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 causes the relay to be energized when the input voltage exceeds the voltage value of...
The circuit we present is suggested by Linear Technologies (www.linear.com) and makes use of an...
Found in American documentation from the 90s, this circuit can be used as a shield with the...