Continuity tester

The continuity tester is based on the well-tried ~A741, which is used as a comparator that operates a buzzer at its output. The inverting (~) input is at half the supply voltage via R3 and R4. When the potential at the non-inverting (+) input is lower than that at the -ve Input, which is the case when the resistance between the two terminals is small enough, the buzzer will be actuated.