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SILICON CHIP’S 20 best car projects are now all together in this 112-page book ON SALE NOW AT SELECTED NEWSAGENTS This book has 20 electronic projects for cars, including high energy & breakerless ignition systems, an ultrasonic alarm, a digital tachometer, a coolant level alarm, a flashing alarm light, a talking headlight reminder, a UHF remote switch & a thermostatic switch for electrically operated radiator fans. And there are eight quick circuit ideas as well. Price: $8.95 (plus $3 p&p if ordering from Silicon Chip) Yes! Please send me ____ copies of 20 Electronic Projects For Cars 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___________ Or fill in & mail or fax this easy-order form Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the coupon & fax it to (02) 9979 6503; or mail the coupon to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Vol.8, No.8; August 1995 Contents FEATURES 4 Electronic Diesel Engine Management Electronic technology is greatly improving the performance of diesel engines. Here’s a look at the electronic control system used by Detroit Diesel on truck engines – by Julian Edgar 14 133MHz Pentium Processor Now Available FUEL INJECTOR MONITOR FOR CARS – PAGE 24 The Pentium is about to become the mainstream processor in PCs. We take a look at its main features & give some details on Intel’s latest 133MHz Pentium processor PROJECTS TO BUILD 18 Vifa JV-60 2-Way Bass Reflex Loudspeaker System These new 60-litre systems use two 170mm woofers & a tweeter with a ferro-fluid voice coil – by Leo Simpson 24 A Fuel Injector Monitor For Cars This circuit monitors the fuel injectors & displays a reading that’s directly proportional to the injector opening time – by Rick Walters 30 A Gain-Controlled Microphone Preamp Use it with PA systems to maintain a constant level – by John Clarke 54 Audio Lab: A PC-Controlled Audio Test Instrument Monitors frequency, resistance, capacitance, and AC & DC voltage; and performs frequency response plots – by Roger Kent 60 Build The Mighty-Mite Powered Loudspeaker It uses a miniature IC & delivers an output of 1W – by John Clarke 75 Build A 6-12V Alarm Screamer Module It comes as a kit & puts out 110dB of noise SPECIAL COLUMNS 40 Serviceman’s Log It took a little longer than usual – by the TV Serviceman VIFA 60-LITRE 2-WAY BASS REFLEX LOUDSPEAKER SYSTEM– PAGE 18 72 Computer Bits An easy way to identify IDE hard disc drive parameters – by Geoff Cohen 80 Vintage Radio A couple of odd radio repairs – by John Hill DEPARTMENTS 2 Publisher’s Letter 37 Mailbag 38 Circuit Notebook 53 Bookshelf 59 Order Form 86 Product Showcase 90 Ask Silicon Chip 94 Market Centre 96 Advertising Index 94 Notes & Errata PC-CONTROLLED AUDIO TEST INSTRUMENT TO BUILD – PAGE 54 August 1995  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Keep those letters coming In the routine of producing SILICON CHIP every month it is easy to become disenchanted with the workload and sometimes we might wonder if all the detail work is really worth it. This is especially the case as we get close to the final deadlines and everything has to be delivered to the printer. These thoughts were prompted by two items of mail which arrived on my desk this morning. One was a note from a reader which he included with his twoyear subscription renewal. It was just a few words of appre­ciation about the magazine and how he enjoys it. The other item was a large postcard from New Zealand from a reader who had just received one of our project books. Again, he was very complimen­tary. Now both of these items gave me a real buzz. They were timely because they arrived at the peak pressure time and they were especially appreciated because they give the feeling that the close attention to detail by all the magazine staff is really worthwhile. To those two readers and all of you who pass on these remarks of appreciation from time to time, thanks very much. All of which is a comment on the whole subject of corre­spondence with which we have a love/hate relationship. The mail seems to come in waves. Sometimes we are overwhelmed with the volume of it and wonder what has moved so many people to suddenly write and order various items, to ask for circuits and so on. We then have a battle to catch up with it, especially if it has arrived at close to deadlines and editorial work has taken prece­dence. That explains the “hate” part of the love/hate relation­ship – we hate trying to catch up with it. At other times the mail might slow to a dribble and we again wonder why everybody has gone quiet. At those times, we would “love” to receive more mail. Apart from giving us a feeling that we’re appreciated, your letters can help make the magazine better and give you more of what you want. Many articles and circuits that appear in SILICON CHIP are the result of suggestions by readers. We can’t always help with your queries but we do manage to respond positively in most cases. So please feel free to write in, make comments on the maga­zine content or on topics of current interest, contribute cir­cuits for publication or request information on circuits that have been published. We respond as quickly as we can and most orders for back issues and other products are sent out on the same day. 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 HEWLETT PACKARD 334A Distortion Analyser HEWLETT PACKARD 200CD Audio Oscillator • measures distortion 5Hz600kHz • harmonics up to 3MHz • auto nulling mode • high pass filter • high impedance AM detector HEWLETT PACKARD HEWLETT PACKARD 3400A RMS Voltmeter 5328A Universal Counter • voltage range 1mV to 300V full scale 12 ranges • dB range -72dBm to +52dBm • frequency range 10Hz to 10MHz • responds to rms value of input signal • 5Hz to 600kHz • 5 ranges • 10V out • balanced output HEWLETT PACKARD 5340A Microwave Counter • allows frequency measurements to 500MHz • HPIB interface • 100ns time interval • T.I. averaging to 10 ps resolution • channel C <at> 50ohms • single input 10Hz - 18GHz • automatic amplitude discrimination • high sensitivity -35dBm • high AM & FM tolerance • exceptional reliability $1050 $79 $475 $695 $1950 BALLANTINE 6310A Test Oscillator BALLANTINE 3440A Millivoltmeter AWA F240 Distortion & Noise Meter ...................... $425 AWA G231 Low Distortion Oscillator ...................... $595 EATON 2075 Noise Gain Analyser ...................$6500(ex) EUROCARD 6 Slot Frames ........................................ $40 GR 1381 Random Noise Generator ........................ $295 HP 180/HP1810 Sampl CRO to 1GHz ................... $1350 HP 400EL AC Voltmeter .......................................... $195 HP 432A Power Meter C/W Head & Cable .............. $825 HP 652A Test Oscillator .......................................... $375 HP 1222A Oscilloscope DC-15MHz ........................ $410 HP 3406A Broadband Sampling Voltmeter ................................................................ $575 HP 5245L/5253/5255 Elect Counter ....................... $550 HP 5300/5302A Univ Counter to 50MHz ................ $195 HP 5326B Universal Timer/Counter/DVM ............... $295 HP 8005A Pulse Generator 20MHz 3 Channel ........ $350 HP 8405A Vector Voltmeter (with cal. cert.) ......... $1100 HP 8690B/8698/8699 400KHz-4GHz Sweep Osc ............................................................ $2450 MARCONI TF2300A FM/AM Mod Meter 500kHz-1000MHz ................................................... $450 MARCONI TF2500 AF Power/Volt Meter ................. $180 SD 6054B Microwave Freq Counter 20Hz-18GHz ......................................................... $2500 SD 6054C Microwave Freq Counter 1-18GHz ............................................................... $2000 TEKTRONIX 465 Scope DC-100MHz .................... $1190 TEKTRONIX 475 Scope DC-200MHz .................... $1550 TEKTRONIX 7904 Scope DC-500MHz .................. $2800 WAVETEK 143 Function Gen 20MHz ...................... $475 FLUKE 8840A Multimeter RACAL DANA 9500 Universal Timer/Counter • true RMS response to 30mV • frequency coverage 10kHz1.2GHz • measurement from 100µV to 300V • stable measurement • accuracy ±1% full scale to 150MHz • list price elsewhere over $5500 • 2Hz-1MHz frequency range • digital counter with 5 digit LED display • output impedance switch selectable • output terminals fuse protected $350 $795 HEWLETT PACKARD 1740A Oscilloscope RADIO COMMUNICATIONS TEST SETS: IFR500A ............................................................... $8250 IFR1500 .............................................................. $12000 MARCONI 2955A .................................................. $8500 SCHLUMBERGER 4040 ........................................ $7500 TEKTRONIX 475A Oscilloscope TEKTRONIX 7603 Oscilloscope (military) • frequency range to 100MHz • auto trigger • A & B input controls • resolution 0.1Hz to 1MHz • 9-digit LED display • IEEE • high stability timebase • C channel at 50 ohms • fully programmable 5½ digit multimeter • 0 to 1000V DC voltage • 0.005% basic accuracy • high reliability/self test • vacuum fluoro display • current list $1780 $695 $350 TEKTRONIX FG504/TM503 40MHz Function Generator TEKTRONIX CF/CD SERIES CFC250 Frequency Counter: $270 • DC-100MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej $990 • 250MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF rej, HF rej • mil spec AN/USM 281-C • triggers to 100MHz • dual trace • dual timebase • large screen $1690 $650 The name that means quality CFG250 2MHz Function Generator $375 • 0.001Hz-40MHz • 3 basic waveforms • built-in attenuator • phase lock mode $1290 CDC250 Universal Counter: $405 NEW EQUIPMENT Affordable Laboratory Instruments PS305 Single Output Supply SSI-2360 60MHz Dual Trace Dual Timebase CRO • 60MHz dual trace, dual trigger • Vertical sens. 1mV/div. • Maximum sweep rate 5ns/div. • Built-in component tester • With delay sweep, single sweep • Two high quality probes $1110 + Tax Frequency Counter 1000MHz High Resolution Microprocessor Design CN3165 • 8 digit LED display • Gate time cont. variable • At least 7 digits/ second readout • Uses reciprocal techniques for low frequency resolution $330 + Tax Function Generator 2/5MHz High Stability FG1617 & FG 1627 • • • • • • Multiple waveforms 1Hz to 10MHz Counter Output 20V open VCF input Var sweep lin/log Pulse output TTL/CMOS FG1617 $340 + Tax FG1627 $390 + Tax PS303D Dual Output Supply • 0-30V & 0-3A • Four output meters • Independent or Tracking modes • Low ripple output $420 + Tax • PS305D Dual Output Supply 0-30V and 0-5A $470 + Tax PS303 Single Output Supply • 0-30V & 0-3A • Two output meters • Constant I/V $265 + Tax Audio Generator AG2601A • 10Hz-1MHz 5 bands • High frequency stability • Sine/Square output $245 + Tax • 0-30V & 0-5A $300 + Tax PS8112 Single Output Supply • 0-60V & 0-5A $490 + Tax Pattern Generator CPG1367A • Colour pattern to test PAL system TV circuit • Dot, cross hatch, vertical, horizontal, raster, colour $275 + Tax MACSERVICE PTY LTD Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic., 3167   Tel: (03) 9562 9500 Fax: (03) 9562 9590 **Illustrations are representative only By JULIAN EDGAR Electronic diesel engine management Just as electronics has brought great strides in the performance & reliability of petrol engines, the application of similar techniques to diesel engines has led to improvements in fuel economy & a reduction in pollution. Here we examine the electronic control system used by Detroit Diesel on some truck engines. Diesel engines are widely used in railway locomotives, ships, heavy industry and trucks. Although of a similar age to the spark internal combustion engine, the diesel engine has not been widely adopted for use in passenger cars. However, just as elec4  Silicon Chip tronic engine management has been widely adopted to improve the performance of cars, similar techniques have been applied in diesel engines for trucks, particularly those used for long distance haulage. As a result, typical electronically controlled diesel engines are as much as 20% more fuel efficient than their predecessors. Although the basic design of petrol and diesel engines is similar (both are two or four-stroke designs which use recipro­cating pistons driving a crankshaft), a diesel engine does not ignite its fuel charge by the use of a spark plug. Instead, only air is compressed on the compression stroke. The fuel charge for the power stroke is accurately metered and pressurised by a fuel injection pump, of which there is one for each cylinder. It then passes to the high pressure injector and is sprayed into the combustion chamber, where it mixes with the hot compressed air and self-ignites. In a petrol engine (even one using fuel injection), the fuel and air are mixed prior to entry to the combustion chamber. The fuel/air mix is drawn into the cylinder on the intake stroke and so the injectors or carburettor need only mix the fuel and air at close to ambient air pressures. On the other hand, diesel injectors must operate at pressures of over 20MPa (3000 psi) and inject minute quantities of fuel at a rate of 2.5-25Hz. In order that the air in the diesel’s cylinders becomes hot enough for combustion to occur, the compression ratio is much higher than in a petrol engine. Compression ratios of 14:1 to 24:1 are commonly used, giving a cylinder pressure when the air is compressed of up to 3800kPa (560 psi). At a compression ratio of 16:1, the air temperature will theoretically be at 525°C, with actual temperatures being around 425-550°C in working diesel engines. Table 1 gives a summary of some of the differences between petrol and diesel engines. Because no throttling of the intake air occurs in a diesel engine (load changes are catered for by changing the mass of fuel introduced), a diesel engine needs to be governed to limit maxi­mum engine speed. In comparison to petrol engines, the maximum engine speed of a diesel is quite low, typically 2500 to 5000 RPM. This is because of the inertial loadings created by the heavy internal components which are required to absorb the very high cylinder pressures created during the power stroke. In order that the correct amounts of fuel are introduced to the combustion chamber at the right time, a complex mechanical system is usually employed. Mechanical fuel delivery The mechanical delivery of fuel to a diesel engine is com­plicated because of the high fuel pressures and short delivery times available. In fact, the processes occurring during injec­tion are more akin to acoustic principles than geometric laws of displacement. In a mechanical system, an engine-driven camshaft drives an injection pump’s plunger which feeds a high-pressure gallery. The delivery valve opens and a pressure wave proceeds toward the injec­tion nozzle at the speed of sound (approximately 8 10 7 9 11 4 6 5 2 3 1: FUEL TANK 2: GOVERNOR 3: FUEL SUPPLY PUMP 4: INJECTION PUMP 5: TIMING DEVICE 6: DRIVE FROM ENGINE 7: FUEL FILTER 8: VENT 9: NOZZLE AND HOLDER ASSEMBLY 10: FUEL RETURN LINE 11: OVERFLOW LINE 1 Fig.1: schematic of a mechanical diesel injection sys­tem: (1) Fuel tank; (2) Governor; (3) Fuel-supply pump; (4) Injec­tion pump; (5) Timing device; (6) Drive from engine; (7) Fuel filter; (8) Vent; (9) Nozzle-and-holder assembly; (10) Fuel return line; (11) Overflow line. 1400 metres per second under these conditions). When the injection nozzle’s opening is reached, the needle valve overcomes the force of the injection nozzle spring and lifts from its seat so that fuel can be injected from the spray orifices into the engine’s combustion chamber. Fig.1 shows a schematic diagram of an in-line fuel injec­tion pump system with a mechanical governor. The mechanical Detroit Diesel system differs slightly from this in that a combined plunger-type injection pump and hydrauli­ cally-controlled injector is used for each cylinder. The amount of fuel injected is governed by the period of injector flow. This is Table 1: Diesel vs. Petrol Engines Feature High Speed Diesel Petrol Engine Admission of fuel Direct from fuel injector From carburettor via the manifold, or injected into the inlet port Compression ratio 14:1 to 24:1 7:1 to 10:1 Ignition Heat due to compression Electric spark Torque Varies little throughout the speed range Varies greatly throughout the speed range Brake thermal efficiency 35-43% 25-30% Compression pressure 3100-3800kPa 450-1400kPa Compression temperature 425-550°C August 1995  5 Up to 230°C ENGINE SENSORS BOOST PRESSURE AIR TEMPERATURE OIL TEMPERATURE OIL PRESSURE OIL LEVEL FUEL PRESSURE ELECTRONIC CONTROL MODULE PWM INJECTOR DRIVERS GMSCM EPROM OPERATOR INTERFACES ELECTRONIC FOOT PEDAL ELECTRONIC TACHOMETER DIAGNOSTIC LIGHTS OPTIONS ENGINE BRAKE CRUISE CONTROL ROAD SPEED GOVERNOR POWER TAKE-OFF POWER CONTROL STOP ENGINE OVERRIDE (SRS) EPROM (TRS) VEHICLE SENSORS VEHICLE SPEED COOLANT LEVEL RAM SERIAL COMMUNICATION LINKS (3) PWM AUXILIARY CONTROL PORTS Fig.2: the DDEC-II system uses a large range of sensors to set the engine operating conditions. In addition, there is an engine protection system which is activated when the ECM receives an outof-specification signal from the oil or coolant tempera­ture sensors, the oil pressure or coolant level sensors, or two additional sensors which can be specified by the truck manufacturer. to the cylin­ders by the electronic injectors which are cam-driven for pres­ surisation of the fuel and controlled by solenoid-operated valves to give precise fuel delivery. DDEC electronics The electronic unit injector incorporates a solenoid-operated poppet valve which performs the injection timing & metering functions. Oil & fuel temperature sensors are also used. The oil tempera­ture is used as part of the engine protection system incorporated into DDEC-III, while fuel temperature is monitored to aid in the calculation of fuel economy. dictated by the opening and closing of ports within the injec­tor body itself, which in turn are dependent on mechanical link­ages to the governor mechanism and the throttle. Electronic management The air temperature sensor is used to provide one of the ECM’s inputs. White smoke suppression & improved cold starting result from the use of this sensor. Other sensors monitor the intake mani­fold temperature & the oil temperature 6  Silicon Chip Detroit Diesel Electronic Control (DDEC – pronounced ‘Dee-Deck’) was introduced in September 1985. DDECII was released in 1986 and the system currently in use is DDEC-III, released in 1994. The major subsystems of DDEC are the electronic injectors, the electronic control module (ECM) and the sensors. Fig.2 shows a schematic diagram of DDEC-II. Fuel is delivered The DDEC-II system uses a microprocessor designed by Gener­al Motors (Detroit Diesel Allison is a subsidiary of General Motors Corporation). Similar to the Motorola MC68­HC11, its features include 2Kb of EEPROM and 256 bytes of static RAM. DDEC-III has a much improved microprocessor which runs eight times faster, has seven times more memory and is 50% smaller. Electronic injectors operate on a similar principle to DDA mechanical injectors but a solenoid-operated control valve per­forms the injection timing and metering functions. Unlike a petrol EFI system, it is the closing (rather than opening) of the solenoid valve which initiates the beginning of injection. A bypass for the fuel is blocked when the valve closes, forcing the fuel to pass through the injector nozzle and into the combustion chamber. Conversely, opening the valve causes pressure decay and the end of injection. A pulse width modulated (PWM) driver pulses the current to the injector solenoids at about 10kHz during the injection phase. Fig.3 shows the sequence of events during injection. DDEC III Features • • • Watertight connectors are used to connect the sensors to the ECM. In engine management systems, connectors & the wiring loom are responsible for most of the faults which occur. When voltage is applied to the injector solenoid, current begins to flow through the coil. The current increases until the magnetic field creates enough force to move the armature and valve assembly against the return spring force. Once a preset current flow is reached, the driver circuitry regulates the voltage and monitors the current. A detection circuit is used to monitor the time at which the valve closes and injection actually starts; this is critical in maintaining injection timing and fuel quantity con­trol. After the detection circuit signals that the valve is closed, the current passing through the coil is set to a level sufficient to keep the valve closed. At the end of the command pulse, the low inductance coil design promotes rapid current decay and fast valve opening. During the first portion of the command pulse, the time needed for the valve to close is depend­ent on the rate at which energy is supplied to the magnetic field. This is highly dependent on battery voltage and the feed­back signal supplied by the detection circuitry is used to com­pensate for this variable. Fuel injector timing of better than ±0.25 crankshaft degrees is obtained with this system. Engine control module Unlike the electronic engine management systems employed in cars, the DDEC system uses an engine-mounted ECM and the circuit boards are designed to withstand the rigours of vibration, heat and dust. Large components are hot-melt glued to the boards and the board supports are designed to prevent low fre­quency resonances. Elastomer mounts are used between the ECM and the engine, reducing vibration levels to less than 1G RMS for the majority of the frequency spectrum. Fig.4 shows the measured vibration of the ECM with and without the isolation mounts. Under-bonnet temperatures can run as high as 150°C but the module is protected from these extremes by being mounted on a fuel-cooled plate. Using the fuel to keep the ECM cool might seem odd but water cooling would not be suitable since the tem­perature is too high, at above 120°C (due to pressurisa­tion of the cooling system). The diesel fuel, on the other hand, is normally at ambient temperature and so the ECM is kept consid­erably cooler than engine block temperatures. In addition, all electronic components in the ECM are rated for operation at up to 125°C. Sensors & engine protection As with cars, lots of sensors are used in the DDEC-III system. Some are used to adjust the engine operating conditions while others can bring the engine protection system into play. The engine protection system is activated when the ECM receives an out-of-specification signal from the oil or coolant tempera­ture sensors, the oil pressure or coolant level sensors, or two additional sensors (which can be specified by the truck manufac­turer). Each of the above sensors can be programmed to cause one of two results. The first is complete engine shutdown, 30 seconds after a dash • • • • • • • • • • • • • Excellent engine performance Optimum fuel economy Emission laws met without exhaust gas after-treatment Engine diagnostics Simple programming Engine protection system Cruise control Cooling fan control Engine fan braking Vehicle speed limiting Vehicle over-speed diagnostics Vehicle ID number Idle speed adjustment Idle timer shutdown Warning lights for low DDEC voltage, low coolant, low oil pres­sure, high oil temperature, high coolant temperature Communication links – SAE J1587, J1922, J1939 warning light comes on. This could happen, for example, after loss of oil pressure. The second possible result is “Ramp Down” which illuminates a yellow dash warning light and cuts the engine power to 70%, then a red dash light comes on and the power is reduced to 40%. Alternatively, any of the sensors can illuminate warning lights on the dash. Both the Ramp Down and Shut Down modes can be overridden by the driver if a switch is operated every 30 seconds, allowing a return to 70% of operating power. This could allow a driver to proceed safely to his destination, or at least to a safe posi­tion by the roadside. Engine fuel control There are sensors for air temperature, intake mani­ fold temperature, and for oil temperature. Both are used to adjust the idle speed and fuel injection, to reduce white smoke emissions and improve cold starting. As well, there is a coolant temperature sensor which allows the ECM to measure engine temperature and also to trigger an over-temperature alarm. The fuel temperature sensor does not affect engine running but does provide an input in the calculation of fuel consumption. Similarly, the fuel August 1995  7 The oil pressure sensor is used as an input to the engine protec­tion system. This sensor is designed specifically for fire truck operation & measures fire pump water pressure. The engine speed is then adjusted by the ECM to give a constant water pressure. pressure sensor provides an input for consumption calculations. Fire pump pressure sensor As you might imagine, this facility is only used on fire trucks, to monitor water pressure for the Pressure Governor System. This signal causes the ECM to set the engine speed to allow the fire pump to maintain a constant pumping pressure. Perhaps the most crucial sensor is that for throttle posi­tion and this is a major area of difference to the control of petrol engines. Whereas the accelerator pedal for a petrol en­gined car directly controls the butterfly valve in the throttle body, the accelerator pedal for a DDEC-fitted diesel has no direct connection to the engine. The driver “demands” a certain amount of power by depressing the accelerator pedal but how much he gets is determined by the ECM. In effect, this is a “fly-by-wire” system. One of its bene­ficial effects is that it stops the emission of clouds of smoke as a diesel truck accelerates –because the fuel is always preci­sely controlled, it can never be over-rich and therefore, smoke is minimised. Timing sensors Two timing sensors are used to control the fuel injection. The “SRS” –synchronous reference sensor – provides a ‘once per cam revolution’ signal, while the “TRS” – timing reference sensor – provides 36 pulses per crankshaft revolution. Both sense the rotation of a toothed cog (called a “pulse wheel”) on the crank shaft. Working together, these sensors allow the ECM to sense which cylinder is at The Diagnostic Data Reader can be used to program factors such as the cruise control settings, vehicle ID number, engine power rating & vehicle speed limiting. It also can download engine faults logged in the ECM’s memory. 8  Silicon Chip Fig.3: the relationship between the electrical events & injec­tion. BOI indicates the Beginning of Injection. Top Dead Centre. Precise monitoring of piston position allows optimum injection timing. Other sensors include those for (1) vehicle speed (for use with cruise control, vehicle speed limiting, and progressive engine braking); and (2) turbo boost (for monitoring the compres­sor discharge pressure, for smoke control during engine accelera­tion). Control functions The fundamental variable controlled by the DDEC system is the engine fuel input. This is accomplished by the fuel pulse width and timing signals applied to the injectors. The ECM calcu­lates a desired torque level based on the driver’s throttle position and the engine RPM. The basic torque request and injec­tion timing are modified during transients to control smoke and noise emissions. Several governing modes which modify the basic torque request are available to control engine and vehicle speeds. These are as follows: (1) The idle governor – this provides fixed speed control over the whole of the torque capability of the engine. The idle speed is set as a function of engine temperature to provide optional cold idle boost. This controls cold white smoke suppression and provides faster engine warm-up. (2) The cruise control – this in- Using the ‘ProDriver’ option, the DDEC system can also be inter­rogated via its dash-mounted data link. Fuel economy, trip dis­tances & the number & status of logged cludes set, resume and coast features, as well as an acceleration mode which provides a fixed speed increase for each application. (3) Road Speed Limiting – this enables the customer to determine the maximum vehicle speed attainable, independently from the engine-governed speed. (4) Engine Speed Limiting – this provides a programmable maximum engine speed. Once all of the modifications to the base requested torque have been calculated, a high precision torque to injector pulse width output calibration is performed to drive the injectors. The sensing of the beginning of injection interacts with the fuel rate algorithm to control noise and ex­haust emissions. faults can all be sourced from the engine management computer. The photo above shows the internal details of the electronic control module of the DDEC-III system. The fuel injection timing is carefully con­trolled during starting to reduce cranking times, allowing unaid­ ed starting down to ambient temperatures of -12°C. User definable programming Because the DDEC system is used on a variety of engines and trucks, the system must be programmed to suit each application. An EEPROM is located within the ECM and is programmed via the serial communication link. During engine assembly, and just prior to the final test, the ECM is interfaced to the factory schedul­ing computer to program the EEPROM to the specific sales order for the engine. Data such as the engine’s horsepower rating, torque curve and maximum engine speed is downloaded. Unlike any car engine management system, some aspects of the DDEC system can be reprogrammed by the customer, using a DDEC Diagnostic Data Reader, via a connector on the dashboard. This allows the following features to be customised: engine power ratings, variable speed governor, engine protection, cruise control, vehicle ID number, idle speed, engine braking and vehi­cle speed limiting. Data logging Fig.4: engine vibration spectrum, before & after the installa­tion of elastomer vibration-suppressing mounts. The DDEC system is unusual in that the ECM is mounted on the engine. Part of the EEPROM is used for logging accumulated operat­ing hours, fuel consumption, diagnostic codes and other cumula­ tive information. By the use of an additional electronic module (dubbed ‘ProDriver’) and dedicated software, the SAE diagnostic data link can be used to extract information such as total dis­ tance travelled; average, shortest and longest trips; total fuel use and fuel used during idling, driving and cruising; and perhaps most importantly, the number and status of engine alerts. The self-diagnosis function of the ECM can register intermittent and continuous faults and then display these via flashed codes on an in-cabin ‘check engine’ light. No less than 57 different fault codes can be registered, including any of the sensors being either too high or low in output, engine or vehicle overspeed, torque overload, slow injector response time, data link and EEPROM faults. In short, while those large and imposing trucks and semi-trailers may seem like ponderous beasts, as indeed they are, underneath the bonnet they are often every bit as advanced as the best car engines. And, at least with the DDEC system, electronic circuitry plays an even greater role in providing information and control. References (1). Asmus, A. & Wellington, B., Diesel Engines and Fuel Sys­tems, Long­man Cheshire, 1992. (2). Bosch Automotive Handbook, Third Edition, 1993. (3). Detroit Diesel Series 60 – A Success Story, [pamphlet]. (4). Detroit Diesel Electronic Controls, [pamphlet]. (5). Electronic Diesel Engine Controls, SAE Collected Papers SP-819. (6). Hames, R. (et al), DDEC II - Advanced Electronic Diesel Control, SAE SC Technical Paper 861110, 1986. August 1995  9 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Advances in computer technology 133MHz Pentium processor now available In June 1995, Intel introduced the 133MHz version of the Pentium processor, the ninth in the series and with more than twice the performance of the original 60MHz Pentium released in March 1993. In this article, we give a technical background to the Pentium which will shortly be the mainstream processor in PCs. So fast has the Pentium become accepted in the marketplace that it is rapidly displacing 486 processors, to the extent that they are likely to disappear some time after 1996. By the end of this year, Intel expects that most PCs, portables and notebook computers will be using the Pentium, in either 75MHz or 90MHz versions, with the 100MHz, 120MHz and 133MHz processors being employed in high-end machines. While incorporating new features and improvements, the Pentium is ful- ly software compatible with previous members of the Intel microprocessor family. The Pentium processor incorporates a superscalar architecture, improved floating point unit, separate on-chip code and write-back data caches, 64-bit external data bus, and other features designed to provide high performance. In its 75, 90, 100, 120 and 133MHz versions, the Pentium has power management (SL technology) and multiprocessor support. The on-chip multiprocessor interrupt controller can support up to 16 processors. Intel offers a 273-pin pin grid array (PGA) package for the 60 and 66MHz processors and a 296-pin staggered pin grid array (SPGA) package for the higher clock speed versions. In recent years, developments in semiconductor design and manufacturing have made it possible to produce increasingly higher performing microprocessors in smaller sizes. Foremost among these has been the development of Bi CMOS (bipolar comple­mentary metal-oxide semiconductor) technology with track sizes of less than a micron (one millionth of a metre). This allows more transistors to be fitted on a chip. First generation Pentiums (60 and 66MHz) are implemented in 5V, 0.8 micron BiCMOS technology with 3.1 million transistors, while the 75MHz and higher Pentiums use 3.3V, 0.6 micron BiCMOS technology with 3.3 million transistors each. The 133MHz Pentium is implemented in 3.3V, 0.35 This photo shows the 296-pin staggered pin grid array (SPGA) package for the higher clock speed (75MHz and above) versions of the Pentium. Note that the chip is labelled with the clock speed and the iCOMP® benchmark speed figure. 