This circuit is from Mullard 1969 documentation. The circuit operates at a relatively high supply voltage and has a 10 Vpp output. The transistors are of the time, but admit equivalents.
We found this circuit in a 1968 Electronics World. The circuit uses a transistor of the time...
This simple humidity sensor can be used in rain or leak detectors. The circuit is for 12 V supply,...
The circuit shown in the figure is recommended for applications where a visual indication is...