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Problem with EKG signal conditioning part (SLAA280A)

Pakkiresh Badami
Prodigy 30 points
Other Parts Discussed in Thread: MSP430FG439, OPA2251, INA117

Hi,

I have a problem in implementing the analog front end module to condition the ECG signal prior to giving it as input to ADC. I have used two ECG leads and wet electrodes unlike shown in slaa280a App note i.e. two copper plates to pick up the ECG signal  and there is nothing other than noise. Please, I request you to help me sort out this problem...

i have used INA122PA instead of INA321EA and also OPA2251 in place of internal op amps of MSP430FG439.. 

 

  • 0
    Genius 4680 points

    Isn't it contamination of electrical activity of muscles (EMG: electromyogram)?

    Relax arm muscles, and touch to the electrodes softly.

    I wrote about points to take EKG in this post.

    If it doesn't work, post your schematic to discuss on your circuit.

    Tsuneo

  • 0 in reply to Tsuneo Chinzei
    Prodigy 30 points

    yes, I think you are right... In that circuit, we get a gain of 1000x approximately and the resultant voltage is in the range of 100V after amplification.. It seems we are amplifying EMG signal.. How to get rid of it.. Any specific methods other than one already mentioned in your reply.. Thank you for your reply

  • 0 in reply to Pakkiresh Badami
    Genius 4680 points

    Pakkiresh Badami said:
    It seems we are amplifying EMG signal.. How to get rid of it..


    Just relax the muscles :-) It isn't so difficult.

    Rather, noise from environment (power line, cell phone, etc) may disturb the amplifier.

    a) Input filter
    EKG monitors around 0.5 - 80 Hz signal.
    Add capacitors to the front-end differential amplifier.
    This app note describes well about common mode / differential mode filters.

    INPUT FILTERING THE INA117 ±200V DIFFERENCE AMPLIFIER
    http://www.ti.com/lit/an/sboa016/sboa016.pdf

    b) Indifferent electrode
    You may add third lead to the circuit, to stabilize common mode potential.
    In the "Figure 10. Schematic Diagram" of TI's EKG app note,
    the third lead connects to the node of R17 and R20.
    The other end of the lead attaches to a leg, far end from heart.

    Tsuneo

  • 0 in reply to Tsuneo Chinzei
    Prodigy 30 points

    Thank You.. I'l try your suggestions...

    1.what does it mean by 'DNP' written on both resistors and capacitors in Fig. 10 of App note.. There is nothing related to their values in the whole report..

    2. Its written that slightest difference in the electrode lengths can cause offset which in turn results in noise at the output.

    3. I'm checking it directly after passing through processor.. Do you think we should first observe the output before sampling it in the processor..I decided to watch it after sampling as i read a report  http://www.analog.com/library/analogDialogue/archives/37-11/ecg.html    watch fig. 5

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