and instructions. The power supply requires 4-6V <at> 2mA DC enable to run. Brand new components. Giveaway price: $65 27MHz TRANSMITTERS These new Australian made transmitters are assembled (PCB and components) and tested. They are Xtal locked on 26.995 MHz and were originally intended for transmitting digital information. Their discrete component design employs many components, including 5 transistors and 8 inductors: circuit provided. A heatsink is provided for the output device. Power output depends on supply voltage and varies from 100mW to a few watts, when operated from 3-12V DC. These are sold for parts/experimentation/educational purposes, and should not be connected to an antenna as licensing may be required: $7 ea. or 4 for $20. 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 CD MECHANISMS Used compact disc player mechanisms. Include IR laser diode, optics, small conventional DC motor, gears, stepping motor, magnets etc. Great for model railway hobbyists: The motor/gear assembly produces a linear movement of approx. 60mm. The whole assembly is priced at less than the value of the collimating lens, which is easy to remove: $6. We also have some similar CD assemblies that have linear motors. Used CD mechanisms with linear motors: $4. IMAGE INTENSIFIER TUBES Used but in excellent condition second generation image intensifier tubes. Can be used to make a small and very sensitive scope that can produce high resolution pictures in very low illumination. US made tubes that produce superior results! $650 We should have a complete kit of parts for a small scope available at the time of the publication of this advertisement: “Ring”. 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: 10-14V DC/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 approximately 30M by the use of a small directional UHF antenna. INCREDIBLE PRICING: $25. IR REMOTE SWITCH KIT Consists of a PCB and all on board components kit for an IR receiver with a toggle output, and a brand new commercial ready made slimline IR remote control transmitter, which was designed for a CD player. Simply press any button on the IR transmitter to toggle the output on the receiver. The system has up to 20M range and will also work from most other IR remote controls! Receiver uses an IC “front end”, has a toggle output, operates from 8-15V DC, and will drive a relay. Transmitter operates from two “AAA” batteries (not supplied). Unbelievable pricing: $18 For the slimline IR remote control transmitter and a kit for the IR receiver. Suitable 12V/8A relay with 4kV isolation: $3, 12V DC plugpack: $10. PRINTER MECHANISMS Brand new Epson dot matrix printer mechanisms: overall dimensions are 150 x 105 x 70mm. These are complete units and contain many useful parts: 12V DC motor (50mm long - 30mm diam.) with built in tachometer, gears, solenoid, magnet, reed switch, dot matrix print head etc.: $12. VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nM laser diode modules. Overall dimensions: 11mm diameter by 40mm long. Have APC driver built in and need approximately 50mA from 3-6V supply. $60. SOLID STATE “PELTIER EFFECT” COOLER-HEATER These are the major parts needed to make a solid state thermoelectric cooler-heater. We can provide a large 3.4A Peltier effect semiconductor, two thermal cutout switches, and a 12V DC fan for a total price of: $35. 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. 12V-4.5A Peltier device only: $25. DOT MATRIX LCDs Brand new Hitachi LM215 400 x 128 dot matrix Liquid Crystal Displays in an attractive housing. These have driver ICs fitted but require an external controller. Effective display size is 65 x 235mm. Available at less than 10% of their real value: $25 ea. or 3 for $60 VISIBLE LASER DIODE KIT A 5mW/670nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept. 94 EA) UNBELIEVABLE PRICE: $35. The same kit is also available with a 3mW/650nM laser diode: $60. 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. $215 CCD VIDEO SECURITY SYSTEM 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. This new model camera is about half the size of the unit we previously supplied. It is slightly bigger than a box of matches! Can be used in total darkness with Infra Red illumination. NEW LOW PRICE: $180 With every camera purchased we can supply an used but tested and guaranteed 12V DC operated Green computer monitor. We can also supply a simple kit to convert these monitors to accept the signal from the CCD camera: monitor $25, conversion kit $10. A COMPLETE 12V CCD VIDEO SECURITY SYSTEM FOR $215!! LOW COST 1-2 CHANNEL UHF REMOTE CONTROL A single channel 304MHz UHF remote control with over half a million code combinations which also makes 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. is available: suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. BLEMISHED 3 STAGE TUBES We have accumulated a good number of 40mm three stage fibre optically coupled 3 stage image intensifiers that have minor blemishes: similar to above but three tubes are supplied already bonded together: extremely high gain!! Each of these tubes will be supplied with the power supply components only. See SC Sept. 94. $200 For the 3 stage 40mm tube, supply kit. We can also supply the full SC Sept. 94 Magazine: $5 TDA ICs/TRANSFORMERS We have a limited stock of some 20 Watt TDA1520 HI-FI 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 overrated 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 HI-FI Stereo/Guitar/P.A., amplifier. Only a handful of additional components are required to complete this excellent stereo/twin amplifier! Incredible pricing: $25. For one 240V-28V (80W!) transformer, two TDA1520 monolythic HI-FI amplifier ICs, two PCBs to suit, circuit diagram/layout. Some additional components and a heatsink are required. RUBY LASER HEADS These complete and functional heads include a flash tube, mirrors, and 4" ruby rod! Produce a high intensity visible red beam! We should have suitable circuits - components to drive these available. Dangerous units with restricted sales. Limited quantity. $695 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 INCREDIBLE PRICES: COMPLETE 1 CHANNEL TX-RX KIT: $30 COMPLETE 2 CHANNEL TX-RX KIT: $36 ADDITIONAL TRANSMITTERS: $10 We can also supply a 240V-12V/4A-5V/4A switched mode power supply to suit for $30. FIBRE OPTIC TUBES Originally designed for bicycles, but these suit any moving vehicle that has a rotating wheel! A nine function computer with speed, average speed, maximum speed, distance, odometer, timer, scan, freeze frame memory, and a clock. Its microprocessor based circuitry can be adapted to work with almost any wheel diameter. Simply divide the wheel diameter in millimetres by 6.8232, and program the resultant figure into the computer. We have a good supply of some tubes that may have a blemish which is not in the central viewing area! These produce a very high resolution image but would require IR illumination: !!ON SPECIAL!! $50 for a blemished 25 or 40mm (specify preference) image intensifier tube and supply kit. Matching good quality eyepiece lens only, $2 extra! That’s almost a complete night viewer kit for: $52. 12V-2.5 WATT SOLAR PANEL KITS 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” angle 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: $20 ea. or 4 for $60 Each panel is provided with a sheet of backing glass, terminating clips, an isolating diode, and the instructions. A very efficient switching regulator kit VEHICLE COMPUTERS $29.90 $70. SWITCHED MODE POWER SUPPLIES: mains in (240V), new assembled units with 12V-4A and 5V-4A DC outputs: $32. ELECTRIC FENCE KIT: PCB and components, includes prewound transformer: $40. 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 nonferrous metals at close proximity, AC or DC powered types, three 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 ea. or 6 for $100. BRAKE LIGHT INDICATOR KIT: 60 LEDs, two PCBs and ten Rs, makes for a very bright 600mm long high intensity red display: $30. IEC EXTENSION LEADS: 2M long, IEC plug at one end, IEC socket at other end: $5. MOTOR SPECIAL: these permanent magnet 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 diam.