This conventional relay light detector circuit uses a 741 as a voltage comparator. The sensitivity adjustment is made in R1. The supply voltage depends on the relay used.
One of the problems with common multimeters, especially analog ones, is that their low resistance scales...
This circuit is from the November 1974 issue of Radio Electronics magazine. The capacitor...
This circuit was found in a 1980s documentation for amateur radio. The circuit makes use of...