Constructing an Electromyogram Circuit

Discussion in 'The Projects Forum' started by working_on_EMG, Dec 9, 2010.

  1. working_on_EMG

    Thread Starter New Member

    Dec 4, 2010
    Hello everyone. Im currently working on constructing an Electromyogram (EMG) circuit for an electronics class project. The objective is to obtain EMG signals from the two major muscles in the forearm responsible for hand grip strength, namely the extensor carpi radialis longus and Flexor Digitorum Superficialis.

    For shielding, I have used an RCA to stereo cable to connect the Argentum Chloride surface electrodes to the input pins (2 and 3) of the INA 128 Burr Brown Instrumentation amplifier (please refer to attached file EMG Circuit Plan.pdf). I sliced of the banana plugs and replaced them with crocodile clips in order to clipp onto the press studs on AgCl electrodes.

    The stereo audio jack at the end of the RCA to stereo cable is connected to a female connector - the female has three parts (positive, negative and ground).. From this female connector, the positive and negative parts are wired to the inputs of the instrumentation amplifier.

    Figure 2 shown a portion of the EMG amplifer used in Saksit's thesis. This circuit provides both right leg drive and shielding. The RCA to stereo cable is represented as a phone plug in the circuit schematic in Figure 2. The ground part from the female connector is wired to the inverting input of U2A. U2A plays a significant role for right leg drive and also shielding. At the op amp U2B, the resistors R4 and R3 provide a gain = 39, R4/R3. Im not exactly sure what R5 does though..

    I would like to ask:

    1) If I want to filter frequencies below 20Hz (caused by movement artifact) and frequencies above 500 Hz, can I cascade a sallen key band pass filter like the one shown in figure 3 to the output of the circuit in figure 2? Do you guys have any suggestions on what type of op amp, capacitors and resistors for this band pass filter that I should use to achieve high signal to noise ratio?

    2) Im using a Tektronix digital oscilloscope, is there any way I can observe the signal to noise ratio? perhaps by connecting the oscilloscope to a laptop running matlab?

    Thanks! Would really appreciate feedback and comments from all of you out there..
  2. leonel

    New Member

    Aug 31, 2010
    hey plz can u email me your circuit diagram?i cant download it i dont knw why
    plz i ll apreciate
    Last edited by a moderator: Mar 2, 2011