-57mm long: $5. EPROMS: 27C512, 512K (64k x 8), 150nS access CMOS EPROMS, removed from new equipment, need to be erased, guaranteed: $4. 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. MODULAR TELEPHONE CABLES: 4 way modular curled cable with plugs fitted at each end, also an 4M long 8way modular flat cable with plugs fitted at each end, one of each for: $2. 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: ON SPECIAL $15. 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: $20. 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.2: high quality - high stability, suit radiomicrophones 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.1: 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. BATTERY CHARGER S2: accessory set for Telecom Walkabout “Phones”. Includes cigarette lighter cable, fast rate charger, and desktop stand. Actually charges 6 series connected AA Nicad batteries: $27. LITHIUM BATTERIES: button shaped with pins, 20mm diameter, 3mm thick. A red LED connected across one of these will produce light output for over 72 hours (3 days): 4 for $2. SUPERCAPS: 0.047F/5.5V capacitors: 5 for $2. PCB MOUNTED SWITCHES: 90 deg. 3A-250V, SPDT: 4 for $2. 3-INCH CONE TWEETERS: sealed back dynamic 8-ohm tweeters: $5 ea. CASED TRANSFORMERS: 230V-11.7V 300mA AC-AC transformers in small plastic case with separate input and leads, each is over 2 metres long: $6. 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: SC DEC 93: 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 12V DC supply-plugpack: MORE ITEMS AND KITS Poll our (02) 579 3955 or (02) 579 3983 fax numbers for instructions on how to obtain our Item and Kit lists. MANY MORE ITEMS AND KITS THAN ARE LISTED HERE!! You can also ask for a copy of these to be sent out with your next order. March 1995  79 AMATEUR RADIO BY DARREN YATES Simple 2-transistor CW filter If you’re having trouble picking CW signals out of the mud, then try this handy little circuit. It’s a 2-transistor CW filter & it’s just the shot for beefing up those buried signals. Deciphering CW signals on a noisy band can often be quite difficult, particularly for novice operators with only basic equipment. Fortunately, there are various techniques that can be used to “clean-up” the signal. By far the most common technique is to employ a CW filter. A CW (or continuous wave) transmission, as used for Morse code, is essentially an interrupted carrier; ie, the carrier is switched on and off by the Morse key. When you tune your receiver, you tune it close enough to the incoming carrier to give an audible beat. Most people tune their receiver to give a beat somewhere below 1kHz. This is particularly the case where you have a noisy signal; a lower audible frequency can be somewhat easier to distinguish from the noise and this is where this CW filter comes in. It is essentially a notch filter set at 750Hz which effec­ tively attenuates noise either side of this frequency and thus greatly improves signal reception. In use, you tune the receiver so that the audible beat is right on 750Hz, at which point the modulated carrier will stand out well above the noise. AUDIO PRECISION FREQRESP AMPL(dBr) vs FREQ(Hz) 50.000 11 JAN 95 01:27:07 40.000 30.000 20.000 10.000 0.0 The circuit itself uses just two transistors and a handful of passive components. It is built on a PC board measuring just 46 x 36mm, which should be small enough to fit inside most re­ ceivers. The power supply requirements are a 9-12V DC at just a few milliamps and this can easily be derived from an existing supply rail. Fig.1 shows the frequency response of the filter, as measured on an Audio Precision audio test set. As can be seen, it effectively provides around 40dB of gain at 750Hz. Circuit details Refer now to Fig.2 for the circuit details of the CW Filt­er. It is basically a 2-transistor amplifier with a twin-T filter in the feedback path. In greater detail, transistors Q1 and Q2 make up a DC feed­back pair, with negative feedback applied from Q2’s collector to Q1’s emitter via the twin-T filter network. The input signal is applied via a 0.1µF capacitor to Q1’s base, while the 120kΩ and 150kΩ resistors set the bias for this stage. The 330Ω resistor and series 1µF capacitor roll off the low-frequency response of this first stage, to make the overall filtering more effective. The resulting amplified output on Q1’s collector is then fed directly into base of PNP transistor Q2. Note the 33kΩ load resistor on Q1’s collector. This is not strictly necessary but has been included since it significantly reduces distortion. Finally, the amplified signal on Q2’s collector is coupled to the output via a 10µF capacitor. Twin-T filter -10.00 10 100 1k 10k 20k Fig.1: the frequency response of the filter. The passband is centred on 750Hz. 80  Silicon Chip Six components are used in the twin-T filter network: two 2.2kΩ resistors, a 1.1kΩ resistor, two 0.1µF capacitors and a 0.22µF capacitor. Its +9-12V 120k 0.1 CW SIGNAL IN C B Q1 BC548 E 150k B E Q2 BC558 B 33k 10 E 16VW C 2.2k 10 16VW 2.2k 330  0.1 1 63VW 0.22 0.1 1.1k OUTPUT SIGNAL 10k 0V 1k Fig.2: Q1 & Q2 make up a DC feed­back pair, with negative feedback applied from Q2’s collector to Q1’s emitter via a twin-T filter network. PARTS LIST 1 PC board, code 06104951, 46 x 36mm 6 PC stakes Semiconductors 1 BC548 NPN transistor (Q1) 1 BC558 PNP transistor (Q2) Capacitors 2 10µF 16VW electrolytic 1 1µF 16VW electrolytic 1 0.22µF MKT polyester 3 0.1µF MKT polyester C VIEWED FROM BELOW ACTIVE FILTER FOR CW RECEPTION notch frequency is determined by the formu­la F= 1/(2πRC). Since the impedance of the twin-T network is a maximum at this frequency (in this case, 750Hz), this corresponds to minimum negative feedback and the maximum gain. Note that because the circuit has considerable gain at the notch frequency, the input signal needs to be below 20mV in order to prevent clipping at the output. If you have too much signal, just wind back the volume control or use a resistive attenuator to reduce the input level. Construction 10uF 2.2k 10uF 330  10k 1k 0.22 1.1k 0.1 Q1 2.2k 0.1 CW SIGNAL INPUT GND colours can be difficult to decipher. Be sure to install the electro­lytic capacitors with the correct polarity. Finally, complete the assembly by installing the two tran­sistors. The finished PC board can be mounted inside the receiver or installed in a plastic case and run off batteries or a DC plug­pack. If you elect to mount the unit separately, then you will need to fit an on/off switch. The filter can be driven from the volume control, from the headphone output, or from the “record” output of most receivers. In fact, by using the record output, which allows the loudspeaker to operate in normal fashion, it is possible to compare the filtered and unfiltered signals. You will be amazed at the dif­ference. Finally, note that careful tuning of the receiver will be necessary to ensure that the beat frequency is centred within the narrow filter passband. This is not as difficult as it sounds and is SC readily done by ear. The PC board is small enough to fit inside most receivers. Begin construction by installing PC stakes at the external wiring points, then install the resistors and capacitors. Table 1 lists the resistor colour codes but it is also a good idea to check them on your multimeter, as some +9-12V 0.1 Q2 33k 120k 150k All the components for the CW filter are installed a PC board coded 06104951. Fig.3 shows the details. Resistors (0.25W, 1%) 1 150kΩ 2 2.2kΩ 1 120kΩ 1 1.1kΩ 1 33kΩ 1 1kΩ 1 10kΩ 1 330Ω 1uF SIGNAL OUTPUT GND 0V Fig.3 (left) shows how the parts are installed on the PC board while Fig.4 (right) shows the full-size etching pattern. TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 Value 150kΩ 120kΩ 33kΩ 10kΩ 2.2kΩ 1.1kΩ 1kΩ 330Ω 4-Band Code (1%) brown green yellow brown brown red yellow brown orange orange orange brown brown black orange brown red red red brown brown brown red brown brown black red brown orange orange brown brown 5-Band Code (1%) brown green black orange brown brown red black orange brown orange orange black red brown brown black