This relay triggered by voice or by another sound was found in an Elektor from the 90's. The circuit uses a 12 V sensitive relay and has no sensitivity control.
This circuit was obtained in a 90’s Popular Electronics. The frequency depends on C1, a component...
This short-range circuit can act as a wireless microphone. We got the schematic and the printed...
This sophisticated function generator circuit appeared in the September 1972 issue of Radio...