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 found in 1960s Radio Electronics. The circuit uses components from that time. The...
Figure bellow shows another configuratíon for a Iow-frequency sine wave oscillator using CMOS...
Found in an 80's documentation this circuit uses an integrated from the uncommon era today. Other...