black red brown red red black brown brown brown brown black brown brown brown black black brown brown orange orange black black brown March 1995  81 PRODUCT SHOWCASE NAD 513 carousel compact disc changer CD changers have been around for some time, in permutations such as magazine, carousel or internal storage systems, each with their specific ad­ vantages and disadvantages, but al­most always with a capacity of five discs. After careful market research, NAD found that most people do not need to play more than two or three CDs after one another, as the total playing time of three CDs can be as much as 3 hours and 45 minutes. With this in mind, NAD engineers developed the model 513. By employing the carousel principle and limiting the number of discs it can hold to three, the end result is a CD changer with the performance and price of single disc CD player. Like other NAD CD players, the 513 uses a single-bit MASH circuit, while balanced filtering removes ultrasonic byproducts of the decoding process without affecting the audio performance. Despite its simplicity, the NAD 513 offers all the facilities normally asso­ciated with carousel CD changers - two discs may be changed while the third is playing; the remote control allows changing discs and selecting tracks without having to touch the front panel, the programming facility for 32 tracks over three discs makes Cordless infrared headphones Instrumentation catalog National Instruments has an­ nounced its new 584 page catalog which describes more than 900 software and hardware products. The 1995 catalog is colour-coded into five sections: software, GPIB/ serial interfaces, data acquisition, VXI/MXI and customer education. The first four sections feature com­ p rehensive tutorials, complete with application examples, to help readers learn more about IEEE 488.2, SCPI, plug-in data acquisi­tion (DAQ) systems, signal condi­tioning accessories, VXI and MXI. Complete ordering, pricing and warranty information is also in­cluded. Expanded sections are included on how to choose hardware and software for IEEE 488, plug-in DAQ, serial and VXIbus products. Also 82  Silicon Chip track selection a breeze; and with the Random function engaged, all tracks from all three discs will be played without repetition. NAD products are available from authorised NAD dealers across Aus­ tralia. For further information please contact Marantz Australia on (02) 742 8322. new to the 1995 catalog are separate listings of instrument driv­ ers by industrial I/0 and test and measurement categories. To request copies of the free catalog or for product information, contact National Instruments Aus­ tralia, PO Box 466, Ringwood, Vic 3134. Phone (03) 879 9422 or fax (03) 879 9179. Amber Technology has announced the Beyer IRS890 & IRS790 cordless infrared headphones which combine freedom of movement with audio per­ formance normally only associated with wired headphones. Position Vacant Electronics Designer Silicon Chip, Australia’s dynamic electronics magazine, is looking for an electronics project designer to work for us. The successful applicant will have a good knowledge of electronics and computers and should be able to program in Basic. Good writing skills are desirable. If you think you could be that person, apply in writing to the Publisher, Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097; or fax your application to (02) 976 6503. The system comprises three components – the IRH890 cordless headphone, featuring comfortable, soft ear cushions, automatic level control, in­dividual channel volume controls, switchable to stereo, mono-left or mono-right, and powered via 2 x 1.5V AA cells; the IS890 infrared transmit­ter; and the LG890 power supply. Additional pairs of IRH890 headphones may be operated simultaneously from the same transmitter, while coverage in other rooms can be ob­tained with the addition of the ISS890 slave transmitter. The system has a claimed frequency response of 18Hz to 24kHz with a maximum SPL of 1 l0dB and has a recommended retail price of $579. The IRS 790 offers similar features and pro­ vides 20Hz to 23kHz frequency re­sponse with 116dB SPL capability. It has a recommended retail price of $499. For further information, contact Amber Technology Pty Ltd, Unit B, 5 Skyline Place, Frenchs Forest, NSW 2086. Phone (02) 975 1211 or fax (02) 975 1368. New catalog from All Electronics Components All Electronic Components has announced their first catalog list­ing their full range. As the catalog shows, they are strong in semi­ conductors and have a comprehensive range of passive components as well. The catalog has a $2 cover charge bit is available free to readers of Silicon Chip provided they send a cou­ple of 45 cent stamps with their re­quest. For your copy, contact All Electronic Components, 118-122 Lonsdale Street, Melbourne, Vic 3000. Phone (03) 662 3506 or fax (03) 663 3822. Combination CD-ROM & hard disc Teac Corporation of Japan has released a combination fast CD­ROM drive and integrated hard disc. Three models are available: 250Mb, 360Mb and 540Mb. The CD-ROM drive is a quad speed AT interface drive with a fast access time of 195ms and a sustained data transfer rate of 600Kb per second. It will read both 12cm and 8cm discs of CD-DA, CD-ROM Mode-1, XA Mode-2 (Form-1, Form2) formats and is multi-session Photo-CD compat­ible. The AT interface is compat­ ible with SoundBlaster sound cards. The hard disc has an IDE inter­ face, requires only 5V, is lockable and changeable. The Combo Drive SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 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. is supplied with an interface card for the CD-ROM plus data and sound cables, device driver, user’s manuals, mounting screws and configuration software for the hard disc drive. For more information please contact Rick Stanford at Southend Data Storage on (02) 541 1006. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 March 1995  83 SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. First pub­ lished 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer's Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 These two new digital storage oscilloscopes from Tektronix are right at the leading edge of technology. The TDS 784A at left, has a bandwidth of 1GHz & 4-gigasamples/second maximum sampling rate. The TDS 744A at right operates at real-time speeds up to 500MHz & with a maximum sample rate of 2Gs/s. Both have liquid crystal shutters to provide colour displays & have an unsurpassed ability to catch & display rare glitches in signal waveforms. Tektronix TDS 784A TruCapture oscilloscope Tektronix has really taken the bit in its teeth over the last few years in developing the art of digital storage oscilloscopes. Now it has taken another big step forward with its TDS 784A & TDS 744A scopes which can display up to 400,000 acquisitions per second. This is a huge improvement over previous digital scopes. By LEO SIMPSON While digital scopes have come a long way over the last few years, they still have drawbacks in the way they display signal waveforms. Partly this is due to the sampling system which shows the waveform as a series of dots. On a signal which has superim­posed noise, the resultant waveform can be quite jagged and quite different from what would be displayed on a conven- tional analog oscilloscope. The truth is that the both oscilloscopes show the waveforms differently and both conceal information. Actually, a major shortcoming of digital storage oscilloscopes (DSOs) has been the small fraction of time they spend capturing waveforms. This is quite different from the impression that you get when the display is updated at 60 times per second. For ex­ample, if the DSO is set at an appro priate sweep speed to display a 10MHz clock signal, each refreshed display will show about five clock signals or half a microsecond (500ns). This means that in 60 displayed waveforms, only 30 microseconds of signal will be acquired by the scope in one sec­ond. This is 30 parts per million or just .003% of real time. So while things appear to happening rapidly on the screen, in reality the scope is