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 oscillator circuit for sinusoidal audio signals with operational 741 requires a symmetrical power...
Found in a 1974 Radio Shack documentation. This circuit must have a connection to the ground of...
This sensitive circuit detects the live pole of a power grid or outlet. The circuit makes use of a high...