Found in a Raytheon transistor manual from the 1950s, this circuit uses one of the first commercially available transistors, the CK722. The circuit is for using a small speaker as a microphone.
This simple alarm circuit was found in the May 1990 issue of Radio Electronics magazine. The...
The oscillator in figure 1 can be used in alarm, call or warning systems, producing a sound of...
The purpose of this 2000 documentation circuit is to decode SSB (BLU) signals to be audible on...