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Contents SILICON CHIP www.siliconchip.com.au Vol.24, No.7; July 2011 Features   14  Australia Hears . . . And So Do I New digital hearing aids developed in Australia are now available for a fraction of the cost of other aids. You can even program them yourself – by Ross Tester   21  Could There Be A SIM-LEI Electric Car In Your Future? The evolution of electric cars continues. This one has in-wheel motors, does 0-100km/h in just 4.8s and has a range of 300km plus – by Ross Tester   22  Control Your World Using Linux PCs running Linux are quite open to the experimenter. Here’s how to use your computer to control external equipment – by Nenad Stojadinovic   72  A Look At Amplifier Stability & Compensation Ultra-LD Mk.3 200W Amplifier Module – Page 30. Portable Lightning Detector – Page 42. The Ultra-LD Mk3 amplifier described in this issue has a new frequency compensation arrangement to lower distortion. We explain why amplifier frequency compensation is necessary and how it works – by Nicholas Vinen Pro jects To Build   30  Ultra-LD Mk.3 200W Amplifier Module Upgraded design has even lower distortion than before. It also boasts much improved thermal stability, has a flatter frequency response and can deliver 135W RMS into 8Ω or 200W RMS into 4Ω – by Nicholas Vinen   42  A Portable Lightning Detector This device could literally save your life. It gives advance warning of approaching thunderstorms, giving you time to take shelter if out in the open or to disconnect valuable gear from the mains if at home – by John Clarke   62  Rudder Position Indicator For Power Boats Easy-to-build unit senses the rudder position and sends the information to a companion receiver unit via a 433MHz RF link – by Nicholas Vinen   82  Build A Voice-Activated Relay (VOX) Turn devices on or off by speaking (or by using some other sound) with this simple VOX circuit. It features adjustable sensitivity and delay– by John Clarke Special Columns  57 Serviceman’s Log Restarting after the Christchurch earthquake – by the Serviceman   87  Circuit Notebook (1) Surf Sound Synthesiser; (2) Geiger Counter Uses Cockroft-Walton Multiplier; (3) PICAXEL The Electronic Cricket; (4) Wein Bridge Oscillator Uses An LM386 Power Amplifier; (5) Synthetic 5-Segment Potentiometer Rudder Position Indicator For Power Boats – Page 62.   92  Vintage Radio Hotpoint Bandmaster J35DE console radio, Pt.1 – by Maurie Findlay Departments    2  Publisher’s Letter   4 Mailbag  40 Product Showcase   98  Ask Silicon Chip siliconchip.com.au 101  Notes & Errata 102 Order Form 103 Market Centre Build A Voice-Activated Relay – Page 82. July 2011  1