how does this strike you?

99 "Energy crisis" is becoming something of a catch phrase nowadays, for one reason or another. Whether this is due to a shortage in fossil fuel or simply because the power "isn"t on", is another matter. While one of our designers was poring over a history of electronics, by candlelight, with knees knocking from the cold, he was suddenly struck by a brilliant flash of inspi- ration. Tap an unused natural source! The basic idea is shown in the accompanying diagram. The neon lamp (a one killervolt type) limits the voltage across R1 and R2 to 1000 V. These resistors are connected in a voltage divider configuration, providing 15 V at the centre tap; this voltage is rectified and stabilised by D1, R3 and D2. The battery (10 Nicads in series) is charged through D3. Readers are advised that some components may suffer from instability. The circuit was originally intended as a back-up for the solar cells in very remote applications — repeater stations in the Himalayas, orbiting spacecraf...