sitting there doing nothing most of the time and many “events” could occur which are just not captured. Analog scopes do a lot better in terms of their “display refresh” rate; ie, the number of times the screen display is updated. The best analog scopes can refresh the display at sev­eral hundred times a second (at a sweep speed of higher than 1µs/div) but then they also have trouble dis­playing rare events; March 1995  85 Displaying a 3MHz signal of a Tektronix 2465 analog scope shows a waveform which is clean and apparently free of any glitches. The same 3MHz signal displayed on a Tektronix 2467B, one of the world’s fastest analog scopes which has an enhanced CRT. Here a glitch is apparent in the form of a “runt” pulse (about half the full height), although the reproduction of this photo may not show this. the writing speed of the phosphor used in cathode ray tubes (CRTs) is too slow for single glitches to be observed by the user, even if a viewing hood is employed. The only way to see very fast glitch86  Silicon Chip es buried in a repetitive signal with an analog scope is use one that includes an electron multiplying plate between the deflection plates and the phos­phor of the CRT. Examples of such scopes are the Tektronix 2467B and 7104 but these are expensive scopes indeed. Of course, some high-end digital scopes can be programmed to find glitches in repetitive signals but you have to know what you are looking for in order to do the programming. And since the digital scope spends so little time actually acquiring the signal, you might have to wait a long time before the glitch actually is found, if at all. And while analog scopes can be bet­ter at finding glitches, you have to spend unconscionably long times glued to the screen in order to actually see them. Sometime in the future, digital scopes must equal the glitch finding ability of the best analog scopes but according to theory, this would re­quire a display system capable of sev­eral thousand full screen acquisitions per second. The instrument would then have to rasterise these acquisi­tions at nearly 200 million pixels per second (compare that to today’s VGA screens at about 55 million pixels per second. 1024 x 768 x 70). In addition, the data move:gient between the ac­ quisition system and the display would need to be around 200 mega­bytes per second. Now while these parameters are technically feasible, there is no digital scope available to­day which comes within cooee of them. All of which leads up to how Tektronix has gone about achieving the desired result by taking another approach – changing the architecture of the digital scope. Briefly, these changes are as follows. first, the rasterisation capability of the display system is duplicated in the acquisi­tion system, next, the rasteriser is al­lowed to use a portion of the high speed acquisition memory to build display images; and third, the acqui­ sition hardware is allowed to start acquisitions without the intervention of the instrument’s firmware and to calculate its own trigger positions. This new architecture is used in the Tektronix TDS700A TruCapture dig­ital scopes in a mode called “InstaVu” acquisition. When this mode is ena­bled, the data moved from the acqui­sition system is a complete rasterised image of many triggered acquisitions of the input signal. By the way, perhaps we should briefly explain the term rasterisation as it pertains to digital scopes. It refers to the display system. In a conven­tional analog scope, the input signal is applied directly to the deflection plates of the CRT and so the signal on the screen is an “analogue” of the input; it is also a vector display with the electron beam tracing out the signal on the screen in response to the deflection voltages on the plates. A raster signal, by contrast, is the same as a computer video display; the electron beam scans the whole screen at rates similar to a computer VGA display and the beam is modulated on and off by the video signal to produce the individual pixels (picture ele­ments). In essence, the DSO converts the input signal to digital data and stores it in high speed video memory. Getting back to the plot, we talked about moving a complete rasterised image from the acquisition system to the display. Transferring this 500 x 256 pixel map requires a lot more data to be transferred between the two systems but the raster is only moved at the refresh rate of the scope’s display and contains information from tens of thousands of acquisitions. Doing it this way makes the data transfer rate manageable and in fact, it equates to 417Kb/sec. Tektronix has had to develop a considerable range of new semiconduc­tor hardware to achieve its new architecture and among these is a new kind of demultiplexer which integrates 360,000 transistors into a CMOS IC with 304 pins. It dissipates about 2.5 watts when running at full speed. Normally, the only function of this IC would be to demultiplex (ie, switch) data from the analog to digital converter and store it in a high speed static RAM. One third of this new demultiplexer is devoted to that job. The remainder is split between a high speed rasteriser and a digital signal processor (DSP). The DSP is included for, among other things, mathematical algorithms and trigger position cal­culations. We could discuss this new technology at greater length but none of it really means much until you see the results. To this end, four screen pho­tos are included with this article, showing how different scopes behave when displaying a 3MHz waveform with buried glitches. Briefly, all but the best analog scopes never reveal the glitches and nor does the Tektronix 544A colour digital scope (reviewed in Silicon Chip, November 1993) but the TDS784A and TDS744A, with On a Tektronix TDS 544 digital colour scope, the 3MHz signal results in a waveform which is similar to that shown on the Tektronix 2465 analog scope. Note that it has been sampled at a rate of 500 megasample/second. Finally, this is the 3MHz signal depicted on a Tektronix TDS 784A digital colour scope in InstaVu mode. Here the runt signal is clearly visible, made doubly by the colour display (although not reproduced in this B&W photo). Note that the acquisition rate is also 500Ms/s, the same as for the TDS 544A, but the number of acquisitions is a great deal more (75,896 versus 1156). their extremely high sampling rates and high acquisition rates, do reveal the glitches and do so even more dra­matically with the aid of a colour screen. Most impressive. For more information and prices on these new digital oscilloscopes, con­tact Tektronix Australia Pty Ltd, 80 Waterloo Road, North Ryde NSW 2113. Phone (02) 888 7066. SC March 1995  87 Silicon Chip Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. 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. 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. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. 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. 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). 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. 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; Voice-Operated Switch (VOX) With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise 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 Tele­phone; 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 Home-Brew 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 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. ORDER FORM Please send me a back issue for: ❏ June 1989 ❏ July 1989 ❏ December 1989 ❏ January 1990 ❏ June 1990 ❏ July 1990 ❏ November 1990 ❏ December 1990 ❏ April 1991 ❏ May 1991 ❏ September 1991 ❏ October 1991 ❏ February 1992 ❏ March 1992 ❏ July 1992 ❏ August 1992 ❏ February 1993 ❏ March 1993 ❏ July 1993 ❏ August 1993 ❏ December 1993 ❏ January 1994 ❏ May 1994 ❏ June 1994 ❏ October 1994 ❏ November 1994 ❏ March 1995 ❏ April 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 September 1989 February 1990 August 1990 January 1991 June 1991 November 1991 April 1992 September 1992 April 1993 September 1993 February 1994 July 1994 December 1994 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 May 1993 October 1993 March 1994 August 1994 January 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 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 ___________ 88  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. ✂ v March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Build A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. 