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Advertising Index A To Z Electronix.......................... 55 ADM Instruments......................... 61 Altronics................................catalog Blamey & Saunders Hearing........ 11 Emona Instruments................. 15,57 Grantronics................................... 95 Hare & Forbes............................. 2-3 High Profile Communications....... 95 Instant PCBs................................ 95 Jaycar .............................. IFC,45-52 Ask SILICON CHIP . . . continued from p94 a pause feature plus the rate change. Perhaps the Fast Clock published in December 1996 would be suitable. It is a small circuit that drives a standard sweep hand clock. The speed is adjustable from 4.5 to 8.5 times normal but changing the series resistor (820Ω to 220kΩ) that connects to the trimpot will allow a wider adjustment range. Additionally, changing the 150nF timing capacitor will alter the overall rate. Adding a pause feature would be as simple as including a switch in the connection to the clock motor. One disadvantage of the clock is that it is not 24 hour. However, the clock rate could be made slower so it takes 24 hours (model railway time) for the hour hand to rotate 360°. The clock face could then be remarked to show 24 hours rather than 12 hours. Note that the PCB for this project is no longer available but the circuit is quite simple with only two ICs and you could easily build it on a piece of Veroboard. Converting a 3-wire speed sensor I own a 2001 VH Ford Transit van with a 2.3-litre petrol engine and a 5-speed manual gearbox. I have just converted the van to automatic, using a Jatco 4-speed overdrive box from a 1986 Nissan Pintara. This gearbox has a 3-wire VDO speed sensor whereas the Transit’s manual box had a 2-wire speed sensor (like a single magnet with a toothed disc in box). I know nothing about all this but from what I have read the 3-wire sensor is a “Digital Square Wave Pulse” 96  Silicon Chip DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305 Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au and the 2-wire sensor is an AC sinewave device. I went to my local Jaycar store but they couldn’t help me with anything to convert the digital signal to a sinewave. Do you know of any way of doing this with some sort of a kit? I would appreciate any help with this problem. (N. C, Caboolture, Qld). • To convert the digital output of the 3-wire sensor to an AC signal, connect one lead of a 10µF NP (non-polarised) capacitor to the output of the sensor. The other lead from the capacitor will provide the AC signal and should be referenced by connecting a 10kΩ resistor between this AC signal and chassis. It’s not necessary to convert to a sinusoidal wave shape since an AC square wave signal will be suitable. Note that the VDO speed sensor will require power to its positive lead (+5V or +12V, depending on its requirements), while its GND lead must be connected to chassis. The output will be an open-collector transistor (which is located internal to the speed sensor). This will require a 1kΩ or similar value pull-up resistor from the output lead to the positive supply. Temperature switch for fan control I wish to switch on a series of small fans (65V <at> 50mA) when the temperature on a heatsink reaches approximately 60°C. I do not require Keith Rippon................................. 95 KitStop.......................................... 40 LED Sales.................................... 95 Low Energy Developments.......... 95 Microchip Technology............... OBC Mikroelektronika............................. 7 Oatley Electronics...................... IBC Ocean Controls............................ 12 Quest Electronics......................... 95 Radio, TV & Hobbies DVD....... 40,77 RF Modules.................................. 96 RMS Parts.................................... 73 Rohde & Schwarz........................ 13 Sesame Electronics..................... 95 Silicon Chip Binders........... 10,16,29 Silicon Chip Order Form............... 89 Silicon Chip Partshop................... 88 Silicon Chip Subscriptions........... 87 Splat Controls............................... 95 Star Components......................... 95 Truscotts Electronic World............ 95 Wiltronics..................................... 8,9 Worldwide Elect. Components..... 96 anything too precise or complex. Have you published any such circuits, possibly using the LM335Z? I see that Jaycar sells a Temperature Switch kit which may be based on one of your designs. (A. R., via email). • The Temperature Switch is a SILICON CHIP design sold as a kit by Jaycar and this can be used. Or just use a 60°C thermostat (Jaycar Cat. ST-3821) that opens its contacts at 60°C and re-closes at 40°C. Other temperature switch point thermostats are also available SC from Jaycar. siliconchip.com.au