DIY Non-Contact Voltage Detector

Description: Non-contact Voltage Detector
Skill Level: Beginner
Assembly Time: approximately 30 minutes

Electricity can cause injury or even can become the cause of death that is why safety must come first when working with electrical devices or electricity .In this article, we will show you how to design a simple efficient Non Contact Voltage detector by using transistors.  You can build this circuit by using simple components and test the presence of AC voltages. You need not worry about getting zapped because it is a non contact voltage tester.

Table of Contents


non connact ac test

In this modern age almost every thing we use with electric current. Before working with AC object we must verify that current is not presence where we work. So we use tester, A non-contact voltage tester is safe way to make sure that the AC power is off.

In this project, we have designed a very simple Non Contact Voltage Tester Circuit by using transistors. we have used only one type of transistor in this project.

circuit diagram


Components Required For Non Contact Current Tester

Qty. Part Description Mfr. Part No.
3 Transistors BC547 (NPN)
1 LED, Red or any color
1 Buzzer (optional) 3v
1 Switch ny type
1 9V Battery or 3v can be used also  or supply
1 Battery Snap
1 Case any plastic cover plastic cover

Required Tools:
Soldering Iron
Drill and drill bits (for making holes in the box)
Copper Wire
Cutters (for copper wire)
Adhesive Tape

Circuit Design of Non Contact Voltage Tester

Make antenna with small piece of copper wire and is connected to the base of the first Transistor (BC547). Antenna detects the magnetic field when we placed it near AC objects like cables and switches and etc, it gets a small amount of current and activates the first transistor through base.

The output of first transistor drives the second transistor, it gets activated and third transistor activated with 2nd transistors output. As the third transistor activates, the LED is turned ON.

We can use small buzzer on the place of LED. Buzzer will alert you through voice, Buzzer should 3 volts because we are using 3v battery.

How to Operate Non Contact Voltages Tester?

  • Make the connections as per the circuit diagram.
  • Connect the battery to the circuit.
  • You can place the circuit in small box.
  • Place the antenna near to the electrical appliances.
  • LED will run if the voltages are passing through the objects.


  • This simple Tester can be used on many places and near near many objects like switches, cables, outlets, cords, junction boxes, circuit breakers, fans, motors  etc.
  • you can make it portable by fixing it into small box.

Two Transistors  voltage tester

Thank you so much for visiting our website if you have any question about this circuit or any circuit about electricity or electrons you can discuss freely.