Dry Electrodes & Headband, high impedance with Cyton

CidCid Vancouver
edited May 28 in Electrodes

Hi,
I've been trying to use the dry electrodes and headband from the OpenBCI Instructional kit with the Cyton board. What I found is that while the dry electrode provides some signal during the first session, after stopping and starting the session again, the channels with the dry electrodes have 0 voltage and railed impedance readings. We also tried restarting the app, the computer, and the Cyton board, and it still has the same problem. When I swapped the dry electrode for a paste electrode in the same channel, however, the paste electrode would work. I have checked the electrical connections of the dry electrodes with a multimeter and they seem fine, but I cannot seem to get any readings from the Cyton board when I look at the GUI.

We used to do these tests more than a year ago with the exact same hardware (electrodes and board) and it would work. We have also tried with the older version of the OpenBCI_GUI (through Processing 3.5.4), but it also has the same problem.

We are very unsure of what the reasons for this problem are. Do you have any suggestions that we should try to fix this?

Thanks,
Cidnee

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Cidnee, hi.

    Check the appearance of your comb or cone dry electrodes (especially the tip areas). It should be a uniform grey color on all surfaces. If you see any other coloration, it may mean that the 'silver chloride' coating has worn off. These electrodes have a plastic base layer, then plated with silver, then chlorided.

    Also, the skin on the subject should be clean, and free of excessive skin oils, conditioners, hair products, etc. If you can have success with a new (or little used) dry electrode, then also suspect the worn electrode may be the cause.

    The original 'spikey' comb electrodes, are also known to last longer than the newer, longer 5mm comb electrodes. This is because the 5mm combs, being longer, get more tip wear.

    Regards, William

  • CidCid Vancouver

    Thanks for your reply! I also have the IDUN dryode electrodes which I have been trying to test on the forehead, and I get the same result; I know that the dryode electrodes should work because I have gotten good impedance and signal from them when I tried using a desktop EEG system, but they seem to not work on the openBCI board. Are there potentially any settings in the GUI that are preventing the dry electrodes from providing any recordings? I'm also wondering if there is any effect with the skin electrode impedance due to the capacitance of the dry electrodes that may be affecting the board. If the capacitance is the issue, do you have any suggestions on how to potentially reduce the impedance due to the capacitance of the dry electrodes?

  • wjcroftwjcroft Mount Shasta, CA

    Have you used the GUI to measure impedance? What do you see, paste vs dry vs IDUN ?

  • CidCid Vancouver

    For the paste I saw below 5kohm consistently, but for the dry and IDUN it just says railed, or during the short random periods of time when the dry and IDUN electrodes did work on the board, they were around 50kohm.

  • wjcroftwjcroft Mount Shasta, CA

    It sounds like your dry and IDUN electrodes are 'used up'. IDUN dryode's have limited lifetime, as well as the comb and cone silver chloride dry electrodes. Did you check the tips of the combs for change in color? Do you have the spiky combs or the 5mm combs. The later wear out faster.

    If you are seeing changes in impedance measurements, that is a sign the issue is with your electrodes.

  • wjcroftwjcroft Mount Shasta, CA

    If you are using dry electrodes with the headband straps, the tension on the straps is directly correlated to impedance reduction. When these electrodes are used with the Ultracortex, uniform spring pressure is applied to each electrode.

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