Ganglion, dry electrodes, expected impedance ?

edited March 11 in Ganglion

Hello,
I recently got a strarter kit with Gaglion board and dry electrodes. I also looked at some tutorials and saw that I needed to do an Impedance check to make sure the lights next to each channel are green. However, I can only get the flat electrodes to go just below 200 (and that is if I really press on them with my fingers), otherwise they are in the 250-350 rage. The other ones that are meant to go between the hair are usually in the 400-500 + range. I think I need to get to 40-50 or below for the lights to turn green vs. red I am getting now - see image attached.

Some of the things I tried:

  • scruppbing my foreahead with soap, washing off, wiping with a towel
  • pressing electrodes hard against my head
  • applying a small dropplet of water between the skin and flat widget that snaps into electrode for greated conductivity
  • taking off the little widgets that electrodes snap to and touching the electrodes to my skin - forehead and parts of hands, just to see what happens.

Still no results....

Any ideas as to what may be causing this? Thanks a lot!
Ivan

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited March 11

    Hi Ivan,

    There is an informative Forum post regarding dry electrodes with Cyton at this link. Essentially, dry silver chloride electrodes cannot achieve the 50K or lower impedances seen with 'wet' electrodes that use paste, gel, or other electrolytes.

    https://openbci.com/forum/index.php?p=/discussion/comment/13328/#Comment_13328

    I suggest you also email (contact at openbci.com) which is customer support. Some text in the online docs for the dry electrode systems should mention this fact. But do not currently.

    The link above contrasts the skin impedance at the electrode, with the INPUT impedance of the Cyton amplifier chip (ADS1299) which is very high, 1 gigaohm. This allows more latitude with the Cyton skin impedance requirements when using dry electrodes.

    However, the input impedance of the Ganglion is not as well characterized as Cyton. Customer service may be able to shed more light. A related thread on Ganglion input impedance is here:

    https://openbci.com/forum/index.php?p=/discussion/1466/input-impedance-of-the-ganglion-board

    If you email customer service, include a link to your own Forum post with replies, for clarity.

    William

  • edited March 12

    Thanks, William. One of the turorials I saw online using Ganglion said to run impedance check and make sure the lights are green:

    • at 8:25 mark - see green letters at bottom of video).

    I did email customer service for clarification as you suggested.

  • wjcroftwjcroft Mount Shasta, CA

    Assuming you read the link on what impedance Ultracortex (dry electrodes) are typically seeing. Dry electrodes cannot achieve the low impedances seen with wet electrodes.

  • Yes, I did. Thanks, William.

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