EMG design help!

Discussion in 'The Projects Forum' started by formula_pacific81, Jan 27, 2016.

  1. formula_pacific81

    Thread Starter New Member

    Jan 27, 2016
    2
    0
    Hello! I'm trying to design EMG electrodes using the LMP7704 and I have the schematic (attached) breadboarded. It is using a DRL as well. As you can see E1 and E2 are the electrode inputs and I'm using Eout to view the signals on a oscilloscope but eventually it will go to a MCU. So, when Eout is connected to a scope I would expect to see some kind of muscle contractions in the form of high frequency oscillations; however, it seems like the inputs are not sensitive enough to detect them. Vcc = 2.5 and Vdd = -2.5. The circuit seems like it should work but I'm inexperienced in biopotential acquisition so maybe I'm missing something. As you can see there is no filtering, rectification, etc. of the signal, yet. I want to see the raw EMG signal first if possible. Any insights are much appreciated, thanks in advance!
     
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  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,523
    1,247
    What is the DRL output and why does it have a gain of 10?

    Muscles are a fairly high impedance source. That combines with C1 and C2 to form low pass filters. You might be filtering way all of the signal.

    ak
     
  3. formula_pacific81

    Thread Starter New Member

    Jan 27, 2016
    2
    0
    Hi ak, as I understand it, the DRL or driven-right-leg is used to reduce common mode voltage. It's basically a third electrode. In regards to the DRL gain, the circuit that I based this design off of had a DRL gain of 200 but in my testing it seemed too high so I reduced it. Lastly, C1 and C2 are not installed they are there as place holders.
     
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