Different values for uVrms between CYTON and DAISY boards
zarourmadhi
Montreal, Canada
Hi,
I am trying to get EEG measures using cyton and daisy board with dry electrodes, and it seems I barely have signals, I searched for answers in the forum but still could not solve the issue. I am relatively new to EEG, can I get some help, here are the things I tried:
- I switched electrodes between 3 and 10 and it did not change things, so I assume the problem is not within electrodes, also when touching the electrode 3 for example with my finger, sometimes I have a signal, and sometimes not at all
- I tested continuity of all cables with a multimeter and there was no problem
- I used brand new batteries
- I put the dongle 1m away from all electronic objects
Comments
Hi Zarour,
Have you gone through the tutorials on these pages?
https://docs.openbci.com/AddOns/Headwear/MarkIV/#examine-your-brain-waves
https://docs.openbci.com/GettingStarted/Boards/CytonGS/
Can you see any alpha waves with your eyes closed? Have you checked the ear clips / leads, which are reference and ground / Bias? These are shared with all channels, and could account for a large group of low amplitude channels.
If it appears your Daisy is very low in amplitude, suspect the connection of your 'Y-cable' that connects the SRB2 pin from the Cyton mainboard, to the Daisy SRB2 pin.
https://docs.openbci.com/AddOns/Headwear/MarkIV/#wiring-electrodes
Regards, William
Thank you for your response, I check the links and changed the ear clips electrodes but the results are still similar, also I don't really see a change in alpha wave when I close my eyes. Also is there a problem if the amplitudes are different (like in my case) ?
Did you check the Y-cable connections, as mentioned previously? Most of your Daisy amplitudes are very low, as opposed to what is happening on the mainboard.
Not every individual shows an alpha increase with eyes closed. But most do. You could try measuring a friend.
Have you emailed OpenBCI tech support, contact at openbci.com ?
William
Hi, what I did at the end was make another headset with new cables and electrodes and using a new cyton board, I think I had a problem with one of my ear clips, thank you very much for your suggestion. What I am getting now is this:
As you you can see I don't have signal at a few locations, if I press slightly the non-conductive parts of the electrode with my finger, I start to have signal, but otherwise I don't. Do you have any ideas to make it work please ? all electrodes except fp1 and fp2 use long hair spikes.
If you have longer hair, it is suggested to 'wiggle' around the headset and combs so that they reach the comb tips through the hair. If you are using the original 'spiky' electrode combs, there is a longer type with 5mm tips.
https://shop.openbci.com/products/5-mm-spike-electrode-pack-of-30
Thank you very much for all your answers William, it was really helpful. After spending a lot of time searching for the problem, I am more or less convinced the problem came from the headset tissue (I use an FRI-1000M-19 model). What I am doing now to avoid the problem is adding another non conductive layer on top of the headset to make sure it touches the scalp of the head (I have always been using the 5mm spiky electrodes). It seems correct to me, please let me know if what I am doing is absurd. I just wanted to thank you for your help
.
Hi Zarour, thanks.
I did not realize you were using the FRI dry elastic cap,
https://fri-fl-shop.com/products/19-channel-eeg-cap-with-electrodes-and-leads
I thought instead you were using the Ultracortex. Should have asked previously. With the Ultracortex you can adjust each electrode pressure individually. By screwing in or out the electrode holder. With the elastic cap, you are at the mercy of the cap dimensions compared with the dimensions of your head / skull / hair mass.
I don't have this cap, but from the photos it may be possible to "tighten up" the fit by interspersing some small safety pins in strategic locations. For example by 'pinching' the spandex material where it is looser, and then securing a pin there to hold the 'pinch' in place. I've found these plated steel safety pins to be of high quality,
https://www.amazon.com/gp/product/B001Q8YLR8/
"Safety PINS Size 0 (7/8") Silver Tone Bulk PK/100 Made in USA"
Regards, William
This is exactly the cap I am using, thank you for your suggestion William, I will se how I can implement it.
Regards, Mahdi.