14  Silicon Chip Fig.1: this graph shows the very fast market transition which has occurred with the introduction of the Pentium processor. The changeover from 286 to 386 processors (with the 386 becoming predomi­nant) took about four years and the changeover from 386 to 486 took about three years. By contrast, the changeover from 486 to the Pentium has been much faster at around 2½ years and the numbers are growing at a staggering rate too. micron BiCMOS technology with 3.3 million transistors. This has allowed a 50% reduction in the die area (compared to 0.6 micron chips) and also allows the significant increase in clock speed. By the way, while the clock speed is 133MHz, the external bus speed is 66MHz. The increase in the number of transistors has made it possible to integrate components that were previously external to the processor, such as maths coprocessors, caches and multi­ pro­ cessor interrupt controllers. Placing these components on-board the chip decreases the time required to access them and increases performance dramatically. Another way to decrease the distance between components and at the same time increase the speed at which they communicate is to provide multiple layers of metal for interconnection. Intel’s 0.35 micron BiCMOS technology uses four layers of metal interconnections. Intel’s microprocessor family In 1985, Intel introduced the 80386, a 32-bit microproces­sor that handled 3-4 million instructions per second (MIPS). Available in speeds ranging from 16MHz to 33MHz, the 80386 ad­ dresses up to 4 gigabytes of physical memory and up to 64 Tera­bytes (1012) of “virtual memory”, which allows systems to work with programs and data larger than their physical memory, by employing spare capacity on hard disc drives. The 80386 provided for multi­ tasking and the ability to create “virtual 8086” systems, each running in its own 1-megabyte address space. Like its predecessors, the 386DX microprocessor spawned a new generation of personal computers, which had the ability to run 32-bit operating systems and ever more complicated applications, whilst maintaining compatibility with previous members of the Intel family. In 1989, Intel shipped the 486DX microprocessor, which incorporated an enhanced 386-compatible core, a maths coproces­sor, cache memory and cache controller – a total of 1.2 million transistors – all on a single chip. Operating at an initial speed of 25MHz, the 486DX processor provided up to 20 MIPS. At its peak speed of 50MHz, the 486DX processor operated at up to 41 MIPS. By incorporating RISC principles, the 486DX was able to execute most instructions in a single clock cycle. With the 1992 introduction of the 486DX2 microprocessor, Intel increased the speed of the 486 family by as much as 100 percent. The DX2 used “clock doubling”, which allows the proces­sor to operate twice as fast internally as externally. At its current peak speed of 66MHz, the DX2 processor executes up to 54 MIPS. With the introduction of the first versions of the Pentium in March 1993, even higher levels of performance became avail­able. Pentium now offers seven performance levels and has been designed into mobile computers, mainstream desktop systems, work­stations and servers. The newest member of the family, the 133MHz Pentium, executes up to 219 MIPS – four times that of the 486DX2. Superscalar design For those familiar with the architecture of small micropro­cessors such as the Z8, 8051 or PIC series, the technology in the Pentium is something else again, and the terminology is pretty foreign too. The heart of the Pentium processor is its supersca­ lar design, built around two integer instruction pipelines, each capable of performing independently. The pipelines allow August 1995  15 rounding and writing of the result to the register file and Error Reporting. The FPU incorpo­rates new algorithms that increase the speed of common opera­ tions, such as ADD, MUL & LOAD, by a factor of three. Performance improvements iCOMP® Fig.2: the new 133MHz Pentium has about double the performance of the original 60MHz version, according to the iCOMP® index used by Intel for speed comparisons. the Pentium to execute two integer instructions in a single clock cycle, nearly doubling the chip’s performance relative to an Intel 486 chip at the same clock speed. The Pentium’s pipelines are similar to the single pipeline of the 486 but they have been optimised to provide increased performance. Like the 486’s pipeline, the pipelines in the Penti­um execute integer instructions in five stages: Prefetch, In­struction Decode, Address Generate, Execute and Write Back. When an instruction passes from Prefetch to Instruction Decode, the pipeline is then free to begin another operation. In many instances, the Pentium can issue two instructions at once, one to each of the pipelines, in a process known as “in­struction pairing”. In this case, the instructions must both be “simple”; the v-pipe always receives the next sequential instruc­tion after the one issued to the u-pipe. Each pipeline has its own ALU (arithmetic logic unit), address generation circuitry and interface to the data cache. While the Intel 486 microprocessor incorporated a single 8Kb cache, the Pentium features two 8Kb caches, one for instruc­tions and one for data. These caches act as temporary storage for instructions and data obtained from slower, main memory; when a system uses data, it will likely use it again. Fetching it from an on-chip cache is much faster than fetching it from main memo­ry. The Pentium’s caches are two-way 16  Silicon Chip set-associative, an im­provement over simpler, direct-mapped designs. They are organised with 32-byte lines, which allows the cache circuitry to search only two 32-byte lines rather than the entire cache. The use of 32byte lines, up from 16-byte lines on the Intel 486DX, is a good match of the Pentium’s 64-bit bus width with four-chunk burst lengths. When the circuitry needs to store instructions or data in a cache that is already filled, it discards the least recently used information (according to an “LRU” algorithm) and replaces it with the information at hand. The combination of instruction pairing and dynamic branch prediction can speed processor operations considerably. For example, a single iteration of the classic Sieve of Eratosthenes benchmark requires six clock cycles to execute on a 486. The same code executes in only two clock cycles on the Pentium. Improved floating point unit The floating point unit in the Pentium has been completely redesigned from the 486 FPU. It incorporates an eight-stage pipeline, which can execute one floating point operation every clock cycle. In some instances, it can execute two floating point operations per clock (when the second instruction is an Exchange). The first four stages of the FPU pipeline are the same as that of the integer pipelines. The final four stages consist of a two-stage Floating Point Execute, The Pentium’s architectural features, superscalar design, separate instruction and data caches, write-back data caching, branch prediction and redesigned FPU, enable the development of new applications software, in addition to improving the perfor­mance of current applications in a manner that is completely transparent to the end user. The external data bus to memory is 64 bits wide, doubling the amount of data that may be transferred in a single bus cycle compared to a 486. The Pentium supports several types of bus cycles, including burst mode, which loads large portions of data into the data cache in a single bus cycle. The 64-bit data bus allows the Pentium to transfer data to and from memory at least five times faster than the Intel DX4. Several instructions, such as MOV and ALU operations, have been hardwired into the Pentium, which allows them to operate more quickly. In addition, numerous microcode instructions exec­ ute more quickly due to the Pentium’s dual pipelines. Finally, the Pentium features an increased page size, which results in less page swapping in larger applications. Due to the architectural improvements of the Pentium pro­cessor family, the 133MHz Pentium’s performance is more than three and a half times that of the 66MHz DX2. Error detection Error detection is performed on two levels, via parity checking at the external pins and internally, on the on-chip memory structures (cache, buffers and microcode ROM). Where data integrity is especially crucial, the Pentium supports Functional Redundancy Checking (FRC). FRC requires the use of two Pentium chips, one acting as the master and the other as the “checker”. The two chips run in tandem and the checker compares its output with that of the master Pentium to assure that errors have not occurred. FRC results in error detection greater than 99%. The Pentium also has a built-in feature for testing the reli­ability of the chip. This tests 70% of the Pentium’s components upon resetting the chip and is an implementation of the IEEE 1149.1 standard (Test Access Port and Boundary Scan Architecture). 75, 90, 100, 120 and 133MHz Pentiums have fully static 3.3V BiCMOS process technology. The static design allows the clock frequency to be reduced to zero, where the processor uses very little power. Typical power consumption is 3-4 watts. Power management Notebook computers need to match desktop performance while constrained by mechanical and electrical design considerations. These considerations have driven the development and implementa­tion of Intel’s Voltage Reduction Technology. The external pins of the Pentium processor with Voltage Reduction Technology are powered at 3.3V, which allows the processor to communicate with existing 3.3V components in the system. The internal core of the processor operates at 2.9V, resulting in up to 30% power savings over its desktop counterpart. Conse­ quently, system vendors can design with higher performing Pentium processors without loss of battery life. Pentium processors for notebooks and subnotebooks are of­fered in two encapsulations, a 320-lead tape carri- The Pentium incorporates the same power management capabil­ities as the Intel 386SL, 486SL and SL Enhanced 486 processors. This operates at the system level, controlling the way power is used by the entire system, including peripherals, and at the microprocessor level. In the latter mode, the processor is put into a low power state during non-processor intensive tasks such as word processing, or into a very low power state when the computer is not in use (“sleep” mode). Intel’s SL technology centres around SMM (system management mode) to control power at the system level. This allows the microprocessor to slow down, suspend or completely shut down various system components to maximise energy savings. Special notebook features er package (TCP) for the 75MHz and 90MHz versions and a conventional stag­ g ered pin grid array (SPGA) package. Multiprocessor support The Pentium’s Advanced Programmable Interrupt Controller (APIC) can support up to 16 processors. This supports symmetric multiprocessing, meaning that all processors appear equal to the operating system. Multiprocessor operating systems such as Wind­ows NT, OS/2 and new UNIX implementations use the symmetric multiprocessor model. Pentiums also include a dual processor mode which enables two processors to share a single second-level cache in a low-cost multiprocessor system. Pentiums include on-chip logic to maintain cache consistency between the two processors and to arbitrate for the common bus to the second-level cache. The on-chip APICs handle interrupts. A single processor desktop or server system design can be made multiprocessor ready by adding a second sock­et, an I/O APIC to the chipset SC and a few BIOS changes. ANOTHER GREAT DEAL FROM MACSERVICE 100MHz Tektronix 465M Oscilloscope 2-Channel, Delayed Timebase VERTICAL SYSTEM Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or less for DC coupling and -15°C to +55°C. Bandwidth Limit Mode: Bandwidth limited to 20MHz. Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C. Uncalibrated, continuously variable between settings, and to at least 12.5V/div. Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from 10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.) Display Modes: Ch 1, Ch 2 (normal or inverted), alternate, chopped (250kHz rate), added, X-Y. Input R and C: 1MΩ ±2%; approx 20pF. Max Input Voltage: DC or AC coupled ±250VDC + peak AC at 50kHz, derated above 50KHz. HORIZONTAL DEFLECTION Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-2-5 sequence). X10 mag extends fastest sweep rate to 5ns/div. Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div. Horizontal Display Modes: A, A Intensified by B, B delayed by A, and mixed. CALIBRATED SWEEP DELAY Calibrated Delay Time: Continuous from 0.1µs to at least 5s after the start of the delaying A sweep. Differential Time Measurement Accuracy: for measurements $900 of two or more major dial divisions: +15°C to +35°C 1% + 0.1% of full scale; 0°C to +55°C additional 1% allowed. TRIGGERING A & B A Trigger Modes: Normal Sweep is triggered by an internal vertical amplifier signal, external signal, or internal power line signal. A bright baseline is provided only in presence of trigger signal. Automatic: a bright baseline is displayed in the absence of input signals. Triggering is the same as normal-mode above 40Hz. Single (main time base only). The sweep occurs once with the same triggering as normal. The capability to re-arm the sweep and illuminate the reset lamp is provided. The sweep activates when the next trigger is applied for rearming. A Trigger Holdoff: Increases A sweep holdoff time to at least 10X the TIME/DIV settings, except at 0.2s and 0.5s. Trigger View: View external and internal trigger signals; Ext X1, 100mV/div, Ext -: 10, 1V/div. Level and Slope: Internal, permits triggering at any point on the positive or negative slopes of the displayed waveform. External, permits continuously variable triggering on any level between +1.0V and -1.0V on either slope of the trigger signal. A Sources: Ch 1, Ch 2, NORM (all display modes triggered by the combined waveforms from Ch 1 and 2), LINE, EXT, EXT :-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM, EXT, EXT :-10. Optional cover for CRT screen – $35 through the vertical system. Continuously variable between steps and to at least 12.5V/div. X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth: DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz. DISPLAY CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosphor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm markings with horizontal and vertical centerlines further marked in 0.2cm increments. 10% and 90% for rise time measurements. Australia’s Largest Remarketer of markings Graticule Illumination: variable. Beam Test & Measurement Equipment Finder: Limits the display to within the graticule area and provides a visible 9500; Fax: (03) 9562 9590 display when pushed. X-Y OPERATION Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence) MACSERVICE PTY LTD 20 Fulton Street, Oakleigh Sth, Vic., 3167. Tel: (03) 9562 **Illustrations are representative only. Products listed are refurbished unless otherwise stated. August 1995  17 Build the JV60 Here’s your chance to build a modern high performance loudspeaker using high quality drivers made by Vifa of Denmark. This is a tower design producing lots of bass. It uses two 170mm woofers and a 25mm aluminium dome tweeter with a ferrofluid cooled voice coil. By LEO SIMPSON Handsome and well finished, the JV60 cabinets have a capacity of 50 litres and only take up a modest amount of space in your listening room. T HESE DAYS, you have two main choices as to the type of loudspeak­er system to buy from your hifi retailer. The first is a compact bookshelf style system and the second is a tall narrow cabinet generally referred to as a “tower” style using two small woofers. Now it might seem that the compact bookshelf system is the one to go for if you don’t have a lot of space or you are on a budget. But you will always find that the manufacturers recommend that their compact systems be placed in floor stands to give the best overall performance. Typical floor stands are about 400 to 500mm high and have a “foot print” 18  Silicon Chip which is about 350mm square. So while the loudspeak­er cabinet might be quite compact, its effective bulk and the floor space it takes up are much greater. If you can afford it, the tower option is always the better choice. You get a bigger cabinet and this almost always means better bass (cleaner and more extended). And this is the benefit provided by the tower speakers presented here. By building the kits you save money and thereby you can afford a system that otherwise could be out of reach. And if you can make your own cabinets, you can save more money into the bargain. On the other hand, a big bonus of the kit presented here is that the cabinets themselves are supplied fully assembled. There is absolutely no carpentry work to be done and the cabinets are very professional in appearance. Virtually all you need to assem­ble these fine loudspeakers is a Phillips head screwdriver and a soldering iron. Nor do you have to put the crossover network together since it is also supplied fully assembled. Dimensions of the JV60 system are 895mm high, 260mm wide and 315mm deep, which includes the thickness of the grille cloth frame. Made of 16mm particle board and internally braced, the cabinet has a volume of close to 50 litres. By the way, this design has been produced exclusively for Jaycar Electronics by Australian Audio Consultants, PO Box 11, Southport, SA 5410. The loudspeaker line-up is two 170mm woofers and a 25mm dome tweeter but the system is not strictly two-way. A glance at the circuit of Fig.1 shows that the crossover is a modified twoway system with one of the woofers (W2) effectively handling bass and midrange frequencies while the other (W1) handles bass frequencies below 200Hz. This has been done to achieve a strong and extended bass, as we shall see. This system is geared par­ticularly to those people who love plenty of bass, without the need for any boost from the amplifier. Ferrofluid cooled tweeter The Vifa tweeter featured in this system is the D25AG-35-06. It has a couple of unusual features, not the least being the fact that it has an aluminium dome tweeter instead of the more usual Mylar or synthetic fabric dome. The 25mm aluminium dome is protected from prying fingers by a plastic shield which is de­ signed to avoid phasing and beaming effects which can occur with any sort of obstruction in the beam of a tweeter. Also unusual is the ferrofluid cooling of the tweeter’s voice coil. This has been a feature of high-quality tweeters for quite a few years now but it has seldom, if ever, been featured in a kit-built system such as this. Ferrofluid is a patented synthetic oil mixture with sus­pended iron powder. Loudspeaker System These are the Vifa drivers, crossover network and rear terminal panel provided for each speaker system. Also included in the kit are Innerbond filling and mounting screws. The suspended iron means that the oil has no effect on the magnetic circuit of the tweeter. It has two bene­fits for a tweeter. First, it helps cool the tweeter voice coil which can otherwise become very hot when operating at high pow­ers. This can be easily understood since a tweeter voice coil is a very light assembly and it is suspended in the magnetic gap where air flow is very slight. With the ferrofluid, the heat in voice coil is conducted away to the magnet and frame of the speaker where it can be dissipated harmlessly. The other benefit of ferrofluid is that it applies a degree of damping to the suspension of the tweeter and thereby can help smooth the overall response. Other specifications of the tweeter include a nominal impedance of 6Ω, a free air resonance of 850Hz and a nominal power handling (IEC­268-5) of 100 watts. Woofers For the bass and midrange there are two 170mm woofers, type P17WJ-00-08. These units feature a cast magnesium basket with a synthetic rubber surround. The cone material is mineral filled polycarbonate. It has a sensitivity of 88dB and a frequency response usable to 4kHz. One of the best aspects of using Vifa drivers is their consistency. The drivers were measured using the Loudspeaker Measurement System (LMS) and these measurements were compared with the manufacturer’s published data. To some extent, driver parameters will vary on the production line, even within a batch. A manufacturer who is consistent manages to maintain these varia­tions in such a way that the repercussions August 1995  19 RED P2 RDE245A C5 0.1 POLYESTER P1 RDE070A C3 6.8 BP INPUT FROM AMPLIFIER YELLOW TWEETER D25AG L3 0.22mH BLACK L2 0.39mH BLUE R2 5. 6  5W C6 0.1 POLYESTER W2 WOOFER P17W1 C2 10 BP L1 4mH RED R1 5. 6 5W C7 0.1 POLYESTER C1 33 BP W1 WOOFER P17W1 JV60 SPEAKER SYSTEM Fig.1: the JV60 is a modified two-way bass reflex system with one of the woofers (W1) only handling bass frequencies below 200Hz. are negligible. All driver parameters are related and if one group are a little high then another grouping should be a little low, counteracting any change. Vifa seem to manage this effortlessly. The 50-litre enclosure has two 66mm ports 197mm long. The internal brace is an essential feature of the cabinet and is placed underneath the topmost woofer. A shelf brace should never be placed in the centre of an enclosure. This method of bracing carries out several functions, the first of which is to connect adjoining panels and help to dissipate vibrations. A shelf brace also divides panels into smaller segments, thus moving reson­anc­es to higher frequencies and Solder the wires to the rear terminal panel, before fitting it into place. 20  Silicon Chip lowering vibrational energy. Constructors who wish to build their own cabinets may use the drawing of Fig.2 as a guide. Increasing wall thickness to 18mm will have very little effect, although increasing it to 25 or 32mm will be a considerable advantage (but make it much heavi­ er). Ensure that the internal volume remains the same, even allowing for the increased brace thickness. The cabinet is tuned for a corner frequency of about 35Hz (-3dB point) and, as such, it produces copious amounts of bass. Before we look at the crossover network, let’s take a quick look at contemporary design techniques in this area. In the past crosso­vers were designed by placing textbook components into the cir­ cuit and assuming that they would do the job. However, this does not take into consideration several factors, the two principal ones being (a) the drivers’ natural roll off slopes and (b) the interaction between the drivers’ motor system (ie, magnet, voice coil and suspension) and other components. Nowadays, CAD packages such as the Loudspeaker Enclosure Analysis Program (LEAP) allow a designer to check and recheck systems at every stage of development. Computer optimization allows one to consider all variables when designing crossovers. Crossover design The crossover design is unusual, as can be seen from the diagram of Fig.1. It is based on a second order (12dB slope/octave) Linkwitz-Riley filter. The tweeter section uses a 0.22mH inductor and a 6.8µF capacitor operating at nominally 3.5kHz, well above the free air resonance of 850Hz. As noted above, the two woofers have separate crossover networks. Woofer W2 can be regarded as the main woofer as it handles the mid­ range frequencies as well. Its associated inductor L2, 0.39mH, provides a roll-off of 12dB octave above 3kHz by virtue of the inductor’s impedance and the driver’s natural roll-off characteristics. R2 and C2 provide impedance equalisation so that the woofer “looks” like a resistor as far as the inductor is concerned. L1 is a 4mH inductor and rolls off the second bass driver W1 at 6dB per octave above 200Hz. In effect, the second woofer is there to provide a Fig.2: use this diagram as a guide if you are building the cabi­nets yourself. The dimensions may be varied slightly but the capacity should still be close to 50 litres and the shelf brace must be included. 808 A B 253 655 507.5 895 (863) C BRACE MOUNTED 9 BELOW THE BOTTOM OF HOLE B 360 D 227 INTERNAL BRACE 4 HOLES 80 x 80 SPACED 23 APART ABOUT BRACE CENTRE 207 E MATERIAL: 16 PARTICLE BOARD CL HOLE SIZES: A AND E : 76 DIA. B AND D : 146 DIA. C : 74 DIA. DIMENSIONS IN BRACKETS ARE INTERNAL * ENCLOSURE BACK INSET 11 FROM REAR EDGE 296 * (253) 259 (227) DIMENSIONS IN MILLIMETRES JV60 SPEAKER ENCLOSURE August 1995  21 The crossover is mounted on the rear panel of the cabinet, beneath the terminal panel. Identify all the wires first before installing the crosso­ver. 3dB boost to frequencies below 200Hz. R1 and C1 again provide impedance equalisation for the woofer. The only capacitors not mentioned so far, C6 & C7, are included to improve the power factor of the bipolar electrolytic cap­ acit­ors and thereby improve the sound quality. Two levels of overdrive protection are provided by Poly­switches. Poly­ switches are special low resistance thermistors with a positive temperature coefficient. Normally they have a very low resistance and thus have minimal effect on the signal fed to the drivers. But when the signal current exceeds a critical level, the Poly­ switches suddenly switch to a high resistance state which effectively removes the drive signal. After a period which depends on the initial overload, they revert to their low resistance state and the signal can pass once more. The important aspect of Poly­ switch­ es is that they are in­ tended as insurance against damage. The speakers should not be repeatedly overdriven otherwise the characteristics of the Poly­switches will alter and thus their future performance can be prejudiced. Two polyswitches are included in this design, one to pro­tect the whole system and the other to protect the tweeter which is the driver most likely to be damaged if an amplifier is driven heavily into clipping. This JV60 system can be used with amplifiers capable of 20-100 watts. Assembly As already noted, the JV60 cabinets are supplied ready-built so there is no carpentry required. The first task is to fit the crossover network inside the enclosure. As can be seen from the photos this is hand-wired on a piece of medium density fibre board. It should be attached to the rear panel Take care when fitting the drivers not to damage the cones. They are well made but if you are ham-fisted you could damage them. 22  Silicon Chip AUDIO PRECISION 50 K ALEX IMPEDANCE (OHMS) vs FREQUENCY (Hz) The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES 10 ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS 1 10 ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic 100 1k 10k 20k Fig.3: this is the impedance plot for the JV60 loudspeakers. with a couple of screws, just above the terminal panel. Before you do mount the crossover network, you need to identify all the wires on it so that you can make the correct connections to the various drivers. First, identify the two input wires. The red wire connected via the large yellow Polyswitch is the hot (+) input wire. All black wires go to the negative terminals of the drivers. The positive terminal of each loudspeaker driver is marked with an adjacent spot of red paint. The red wire connected via the small yellow Polyswitch goes to the tweeter and the blue wire goes to the main woofer (W2). The remaining red wire goes to the second woofer (W1). Having mounted the crossover on the rear panel, connect and solder the two input wires to the rear terminal panel, then screw it into place. Install the two plastic port tubes and screw them into place. Connect and solder the two wires to the tweeter and then screw it into its central position on the baffle. Next, connect the two wires to each of the two woofers. The main woofer (W2) mounts at the top of the cabinet while the second woofer is mounted at the bottom. Before fixing the woofers into place on the baffle, you need to insert the Innerbond wad­ding into the enclosure. For two cabinets you will be supplied with a little over a metre of 900mm wide Innerbond. Half this should be placed in each enclosure. You will need to place about a third of it in the top section and the other two thirds in the bottom section. Just pack it in loosely and then place the woof­ers in position on the baffle and screw them down. Note that it is important not to over-tighten the screws otherwise they will strip their holes. If this happens, drill pilot holes in a slightly different position and re-fasten the screws. Listening tests When you have finished one loudspeaker system, hook it up to your amplifier and have a listen. If all is well, go ahead and assemble the other loudspeaker. If the sound is not quite right, make sure that you have connected all the speakers correctly. If the phasing is wrong, the speakers can sound quite strange. If the woofers are out of phase with each other, the bass will be practically nonexistent. Kits for the JV60 loudspeakers are available from all Jaycar Electronics stores and their dealers. Prices are as fol­lows: (1) Speaker kit – includes four woofers, two tweeters, two crossover networks, two rear terminal panels, Innerbond and mounting screws, $579.00; (2) Cabinet kit – includes a pair of cabi­nets finished in blackwood veneer and two grille cloth frames with SC grille cloth fitted, $299.00. ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 August 1995  23 A FUEL INJECTOR MONITOR FOR CARS Have you ever wondered how much petrol you use when you accelerate away from the traffic lights? Perhaps you would like to know how your fuel consumption increases as you climb a hill. If you have a fuel injected car, this project is for you. By RICK WALTERS & LEO SIMPSON Back before cars had engine management computers, they often had a vacuum gauge which was supposed to give an indication of fuel economy. Low vacuum readings meant you were using lots of juice while high vacuum meant that you were driving with a light throttle. In practice, a vacuum gauge was often a distraction as it fluctuated wildly each time you depressed the accelerator, as you moved up or down through the gears. Some drivers even 24  Silicon Chip went so far as to cover up the vacuum gauge to avoid its distraction. Now we’re in the 90s and vacuum gauges are decidedly “old hat”. Most modern cars have fuel injection and the drive signal to the injectors can be monitored to provide a very good guide to fuel use. The amount of fuel provided by the injectors is con­trolled by the amount of time they are open. When your car is at idle, the injectors are open only about 5% of the time. During normal driving, the injectors are open between 10% and 20% of the time. And when you are accelerating absolutely flat out, with the engine wound out to 5000 RPM or more and the accelerator fully open – “pedal to the metal” – the injectors will be open for more than 90% of the time. Since the injectors are fed from the fuel rails at essen­tially constant pressure, the fuel used by the motor is directly proportional to the injector opening time. The Fuel Injector Monitor is housed in a compact case, allowing it to be conveniently placed on your car’s dashboard at eye level. The straightline display consists of 20 light emit­ ting diodes (LEDs), 18 green, one orange and one red. The display is semi-logarithmic, with the first 10 LEDs showing 10 steps of 1% from 0-9%, while the second group of LEDs covers from 10% to 100%. The LED display takes the form of a bargraph which shows the average +15V 0.1 10k D1 1N914 LK2a 10k INPUT IC1b LK2b CA3260E LK1b 6 LK1a D2 1N914 16 8 5 2 VR1 10k 7 2 bx 3 cy 13 ay 1 IC1a 3 4 47k D3 1N914 4.7 2.2M IC2 5 4053 cx 12 ax 10 10 4.7k 10k +15V 1 C 9 11 A 10 B c 4 14 a 15 b by 6 7 8 +12V LED9 LED10 GRN GRN A LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8 GRN GRN GRN GRN GRN GRN GRN GRN A A A A 10   A K  1 K 18 K  A K  17 K 16  A  K 15 K 14  22k A 13 K 12  A K  11 K 10 6 7 4 8 2 K 18  A K  1 9  A K  IC3 LM3914 5 LED11LED12 LED13LED14 LED15 LED16LED17 LED18LED19LED20 GRN GRN GRN GRN GRN GRN GRN GRN YEL RED A A A A A  K 17 K 16  A  K 15 K 14 10  A  K 13 K 12 A  11 K 10 IC4 LM3914 5 3 3 6 7 820  820  8 4 2 9 6.8k 680 ZD1 5.6V 400mW +12V +12V 0.1 33k 7 0V 47k 4 8 IC5 555 6 2 3 5 1 D5 IN914 100 IN D4 1N914 REG1 7815 GND 100 OUT +15V 4.7k 10k 10 B .01 Q1 BC327 C +12V .01 E B A K E A K 100k C VIEWED FROM BELOW I GO FUEL INJECTOR MONITOR Fig.1: the 4053B multiplexer (IC2) enables the LM3914 LED drivers to give a dot and bar display to indicate the average and peak injector duty cycles. The 555 timer (IC2) controls the switching of the 4053 and also steps up the battery voltage to provide for a +15V regulated supply. opening times, combined with a brighter “peak” LED which shows more rapid fluctuations of the injector openings, as can happen, for example, when you blip the throttle. The peak LED is actually a “peak-hold” display which captures the rapid tran­sients and “holds” them so that they can be more easily seen. Unlike some car circuits, installation of the Fuel Injector Monitor is quite straightforward: one lead to ground (chassis) and two leads to the injector leads (one switched and the other battery positive) – more about that later. Circuit details The circuit of Fig.1 consists of five ICs plus a regula­tor, the 20 LEDs and a few other minor components. In most modern cars, all the injector solenoid coils are wired in parallel with one side connected to the battery posi­tive, through the ignition switch. The coils are switched to ground via a transistor when fuel is to be injected. This means that the pulse waveform fed from the injectors to our monitor is a +12V signal going to ground. While most cars have negative-going pulse injector wave­ forms, we have provided for vehicles with the opposite waveform polarity. This is done via two links to allow the selection of either system. The input circuit consists of IC1, a dual opera­ tional August 1995  25 amplifier. IC1b is used as a comparator while IC1a is used as a peak detector. The injector signal is applied via a 10kΩ isolation resis­ tor to diodes D1 and D2. These diodes provide transient protec­tion for the following op amp by clamping any input signal bet­ween ground and +15V (more pre- LED1-LED20 0.1 820W VR1 IC1 CA3260E +12V 4.7k 1 LK1a LK2b LK2a D3 1 D4 .01 .01 0.1 IC5 555 100uF 4.7uF 47k 33k 1 10uF 2.2M 10uF 0V IC2 4053 10uF 10k 680  100k ZD1 100uF LK1b 6.8k 47k D1 820W 10uF D2 INPUT Q1 1 1 10k IC4 LM3914 4.7k IC3 LM3914 10k 22k 10k K 10uF A D5 REG1 7815 Fig.2: install the parts on the board as shown here. The electrolytic capacitors must all lie flat on the board, otherwise it will not fit into the plastic case. Fig.3: this is the full-size etching pattern for the PC board. 26  Silicon Chip cisely, to between -0.6V and +15.6V). IC1 can accept signals in this range without damage. Our circuit description will apply to cars with a negative-going injector signal (the most common situation) and so links LK1a and LK2a will be installed. Ignore the links LK1b and LK2b which are shown dotted. Hence, the injector signal is applied via a 10kΩ resistor to pin 6 of IC1b. Pin 5 of IC1b is held at ap­proximately +5V via a voltage divider consisting of 10kΩ and 4.7kΩ resistors. Thus, whenever the injector voltage falls below +5V, the output (pin 7) of IC1b will go high. The output of IC1b is fed to trimpot VR1, a 10kΩ pot wired as a variable resistor. VR1, in conjunction with the 4.7kΩ resis­ tor to ground, provides calibration for the circuit. The output of IC1b is used to charge the 220µF capacitor. This becomes the “average” value of the pulse signal and is used to drive the bargraph portion of the LED display. The “average” signal from the 220µF capacitor is fed to pin 3 of IC1a and to pins 5 & 12 of IC2. IC1a and diode D3 function as a peak detector to charge a 4.7µF capacitor to the “peak” value of the voltage appearing at pin 3. The 4.7µF capacitor is slowly discharged by the 2.2MΩ resistor and so it provides the “peak hold” value for the peak DOT on the LED display. So now we have two voltages, the peak and average values of the injector pulse widths which must be shown on the same 20-LED bargraph. How do we do this? It is done by a technique known as multiplexing whereby two values are alternately flashed onto the LEDs, each value being shown for part of the time. This switching of the signals happens very rapidly so that our eyes are not aware of it. IC2, a 4053, does the multiplexing and is described as a triple 2-channel analog multiplexer. It alternately switch­es the bar signal (pins 5 & 12) and the dot signal (pins 3 & 13) to the LED display drivers (IC3 & IC4). IC5 controls the switching of IC2 and serves another purpose – to step up the car’s battery voltage. The vol­ tage step-up is necessary to enable the display drivers to handle the full range of signal voltage from IC1. We’ll explain more about this later. The 555 timer is arranged as an astable oscillator, with a frequency of about 1kHz. Its pulse output waveform All the LEDs are arranged to sit flat along the edge of the PC board but because of the pin layout of the LM3914 drivers, the display reads from right to left. Consequently, the board hangs upside down in the case to make the display read from left to right. is fed to a voltage doubler consisting of diodes D4 & D5 together with two 100µF electrolytic capacitors. The resulting voltage of about +19V is fed to the 7815 regulator which delivers a stable +15V. Multiplex operation We have already referred to multiplex operation so let’s now look at it in more detail. As noted above, we need to display two signals (the “average” and “peak” values) and at the same time we need to switch the display drivers, IC3 & IC4, between dot and bar modes. IC2, the multiplexer, has three internal switches and while these are not shown on the circuit, they can be identified in the following way. Switch A involves pins 11, 12, 13 & 14; switch B involves pins 1, 2, 10 & 15 and switch C involves pins 3, 4, 5 & 9. Pins 9, 10 and 11 control the position of each associated switch; eg, if pin 9 (the C switch control input) is high, pin 4 (c) is connected to pin 3 (cy) while if pin 9 is low, pin 4 is connected to pin 5 (cx). Returning now to IC5, which provides the switching signal, when pin 3 is low, pins 9 & 11 of IC2 switch the “average” signal to the pin 5 inputs of the display drivers IC3 and IC4. At the same time, pins 9 of IC3 & IC4 are pulled low to select the bar mode. Conversely, when pin 3 of IC5 is high, the “dot” signal at pins 3 & 13 of IC2 are switched to pins 5 of IC3 & IC4 which are then switched into the dot mode. Just to reiterate, the bar mode displays the average signal while the dot mode displays the peak which is RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  1 ❏  1 ❏  4 ❏  1 ❏  3 ❏  2 ❏  1 Value 2.2MΩ 100kΩ 33kΩ 22kΩ 10kΩ 6.8kΩ 4.7kΩ 820Ω 680Ω 4-Band Code (1%) red red green brown brown black yellow brown orange orange orange brown red red orange brown brown black orange brown blue grey red brown yellow violet red brown grey red brown brown blue grey brown brown 5-Band Code (1%) red red black yellow brown brown black black orange brown orange orange black red brown red red black red brown brown black black red brown blue grey black brown brown yellow violet black brown brown grey red black black brown blue grey black black brown August 1995  27 Fig.4: this fuel injector waveform was taken from a Ford Laser S with a 1.8 litre engine. The duty cycle is under 10% at around 2000 RPM with the car stationary. The lower waveform is taken directly from the injector, while the upper waveform is the output of IC1b at pin 7. always equal to or higher than the average. To make the peak (dot) display brighter than the average, it is turned on for longer than the average and this is arranged by giving the pulse signal from IC5 a duty cycle of more than 50%. Part of the switching function controlled by IC5 is per­formed by transistor Q1 but because IC5 runs from 12V rather than 15V, its output cannot swing to the +15V necessary to ensure that Q1 is turned off. Therefore, zener diode D4 is included to allow Q1 to turn off when IC5’s output is high. IC3 and IC4, the LM3914 dot/ bar display drivers, which accept analog input signals from IC1, have 10 internal compara­tors which drive 10 external LEDs. The input range is determined by one or two resistors. IC3 is set by the 820Ω resistor between Fig.5: taken from a VP Holden Statesman with a 5-litre V8 engine, these injector wave­forms are again at around 2000 RPM and the duty cycle is under 20%. The lower waveform is the fuel injector driving voltage, while the upper waveform is the output of IC1b at pin 7. pins 6 and 7 and ground, to accept 0.125-1.25V and dis­ play 10 output steps from 0-9%. IC4 with its extra resistors accepts 1.265-12.65V for its 10 outputs, from 10% to 100%. Actually, these display steps should not be thought of as being absolutely precise. For example, if the 10% LED is lit, the injector pulse width can only be regarded as being above 10% but less than 20%. Similarly, if the 30% LED is lit, the injector pulse width is above 30% but below 40%. Construction All the components for this project, including the 20 LEDs, are mounted on a small PC board coded 05108951 and measuring 120 x 102mm– see Fig.2. The PC board is mounted in a small plastic case measuring 141mm wide, 36mm high and 110mm deep. The case Fig.6: this is another injector waveform, taken with a Tektronix TDS744A digital oscilloscope from a Ford Laser S at idle. Note the very narrow pulse width. 28  Silicon Chip splits into two sections, upper and lower, with two removable pieces for the front and back sections. The lower section has four integral pillars for the PC board but because of a layout constraint caused by the LM3914 display drivers, the PC board has had to be designed so that the LEDs run from right to left (to minimise the number of links required). To make the display read from left to right as it should, the PC board is mounted on the base of the case and then it is inverted, so that it “hangs from the roof”. Before you begin assembly, carefully check the PC board for broken or shorted tracks, especially between the pads on IC2 and IC4. First, install the six links, diodes and resistors. The capacitors are next. Be sure to lie the electrolytics flat, as the board will not fit into the case if you stand them up. Be sure to bolt the regulator down flat onto the PC board. Lastly, fit the LEDs, ICs, trimpot and transistor. The LEDs should be mount­ed so that they are flush with the front edge of the PC board. We could not obtain a 5mm square orange LED for our proto­type so we fitted a 5mm round one in that position. We used a thin piece of tinted plastic for our front panel and made an adhesive front-panel label with a rectangular cutout for the LEDs. The PC board is mounted to the integral pillars using 6mm spacers and 12mm long self-tapping screws. After you have carefully checked all your assembly work and soldering, you are ready to do an initial power check. If you don’t have a 12V power supply, you could apply power from a 12V car battery or from your car’s cigarette lighter socket. Make sure that you connect the 12V leads the right way around otherwise you will damage the circuit, with IC5 (the 555 timer) the most likely casualty. Just connect the 12V supply at first, without connecting the input lead from the injectors. All the LEDs should flash once and then the peak LED moves slowly from right to left. Now connect the injector input lead to 0V and most, if not all, LEDs should come on and stay on. If that checks out OK, you can move to the next step which is calibration. be slightly less, at around 13.8V. This latter lead is the one we’re looking for and is the one which we will make the permanent connection to. Now remove the pin from the other injector lead. To make a permanent connection, again the easiest method is to use a pin. This time, push the pin right through the centre of the injector lead and bend it over and twist the ends together. This way, the integrity of the injector lead itself is preserved. Now solder a lead to the pin while making sure that you don’t damage the injector lead insulation. (Perhaps you might like to practice soldering to a sample pin before you do the actual job on your car!) Having made the connection, carefully wrap it with insula­ tion tape. Having done that, the most convenient place to pick up +12V to power the circuit is from the other injector lead, so repeat the pin soldering to the other injector lead. Now anchor the two leads running away from the injector harness with a plastic cable tie to a convenient point on the engine so that vibration is unlikely to dislodge them. You will need to pass the two leads through the firewall into the passenger compartment. You will then need to make a connection to chassis for the 0V lead. It would also be prudent to install an in-line 1A fuse in the +12V line from the injector harness. Now make your connections to the Fuel Injector Monitor and turn on the ignition. With the engine stopped, all LEDs should be alight. When the engine is started, the LEDs will light up to about 60% or higher and then gradually drop back to the normal idle value of around 5% or 6% as the engine warms up. Calibration This will be the easiest calibration you have ever done. With the input lead connected to the 0V terminal, carefully adjust the trimpot until the red LED just comes on. You will need to wind the trimpot anticlockwise initially and then clockwise until the red LED just comes on. This calibrates the unit to correctly display an injector opening of 100%. Installation The trickiest part of the installation is to identify which of the two injector leads to make the connection to. Unless you have a wiring diagram for your car, you will need to make a voltage measurement on the two leads while the engine is running. In practice, the easiest way to make a temporary connec­tion to your injector leads is to push a pin right through the centre of each of the wires. Now start the car and let it idle for a couple of minutes to let the battery voltage stabilise. Now measure the voltage between each injector lead and chassis. One injector lead will be at the same voltage as the battery (eg, 14.4V) while the other injector lead will Fault finding If you have a problem, the first thing to check is the +15V rail. There should be about +19V into the 7815 regulator and +15V at its output. If the input voltage is 0V to the 7815, then IC5 is FUEL INJECTOR MONITOR 0 1 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 90 100 Fig.7: this is the full-size front panel artwork. PARTS LIST 1 PC board, code 05108951, 120 x 102mm 1 plastic case, 141 x 36 x 110mm 1 front-panel label, 132 x 28mm 1 10kΩ horizontal trimpot (VR1) 1 3mm x 8mm roundhead screw 1 3mm nut 1 3mm SP washer 4 6mm spacers 4 12mm self-tapping screws Semiconductors 1 RCA CA 3620E dual op amp (IC1) 1 4053B triple 2-channel analog multiplexer (IC2) 2 LM3914 dot/bar display drivers (IC3,IC4) 1 555 timer (IC5) 1 7815 15V regulator (REG1) 1 BC327 transistor (Q1) 5 1N914 diodes (D1-D3, D5, D6) 1 5.6V 400mW zener diode (ZD1) 18 LTL9234A 5mm square green LEDs or equivalent (LED1-18) 1 5mm square or round orange LED (LED19) 1 LTL4223A 5mm square LED or equivalent (LED20) Capacitors 2 100µF 25VW PC electrolytic 5 10µF 50VW PC electrolytic 1 4.7µF 50VW PC electrolytic 2 0.1µF MKT polyester 2 .01µF MKT polyester Resistors (0.25W 1%) 1 2.2MΩ 4 10kΩ 1 100kΩ 1 6.8kΩ 4 4.7kΩ 1 33kΩ 2 820Ω 1 22kΩ 1 680Ω not oscillating. Check the component values and soldering around this IC. With the input connected to 0V (as explained in the cali­ bration procedure), pin 7 of IC1 should measure around +14.5V. When the injector input is not connected, pin 7 should be near 0V. If your monitor reads 100% at idle and falls as you accel­ e rate, it means your injector signal is the wrong polarity. Remove links LK1a and LK2a and replace them in positions SC LK1b and LK2b. August 1995  29 A Gain Controlled Microphone Preamp By JOHN CLARKE Designed for use with PA systems, this gain controlled microphone preamplifier will provide a constant output level for a wide range of input levels. It ensures that the amplified sound level is always the same, regardless as to how loudly (or softly) a person speaks. How often have you heard a public address system where the sound level varies all over the place? This problem occurs be­cause different people speak at different sound levels. For exam­ple, if the person using the microphone speaks loudly, then the gain control has to be reduced to bring the amplified sound back to the correct level (or to prevent overload). Conversely, if the person speaks quietly, then the gain control has to be advanced to maintain good audibility. Indeed, a very quiet talker may not provide enough signal to ensure an adequate sound level, even if the amplifier is set to maximum gain. Level fluctuations can also be 30  Silicon Chip caused by people who turn their heads from side to side as they speak, and by people who alternately move closer to and further away from the microphone. Main Features • • • • • • • Suitable for dynamic microphones Balanced input Constant output over 50dB input range Powered by 9VDC plugpack Low input impedance Low distortion Fast response A sound system operator can compensate for some of these problems by riding the gain control on the amplifier. However, there is always a delay in the response because the operator first has to hear the incorrect level before making changes. Another approach is to use a less directional microphone to reduce level variations from people who move around while speak­ ing but this greatly increases the risk of feedback. A gain controlled microphone preamplifier, such as the unit described here, will help to solve these problems. It automati­cally varies its gain in response to the microphone signal to ensure that a constant level is fed to the PA amplifier. As the output signal level from the microphone goes down, the gain of the microphone preamplifier goes up, and vice versa. As a result, the amplified audio level is essentially con­stant for virtually all people, regardless of their speaking style or how they move about in front of the microphone. In effect, it’s just like having a person constantly riding the gain control on the amplifier, except that it’s all auto- C1 2 4 INPUTS Fig.1: block diagram of the Plessey SL6270DP voice operated gain adjusting device (VOGAD). It contains two amplifier stages & an AGC detector block. V+ 7 3 GAIN CONTROLLED AMPLIFIER 1 10k 680  8 5 OUTPUT AMPLIFIER 2 2k AGC DETECTOR SL6270 1 RT 6 CT matic. And of course, an electronic circuit responds far quicker to any level changes than a human operator, so that the adjustments are imperceptible. In technical terms the preamplifier has a gain of around 50dB for low input signal levels (ie, 70µV) but limits once the input signal reaches about 1mV. The output signal level remains virtually constant at 100mV for input signals ranging from 1mV to beyond 100mV. As can be seen from the accompanying photograph, the unit is housed in a small low-cost plastic case. A 3-pin XLR socket fitted to one end of the case accepts a balanced microphone input, while a 6.5mm phono socket on the other end provides the single-ended (or unbalanced) output signal. Power for the circuit comes from a 9V DC plugpack supply. Block diagram Refer now to Fig.1 – this shows a block diagram of the Plessey SL­ 6270DP voice operated gain adjusting device (VOGAD) which forms the heart of the circuit. Let’s see how it works. Inside the SL6270DP IC are two amplifier stages and an AGC detector block. The AGC detector monitors the output level from amplifier 2 and provides a DC control signal which sets the gain of amplifier 1. +8V 0.1 BALANCED MICROPHONE INPUT 2 SHELL 3 2.2 3 100 2 OUTPUT 47k 1 1M 6 47 9V INPUT I GO 10 8 IC1 SL6270 1 K R1 .0033 5 100 4 A 7 IN 10 REG1 7808 GND OUT 10 +8V 1k A  LED1 K GAIN CONTROLLED MICROPHONE PREAMPLIFIER Fig.2: the final circuit of the Gain Controlled Microphone Preamplifier. Resistor R1 allows the gain (& thus the AGC range) to be adjusted – see text & Table 1. Power comes from a 9V DC plugpack & is regulated to 8V by REG1, while LED 1 provides power on/off indication. In greater detail, amplifier 1 is a DC-controlled balanced input amplifier which accepts signals from the microphone. This stage in turn drives amplifier 2 via a 680Ω resistor and external capacitor C1 which rolls off the low-frequency response. Amplifier 2 has a gain of about 15, as set by the 10kΩ feedback resistor and the 680Ω input resistor. Its output appears at pin 8 and is also fed to the AGC (automatic gain control) detector block which provides the DC control signal. The 2kΩ resistor and external capacitor CT set the AGC attack time, while RT provides a discharge path for CT. Finally, the control voltage across CT is applied to ampli­fier 1, which adjusts its gain accordingly and thus sets the output level on pin 8. Circuit details Refer now to Fig.2 for the final circuit. In addition to the SL6270 (IC1), there’s just a 3-terminal regulator, a power indicator LED and a few resistors and capacitors. As shown, the balanced inputs from the microphone are cou­pled to pins 4 & 5 of IC1 via 100µF capacitors. These capacitors are necessary to prevent DC current from flowing in the micro­ phone. The 2.2µF capacitor between pins 2 & 7 sets the low fre­ quency roll-off to 300Hz, while the .0033µF capacitor between pins 7 & 8 (ie, in the feedback path of amplifier 2) sets the high frequency roll-off to 5kHz (R1 open circuit). Resistor R1 has been included to tailor the AGC range. This resistor is in parallel with the internal feed­back resistor between pins 7 & 8 of IC1 and so reduces the gain of amplifier 2. Table 1 shows the effect of different values of R1 on the sensitivity and the resulting affect on the signal-to-noise ratio. Note that as R1 decreases (ie, the gain goes down), pro­gressively higher input signal levels are required to maintain the -3dB output level. It is this reduction in gain that gives the improved signal-to-noise ratio. The output at pin 8 is AC coupled to the output socket via a 10µF capacitor. Note the associated 47kΩ resistor to ground. This provides a charging path for the 10µF capacitor when no load is connected, to prevent large thumps when the unit is subse­quently plugged in. The 47µF capacitor and the parallel August 1995  31 This view shows how the PC board & the various sockets fit inside the case. Take care to ensure that the supply polarity is correct before soldering the leads to the DC power socket. 1MΩ resistor on pin 1 of IC1 set the time constant components for the automatic gain control. The 47µF capacitor sets the attack time to 18ms, while the 1MΩ resistor sets the decay rate the 20dB per second. Power for the circuit is derived from a 9VDC plugpack. This feeds 3-terminal regulator REG1 which delivers an 8V rail to power IC1. The 10µF capacitors at the input and output of REG1 are for stability and supply ripple rejection. LED 1 provides power indication and is driven from the 8V rail via a 1kΩ limit­ing resistor. Construction The Gain Controlled Microphone Preamplifier is built onto a PC board coded 01207951 and measuring 49 x 48mm. Fig.3 shows the wiring details. Begin the assembly by installing PC stakes at the external wiring points. The remain­ing parts can be installed in any order but take care with the OUTPUT SOCKET 47uF 1M XLR PANEL SOCKET orientation of the electrolytic capacitors and the IC. Resistor R1 can be left off the board at this stage, as it may not be necessary with your particular microphone. The 3-terminal regulator is installed with its leads bent at right angles to mate with its mounting holes and is bolted to the board using a screw and nut. Take care with the orientation of the LED – its anode lead will be the longer of the two. It should be mounted with its top 25mm above the board surface, so that it will later protrude through a hole in the lid. Note that it may be necessary to extend its leads in order to obtain the correct height. That completes the PC board assembly. It can now be in­stalled inside a plastic zippy case measuring 82 x 54 x 32mm. First, drill and cut out the holes for the XLR, phono and DC sockets at either end of the case – see Fig.3. You will also need to shave back the ribs in the side of the case so that the PC board can sit directly on the base. Next, attach the front-panel label to the lid and drill out the four corner mounting holes and the hole for the LED. This done, fit the PC board inside the case and mount the XLR, phono and DC sockets. Finally, complete the wiring as shown in Fig.3. Note the link between pin 1 of the XLR socket and its earth terminal. 100uF 1 2 3 0.1 1 100uF IC1 2.2uF SL6270 01207951 R1 10uF .0033 10uF 47k 10uF 5 REG1 4 1k A K 4 5 DC SOCKET LED1 Fig.3: install the parts on the PC board & complete the wiring as shown here. Note that the LED is mounted with its top 25mm above the board surface, so that it will later just protrude through a hole in the lid. Fig.4: check your board carefully against this full-size pattern before installing any of the parts. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  1 32  Silicon Chip Value 1MΩ 47kΩ 1kΩ 4-Band Code (1%) brown black green brown yellow violet orange brown brown black red brown 5-Band Code (1%) brown black black yellow brown yellow violet black red brown brown black black brown brown Specifications PARTS LIST 1 PC board, code 01207951, 49 x 48mm 1 Dynamark front panel label, 50 x 79mm 1 plastic case, 82 x 54 x 32mm 1 XLR 3-pin panel socket 1 6.5mm mono phono socket 1 2.1mm DC panel socket 3 3mm dia x 6mm long screws & nuts 7 PC stakes 1 9VDC 300mA plugpack Input impedance .................................. 150Ω unbalanced; 300Ω balanced Supply current ..................................... 20mA Supply voltage ..................................... 9VDC plugpack Output level ......................................... 100mV nominal Voltage gain ........................................ 52dB for 72µV input Distortion ............................................. 2% <at> 90mV input Signal to noise ratio ............................. see Table 1 Attack time .......................................... 20ms Decay time .......................................... 