Bias for EOG in OpenBCI Python

JayroMartinezJayroMartinez Tübingen, Germany
edited May 2019 in Cyton
Hello everyone,

I'm not sure if this post belongs here or not. I'm trying to use OpenBCI to acquire some EOG data using the Python SDK, but I'm not sure about some things.

I've read that for EOG the best option is to use differential mode, so connect two electrodes to the same channel to acquire the voltage difference (in my case one channel for vertical signal and other channel for horizontal signal). The problem is that I'm not sure if I should not use a "reference" because in differential mode each electrode is referenced with the other electrode in the same channel or if I should use bias or SRB. 

Before acquiring the data I'm sending the parameters to the Cyton board to disconnect the channels that I'm not going to use and also I'm sending the command ser.write(b'x Channel 0 6 0 0 0 0 X') to use normal mode, remove channels from bias and not connect it to the SRB. Is that correct? Or should I change the input mode?

Also, is there any difference in connecting the electrodes V1 to P1 and V2 to N1 and do it in the opposite way (V1 to N1 and V2 to P1)? Because the values that I have now are negative values and this feels strange for me.

Thank you very much in advance for your help.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited May 2019
    Jayro, hi

    Have you done the Cyton tutorial? The EOG case is not much different than the EMG case shown in the tutorial. Both are differential. You just disconnect those channels from the SRB bus. Your Bias can only be applied to those scalp channels used for EEG (referential, not differential).

    Play around a bit with the GUI Settings page, which has these same controls, but not at SDK command level.

    Not sure your terminology of V P N. The input pins are labeled IN1N, IN2N, IN*N, the row of pins closest to board, used for EEG channels. And IN1P, IN2P, etc. Farther pins. Only used in differential applications.


    Regards,

    William

  • JayroMartinezJayroMartinez Tübingen, Germany
    Hi William,

    Thank you very much for your reply, I think everything is clear now.
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