This circuit was obtained from a Radio Electronics issue from January 1989. The indicator is a ceramic transducer, and the frequency of the emitted sound is given by C3.
This two-transistor circuit was found in the January 1994 issue of Electronics Now. The circuit can...
This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent...
This circuit consists of a small inverter to light a low voltage neon lamp. The circuit is from a...