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 triac circuit was taken from an article in the July 1970 Radio Electronics magazine. Note the...
When this circuit picks up a louder sound it produces a pulse that briefly charges the 10 uF...
This 10 A solid state relay was found in a 1980s documentation. It can work as a shield and...