This circuit, which uses a quadruple comparator, was found in old American documentation. The response curve is shown next to the diagram and can be adjusted in the trimpots.
Approaching the hand or an object to the sensor of this circuit, the relay closes its contacts. The...
This circuit is from a Popular Electronics from 1992. The circuit powers an LED when triggered....
This 1995 circuit uses interruption sensors or NC connected in series in any quantity. With the...