connect 1 OpenBCI to 2 bodies, pin interference?

roithamerroithamer
edited August 2015 in Hardware
Hey there. I'm seeing some relation between channels that I don't think I should be seeing. On my V3 board I have one pair of electrodes connected to the 2N and P pins and another pair connected to the 8 N and P. All other pins are turned off, SRB2 is off for all pins, SRB1 is off, BIAS is excluded for all pins and there are no other physical connections to the board. The two pairs of electrodes are not connected to the same body. The two signals appear to be rough inversions of one another where I would expect discrete data. Any ideas?

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Comments

  • wjcroftwjcroft Mount Shasta, CA
    Just as a first guess, the ADS1299 chip is not designed to run without a Bias connection. The Bias does both common mode noise cancellation, and provides for the differential amplifiers to 'center' themselves. Can you try just using a Y-connection and run Bias to both people, then turn Bias back on? Not sure if you should turn it back on for just one, or both. Experiment.

    Also connecting two people like this might increase your exposure to noise, as the 'antenna' is much larger. You could also experiment with perhaps shielding some of the leads involved.

    Can you describe what your goals are with the 2 person experiment? Is this ECG, EEG, etc.

  • chipaudettechipaudette
    edited September 2015
    Hi roihamer,

    I've got some experience on this issue...for our brain-controlled shark hack, we connected five people to a single OpenBCI unit.  My write-up is linked below, including pictures of how we connected ourselves to my OpenBCI unit and including screenshots of how we configured the OpenBCI unit via the GUI...


    As it describes, we had each person on their own P and N channel, just like you tried for your own experiment.  For our hack, though, we also connected each person to the Bias line so that their DC value wouldn't float off to an unacceptable value.  To get five people attached to the Bias pin, we needed to solder more pins to the existing bias pin, but that was easy enough to do.

    I hope that this helps!

    Chip

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