This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
This circuit applies to an old dial phone by detecting light pulses in the dial. The circuit is...
This circuit conditions an audio signal, acting as a filter, control, and reaper of signals. The...
Found in old documentation, this timer uses a sensitive relay and a 2N2646. The time is given by...