This circuit was found in a 1964 Electronic Design. The circuit makes use of transistors of the time. Current equivalent transistors may be experienced.
This simple humidity sensor can be used in rain or leak detectors. The circuit is for 12 V supply,...
We found this circuit in a 1975 circuit manual. The operational amplifier is of the old type and...
The operational amplifier for this circuit found in a 1979 documentation may be the 741. We can...