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. Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. 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. 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. 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. 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. 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. 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. 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 Sine­ wave Inverter, Pt.5. 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. March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. 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. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. 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. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2 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; 50-Watt/ Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. 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: IR 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 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 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 Micro­controller – 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 Micro­ controller – 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. 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. 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. August 1992: Build An Automatic SLA Battery Charger; February 1994: 90-Second Message Recorder; Compact 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; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11. 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; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems: How They Work; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Build A Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers , Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt2; Remote Control System For Models, Pt.2. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, November 1988, December 1988, January, February, March and 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 (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. March 1995  89 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Modification to coolant level alarm I am about to build the Coolant Level Alarm, as described in the June 1994 issue of SILICON CHIP. Could you please advise me how I can modify this circuit to replace the rather fragile 8Ω mini loudspeaker with a piezo transducer as marketed by Dick Smith Electronics (Cat L-7022)? (L. A., Winn­ ellie, NT). • You can connect the piezo transducer directly in place of the loudspeaker. If you wish, you can also omit the series 47Ω resistor and 2.2µF capacitor but in practice they will make negligible difference to the sound output. Fast charger for six cells I have seen the “Fast Charger for Nicad Batteries” in the May 1994 issue. As I do a fair amount of wedding photography, I could use a charger as presented as my flash batteries will sometimes become exhausted before I Questions on weather beacon radio I am constructing the Long Wave AM Receiver for aircraft weather beacons, as published in the September 1994 issue. Is it possible that IC1 on the overlay diagram, page 56, should be a YS414 type, not a ZN414 as in the parts list? The problem that I have is that when moving VC1 full travel both ways I can only pick up 612kHz (radio station). I have checked VC1 with a capacitance meter and it is OK. The 10mm ferrite rod came out of an old radio and is a little longer than 85mm. Is this length critical? Perhaps you can help me with this problem? (D. C., Bris­ bane, Qld). 90  Silicon Chip am finished, and being able to recharge one of them in less than an hour would solve the problem. Alas, my Metz 45CT5 flash uses a battery holder containing not four but six AA nicad cells which can only be accessed for charging at their 7.2V output terminals. Is it possible to modify the charger circuitry to charge six 720mA.h cells in series? There would appear to be enough supply volts (12V) as the cells need 9V to push 950mA through them. Your help would be greatly appreciated. Incidentally, I bought six of the new metal hydride re­chargeable batteries and when charging at the 5-hr rate (360mA) as quoted on their information sheet, one of them exploded. I could easily have been blinded if I had been near it at the time. The company replaced the cells and the $50 battery holder and I tried again at 100mA. No explosion, but they all had different amp-hour and short circuit capabilities and my flash took 20 seconds to build up where it normally takes eight seconds with fully charged batteries! So I went back to nicads – a • The YS414 and ZN414 are equiv­alent devices so you should not have a problem there. Both are shown on the circuit diagram, by the way. Indeed the circuit is apparently working, even though you can only pick up 612kHz. This frequency should be tuned when the capacitance of the tuning gang is towards the minimum. If this is so, your circuit is working correctly and it is then a question of how far away you are from the nearest LF beacon. If you cannot receive signals indoors, try it outside, especially if you are in a weak signal area and the building you are in is of reinforced concrete or steel construc­tion or has aluminium sarking in the roof. The length of rod is not critical – in fact, the longer the better. great disappointment. (N. W., Peak­ hurst, NSW). • It is possible to use the Fast Charger without modification to charge six nicad cells but there are a number of constraints. First, the end-point voltage of a 6-cell pack will be around 10.2V. This, combined with a maximum switching duty cycle of 78% for the TEA1100, means that the circuit will fully charge the batteries only if the input voltage is above 13V. Ideally, it should be about 14-15V DC. This could be obtained from a 1-amp DC plugpack with a nominal rating of 12V or more. Alternatively, you could elect to charge two or three cells at a time, provided you can remove them from the battery pack. Component tester for oscilloscope I refer to an Altronics advertisement in December 1989 for a Labtech 20MHz CRO which shows that it has the capability to display component test status patterns. Is it possible that there are circuits available as an “addon” to old CROs that would allow one to test capacitors and zeners? (B. S., Bur­wood, Vic). • We have not published anything on this topic to date and shall put it on our list of projects to be considered. Sending audio signals along the AC mains Have you ever thought about designing a converter and asso­ ciated receiver-amplifier along the lines of a mains connected intercom? The converter feeds stereo signals into the house wiring and speakers can be plugged in anywhere in the house. Your comments on such a system, please. (W. J., Tranmere, SA). • There is no reason why stereo signals could not be sent via mains AC wiring using an FM carrier and stereo multiplex encod­ing. Funnily enough, shortly after your letter arrived one D1-D4 4x1N4001 A 240VAC FROM SECURITY LAMP IN 12V N Buzzer for infrared security light I have an infrared sensor on my house with a spotlight to detect any visitors and turn on the light. This light can be set for seconds or minutes at a time. What I would like to do is attach a buzzer that would sound for only one or two seconds each time the detection field was broken and then not sound again until the light had turned off and then on again. I imagine this would be possiof our contributors sent in a design along these lines. We hope to publish it within the next few months. Electronic ballast coil confusion Being a circuit junky, I