This proximity relay circuit was found in the July 1990 Radio Electronics magazine. The supply voltage should be according to the relay used.
This circuit can function as an output shield for microcontrollers, being compatible with TTL...
This circuit is from a 1979 publication, using displays of 7 segments of common cathode. The...
This circuit is from an English publication of 1982. The bipolar transistor can be a BC548 and the...