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Project Help and Ideas » EOG circuit using the NerdKits

February 02, 2011
by lcruz007
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Hello,

I'm working on an EOG bioamplififer and using the microcontroller included in the NerdKits to read the signals across the eyes. I'll have more details posted in the forums when I complete my main project in the following weeks.

You can watch the video here: http://www.youtube.com/watch?v=ALqYJ8nc7hY

February 03, 2011
by Rick_S
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Pretty cool project. Looking forward to seeing the final project!

Rick

February 03, 2011
by Ralphxyz
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What is "EOG"?

Where did you get the sensors?

What are you actually sensing (I would probable know this is I knew what EOG was).

What ever it is cool project, I want one.

Ralph

February 03, 2011
by Rick_S
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I believe he's sensing eye movement to light the LED's based on where he's looking.

Rick

February 03, 2011
by Rick_S
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EOG = electro-oculogram (Just looked it up) :D

It records eye movements via a voltage difference between the cornea and retina. So my guess would be the wires on his head are some sort of electrode to sense the nerve impluses like in a heart monitor.

Rick

February 03, 2011
by mrobbins
(NerdKits Staff)

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Hey lcruz007,

How big is the original signal you're reading? I saw the "1 V/div" on the oscilloscope part of your video, but I don't know how much amplification you're using.

Looks like one "ground" electrode on the center of the forehead, and a sense electrode near the outer corner of each eye.

The oscilloscope signal looked amazingly clean for a bioelectrical signal... nice clear slow square pulses with a repeatable zero level! What were we looking at?

Mike

February 03, 2011
by lcruz007
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Hello! Thanks for your comments.

The EOG is a technique used in the biomedical field to detect the voltage across the eyes (there's a potential between the retina and the cornea). When the user moves the eyes, one electrode is more negative and the other is more positive with respect to the ground electrode in the forehead.

What you're seeing on the oscilloscope is the voltage difference between the electrodes. Since one electrode is more negative than the other (depending on the eyes' position) the signal will change polarity. So on this case when I move the eyes to the left the signal has the highest peak, when I move them to the right it's the 'negative' signal. If I am looking to the center the signal will have a constant voltage. Those voltages originally just have a few microvolts of amplitude though, so everything has to be amplified (I have a gain of around 400) and filtered very carefully, especially the 60Hz interference and high frequency noise. I was originally using several second-order filters using op amps, but to keep it simple though, I have been researching and testing my system in order to have as few filters as possible!

Like I said in the previous post I'll have more details (including schematics) in the following weeks when I get to finish the project. :)

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