This circuit with two transistors was found in ancient European documentation. Transistors support equivalents. The indicator on this circuit is an ordinary 50 to 100 mA lamp.
This circuit was found in a 1975 documentation. Current general-purpose transistors can be used,...
We found this circuit in a publication for radio amateurs in 1974. The bipolar transistors can be...
This conventional humidity or water alarm circuit was found in an English documentation from 1974....