[EEG] Useful EEG frontend electronics article, connector information

Christopher Abad aempirei at gmail.com
Fri Mar 12 15:22:43 PST 2010


i guess if you think about it, an eeg machine is a low noise high gain
direct coupling subwoofer pre-amp.

On Fri, Mar 12, 2010 at 10:51 AM, Kelly <hurtstotouchfire at gmail.com> wrote:
> 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
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