This circuit is from an Italian magazine of 1983, but it can be assembled with the most modern equivalent transistors BC548 and BC558 and for the transducer a small speaker can be used. One or two ordinary batteries can be used for power.

This circuit is from an Italian magazine of 1983, but it can be assembled with the most modern equivalent transistors BC548 and BC558 and for the transducer a small speaker can be used. One or two ordinary batteries can be used for power.