Electrode cap signal quality drops out
DreamBigDreamLucid
CT USA
Hello All,
I'm using the Cyton+Daisy configuration with the EEG headset but I am having a problem with the signals dropping out - all but one remains the others just flatline. Why is this happening? The EEG cap is nice and tight, with plenty of gel, and the wires are all set up correctly per the most recent documentation. Also, my laptop is on a separate table and unplugged from the power supply to limit all noise. Should I add the WIFI shield?
I appreciate any insights for troubleshooting.
Comments
It's very important to make sure the earclip electrodes are attached properly to the Cyton+Daisy and are being worn.
https://docs.openbci.com/docs/01GettingStarted/01-Boards/DaisyGS#2-connect-y-splitter-cable
Isn't there a REF defined on the cap already for this purpose? To clarify, this is the cap I am using: https://shop.openbci.com/collections/frontpage/products/openbci-eeg-electrocap-kit
Dream, hi.
Yes, the cap contains a reference position on the midline. So earclips are not used in this case.
If you are getting flatlines on most of your channels (all but one), that still points possibly to an issue with your reference, since the reference is shared with all other channels. (EEG is differential between the reference and each channel.) Not sure why you are still seeing one channel, but could be a wiring issue with the header pins.
A disconnect could be happening anywhere in the cables from the cap, through the touchproof to header adapter, to the header pin connectors themselves.
Has this cap ever worked correctly? When did you purchase?
William
Hi William, I think it worked correctly, I ordered back in October, all the channels seemed to mimic the same reading, Im not sure if that is helpful to know or not? Maybe its my pin configurations that are wrong?
Can you clarify? Are you saying that you are STILL seeing the identical time series on each channel? If that is the case then the previous comment still applies:
You also ask:
I believe there is a quality control phase at the factory. But it is remotely possible that there has been a mis-wiring / miss labeling. Do you have a DVM / multimeter? These have an 'ohms' or 'continuity' mode for checking with two probes between two points. The first location you want to check is the cap site labeled 'REF'. Generally with caps like this such 'extra' sites are on the midline. For this cap it looks like site CPz, the point midway between Cz and Pz. Other caps such as Electro-cap use AFz.
Note that some caps refer to this as 'Reference' but others call it 'Ground'. It's your choice what you want to use it for. If you use it as Ground / Bias, you can place the reference anywhere you like. Typically in neurofeedback / QEEG, reference is done with what is called "linked-ears'. Or in some cases such as Ultracortex, one ear serves as reference and the other as ground / Bias. It's really your choice. More balanced locations for the reference (centered) result in EEGs that are not higher amplitude on one hemisphere than the other.
William
Dream, hi. I did not see your reply after our Feb 11 exchange. Let us know how the cap is working.
Also, from your username and other posts, I got the impression you may be using the cap for overnight recordings? How is that working out? Does the gel last for the sleep time? Depending on how the cap exposes the gel to the air, there may be less conductivity after some hours. Another cap type I've used (Electro-cap), is basically only used for relatively short QEEG recordings. Usually done within 30 minutes.
Regards, William