Wireless mains voltage tester.

john September 22, 2009 21 Comments

This circuit can be used to test whether mains voltage is present or not without having electric contact with mains line. The CMOS IC CD4033 is the heart of this circuit. The CD4033 consists of a 5 stage decade Johnson counter and an output decoder for converting the Johnson code to a 7 segment decoded output for driving 7 segment LED display. A 10cm long insulated copper wire connected to the clock pin (pin1) of the IC serves as the sensor. The sensor wire has to be placed in the vicinity of the mains wire to be tested. When there is no voltage in the mains line, no voltage will be induced in the sensor wire and the display will show a random digit. When there is voltage in the mains line, a small voltage will be induced in the sensor wire due to electromagnetic induction and this voltage is sufficient enough to clock the CMOS IC CD4033. Now the display will count from zero to nine and repeat.

Circuit diagram.

wireless mains indicator


  • The circuit can be assembled on a Vero board.
  • Use 9V PP3 battery for powering the circuit.
  • Use a 10cm insulated wire as the sensor.
  • The IC must be mounted on a holder.
  • Switch S1 can be a miniature ON/OFF switch.

  • krist
    February 14, 2015

    Is there any equivalent for IC CD4033 for this circuit ?? Coz i didn’t find any around my city . Plz answer thanks !

  • April 5, 2014

    Plz perfactly explain the test of main supply any contact

  • shivani garg
    November 16, 2013

    this ckt is really works… thanx for the ckt…thats my mini project..

  • October 21, 2013

    The mains voltage tester is a nice circuit to test the voltage. These type of Circuits are kind of foundation for the modern Testing Tools like Smart Tweezers.

  • tushar
    March 28, 2013

    what is the roll of resistors and capacitor in this wireless voltage tester?please suggest and reply

  • March 14, 2013

    Thanks, it works, it’s beautiful! But more than count from 1 to 9 and to repeat, it seems that trembles, because the count is too fast. It looks more like a vibration that counts. If you can slow down this count, how to do? Thanks again, Toni Ipnos.

  • March 5, 2013

    Wireless mains detector can also be built using 3 NPN transistors, 3 resistors & a 6v power supply. I have built this circuit and reviewed it. You can watch it at https://www.youtube.com/watch?v=RuNXPX-Mtxw&feature=youtube_gdata_player

    • priyanka
      July 5, 2013

      please help me… i had made the same ckt about which u tell bt led continuously glowing… it does nt sense mains voltage..tell me what to do..?

      • shivani garg
        November 16, 2013

        use copper wire small…becoz it sense rapidly…

  • shradha
    January 8, 2013

    which type of probes should be installed???

  • June 9, 2012

    Hai Readers,

    The 7 segment display will blink continously.
    So you can use this only for voltage indication purposes.

    If you like you can try this

    Wireless Mains Voltage Counter Circuit

    this uses 3, 7 segment displays

  • RICK
    March 28, 2012

    Be Careful Folks when using this,,,,,,Safety Always FIRST!! Nice Circuit Never The Less!!!!

  • Seetharaman
    March 10, 2011

    Hi Suyog you have to use common cathode display, cathode being connected to -ve common.

  • suyog tadke
    March 9, 2011

    which 7 seg display(anode or cathode) should i use

  • vinesh
    March 4, 2011

    hello sir, i purchased this equipment. I connected correctly but not working. It shows all segments are blinking but not induced any voltage when placed nearer to tested wire. Please tell me the solution sir.

  • Anshul
    November 15, 2010

    Hi Chethan Babu.s 0.1 µf is ceramic disc type capacitor.9V PP3 Battry will work.You Must Use 7 Segment Common Cathode Type Display.Pin 3 or 8 connected to ground respictly.I made and it still work.Display fast count 1 to 9.You can see that all displays are blinking because they change at 50 Hz.

    • priyanka
      July 4, 2013

      can ordinary 9v battery in not used here…? 9v pp3 is not yet available… tell me solution… i am waiting.. please reply fast

  • April 3, 2010

    Wireless main voltage tester -I have purchased componenta and connected correctly but not working…, I doubt Ordinary 9V battery can use and wat typof capacitor is used 0.1uF —-? Volt..,

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