Electromyogram help

Discussion in 'The Projects Forum' started by MartinV, Feb 25, 2015.

  1. MartinV

    Thread Starter New Member

    Jun 2, 2011
    I came across some EKG (electrocardiogram) electrodes, and I'm planning on doing a little EMG project. I have started to read here and there but I could find any complete article on it, and I don't really know where to start. I tried using some differential amplifiers but couldn't really see even the slightest difference in the signal (The calculated Gain should have been about 100). I saw some ideas about using a instrumental amplifier, but I couldn't get anything from the simple differential amp. No movement in the signal what so ever, only some noise from the power grid (I think).
    What I want to ask you is:
    Can I use these EKG electrodes to detect EMG signal?
    Can someone help and show me where to start?

    Lessa EKG electrode front side:
    Lessa EKG electrode back side:

    Thank you!
  2. Reloadron

    Active Member

    Jan 15, 2015
    Not to dissuade you in this but I don't see an EMG as being much like an ECG or EKG. The following is taken from the WIKI regarding the probes:

    The entire read can be found here. Surface type probes just don't seem a viable way of going about this. There is quite a bit to doing it including excitation of the muscle tissue. Since you have the surface pads you may want to think about an ECG?

  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    An instrumentation amp is best. Electrode location is critical. Only use battery operated circuits for safety.

    You also need a dual power supply and use the mid voltage as your zero volt common (ground).

    You should also use an active virtual ground (using a unity gain op amp and a simple voltage divider as the input). Or, you can use the midpoint of two 9v batteries as your ground.

    The ground should be attached to your leg - this rejects noise. Put the electrodes as described on various sites.
    You also need some type of conducting electrolyte gel between electrode and skin. Epsom salt dissolved into and hand lotion should work for your experiment.
  4. MartinV

    Thread Starter New Member

    Jun 2, 2011
    EMG and ECG both work on the principle of detecting EM signals. The difference are the characteristics of the signals (such as amplitudes and freq ranges) and the positioning of the electrodes, as shown in the first table in this link: http://www.ni.com/white-paper/5593/en/

    The electrodes I have obtained are equipped with electrolyte gel, but I was thinking if it would be possible to make them work even without it. Probably should look around on the internet for that.
    Also, is it necessary to put the ground electrode on the leg? Can't it be a non-muscular part such as an elbow, or the little bone sticking out near the ankle of the hand.

    The Instrumentation amplifier circuit I intend to use looks like this. I can't seem to find INA128 around (I'm not from the USA, so some electrical components are really hard to find here), so I'll be making it according to the datasheet circuit given. And probably another circuit for a band filter, probably 300Hz - 3000 Hz. That 50 microFarad capacitor is meant to set a cutoff frequency of 15 Hz in an article I found, but I'll probably change that (do I need to?).