Found in an Electronic Engineering from the 80's, this circuit makes use of components of the time. The circuit can be implemented with modern equivalent components.
This sonic switch, sound relay or simply vox uses a medium impedance speaker as a microphone. The...
This circuit is an impedance adapter. The circuit is from a Radio Electronics from April 1966. The...
This circuit using components that are still common in our market was found in a 1987...