This continuity tester is build using transistors and a few passive electronic component. Output frequency is determined by the measured resistance. Small and extremely easy to use, the tester will allow you to focus on the connections that you want to examine, instead watch an LED indication of a display, tester produces a beep.
The circuit consists of a two-transistor oscillator whose output frequency is a function of the measured resistance between the input terminals A and B.
Tones frequency decreases with increasing resistance tester measured.
Potentiometer P1 is adjusted so as to obtain a pleasant tone input terminals shorted.