This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V power source must be isolated from the mains.
This circuit, which appears at other points on this site, can be designed with both 4011 and 4001...
We found this circuit in an American documentation from the 90s. The circuit applies to vehicles...
Found in Motorola documentation from 1967, this circuit shows how it is possible to obtain a...