Sunday, 26 May 2019


Here is an easy to build EM Field detector with 4 stage LED strength indication and which has a wide range of applications. This circuit will detect electromagnetic fields and also static electricity. It detects if there is mains hum on a 240 Volt (or 110V) wall socket or cable without having to touch the object. It is enormously sensitive to any changes of the EM field surrounding it so it could be used to detect lightning (proof is in the video below) or maybe even ghosts. (No video proof of that alas! At least not yet  ^__^ )

Here is the circuit (click on image to display full screen):

(Last revised: 02-june-2020: Changed 1M potmeter for 20 to 50K potmeter.)

Parts list:

8 x BC547 

1 x 680 Ohm 
4 x 470 Ohm
1 x 220 Ohm 
1 x 4K7 
1 x 3K3 
2 x 2K2 
1 x 100K
1 x 1M 

1 x 20K or 50K potmeter (use either a trimpotmeter or a panel potmeter if you're building this into a case.) 

LEDs (3mm):
3 x green, 1 x yellow, 1 x red

1 x 1N4148

9V battery clip, 1 switch (SPDT Toggle Switch ON-ON), 1 Bullet conncector for antenna. (optional)

Before I go on with the rest of the explanation, here's a video showing this EMF Detector in action in a lightning storm. In the background audio you can hear the crackle of the lightning on an AM radio I had switched on, and you can see that the meter lights up as the radio crackles and lightning occurs. Sometimes it even detects the build up of the electric field in the air before lightning happens. I'm not influencing the meter in any way. I'm just holding it by the 9 volt battery underneath. Here it is:

I designed this because I always found it a shame that these "everything detectors" or 8 Million times amplifiers never had a strength indicator so you could actually see if and how it's working. So I tried combining two pre-existing circuits and see if I could make them work together and it turned out to work very well. The first of these circuits is this 4 LED signal strength indicator

and the second is this circuit which is the actual detector stage, consisting of the 8 million times amplifier.

You can easily build this on a piece of stripboard.
The circuit needs only 8 transistors (BC547 or 2N3904), 5 LEDs and 11 resistors. The extra (5th) LED is there simply to function as a on/off indicator and could be left out if you so wish. I used 3mm LEDs on this project but 5mm will work too. Don't use LEDs that draw a lot of current though like bright white LEDs or blue LEDs. The circuit is fed from a normal 9 Volt battery.

The sensitivity of the circuit can be changed with the 20K or 50K potmeter. If you're using it like me, without a case, you can use a trim-potmeter. If you're building this into a little case then use a panel potmeter for sensitivity.

The circuit is very sensitive and it reacts to all sorts of things. If you hold this EMF Detector  near any mains cables it will instantly detect the voltage, I noticed that if you hold it near metal it will detect that too and even in an open space it will sometimes indicate a field even if there's nothing visible there but it's not a malfunction because it will keep indicating on the same spot in the room.
Here are some pictures of the detector I build:

Enjoy building this awesome little "everything detector" ^____^ oh and hey, while you're here, please leave a comment! That'll be cool! :-)


  1. Hello Eddy, could I horizontally mirror the LED schematic part by placing the detector schematic below it, making the project look more like the K-2 EMF Meter?
    Following is the link of your duly altered drawing for better understanding >>>


    1. Yes I think that should work fine. It's pretty much the same setup.

  2. Hello Eddy, after I contacted you I thought better, I think I would put the detector circuit above the LED circuit, it would look more elegant >>>
    Thanks again :v

  3. Can you use any NPN transistor?

    1. I'm not sure but I don't think it's very critical which transistors you use. The 2N3904 should work just as well. But I haven't tried it with other transistors so I can't be sure.

    2. The 2N3904 work perfectly, I just finished today. It detects any and all electricity, it's just what I was looking for thank you so much.

    3. Fantastic! Thanks for letting me know. I'm glad it worked so well. That makes me happy too. It's a handy little circuit isn't it.

    4. I added in the text that you can also use the 2N3904, now that we know this for certain. Thanks again! :)

  4. Hello, do you have any tips as to how to have this work on a lower voltage? I'm trying to use 2 3v coin cell batteries. Would lowering the base emitter resistors on the stength meter do the trick?

    1. I'm not sure if this will work with such low voltages. Maybe you will need to use different transistors but I have no experience with that so you will have to experiment with that.

  5. bonjour, le transistor BC546A est aussi un très bon remplaçant...testé & validée.

  6. Hey Eddy!!

    Would it be possible to add a sound output so as to hear that signals, I mean, in a way like 'soma labs ether'... And record the noises to make music.
    Forgive me, but I've just built a lyra 8 diy and I'm almost obsessed with that kind of noisy industrial stuff.

    Thank in advance

    1. Hey, that's actually a very good idea! I think this will be no problem if you use an opamp connected to the collector of the 2nd transistor to the right. The first one is just an on/off indicator but the second should carry the full signal. An opamp will insure you don't put a load on the circuit. Try it out! And if you do, let me know how it goes, I will add it to this article if it works. ^___^

  7. hey! 20 to 50k potentiometer work fine as well right?