Subject:
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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 19:58:46 GMT
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Original-From:
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Taweesak Opasvorarat <opasvt@^spamcake^hotmail.com>
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Viewed:
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540 times
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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 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.
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Message has 4 Replies:
 | | Re: How can I build sensor to measure eeg
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| (...) First of all, you'd simplify things if you made your amplifier center around 2.5 volts rather than 0. Then your amplified signals would become 2.5 +/- 2.5 which the RCX will like. And if you run the amplifier from a stabilized 5 volt supply, (...) (23 years ago, 6-Aug-01, to lugnet.robotics)
| | | Re: How can I build sensor to measure eeg
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| (...) 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 ((URL) that describes such a beast, but it's not on the web and I don't (...) (23 years ago, 6-Aug-01, to lugnet.robotics)
| | | Re: How can I build sensor to measure eeg
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| (...) 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 (...) (23 years ago, 6-Aug-01, to lugnet.robotics)
| | | Re: How can I build sensor to measure eeg
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| (...) Try searches for "instrumentation amplifier schematic". Everything must be battery-powered, as you have to break down the skin's electrical resistance with things such as KY jelly or salts-based electroconductive gel (very irritating to the (...) (23 years ago, 7-Aug-01, to lugnet.robotics)
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