On this venture, I’ll present you find out how to design a easy however environment-friendly Non-Contact Voltage Tester. Introduction

Electrical energy has to turn into a fundamental want for humanity as virtually every thing we use in our everyday life runs on it. But when you don’t take mandatory security precautions whereas working with electrical energy or electrical home equipment, it may possibly trigger extreme accidents and even death.

So, earlier than working with AC Mains provide close to junction packing containers like putting in a brand new system, for instance, you have to flip off the provision and confirm that there is no such thing as a voltage within the swap board.

Voltage Testers are units that detect and signifies the presence of voltage in energy cables, electrical cords, lighting, circuit breakers, wires, energy shops, and many others. A Non-Contact Voltage Tester, because the title suggests, is a voltage detector system that doesn’t want any contact with cables, cords or shops.

On this venture, I’ve designed an easy battery-powered Non-Contact Voltage Tester Circuit that can be utilized to confirm the presence of voltage close to all of the above talked about locations.

Precept of Operation

Any present carrying conductor produces a small magnetic discipline round it and the kind of magnetic discipline relies on the kind of present passing by way of the conductor. For instance, if AC (alternating present) is flowing by way of the conductor, then the magnetic discipline across the conductor additionally varies periodically.

The precept of this circuit is to detect this various magnetic discipline and point out whether or not voltage is current or not.

As a way to detect the voltages, I shall be utilizing three NPN Transistors. Relying on the quantity of base present, the collector – to – emitter present is decided in a transistor. The ratio of the collector-emitter present to base present is named Acquire and in the case of 2N3904 (which is the transistor used on this venture), this worth is roughly 200.

If the output of 1 transistor is related to the base of the following transistor, the online acquire is the product of a particular person’s positive aspects.

Equally, if we add one other transistor, the entire acquire is acquire of a single transistor raised to the ability of three (200x200x200).

Circuit Diagram

The next is the circuit diagram of Contactless Voltage Tester.

Parts Required

  • NPN Transistors – 2N3904 X 3
  • 1MΩ Resistor
  • 100KΩ Resistor
  • 220Ω Resistor
  • 5mm LED
  • Small piece of copper wire wound as an antenna
  • 3V CR2032 Battery with holder
  • Small perf board

Circuit Design of Non-Contact Voltage Tester

A small copper wire (about 12CM) is wound as an antenna and is related to the bottom of the primary NPN Transistor. If this antenna detects the magnetic discipline when positioned close to AC energized objects like cables and switches, it will get induced with a small present (because of electromagnetic induction) and therefore prompts the primary transistor.

For the reason that the output of the primary transistor drives the second transistor, it will get activated as so on. Because the third transistor is activated, the LED is turned ON indicating the presence of a voltage.

Moreover, you may place a small buzzer in collection with the LED in order that it’s activated at any time when the circuit detects any voltage.

Learn how to Function Non Contact Voltage Tester?

  • Make the connections as per the circuit diagram on a perf board and solder the parts.
  • Join the battery to the circuit and the system is now powered on.
  • You’ll be able to place the circuit board in a small field with solely the antenna protruding out.
  • Place the antenna close to electrical shops, switches, circuit breakers and many others.
  • If voltage is passing although these parts and units, the LED will gentle up.
  • To avoid wasting the battery, disconnect it from the circuit when it’s not getting used.


  • This straightforward Non Contact Voltage Tester can be utilized in a number of locations and close to a number of objects like cables, cords, shops, swap boards, junction packing containers, circuit breakers and many others. to detect voltage with out making any contact.
  • Since it’s battery operated, you may insert the circuit is a small field and make it moveable.
  • It may be utilized in numerous fields like safety, communication, irrigation, leisure, atmosphere and many others.

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