No brain signals -> intermittent reference lead, DC offset
Well my board arrived a couple of days ago and I have had limited success with it so far.
I connect lower bias pin to my left ear, lower reference pin to my right, and lower channel 1 to Cz using electrode gel.
The board connects to the dongle fine giving a solid red light, and I can see activity in the GUI when I stroke the pins.
It is also detected in Neuromore, and again if i stroke the pins I see activity but otherwise all channels remain flatlined showing -201.34uV, including the one attached to my head. Removing any of the leads makes absolutely no difference to this no show of data, but if i shake the thing or touch the pins I see lines on the screen and plenty of interference if it goes within a couple feet of my laptop.
What am I doing wrong?
Comments
Have you tried swapping through some of your leads. It's possible you have a bad reference connection or bad channel connection.
When you connect all 3 leads, channel, bias, and SRB2 together (with clips or a blob of paste) -- that should produce a signal close to 0 uV.
Since this board was working correctly at one time, it sounds like a connectivity issue. Make sure also that you are not in any strong EMF fields such as from transformers or power lines. Select the proper notch filter (50 or 60 hz) for your region.
You mention 'gel', are you referring to the Ten20 paste?
That's very unusual. Standard setup is with reference on one ear and bias on the other. I asked you to try swapping electrode leads, rather than just checking with a meter. Because if the leads are intermittent when some tension is placed on the wires, connectors, or cup attachment, then you may have different results than with just doing a static meter check.
It looks like you're getting more normal readings now. Put your electrode on O1 O2 or Pz and see if you can pickup the alpha with your eyes closed.
Another typical location used for the Bias lead (if both ears are linked in "linked ears" configuration) -- is to place the Bias somewhere on the midline, at an unused site. The Electro-Caps put Bias/Ground at AFz. Cz would also be fine. The reason for the midline Bias is so that the power lines cancellation injection hits both sides of the head more evenly.
> if I unclip the bias cable from my ear it makes no difference
Try placing it on the midline instead. Bias is part what keeps the differential amplifier "centered" and within limits. If you already had a connection moments ago, then that condition persists for some time. However you should see a reduction in 50 hz level with Bias connected
You can disable the unused channels so that they are not showing "Railed".
The ADS1299 and OpenBCI are what is called full band EEG,
http://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg
In general, when dealing with VPL element blocks, the raw EEG signal must first be subjected to a filter to remove the millivolt DC offset. Typically a high-pass filter at .1 or .5 hz will do this just fine.
William
You have some type of intermittent connection with your reference lead. The standard way to debug that is to swap out with another lead. Body fat should have nothing to do with it. It may be possible that skin surface oils are influencing the electrode cup / skin interface. Try wiping the area with some alcohol first before applying. Use an additional piece of tape to hold it on your ear.
Were you able to see the alpha with your eyes closed in the GUI? Also try some of the other tests shown in the tutorial doc.
http://docs.openbci.com/tutorials/01-GettingStarted#getting-started-w-openbci-v-connect-yourself-to-openbci-1-what-you-need
http://docs.openbci.com/research tools/Neuromore
It's possible the neuromore highpass might have an issue. You could instead use a Butterworth bandpass from say .5 to 45 hz. The filter order also makes a difference in terms of how sharp the skirts are. BrainBay, BioEra and Bioexplorer will all draw a graph of the filter bandpass characteristics; if you look inside the filter element block. Bioexplorer will also even show you the changes in milliseconds delay over that bandpass.
Try the BrainBay tutorial, then if you want to get neuromore to work, play with the filter specs there. Something must be amiss, or they have a glitch in their implementation that you just happened to stumble on.
https://sites.google.com/site/biofeedbackpages/brainbay-openbci
re: capacitors. No. To process full band EEG, you simply have two data flow paths in your element blocks. One raw stream from the channel is conventional EEG and has the high pass filter as the first stream element. The 2nd raw stream from the same channel is your ILF path and can be filtered completely differently. You can choose your conventional path highpass filter any way you like: .5 and .1 hz could be other highpass values used.
https://communities.intel.com/thread/41853?tstart=0
Lots of NUC users apparently have trouble with getting their HDMI audio to mate with the attached equipment.
No NUCs have an "audio device" on the board. Instead audio is encoded by the HDMI chip and sent out that port, provided a compatible driver and mating equipment is alive at the other end of the HDMI cable.