touch proof electrode adapter with Electro-cap

laerciosilvajuniorlaerciosilvajunior Brazil
edited October 2016 in Electrodes
Good night.

I have had problems with touch proof electrode adapter for some time. It does not work.

When
I try to use them the signal appears ¨Railed¨ in all channels and there
is no change even when I try to touch the electrodes with my fingers,
but when I replace the adapters for the gold cup electrodes the signal
is OK.

Does anyone know what is the problem and how to solve?

Thank you in advance.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    The adapter consists of many individual wires, touchproof socket on one end, header plug on the other. It seems unlikely that they could all go bad at once. Is it possible that just your reference (SRB2) or Bias wires are bad? Have you tried swapping leads, especially the reference or Bias leads. Do you have a multimeter there, can you check the ohms resistance between one end and the other on each wire? Should be close to zero on good leads.
  • biomurphbiomurph Brooklyn, NY
    What is your setup? Please describe the montage you are using so that we can help trobleshoot.
  • laerciosilvajuniorlaerciosilvajunior Brazil
    First of all thank you for your answer.

    My equiment: The board is the OpenBCI
    32bit Board and there is the option to use it together with the Daisy
    Module, but I did not use, hence, the teste was made with 8 channels.

    My first test was performed with a eeg cap, this eeg cap looks like the one in the following link: https://i.ytimg.com/vi/AVObCd2pAR0/hqdefault.jpg
    This equipment has touch proof connection and I used it together with the cables that came with OpenBCI.

    I connected 10 cables (8 channels + 2 references) in the OpenBCI board. One reference was connected in SBR pin and the other one was connected in BIAS pin, these electrodes were plugged on my ears. The 8 channels were connected from NP1 to NP8. If we see the board putting the pins in front of our eyes, I used the bottom part of the pins. Is that correct?

    When I tried to performe the test, all channels were not responding, the only thing that I could see in my screen was ¨Railed". After that, I tried to generate a signal by touching the electrodes with my finger and it did not work.

    I replaced the eeg cap for the gold cup electrodes that came with OpenBCI and it worked. I used the same pins and I could read some signals, just to be sure, I put all leads together and the answer was a signal close to 0uV.

    Did I do something wrong?

    Thank you again


  • wjcroftwjcroft Mount Shasta, CA
    Laercio, hi.

    The cap you show, the Electro-cap, uses tin electrodes. I assume you used the spring clip-on ear electrodes, also from Electro-cap, and also made of tin. It's not recommended to mix gold and tin, that can cause a "battery" like effect when the conductive gel is applied. Did you use the Electro-gel that comes with the cap? There are some videos on the web that cover how to inject the gel at each hole and also on the ear clips. You must have good gel-skin connection for the Electro-cap to work properly.

    As I suggested earlier, did you check the ohms reading on each individual touchproof adapter wire segment. Measure between the touchproof on one side and the header connector on the other. You should see close to 0 ohms if the cable is good. If it is bad, it will show "infinity" or some high or intermittent value in ohms.

    All the OpenBCI mainboard connections are made with the pins closest to the board. Since you got your system to work with the gold cups, you must have that already.

    William

  • laerciosilvajuniorlaerciosilvajunior Brazil
    edited October 2016
    [new thread titled: How to validate an EEG signal using headset]

    Hi everyone

    I bought the Ultracortex IV, but meanwhile I need to
    perform some experiments using a headcap. How can I know that the
    acquired signal is ok?

    I have been using a headcap that looks
    like with this one:
    https://www.biopac.com/product/electrode-cap-sys-touchproof/ . I saw
    this here:
    http://openbci.com/forum/index.php?p=/discussion/191/elastic-head-caps-electro-cap-g-gammacap-etc
    and in this discussion is said that it is possible to use a headcap
    like this with OpenBCI. Is there any math that I can do to prove it or
    any scientific way to prove it?

    Thank you advance,

    Laercio
  • wjcroftwjcroft Mount Shasta, CA
    Hi Laercio, I merged your new thread into this existing thread regarding your previous questions on the Electro-cap. This is a standard Electro-cap. It's easy to use after injecting the gel.


