EEG newbie help needed !

Richard Norman rsnorman at mediaone.net
Sat Jan 29 22:49:48 EST 2000


Try searching for Bioinstrumentation.

The EEG signal is microvolt level signals with a frequency range from below
1 Hz to
perhaps 30 to 50 Hz.  You MUST use differential amplifiers with substantial
common
mode rejection (60 db at least).  You MUST use special techniques to
eliminate
noise.  Although white noise is not so much of a problem with this limited
bandwidth,
"pink" noise (random noise with 1/f frequency characteristic) is a major
problem
because of the low frequencies needed.  This noise produces excessive
wandering
or drift of the baseline.  Also, 60 Hz interference (or, in some countries,
50 Hz) from
the AC power system is a BIG problem.  Ground loops, where multiple
interconnections of a supposed 0 V "ground" lead actually carry current and
produce voltage offsets, is another BIG problem.

One other MAJOR problem is patient safety.  If some problem develops in your
electronics, are you sure you are not going to drive 120 VAC through your
subject's
head?  Electronic systems are ordinarily grounded to the third wire in the
AC
power cord.  If some problem develops in the electronics or in the system
wiring,
are you sure that the "ground" is not going to carry live 120 VAC?  Even if
you
make your EEG amplifier battery powered, unless you use optical isolation
the
ground circuit is connected directly from the patient through your equipment
into the computer power supply.

Notwithstanding all these problems, almost any sufficiently high gain, low
frequency
amplifier will work.  Your next problem will be in interpreting what you
find.  That is
by far the harder job!


<bunny_nuke at hotmail.com> wrote in message
news:8703sd$rvs$1 at nnrp1.deja.com...
> I would like to have a go a building my own basic
> Electroencephalography (EEG) system which would interface with my PC.
>
> Firstly I could do with looking at circuit diagrams of existing basic
> systems. I've had a look on the net with no luck yet.
>
> I studyed a HND in Engineering Mechatronics when I was younger, and I
> have lost a lot of my knowledge as I have not used it since. I've just
> started studying Neurology and Behaviour at Degree level (OU
> Biology:Brain & behaviour, I already have a B.Sc Business IT) hence my
> interest, but I need as much help as possible.
>
> I'm also interested in alternative methods akin to technology used in
> radio telescopes (Or anything else), any ideas ?
>
> Leads, leads and more leads would be brill.
>
> Many thanks in advance.
>
> Bunny (alias Adrian Hamer)
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.






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