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.
September 2016 - It can be obtained from Mouser Electronics new LED indicators for panel mounting...
This circuit can provide constant currents adjustable between 1 and 10 mA. The transistors can be...
This circuit is from American documentation from the 90s. The configuration is very current and can...