had a butcher’s at the Electronic Ballast for Fluorescent Lights in the October 1994 issue. John Clarke has once again delivered an interesting circuit that is sophisticated but straightforward, without unnecessary complexity. The power factor correction is a good idea and I can tell that the MC34262P needs closer study. Thanks for bringing it to my notice. Unfortunately, there is some confusion over the connection of L1 and L2. On page 45 you say that “L1 & L2 are wound onto a common toroid in antiphase so that the inductor works to elim­ i nate common mode high frequency signals without saturation from the line current”. Figs. 7 & 8 show the inductors wound and connected this way. This is quite reasonable and is exactly how such inductors are used in most commercially available mains filters. However, the circuit diagram (Fig.6, page 45) and the front cover show the inductors connected such that the load current in each inductor adds; ie, they are in phase. As such the inductors 220 25VW 7812 OUT GND +12V 2.2M 7 470k 4 IC1 555 6 2 2.2M 1 8 3 D5 1 1N4001 BUZZER 0.1 ble to do: a unit that would plug into the light socket and operate through a step-down trans­former to run a timer circuit of some type and a buzzer. I have the experience to construct such a project but not the knowledge to design the needed equipment. Hoping you can come up with a possible will not reduce common mode signals (noise) and in some circum­ stances saturation may occur, reducing the effective inductance and hence reducing their effectiveness. As you are aware, the phasings of windings on a toroidal core is determined by which way they pass through the hole. For a common mode choke, the wires to the mains must come from the same side of the toroid, and naturally the wires to the load must come from the other side of the toroid. The direction that the wind­ings take around the toroid is irrelevant except to parasitic components. It is probably the extra series inductance that the differ­ential mode connection adds that causes the flat topping on the 240V waveform (see oscillograph, top of page 51). This is quite similar to the waveform seen at the secondary of a mains power transformer driving a full wave bridge rectifier with filter capacitors, the leakage inductance of the transformer being the cause in that case. But there is a twist. With L1 and L2 connected as shown in the circuit diagram, they will reduce any differential mode noise (ie between active and neutral) that may be present. Considering the circuit generates moderate levels of high frequency power, this may not be such a bad thing as long as L1 and L2 do not circuit to do this job. (A. F., Seaton, SA) • It should be possible to achieve your purpose with the circuit shown here. Essentially, it is based on a 555 mono­stable timer (IC1) and this operates a buzzer for two seconds each time the light comes on. saturate. In some two-stage mains filters this connection is used along with inductors connected to reduce common mode noise. At this point you probably expect me to give the solution but this is not a simple thing to do. Noise on the mains can have differential and common mode components and, as I have stated, the inductors can be connected to block one or the other, but not both simultaneously. The answer to which connection is best depends, to some extent, on the installation; ie, the wiring, the nature and sensitivity of appliances connected to the mains, etc, over which we have no control. I think that probably the best way to go is to connect it in the common mode. This should eliminate the possibility of saturation in the ferrite and maximise the useful inductance. Besides, the filter capacitors should reduce the high frequency differential mode noise and the power factor correction should take care of the harmonic garbage that would otherwise be gener­ated by the rectifier and filter capacitor combination. I am glad to see that you have made a serious effort to design a quiet and efficient circuit. It is much better to have noise stopped at its source than to have to deal with it every­where else. (P. D., Sydney, NSW). • The phase of the windings for L1 March 1995  91 More light on power factor controller Could you please elaborate a little more on the operation of the power factor controller circuit, Fig.4, page 44 of your October 1994 edition. What I want to know is at what point is the switching of Q1 affecting the 400V output given that, according to your diagram, Q1 is switched on and off over the full half cycle. It seems a bit much to step, say, 50V coming from the bridge rectifier to over 400V at that point in the half cycle, or is using R1 & Lx as a load sufficient to cause Iav to be in phase with Vin regardless of the tube current? Also, your parts list for that project describes the 1N5062 as a transient protected diode. What do you mean by this? (G. F., Nairne, SA). • The boost converter comprising IC1, Q1, Lx, Dx and C2 begins to operate from a relatively low voltage within the AC waveform, as shown in Fig.4 on page 44. Typically, it starts at around 50V. While it may seem impossible for the converter to boost the voltage from 50V to 400V, it is the and L2 is not very clear in the front cover photo. However, we can assure you that the wind­ings in the prototype are as per Fig.7 and a better photograph of the actual winding directions can be seen on page 52. Yes, we concede that the circuit diagram phase dots are incorrect. The flat topping of the mains is due to the supply that we obtain here in Warriewood. This flat topping can also be seen in the oscilloscope photographs for the High-Power Dimmer for Incandes­cent Lamps, as published in August 1994 (see page 32 and the caption referring to flat topping). Input capacitor wrongly polarised After seeing your 25W amplifier design in the December 1993 issue, I purchased two of these modules as I was constructing an amplifier at the time. I also took the tone control section from the circuit for your Studio 92  Silicon Chip rate of change of current through Lx which develops the voltage into C2 rather than some form of transformer action. Consequently, it is possible to boost the voltage to very high values. Note that the current drawn by the power factor circuit is also sinusoidal and follows the input voltage waveform. This is shown in the top waveform on page 51. The current flow is forced this way by the multiplier which sets the current through R1. This depends on the phase of the incoming voltage at pin 3 of IC1. The transient protected diode is also called a controlled avalanche type. It refers to the diode’s perfor­ mance when in the breakdown region of its V1 curve. Once in this region, where reverse voltage is sufficient to force the diode into breakdown, a normal diode will possibly fail since its impedance suddenly drops to a low value to allow a high current flow. Transient protected diodes, on the other hand, have a soft breakdown characteristic, so that when breakdown does occur, the impedance remains relatively high. This prevents damage to the diode. Twin Fifty Amplifier (March & April 1992) to complete the project as an amplifier to power a pair of scratchbuilt 40-watt 3-way speakers. Upon testing of the amplifier modules I was initially de­lighted with the performance. However, after attaching them to a pair of different speakers having a higher sensitivity, I noticed that a substantial amount of noise appeared at the output when any input (including a direct ground, 50kΩ pot or preamp output via latter) was connected to the input of the module. I constructed the single supply version of the project and was quite certain that the kits were constructed perfectly, and indeed the fault showed up in both modules. Extensive testing using different power supplies and checking things with the CRO yielded nothing so I looked to the 1µF input capacitor. It seemed suspect and a quick multimeter measurement show­ed that it did not sit at half supply voltage as expected from the 22kΩ divider net- work. I substituted the nearest thing I had, a 0.47µF greencap and had immediate success. Why? The answer was extremely