The main feature of this circuit found in an old American publication is that it is powered by the very signal it converts. The transistors are of the time and can be replaced by current types.
This circuit, found in 2002 documentation, triggers LEDs when a phone call is received. The LEDs...
This simple version of a function generator with the XR2206 was found in the May 1977 issue of...
A pulse triggers this 800 Hz horn for a time determined by capacitor C1. Powered by 5 V the...