This resistive sensor was found in a 1969 US documentation. The circuit uses transistors of the time, but current equivalents can be employed.
We found this circuit in an English publication of 1976. It can be easily assembled by changing the...
This circuit is from an 80's documentation, applying to ordinary comparators. The source does not...
This experimental circuit is from a 1975s publication. The coil consists of 80 turns of wire AWG...