simple. The electro had been shown with incorrect polarity on the parts layout on page 34! It is shown correctly in the circuit diagram. On the same topic, I believe the input capacitor on the dual supply version should be a bipolar or other non-polarised type. The completed project now sounds superb, and the tone controls are excellent as well – in my opinion better than the five-plus band graphic equalisers found commonly on middle of the range equipment today. Secondly, also on the topic of audio amplifiers, I need to build an amplifier for my car stereo. Its signal will have to be derived from the unit’s speaker outputs and I will provide tone controls to try and extract some reasonable audio from my $45/pair speakers. I looked at a few different amplifier designs, including that mentioned above, but 13.8V operation did not suit any. However, I then remembered your data page on the LM383 in the March 1991 issue. It (Fig.5, page 39) shows two of these devices connected in bridge mode, which can supposedly deliver 16 watts into 4Ω; perfect for my application. It supposedly achieves this by the fact that bridged amplifiers effectively “see” only half the speaker impedance; as you again mention replying to G. F. on page 92 of the November 1994 issue. My knowledge of bridge amplifier theory is virtually non-existent but I don’t believe in any case that an amplifier can deliver a peak-peak output greater than its DC power supply voltage. In this case, with a 14V DC supply rail, the output power into 4Ω amounts to a little over 6W; although if the speak­er impedance is taken as 2Ω this value changes to double that. Is this theory correct? If so, how does this circuit deliv­er 16W? Otherwise could you recommend a source of suitable ferr­ite components to be used in a voltage step-up circuit to power a pair of 25W modules? A 30W continuous power rating would be ample to power two of these with normal music. I have seen your DC-DC converter kit but this is far too expensive and overkill for the power my car speakers can handle. Are there any other ways of getting reasonable power from car battery voltage into 4Ω loads? Still on audio topics, I would like to express my annoyance at the PMPO marketing terms used by reputable audio equipment manufacturers to sell hifi equipment. Words like 400W PMPO are a common sight on cheap midi systems which don’t even draw more than 50W or so from the mains. In fact, looking at the amplifiers and drivers in these systems, they don’t look like they can deliv­er more than 10-15W RMS per channel. I am quite sure there is no mathematical basis for these figures and they simply make it hard to choose an amplifier with the power you require. I am pleased to say, however, that quality Japanese brands such as Sony and JVC do use correct RMS terminology and believ­able figures. Surely the use of such meaningless figures should be prohibited by Australian standards. Similar situations apply with car speakers; the $45 speak­ers I mentioned above are marked “80 watts maximum music power” though they are sold as 40W speakers and in practice they don’t like much volume through a true 20W RMS good quality amplifier. (S. Longer fade for diesel horn I always enjoy the magazine and the model railway projects. The whistle and horn described in the July 1994 issue have a very good tone but the diesel horn needs to have a longer fade as the air bleeds off and the horn trumpet continues to “ring” in the prototype. If you could change that, it would be perfect. Any suggestions? A very impressive digital controlled throttle was demon­strated at the October 1994 Liverpool model railway exhibition with AC on the track permanently and locos addressed by the controller. This seems the way of the future. Do you see it as a viable project? Finally, I must say how much I like your circuit diagrams, compared with those tiny computer generated symbols of some other magazines. (T. B., Kogarah, NSW). • It is possible to increase the fade time by using a bigger capacitor for the 22µF capacitor at the base J., Surrey Downs, SA). • You are right about the input coupling capacitor’s polarity and, ideally, the input capacitor for the balanced supply version should be a bipolar type. The LM383 can deliver around 1112W in bridge mode since its output swing is doubled and it “sees” a 2Ω load. The figure of 16W is only possible at the higher supply voltage of 20V. We don’t have any simple answers to your need for power amplifiers run from 13.8V DC; a big inverter is the only way. We agree with you about the absurdity of amplifiers with PMPO figures. To our knowledge, an Australian stand­ ard for hifi equipment has never been promul­gated although our publisher spent a good deal of time in the 1970s sitting on a standards committee for that purpose. Since so little hifi equipment is manufactured in this country, there seems little point in having a local standard anyway. Car speakers are rated with nonsensical figures and even those that do have high ratings are often quite inefficient so that the overall loudness and dynamic range is not marvellous. of Q2. Try 100µF or larger. Alternatively, try connecting a 100kΩ or larger resistor in series with diode D1. We are familiar with the train control you mention which was featured at the October model railway exhibition. Generally called “Command Control”, these systems enable realistic control of a large number of locomotives on a layout, without the need for block switching and so on. The drawback is that they are quite expensive and require a control receiver to be installed in every locomotive, together with a changeover switch if it is desired to run the loco on other layouts with conventional con­trollers. Thanks for the compliment on our circuit diagrams. They are actually generated on a CAD system but our draughtsman, Bob Flynn, has spent a considerable amount of time to produce a library of symbols which look very similar to those used when our diagrams were hand-drawn. Notes & Errata 25W Amplifier Module, Dec. 1993: the wiring diagram for the single supply version (Fig.3) shows the 1µF input capacitor installed the wrong way around; the circuit diagram is correct. Also the 1µF input capacitor for the dual supply version should be a bipolar electrolytic or other non-polarised capacitor such as an MKT polyester. Multi-Channel Remote Control, May 1994: the Vcc (supply line) to a number of ICs (IC4, IC6, IC8, IC9, IC10 & IC11) is open circuit on the PC board, as sup­plied by the author. This pre­sents a problem when using the outputs for latched operation. To correct the error, wire a link from pin 7 of IC2 to the pin of C7 (.0047µF) which is closest to the outside edge of the PC board. A corrected PC pattern is available if necessary. Some codes may not operate correctly due to the thresholds being quite critical on IC12a. This causes the rate pin (RB) of IC1 to pulse erratically and therefore IC1 is not able to receive a valid code. To correct this problem, replace R5 with a trimpot and adjust it so that the voltage on pin 6 of IC12b is halfway bet­ween the voltage at pin 5 when transmitting a valid code with link SW13 (on the transmitter board) in and when transmitting a valid code with link SW13 out. The author has experimented with this and, with a supply rail of 6.39V, the value for R5 worked out at 6.8kΩ. The voltages on pin 5 varied between 2V and 3V and so the threshold was set for 2.5V. 50-watt Stereo Amplifier Module, Feb. 1995: the parts list should show 2 x 22µF 16VW electrolytic capacitors (not 4). In addition, 2 x 47µF 16VW electrolytic capacitors should be added to the list. Digital Effects Unit, Feb. 1995: The parts list should show 19 330Ω resistors rather than one. On the circuit (Fig.2), the 3.3kΩ resistor shown at the input to the modulation filter should be 22kΩ. An extra 3.3kΩ resistor should be included bet­ween the positive side of the 100µF capacitor and the junction of the 1.8kΩ and 22kΩ resistors. Finally, the two 56pF capacitors shown on the PC board overlay (Fig.3) should each be 560pF, while the unmarked electrolytic capacitor at top right should be labelled 10µF. SC March 1995  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. HD 64000 DEVELOPMENT SYSTEM. All plug-ins, emulation pods, ASM, C and Xcompilers, software and very full documentation for 64000 systems, Z80 NSC800, 80xx, 68xxx, $2.5k. P. L. Christie (08) 223 2296 AH. