EMG signal to .wav

Discussion in 'General Electronics Chat' started by Dritech, Nov 9, 2015.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi all,
    The EMG signal is the signal picked up by surface electrodes when a muscle contracts. The average applitude of an EMG signal is approximately 0 to 5mV and the frequency is arround 10 to 500Hz. (please refer to attached diagrams of raw EMG signals).

    Is it possible to connect the surface electrodes to the microphone input of the computer so I can monitor and save raw EMG signals?

    Thanks in advance.
    [​IMG]
    [​IMG]
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,282
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    You will need a couple of stages of a good low noise preamp to get the voltage up to the line in of the PC.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
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    This sounds like a job for an above-average-quality microphone preamp, but beware the low frequency spec. Really flat response down to 10Hz means a low frequency corner freq of around 1 Hz. A mic preamp usually doesn't go that low because it would pick up more breathing noise. However, if you find a preamp circuit you like, we probably can recommend mods to get the low freq response.

    And, a large numer of ebay chinese mic preamp modules actually use a speaker amp chip. Do not consider anything based on an xx386.

    ak
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The frequency response of the PC sound card/module will determine the lower useful frequency limit. You'll be lucky if it goes below 20Hz.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yeah, I thought of that after I posted. Another approach is an external preamp driving a USB general purpose instrumentation A/D converter, followed by capture software that will create a .WAV. As always, it's the software that will be the problem.

    ak
     
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Thanks for the replies. So if the soundcard will block frequencies below 20Hz, is it possible to use a USB microphone? or will it still have a filtering module?
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Anything designed for audio almost certainly will have low frequency rolloff starting higher than you want. General purpose audio 20 Hz-ish. Microphone audio, 50 Hz-ish or higher. Rolling off the deep bass reduces picking up rumble from HVAC air movement, outside wind moving the building, and all kinds of other low freq events. OTOH, a data acquisition device must be good down to DC for things like power supply monitoring, liquid level sensing, and other super-low-freq signals. There are many 12 or 16 bit USB data acquisition devices, and this forum loves to ramble on about preamp designs. The problem is finding an A/D with the right software support.

    ak
     
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