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EMF Detector

Discussion in 'General Electronics Discussion' started by Capsos, Jun 18, 2017.

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  1. Capsos

    Capsos

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    Jun 18, 2017
    Hi everyone. Ive worked with electronics for years but never progressed past basic. But for my job I want to build a hand help emf detector. Some jobs I go to they have issues with there WiFi and it's sometimes down to this and want a way to detect it and if so how much. Does anyone have a diagram and a parts list so I could build one please.
     
  2. Alec_t

    Alec_t

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    Welcome to EP!
    'EMF' = voltage, which you can detect with a multi-meter.
    Do you mean 'EMI' (Electro Magnetic Interference)?
     
  3. Irv

    Irv

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    http://www.instructables.com/id/Arduino-EMF-Detector/

    You should be able to build this in 10 minutes with a few dollars worth of parts.

    I would use a smaller Nano (Chinese copy of Arduino, 3 for $10 from Amazon),
    and an OLED for readout ($10 same source) because of the low power requirements.

    I run one from one of those little tube-shaped $5 cell phone rechargers for 50-60 hours before recharging. Makes it very portable. 9v battery works, also.

    The program and pin connections will have to be modified slightly if you use the OLED, but the OLED is more like a tiny text terminal, rather than a simple 7 segment display. Obviously, more versatile.

    I would fit the whole thing into a clear plastic tube 8 or 10" long, very portable and professional looking.
     
    Last edited: Jun 18, 2017
    hevans1944 and davenn like this.
  4. Externet

    Externet

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  5. Capsos

    Capsos

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    Jun 18, 2017
    Yes sorry. EMI "autocorrect"
     
  6. Irv

    Irv

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    Jun 7, 2017
    Arouse1973 likes this.
  7. davenn

    davenn Moderator

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    do you really want to detect 'EMI' (Electro Magnetic Interference)?
    you first post didn't indicate that ....
    but detecting interference is a whole different ball game involving very wideband scanning equip like spectrum analysers


    you were right the first time
    EMF = Electro Magnetic Field

    EMF just happens to have another meaning that Alec_t latched onto

    Are you specifically only wanting to detect WiFi signals ? there are units available to do that sort of thing
    I use one when I am travelling to detect WiFi coming from motels etc that I may be able to log into whilst storm chasing
     
  8. Irv

    Irv

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    I would guess that he's suspects there's some machinery which generates RF noise which interferes with WiFi signals in the client's workplace. If that's the case, then walking around with an EMF detector would probably do the job, since the noise itself would likely be wideband.

    On the other hand, there "could" be a source of interference which is on the same frequency as the client's wifi. (an illegal transmitter, perhaps?). That would take something different (maybe the FCC would like to know)
     
    Arouse1973 and Capsos like this.
  9. Capsos

    Capsos

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    Jun 18, 2017
    I go to jobs when there WiFi / WAP units are having issues and sometimes its due to hi levels of EMI from hi voltage cables or power lines or something else. I wanted to make a scanner that could direct me to what ever is giving out high levels of EMI
     
  10. Capsos

    Capsos

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    Jun 18, 2017

    Yes that's it ! I try and trace the RF causing interface to the WAP / WiFi unit.
     
  11. davenn

    davenn Moderator

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    as I suggested that's where a high quality scanner or spectrum analyser are valuable for finding EMI :)
     
  12. Irv

    Irv

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    OP said he wanted to build one. Building a spectrum scanner or analyser is possible.
    He also said he's a beginner. Not so possible.
    A beginner building a high quality spectrum analyser? Still possible?

    None of that is necessary, unless the noise is actually coming from a tuned circuit acting as a transmitter or an actual transmitter.

    Any of the simple circuits posted earlier should do the job, with varying degrees of accuracy.

    If you just want a light to flicker when some EMF is detected, use one of the 741 op amp circuits.

    The Android circuits could give you a bit more info, such as relative level, if you need that.

    If you want a user-built "spectrum scanner", then a $20 SDR would - sort of - work.
    I have a couple of those, and they work to scan the spectrum, but:
    1. they don't usually do well above 2ghz, and WiFi uses 2.4 and 5 ghz, and
    2. they have lots of spikes from harmonics of the SDR and the computer that you use with it.
    Most of those spikes won't be the spike you're looking for.

    Or, buy a spectrum analyser, a few hundred to a few thousand dollars.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    If it's for detecting interference with WiFi then all you need is a WiFi module that can report noise levels.

    There's a simple project using the nrf24l01 module that does just this.
     
    davenn likes this.
  14. Irv

    Irv

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    Could there be another wifi router using the same frequency? There are free apps for phones/tablets that can display that info.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It could just be a leaky microwave oven.
     
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