Non contact AC voltage detector circuit

A non-contact AC detector is an easy and safe AC live line tester. It can detect electricity in a conductor without any physical contact. The device can indicate as it reaches near to a charged line.

Here a simple AC detector circuit using a 4017-decade counter IC. The circuit can use to detect the current through insulated wires, conduit wirings, etc.

non-contact ac mains voltage detector circuit

As shown in the circuit, a probe or antenna (a wire is enough for the purpose) has connected to the pin 14 of the IC. That is the clock input of the IC which receives the input pulses. AC main phase supply near the line is detected by means of a dielectric coupling produced between the line and the probe. So, If the line has any pulsating EMF (i.e., an active line) the LED flashes and indicates whether the line has any charge.

The output of the counter shifts from output 0 to output 10 for each positive edge trigger pulse received at pin 14. As the LED has attached to one of this 10 outputs, the LED flashes once for 10 clock pulse inputs. Thus, in a normal 50HZ supply the LED flashes at a rate of 5 times per second.

The sensitivity of the circuit will vary with the length and conductivity of the probe. The clock input of the IC has very high sensitivity. Here it will be extra sensitive as it has connected with a wire or probe. So the circuit requires a proper grounding to work satisfactorily.

While using the circuit, make sure it has no any direct contact with the live terminals. Because it can cause a direct electric shock from the supply. Always use the probe over an insulated surface or use an insulated probe. Ensure a complete electrical isolation between the circuit and charged conductors to prevent any accidental contact.

Components required

IC – 4017

Resistor- 680ohms


Supply – 6v

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2 Responses

  1. ss says:

    How to change the range of antenna for non-contact voltage detection?
    For example I would like to detect 220 VAC at 1 cm, 2 cm or 5 cm. Can I make these changes with potentiometer or 2 keys?

    • admin says:

      To some extent, you can adjust the range by varying the antenna length. But the detection range varies or it mainly depends on the intensity of the current through the AC phase than the circuit parameters. So, I don’t think it is possible to set accurate ranges of 1cm or 5cm. But you can experiment by changing antenna length or with a high-value resistor or potentiometer.

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