In this project, I will show you how to design a simple but effective non-contact voltage tester. This is a do-it-yourself project where you can build and test the presence of voltage using very simple components. Since it is a non-contact voltage tester, you don't have to worry about whether it will be destroyed.
A small copper wire (about 12 CM) is wound as an antenna and connected to the first NPN transistor on the pedestal. If this antenna detects a magnetic field while placed near an AC-energized object (such as a cable and switch), it will be induced with a small current (due to electromagnetic induction), thereby activating the first transistor.
Since the output of the first transistor drives the second transistor, it is activated. When the third transistor is activated, the LED indicator lights up to indicate the presence of a voltage.
In addition, you can connect a small buzzer in series with the LED so that it is activated whenever the circuit detects any voltage.