- on Miscellaneous Electronics
- Published in issue 7/2001 on page 0
This circuit takes advantage of back-e.m.f. (electromotive force) to amplify the voltage across a piezo sounder. Ordinarily, IC1 would only achieve a gentle beep. However, the addition of a very high inductance choke of a few Henry — in this case the coil of a miniature reed relay is used — achieves a penetrating screech, and represents an easy method of obtaining considerably more volume in such a circuit.