Sunday, 26 May 2019

ELECTRO-MAGNETIC FIELD DETECTOR.

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:

Transistors:
8 x BC547 

Resistors:
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 

Potmeter:
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

Diode:
1 x 1N4148

Miscellaneous:
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. Make sure there's a grounding point when you build it into a case. Some connector from where you can ground it.

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. 
This meter works best if it is grounded properly, either by connecting minus to a metal case in which you build the meter and then holding it in your hand  or by  grounding it to some metal item (do NOT connect to ground of mains power supply!!!)
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! :-)

28 comments:

  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 >>> https://prnt.sc/q2mp1l

    Thanks
    Anderson

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

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  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 >>> https://prnt.sc/q2soe7
    Thanks again :v
    Anderson

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  3. Can you use any NPN transistor?

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    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.

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    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.

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    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.

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

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  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?

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    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.

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

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  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

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    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. ^___^

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    2. I think the sound output is also an excellent idea maybe a small piezo . Has anyone tried it ?

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

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  8. Hi, would it be okay if I use this circuit in a video if I credit you as author and post links to both this site, and your Youtube channel in the description?

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    1. Oh, I had a further question: Since I'm using through-hole components, is it okay to mount the resistors vertically to save space. It looks like the phase stays the same throughout the circuit, so would it even matter? For that matter is a flooded ground plane even necessary other than to spare the etchant? (I plan on making a PCB, rather than using strip board or similar)

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    2. Yes for both questions. You can use anything on this website in your video, no problem. And I think if you mount the resistors it would, if anything, work even better so that won't be a problem. I look forward to seeing the video :) Good luck!

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    3. * mount them vertically, I meant. As for the ground plane, with RF signals it's always a good thing to have a good ground plane but by all means experiment with this circuit. I'm sure it can be made even better in some ways. I'm no expert in these things. I just decided to put two circuits together and see if they worked together and they work really well. =)

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  9. Thanks! Yeah, I assume all the resistor leads are dong is making the antenna a bit longer. The video will be unlisted for a while, but I'll be able to send a link. I'll be scheduling all these videos to go live throughout October, since it's the time interest in these things picks up.

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    1. Yes over the summer time I can see the views for my website go down too as people do more outdoor things, although with the pandemic there are still a significant number of people who throw themselves onto their synthesizer hobby. Send me a link if you can and I'll keep it totally to myself. You can message me on Facebook.

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  10. oi,, pode enviar pcb pdf ? ou postar ?

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  11. Just built this circuit, it works surprisingly well! One interesting phenomenon I found was my cat's footsteps were registered while he was walking on a carpet about 5ft away. I used a slightly larger antenna, made from about 3 or 4 feet of leftover CAT5 internal wire wrapped around a PVC pipe.

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    1. Your cat must have generated some static electricity. That's amazing!

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