20dB/second Frequency response ........................... -3dB at 100Hz & 5kHz Semiconductors 1 SL6270DP voice operated gain adjusting device (VOGAD) (IC1) 1 7808 8V 3-terminal regulator (REG1) 1 3mm red LED (LED1) Table 1: The Effect Of Changing R1 .0033µF 120µV 44dB unweighted 3.9k .0082µF 200µV 52dB unweighted 2.2k .015µF 540µV 57dB unweighted 1k .033µF 900µV 63dB unweighted 680W .047µF 1.2mV 66dB unweighted Adjusting R1 + Depending on the microphone, that may be all there is to it. However, if you now find that the microphone is now noisy or too sensitive, or that unwanted background noises are audible, it will be necessary to add R1 to reduce the AGC range and the gain. This will have to be done on a trial and error basis using the values list- DC IN + Carefully check the polarity of the DC plugpack connector before plugging it into the power socket. When you are satisfied that it is correct, apply power and check that the power indica­tor LED lights. Check also that the output pin of the 3-terminal regulator (REG1) is at 8V. If you don’t get the correct voltage, switch off immediately and check for OUTPUT Testing wiring faults. If the output voltage is correct but the LED fails to light, then it is probably incorrectly oriented. Assuming that all is OK, you can now test the unit with a microphone and amplifier to verify that it is working correctly. + The wiring connections and the DC sockets should be sufficient to secure the PC board in position. However, if necessary, you can further secure the board to the bottom of the case using machine screws and nuts. Capacitors 2 100µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 3 10µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic 1 .0033µF MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 1kΩ 1 47kΩ1 R1 (see text) ed in Table 1 (note that the feedback capacitor in parallel with R1 must be changed as well). For example, if R1 is 1kΩ, the gain and AGC range will be reduced by 17dB, with a corresponding improvement of 19dB in the signal-to-noise ratio. There is a limit as to how far you can reduce R1 though and this will be determined by the sensitivity of the SC microphone being used. + open BALANCED INPUT Signal-To-Noise Ratio + -3dB Input Voltage GAIN CONTROLLED MICROPHONE PREAMPLIFIER Parallel C + R1 Left: the XLR microphone socket is mounted on one end of the case, while the output & DC power sockets are on the opposite end. Above is the full-size front panel artwork. August 1995  33 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: 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 MAILBAG Pull the plug for mains safety As a licensed electrical contractor, I must comment on the letter from Mr Strawbridge and your reply in the April 1995 issue. Normally, the right thing to do is remove the plug from the point for safety but to leave the lead in for the purposes de­scribed is quite safe if the power point is turned off, as it should have been when your technician got his shock. Surely that is obvious but, of course, even that depends on the power point being switched in the Active conductor as is normal. M. Tremble, Beacon Hill, NSW. Comment: we take the view that the only way to be absolutely sure that an electric appliance is safe to work on is to have the plug removed from the wall socket. Our staff member who received a shock did not do that. OM350 not suitable for masthead amplifiers I am writing in response to a query in the Ask Silicon Chip section of the February magazine concerning poor results when using the OM350 as a masthead amplifier for TV reception. After a new employee asked me to look at a kit he had built which was not working as he expected, and after finding no prob­lems with his assembly, I assured him that a commercial masthead would solve his problem. This it did and after previous experi­ ence with these ICs I decided that they were just not up to the job. It was probably several years later that I realised what the problem is and anyone with commercial masthead experience would do the same as they read the specifications. At a quoted 7dB noise figure, the OM350 is just not clean enough. Commercial amplifiers quote 2-3dB of noise and even among these there are discernible differences in the amount of grain in the picture after boosting a low- level UHF signal. The average TV set needs 45-50dB µV of raw signal to pro­duce a clear picture. Using some inexpensive Australian masthead amplifiers, I have consistently produced clear results from as little as 30dB µV on Band IV UHF. By comparison, you need about 35dB at the antenna on Band III (VHF high) and about 45dB on the bottom end of Band I (VHF low) to achieve a clear picture after amplification. In layman’s terms, using an inexpensive commercial masthead amplifier will turn a very snowy UHF picture with no colour into a clear picture. A moderately snowy channel 6-11 picture will come clear, as will a slightly snowy channel 0-2 picture, with commercial units. Unfortunately, using an OM350 will tend to degrade what little signal you have. It is only suitable as a line amplifier, where you already have a clear picture and want to overcome the losses of a splitter in feeding several sets, but I still would not guarantee that it will perform adequately here. No, far better to throw the OM350 unit away and spend just a few dollars more on a proper masthead amplifier or line ampli­ fier. If you must build a kit, do it using discrete components such as BFR91s, but be prepared for a lot of trouble in making it stable. T. Graetz, The Aerial Shop, Culcairn, NSW. Fire risks and surge protectors I was interested to see your Publisher’s Letter in the June 1995 issue commenting on the fire risks associated with leaving computer equipment on permanently (which is what I’ve done for the last 3 months!) I do this because I was told by a technician that just as taking off and landing is the most dangerous time to be in an aeroplane, start-up time is when most VDUs and HDDs go bung. With the thought of fire in the back of my mind, I in­stalled a surge protector and earth leakage cutoff switch but these have no sense of heat. I’m wondering whether you could come up with a cutoff switch connected to a thermistor rated at say 45 degrees (which is when HDDs are supposed to melt down anyway) that could be mains interconnected? I guess the ability to add thermistors would make it adapt­able to the growth of printers, faxes and scanners. (In my dreams, it could shake a stubbie and open it to douse the situation!) P. Dudman, Dulwich Hill, NSW. Perhaps we have been lucky but in eight years of operation we have not experienced a hard disc failure. We have had floppy discs and monitors fail but not generally at switch-on. We do not think that surge protectors or thermistors will provide much protection against fire, particularly as far as your computer monitor is concerned. We stick to our original caution: turn your computer off when you’re not there. Red face phase error Just to point out an error in the May 1995 Headphone Ampli­ fier project. Maybe John Clarke has been using his headphone amplifier for too long and phase cancellation effects have pro­duced a black hole in the centre of his head. Headphones connected in series through the two tip contacts cannot be in phase; this will only help to give the budding Tommy Emmanuel a headache instead of the neighbours! Maybe this is the intention? Seriously though, I have been an avid reader of this maga­ zine since the outset and only wish there were more than 12 months in a year, then I wouldn’t have to wait so long between issues! J. Richardson, Southport, Qld. Glad you love the magazine. You’re dead right about the phase error, we must admit. Still, you can operate 32Ω Walkman-style headphones in parallel to provide an in-phase 16Ω load to obtain optimum performance from the LM386. To achieve this, you would need to wire the headphone socket in a more conventional way, with the ring and tip connections joined together and the sleeve connected to GND (0V). August 1995  37 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. Relay driver board with high voltage supply The inputs of the flipflops are each filtered with a 22kΩ resistor and a .015µF capacitor. Each time the input goes high, the flipflop changes state and turns its respective transistor on or off, to operate the relay. Diodes D5-D8 are connected to the collectors of transistors Q1-Q4 and operate as a 4-input NOR gate. If any one of the tran­sistors is on (ie, low), the base of Q5 is pulled low, turning it on. This relay driver board uses four cheap 48V relays driven by flipflops and fed by a high voltage supply generated by a 555 timer and a diode string. Fig.1 shows the circuit. Two 4013 dual-D flipflops are used to provide latching operation of the four relays.  LED1  LED2 C1 .015 D2 G1G R3 22k C2 .015 D3 G1G R5 22k C3 .015 D6 1N4148 R10 22k R9 4.7k C22 0.47 R11 10 C5 100 R14 2.2M C15 0.47 TIN R13 1 4.7k R15 22k R7 22k E C14 .015 4 5 D R Q 1 IC2a 3 4013 2 CK S Q 6 TOUT 1 4 R12 47k 11 C17 .015 C11 D11 10 D12 C10 10 3 5 IC2b C13 D13 10 D14 CK S Q 8 7 C12 10 C E B VIEWED FROM BELOW +12V R21 2.2M +12V 12 6xG1G C19 0.47 TIN R19 3 4.7k R20 22k C18 .015 R24 2.2M 4 5 D R Q 1 IC3a 3 4013 2 CK S Q C21 0.47 TOUT 3 10 14 TOUT 9 D R Q 13 4 TIN R22 4 4.7k 6 FOUR RELAY DRIVER Fig.1: the circuit uses two 4013 dual-D flipflops to provide latching operation of the four relays. 38  Silicon Chip E D8 1N4148 C7 1 .0015 10 14 TOUT 2 9 D R Q 13 TIN R16 2 4.7k R18 22k 8 IC1 555 6 2 R17 2.2M C16 0.47 C4 .015 D9 C8 10 C6 .015 R25 47k RL4B Q4 2N5551 C B D7 1N4148 Q5 8550 E B C RL4 R8 RL4 22k C9 10 D10 C23 100 D4 G1G RL3B Q3 2N5551 C B +12V 0V RL3 R6 RL3 22k E D5 1N4148 RL4A RL3A RL2B Q2 2N5551 C B R4 RL2 22k E RL2  LED4 RL2A RL1B Q1 2N5551 C B R1 RL1 22k R2 22k RL1  LED3 RL1A D1 G1G This applies power to the 555 which oscillates and drives a Cockroft-Walton voltage multiplier consisting of diodes D9-D14 and associated 10µF capacitors. This generates a supply of about +32V to feed the relays. With none of the relays energised, the circuit has a very low current drain by virtue of the following conditions. When power is first applied and no relays are operated, all transis­tors are R23 22k 11 C20 .015 IC3b CK S Q 8 7 12 RELAY 1 RELAY 2 RELAY 3 RELAY 4 22k RL3 22k RL4 TOUT 1 1 0.47 TOUT 2 10uF 4.7k 22k D13 10uF D14 D10 47k 1 D12 100uF IC1 555 10uF .015 TIN 1 10uF .015 0.47 0.47 4.7k 22k 10uF 2.2M 10uF IC3 4013 .015 4.7k 22k Automatic antenna controller for cars This circuit converts a semi-automatic antenna, normally controlled by a switch, to fully automatic operation. It is trig­gered by an input from the antenna control line of the radio or by the accessories conANTENNA nection to the ignition CONTROL UP +12V switch. DOWN 0V The circuit operates as follows. The antenna control input has a turn-off delay of about 15 seconds using diode D1 and the associated RC network. This is to prevent the controller becoming confused if the antenna control line changes condition while the antenna is being driven. Transistor Q1 switches relay RLY1 to supply +12V to the antenna; relay RLY2 is still off at this stage, providing the 0V connection to the motor and driving the antenna up. At the same time, +12V is applied by relay RLY1 to a 33kΩ resistor connected to pin 3 of IC1, a 555 timer. This monostable timer 0.47 0.47 22k D8 22k D7 .015 Q4 .015 RL2 D9 Q5 22k 22k D6 D5 22k D1 Q3 D11 .015 RL1 .015 Q2 100uF .015 TOUT 4 GND TOUT 3 1 K D1 D1 Q1 22k K LED4 A K LED3 A K LED2 A D1 +12V .015 4.7k 22k C NC 2.2M 47k C NC TIN4 4 IC2 4013 C NC 4.7k C LED1 A .001 TIN 3 NO 22k NO 2.2M NO NC 10 off and only the 4013s draw any current. The +12V supply is applied to the four high voltage transistors via diodes D9D14 and the associated relay coils. Since these transistors are off, the base of Q5 is held high by the four associated diodes (D5-D8) and hence the 555 timer can draw no current. The circuit can also be configured for momentary operation of the relays by applying the inputs directly to the four driver transistors, rather than via the 4013 latches. A PC board has been designed for this circuit and the parts layout is shown in Fig.2. Take care to ensure that all polarised parts are correctly oriented. A complete kit of parts for this circuit is available for $28 from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 570 7910. NO 2.2M Fig.2 (right): install the parts on the PC board as shown in this layout diagram. The board can be powered from any suitable 12V DC supply (eg, a plugpack). TIN2 330  LED1 UP +12V 270  D2 1N4004 D1 1N4004 RLY1 4 Q1 BC548 33k 33k IC1 555 6 2 100 330k 8 LED2   DOWN D3 1N4004 ANTENNA MOTOR RLY2 3 5 1 0.1 100 monitors the condition of RLY1 and after a delay of about five seconds, switches RLY2 on, resulting in the antenna motor having +12V on both sides of the motor, effectively switching it off. The system remains in this condition until the antenna control signal is turned off. After the 100µF capacitor connected to D1 dis­charges (about 15 seconds), Q1 and hence RLY1 turns off. This applies 0V to the opposite side of the motor and drives the antenna down. After a delay (of about 6 seconds), the 555 turns off RLY2, bringing the other terminal of the motor to 0V, turning it off. LEDs 1 & 2 indicate the direction of the motor while D2 & D3 protect Q1 and the 555 from damage from back-EMF generated when the relays turn off. The +12V supply to the circuit must be connected to the battery of the car (not switched by the ignition) so that the antenna can wind down after the off delay. D. O’Connor, Aldgate, SA. ($35) August 1995  39 SERVICEMAN'S LOG It took a little longer than usual At the risk of seeming to state “the bleedin’ obvious” – as our English colleagues would say – my main story this month is an unusual one. But then they usually are. OK; so this one is more unusual than usual, if that makes sense. The story really started over two years ago but can only be told now because that’s how long it took to finalise the job. Well, as I said, it is an unusual story. The device involved was a Philips colour TV set, fitted with a KT-3 chassis. The KT-3 chassis was fitted to a whole range of Philips sets and this one was a 48cm model about 14 years old – the age being a matter of some importance as it turned out. And the complaint was simply that the set would fail inter­mittently. Sometimes it would fail at switch-on, sometimes after it had been running for some time. More importantly, from the owner’s point of view, what had begun as a very occasional prob­lem had become progressively worse. It was now likely to be off more than it was on. On the bench it was just as the customer had said; it was only nominally intermittent and faulty most of the time. But when it was functioning, it performed very well. But there was a major symptom which he had not noticed; the power supply was hiccuping away quite merrily. This symptom normally indicates an overload of some kind, such as a failed horizontal output transistor, or something in this part of the circuit. It looked fairly straightforward, as over­ loads are not usually all that hard to track down. The trouble was, I didn’t see Murphy lurking in the corner. I pulled out the horizontal output transistor and checked it. It checked OK but I replaced it anyway. I doubted that this was the culprit. I’ve never known this component to fail inter­ 40  Silicon Chip mittently; when they fail they don’t muck about but there is always a first time. I also checked the insulating washer. It looked OK but I replaced it also. What about the horizontal output transformer? Could be, except that I would expect it would start overheating if allowed to run in fault condition for even a short period. But no; no sign of trouble there. A puzzling aspect of the fault was the effect on the HT rail. This was down to around 35V but varying up to about 50V at times. This seemed to rule out a dead short and, in fact, resist­ ance measurements failed to find any evidence of short circuits anywhere. This seemed to suggest that it was either an AC fault of some kind, or something breaking down at operating voltage. But what? Replacement boards In a sense, I had come to something of a dead end. All the usual approaches to a fault of this kind had failed and I had to think of a new one. Fortunately, over the years, scrapped chassis had provided me with a useful collection of boards for this and similar chassis. So this was my next step; replace each suspect board until I found the culprit. In all, there are six plug-in boards, plus a plug-in IF pack and the ELC2060 tuner which is permanently fitted. I imag­ined swapping a couple of boards would probably be enough to give me a clue, unless I was very unlucky. And the truth is, I was very unlucky. I finished up chang­ing every board and was no closer to solving the problem. The only thing that had changed was that the fault was no longer intermittent but was now permanent. This was a minor plus in terms of convenience but no help otherwise. At this point, I had really run out of ideas. I needed time to think and there were other more urgent jobs waiting, so I put it to one side. I find it is often a help to take a break like this; one can dwell on a problem for too long and frustration clouds one’s judgement. It is surprising how often an idea will suddenly pop up when least expected. It didn’t quite happen like that this time but I’m sure that the break did help. When I pulled the set out of the corner of the bench a couple of weeks later, I could take a broader look at the problem. What had I missed; what hadn’t I checked? Well, I hadn’t checked the scan coils. That idea was a long shot – scan coil failures are extremely rare. I doubt whether I have encountered half a dozen in the last 20 years. More particu­larly, I had never had one in a Philips set. So, against that background, one tends to take them for granted. But I couldn’t take this one for granted; the scan coil assembly had to come out. It’s a simple enough operation – release the neck board and ring convergence magnets, then undo the clamp holding the scan coil assembly and slip it off the neck of the tube. My idea was to hook it up to my shorted turns tester, a shorted turn being the most likely fault. And I was right about that. But I didn’t need the tester to tell me; one glance was enough. There was a large blackened patch on one of the horizon­tal windings, surrounded by spots of green corrosion which had obviously caused it all in the first place. So that was it; the scan coils were a write off. Well, at least I’d diagnosed the problem, even if it had taken more effort than I would have liked. And the solution seemed simple enough – a new set of coils. But it wasn’t that easy. A new set of coils would be in the $100 plus category which, with labour costs, might be difficult to justify for a 14 year old set. And, unfortunately, scan coils for this set was one thing I didn’t have in the junk pile. So I rang the customer with a typical good-news-bad-news report. The set could be fixed but the cost might be hard to justify. All I could suggest was that I might be lucky enough to score a set of coils if another customer’s set was written off. But, of course, we had no way of knowing when, or even if, this would happen. He thought about it briefly, then decided that a new set of coils was not a proposition. On the other hand, he asked if he could leave it with me for the present, in the hope that another set of coils might turn up. He is a good customer, so I readily agreed although I wasn’t very optimistic. And that is about the end of that part of the story, which all happened over two years ago. I relegated the set to spot in the junk store and more or less forgot about it except when another such set came through the workshop. Unfortunately for this customer, they were all routine jobs. Back to the present Which brings us to the present time. And to another charac­ter who became part of this story. I’ll call him Lance for con­venience but that is not his real name. He is a young married bloke who, to put it mildly, has had a pretty rough trot. Lance’s main activity is repairing or rebuilding discarded sets which he donates to a local charity that has stood by him and his family over the years. His main source of scrapped sets is a dealer/serviceman in a nearby suburb but he also drops in on me – and some of my colleagues – from time to time for a word or two of advice and to scrounge a few parts from stuff earmarked for the tip. Soon after I first met Lance, I raised the matter of a set of scan coils for the KT-3, asking him to a look out for such a set. That was over a year ago and he had had no luck whatsoever. Then, a couple of months ago, Lance walked in with what looked like a complete KT-3 set. In fact, it wasn’t complete, consisting only of the cabinet (in very good condition) picture tube and scan coils. There was no chassis. A visit to my store room produced a chassis plus a set of boards and so we had the makings of a complete set. Unfortunate­ly, it didn’t work out that way. When we fired it up, the set went into a hiccup mode exactly like the previous one. I wasn’t sure it was the same fault, of course, and I made a few routine checks initially but I could find nothing else ob­viously wrong. So off came the scan coils and, yes, that was it; August 1995  41 exactly the same pattern of corrosion and self-destruction. Which put us back pretty well to square one, except that we now had two sets needing scan coils. The only difference was that set number two was something of an unknown quantity – we had no way of determining the condition of the picture tube. Neverthe­less, we agreed that it was now worthwhile looking for two sets of coils. That was being somewhat optimistic, I suppose, but he did eventually find one set of coils, which he turned up with a few days ago. They looked to be in good condition, so I lost no time in fitting it to my customer’s set. And it worked. However, before doing any setting up, I pulled the coils off again and fitted them to Lance’s set. Unfor­tunately, it wasn’t such a good result this time. The tube was a write-off, one gun being completely dead. I even tried boosting it but to no avail. So the coil assembly was refitted to my customer’s set and I went through 42  Silicon Chip the setting up procedure, after which the set delivered a first-class picture. Finally, I rang the customer and advised him to come and collect the set. He was happy that the repair bill had been kept to a reasonable level and I was happy to finally be reimbursed for my time and effort. Regrettably, Lance didn’t come out of it quite as well, although he is still looking and hoping. But he needs both a picture tube and a scan coil assembly now, so he will need to be extra lucky. That said, he has scored a chassis and learnt something about scan coil failure and the symptoms it produc­es, so it hasn’t been a completely wasted effort on his part. All of which just goes to show what can be achieved if the customer is prepared to wait. But I must concede that this has to be regarded as a one-off; one that just happened to work out. The flasher My next story is about a lady customer who was troubled by a flasher. No, not one of the raincoat mob – rather, a TV set. To be more precise, it was a Samsung 51cm colour set – a model CB-515F fitted with the P-50F chassis. According to the lady, the problem was random white flashes on the screen. Initially, this happened only occasionally and she put it down to interference from some external source. This theory was reinforced by the fact that she lives in a gully which is a relatively poor signal area. More recently, the problem had become more frequent and, at times, much worse. Sometimes, it was so bad as to make the pic­ture virtually unwatchable. Still thinking that it might be interference, she took the opportunity to operate the set while staying with a friend in a much better signal area. And it did clarify the point; the problem was just as bad in this location. And so the set finally landed on my bench, along with the above explanation. I put the set on the air while the lady was still in the shop but, of course, Murphy was lurking in the corner – it behaved perfectly. All I could do was suggest that she leave it with me, which she did. I set it up in a corner of the bench and it Fig.1: the front end of the Samsung CB-515 colour TV set. The tuner (TU001) is at top left, the IF IC (IC101) at lower right, & the SAW filter & its associated components below the tuner. ran for several days without any sign of trouble. But then came the first hint; a brief white flash, no more that a few centimetres long on one line. Blink and you’d miss it. Nothing more happened for about a week then, one day, it really turned on an act with flashes all over the screen. These became progressively worse until it was quite unwatchable. Well, at least I’d seen the problem and that is always useful. And, in fact, I’d already made a tentative diagnosis – I was sure it was a front-end problem, most likely the tuner (TU001). Fortunately, this was a relatively simple theory to prove – or disprove. I had a spare tuner on hand and it was easy enough to substitute it. And the set ran perfectly after that – for about a day and a half. Then it was back in flashing mode. OK, but I still felt sure that it had to be somewhere in the front end. So the next thing to try was the transistor in the first IF stage (Q161, 2SC388), mainly because it was a simple operation. But again, no joy. Desperation measures Things were looking somewhat desperate now but there was one good point; I had a good stock of spares from previously junked sets, which meant that I could replace almost any compon­ent, at least in the front end. This is a useful approach in such circumstances but it can be time consuming. So, in turn, I replaced the SAW filter (Z101), it’s asso­ciated matching transformer (T101), the video detector coil (T171), the AFT balance coil (T172) and, in desperation, the IF IC (IC101, LA7520). As readers will appreciate, all this took a lot longer than it does to write about it. In fact, the entire process took several days, taking into account the time taken to monitor each change. And in the end it was all to no avail; I was back to square one. So was it in the front end? Or could it be a fault in the horizontal scanning system; a breakdown or flashover which was generating interference? I rang the Samsung service department and spoke to a contact there who has always been very helpful. He wasn’t able to offer any ideas based on actual cases but he did agree that the idea of interference from the scan system was worth investigating. And he went on to offer some ideas as to how the front end could be operated with the scanning systems shut down. As a result, I finished up with the rear end of the set shut down and the front end operating on 12V and 33V from a bench power supply. I then hooked up the CRO to monitor the IF envelope – it has enough bandwidth to do this – and fired up the front end independently. Glitches Sure enough, in the fullness of time, I could clearly see a succession of glitches on this envelope. I had no doubt now that I had been right the first time; the fault was somewhere in the front end. But where? I had checked or changed all the likely components in this section. Or had I? No, there was one section I hadn’t checked; the channel selector pushbutton assembly, shown as PWB-SELECTOR. There are in fact two versions of this unit, an 8-key assembly and a 12-key assembly, the latter being the one shown. This assembly carries the push­ buttons which are used to select the preset channels, plus the preset controls themselves. The pushbuttons are shown in the centre of Fig.2, August 1995  43 SERVICEMAN’S LOG – CTD designated as SW01, SW02, etc. They have two sets of contacts, those on the right performing the channel selection function and those on the left selecting the appropriate band. These latter contacts also activate the associated indicator LED (DL01, DL02, etc) from the 12V rail. These LEDs are connected in series and all but the wanted one are shorted out. There are two preset controls for each channel. On the extreme left are the 3-position band selector switches, marked VL (VHF low), VH (VHF high) and U (UHF). These are preset for the band appropriate to the channel chosen for that position. They are connected to the 12V rail when a channel button is activated and apply base voltage to one of three transistors – SQ101, SQ102 and SQ103. The selected transistor then turns on and connects the main 12V rail to the appropriate section of the tuner. The chosen channel is selected by the corresponding vari­able resistor on the right (VR01, VR02, etc). These are fed from the 33V rail and feed an appropriate voltage to the varicap diodes in the tuner (terminal VT). As an example, switch SW06 is shown in the active position (with the LED illuminated), VR06 is connected to the 33V rail, and the 12V rail is 44  Silicon Chip connected to the VH position of the band selector switch. All of which should give the reader some idea of the com­plexity of these assemblies. And to be truthful, they have more than their fair share of troubles although, until now, these have all involved channel selection problems. These are easy enough to diagnose and there is only one practical solution; replace the entire assembly. However, I have never experienced, or heard of, these units causing the kind of trouble evident in this set. But, with all other likely culprits exonerated, this one had to be a suspect even though it was something of a long shot. Fortunately, I had a spare unit on hand and this was duly fitted. And that was the answer. The set was run for several days with no sign of the fault and I eventually returned it to the customer. But I warned the lady to contact me immediately if it should reappear. That was many weeks ago and all is quiet so far. More flashers That wasn’t the last of the flashers. Within a few weeks, I had no less than three more and all from the same cause. The only difference was that it involved different bands; one was on low VHF, one on high VHF, and one Fig.2: this diagram shows the channel preset & channel selector circuitry in the Samsung CB-515. Note the active setting for switch SW06. on UHF. And they were not all CB515s; one was a CB-349 and one an Akai CT-K115, both of which use the P-50F chassis. Granted, these were the bands favoured by each customer and my checks confirmed that the fault occurred only on the particu­lar band. And there was a fourth set with an even weirder fault in this section. The set worked normally on UHF but suffered from very low gain on low VHF. For some reason (probably due to leakage), when it turned on the low VHF transistor (SQ101), it also turned on the high VHF transistor (SQ102) at the same time. The effect was to completely wreck the low band gain. So be warned; any similar funnies and you’ll know where to look. 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. