The circuit shown here is quite simple and sensitive, it is using only few commonly available parts and performs very well. An LED and a peizo buzzer is connected at the output of the circuit to show the audible and visual indication of a good connection. A buzzer plays very important part in a continuity tester because you can identify a connection while looking in the faulted circuit by hearing the buzzer sound and you don't have to look at the continuity tester frequently.
The circuit is using a commonly available 2N3904 transistor. Sensitivity of the circuit can be adjusted with the 50K variable resistor. Operating voltage of the circuit is 5V to 9V DC.
If you are working with your electronic projects or repairing any electronic circuit a continuity tester is an important device to have on your bench. A continuity tester identifies a connection between two points. It will let us know if a wire or connection on the pcb is broken or if a circuit has become open due to
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