Mains Detector





Introduction: Mains Detector

This device detects mains and has tested more reliable than commercial models.

NOTE:If this device fails and you are hurt, i will take no responsibility. Test the device before use.

That said, this is what you need:

1)5 npn transistors
3)9v & clip

Step 1: Wire the Circuit

The circuit is simple.
Wire up using the picture below.

Step 2: You Are Done.

You are done.

To use it put the antena by the mains you will hear a buzzing sound from the speaker if they are live.
It should sound like this:



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    13 Discussions

    I built the circuit using 2n2222A transistors (npn) on a breadboard, and I used an LED with 14 kohm resistance in series with it, instead of the speaker. I've noticed a weird effect where the circuit seems to work well: The LED will be dim and as I bring it closer to a wall tranformer the LED brightens, then dims as I move it away again. However, if I let the circuit sit somewhere, the LED gradually increases in brightness, all by itself, even if I put it on a table far away from any EMF sources. What do you think might be causing this? I want to send output from the circuit to an arduino to detect EMF, but if the input signal is unpredictably drifting upwards this will cause problems. Any suggestions would be appreciated, thanks!

    1 reply

    The LED is increasing in brightness due to very minute charges being applied to the transistor chain. Try adding a very high value resistor to offset the unwanted charge on the antenna.

    Do you really need 5 transistors? What's your aerial design - I'm thinking that a loop might be good?


    10 replies

    The sound is already hard to hear with 5.
    You could try 4 with headphones.

    3rd time - what is your aerial like? Might you get more signal by redesigning it?


    It is a simple wire on v1 on v2 it is a bar.
    I tried a coil on my first version.
    The closer and more surface area the better.

    The coil wasn't better? I'm thinking of building one, which is why I'm asking.


    The coil did not seem to improve the device.
    I used a coil with 4 inches of turns around a 1cm inch stick.

    OK thanks for trying that, if I do make one that works, I'll let you know.


    what if i use darlington pairs? i think i can use 3 darlington transistors and get the same output