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au BOOKSHELF Surface Mount Technology Surface Mount Technology by Rudolph Strauss. Published in 1994 by ButterworthHeinemann, Oxford. Hard covers, 361 pages, 240 x 160mm, ISBN 0-7506-1862-0, $99.00 This book will provide informative reading for any person presently involved with wave soldering equipment for through-hole mounting components or anyone considering the assembly of PC boards with surface mounted devices (SMD's). In the first chapter the Author asks the same question we all ask. Why SMD's? What is wrong with existing components? But after a moment's thought we realise that components have always been getting smaller. From valves to transistors to integrated circuits, the package size has shrunk dramatically. Microprocessors have gone from 16 pin devices to 40 pins to 169 pins and so on. The trend to higher packaging density of IC's and to higher frequency operation, requires shorter IC interconnecting leads and components with very short (low inductance) leads. Thus SMD's have come to the rescue. In chapter 2 the Author discusses SMD shapes including MELF's (Metal Electrode Faced Components), chips, small outline devices (Transistors-SOT's, Integrated Circuits-SOIC's etc) and discusses their solderability and mechanical stability in wave soldering machines. Chapter 3 covers soldering methods, fluxes, solder composition, the effects of impurities in solder baths and the properties of soldered joints. Chapter 4 describes wave soldering in detail, including the relative simplicity before SMD's. Wave soldering is a technique where the PC board, with all components physically mounted or glued, is passed over a wave of molten solder. The solder is pumped through a vertical nozzle, usually the width of the machine and as it flows up and out the PC board is moved through this "wave". Other topics in this chapter include fluxes, board preheating, the solder wave, oxygen-free atmospheres and the role of adhesives. Chapter 5 covers reflow soldering. What is the difference? In wave soldering, as in hand soldering the flux comes first, the solder and heat come at the same time. With reflow, the heat comes last, the flux and solder or solder paste having already been placed on the PC board and sometimes on the component leads as well. The Author points out reflow soldering is not new. Plumbers use reflow when joining modern copper capillary fittings. These are supplied with an insert of flux and solder. The plumber only needs to clean the copper pipe he intends to use, push it into the fitting and apply heat. The flux and solder inside the fitting will now do their job and make a waterproof joint. Strauss then discusses one pass and two pass soldering, where the PC board is reflowed on one side then turned over and the second side soldered. You would think that the components on the bottom would fall off on the second pass and they will if they are too heavy. Believe it or not, the surface tension of the softened solder holds the smaller components in place. One layout requirement for two pass SMD's is to keep all the heavy components on one side of the board. The rest of the chapter covers various methods of reflow, including vapour phase, infrared, hot air or gas, laser and impulse. Chapter 6 details the requirements for PC boards for SMD's. This covers layout procedures, which should take into account the direction of the board through the solder machine as most components will be more mechanically stable in one orientation. Chapter 7 discusses the placing of components on the PC board, from manual methods to fully automatic placement. Chapter 8 discusses the methods used to clean the boards after soldering. Historically CFC's have been used but now they have been phased out due to their environmental unfriendliness; new cleaning compounds and methods have evolved. The final chapters cover quality control, inspection and rework. These are interrelated, for obviously, the better the quality control the less rework. Inspection before soldering and rectification of faults can be far easier and cheaper than repairing the same fault after the solder bath. To sum up, this is a very interesting book, written by an Author who knows his subject - a must for the production manager of any electronics manufacturing company not yet into SC SMD. (R.J.W.) August 1995  53 Design by ROGER KENT* Audio Lab: a PC-controlled audio test instrument Introducing Audio Lab, a PC controlled test instrument capable of a range of DC and AC measurements with particular emphasis on audio applications. Audio Lab is connected to the serial port on your computer and does not require any internal cards. These days, PC controlled instruments are becoming widely used, whether it is equipment fitted with the GPIB (HP’s General Purpose Instrument Bus) or simpler gear with a serial communica­tion link. Now, by special 54  Silicon Chip arrangement with R.S.K. Electonics Pty Ltd, of Perth, we are pleased to present Audio Lab. Anyone involved in the electronics field whether as a hobby, as a design engineer or as a technician, relies on equip­ ment to measure and test the project being worked on. For audio applications, an ideal workshop setup should include facilities to monitor frequency, resistance, capacitance, impedance, and DC and AC voltage, along with the capability to perform and print fre­quency response plots for the unit under test. To achieve these results using conventional methods, a considerable amount of test gear would be required. Audio Lab has been developed to incorporate all the above features into one PC based measuring system. Data transfer from Audio Lab to the PC is via an RS232 link and no power is taken from the PC. No test equipment, apart from a multimeter, is required to build Audio Lab and all calibrations are performed by using the supplied setup software on the PC. The accuracy is a function of its 1.26V internal voltage reference which is better than ±2%. The frequency generator section is a calibrated crystal controlled module with a drift tolerance of 50ppm (parts per million). System features Audio Lab can measure DC and AC voltages in nine ranges from 50mV to 100V. AC measurements are true RMS rather than the less precise RMS indication based on a form factor of 1.11, as for a sinewave. It can also measure DC resistance from 2Ω to 10MΩ in eight ranges; capacitance from less than 5pF to 5000µF in eight ranges; and impedance from 2Ω to 10MΩ in eight ranges, for test frequencies between 10Hz and 20kHz and frequencies between 1Hz and 30kHz. As a generator, Audio Lab can deliver a sinewave at any frequency between 0.5Hz and 30kHz in 0.5Hz steps at any amplitude between zero and 2V RMS, with coarse and fine adjustments avail­able. The sinewave has a total harmonic distortion (distortion plus noise) of -40dB; ie, 1%. The generator mode can also produce a logarithmic frequency sweep from 10Hz to 20kHz or a linear sweep with selectable start and frequency increments. The selected frequency is entered from the PC with the output voltage being simultaneously monitored and displayed. Printouts of frequency plots and full screen displays can be made at any time. Audio Lab is housed in a standard plastic instrument case with three knobs on the front panel, a couple of toggle switches, three RCA sockets, a 6.5mm microphone jack, two binding post terminals and a bunch of LEDs which display (mimic) the function and range being monitored. Computer system requirements for Audio Lab are an IBM PC 286 compatible or better, with a 386DX/40 recommended as the minimum to take full advantage of the display graphics. Also required are a minimum RAM of 1Mb, 2Mb free on the hard drive, EGA/ VGA graphics, DOS 3.3 or later and a Microsoft-compatible mouse. Fig.1: this is the opening screen of the Audio Lab. From here, you can switch to measurements for AC & DC voltage, resistance, capacitance and impedance, and you can generate linear and logarithmic frequency sweeps. Fig.2: this screen shows a capacitor of 1.5pF being measured at a test frequency of 10kHz. Fig.3: this is an impedance plot for a bass reflex loudspeaker system. The double peaks in the low frequency region demonstrate the reflex tuning. Audio Lab is built on four doublesided PC boards with plated-through holes. The four PC boards and the signal flow around them are shown on the diagram of Fig.4. The four boards comprise the Boot August 1995  55 The Boot PC board accommodates an 80C31 microprocessor, RAM and EPROM, and an RS232 serial interface for the PC. interface built in, along with the option to take either 8K or 32K of static RAM. Access to the full micro bus has been implemented to enable various daughter boards to be plugged in for a range of applications without having to redesign the micro­processor part of the project. When the first byte of data is received from the PC, the code is written into RAM which is configured as Data memory, the EPROM being Program data. After the last byte of code has been transmitted, memory usage is switched so that the RAM becomes Program memory and the EPROM becomes Data memory. The program then runs from RAM, starting at address 0000H. An ADM232 RS232 interface is connected to bit P3.0 of the 80C31 as RXD with bit P3.1 as TXD, with the processor controlling the baud rate. By using the ADM232, correct specifi­ cations for the RS232 link are achieved and no compatibility problems when connected to the PC’s serial port will occur. Contained in the EPROM is the boot code to enable the transfer of the full program from the PC, along with several diagnostic programs which, when used with the diagnostic card and software, aid in debugging the mother­board. The EPROM also contains a 28.8K look-up table for the generation of sine waves. A-D board This is the A-D board which stacks on top and interfaces with the micro bus from the Boot board. It features an ADC0804 analog-to-digital converter and an AD736 true RMS converter. The on-board module is used generate sinewaves. PC board which accommo­ dates the system microprocessor and EPROM, the analog to digital (A-D) converter board, the front panel board and the power sup­ply. Let’s deal with the Boot board first. 80C31 microprocessor All of the functions in Audio Lab are controlled by an 80C31 microprocessor. This device was chosen because of its on-board I/O ports and ease of 56  Silicon Chip use via a serial communication link. It has separation of program and data memory which makes it simple to dump code for the processor from the PC via the serial port. What this implies is that any upgrades or changes to the code do not involve changing the EPROM but simply downloading new software from the PC. The Boot board has its own 5V regulator and bidirectional RS232 This board stacks on top and interfaces with the micro bus from the Boot board. An ADC0804 analog-to-digital converter is used to convert the selected analog information into 8-bit digital format at a sampling rate of about 15kHz. The 1.26V voltage reference gives an input range of 2.52 volts for the converter. A 74HC574 8-bit latch is used to select the different inputs, ranges and mode options; eg, RMS/ linear, component, frequency measure, etc. Switching between RMS and linear modes is achieved by a 4052 analog switch using bit D7 from the 74HC574 8-bit latch. The RMS value of the selected Input voltage is computed using an AD736 true RMS converter. This converter does not rely on measur­ ing peak-to-peak voltages and form factors to perform an RMS conversion but performs the correct algorithm; ie, square, mean and square root, to Mounted behind the front panel, this board accommodates most of the analog circuitry in Audio Lab. Here is where the scaling, monitor switching, mimic decoding and buffering functions are performed. Accurate calibration is achieved by two multiturn trimpots, to set the divide by 100 & 1000 ranges. The “Set-up” software makes calibration simple. calculate the RMS of any waveform, not just sine waves. The linear signal from the front board is amplified and converted to a square wave by a 4093 Schmitt trigger. Control bit D6 gates either the interrupt from the A-D converter, when measuring RMS or linear voltages, or the output of the Schmitt to the interrupt on the 80C31 processor. The micro then either con­verts the analog signal into serial format and dumps the data to the PC or when measuring frequency, counts the number of cycles in one second, then dumps the frequency via the serial port to the PC. The calibrated sinewave module is on this board and data is transferred to it from the 80C31 via control bits from port 3. Three multi-turn trimpots calibrate RMS gain, linear zero and linear gain, calibration being done using the “Set- up” pro­gram supplied with the project. Connection to the power supply board is via a 3-way connec­tor which supplies ±5V. These rails are derived from separate regulators to those for the boot board’s supply, to minimise any interference problems between the digital and analog sections of the system. To simplify inter-board wiring, connections from the A-D board and the Front board are by a 16-way ribbon cable. Front board The main analog section of the system is on this board. Here is where the scaling, monitor switching, mim­ ic decoding and buffering functions are performed. The overall scheme, though simple in concept, is very complex in operation and would require a complete article to fully describe the philosophy used when designing the system. In brief, the switching data, sine­ wave out and analog information from the A-D board arrives via the 16-way IDC (insulation displacement cable) connector. A 4051 8-input analog switch is used to choose which of the various inputs is selected for processing by the A-D board. The required BOOT PCB CPU EPROM RAM SERIAL I/O input is gated through by control bits D2, D3 & D4 from the 74HC574 8-bit latch. To achieve the different ranges when “INPUT” is se­lected, the voltage first passes through a digitally controlled attenuator, giving attenuation of 10, 100 and 1000 using control bits D0 & D1. Accurate calibration is achieved by two multiturn trimpots, to set the divide by 100 & 1000 ranges. Again, the “Set-up” software makes calibration very simple. The output from the attenuator feeds an op amp with a fixed gain of 20 which feeds a digitally controlled amplifier with gains of 1, 2 & 4 using control bits D2, D3 & D4. This selects different input resistors and sets the corresponding gain of the output buffer amp. Full scale on the analog to digital D0-D7 A TO D PCB P3.2-P3.7 C000 A000 A TO D SELECT RMS/LIN SINE GENERATOR SELECTVOLTS/ FREQUENCY C000/A000 DECODE INTERRUPT C000 READ=VOLTS C000 WRITE=SELECT RESET DC INTERRUPT SERIAL I/O PSU PCB +/-5V +/-5V AC SERIAL PC DATA OUT V OUT SINE FRONT PCB Fig.4: this diagram shows the four PC boards and the signal flow around them. RANGE SELECT I/P SELECT LED MIMIC August 1995  57 Communication with the controlling PC is via the in­built RS232 serial interface. Power comes from a DC plugpack. converter is set by the preset gain controls on the A-D board to be 2V, so by using combinations of attenuation and amplification the full nine ranges are obtained. The digital range switching used was the only configuration that achieved the desired results with ade­quate frequency response and accuracy, without the need for adjustable compensation capacitors. The Mike input is a conventional amplifier with a variable gain of 10 to about 100. A switch on the front panel enables the use of either a normal or electret microphone and the output is selected for display by control bits D2, D3 & D4. Impedance plots With the inputs described so far and the ability to deliver known AC voltages and frequencies, Audio Lab can measure and plot the impedance of any component. If a known voltage, at a known frequency is applied across a simple potential divider network, with the impedance of one of the components known, then by meas­uring the RMS voltage (Vx) at the junction 58  Silicon Chip of the two components it is a simple matter to calculate the impedance of the unknown component. Once the impedance is known the capacitance, resist­ance or inductance can be easily computed. For example, to measure resistance, if a fixed 1V RMS signal at 1kHz is used as the reference and this signal is ap­plied to one end of the unknown resistance, the other end being ground­ed through a known resistance of 10kΩ, the value of the unknown resistance can be calculated, as follows: R = 10(1-Vx)/Vx kilohms Similarly, for a capacitor: C = Vx/2πF.R(Vx2 - 1)0.5 So by varying the frequency and the known resistance, a wide range of capacitance can be measured. Load resistors of 1kΩ, 10kΩ & 100kΩ are selected via control bits D0 & D1 and the com­ponent measure output is selected by D2, D3 & D4. The 1kΩ and 10kΩ reference resistors are accurately set using multiturn trimpots and 1% calibration resistors. In the result, the accura­cy for impedances from 300Ω to 10MΩ was good but below 300Ω was unacceptable. To get round this problem, the potential divider was re­versed. By using the High/Low switch, the function is inverted so that the test voltage feeds the known resistance and the unknown impedance now is grounded. Through various scaling routines, the system is accurate for reading impedances to below 5Ω at frequencies between 10Hz and 20kHz. Impedance plots for loudspeakers and crossover units can be done by connecting the unit to be measured across the “Component” terminals and selecting Log sweep from 20Hz to 20kHz with the range switch set to low. Further decoding of control bits D0-D7 by analog switches is used to provide signals to drive the 12 mimic LEDs. These provide visible indication as to what input is being monitored and what function is being performed. All the functions, ranges, etc are selected from the PC using the graphical software which will be discussed along with further details of the project in next month’s issue. *Roger Kent is the managing director of R.S.K. Electronics Pty Ltd. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL 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. $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. 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Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia August 1995  59 e t i M y t h g i M Powered Loudspeaker Build the Revitalise the sound card in your computer with the Mighty-Mite Powered Loudspeaker. It uses a miniature surfacemount IC amplifier which only requires a 5V supply to deliver a 1W output. By JOHN CLARKE Sound cards for computers and multimedia are all the go at present. But without suitable loudspeakers, much of the impact of the sound can be lost. By building the Mighty-Mite Powered Loud­speaker, you can obtain sound quality that’s far superior to that available from low-cost multimedia loudspeaker systems. The system to be described is based on an LM4860M integrat­ ed circuit (IC) audio amplifier and this drives a 100mm dual-cone loudspeaker. Both the amplifier circuitry and the loudspeaker are housed in a compact sealed plastic case. The only front panel control is for volume while at the rear are the signal input and DC supply sockets. The amplifier circuit is powered from a 5V rail and this can come from 60  Silicon Chip VDD CS 0.1 Rf 10k AUDIO INPUT C1 1 Ri 10k VDD 13 -IN GAIN-OUT Vo1 10 14 +IN 40k AMP1 5 BYPASS Vo2 15 VDD/2 AMP2 Av = -1 50k 6 HP-IN1 7 HP-IN2 RL 8 40k 50k LM4860 CB 0.1 PARTS LIST BIAS 3 HP-SENSE 2 SHUTDOWN GND 1,4,8,9,16 Fig.1: the internal arrangement of the LM4860M audio amplifier IC. Amp1 is the main amplifier & is connected in inverting mode. Its output appears at pin 10 & also drives inverting amplifier stage Amp2 to derive an out-of-phase output at pin 15. L1 FX115 or sim. 47 16VW +5V 6.8pF Semiconductors 1 LM4860M surface mount 1W audio amplifier (IC1) 100k INPUT VOLUME VR1 10k LOG 1 16VW 22k 13 14 12 11 IC1 LM4860 5 2 3 1,4,6, 7,8,9, 16 10 15 4 OR 8 10 16VW MIGHTY-MITE Fig.2: this diagram shows the complete circuit details for the Mighty-Mite Powered Loudspeaker. It operates with a gain of nine & this provides an input sensitivity of about 320mV for 1W output into 8-ohms. the computer itself – either from the games port or from the sound card input/output port (see Fig.4). Alternatively, the circuit may be powered from a 9-12VAC plugpack via an option­al 5V regulator circuit which is also described here. Of course, the Mighty-Mite is not just suitable for multi­media applications. It can be used anywhere a powered loudspeaker system is required; eg, as part of a low-cost audio system or in a workshop. If you do use them with a computer system though, be sure to heed the accompanying warn- 1 PC board, code 01305951, 33 x 25mm 1 sealed ABS box, 171 x 121 x 55mm (Jaycar HB-6128 or equival­ent) 1 dual-cone 100mm loudspeaker, 4Ω or 8Ω (DSE Cat. A9651 or equiv­alent) 1 10kΩ 16mm log pot (VR1) 1 FX115 ferrite bead or equivalent (L1) 3 self-adhesive labels 1 16mm dia. knob 1 DC panel socket 1 chassis mount RCA panel socket 2 25mm long x 3mm dia. screws & nuts 2 9mm tapped spacers 2 6mm long x 3mm screws 4 black countersunk 4mm diameter screws & nuts (to attach loud­speaker) 9 PC stakes 1 25mm length of 0.8mm tinned copper wire ing panel. Unlike most multimedia loudspeakers, these units are not magnetically shield­ed, so don’t place them too close to the monitor. The audio amplifier IC One of our first tasks in designing this system was to choose a suitable audio amplifier IC. There are many such units available, most capable of providing excellent results. We final­ly settled on the LM4860M because of its excellent specifications (considering its small surface-mount package), its 1W (RMS) power output and its ability Capacitors 1 47µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 6.8pF ceramic Resistors (0.25W, 1%) 1 100kΩ 1 22kΩ Optional 5V Regulator 1 PC board, code 01305952, 59 x 35mm 1 heatsink, 26 x 29 x 13mm 1 7805T 3-terminal regulator (REG1) 1 B104 bridge rectifier (BR1) 1 470µF 25VW PC electrolytic capacitor 1 10µF 16VW PC electrolytic capacitor 4 PC stakes 1 6mm long x 3mm dia. screw & nut to operate from a 5V supply. At first glance, it might seem impossible to obtain a 1W output into 8-ohms from such a low supply rail. August 1995  61 SPEAKER DC INPUT 6.8pF L1 100k 22k IC1 INPUT 47uF 1 IuF VR1 10uF Fig.3: install the parts on the PC board & run the external wiring as shown in this diagram. Note that IC1 is a surface mount device & is mounted on the copper side of the board (see text). This is because, to obtain 1W, the amplifier would have to deliver 2.83V RMS or 4V peak into the load. In other words, it would have to deliver 8V peak-to-peak, which is greater than the supply voltage. However, the LM3860M is a bridge amplifier which drives both terminals of the loudspeaker. Thus, when one terminal of the loudspeaker is driven high, the other terminal is driven low with the opposite phase. As a result, the effective power output from a bridge amplifier is four times that available from a standard amplifier (P = V2/R). Fig.1 shows the internal arrangement of the LM4860M and the typical external connections. Amp1 is the main amplifier and this is connected in inverting mode. Its gain is set by the ratio of the feedback resistor (Rf) to 62  Silicon Chip the input resistor (Ri), and in this case is set to -1. The non-inverting input is set to half-supply by two internal 50kΩ voltage divider resistors and is decoupled using capacitor CB. The output of Amp1 appears at pin Fig.4: a 5V rail to power the Mighty-Mite can be derived from a games or sound card port of a PC. This diagram shows the supply connections. You will need to make up a suitable power cable which is fitted at one end with a matching DB15 connector. 10 of the IC and also drives the inverting input of a second internal amplifier. Desig­nated Amp2, this amplifier is also connected in inverting mode, with its gain set to -1 by two internal 40kΩ resistors. Its signal output appears at pin 15 and is 180° out of phase with the signal at pin 10. This arrangement forms the bridge amplifier configuration. Compared to a single-ended amplifier, it effectively doubles the output voltage swing applied to the loudspeaker and thus quadru­ples the power. Note that the overall gain of the amplifier is 2Rf/Ri, due to the bridge configuration. With no signal applied, the outputs of Amp1 and Amp2 will be at the same voltage because both amplifiers are biased at half supply. Consequently, there is no need for an output coupling capacitor to prevent DC from flowing in the voice coil. This not only reduces the component count but also improves the low fre­ quency response. As well as the internal amplifiers, the IC also contains a shutdown feature which can be used to reduce the power consump­tion when the amplifier is not in use. It is activated by con­necting pin 2 to the positive supply rail (or to some other point above 3V). This reduces the no-signal supply current from a nominal 7mA to 500µA. Alternatively, the shutdown feature can be activated via an internal OR gate which has its pin 3 output connected to pin 2. The amplifier is then shut down by feeding control signals to the pin 6 and pin 7 OR gate inputs. When either or both of these inputs are at a logic high, the amplifier is disabled. These control inputs are typically used to shut down the amplifier in situations where a set of headphones is plugged into a preceding stage. In this case, the control input is derived by switching in a suitable voltage via an internal switch in the headphone socket. Circuit details Refer now to Fig.2 for the final circuit details of the Mighty-Mite Powered Loudspeaker. In this circuit, the gain has been set to nine by the 100kΩ feedback and 22kΩ input resistors. This provides an input sensitivity of about 320mV for 1W output into eight ohms. In addition, a 6.8pF capacitor has been connected across the feedback path and this rolls off the high-frequency response above 230kHz to prevent instability. The incoming audio signal is applied to IC1 via volume control VR1 and a 1µF coupling capacitor. This coupling capacitor is necessary to prevent DC current from flowing through the 22kΩ input resistor and VR1. It rolls off the response below 7Hz. The 10µF capacitor decouples the half-supply rail at pins 5 & 14 to improve supply rejection and reduce the distortion below 100Hz. Note that pins 6 & 7 (the OR gate inputs) are tied low, while the OR gate output at pin 3 is tied to the shutdown input at pin 2. Because the OR gate output is always low in this design, the amplifier is permanently enabled. Finally, the power supply to IC1 is isolated using a ferr­ite bead and decoupled by a 47µF capacitor. This measure helps to reduce noise injection into the amplifier if it is powered from a 5V computer supply (a computer supply rail usually has a fair degree of hash and high frequency noise). This view shows the completed amplifier module. Note that the volume control potentiometer (VR1) is mounted by soldering its terminals to three PC stakes at one end of the board. Construction The Mighty-Mite is built onto a PC board coded 01305951 and measuring 33 x 25mm. Fig.3 shows the wiring details. Begin construction by installing PC stakes at the external wiring points; ie, at the loudspeaker outputs, the +5V and 0V supply inputs, and at the signal inputs. In addition, install PC stakes at the three wiring points for VR1. Once the PC stakes are in, IC1 can be installed. Because this is a surface-mount component, it is mounted on the copper side of the board. Before soldering IC1, the copper lands should be pretinned using a fine-tipped soldering iron. This done, place the IC on the board with the notch in its plastic body towards the 1µF capacitor position, then carefully tack solder a couple of pins to the pretinned lands by heating them gently with the iron. The pins can then all be carefully soldered. Be sure to use only small amounts of solder during this job, to prevent unwanted shorts between adjacent pins of the IC. In fact, it is a good idea to carefully inspect the completed job under a magnifying glass to ensure that all is correct. This close-up view shows the mounting details for the amplifier board. It sits 27mm above the floor of the case on two 9mm-long spacers which are screwed onto 25mm long x 3mm dia. mounting screws. Performance of Prototype Output power ����������������������������� 1.3W into 4Ω at onset of clipping; 1W into 8Ω at onset of clipping Distortion ����������������������������������� <1% see graphs Signal-to-noise ratio ������������������ 76dB with respect to 1W with 1kΩ input resistor & 20Hz to 20kHz bandwidth; 91dB A weighted Frequency response ������������������ -2dB at 10Hz & 100kHz Sensitivity for 1W out ���������������� 320mV RMS Supply voltage ��������������������������� 2.7-5.5V Quiescent current ���������������������� <15mA; typically 7mA Output offset voltage ����������������� <50mV August 1995  63 Building The Optional 5V Regulator Board BR1 B104 9-12VAC INPUT IN 470 25VW REG1 7805 GND OUT +5V 10 16VW 0V +5V REGULATOR I GO Fig.5: you will need this simple regulator circuit if you intend powering the unit from an AC or DC plugpack supply. BR1 The regulator board only takes a few minutes to assemble. Make sure that all parts are correctly oriented & use PC stakes at external wiring points. 470uF REG1 7805 9-12V AC INPUT 10uF HEATSINK GND 5V OUTPUT Fig.6(a): here’s how to install the parts on the regulator board. Note that REG1 is bolted to a small U-shaped heatsink. If you wish to power the unit from a 9-12VAC (or 9-12V DC) plugpack, then you will need to add the 5V regulator circuit shown in Fig.5. As shown, the output from the plugpack is fed to a bridge rectifier (BR1) and this in turn drives 3-terminal regulator REG1 to derive a regulated 5V rail. The 470µF and 10µF electrolytic capacitors provide filtering for the IN and OUT terminals of the regulator The LM4860 IC (IC1) is mounted on the copper side of the PC board as shown here. Use a fine-tipped soldering iron for this job & make sure that the device is correctly oriented. 64  Silicon Chip Fig.6(b): this is the full-size etching pattern for the regulator PC board. Check the board carefully before installing any parts. respectively. A PC board (code 01305952) has been designed to accommodate the regulator components – see Fig.6(a). Install the parts on this board exactly as shown and note that REG1 is bolted to a small finned heatsink to ensure adequate heat dissipation. Apply a thin smear of heatsink compound to the metal tab of the regulator before bolting it down. The remaining components mount on the top of the PC board. Take care with the electrolytic capacitors - they must be orient­ed with the correct polarity, as shown on Fig.3. The resistors mount end on, while L1 simply consists a short length of tinned copper wire fed through the ferrite bead. Finally, the board assembly can be completed by soldering VR1’s terminals to the top of the PC stakes. The completed amplifier, along with the loudspeaker, is housed in a sealed ABS box measuring 171 x 121 x 55mm. In no circumstances should you power the amplifier from a voltage greater than 5.5V. The audio amplifier chip could fail if you do. The 5V regulator board can either be mounted inside the case of the Mighty-Mite, or mounted in a separate case and used externally. Take care to ensure that the supply connec­tions to the amplifier board are correct. This box is fitted with three adhesive labels – two on the front panel and one on the rear. Fit these labels to the locations shown in the photographs, then drill mounting holes in the rear panel for the DC power socket and the RCA input socket. Similarly, on the front panel, drill a hole for the volume control shaft. Note that it’s best to start with a small pilot hole and then carefully enlarge the hole to the correct size using a tapered reamer. Once this has been done, mark out and drill the loudspeaker YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT Fig.7: this graph shows the distortion as a function of output power into an 8-ohm load. Note that the distortion is less than 1% for output powers up to 1W & rises steeply beyond this level of output. YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au Fig.8: distortion vs. output power into a 4-ohm load. The distortion is less than for 8-ohm loads, while slightly more output power (1.3W) can also be obtained. mounting holes plus a circular pattern of holes in front of the cone position to let the sound escape. Next, carefully measure out, mark and drill the mounting holes for the PC board in the base of the case. The PC board assembly is then installed in the case as shown in one of the photos. To do this, first fit two 25mm long x 3mm dia. screws to the mounting holes and secure them with nuts. A 9mm spacer is then fitted to each screw. Screw these spacers down until their top surfaces are 27mm above the base of the case, then fit the PC board and secure it to the spacers with 6mm long screws. YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 August 1995  65 Below: the input & DC power sockets are mounted on the rear panel. At left is the view inside the prototype. All that remains now is to run the small amount of internal wiring – see Fig.3. This consists of: (1) connecting the supply leads from the DC socket to the PC board; (2) running a short length of shielded cable from the RCA socket to the input termi­ nals; and (3) running a length of figure-8 cable from the board to the loudspeaker terminals.   Warning Unlike most multimedia loudspeakers, the MightyMite design does not include magnetic shielding. As a result, the strong magnetic field around the loudspeaker can cause colour distortion if placed too close to a monitor screen, due to magnetisation of the shadow mask. Usually, this problem will be cured by the internal de­gaussing circuitry of the monitor each time it is switched on. Severe cases, however, will require the use of a degaussing wand, which means a trip a professional service organisation. To avoid this problem, do not place the Mighty-Mite Powered Loudspeaker any closer than about 300mm from a monitor or TV set. Testing To test the unit, first connect a 5V DC supply to the DC socket, taking care to ensure that the polarity is correct. This done, switch on and check that the wire link through the ferrite bead is at +5V with respect to ground. If this is correct, check that the accessible lead of the 22kΩ resistor is at 2.5V (ie, half supply). The two loudspeaker terminals should also each be at 2.5V, give or take 50mV. If all checks out, then you are ready to try the Mighty-Mite out. This simply involves completing the case assem- VOLUME Fig.9: here are full-size artworks for the three labels plus a full-size etching pattern for the Mighty-Mite amplifier board. 66  Silicon Chip + MIN MAX Power supply As mentioned previously, the Mighty-Mite can be powered directly from a games or sound card port. Fig.4 shows the +5V and GND (0V) connections for these ports. You will need to make up a suitable power cable which is fitted at one end with a matching DB15 connector. Note that the +5V rail can be derived from pin 1, pin 8 or pin 9. Alternatively, you can assemble the optional 5V regulator board & power the unit from an AC or DC plugpack SC supply. 5VDC MAX. + MIGHTY-MITE bly, fitting the knob and feeding in a suitable signal from your computer’s sound card, or from some other suitable audio source (eg, a tuner or tape deck). + SIGNAL IN - + SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd 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 COMPUTER BITS BY GEOFF COHEN An easy way to identify IDE hard disc parameters Losing the CMOS setup in your computer is a real nuisance if you don’t have a copy of the hard disc drive parame­ters. Diskinfo.exe is a nifty little utility program that will automatically retrieve the required disc parameters for you. This article was written in response to an earlier article entitled “CMOS Memory Settings – What To Do If The Battery Goes Flat” (SILICON CHIP, May 1995). In that article, the author described how to re-enter a PC’s CMOS setup values if they were lost. One of the things emphasised in the original article was that all PC owners should keep a record of their hard disc drive parameters for just such an eventuality. Unfortunately, not all owners do that and the relevant information is not always at­tached to the drive unit. I have been designing electronic hardware, writing software and repairing PC problems for many years now, so having PCs crash on me is no novelty. As a full-time computer professional, there are two problems that have given me considerable hassles with PCs over the past few years. These problems are: (1) what to do if the CMOS crashes with a good battery; Fig.1: this screen grab shows the information returned by the program. As well as the number of cylinders, heads and sectors per track, it also includes the drive capacity, its model and serial numbers, the buffer size and the number of bytes per sector. 