2 cyton boards EEG + ECG, Bias conflict?

BioPotentialBioPotential
in Cyton
If I use a Cyton for EEG and another board configured as ECG, would there be issues with the bias of both boards, since they might now get added in the body in a funny way.
Would this be a cause for concern?
If it is, is there a way to configure both boards with a common bias?
Probably the obvious answer here is to use a Cyton + Daisy addon and everything sorts itself out. But I prefer having 2 boards one on the head and another on the chest so that way the electrodes are kept as short as possible for each board.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    I would suggest for the EEG board, to leave the settings in the default state: SRB2 reference, Bias enabled on all channels.

    For the ECG board, I assume you are using some differential channels. Disconnect those from SRB2 and SRB1, also turn off the Bias generation on those channels.

    The ECG board will still use the Bias / Ground connection as centerpoint for the differential amplifiers, but will not sense or generate a Bias offset (DRL) to inject. Just use a notch filter at mains frequency.
  • wjcroftwjcroft Mount Shasta, CA
    On the ECG board, you still will run the Bias / Ground to the subject. It just won't be injecting counter-common-mode voltages.

    And... Try it both ways, on the ECG system, TURN ON the Bias and see if you get a substantial improvement in mains rejection. I doubt it.

  • BioPotentialBioPotential
    So the ECG board would be using the bias from EEG is that correct? I was wondering how would that work out, since both boards use separate set of batteries and are not connected in anyway so are floating with respect to each other.
    Also I have only one board so cannot really test this out practically, I wanted to know if this would surely work so I can make provisions accordingly.
  • wjcroftwjcroft Mount Shasta, CA
    No, the Bias lead from the EEG is on the scalp. The Bias lead from the ECG is on the lower right abdomen position. The earlier comments on this thread mention this. And suggest turning off the 'Bias' setting on your channels for the ECG device. That way the ECG Bias is only acting as a centering mechanism for the ADS1299 differential amps. The ECG Bias will not be pushing a counter common mode (mains) cancellation voltage into that electrode. I also suggested above that you try it initially with Bias setting OFF, then turn ON to just see if any difference happens in the mains rejection. Recommended setting is OFF.

    The Bias injection is very weak to begin with, and I doubt would carry from scalp to abdomen.

    Clinical ECG machines may take a different approach. ADS1299 is targeted at EEG applications.
  • BioPotentialBioPotential
    Ok, thanks for reaffirming that. So in this configuration the ECG is not cancelling the common mode noise signals correct while the EEG is. Probable the best way to know it is to test it. I'll try and get my hands on another Cyton board.
  • wjcroftwjcroft Mount Shasta, CA
    Correct. You use notch filters on both the EEG and ECG units, they handle the majority of the mains issues. I think the counter-mains injection of the Bias idea is overrated. It may be a different story in clinical grade ECG equipment.
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