Non-Contact Voltage Detector: Electricity can cause injury or even can become the cause of death which 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 testing the presence of AC voltages. You need not worry about getting zapped because it is a noncontact voltage tester.

Non-Contact Voltage Detector Components

Circuit Diagram of  Non-Contact Voltage Detector

Non-Contact Voltage Detector by using transistor

In this modern age almost everything we use with an electric current. Before working with the AC object we must verify that the current is not present where we work. So we use the tester, A non-contact voltage tester is a 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 Non-Contact Voltage Detector

Non-Contact Voltage Detector using Transistor

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 any 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 an antenna with a small piece of copper wire and is connected it to the base of the first Transistor (BC547). The 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 the base.

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

We can use a small buzzer in place of an LED. The buzzer will alert you through voice, Buzzer should be 3 volts because we are using a 3v battery.

How to Operate a non-contact-voltage-detector?

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

Applications of non-contact-voltage-detector

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

Two Transistors voltage tester

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