We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer unusual in our day. The transistor is general purpose type.
Suggested by Siliconix in documentation from the 90's, this circuit supports current equivalent...
This circuit decodes a 1800 Hz tone used in communications. The circuit is from an American...
This circuit was obtained in 1981 documentation. It is an FM transmitter that can serve to emit...