This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is 1000 M ohm.
This is another quick adder that we found in an Electronic Design from the 80s. It also applies to...
The idea of this circuit is a resistance meter or continuity test with a common microammeter or...
This circuit turns off after a time that depends on C1. The circuit is from an Electronics Now...