Ganglion board noise -> bad ear clips

chrismourchrismour Cyprus
edited February 2018 in Ganglion
Hello,

I a new user of Ganglion Board. I followed all instructions from OpenBCI Ganglio tutorials.

I also followed these tutorials : 

I managed to connect successfully to the Ganglion board using the OpenBCI GUI. I have tried many things with the notch filter enabled at 50hz, power supply (battery 3.7V-500mAh, the battery kit provided-4 AA 1.5V batteries, 5V DC from plug etc): 
a) connect all 4-channels to electrodes with crocodile clips on the ears
b) nothing connected to the ganglion board
c) connect a channel to a ground etc

but I am always getting noise signals around 400-500uV with some periodical peaks around 1300uV or more (please check the image attached). I did not manage to get any EEG signals as I only see this noise. I tried everything. What am I missing? Is this behavior normal?

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited February 2018
    Chris, hi.

    You mention "crocodile" (alligator?) clips on the ears?

    (1) that must be really painful.
    (2) the metal used in these clips (steel or nickel plated steel), makes a terrible EEG electrode.

    Do you have a set of gold cup or other EEG electrodes? And the Ten20 paste to put them on the scalp / ears? Other metals that can work for electrodes are silver, tin, silver chloride.

    William

  • chrismourchrismour Cyprus
    Hello wjcroft!

    Thank you for the reply. 

    I am just touching my ears with them. So, it is not painful. I do not have the ear clips. Even without the crocodile clips I am getting the noise in the image above. 


    Is it possible to get any EEG signals without the ear clips? Are there any other DIY alternatives (for D_G and REF pins)? Could you please tell me a working scenario with the packet that I have? 

    Sorry for my newbie questions but I am struggling to understand how this works.

    Thank you very much
  • wjcroftwjcroft Mount Shasta, CA
    Doesnt the headset come with the silver chloride ear clips? You have the flat and spikey electrodes, they are made of plastic that is first silver plated, then chlorided. 

    In general you should not mix electrode metal types. Because galvanic 'battery' effects are generated. And more noise.

    You absolutely must have a good reference electrode connection on the ear for any EEG to work. Bias / ground important also. EEG is a differential voltage amplifier, between reference and the channel on the head. Without a good reference connection, you will simply get noise.

    As an alternative to the silver chloride ear clips, you COULD use a gold cup with Ten20 paste. But it sound like you have no cup electrodes.

    You're just going to have to get decent ear electrodes. No other way.
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