Phone circuit (CB8709E)

With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a basic intercom.

Laser trigger (CB7225E)
Found in an American publication in 1967, this circuit generates pulses for the triggering of a LASER of...
Adjustable Current Limiter LM317 (CB15314E)
The maximum current of this circuit is 1.5 A. The circuit has the formulas next to the diagram to...
Biestable Sound Switch (CB5991E)
This biestable vox circuit was found in an old documentation. The circuit makes use of components of...