72  Silicon Chip and (2) finding out the hard disc type if you do not have easy physical access to the drive itself (eg, in laptop PCs), or if the details are not attached to the drive in the first place. Why does the CMOS crash? Let’s take a look at the CMOS memory problem first. In my experience, it is not always a flat battery that causes the CMOS to crash. In fact, some motherboards are prone to losing their CMOS setup when combined with certain power supplies. As a rule of thumb, if this happens with a good battery more often than once every two months, then it’s quite possible that there is a fault on the motherboard, in the power supply or, very occasionally, on a bus card. If this is occurring with your PC and it is still under warranty, you should return it to your supplier as soon as possi­ble. Some intermittent faults can take a long time to track down, since there are usually a lot of possible causes that have to be eliminated. However, if the fault is reported to the supplier before the warranty period expires, they have to fix the problem, even if the warranty period expires before the fault is finally rectified. I have also noticed that CMOS memory problems are more likely to occur in the “el cheapo” motherboard upgrades, although this problem is not as frequent as it once was. I usually find out about it after my customer has had their old “AT” or 386 PC upgraded to a 486 and then, after it fails, can’t get it fixed under warranty, as the “el cheapo” supplier is no longer in business. Just another example of Notes On The Operation Of DISKINFO.EXE Diskinfo.exe is a C utility program written by Geoff Cohen and Alan Vidler. It retrieves the IDE hard disc details from IBM (& compatible) AT, 386, 486 and Pentium PCs, independently of the state of the CMOS or BIOS. This is useful when the CMOS is incor­rect or has no hard disc details entered, as happens with a new motherboard. The Diskinfo.exe program uses the standard ATA (IDE) disc com­mand set, sending commands to and receiving status details and textual data from the ATA disc drive. I found a lot of useful details in AT attachment interface specifications ATA2-R3.DOC, which I downloaded from the Internet before we started writing Diskinfo.exe. Alan Vidler looked at the Linux hard disk I/O source code and did most of the initial design of the program. While the complete list of commands is too long to go into, the basic operation of Diskinfo.exe is: (1). Check if the drive is an IDE type & exit if not; (2). Send the Identify Drive command; (3). Receive the details, format & display on screen; (4). Repeat steps 1-3 for Drive 1 On a more detailed level, the program first checks if Drive 0 (ie, C:) is an ATA (or IDE) drive, by sending the command HD_CURRENT (0x1f6) to I/O port A0. It then waits 20ms, checks if the ready bit (0x40) is set, and exits if it isn’t. Next, it sends the identify drive (0x1f7) command to the I/O port, waits 20ms, then reads the information returned from the ATA disc drive and displays it on the screen. This complete procedure is then repeated for Drive 1 (ie, D:), the only difference being that the commands are sent to I/O port B0 instead of A0. In addition, the message “press any key for drive D Information” appears on the screen. It is also worth mentioning that this information can be sent to a file by redirecting the output. This is done by typing (at the A:> prompt): DISKINFO>FILENAME TANSTAAFL1, I guess (1there ain’t no such thing as a free lunch). Another less frequent cause of CMOS problems is the 240V mains power. In particular, mains spikes may propagate through the power supply to the CMOS while the computer is running. This can cause an error the next time the computer is switched on but usually the PC just hangs when the spike arrives. I always recommend fitting a mains spike suppressor for every PC installation. As far as I am concerned, mains spike suppressors are like chicken soup – they may help and they cer­ tainly won’t hurt. For network and small commercial systems, a UPS (uninterruptable power supply) is a must – at least for the server. If you write programs, another source of CMOS errors is the odd program crashing when you try to run it and then going haywire. Of course, this has never happened to me; well, would you believe hardly ever? When a program runs haywire, there is a low but finite probability that it will write odd characters all through your PCs memory and this can very easily put rubbish into the CMOS memory. C and Assembler are really good at this and I have even managed to get normally well-behaved compilers to crash the CMOS, but I really had to work at it. What hard disc is it? Now we get to the difficult part – finding out what type of hard disc is lurking under your PC’s cover when the CMOS thinks you don’t have a hard disc at all. In the past, I have nearly gone mad trying to find what the hard disc parameters were on a PC (ie, the number of heads, cylinders and sectors per track). This is even more difficult if my client is in another city, as I cannot personally open the case and have a look inside. Physically checking for hard disc information has become easier of late, with most manufacturers now printing the specifi­cations on a label attached to the top of the disc drive. Of course, this is no help if you own a disc drive that doesn’t have a specifications label. And even if the information is there, you still have to open your PC to inspect it. This can take a fair amount of time on some PCs, especially if the hard disc is buried in the drive bay beneath one of the floppy disc drives and has to temporarily be removed so that the label can be seen. When servicing older PCs, I have sometimes had to complete­ly remove the hard disc from the computer, just to discover the brand and model, and then try to find the details in assorted lists supplied (sometimes grudgingly) by the hard disc manufac­turers. Sometimes, even this didn’t provide an answer and I was forced to enter the most common hard disc values into the CMOS on a trial and error basis, sometimes spending hours on the more obscure models. Diskinfo.exe Fortunately, these trials are no longer necessary, as there are now some really nifty utilities around which will retrieve the hard disc parameters from a PC, even when the CMOS is com­ p letely cleared (non-computerese for trashed). I normally use one written by myself and Alan Vidler (of AV Software), which we have placed in the public domain. Called DISKINFO.EXE, it provides details on IDE drives. These form the overwhelming majority of the small to medium-capac­ity hard disc drives sold over the last few years. In operation, the program bypasses the system BIOS and accesses the drive (or drives) directly. The disc drive parameters are then displayed on the screen. Fig.1 shows the information returned by the program. As well as the number of cylinders, heads and sectors per track, it also includes the drive capacity, its model and serial numbers, the buffer size and the number of bytes per sector. Note, however, that the software will not work with SCSI drives or with some types of caching controllers and other non-standard controllers (even if they are controlling an IDE drive). If August 1995  73 How To Make A Bootable Diskinfo.Exe Floppy When you receive your copy of DISKINFO.EXE, you will need to copy it to a bootable floppy, so it can be used if your CMOS becomes corrupted as some later date. First, go to the DOS prompt, then put the disc containing DISKINFO.EXE in floppy disc drive A and copy it to drive C by typing: COPY A:DISKINFO.EXE C:\ (or COPY B:DISKINFO.EXE C:\ for drive B. When this has finished, remove the DISKINFO.EXE floppy disc and install the floppy disc that is to become your boot disc in drive A. Now, from the C:> prompt, type: FORMAT A:/S (or FORMAT A:/S/U for MS DOS 6). When this is complete, type: COPY C:\DISKINFO.EXE A: After this is completed, you can test that the boot disc functions correctly by rebooting the PC with this disc still in drive A. When the PC has booted up, you need to press <Enter> twice to get past the time & date questions. If you now type DISKINFO at the A:> prompt, the screen should display data simi­lar to that shown in Fig.1. It would, of course, be a good idea to write this informa­tion down now, rather than after the CMOS information is lost. I always write the hard disc parameters (number of heads, cylinders and sectors per track) on a self-adhesive label and stick it to the back of the PC. a non-supported controller is found, a reject message is displayed and the program exits. Alternatively, with some caching controllers, the program will display nonsense results and fail to show the Model Number, Firmware Revision number or Serial Number. In either case, this doesn’t cause any problems since the program cannot write to the disc or alter any of its parameters. Assuming that your CMOS has crashed, the procedure is to first restore all the CMOS settings (see the May 1995 article), except for the hard disc type. This should initially be left at “None” (sometimes called “Type 0” or “No Hard Disc”). Now return to the Main Menu of the CMOS Setup utility and carefully check the menu items. Many late-mod- el PCs have an option which will automatically fill in the hard disc numbers for you. This menu item is usually called “IDE HDD (Hard Disc Drive) Auto Detect”, or someting similar. If your PC has this option, then select it and press the <Enter> key. This will run a HDD auto detect utility and will write the correct hard disc details (number of heads, cylinders and sectors per track) into the CMOS memory. You then only need to return to the Main Menu of the CMOS Setup and save these corrected settings. The PC will now reboot with the hard disc running normally. If your PC does not have this option, you will need to boot the machine from a floppy disc containing the DISKINFO.EXE utility. When you run the utility (ie, type DISKINFO at the A:> prompt), it will show a screen similar to that shown in Fig.1. Note the number of cylinders, heads and sectors per track, then remove the floppy disc, reboot your PC and again proceed to the CMOS Setup screen. This is usually accomplished by pressing the <Del> key when prompted to do so, as described in the earlier article. Now go to the Standard CMOS Setup, select Hard Disc C Fig.2: most manufacturers now print the disc drive (sometimes called Hard parameters on an attached label. 74  Silicon Chip Disc 0) and select Type 47 (may also be called “User” or “User Defined”). As indicated by the legends at the bottom of the screen, you select the entries using the arrow keys and modify the entries using the Page Up and Page down keys. The hard disc parameters that you obtained from DISKINFO.EXE (and wrote down) are now entered. This is done by selecting the relevant heading and entering the appropriate value directly via the keyboard. These headings are: Cyl = number of cylinders; Head = number of heads; and Sect = number of Sectors per track. The other two hard disc entries are not critical. I usually enter 65535 for WPcomp (sometimes called Precomp) and 1024 for Lzone (sometimes called LandZone). The Setup screen should now show the correct hard disc size underneath the “Size” head­ing. All you need to do now is to return to the CMOS Setup’s Main Menu and save these new settings. Your computer should now boot normally from the hard disc drive, just as it used to before the CMOS setup was lost. As a final point, note that if you have a SCSI hard disc, you must always choose “Type 0” for this type of drive. I have received frantic calls from customers with SCSI hard discs, asking why their PC won’t boot up after they have restored (or changed) the CMOS Setup. Despite what is in the hard disc manual, they sometimes choose a “Type 47”, often because of a helpful friend who “knows all about computers” and thinks that a “Type 0” is incorrect. Of course, when they attempt to boot up the PC, it either hangs or gives a hard disc error message. The remedy is simple – just reset the hard disc to a Type 0. Obtaining DISKINFO.EXE The program DISKINFO.EXE is available for $10 (incl. p&p) from Silicon Chip Publications (see software advert), or directly from the Author at PO Box 136, Kippax, ACT, 2615. Alternatively, you can email me at gcohen<at>pcug.org.au for a copy via the Internet. I log on to the Internet daily, or via Compuserve at 100026,307 (but I only check here once a week). I am also available at any of these addresses for anyone who has problems that they SC can’t solve on their own. Do you want to know what 110dB of noise sounds like? Well now you can easily find out. This circuit puts out between 108dB and 111dB at a distance of about one metre. Build a 6-12V alarm screamer module There are many applications where a low-cost alarm siren is required. This very effective unit from DIY Electronics certainly makes a racket and could serve as the siren in a house alarm system, in a car, or in many industrial applications. For exam­ple, you could R1 1.5M 1 D1 1N4148 R2 1.5M 2 4 14 IC1a 7556 6 C1 0.1 RED R3 15k 5 10 7 C2 .01 T1 C3 10 9 C 1 13 12 R5 27k E C VIEWED FROM BELOW D2 1N4148 8 C4 .01 T2 V+ Q1 BC639 R6 B 1k R7 1k Q2 BC639 B E B C5 0.1 R4 27k V+ 2 PIEZO 1 IC1b 11 3 3 BLACK wire it to a door switch in your car via an exter­nal on/off switch to serve as an intruder alarm. As shown in the photographs, the unit is housed in a spe­cially-designed plastic case fitted with a mounting bracket (which also forms the rear RED 3 2 PIEZO 2 C 1 BLACK panel). Its overall dimensions are 84 x 55 x 33m (L x W x D), not including the mounting bracket. What’s so special about the case? Well, to make the unit as effective as possible, it features two integral resonant cavities for the two piezo transducers that are used to V+ generate the noise. The unit is +5-12V supplied with these two piezo transducers pre-glued to the resonant cavities – all you have 0V to do is assem­ ble a small PC board, connect a few leads and a power supply, and stand back to avoid being deafened. It is interesting to note that without the resonant cavi­ ties, the sound generated by the piezo transducers in open air is barely audible. It’s a completely different story with the reso­nant cavities, though. E T1 AND T2: WINDING 1-2 1500T, 44SWG ENCU WINDING 2-3 220T, 44SWG ENCU "SCREAMER" ALARM Fig.1: the circuit employs two oscillator stages based on IC1a & IC1b. IC1a frequency modulates IC1b which in turn drives two piezo elements via transistors Q1 & Q2 and autotransformers T1 & T2. How it works Refer now to Fig.1 for the circuit details. In addition to the piezo transducers, it’s mainly based on a dual 7556 timer IC, two transistors and a couple of autotransformers. IC1b is wired in astable August 1995  75 Electronic Projects For Cars FROM NEW N CHIP O SILIC On sale now at selected newsagents Or order your copy from Silicon Chip. Price: $8.95 (plus $3 for postage). Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. ➦ Use this handy form Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ 76  Silicon Chip The case is supplied with the two transducers glued to two internal resonant cavities. All you have to do is assemble the PC board, connect a few leads and apply power. configuration and oscillates at about the resonant frequency of the piezo transducers. This frequency is set by R4, R5, D2 & C4 and is about 2.7kHz. In order to produce a realistic siren sound, IC1a is used to frequency modulate IC1b at a low rate. It does this by apply­ing a triangular waveform voltage to IC1b’s control pin (pin 11). As with IC1b, IC1a functions as an astable oscillator but in this case its frequency of oscillation is only about 5Hz. Note that diodes D1 and D2 ensure that IC1a and IC1b both function with a 50% duty cycle. The output from IC1a appears at pin 5 and is a square wave. This is then converted to a triangular wave by R3 & C3 before being applied to pin 11 of IC1b. As a result, IC1b produces a modulated output at its pin 9 which constantly sweeps back and forth through the resonant frequency of the piezo elements. As well as modulating the frequency to produce a siren sound, this technique means that no trimpot is required for frequency cali­bration. The pin 9 output from IC1b drives transistors Q1 and Q2 with the modulated 2.7kHz signal. Note that these two transistors are driven in phase. Q1 in turn drives piezo 1 via auto­ transform­er T1, while Q2 drives piezo 2 via autotransformer T2. In greater detail, each time the transistors turn on, cur­rent flows in the 220-turn winding of each auto­ trans­former. Con­versely, each time the transistors turn off, the magnetic field in these windings collapses and this induces a much higher signal in the 1500-turn windings. As a result, the autotransformers significantly step-up the signal voltage that’s used to drive the piezo transducers. In fact, a potential of over 200V is PIEZO 1 PIEZO 2 3 2 1 0V V+ T1 0.1 D1 1 2 3 .01 0.1 1k 27k 27k 1 IC1 7556 1.5M 1.5M .01 15k 1k Q1 D2 10uF T2 Q2 Fig.2: follow this wiring diagram when installing the parts on the PC board and take care to ensure that the two autotransformers are correctly oriented (see text). The photograph at right shows how the PC board is installed in the case. induced which can give you quite a shock if you are careless enough to touch the auto­transformer leads or the transducer terminals. This also means that the piezo elements are overdriven and this has been done deliberately to give maximum noise output. This causes no harm to the piezo elements and test circuits have been run for several hours at a time without component failure. Power for the circuit can come from any 5-12V DC source; eg, batteries or a 9V DC plugpack supply. Do not use a 12V DC plugpack as this could deliver more than 16V when lightly loaded. Assembly The parts for the Screamer Alarm are all installed on a small PC board measuring 78 x 48mm. This board features screened lettering to show where all the parts go and should only take about 10 minutes to assemble. Fig.2 shows the assembly details. Install the resistors first, followed by the two diodes and all the capacitors. Take care to ensure that the diodes and the 10µF electrolytic capaci­tor are installed with the correct polarity. The remaining ca­pacitors can be installed either way ar­ound. Next, install the two transistors and the IC socket. The IC can then be plugged into the socket, taking care to ensure that the notch in the IC body goes towards the 0V & V+ supply termi­nals (ie, pin 1 must be adjacent to the two 1.5MΩ resistors). Pin 1 will also generally be indicated by an adjacent dot in the IC body. Now complete the board assembly PARTS LIST 1 case with two piezo elements plus 4 screws 1 PC board (DIY Kit 15) 1 16-pin IC socket 2 autotransformers 2 150mm-lengths of hook-up wire (red, green) Semiconductors 1 GLC556, 7556 dual CMOS timer (IC1) 2 BC639 NPN transistors (Q1,Q2) 2 1N4148 diodes (D1,D2) Capacitors 1 10µF 16VW electrolytic 2 0.1µF monolithic 2 .01µF greencap Resistors (0.25W, 5%) 2 1.5MΩ 1 15kΩ 2 27kΩ 2 1kΩ Where to buy the kit A complete kit of parts for the 12V Screamer Alarm (DIY Kit 15) is available from: DIY Electronics, 22 MacGregor St, Nu­murkah, Vic 3636. Phone (058) 62 1915. The price is $23.50 plus $3.50 p&p. by installing the two auto­transformers (T1 & T2). These are oriented in opposite directions to each other and must have their leads bent through 90 degrees so that they lie flat against the PC board. Note that in each case, the centre terminal must be towards the top of the device (see photo). Two “tie-down” pads have been provided next to the body of each autotransformer and you can loop wire links over the auto­transformers at these locations. In practice, the leads on the autotransformers will usually be strong enough to stop them from moving. Finally, solder the six leads to the PC board at the desig­nated locations. There are two each for the piezo transducers (red to positive, black to negative), plus two more for the power supply connections. This done, the board can be mounted upside down inside the case, with the supply leads exiting from the notch, and the cover secured using the screws supplied. Testing Before applying power, wrap the unit in a towel to muffle the sound level (so that you won’t be deafened). After that, all you have to do is connect the power supply and the unit should immediately start. It’s best to start with a supply of about 5V and then test the unit at higher supply voltages – up to 12V. Exercise caution, though – this unit puts out ear-splitting sound, so keep it well wrapped up. If the unit doesn’t work, the most likely reason is poor soldering. Check all solder joints carefully under a good light and reheat any that appear suspect (disconnect the power supply before starting work). Next, check that all the parts are in their correct locations and that the IC, electrolytic capacitor, tran­sistors and autotrans­formers are all correctly oriented. If only one piezo transducer works, then check the transis­tor and auto­ trans­ f ormer associated with the SC non-functioning transducer. August 1995  77 NICS O R T 2223 LEC PC CONTROLLED PROGRAMMABLE POWER SWITCH MODULE This module is a four channel programmable W 0 S 1 N 9 , driver for high power relays. It can be used in 7 y le 70 any application which requires algorithm control 9, Oat Fax (02) 5 rd 8 a x C o for high power switching. This module can work Visa PO B 579 4985 as a programmable power on/off switch to limit fax a rd , ) & C 2 0 e ( r unauthorised access to equipment where the n e e o t n s h : o s a p r h P access to use or change parameters is critical. , M ith rde d o w r a d d c e This module can also be used as a universal B a n k x accepte most mix 0. Orders timer. The timer software application is ine r 1 o m $ f A ) cluded with the module. Using this software l i P a & & m r the operator can program the on/off status (ai s. P t r Z e e N n d . r ; of four independent devices in a period of o rld $10 o w 4 $ <at> a week within an accuracy of 10 minutes. . tley a Aust o : The module can be controlled through L I A M the Centronics or RS232 port. The computer is opto by E isolated from the unit, to ensure no damage can occur to the computer. Although the relays included are designed for 240V operation, they have not been approved by the electrical LEARNING - UNIVERSAL REMOTE CONTROL authorities for attachment to the mains. Power consumption These Learning IR Remote Controls can be used to replace is 7W. Main module: 146 x 53 x 40mm. Display panel: 146 up to eight dedicated IR Remote Controls: $45 x 15mm. We supply: two fully assembled and tested PCBs (main plus control panel), four relays (each with 3 x 10A / NEW CATALOGUE AT OUR WEB SITE 240V AC relay contacts), and software on 3.5" disk. We do We have combined efforts with DIY ELECTRONICS (a Hong not supply a casing or front panels. Kong based company) in producing a WEB SITE on the $92 (Cat G20) INTERNET. At this site you can view and download a text version of both of our latest catalogues and other up to date 3.5 DIGIT LCD PANEL METER information. Email orders can also be placed through here. 200mV full scale input sensitivity, “1999” count, 9 to 12V The combined effort means that you get offered an extensive <at> 1mA operation, decimal point selectable (with jumper range of over 200 high quality, good value kits, and many wire), 13mm figure height, auto polarity indicator, overrange more interesting components and items. The range of kits indication, 100Mohm input resistance, 0.5% accuracy, 2 to offered includes simple to more advanced kits, and they cover 3 readings per second. With bezel and faceplate. Dimensions: a very wide field of applications: educational, experimental, 68 x 44mm. Use in instrumentation projects. EPROM, microprocessor, computer, remote control, high $27 (Cat D01) voltage, gas and diode lasers, night vision etc. We’ll leave it to you to do the exploring at: CCD CAMERA-VCR SECURITY SYSTEM http://www.hk.super.net/~diykit This kit plus ready made PIR detector module and “learning You can also request us to send you a copy of our FREE remote control” combination can trigger any domestic IR catalogue with your next order. remote controlled VCR to RECORD human activity within a 6M range and with an 180 deg. angle of view!. Starts HELIUM-NEON LASER BARGAIN VCR recording at first movement and ceases recording Helium neon 633nM red laser heads (ie tubes sealed in a few minutes after the last movement has stopped; just a tubular metal case with an inbuilt ballast resistor) that like commercial CCD-VIDEO RECORDING systems costing were removed from equipment that is less than 5 years thousands of dollars!! CCD camera not supplied. No conold. These are suitable for light shows. Output power is in nection is required to your existing domestic VCR as the the range of 2.5-7.5mW. Heads are grouped according to system employs an “IR learning remote control”: $90 for output power range. Dimensions of the head are 380mm an PIR detector module, plus control kit, plus a suitable long and 45mm diameter. Weight: 0.6kg. A special high “lR learning remote” control and instructions: $65 when voltage supply is required to operate these heads. With purchased in conjunction with our CCD camera. Previous each tube we will include our 12V universal laser power CCD camera purchasers may claim the reduced price with supply kit MkIV (our new transformers don’t fail). Warning: proof of purchase. involves high voltage operation at a very dangerous energy level. SUPER SPECIAL: FLUORESCENT LIGHTING SPECIAL $80 for a 2.5-4.0mW tube and supply. (Cat L01) A 12V-350V DC-DC converter (with larger MOSFETS) plus a $130 for a 4.0-6.5mW tube and supply. (Cat L02) dimmable mains operated HF ballast. This pair will operate a This combination will require a source of 12V <at> at least 32-40W fluorescent tube from a 12V battery: very efficient. 2.0A. A 12V gel battery or car battery is suitable, or if 240V See June 95 EA: $36 for the kit plus the ballast. operation is required our Wang computer power supply (cat number P01) is ideal. Our SPECIAL PRICE for the Wang power STEREO SPEAKER SETS supply when purchased with matching laser head/inverter A total of four speakers to suit the making of two 2-way kit is an additional $10. speakers (stereo). The bass-midrange speakers are of good quality, European made, with cloth surround, as used in LASER WARNINGS: upmarket stereo televisions, rectangular, 80 x 200mm. The 1. Do not stare into laser beams; eye damage will result. tweeters are good quality cone types, square, 85 x 85mm. 2. Laser tubes use high voltage at dangerous energy levels; Two woofers and two tweeters: $16. be aware of the dangers. 3. Some lasers may require licensing. NEW: PHOTOGRAPHIC KITS SLAVE FLASH: very small, very simple, very effective. ARGON-ION HEADS Triggers remote flashes from camera’s own flash to fill in Used Argon-Ion heads with 30-100mW output in the blueshadows. Does not false trigger and it is very sensitive. Can green spectrum. Head only supplied. Needs 3Vac <at> 15A even be used in large rooms. PCB and components kit: $7. for the filament and approx 100Vdc <at> 10A into the driver SOUND ACTIVATED FLASH: adapted from ETI Project circuitry that is built into the head. We provide a circuit for a 514. Adjustable sensitivity & delay enable the creation suitable power supply the main cost of which is for the large of some fascinating photographs. Has LED indicator that transformer required: $170 from the mentioned supplier. makes setting up much easier. PCB, components, plus Basic information on power supply provided. Dimensions: microphone: $13. 35 x 16 x 16cm. Weight: 5.9kg. 1 year guarantee on head. Price graded according to hours on the hour meter. SINGLE CHANNEL UHF WITH CENTRAL LOCKING Argon heads only, 4-8 thousand hours: $350 (Cat L04) Our single channel UHF receiver kit has been updated to Argon heads only, 8-13 thousand hours: $250 (Cat L05) provide provision for central locking!! Key chain Tx has SAW resonator locked, see SC Dec 92. Compact receiver GEIGER COUNTER AND GEIGER TUBES has prebuilt UHF receiver module, and has provision for two These ready made Geiger counters detect dangerous Beta and extra relays for vehicle central locking function. Kit comes Gamma rays, with energy levels between 30keV and 1.2MeV. with two relays. $36. Additional relays for central locking $3 Audible counts output, also a red LED flashes. Geiger tube ea. Single ch transmitter kit $18. unplugs from main unit. To measure and record the value of nuclear radiation level the operator may employ a PC which is MASTHEAD AMPLIFIER SPECIAL connected to the detector through the RS232 interface. This High performance low noise masthead amplifier covers gives a readout, after every 8 counts, of the time between each VHF-FM UHF and is based on a MAR-6 IC. Includes two count. Main unit is 70 x 52 x 35 mm. Geiger tube housing PCBs, all on-board components. For a limited time we will unit is 135mm long and is 20mm diameter. Power from 12 also include a suitable plugpack to power the amplifier from to 14V AC or DC. mains for a total price of: $75 (Cat G17) $25 EY OATL E 78  Silicon Chip CCD CAMERA Very small PCB CCD Camera including auto iris lens: 0.1Lux, 320K pixels, IR responsive, has 6 IR LEDs on PCB. Slightly bigger than a box of matches!: $180 VISIBLE LASER DIODE KIT A 5mW/670nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept 94 EA). UNBELIEVABLE PRICE: $40 Suitable case and battery holder to make pointer as in EA Nov 95 $5 extra. 12V-2.5 WATT SOLAR PANEL KITS These US made amorphous glass solar panels only need terminating and weather proofing. We provide clips and backing glass. Very easy to complete. Dimensions: 305 x 228mm, Vo-c: 18-20V, Is-c: 250mA. SPECIAL REDUCED PRICE: $20 ea. or 4 for $60 A very efficient switching regulator kit is available: Suits 12-24V batteries, 0.1-16A panels, $27. Also available is a simple and efficient shunt regulator kit, $5. SOLID STATE “PELTIER EFFECT” DEVICES We have reduced the price of our peltiers! These can be used to make a solid state thermoelectric cooler/heater. Basic information supplied: 12V-4.4A PELTIER: $25 We can also provide two thermal cut-out switches, and a 12V DC fan to suit either of the above, for an additional price of $10. BATTERY CHARGER Simple kit which is based on a commercial 12 hour mechanical timer switch which sets the battery charging period from 0 to 12 hrs. Timer clock mechanism is wound-up and started by turning the knob to the desired time setting. Linear dial with 2 hrs timing per 45 degrees of rotation, eg, 270 deg. rotation for 12 hr. setting. The contacts on the timer are used to switch on a simple constant current source. Employs a power transistor and 5 additional components. Can easily be “hard wired”. We supply a circuit, a wiring diagram, and tables showing how to select the charging current: changing one resistor value. Ideal for most rechargeable batteries. As an example most gel cells can be charged at a current which is equal to the battery capacity rating divided by 5-10. Therefore if you have a discharged gel cell that has 5Ah capacity and are using a charge current of 0.5A, the timer should be set for about 10 hours: Or 5hrs. <at> 500mA. This circuit is suitable for up to approximately 5A, but additional heatsinking would be required at currents greater than 2A. Parts and instructions only are supplied in this kit. Includes a T-03 mini fin heatsink, timer switch, power transistor and a few other small components to give you a limited selection of charge current. You will also need a DC supply with an output voltage which is greater by about 2V than the highest battery voltage you need to charge. As an example a cheap standard car battery charger could be used as the power source to charge any chargeable battery with a voltage range of 0-15V: $12 (K72) COMPUTER CONTROLLED STEPPER MOTOR DRIVER KIT This kit will drive two 4, 5, 6 or 8 wire stepper motors from an IBM computer parallel port. The motors require a separate power supply (not included). A detailed manual on the computer control of motors plus circuit diagrams and descriptions are provided. Software is also supplied, on a 3.5" disk. PCB: 153 x 45mm. Great low cost educational kit. We provide the PCB and all on-board components kit, manual, disk with software, plus two stepper motors of your choice for a special price. Choose motors from M17/M18/M35. $44 (K21) Kit without motors is also available: $32 MOTOR SPEED CONTROLLER PCB Simple circuit controls small DC powered motors which take up to around 2 amps. Uses variable duty cycle oscillator controlled by trimpot. Duty cycle is adjustable from almost 0-100%. Oscillator switches P222 MOSFET. PCB: 46 x 28mm. $11 (K67) For larger power motors use a BUZ11A MOSFET: $3. FM TX MK 3 This kit has the most range of our kits (to around 200m). Uses a pre-wound RF coil. The design limits the deviation, so the volume control on the receiver will have to be set higher than normal. 