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.
The transistors of this timing circuit may be more modern types such as BC548 and BC558. The...
A small loudspeaker (2.5 or 5 cm) can be used as a low impedance microphone. A preamplifier and...
We find this circuit in an American 80's documentation. No further information about the...