Non Contact AC Voltage Detector Circuit

Last Updated on March 16, 2024

By using this simple Non Contact AC Voltage Detector Circuit we can identify the presence of AC voltage in wire or we can use it as a wire tracker, and also helps to detect broken supply wires. This circuit may not detect DC supply wire.

This circuit made with few easily available components. It can produce visual and sound alert during the detection of AC supply on wire.

Circuit Diagram

Prototype Video

Components Required

  1. Transistor BC547 = 3 nos.
  2. Buzzer 5 volt.
  3. LED red color.
  4.  Resistor 1MΩ, 100KΩ, 100Ω each one.
  5.  Switch.
  6.  Battery 9 volt.
  7.  Connecting wires.

Construction & Working

Main part of this simple AC voltage detector is transistor, it acts as a amplifier and switch, Buzzer produce sound alert when the wire spiral detects the EMF (electro magnetic field) on AC supply carrying wire, LED also glows to indicate the AC supply detection.

BC 547 Transistor

It is a general purpose NPN bipolar junction transistor, it has three terminals called collector, base, emitter. This transistor widely used in amplification, switching and other active applications.

In this circuit three stage constructed with BC547, transistor Q3 base is connected with wire spiral and it will detect EMF on the AC supply carrying wire, and signal from Q3 transistor is given to the Q2 transistor base, this Q2 gets large bias than Q3 and so it can amplify the input signal and gives to the Q1 transistor base, here the Q1 transistor acts as a switch and when signal reach its base it becomes closed switch and connects buzzer, LED with bias, if no signal then Q1 stays in off condition.

Note:- For this circuit we can use small Copper plate or Wire spiral as a EMF detector, the wire spiral can be made from 15cm insulated wire. Should not touch the spiral wire or bare hand on the AC supply carrying wire, Be extremely care when you handle high volt AC supply.

4 thoughts on “Non Contact AC Voltage Detector Circuit

  1. Why do we need multiple BC547 , I mean it could have been done with single BC 547 also.

    Can you please help me understand this ?

    Also you have used word ” Higher Bias”..what does it mean

  2. Please teach me, Why the Non Contact AC Voltage Detector always alarm like detecting of electricity? on the product out of voltage, e.g. Wood table, plastic another like something that.

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