6V operation only, at approx 20mA. PCB: 46 x 33mm: $18 (K33) LOW COST IR ILLUMINATOR Illuminates night viewers or CCD cameras using 42 of our 880nm/30mW/12 degrees IR LEDs. Power output (and power consumption) is variable, using a trimpotentiometer. Operates from 10 to 15V and consumes from 5mA up to 0.6A (at maximum power). The LEDs are arranged into 6 strings of 7 series LEDs with each string controlled by an adjustable constant current source. PCB: 83 x 52mm: $40 (K36) VHF MODULATOR FOR B/W CAMERAS (To be published, EA) Simple modulator which can be adjusted to operate between about channels 7 and 11 in the VHF TV band. This is designed for use in conjunction with monochrome CCD cameras to give adequate results with a cheap TV. The incoming video simply directly modulates the VHF oscillator. This allows operation with a TV without the necessity of connecting up wires, if not desired, by simply placing the modulator within about 50cm from the TV antenna. Suits PAL and NTSC systems. PCB: 63 x 37mm: $12 (K63) SOUND FOR CCD CAMERAS/UNIVERSAL AMPLIFIER (To be published, EA). Uses an LM386 audio amplifier IC and a BC548 pre-amp. Signals picked up from an electret microphone are amplified and drives a speaker. Intended for use for listening to sound in the location of a CCD camera installation, but this kit could be used as a simple utility amplifier. Very high audio gain (adjustable) makes this unit suitable for use with directional parabolic reflectors etc. PCB: 63 x 37mm: $10 (K64) LOW COST 1 to 2 CHANNEL UHF REMOTE CONTROL (To be published, SC) A single channel 304MHz UHF remote control with over 1/2 million code combinations, which also makes provision for a second channel expansion. The low cost design has a 2A relay contact output. The 1ch transmitter (K41) can be used to control one channel of the receiver. To access the second channel when another transmitter is purchased, the other transmitter is coded differently. Alternatively, the 3ch transmitter kit (K40) as used with the 4ch receiver kit is compatible with this receiver and allows access to both channels from the one transmitter. Note that the receiver uses two separate decoder ICs. This receiver operates from 10 to 15Vdc. Range is up to about 40m. 1ch Rx kit: $22 (K26) Expansion components (to convert the receiver to 2 channel operation; extra decoder IC and relay): $6 ONE CHANNEL UHF TRANSMITTER AX5326 encoder. Transmit frequency adjustable by trimcap. Centred around 304MHz. Powered from 12V lighter battery. LED flashes when transmitting. Size of transmitter case: 67 x 30 x 13 mm. This kit is trickier to assemble than the 3ch UHF transmitter: $11 (K41) THREE CHANNEL UHF TRANSMITTER The same basic circuit as the 1ch transmitter. Two buttons, allows up to 3 channel operation. Easier to assemble than the 1ch transmitter and has slightly greater range. Size of transmitter case: 54 x 36 x 15mm: $18 (K40) ULTRASONIC RADAR Ref: EA Oct 94. This unit is designed to sound a buzzer and/or operate a relay when there is an object at a preset distance (or less) away. The distance is adjustable from 200mm to around 2.5 metres. Intended as a parking aid in a car or truck, also may be used as an aid for the sight impaired, warning device when someone approaches a danger zone, door entry sensor. PCB: 92 x 52mm. PCB, all on-board components kit plus ultrasonic transducers (relay included): $22 (K25) Optional: buzzer $3, plastic box $4. SIREN USING SPEAKER Uses the same siren driver circuit as in the “Protect anything alarm kit”, kit number K18. 4" cone/8 ohm speaker is included. Generates a really irritating sound at a sound pressure level of 95dB <at> 1m. Based around a 40106 hex Schmitt trigger inverter IC. One oscillator modulates at 1Hz another oscillator, between 500Hz and 4KHz. Current consumption is about 0.5A at 12V. PCB: 46 x 40mm. As a bonus, we include all the extra PCBs as used in the “Protect anything alarm kit”. $12 (K71) PLASMA BALL Ref: EA Jan 94. This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. The EHT circuit is powered from a 12V to 15V supply and draws a low 0.7A. Output is about 10kV AC peak. PCB: 130 x 32mm. PCB and all the on-board components (flyback transformer included), and the instructions: $28 (K16) We do not supply the standard light bulb or any casing. The prototype supply was housed in a large coffee jar, with the lamp mounted on the lid. Hint: connect the AC output to one of the pins on a fluorescent tube or a non-functional but gassed laser tube. Large non-functional laser tube or tube head: $10 ELECTROCARDIOGRAM PCB + DISK The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 (K47) TOMINON HIGH POWER LENS These 230mm (1:4.5) lens have never been used. They contain six coated glass lenses, symmetric, housed in a black aluminium case. Scale range is from 1:10 through to 1:1 to 10:1. Weight: 1.6kg. Applications include high quality image projection at macro scales, and portrait photography in large formats: $45 (Cat O14) PROJECTION LENS Brand new, precision angled projection lens. Overall size is 210 x 136mm. Weight: 1.3kg. High-impact lexan housing with focal length adjustment lever. When disassembled, this lens assembly yields three 4" diameter lenses (concave, convex-concave, convex-convex). Limited quantity: $35 (Cat O15) INTENSIFIED NIGHT VIEWER KIT Reference article: Silicon Chip Sept 94. See in the dark! Make your own 3 stage first generation night scope that will produce good vision in starlight illumination! Uses 3 of the above fibre optic tubes bonded together. These tubes have superior gain and resolution to Russian viewers. 25mm size tube only weighs 390g. 40mm size tube only weighs 1.1kg. We supply a three stage fibre optically coupled image intensifier tube, EHT power supply kit which operates from 6 to 12V, and sufficient plastics to make a monocular scope. The three tubes are already bonded together: $270 for the 25mm version (Cat N04) $300 for the 40mm version (Cat N05) We can also supply a quality Peak brand 10x “plalupe” for use as an eyepiece which suits all the above 25 and 40mm windowed tubes well: $18 35mm camera lenses or either of the Russian objective lenses detailed under “Optical” suit these tubes quite well. IR “TANK” TUBE/SUPPLY KIT These components can be the basis of a very responsive infra red night viewer; the exact construction of which we leave up to you. The new IR tube is as used in older style military tank viewers. The tube employed is probably the most sensitive IR responsive tube we have ever supplied. Responds well even to 940nm LED illumination. The resultant viewer requires IR illumination, as without this it will otherwise only “see” a little bit better than the naked eye. Single tube, first generation. Screen diameter: 18mm. Tube length 95mm. Diameter: 55mm. Weight: 100g. Tube can be operated up to about 15kV. Our miniature night viewer power supply (kit number K52) is supplied with its instructions included. Only very basic ideas for construction of viewer is provided. Tube and the power supply kit only: $80 (Cat N06) RUSSIAN SCOPE KIT Our hybrid Russian/Oatley kit design makes this the pick of the Russian scopes in this price range! We supply a fully assembled Russian compact scope housing containing the intensifier tube, adjustable eyepiece and objective lens. Housing is made from aluminium. The objective lens is fixed in focus, but it is adjustable after loosening a grub screw. We also include the night viewer power supply kit (kit number K52) and a small (84 x 55 x 32mm) jiffy box to house the supply in. The box must be attached by you to the scope housing. Operates from a 9V battery. This scope has a useful visible gain but is difficult to IR illuminate satisfactorily. Length of scope is 155mm: $290 (Cat N07) LASER POINTER A complete brand new 5mW/670nM pointer in a compact plastic case (75 x 42 x 18mm) with a key chain. Features an automatic power control circuit (APC) which is similar to our kit number K35 & our laser diode module’s circuit. Battery life: 10 hours of operation. Powered by two 1.5V N type batteries (included). This item may require licensing: $80 (Cat L08) MAGNETIC CARD READER Commercial cased unit that will read some information from most plastic cards, needs 8 to 12V DC supply such as a plugpack. Draws about 400mA. Power input socket is 2.5mm DC power type. Weight: 850g. 220 x 160 x 45mm: $70 (Cat G05) 400 x 128 LCD DISPLAY MODULE - HITACHI These are silver grey Hitachi LM215 dot matrix displays. They are installed in an attractive housing. Housing dimensions: 340 x 125 x 30mm. Weight: 1.3kg. Effective display size is 65 x 235mm. Basic data for the display is provided. Driver ICs are fitted but require an external controller. New, unused units. $25 ea. (Cat D02) 3 for $60 VISIBLE LASER DIODE MODULES Industrial quality 5mW/670nM laser diode modules. Consists of a visible laser diode, diode housing, driver circuit, and collimation lens all factory assembled in one small module. Features an automatic power control circuit (APC) driver, so brightness varies little with changes in supply voltage or temperature. Requires 3 to 5V to operate and consumes approx 50mA. Note: 5V must not be exceeded and there must be no ripple on the power supply, or the module may be instantly destroyed. These items may require licensing. We have two types: 1. Overall dimensions: 11mm diameter by 40mm long. Driver board is heatshrinked onto the laser housing assembly. Collimating lens is the same as used in the above laser pointer, and our visible laser diode kit: $55 (Cat L09) 2. Overall dimensions: 12mm diameter by 43mm long. Assembled into an anodised aluminium casing. This module has a superior collimating optic. Divergence angle is less than 1milliradian. Spot size is typically 20mm in diameter at 30 metres: $65 (Cat L10) This unit may also be available with a 635nm Laser Diode fitted. FLUORESCENT LIGHT HIGH FREQUENCY BALLASTS European made, new, “slim line” cased, high frequency (HF) electronic ballasts. They feature flicker free starting, extended tube life, improved efficiency, no visual flicker during operation (as high frequency operation), reduced chance of strobing with rotating machinery, generate no audible noise and generate much reduced radio frequency interference compared to conventional ballasts. The design of these appears to be similar to the one published in the October 1994 issue of Silicon Chip magazine, in that a high frequency sine wave is used, although these are much more complex. Some models include a dimming option which requires either an external 100K potentiometer or a 0-10V DC source. Some models require the use of a separate filter choke (with dimensions of 16 x 4 x 3.2cm); this is supplied where required. We have a limited stock of these and are offering them at fraction of the cost of the parts used in them! Type A: 1 x 16W tube, not dimmable, no filter, 44 x 4 x 3.5cm: $20 Type B: 1 x 16W tube, dimmable, filter used, 43 x 4 x 3cm: $26 Type C: 1 x 18W tube, not dimmable, no filter, 28 x 4 x 3cm: $20 Type D: 2 x 32W or 36W tubes, dimmable, no filter, 43 x 4 x 3cm: $26 Type E: 2 x 32W tubes, not dimmable, no filter, 44 x 4 x 3.5cm: $22 Type F: 1 x 32W or 36W tube, not dimmable, no filter, 34 x 4 x 3cm: $20 Type G: 1 x 36W tube, not dimmable, filter used, 28 x 4 x 3cm: $20 Type H: 1 x 32W or 36W tube, dimmable, filter used, 44 x 4 x 3.5cm: $20 (Cat G09, specify type). CYCLE/VEHICLE COMPUTERS BRAND NEW SOLAR POWERED MODEL! Intended for bicycles, but with some ingenuity these could be adapted to any moving vehicle that has a rotating wheel. Could also be used with an old bicycle wheel to make a distance measuring wheel. Top of the range model. Weather and shock resistant. Functions: speedometer, average speed, maximum speed, tripmeter, odometer, auto trip timer, scan, freeze frame memory, clock. Programmable to allow operation with almost any wheel diameter. Uses a small spoke-mounted magnet, with a Hall effect switch fixed to the forks which detects each time the magnet passes. Hall effect switch is linked to the small main unit mounted on the handlebars via a cable. Readout at main unit is via an LCD display. Main unit can be unclipped from the handlebar mounting to prevent it being stolen, and weighs only 30g. Max speed reading: 160km/h. Max odometer reading: 9999km. Maximum tripmeter reading: 999.9km. Dimensions of main unit: 64 x 50 x 19mm: $32 (Cat G16) August 1995  79 VINTAGE RADIO By JOHN HILL A couple of odd repairs I recently had two radio receivers to repair for a collector &, in each case, there were unusual problems. Both radios were small post-war 4-valve bakelite cabinet types – one a Kriesler & the other a little Philips Philipsette. Now some people make it difficult for repairers in that they tinker with things before they take it to someone to fix. I know this to be a fact for I have done so myself from time to time and I'm sure that I'm not the only one to do so. It is, therefore, only fair that someone has now done it to me. In the case of the Kriesler radio, the owner had removed a component and lost it. What's more, this component was supposed to be a fairly mysterious one, being described as, "about so long, as thick as a finger, hollow and burnt black". It was its blackened colour that prompted the owner to remove it because it must have been the problem. However, even when the charred part was removed, it was still unidentifiable and what to replace it with was a mystery. Whether it was a resistor, a capacitor or some other component neither he (nor I at that stage) had any idea. There was one consolation, however. The position from which the strange component had been removed had been marked. When I finally started working on the set, it was quite obvious what the missing part was. It was positioned between the two positive contacts of a twin high-voltage electrolytic capacitor and could only be a high tension filter resistor. Yet it was not the usual setup. It would appear that the missing resistor was a high wattage wirewound type because all the current from the rectifier flowed through it before anything was connected to the high tension supply. By contrast, in most small 4-valve receivers, the high tension for the output valve comes from the input side of the filter and a one or two-watt carbon resistor is used in conjunction with a second electrolytic capacitor on the output side to supply the other valves. The value of the missing resistor could only be guessed at. Something around 5kW and 10W was used as a starting point. It did little to bring the set back to life. Voltage checks This photo shows the 4-valve Kriesler that had the missing component. It also had other problems – mainly faulty paper capacitors. 80  Silicon Chip As nothing seemed to be self-destructing, I did a few quick checks with the voltmeter. There was around 240V on the input side of the filter resistor but less than 100V on the output side. A 1kW resistor was substituted with very little difference in output voltage. In this set, A 30kW resistor connected to the output side of the filter applies high tension to the screen grid of the IF amplifier valve. This screen resistor had about 100V on one side and zero volts the other. Based on this evidence, it looked like the resistor was open circuit. Wrong! – when the resistor was removed, it checked out well within tolerance and was replaced from whence it came. So where to from here? This particular screen connection on the IF valve also applies voltage to the 6AN7 frequency converter valve via a connecting lead. When this lead was disconnected, the screen grid on the IF valve suddenly had voltage applied to it. By this stage of the proceedings, the fault was fairly obvious – a short circuit at the point where the screen voltage of the IF valve is applied to the 6AN7 frequency converter socket. As the socket connection at that point had a 0.05µF bypass capacitor to chassis, it seemed likely that this component could be faulty – and it was. After disconnecting the suspect capacitor (an original paper capacitor I might add), it was found to have a complete short circuit. Replacing this faulty capacitor restored the set to working order once again. But although the set was now working, the high tension voltage was still only 150V at the output side of the filter. This small Philips 4-valve receiver is a mighty performer for its size. It had a number of problems, including a faulty valve, faulty capacitors & power transformer faults. Capacitor checks So far only two components had been replaced: the filter resistor and the faulty screen bypass capacitor. All the remaining paper capacitors were originals and it seemed that they too could be a little suspect. Checking the capacitors with a voltmeter revealed that three of them had high tension voltages across them and these were replaced with modern polyester equivalents. This step saw the high tension voltage rise to 210V. The remaining paper capacitors were all replaced with 100V greencaps. Looking back, I don't suppose there was anything really spectacular about this particular repair. It was fairly routine and systematic as it followed the trail from the missing resistor to the shorted paper capacitor, then onto the other leaky capacitors. It does show, however, that one must look beyond the broken down component and locate the real cause of the problem. The real fault in the old Kriesler was four ailing capacitors, not the obvious overloaded resistor. A short-circuited 0.5µF capacitor was one of the problems encountered with the Kriesler repair. The routine replacement of paper capacitors can automatically solve many obscure receiver faults. The final touch to the Kriesler repair was an alignment check. This was most essential as the adjustment slugs in the aerial and oscillator coils were many turns out, thus displacing the tuning to a considerable degree. The Philips receiver Next was the little Philips Philipsette and what a great receiver they were for their size. This one looked a bit of a wreck though; it was very dirty and had no control knobs on it. The missing knobs could be a problem as they are special little red ones that are unique to this particular receiver. I was fairly sure that I had no spares. My concern about the knobs was unfounded. On withdrawing the chassis August 1995  81 electrolytic. The latter looked particularly bad, as the seals at the positive ends were ruptured and split. Despite their appearance, they seemed to be working all right but, of course, they were all replaced. Replacing the paper capacitors cured the distortion problem. The exact fault may have been a leaky coupling capacitor to the grid of the output valve. A leaky capacitor in this position is bound to cause distortion. The high tension voltage rose 20V after the capacitor job was finished. By the way, the term "high tension" is relative when referring to one of these little Philips receivers. The rectifier, a 6V6GT, operates with only about 110V on the plate compared to a typical plate voltage of 250V. A completely dead ECH35 valve and a few sick capacitors were all that prevented the Philipsette from working. The power transformers used in many Philips & Mullard receivers share this common fault – an exposed high tension winding. The winding protrudes outside the paper insulation that separates the layers (probably caused by the paper shrinking with age). This is not the transformer used in the Philipsette in the story but a similar one in worse condition, to show the problem more clearly. from the cabinet, two red knobs fell to the floor. They had been loose inside, rolling around on top of the chassis. Why they hadn't been lost is a miracle. Valve problem The little Philips had a valve problem – the ECH35 frequency converter was very dead in the heater department and needed replacing. The remaining three valves tested OK. 82  Silicon Chip Removing the dirt and grime from the chassis was next, then the valves were refitted for a quick try out. Within 15 seconds from switch on, the set burst into life. But working and working well are two different things. The sound was harsh and distorted and it became worse as the volume was increased. Like the previously mentioned Kriesler, the Philipsette had all of its original capacitors, both paper and Alignment OK These neat little radios are sods of things to align because all of the adjustments are made with those rotten-to-work-with Philips trimmer capacitors. You know the ones – those with the external coil of fine wire. As the alignment seemed to be very good, I chickened out and left it alone, declaring the repair finished. Now both of these receiver jobs were done to a set price. If they had been mine I would have fitted a new dial cord, cleaned the back of the dial glass and maybe installed a new output transformer. But when working to a fixed price, such niceties have to be ignored. These extras take time and money and if a customer will not pay to have such things done, then he must live with the consequences. The Philipsette was working away on the bench while I was cleaning the dust out of the cabinet. Then, quite suddenly, the clear reception went soft and garbled. To make matters worse, the power transformer was rapidly overheating. Faults such as this are annoying to say the least. One minute you have a receiver working normally; the next, there is something sadly amiss. HFT short When a transformer suddenly overheats, it usually has a short circuit in or across one of its secondary windings. In this case, the valves and dial lamp were still lit, so it appeared as though there was a high tension short. A careful examination was made SILICON CHIP SOFTWARE of all valve socket connections. In particular, I checked for loose wires, blobs of solder and broken insulation but everything checked out OK. Even withdrawing all the valves did not prevent the transformer from overheating. It then occurred to me that if the short was still there when the rectifier was withdrawn, then the fault must be on the transformer side of the rectifier socket – perhaps in the transformer itself. A close inspection of the power transformer revealed a blob of solder wedged firmly between one side of the high tension winding and the core laminations. A molten drop of solder could have only fallen in there when the chassis was upside down. As I had done my work with the chassis on its end, I didn't put it there! Removing the solder returned the set to normal operation. The solder was acting like a thermal switch and only caused trouble when heat expansion of the windings caused the solder to short the HT winding to the laminations. In addition, it was noticed that some of the high tension winding was exposed and a couple of turns were hanging out in the open. This is a common fault with this make of transformer because the windings come quite close to the edge of the paper that separates each layer. The loose wires were coaxed back in place SC and held with silicone sealant. 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). ✂ This small blob of solder was shorting out the high tension winding of the Philip's power transformer. The short-circuit only occurred when the transformer became hot enough for the expansion of the high tension winding to sandwich the solder against the core laminations. There's always something different that can cause trouble. 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. August 1995  83 Silicon Chip 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. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1990: 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. 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. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. January 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. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. February 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. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). 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. 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. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. 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. 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. 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. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; 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. 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 May 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ 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 June 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 July 1995 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 84  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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 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. 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. 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. 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 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2; Electronics Workbench For Home Or Laboratory. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/ Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 Micro­controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design For Beginners; Electronic Engine Management, Pt.4. 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 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. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras & Night Viewers; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. May 1995: Introduction To Satellite TV; CMOS Memory Settings – What To Do When the Battery On Your Mother­ board Goes Flat; Mains Music Transmitter & Receiver; Guitar Headphone Amplifier For Practice Sessions; Build An FM Radio Trainer, Pt.2; Low Cost Transistor & Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control. 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. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; A 1W Audio Amplifier Trainer; Low-Cost Video Security System; A Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. 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. July 1996: Low-Power Electric Fence Controller; How To Run Two Trains On A Single Track (Plus Level Crossing Lights & Sound Effects); Setting Up A Satellite TV Ground Station; Build A Reliable Door Minder; Adding RAM To Your Computer; Philips’ CDI-210 Interactive CD Player. 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. 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. 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; August 1995  85 PRODUCT SHOWCASE Car power amplifiers from Kenwood Kenwood has just released three new car stereo amplifiers with balanced inputs and power FET technology. Designated the KAC-PS200 (100 watts/channel), KAC-PS150 (75 watts/channel) and the KAC-PS100 (50 watts/channel) they all feature Kenwood's TRI-Mode operation. This allows them to be configured for three modes of operation: standard two channel stereo mode, mono bridged mode or using a passive network such as Kenwood's KPX-T120 for stereo operation plus a subwoofer channel. This series is designed to operate with Kenwood cassette/CD/receivers or control units and can be mounted either horizontally or vertically in the boot. Cooling fans are incorporated in the 100W and 75W units. Audio Lab The two higher power units incorporate a variable low pass filter, the 50 watt unit a fixed 80Hz filter, for use with the subwoofer configuration. The use of balanced inputs allows the units to be placed in the boot without the signal degradation and noise problems which can be experienced with long, unbalanced inputs. All models are covered by 12 months warranty and are available at selected Kenwood car audio dealers. For further information on these or any other Kenwood products contact Kenwood by phoning (02) 764 1888. The Schaffner range of PC mounting filters has been extended with the introduction of the FN402 and FN402B family. The latter series has extremely Complete Audio Lab kit with PCBs, 1% resistors, PTH screened PCBs, IC sockets, boot Eprom, screen printed case, 8K RAM, 8031 processor and all ICs. Includes calibration and Audio Lab V5.1 software $330 inc. tax. Processor test kit $15. Freight $9. Fully assembled & calibrated complete with plugpack (1-year warranty) $450 5 Ludwig Place, Duncraig, Perth WA 6023 86  Silicon Chip Electrolytic capacitor mounts for PC boards PC mount mains filters R.S.K. Electronics Pty. Ltd. 10 VAC 1A plugpack plus socket $18. 