From: Jim Peters (jim_at_uazu.net)
Date: 2002-01-28 21:45:17
arethereanytagsleft wrote:
> Here http://groups.yahoo.com/group/buildcheapeeg/files/StandAlone.gif
> is a diagram for a simple standalone eeg. As drawn, it
> doesn't plug into a computer, it lights up a bunch of LEDs according
> to frequency. However, rather than building the full circuit, you
> can probably leave out the lower half and just build
> the top half. You will need a resonator to mimic the signal
> being fed into line 18 of the LTC1068 chip (this is the only place
> where signal from lower half feeds into upper half).
Thanks for this. I'm looking at the design that Andreas has put
together, and also I've found the original full BrainMaster spec,
which has some additional notes.
Basically, the Brainmaster circuit that Andreas gave me is just the
same as the first stage of the Circuit Cellar one, except that it uses
the AD620 instead of the AD627, and it has an extra circuit on the REF
input to level off DC drift, plus it has extra capacitors and
resistors on the electrode side.
Actually I can't get the AD620 from my local electronics supplier, but
I can get the AD627. Looking at the spec sheet, I'm hopeful, and
there is a similar circuit in the AD627 spec-sheet showing capacitors
and resistors on the inputs there.
I'm thinking of leaving off the drift-correction thing as Andreas
suggested to start with (they don't have the OP-90) -- I can add it
later -- but I'll use the capacitors/resistors.
I can only get 10% polypropylene capacitors, not 2% ones as specified.
I can get 5% polystyrene ones, though. Maybe I'll buy them all and
try them, or get a better multimeter and try and find a matching pair.
The spec says the AD627 can drive up to 20mA by itself. Hopefully
this will be enough for sound-card input.
> I was ready to build this, but heard soundcard was not viable - YMMV
Well, my soundcard looks viable for rough testing with less than the
full range of frequencies, but not for making a decent quality EEG
unit.
> It now looks like I can pick up a 2nd hand IBVA instead, which will
> give me what I need to start writing software.
Great!
Jim
-- Jim Peters (_)/=\~/_(_) Uazú (_) /=\ ~/_ (_) jim@ (_) /=\ ~/_ (_) www. uazu.net (_) ____ /=\ ____ ~/_ ____ (_) uazu.net
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