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.
The frequency of this circuit depends on the crystal. The transistor supports a modern equivalent. We...
Indicated in Maxim's documentation from the 90's, this circuit has a gain of 40 dB and an output...
The time obtained in this circuit, from a 1978 publication, depends on R3 and C. R3 can have...