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 unity gain circuit was found in the February 1995 Electronics Now magazine. The frequency is 10 kHz,...
Found in a 1967 Electronic Design, this transistorized circuit compresses and then expands a pulse....
This TTL pulse stretcher or stretcher was found in a 90's EDN. The time constant R x C1 determines...