This circuit was found in the Electronics Experimenter Handbook from 1991. The sensor is a diode and the circuit has a relay according to the voltage used in the supply.
This circuit shows how to use flip-flops in a SIPO circuit with serial input and parallel output....
This circuit was found in the National Semiconductor Linear Applications Handbook, published in...
This circuit is from an 80's technical newsletter. The circuit can use any general purpose...