electrode cap railed / all channels display the same data
Hello, complete beginner researchers to EEG here using the Cyton Daisy boards. Currently only testing with the 8 Cyton channels, not using 4 and 8, and the data we get is completely incomprehensible.
Data when not railed: Seems to all be the same even though they are connected to different sensors?
Data when all railed: Unsure why this is happening spontaneously.
Our impedance values look great and strangely enough the channels with worse impedance values seem to produce differing results?
We have checked previous forum questions on background noise cancelling, Notch is 50 + 60 Hz, Smoothing is On, our black wire is connected to the bottom BIAS pin. Is our data interference from background noise? Room is relatively quiet apart from pc which dongle is connected to, the fan noise is unavoidable. Otherwise lights have been turned off and other devices moved away. We have tried the blink test to no avail.
We are also unsure about: single end of white Y-split cable is currently connected to the small square receptor of one of the spare coloured wires, and that wire is connected to the REF of the cap. Is this interpretation correct?
Current setup:
Any help would be much appreciated. Thanks.
Comments
Hi Caroline,
Have you applied the conductive gel as shown in the page on the cap?
https://docs.openbci.com/AddOns/Headwear/ElectrodeCap/
See the paragraph directly ABOVE the Troubleshooting header:
https://docs.openbci.com/AddOns/Headwear/ElectrodeCap/#troubleshooting
Unfortunately this tutorial should have more guidance on how to inject the gel. There are some Youtubes online that do this. Here is one for the "Electro Cap", which is similar.
Note that with the Electro Cap video shown, they are using ear clips for the reference electrodes, whereas the cap you have has a REF electrode which connects to location CPz. This is fine, any reference can be used with EEG. Your cap also has a GND connection which I believe also goes to AFz, as this video shows.
Your Y-cable connecting the two SRB2 pins, is intended to connect to the REF position on the cap.
William
Hi William, thanks for your quick response.
Yes, we have applied the electrode gel. From my understanding, the impedance test will show red values without proper gel application - is that correct? We adjusted the cap and gel until all values were green or yellow, which leads me to believe our gel was applied correctly.
I will recheck the REF electrode and GND connection.
In regard to the Y cable connecting the two SRB pins, it seems impossible to connect its single end directly to the black REF cable of the cap. Our solution was to connect the Y cable single end to another coloured wire (as shown in pic), and use the coloured wire's blue end to connect to the black REF cap cable. Is that correct?
Thanks.
Raine
Correct, the wire from the touchproof adapter cable, acts as an extension cord.
re: railed. It sounds like your REF connection is poor. When all signals have similar noise, the REF connection is shared between all channels. I still recommend you watch the video link given. It shows that some circular motion is recommended to move the hair out of the way.
Also note, your first image shows a substantial amount of mains noise around 50 Hz. Also present in second image. Mains noise is present in many areas of most rooms: extension cords, power supplies, wall warts, conduits in walls floors ceilings, metal tables or cabinets, LED and CFL lighting, wireless gear, etc. Try changing your position to avoid these areas. Only a few feet away is usually sufficient.
Thanks William, will try to apply the gel as the video shows, check REF connection and avoid sources of mains noise. Hopefully that fixes the problem.