Getting railed - using both snap and golden electrodes with Cyton

DrLuDrLu Israel
edited March 6 in Cyton

Hey everyone!
I am using the Cyton board for a Lucid Dreaming sleep research
When I set it up my EEG golden electrodes get “Railed” as in the picture, and stop receiving a signal.

My set up uses 7 channels:
1st EOG
2nd EMG
3rd EMG
4-7th EEG

Channels 1-3 SRB1 is set OFF having 2 electrodes at each channel.
The 6 and 7 EEG channels are golden electrodes, and get railed. The rest of the channels including SRB1&BIAS are snap electrodes.

Another time I tried using 4 channels as EEG – 2channels snap, 2channels golden – and set the SRB1&BIAS with golden instead of snap electrodes.
This runs the 2 EEG golden channels smoothly with low railed percentage, but the 2 EEG snap channels get a high railed percentage and eventually flatten out, stop giving any signal.

Is it possible to use both snap and golden electrodes on the Cyton, and how?
what is the reason channels get railed in the first place?

@retiutut
Appreciate the help! :)

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Hi Dr. Lu,

    Why are you using SRB1 with the EEG channels. The default Cyton Hardware Settings uses SRB2 for the reference pin. SRB2 creates a 'bus' by tying together all the top pins of each channel. This is then the reference for all the lower pins. If you have EMG / EOG channels, you want to disconnect those from the SRB2 and Bias. See this page,

    https://docs.openbci.com/GettingStarted/Biosensing-Setups/ExGSetup/

    William

  • DrLuDrLu Israel

    Hey William! Thanks for the replay.

    first of all wooooppsss - it was SRB2, writing SRB1 was a mistake.
    still trying to understand how to use both snap and golden electrodes at the same time, take this setup for example:
    channel 1 EOG snap electrode
    channel 2 EMG snap electrode
    channel 5 EEG snap electrode
    channel 6-7 EEG golden electrode

    Hardware settings
    for channel 1-2 SRB2&BIAS are off, also connected is an electrode to AGND
    channels 5-7 are 'yes' for SRB2&BIAS
    SRB2&BIAS are connected with golden electrodes

    as you can see from the picture, channel 5 EEG which is snap electrode gets immediately near railed and climbing, eventually completely railed if will stay long enough I take it from my last trails.

    here I switch SRB2&BIAS for snap electrodes instead of golden, you can see the reverse happening:

    channels 6-7 EEG golden electrodes get completely railed

    why is this happening?

    this is for comfort sake. It's much easier to use snap electrodes on some frontal/prefrontal areas for EEG, but I can use the golden electrodes if I have no choice.
    the best situation for me would be to be able to get EEG reading using both golden and snap electrodes on a snap SRB2&BIAS.

  • wjcroftwjcroft Mount Shasta, CA

    When you are referring to "snap electrode", do you mean the adhesive type that are pre gelled and have the silver chloride dot inside?

    Did you read the link I gave about how to do mixed signals? Did that change anything?

    In general, in EEG, mixing electrode metal types can produce 'galvanic' / battery-like effects do to the different metals and salt acting as a source of voltage. These effects can also happen with worn gold plated cup electrodes because under the gold layer, the base layer is tin metal. If the gold chips or exposes the tin, a battery is formed.

    I suggest skipping the AGND connection, this is not needed and may be complicating your situation. For the EOG / EMG channels, just use both pins of each channel on opposite side of the muscle you are measuring.

  • DrLuDrLu Israel

    Hey William,
    sorry for the late replay. I did check up the link you gave me, I took the AGND idea from there. The link does not seem to help in my situation, I don't see a guide on the site for using both Gold cup and snap electrodes at the same time ?

    the electrodes I mentioned are bought from the OpenBCI site - Gold cup, Snap .

    Are these snap electrodes the type you thought of?

    @wjcroft said:
    When you are referring to "snap electrode", do you mean the adhesive type that are pre gelled and have the silver chloride dot inside?

    Important to note that all the equipment we use is brand new.
    I want to give further information about how I place the electrodes, I don't think it is necessarily related, but maybe something will come up:
    Gold cup electrodes
    - I use SafePrep paste to clean the area.
    - I put Ten20 paste on the electrode and place it on the desired scalp area.
    - I put the SAC2 paste (scroll down the link) on a piece of cloth and add on the same area to make sure the electrode won't move, sometimes apply tape as well.

    For SRB2&BIAS I would use the Ten20 with a tape on the ear.

    snap electrodes [Above Picture]
    - clean the area with alcoholic pad.
    - attach the electrode with the solid gel "sticker", and place on desired area on the face.

    For SRB2&BIAS I would place on the mastoid bone behind the ear.

    Why do channels get "railed" in the first place? understanding this might help me know how to get the setup I want to work:
    Snap electrodes for:
    SRB2&BIAS
    EOG channel
    2 EMG channels
    2 EEG channels

    Gold cup electrodes for:
    2 EEG channels

    Very thankful for your help and guidance

  • wjcroftwjcroft Mount Shasta, CA

    @DrLu said:
    ...
    Why do channels get "railed" in the first place? understanding this might help me know how to get the setup I want to work:

    The 'RAILED' status depends very much on the signal range you have set on the time series graph. If the incoming signal exceeds the range you have selected, then the channel is RAILED. The most straightforward option is to just increase the signal range using the 'Vert Scale' drop down menu at the top of the Time Series. Normal EEG is generally below 100 uV. But motion and EMG artifacts can drive it beyond that range. So it's fine to set it as high as needed to avoid RAILING. Just note that signals over 100 uV are likely invalid EEG.

  • DrLuDrLu Israel

    correct me here if I didn't completely follow

    is this the vert scale drop down you meant?

    if so, isn't this acts only as a "visual display" on the GUI and does not really effect the Cyton's settings?

    I notice that even when the channel starts climbing to get railed the uVrms (if that's the same thing we're talking about) still remains well bellow 100, but since the channel eventually gets railed it doesn't really matter..

    I changed the vert scale and did not see any effect on the data, the channel still get's railed, hmmm...

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