This circuit was found in 1980s American documentation. The transducer is a piezoelectric capsule and the power supply voltage can be between 3 and 18 V.
Published in Radio Electronics in January 1963, this circuit uses 5 transistors of the time. The...
The transistor of this old mixer can be the BC558 and the power can be done with batteries,...
The output voltage of this regulator circuit can be cut (dropping to 1.2 V) from a high level...