This circuit also detects IR, providing LED indication. The circuit is used to indicate humidity in bench tests. We found it in the Radio Electronics magazine of February 1990.
We found this circuit that warns when the gate of a house is opened in an old documentation,...
With 3 transistors, we found this receiver in a documentation from 1966. The circuit has an output...
Generating a square signal (50% active cycle), this circuit was found in Siliconix documentation from...