noise spikes seen with Ganglion
Radha_openbci
United Kingdom
I have been using Open BCI Ganglion for quite a long time now(7 months). I purchased a new board and started using it a month ago. I am using Gold cup electrodes. Since a week it has started giving more amplifier saturations and sometimes it samples very slow. Typically, now the data can look like:
The first 3 are raw from the time it was sampling slow. The last one is filtered, and I am referring to the double spike on the left that comes frequently now. I am using bled112 dongle. What can be the issue here?
Comments
https://ibb.co/2NjvR0B
https://ibb.co/hLGMvYJ
Thanks for the feedback. But the same happens in now 4 different environments on all people. I don't know why the electrostatic buildup would happen even after opening the encasing.
Before a month i was using another Ganglion and it seemed to work fine for many months. I will post here if i figure out something.
Radha
@Radha_openbci, hi.
Here is one of the Cyton graphs you posted on the NeuroTechX #tutorials channel.
Was your previous Ganglion noise similar in character to this Cyton noise?
William
Hi
This is from Ganglion too and I am getting these bursts for the first time if I recall correctly. Now I have both the open BCIs I can check signals from both in the same environment. I use one if the other is producing noises. Whats the best way to compare?
So if BOTH Ganglion and Cyton are showing similar noise patterns, does that not tend to eliminate a possible issue with the Ganglion or Cyton mainboards? But instead points at either an issue with local environment electromagnetic noise, pops in the electrodes, cables, etc.
Electrode pops can happen for a number of reasons.
https://www.google.com/search?q=eeg+electrode+pop
What electrodes and paste / gel are you using now? Same as with both Ganglion and Cyton?
William
Just to be clear, I do not have any Cyton. These ae 6 channels because the last two are bipolar derivations from 1-2 and 3-4
I don't think its the local environment because the one that had initial errors are still behaving that way in another location. Now I am using brand new Ag/AgCl electrodes with Ten20 gel, same with both.
OK, my misunderstanding of the six channels shown. Did you say previously that the same type of noise was showing up with multiple Ganglion boards? This again, seems to eliminate the mainboard as the issue, and points to something else going on.
This page has some suggestion on the 'electrode pop' phenomena. Press the 'Answer' tab shown.
https://www.thoracic.org/professionals/clinical-resources/sleep/sleep-fragments/electrode-pop.php
I tend to change boards if one behaves weirdly. I do get noises-same or different in both. I think I agree with you that board isn't the problem. I do place my reference electrode on the left/right mastoid, so that explains the issue. MAybe whenever I notice the issue I should reapply the reference electrode.
Thanks, it gives some closure although why is it always 1 dual peak in say 5-10 minutes and not single peaks regularly if the reference is bad?
When the reference is having issues, it is usually mirrored in all the channels, not just a single channel. In the graph of yours that I pasted above, this is the case. Although the effect in channel 1 is hard to see; it is still there. The different noise amplitudes are due to the distance of that electrode from the reference.
I don't understand your statement:
Are you saying that ear lobe would easier, this is likely true. Mastoid reference should be fine, as long as the hair is out of the way and the contact is good. If you look at some of the previous comments on this thread, I mentioned that hair conditioners used after shampoo, can sometimes cause issues with electrode pop. Hair should be shampooed but not conditioned.
In the past for neurofeedback EEG, also, NuPrep skin abrasion was used. May possibly help in your situation. See the second video on this page:
https://openbci.com/forum/index.php?p=/discussion/176/placing-electrode-sensors-on-the-scalp
I use NuPrep abrasion before applying Ten20 gel. Yes, I am saying that my peaks could be due to the reference electrode on the mastoid. My reference impedance is generally low. Probably I don't place it on the correct bone every time so could be contact or pressure issues? I can take care of that next time if it happens again to confirm this. I can also confirm to see which side the reference was and which electrode had the peak. But I don't understand the dual peaks?
Try some tests with the reference and Bias placed on the ear lobes. Those are generally easier to deal with.
Once an electrode pop occurs, it means more pops are likely. The peaks simultaneous across channels are due to the shared reference.
I don't use the Bias pin, what is that for?
Sorry, I meant to say 'Ground' or 'D_G' (driven ground). On Cyton Bias is the same as Ground / driven ground.