    After getting good connections on the channels, you should see signals similar to what is shown in the tutorial. The tutorial used gold cups and paste. Your signals with the Electro-cap tin electrodes and gel should be very similar.


    I assume you now have your touchproof adapter working, correct? If not, have you confirmed that you have good conductivity, close to zero ohms with your DVM?

    Many of us have used the Electro-cap successfully with OpenBCI and other EEG amplifiers. It is a standard in the field, used widely in clinical settings.

    William

  • laerciosilvajuniorlaerciosilvajunior Brazil
    Thank you William for your answer and to merge the topics, this is a better way to continue the topiic.

    Answerring your question about the conductivity, yes I have done the and the conductivity is something about 1.8 ohms for the electro-cap and 1.4 ohms for the gold cups, I think that these numbers are similar and its possible to use both electrodes type.

    When I analyzed the signal on OpenBCI_GUI, I saw a signal very similar with an other test that I performed with the gold cups. Nevertheless, is there a scientific prove to validate this signal? I have watched the videos that you sent me and the third video shows a software to analyze the eeg signal, but not to validate it.

    Could I use the FFT on OpenBCI_GUI to validate my signal for example?

    Thank you again,

    Laercio


  • wjcroftwjcroft Mount Shasta, CA
    Laercio, hi.

    The ECI Electro-Caps are used very widely in many settings: medical / clinical use, neurofeedback QEEG, research, even home neurofeedback assessments using Pete Van Deusen's Brain-Trainer protocol suite. So in this sense they have already been widely validated. Some additional links you might explore:


    The FFT function in many applications (OpenBCI_GUI, OpenViBE, neuromore, BrainBay, BioEra, etc.) is certainly helpful for characterizing what frequencies are present. Although I'm not sure I would refer to this as 'validation'. There are papers on the web that study the differences in response of various electrode types such as gold, tin, Ag-AgCl, etc. 


    Regards,

    William

  • wjcroftwjcroft Mount Shasta, CA
    "Could I use the FFT on OpenBCI_GUI to validate my signal for example?"

    I assume you've tried the eyes closed test to see the alpha FFT peak rise at 10 hz. (As outlined in the tutorial.) Occipital or Parietal sites are best for this.

  • laerciosilvajuniorlaerciosilvajunior Brazil
    William,

    Thank you again. I will read all the articles and answer you if it worked or not.

    Best regards,

    Laercio.
  • pablopablo Guatemala
    Hi again Wjcroft, 
    I'm still having trouble connecting the electro-cap with the cyton board and as i could read you have previous experience doing this connection succesfully so i hope you can help me out. Since my Electro-Cap didn´t came with the ear clips electrodes i was using the clips, to plug my earlobes to the SRB2 and BIAS pins, that came with one of your helmets shown in the link below:


    All channels show the message: "Railed" so maybe using those earclips as reference could be the source of the problem as i´m not sure if they are compatible with the electro cap. (I am indeed using the gel and i have measure the ohms resistance of my electrodes and they all are below 0.5 ohms). 

    I tried using the electrode FZ as reference to the SRB2 pin instead of my earlobe and in that case i did got some signals, but not quite sure if they were good signals or just noice. 

    Thanks for your time!
    Regards
  • wjcroftwjcroft Mount Shasta, CA
    It's not advisable to mix different types of electrode metals. Electro-cap uses tin and gel electrolyte. Ultracortex is using sliver chloride dry electrodes (not intended to be geled, as that will encourage corrosion). When you mix metal types, sometimes a 'galvanic' battery effect is produced, which generates millivolts of potential, wrecking your readings.

    I suggest ordering the tin ear clips from electro-cap, as they have a nice spring action (gentle), and cable ending in touchproof connector.

    The electro-cap can be used with other references. So the Fz or AFz (10-10 layout) can be used. Electro-cap brings the AFz out to the DB-25. Be sure to connect both SRB2 and Bias (to another location). You need both.

    Actually on the electro-cap, AFz is intended for Ground / Bias, and the ear clips are "linked", connected together, to form what is called "linked ear" reference. This is how it is used in QEEG for neurofeedback.

    Regards,

    William

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