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ ASIAN ELECTRONICS repairs and service data. Phone Phil 2pm-5pm Mon-Fri (03) 773 3997. LEARN MICROCONTROLLER programming with our Motorola 68HC­ 705K1 & P9 Kits. All code fully commented, provided on floppy disk. Introduction to the K1 (reviewed in Everyday Electronics, 2/94), Reaction Timer (Electronics Australia, 3/94), Number Crunch­er (EA, 9/94), & Codepad (uses P9). DIY Electronics, phone/fax: (058) 62 1915. PELTIER EFFECT solid state modules 3cm x 3cm, 8V/5.4A. One side heats, the other cools. Up to 59 deg. C differential. Also 2.5mw, 635nm LASER DIODE modules, 10 times brighter than 670nm modules. HeNe replacement, 3V to 6V. 3-element glass collimating lens adjustable. DIY Electronics, tel/fax: (058) 62 1915. FAX/SSTV “MFAX” Multipur pose IBM PC plug-in card for Satellite Fax WEAFAX and SSTV. Compatible with JVFAX 7.0, fully assembled and tested 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 YUGA ENTERPRISE BA, LA, LB, LC, UPA, UPB, UPC, TA, Buy TBA, TDA, TEA, & 2SA, 2SB, 2SC, Sell ese 2SJ, 2SK, SAA, Japan STA, STK, STR, s IC & tors HA, AC, KA, KIA, Transis IX, LM, MN, PA TEL: (65) 741 0300 FAX: (65) 749 1048 705 Sims Drive #03-09 Shun Li Industrial Complex Singapore 1438 HEATSINKS GREG BALL ELECTRONICS UNIT 8, 9-11 ABEL STREET, PENRITH PH: (047) 31 5661 FAX: (047) 31 5982 $289.00, kit $249.00, audio cable $15, P&H $10. AM/FM FAX Decoder, ideal for satellite and WEAFAX decoding, kit $118.00, PCB $34.00, LED display kit $29.00, P&H $7. VHF/FM 137MHz APT Satellite Receiver, ideal for NOAA/MET satellites, kit $99.00, PCB $25.00, preamp $34.00, P&H $7. Technocom, PO Box 1313, Mandurah 6210. Phone (09) 581 4297 a/h. RADIOTRON DESIGNERS HANDBOOK, 4th edition (Langford-Smith) approx. 1500pp. Best book EVER about valves and radio design. Good condition, considering 40 years old, $100 each. Broken back, otherwise complete, $80. Plus post * pack (within Australia) $10 each. Also Paleo VCT, valve tester, signal generator, valves, other old radio books, offers? Hurley, POB 245/R, Blackburn, Vic 3130. Tel/ Fax (03) 889 6337. A $2 COIN (or stamps) for Don’s New Menu Driven Promo Disk. Covers all Short Form Kits. COM1: driven 18 I/O $70, LPT1: driven 64 I/O $38, Z80 Dev $38+, PIC16C5x/71/84 Universal PCB $23, Basic Stamps $63. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. TINY VIDEO CAMERAS $10 off! This month from $189. Previous buyers get DOUBLE $20 off. MATCHBOX SIZE PCB MODULES MEMORY & DRIVES PRICES AT APRIL, 1995 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $64/58 4Mb 30-pin $200/200 2Mb 72-pin $148/135 4Mb 72-pin $258/228 8Mb 72-pin $515/470 16Mb 72-pin $780/690 32Mb 72-pin $1560/1380 Parallax “BASIC STAMP”: 8 I/O pins and proto­ typing area. Program it with a PC, 33 simple instructions. Development kit includes one “BASIC STAMP” ($270). Extra modules ($79.85). Chipset and Resonator to make your own $30.25. STAMP Stretch­ er 16 I/O 1 A/D $91.96. Serial input LCD display $102.85. Scarce com­ponents need­ed for Application notes now in stock. Small items XPress post $5, kit $8. Send four 45c stamps for details. Parallax Distributor and technical support in Australia. MicroZed Computers PO Box 634 (296 Cook’s Rd), ARMIDALE 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $405 $90 LASER PRINTER HP with 2Mb $200 DRAM DIP 1Mb x 1 70ns DIP $7.80 256 x 4 70ns DIP $7.80 256 x 16 70ns SOJ $48.00 IBM PS.2 THINKPAD L40/N33 8Mb 4Mb $655 $275 TOSHIBA 3100SX 2100/50 4Mb 8Mb $255 $585 SUN SPARC 5 32Mb SPARC 10/20 64Mb $1780 $3696 DRIVES – SEAGATE 545Mb 14ms 3yr wty $335 1052Mb 9ms 5yr wty $550 COMPAQ 2148Mb 9ms 5yr wty $1470 CONTURA 8Mb $550 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. We buy & trade RAM. 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Tel: (02) 980 6988 Fax: (02) 980 6991 • PELHAM ELECTROSTATIC LOUDSPEAKERS • 3-Panel Full Range Design. Available in kit form or fully assembled. Locally designed & manufactured. • For information brochure, Phone (09) 397 6212 Fax (09) 496 1546 Or write to: E. R. AUDIO, 119 BROOKTON HWY, ROLEYSTONE, WESTERN AUSTRALIA 6111. N.S.W. Ph. (02) 804 6859 S.A. Ph. (08) 332 6513 TAS. Ph. (002) 31 2403 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 each + $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. March 1995  95 Microprocessor For Digital Effects Unit Microprocessor For Stereo Preamplifier Advertising Index Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­ pro­ cessor IC for the Digital Effects Unit described in this issue. Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 979 5644; Fax (02) 979 6503. Now back in stock: the 68HC705-C8P pre-programmed micro­pro­cessor for the Infrared Remote Controlled Stereo Preamplifier (SILICON CHIP, Sept.Oct. 1993). This device also suits the Remote Volume Control published in 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. Altronics ................................ 66-68 from 32 x 32 x 23mm with lens. 16 types. Optional lenses, C lens mounts, cases & technical manuals. ALLTHINGS Ph/Fax (09) 349 9413. VALVES: all types for radio, audio and industrial use. For sale and wanted to buy. SSAE for list. Electronic Valve and Tube Company, PO Box 381, Chad­ stone, Vic 3148. Fax (03) 571 1160. Ph (018) 557 380. MicaSOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools or individual use. Now available in Australia. Send 4 x 45c 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. C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $150.00 each. Macro Cross Assemblers Av-Comm.....................................49 Dick Smith Electronics........... 12-15 E.R. Audio....................................95 Greg Ball Electronics...................95 Instant PCBs................................95 Jaycar .........................................45 L&M Video...................................83 for these CPUs + 6800/01/03/05 and 6502: $150 for the set. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $550. 8051/52 or 80C320 simulator (fast): $75. Demo disk: $5. Network Software: use serial, parallel, Arcnet or Ethernet to share files and printers on your PCs. DOS and Windows compatible. $105 per net­work. All prices + postage. GRANTRONICS, PO Box 275, Wentworth­ville 2145. Ph/Fax (02) 631 1236. Macservice...............................3,44 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 components $75 plus $5 p&p. Optional Z frame stand (includes spacers and chassis DC connector) $25 plus $5 P7P. Available from Prototype Electronics, 1/29 Stewart St, Paramatta, NSW 2124. Phone (02) 890 2960; Fax (02) 630 3148. Pay by cheque, money order, credit card. SC Railway Projects Book.......OBC PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. MicroZed Computers...................95 Oatley Electronics.................. 78-79 Pelham.........................................95 RCS Radio ..................................94 Resurrection Radio .....................77 Rod Irving Electronics .......... 27-31 Silicon Chip Back Issues....... 88-89 Silicon Chip Binders....................62 Silicon Chip Bookshop.................67 Silicon Chip Software..................73 Silicon Chip Wallchart................IBC Tektronix....................................IFC Yuga Enterprise...........................95 _________________________________ PC Boards    SILICON CHIP BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers, are made from a dis­tinctive 2-tone green vinyl & have the SILICON CHIP logo printed in gold-coloured lettering on the spine & cover. To order, just fill in & mail the order form on page 31, or phone or fax your order to: Silicon Chip Publications, PO Box 139, Collaroy Beach, 2097. Phone (02) 979 5644. Fax: (02) 979 6503. 96  Silicon Chip 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. Order by phone or fax from SILICON CHIP - or use the handy order form inside