Noise with electrode Mount, Ganglion Headband

shanksshanks Vienna
in Headware
Hello, 

I order the spiky EEG electrodes combined with the Headband Kit for OpenBCI for my Ganglion board. I designed an electrode holder that covers the back of the electrode with PLA and from the front, a PLA plate is used with a screw to attach it to the headband. After I assembled it together I wanted to measure my EEG with the Open BCI software. The problem was, that I now have noise 10 fold on top of the normal EEG signal. Even if I disassembled the PLA and screw from the band the noise was still there. How could this be? The electrodes are monolinear so it could not be a short circuit. The Ganglion board has electrostatic discharge prevention so this shouldn't be a problem. Anybody an idea what could be the problem? 

Thank you for your help, 
David 

Comments

  • wjcroftwjcroft Mount Shasta, CA
    David, hi.

    Do the original (unmodified) spiky electrodes and headband, still give good signals with your Ganglion? How about the flat electrodes? This sounds like a problem with your electrode cables or connectors. If you have a multimeter (ohmmeter), you can check continuity with your cables. Should be close to zero ohms.

    I don't understand your use of the term 'monolinear'. The grey looking spiky and flat electrodes are made of plastic, first silver plated, then chemically chlorided. The result is called a silver / silver chloride electrode. (Ag-AgCl). Using such electrodes requires that the AgCl coating is not worn or chipped off (exposing the silver or plastic).

    Regards,

    William

  • shanksshanks Vienna
    Hi William, 

    Thank you for your answer! 

    No, after I disassembled the mounting and only used the spiky electrode with the electrode cable it still had noise on them. I tested a second Ganglion with the same spiky electrode and same electrode cable and there was no noise. Therefore the spiky electrode or the cable itself could not be the problem. 

    Here is what I did: I mounted a PLA printed part on the back of the electrode which covers the spiky electrode and the cable completely. This I put on the headband through a hole. From the other side, I used a washer and a small screw to fixate it to the headband. After I assembled it, I connected the Ganglion via Bluetooth to the PC and did an impedance check. The impedance was relatively low even though I did not wear the headband yet. I put the headband on, got the reference impedance low and started sending the signal. On the channel where I had my assembled PLA mount, I had a 10 fold noise on top of my signal. After that, I disassembled the mount and only used the spiky electrode with the cable to measure it again. I got the same results, again 10 fold noise on the same channel. The next step was to use another ganglion with the same spiky electrode and cable but without the mount. There it did not get any noise. Therefore I think maybe through some electrostatic charge I did damage the Ganglion board, could that be?

    Sorry that was the wrong word, I meant single-phase. 
    Do you know which plastic they use? 
    The electrode is not damaged with the mount I used, so this shouldn't be a problem I think. 

    Thanks for your help!
    David 
  • wjcroftwjcroft Mount Shasta, CA
    Yes, electrostatic discharge can damage the boards. The disclaimer statement does indicate this.


    Are all the channels effected on the damaged board, or just some?

  • shanksshanks Vienna
    Ok I understand. Does the cyton also not have electrostatic discharge protection? 

    I need to recheck that, but I don't have them with me right now, but with no electrodes attached they did not have any noise. 

    Best,
    David 
  • wjcroftwjcroft Mount Shasta, CA
    Both Cyton and Ganglion DO HAVE electrostatic / EMI protection ON THE ELECTRODE HEADER pins. However if a person has a strong static charge and they pickup ANY bare circuit board (not just OpenBCI) and touch internal traces -- it can blow out the internal circuit components. Some type of case, enclosure, or even small cardboard box would prevent contact with internal components.

    I suggest running some thorough tests on the suspected Ganglion board. Check each channel with something that has a predictable response, like the alpha wave test in the tutorials. Another test you can do on any EEG, is connect signal channel, to reference. This should produce close to zero microvolts.
  • shanksshanks Vienna
    ok thank you for your help! I will test the Ganglion tomorrow. 
  • shanksshanks Vienna
    I tested it now. Only Channel 1 has the noise even if I attach it to the Reference pin as you mentioned. 



Sign In or Register to comment.

© Vanilla Keystone Theme 2026