Non-contact voltage contact testers are difficult to classify as a tester because they are not subject to a special standard. Non-contact phase testers use a sensor to detect the electric field strength in the immediate vicinity of the conductor and visually signal via a display. A battery is required for operation. Depending on the sensitivity, the existence of voltage can also be determined even when insulation of a cable is present. The fundamental problem, however, is the capacitive functioning of these devices, which is only suitable for detecting alternating voltage and does not detect DC voltages. Many devices also lack the essential safety. Safe detection of voltages above 50 V AC often not possible.
A digital clamp multimeter also does not need a “contact”, however a non-contact voltage tester is a simple, cheap instrument for just understanding whether the voltage is present.
Also, the circuit can be creatively used to build decorative and status lights.
There are many ways to build a non-contact voltage tester circuit. The easiest is to use two 2N3904 transistor, one 220 Ohm resistor, one LED and a 9V battery. Below is the circuit :
You will find the guide here, however this circuit is suitable to build a non-contact status light. This is an open base Darlington transistor amplifier with extremely high gain. If it doesn’t light up that doesn’t necessarily mean there is no live voltage!
We can build quite reliable non-contact voltage tester in more ways such as using IC 4017 Decade Counter or by using a 555 Timer IC or by using General Purpose NPN Transistors or by using an IC 74HC14 or by using IC LM358A and so on.
If you want to build a thing equivalent to the Non Contact Voltage Test Pens sold on Amazon, then the below resources may help you:
555 timer is a common chip used in electronics projects and you can easily build a non-contact tester with it. This circuit is very simple.