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 1988 documentation circuit includes a charger and an inverter to power a small fluorescent lamp. The...
This circuit can act as a receiver for the transmitter of the previous circuit. We found it in...
The power source shown for powering for small TTL circuits was found on a Radio Electronics...