Subject:
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Re: How can I build sensor to measure eeg
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 6 Aug 2001 18:45:40 GMT
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Viewed:
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1466 times
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lego-robotics@crynwr.com (Taweesak Opasvorarat) writes:
>
> I'd like to build a sensor that measures the voltage of the brain wave like
> those EEG machines seen in the hospital. And would like the RCX to log the
> data.
>
> I have scanned thru some sites and they explained that these brain waves are
> about 0 - 200 micro volt in magnitude and have about 30 Hz in BW. Here is
> what I think I should do next. But not sure if it's making sense. (I have
> some experience building electronic kits.)
>
> 1. Build an op-amp circuit to amplify the signal to be (-5) to (+5) volt.
> Is this correct? The gain must be enormous?!?
5V/200uV=25000 (or maybe half it the 200uV go both ways).
Should be no problem to obtain with multiple OpAmps.
There was an article in the german computer magazine c't
(http://www.heise.de/ct/) that describes such a beast,
but it's not on the web and I don't have access to the
c't CDs/paper copies from here:
Mit Gedankenkraft
Elektrische Gehirnaktivität steuert Computer
Report, Gehirn und Computer, EEG, EKP, Neuro, Neuron
c't 6/99, Seite 296
I think they used OpAmps with FET inputs because the signals are so weak
and built a bandpass fillter for the interesting frequencies.
I don't remember if one the standard TL084 with 4 OpAmps suffices,
with multiple OpAmps in a pckage you could get crosstalk problems.
> 2. With (-5) to (+5) volt range, the RCX should be able to read and map into
> the 0 -1023 value well.
Make it 0-5V.
> Should I use the power from RCX sensor port to feed the op-amp? With that
> enormous gain, am I damaging RCX in anyway?
No, as the voltage of an OpAmp is limited by its power supply.
> I read from the Extreme Mindstorm book and found that the RCX sensor port
> would do the switching between feeding the power to the sensor and reading
> the value from it. Could you guys explain how this would affect the sensor
> implementation?
I think the circuit on p259 should be ok.
> How can I find out how RXC do the sampling? I guess in this case the 30 BW
> is so low and RCX would have no problem with it right?
It samples every 3ms (read the book, p250), so 30 Hz is no problem.
> Last question, will this approach work?
I think it can work, but with signals that small/an amplification
that high you can get all sorts of difficulties. And 50/60Hz is
not far away, so you probably need a good filter and carefully
shielded cables.
> Anything I am missing?
Good luck and tell us your experiences
Jürgen
--
Jürgen Stuber <stuber@loria.fr>
http://www.loria.fr/~stuber/
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Message is in Reply To:
 | | How can I build sensor to measure eeg
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| Hi, I just have a quick question. Hope you guys could give me some pointers. I'd like to build a sensor that measures the voltage of the brain wave like those EEG machines seen in the hospital. And would like the RCX to log the data. I have scanned (...) (25 years ago, 6-Aug-01, to lugnet.robotics)
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