2-Metre serial cable $9. low leakage and is mainly intended for medical applications. These units can be used for nominal voltages up to 250VAC, 50Hz or 60Hz, and come in current ratings of 0.5, 1.0, 1.6, 2.5, 4.0 and 6.5A. All filters are suitable for installation in business machines where IEC950 requirements must be met. For further information, contact John Thompson, Westinghouse Industrial Products, 175-189 Normanby Rd, South Melbourne, Vic 3205. Phone (03) 9676-8888 or fax (03) 9676-8777. Phone (09) 448 3787 These plastic mounts provide support for PC mount electrolytic capacitors and come in five standard sizes. Each mount features a slotted cup which supports and insulates the capacitor from surrounding components while allowing venting and proper drainage of fluids or contaminants experienced during board assembly and washing. Each mount raises the capacitor 1.3mm above the board surface. For further information, contact M. Rutty & Co, 1/38 Leighton Place, Hornsby, NSW 2077. Phone (02) 476 4066. FM radio trainer now available We have recently reviewed sample versions of the kit from Dick Smith Electronics for the FM Radio Trainer project featured in the April & May 1995 issues of Silicon Chip. The DSE kit has a well finished screen-printed PC board and comprehensive assembly and alignment instructions. The lab staff at Dick Smith Electronics have made a number of minor changes to the design, to optimise performance with some slightly different components that have been substituted because of availability problems. Having compared their kit versions with our prototype, we are happy to report they perform equally as well. The FM Radio Trainer kit is available from all Dick Smith Electronics stores at $69.95. (Cat K-5026). Surface mount 240V Mosfet Zetex has released surface mount 240V Mosfet for telecommunications equipment. Offering a low threshold voltage and low on-resistance, the ZVP4424G is supplied in an SOT223 package. With a gate-source voltage of 3.5 volts and a drain current of 100mA the device features an on-resistance of 12W. It also exhibits typical rise times of 8ns and fall times of 20ns at currents of 250mA, making it an efficient solution in telephone recall, hook and dialling applications. The ZVP4424G also features a typical input capacitance of 100pF and a gate to source voltage rating of ±40V. The surface mounting version is capable of handling a continuous drain current of 480mA and up to 1A pulsed. Its maximum power dissipation is 2.5W at 25 degrees C. A comprehensive data sheet is available, outlining full Spice model parameters, for computer simulation and testing. For more information, contact GEC Electronics Division,Unit 1, 38 South St, Rydalmere, NSW 2116. Phone (02) 638 1888 or fax (02) 638 1798. High voltage transistor for electronic ballasts Philips Semiconductors have released the BU1706A, a silicon diffused NPN power transistor which they claim is a practical low cost alternative to power Mosfets in electronic lighting ballasts. A peak collector emitter voltage of 1750V and low switching losses allow this new transistor to be used in applications where power Mosfets are prone to failure, for example, in mains voltage switching. Fall times as low as 0.2µs with inductive loads and a Vce(sat) of 1.0V at 1.5A allow the BU1706A to operate with little or no heatsinking in high frequency switching circuits. The transistor is available in the standard TO220 package or the fully isolated SOT186A pack. For more information, contact Karen August 1995  87 PCB POWER TRANSFORMERS 1VA to 25VA Programmable laser scanning system Rack mounting work station has touchscreen For concert and live music applications, the model XYP-1000 Beamscan system is a complete, self-contained, microprocessor controlled laser scanning system. It is capable of producing a very wide variety of patterns, automatic pattern sequences and beam effects. The system consists of a digital controller, scanner head and connecting cable. The controller uses a 20-key membrane keypad for programming and recalling patterns and sequences. A backlit two line by 16 character display is used for verification. Its 8K EEPROM will store 100 user created patterns and up to 360 sequence frames. The system comes programmed with 80 patterns and 20 beam effect sequences. The scanner head contains an open loop X/Y scanner pair, a high speed beam shutter, a diffraction grating with actuator and a connector for the control cable. The head has IN and OUT beam ports 90 degrees apart. Programmed sequences are played back much like a slide show, displaying each frame at a programmed position, for a preset time. Frames can also be advanced by a music trigger using an external sound source to one of the three line level inputs. For further information, contact Spectrum Laser Systems, PO Box 384, Bentleigh, Vic 3204. Phone (03) 9532 1981 or fax (03) 9555 7449. Click Electronics have recently released a rack mounting workstation with a built-in touchscreen. The touchscreen is supplied with drivers for DOS or Windows 3. For use with software that does not have a touch screen interface, it can emulate a mouse. The workstation has a sealed front panel, with an integral 83 key membrane keypad which includes 24 function keys. The unit can accommodate one 3.5" floppy drive, as well as two 3.5" half height, hard disc drives. The built-in 14" 0.26mm dot pitch VGA colour monitor offers a screen resolution of 1024 X 768. A seven slot AT-ISA passive backplane is mounted, along with the disc drives, in a drawer, which slides out from the rear of the work station, for easy access. The card bay is fitted with an anti-vibration clamp. The station offers a range of single board computers, from the low cost 486DLC to the high performance 486DX4-100. A 250W power supply is provided to support any configuration. For more information, contact Click Electronics, PO Box 25, Bangor, NSW 2234. Phone (02) 649 6011 or fax (02) 649 6887. ised data collection system. Each Aspnet terminal has a keypad, liquid crystal data display and an inbuilt battery (in case of external power failure.) Operators can be prompted to enter information or can be given instructions on what to do. Information collected by the system is stored with time and date stamp. Data can easily be transferred to a spreadsheet, database or customised analysis software as required. For larger operations, the system can be extended by the use of a "workblock" which allows the program to collect data from a larger number of sources. For more information, contact Carli Barnes, ASP Microcomputers, 456 North Road, Ormond, Vic 3204. Phone (03) 9578 7600 or fax (03) 9578 7727. Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 Hillerman, Philips Components, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 805 4479 or fax (02) 805 4466. Low-cost production tracking system A new low cost system has been released by ASP Microcomputers, to allow business to gain the advantages of real time production tracking and time costing. The Aspnet hardware consists of miniature readers which accept information from barcodes or magnetic stripes. These readers are connected via a network to a host computer which analyses incoming data as it is received. In addition, the system incorporates an easy to use computer language, Aspnet Basic, which allows users to create their own fully custom88  Silicon Chip Interface boards for connecting Windows PCs to serial devices National Instruments has announced two new interface boards that connect windows PCs to serial devices. The AT485 and AT-232 connect the PC to RS-485 and RS-232 instruments respectively, giving the PC additional serial ports with data transfer rates up to 115.2KB/s. Both boards are available in two and four port configurations. These are the first National boards to use the jumperless "Plug and Play" ISA architecture. For users of Windows 3.1, which does not offer this facility, a board configuration utility is supplied. The AT-485 can connect up to 31 multi-dropped devices to a single PC port. It also includes a special automatic transceiver mode that can communicate with two wire serial devices. The AT-232 can connect laboratory or electronic test instruments, such as oscilloscopes and multimeters, to a PC. Users can communicate with the boards using National Instruments' LAB software or any other industry standard programming languages. For more information, contact Tony O'Donnell, National Instruments Australia, PO Box 466, Ringwood, Vic 3134. Phone (03) 9879 9422 or fax (03) 9879 9179. KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. •• FMTX1 FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. •• FMTX2A FMTX5 $99: both FMTX2A & FMTX2B on one PCB. FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input •connector for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92KHz subcarriers. • AUDIO Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being •soldDIGI-125 since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface •to Max the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with •onlyIBM3 chips and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. 19" Rack Mount PC Case: $999. •• Professional All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4mb RAM 1/2 size card. PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA •PC104 card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. August 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. Charge indicator for SLA battery charger I’ve recently purchased a portable 12 Volt SLA Battery Charger kit as described in the July 1992 issue of SILICON CHIP. Is there any way of adding a small LED to indicate when the battery is being charged or is fully-charged without impacting on the charging and monitoring process itself? (G. P., Vale Park, SA). • While you can connect a LED (in series with a 1kΩ resistor) across the output of the charger to indicate charging, it will not indicate the state of battery charge. This function would require extra circuitry. Solid state vibrator wanted I’m restoring an AWA Cruiser 6-valve car radio, model 931-A, and am having trouble locating a vibrator for the same type: a V5123, non-synchronous 12V. I’ve heard that a solid state device can be purchased in the USA to replace the vibrator unit or one can be made up. I’m hoping you may know of a suitable circuit or maybe a reader does. Hoping you can be of help. (E. Phillis, PO Box 124, Dareton, NSW 2717). Timer with date stamping wanted I wish to construct a low draw, battery operated circuit, centred around a simple event counter, to count up to 10 or more events and auto reset. It needs to have an inbuilt clock circuit that can be used to time stamp each event in a memory and display each time in reverse order of entry when required. When memory capacity is reached (10 or more events), the oldest entry would be erased in order to accommodate latest entry. I would welcome any assistance on 90  Silicon Chip • While such devices were available many years ago, we doubt whether they are still obtainable. Nor do we have a suitable circuit on our files. Perhaps one of our readers can give assis­tance. Capacitor ripple ratings I have built a large Mosfet power amplifier which I am hoping will deliver more than 500 watts into an 8Ω load. The big hurdle though has been the electrolytic filter capacitors which are 10,000µF 100VW can units. While the amplifier has tested OK on the bench, there have now been several instances where it has blown up the filter capacitors. Actually, the capacitors have not been blown up – their inside have been disgorged from the can in a steaming stinking mess. Now the interesting part is that the amplifier was not delivering any power at the time. I know that I am sailing close to the wind with these capacitors because the supply rails nor­mally sit at ±98V but I would have thought this was ac­ceptable. I have someone who really wants to buy this amplifier so I am getting desperate! Can you please help? (B. S., Subiaco, WA). the best method of putting together a circuit to achieve this. (N. H., Loganholme, Qld). • While an event counter might be quite simple, your require­ment for date stamping and memory means that it is quite a bit more complicated and probably requires the use of a microproces­sor, possibly one of the PIC models or the Stamp system adver­tised in the “Market Centre” pages of this magazine. We cannot help you with a design right at this moment but if other readers indicate that they would like a similar design, we will have a look at it. • Merely running electrolytic capacitors close to their vol­tage ratings is not normally a cause for their failure, provided, of course, that they were not faulty when they were installed. A more likely reason for failure is excessive ripple current. To explain, when an electrolytic capacitor is used as a power supply filter capacitor, following the rectifier, it must pass an AC ripple current in order to smooth out the DC voltage. As a rule of thumb, the amount of ripple current is roughly equal to the DC current being drawn from the DC supply. So if the DC supply has to provide 5A, for example, then the ripple current is around 5A too. The frequency of the ripple current will be twice the mains frequency; ie, 100Hz with a 50Hz mains supply and 120Hz with a 60Hz mains supply. Large filter capacitors generally have a quoted ripple current and just taking an example, a 10,000µF 100V electrolytic capacitor sold by Altronics has a ripple current rating of 8.3 amps. That sounds like a lot but when the power supply is feeding an audio amplifier the story becomes rather more complicated. The problem is that an audio amplifier does not draw smooth current from its power supply. Rather, it draws a current wave­form which looks like a half-wave rectified version of the signal it is delivering. That makes sense because a typical class-B output stage has two transistors which each turn on for half the waveform. Ergo, the amplifier draws heavy ripple current from the electrolytic filter capacitors at the signal frequency. So if the amplifier is delivering full power at 1kHz it will be dragging huge ripple currents at that frequency. These currents are in addition to the 100Hz ripple current that the capacitor has to carry to smooth the DC. The rub is that while the capacitor may be rated for a certain current at 100Hz, it may not be able to withstand the same current at high frequencies because it may have considerable internal impedance as the frequency rises. Hence it is good practice to be conservative and for an amplifier with the sort of power that you are aiming for, we would suggest that two or three of these 10,000µF 100VW capacitors should be used for the power supply filtering on the positive and negative rails. Even so, you have given a clue that something else might be amiss with the amplifier – you said it was not delivering any power at the time the capacitors had their unhappy event. That suggests that the amplifier is oscillating at a very high fre­quency. When this happens the amplifier will draw heavy current and the frequency may be very high, way up in the Megahertz region. Electrolytic capacitors hate really high frequencies so this is probably why they disgorged their insides. Interestingly, if you have monitored the output of your amplifier with an oscilloscope, you may not have seen any signs of instability at all. Some time ago we had a Mosfet amplifier design under development (not published) which oscillated at 90MHz, right up in the FM broadcast band! There was no sign at all of any instability on a 20MHz scope but it was as clear as day on a 100MHz scope. Automatic switching of petrol or LPG In my opinion it is vital that a fuel injection engine on a vehicle that is modified to run on LPG is driven more frequently on petrol, particularly when undergoing long journeys, in order to avoid injection blockage and failure. Most fuel injection engines either start on petrol then switch over to gas after reaching 2000 RPM or else by a timing device which locks on to gas until the engine is stopped. Where frequent stops and starts occur, as in metropolitan driving, the problem does not exist. LPG is more often adapted to country vehicles or vehicles used for distance travelling where LPG is utilised for long periods without using petrol. This then means that the petrol in a fuel injection engine is circulated continuously through the engine fuel rails and returned to the petrol tank without being used. Therefore, some of the fuel in the injectors could boil off Solar powered computer system Regarding T. N.’s request for advice on a UPS (Ask SILICON CHIP, June 1995), I would like to offer my own observations on operating a computer (386SX/mono screen) from an Altronics 300W inverter. I live in a house powered by photovoltaic cells and the system has grown in size since its inception eight years ago. I like to know what goes on (or should that be what goes in and out?), so my distribution board has meters for volts, solar current in, load current and a separate amp meter for the invert­er. The 386 with 3Mb of memory draws about 7.5A. The floppy drive adds almost 0.5A to this but you don’t use a floppy drive for more than 2 or 3 minutes at a time generally. This figure in­cludes the monitor – a colour monitor may well draw more power, but I cannot confirm this without testing. My Epson LQ100 24 pin printer uses between 1A and 3A de­ pending on what it is doing but I would allow 2.5A as its average. All of the above adds up to 11 amps. If you allow for a float and form scale or oxidise into fine mud and eventually block the injectors. Fuel in the petrol tank can reach temperatures beyond 70°C where oxidisation can cause severe damage, necessitating the replacement of the entire fuel system. Fuel filters should be replaced more frequently than recommended in the service manual because they cannot remove all the oxidised fuel (mud). Turning off the fuel pump is not an option because the fuel would boil more easily in the engine fuel rails. Vehicles converted to LPG must only refuel to half the capacity of the petrol tank and this quantity used up monthly. To avoid damaging the fuel pump, located in the tank, it should never run to empty. All LPG vehicles have a manual switch to operate the engine on either petrol or LPG. Therefore, would it be possible to adapt a timer circuit to automatically alternate the engine charge of 12.8V in your battery you come up with 140.8W. This should be within the capacity of a 200W inverter – my old 300W unit just gets warm. I think that if it was me I would use a good battery charg­ er that would supply 10A on a continuous basis and leave the battery on charge constantly – I do mean a good battery charger, one that won’t boil the battery dry. The next thing is sinewave inverters. Some of them generate so much electrical “noise” it isn’t funny. AM radios within 20 yards are useless and the interference even gets into the tele­phone line! Anything connected to the DC supply is going to get so much “hash” that filtering will be required, and lots of it! Re the back-up cards, if they have nicad batteries on them, watch out for leaks – I had to ditch a perfectly good mother­board because the battery leaked (a 3.6V nicad). The clock still work­ed, but the “goo” migrated under three ICs and dis­solved quite a few PCB tracks. From now on, batteries are mounted well away from anything that may corrode. (D. H., Beech­ wood, NSW). operation from petrol to LPG on a continuing basis? The engine petrol timer would be needed to start the engine and run for 2-5 minutes (adjustable) before switching over to the LPG timer for 10-20 minutes (adjustable) and then back to petrol or gas, alternately. The timing device could be easily connected across the terminals of the manual switch without affecting the gas conversion. Howev­er, it is vital that manual switching of either petrol or gas be retained. (R. R., Dawesville, WA). • Designing a timer for this purpose should be relatively straightforward and indeed, a 555 timer would probably do the job. However, as you say, you would still need to be able to switch manually between petrol and LPG and the original system control could not be overridden by the timer otherwise the results might be undesirable. It is these August 1995  91 250VAC capacitors for LED circuits We had some correspondence last year on the danger of using DC-rated capacitors as the voltage-dropping elements in 240VAC circuits (Ask SILICON CHIP, November 1994) with particular refer­ence on my part to driving LEDs from the mains. However, I notice that since that time, mains-rated capacitors of suitable size have become readily available; eg, from DSE and Jaycar. Using these, would you now regard such applications as “safe” (I suppose nothing connected to the mains can be complete­ly safe) two requirements which make the design somewhat more complicated. If you have the timer on and then you decide to overrule it by manually switching to LPG or gas, then that setting will be maintained until you remember to switch over to the timer – which rather defeats the purpose of the exercise. We are also concerned about the possibility of the engine faltering if the timed changeover takes place at a critical time, such as when pulling out to pass another car at high speed. With these thoughts in mind, we are reluctant to publish a circuit without more information on the subject. Uninterruptible power supplies for PCs I would like to comment on the matter of making up an unin­terruptible power supply for computers as raised in the “Ask SILICON CHIP” pages of the June 1995 issue. I have had a UPS running for over one year. It was interrupted once when Feather­foots the cat jumped on a charging lead! It consists of a home made battery charger, a 10A Variac to adjust the charging voltage via the battery charger primary, a 1kW 24V modified square wave inverter and a 24V 80A/hr deep draw battery set. The battery charger consists of a 300 watt toroi­dal power transformer driving a 40A bridge rectifier with suitable heatsink and transformer cooling is by small computer fan. A steel case was used as a plastic one 92  Silicon Chip or would there still be some reservations about it? (J. K., Kenmore, Qld). • Provided these capacitors do have the correct 250VAC rating and also a suitably rated limiting resistor is placed in the circuit, such circuits should be safe. The resistor should be designed to fuse in the event that the capacitor becomes a short circuit and thereby fail-safe. However, we are still not really happy with LEDs running directly from the mains and prefer the old-fashioned and reliable neon indicator lamp with inbuilt current-limiting resistor. may melt if the components overheat. A small value high wattage resistor is used in series with the charging lead to limit the possible current draw to that rated for the transformer; in my case, 8A. Don’t be an idiot like me and use a number of power resistors in paral­ lel; the whole lot will fail in cascade! The batteries were specified with bolt type connections and were strapped together with aluminium bar, 3mm x 25mm. Plenty of petroleum jelly was used over the terminals and lead ends at the batteries. Charging and inverter wiring was heavy duty electrical earth cable. In practice, the battery is charged to its rated maximum voltage and the Variac is adjusted, over a day or so, until with the computer load, the batteries stay fully charged. My rather extensive 386 system, less monitor, draws just on 3.4A at around 27V. I can plug the monitor in when I need to; the supply stops my Unix system crashing and on test kept it running for 19 hours continuously. After that, it does take a day or so for the setup to drop right back to 3.4A. I aimed at a charging capacity about double the load draw. The 1kW inverter means that I can run everything except the laser printer for reasonable periods, about six hours if the 20-inch monitor uses about 200 watts. The batteries have needed no maintenance whatsoever since installation thirteen months ago. They have an expected life of five years, limited by internal terminal corrosion. The cost to me of this setup was about $1000 plus an afternoon or so of work and a bit of experimentation. Nothing has had to be done to the unit for many months. It is deliberately made simple for high reliability, hence the Variac rather than automatic voltage control. I have had a big regulated power supply fail to regulate. The device it was driving caught alight when the power Mosfets blew! (R. H., Tranmere, SA). • While we understand your desire for simplicity, using a Variac to adjust the charging current and hence, the final charg­ing voltage, is a little crude. There is a risk that the mains voltage could run at a high level for several days and you could be seriously overcharging without knowing it. Variable rejection filter wanted I was interested to see your simple 2-transistor CW filter in the March 1995 issue of SILICON CHIP and wondered if this could be easily modified to act as a variable frequency rejection filter. I want one which could be used to reject the 9kHz whis­tles on the broadcast AM band and also the various whistles on the international short­ wave bands. (A. S., Denmark, WA). • The CW filter in the March 1995 issue is not suitable as a variable rejection filter. To effectively reject 9kHz whistles without removing too much of the wanted audio signal, you need a filter with a very deep and sharp null, exactly at 9kHz. If the filter is just 10Hz or more off the exact frequency, the rejec­tion is greatly reduced. For that reason, a variable rejection filter is unlikely to be effective as it is too difficult to set it to the exact frequency. We did publish a 9kHz whistle filter as part of the circuit for the wideband stereo AM tuner described in the February, March & April 1991 issues. Notes & Errata Walkaround Throttle, Ask Silicon Chip, page 93, May 1995: the suggested wiring diagram for a centre-tap transformer shows the 10µF capacitor near the 7812 reverse biased. The capacitor’s negative connection should go to SC the centre pin of the 7812. 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 $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 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 August 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. FREE TO A GOOD HOME: same address for 21 years.You have read my ads for years and done nothing. My exciting new micro development kit products leave the others dead in the water. This month my PROMO disk is free. Just ask. Don McKenzie, 29 Ellesmere Cres­cent, Tullamarine 3043. Ph (03) 9338 6286 or 019 93 9799. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ TENDER OFFICIAL RADIO MANUALS, trade journals telephone parts morse keys. 60ft tower, TH7DXCC tribander, hifi amps, meters earphones. Catalogue 85c. Hadgraft, 17 Paxton Street, Holland Park Qld 4121. AH (07) 397 3751. COMPLETE WORKSHOP PROGRAM: suit IBM compatible 386 or better computer. Handles: Stock Control, Customer Records, Debits, Credits, Faults, Manuals and Phone Directory. For demo disk, ring Jack Albers Electronics & Software Development on (045) 71 1640. WEATHER FAX programs for IBM compatibles *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & Rtty receiving program. Needs SSB HF radio & Radfax decoder. *** “MAXISAT” Version 2.3 $75 is a NOAA, Meteor & GMS weather satellite picture receiving program, lots of features, needs WEATHERFAX card, 2Mb of 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 EMS memory & 1024 x 768 SVGA card. Programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 for postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. CHEAP HEATSHRINK TUBING: Australian made, red, black, blue, white, clear, 2.4mm/$1.10pm, 3.2/$1.30, 4.8/$1.70, 6.4/$2.10, 9.5/$2.30, 12.7/$2.70, 19/$3.70, 25.4/$5.10. P&P $3.00 up to 10 metres. Free data sheet. DOMCOR DISTRIBUTORS, 67 King Road, Beechboro, WA 6063. MicroZed has in stock NewMicro 68HC11 board, resident FORTH, with alternative BASIC, Small C and Assembler supplied. YOUR UNUSUAL PARTS source: UCN5804B, DS1620, DS1202, DS­ 2401, DS1215, DS1232, UGN3503U, UDN2998W, UDN2993B, MAX038, MAX691, ISD2590, IR LEDs, PCB mounted switches, latest remote control decoder chip, & more. With data sheets. DIY Electronics, tel/fax: (058) 62 1915. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available in Australia. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $149.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $410 + $6 p&h (save $139) • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h •DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 (inc label). We use and recommend the HILO ALL-07 Universal Programmer • Fixed price PCB layout & photoplots. We use and recommend PROTEL For Windows EDA tools • Credit cards accepted • Call Bob for more de­tails. MICROCRAFT, PO Box 514, Concord, NSW 2137. Phone (02) 744 5440 or Fax (02) 744 9280. C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: MEMORY & DRIVES EX. TAX PRICES AT JULY, 1995 SIMM (all 70ns) Parity/No Parity 1Mb 30-pin $64/58 4Mb 30-pin $250/215 2Mb 72-pin $151/135 4Mb 72-pin $250/232 8Mb 72-pin $515/452 16Mb 72-pin $850/765 32Mb 72-pin $1530/1700 MAC 8Mb P’BOOK CO-PROCESSORS 387S/DX to 40 $450 $90 LASER PRINTER HP with 2Mb $200 COMPAQ CONTURA 8Mb $544 Parallax Basic Stamp DRAM DIP 1Mb x 1 70ns DIP $9.00 256 x 4 70ns DIP $8.10 256 x 16 70ns DIP $55.00 IBM PS.2 THINKPAD L40/N33 8Mb 4Mb $590 $300 TOSHIBA 3100SX 2100/50 4Mb 8Mb $275 $590 SUN SPARC ELC 16Mb SPARC 10/20 64Mb $850 $3872 DRIVES – SEAGATE 545Mb 14ms 3yr wty $280 850Mb 11ms 3yr wty $355 1052Mb 9ms 5yr wty $535 Sales tax 21%. Overnight delivery. Credit cards welcome. Ring for latest prices. We buy & trade RAM. PELHAM Tel: (02) 980 6988 Fax: (02) 980 6991 Shop 6, 2 Hillcrest Rd, Pennant Hills, 2120. $150.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $150 for the set. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $450. 8051/52 or 80C320 simulator (fast): $75. Demo disk: FREE. All prices + postage. GRANTRONICS, PO Box 275, Wentworth­ville 2145. Ph/ Fax (02) 631 1236. MicroZed has PIC Source book in stock. Gives code for Stamp routines to use in your own PIC programs. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses ‘C8 Quick And Easy Circuit Development Get your project going and on the market fast Resident BASIC interpreter Each pin can sink 25mA, source 20mA Minimum extra hardware needed for most jobs BASIC STAMP and accessories available Send 4 x 45c postage stamps for information package and prices for all products. MicroZed Computers PO Box 634 (296 Cook’s Rd), Armidale 2350 V (067) 722 777 F (067) 728 987 Credit cards accepted. and switch mode supply. Features galore!! Contact Mantis Micro Pro­ducts, 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. MicroZed has MicaSOFT Tutor Program. For demo send 4 x 45c to MicroZed (see display advert p.95 for address). PROGRAMMER/EDITOR SOFTWARE for new Lattice EEPROM 7ns Generic Digital Switch ICs. Just connect to PC parallel port! Use to reconfigure circuits 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) 9979 5644 & quote your credit card number; or fax the details to (02) 9979 6503. Please specify 3.5-inch or 5.25-inch disc. August 1995  95 Microprocessor For Digital Effects Unit Microprocessor For Stereo Preamplifier Advertising Index Now available from SILICON CHIP: the 68HC705-C8P pre-programmed micro­pro­cessor IC for the Digital Effects Unit described in the Feb­ruary 1995 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) 9979 5644; Fax (02) 9979 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 Pub­ lications, PO Box 139, Collaroy, NSW 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. Altronics ................................ 34-36 without rewiring! Send SSAE, phone or poll fax. Advanced R & D Solutions, 12 Copeland Road, Lethbridge Park 2770. Ph/Fax (02) 628 1223. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gorizont, Rimsat. Warehouse Sale – 4.6m Dish & Pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 482 3100 8.30-5.00 M-F. 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. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590. MicroZed is now stocking MUSCLE wires, project books and kits. ADD AN IBM KEYBOARD DECODER (EA, Dec. 90) to your project. 8 left. PCB, Programmed 8749 & Disk $20. Av-Comm.....................................65 Car Projects Book......................IFC Dick Smith Electronics........... 10-13 Emona.........................................87 Harbuch Electronics....................88 Instant PCBs................................96 Jaycar ................................... 45-52 Kalex............................................23 Kits-R-US.....................................89 Macservice...............................3,17 MicroZed Computers...................95 15 Romloader 256K upgrade PCBs left. PCB, EPROM, 9346 EEPROM, 74HC­4053, Labels & Disk $25. P&P $5. Tantau Australia, PO Box 1232, Lane Cove 2066. AH (02) 878 4715. SATELLITE EQUIPMENT: we sell quality products at prices you can afford. Dishes from $140. Ku LNB voltage switching with built-in feedhorn from $150. C band LNB 23 deg from $140. Receivers; eg, Pace 919 low threshold is $420. We stock Gardiner, Drake, Pace, Chaparrel, KTI, plus many more. A catalogue is available. Contact Satellite Professionals on phone or fax (03) 803 0215 WANTED WANTED: AR2002 Communications Receiver 25-550MHz and 8001300MHz. Melbourne (03) 9707 2326. Oatley Electronics.................. 78-79 Pelham........................................95 Railway Projects Book.............OBC RCS Radio ..................................94 Rod Irving Electronics .......... 67-71 R.S.K. Electronics........................86 Silicon Chip Back Issues....... 84-85 Silicon Chip Binders....................96 Silicon Chip Bookshop.................93 Silicon Chip Software..................83 Silicon Chip Walchart................IBC Telstra..........................................89 Tortech.........................................23 _________________________________ PC Boards SILICON CHIP BINDERS Printed circuit boards for SILICON CHIP projects are made by: These binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover • 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. Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p. To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. • HT Electronics, Shop 4, 8 Roberts Rd, Hackham West, SA 5163. Phone (08) 326 5567. 96  Silicon Chip