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.
We found this circuit in a 1983 English magazine, but it can be easily assembled today, as all...
This circuit was found in a 1967 documentation. The switch diode is a component of the time and is...
This circuit of very high input resistance was found in a Radio Shack documentation from 1977. The...