[EEG] Useful EEG frontend electronics article, connector information

[Kelly]

Josh or Andreas can send you some data.  I'm interested to hear about
magnetic field noise.  I've printed out that paper, so if it doesn't
cover it, I'll do some googling.

I don't think we have DC offset data.  Andreas might.  We get mostly
60 hz in terms of external noise, but there is broad spectrum noise
when you have bad contact.  Getting good contact at the scalp is the
biggest issue with passive electrodes.  I really want to try making
some active electrodes, to see how much that helps.  But I know from
my experience at Berkeley that even with active electrodes you need
good contact to keep a good signal.

Right now my hope is that we could make a simple 2-4 channel active
electrode set for forehead electrodes, which will have the best
contact.  Then we can see how much we can get out of that in
post-processing.

-Kelly

On Thu, Mar 11, 2010 at 19:30, Albert Alexander
<albert.alexander at gmail.com> wrote:
> Hi all,
>
> I found a great article on noise and circuit design for EEG. Definitely
> worth reading in entirety:
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817545/pdf/CIN2010-630649.pdf
>
> Also, that Amphenol connector (24-28s) is standard and available, but is $45
> a pop. May be wiser to cannibalize that connector that heads to the needles.
>
> Regarding noise/EMI:
>
> At low frequencies, magnetic fields are a much bigger issue than electric
> fields. Magnetic fields are tremendously difficult to shield, especially
> when one end of the shield is open (the electrode cap). I think shielding
> for the electrode leads is probably not going to be very helpful. Unless we
> put the electrode cap inside a metal helmet, which might be pretty sweet.
>
> We should DEFINITELY twist the plus with the return wire for each of the
> leads. This should reduce 60 Hz AC noise substantially. It'll help with
> fluorescent light switching noise, but that stuff is just plain hard to deal
> with.
>
> What type of noise have you guys seen on previous readings? Is it mostly
> high frequency? Is there much DC offset for your input signals? If you have
> data available I'd love to see it.
>
> Best regards,
> Albert
>
>
>
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-- 
Kelly Buchanan
Barker 210E, 510-643-9744
Helen Wills Neuroscience Institute
University of California at Berkeley