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 can be used as an amplifier for musical instruments or even with your cell phone. The...
This circuit, which can act as a shield, was found in a 1970s American documentation. The...
This timer produces a continuous sound at the end of the timer set in potentiometer RV1. The...