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 23:09:43 GMT
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Viewed:
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616 times
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Taweesak Opasvorarat wrote:
> 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 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?!?
> 2. With (-5) to (+5) volt range, the RCX should be able to read and map into
> the 0 -1023 value well.
>
> Should I use the power from RCX sensor port to feed the op-amp? With that
> enormous gain, am I damaging RCX in anyway?
>
> 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?
>
> 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?
>
> Last question, will this approach work? Anything I am missing?
>
> Thanks a lot,
> -topas.
>
> I tried to get to Mr. Gasperi's page to get some more info but the page was
> unreachable.
>
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp
Interesting idea, but I don't think it's simple.
First, normal EEG is between 0.1 and 20 uV, with some exceptions uptil 100 uV. With a special (low noise, high CMRR) instrumentation opamp this would be no problem.
Second, the highest frequency is about 120 Hz, so you need to sample at least at 240 Hz, which isn't possible with the normal firmware, or are you planning to use other firmware ?
Third, electrode placement is difficult, unless you use a special electrode-cap.
But don't give up !
At the moment, I'm just finishing the documentation on an Mindstorms ECG-sensor (ECG has an amplitude of about 1 mV), that I'll post in "lugnet.robotics.rcx" newsgroup this week. For ECG it works quiet good and I get a maximum sample frequency of 70 Hz on single byte transmission. I don't know if it's sensitive enough for EEG.
best regards,
Stef Mientki
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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 (...) (23 years ago, 6-Aug-01, to lugnet.robotics)
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