EEG know how

aquasapien · 2007-02-03 16:03

Its been a few months since I have been able to read posts here but it is great to come back and see so much. I could read for days.

Hope everyone is well.

I have been doing some research into the feasability of a homebrew eeg machine. Has anyone here ever dabbled with this or have any advice?

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Mike Green · 2007-02-03 16:08

There were some articles years ago in maybe Popular Electronics with some kind of kit that was marketed. The biggest problem is in the analog side of things. EEG waves are very very low voltage in an environment with a huge amount of electrical noise. You need good, low noise amplifiers with a lot of filtering to suppress noise, particularly 60Hz power line noise (and its harmonics).

Franklin · 2007-02-03 17:13

Have you Googled "homemade eeg" yet? Lots of stuff.

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- Stephen

allanlane5 · 2007-02-04 03:15

Circuit Cellar Inc. built one years ago. You might google that.

aquasapien · 2007-02-04 17:30

I have googled lots. Just wondering if anyone here has tried or considered. All reading does suggest that environmental electrical noise is a big problem.

It seems to be a bit of a project. Thanks for the input.

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Beau Schwabe · 2007-02-04 17:38

It's been awhile since I have done any work like this... you might also Google "Myo-Electric Sensor" for more information on what the actual EEG signal looks like.
A differential instrumentation amplifier is ideal in this application, not only because of how it can filter out most of your ambient noise, but the nature of the EEG signal
itself can be measured by the phase delay from one differential input to the next. I will see if I can dig up information on any projects I have... I was thinking of a
possible Propeller application for this.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

aquasapien · 2007-02-04 21:58

Much appreciated

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Beau Schwabe · 2007-02-05 04:26

aquasapien,

I have to apologize... I misread your post and thought you were wanting to detect EMG signals instead of EEG signals.

Since EMG signals are also often present within EEG signals I thought that it would still be helpful to post information
about EMG signals below...

2005.iccas.org/submission/paper/upload/1revision-sensor.pdf

Myoelectric signals have frequencies ranging from a few hertz to about 300 Hz,
and voltages ranging from approximately 10 microvolts to 1 millivolt.

www.bortec.ca/Images/pdf/EMG%20measurement%20and%20recording.pdf
www.personal.rdg.ac.uk/~sir02ada/Documents/TRB0234.pdf

www.univie.ac.at/cga/courses/BE513/EMG/

www.univie.ac.at/cga/courses/BE513/

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

aquasapien · 2007-02-13 20:43

Thank you for the links

I found a site with some ECG schematics and they worked well with the opensource software provided.

I solved the problem of the EEG the cheater way....I bought one on ebay.

This has led me to some interesting tests that I may use the stamp for. They say if you generate binural sounds in each ear...say 200 hrtz in one ear and 210 hrtz in the other, the difference in frequencey (10 hrtz) can induce frequency following or resonence in the brain. So it could be possible to induce the desired state.

THis of course is still in the "read alot about it" stages as I would like to make sure I do nothing harmful to me......or my dog

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Beau Schwabe · 2007-02-13 23:29

aquasapien

You said...
They say if you generate binaural sounds in each ear...say 200 hertz in one ear and 210 hertz in the other, the difference in frequency (10 hertz) can induce frequency following or resonance in the brain.

I wonder if there is a relationship here similar to what happens when a person hears themselves speaking a few milliseconds delayed.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

aquasapien · 2007-02-14 01:22

Interesting???

I read once of a researcher who recorded the mind state of a druged individual and then encoded the information in a microwave beam sent into the mind of another sober indidual that then showed frequency shifts similar to the druged subject.

I wonder if the druged guy could sense a lag between talking and hearing.......think I did once back in my college haze daze...

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Derek · 2007-02-14 03:38

I made an EEG amplifier circuit for a class last semester. We used a EEG signal simulator rather than our own biopotentials just for class purposes of obtaining a good signal. I have since dismembered it but now need to reassemble it for an independent study im doing with my roommate

We used a differential amp with a band pass. I have a schematic but it needs to be cleaned up first. If youd like i can attach it for you when i get a chance. Also we used a o'scope for displaying.

As far as advice, you need a high CMRR amp
if possible an internally programmable gain. this reduces noise from component distance and leads, which is important becuase biopotentials are in the range of mV.
and good prep of the area that you are acquiring your potentials from. boney areas are better than fleshy ones.

Hope this helps.

Derek

aquasapien · 2007-02-15 16:59

Yes that would be great. If you find the time I would appreciate it for sure.

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Derek · 2007-02-16 03:50

Howdy,

Made my corrections to the schematic and attached it ( i thinks). I made it in ExpressSCH. Its just the amplification half is all we made and used the o'scope to display like i mentioned before.

The AD524 in the schematic is a bit expensive at about $16 but it has internally programmable gain which helps cut down on noise from external components. For the bandpass after that you may want to use potentiometers for adjustability at the cutoff frequencies. For our class we used .5Hz and 40Hz.

Could you post a link to the kit you bought? I would like to take a look at it, maybe build my own and compare the two. Could be something my instructor would be interested in as well for his class.

Thanks,

Derek

aquasapien · 2007-02-25 18:23

Certainly, the model I bought was a 12 channel "POLYSOMNOGRAPH / EEG-4412P BY NIHON KOHDEN".

I would be more then happy to compare results. I will be picking the device up end of Feb. It would be interesting to see the comparison.

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The singularity is close at hand, Genetics, Nanotechnology, Robotics...and I get to be alive to see it.

Derek · 2007-02-26 05:46

Did a quick google of the one you picked up. Its an actual EEG machine! I thought it was a kit. The circuit we used is no wheres near hospital quality. The comparison may not be all surprizing in that case.

but if your still interested in a homebrew eeg than the circuit I attached is applicable. Just an insturmentation with bandpass into an o'scope is what we did.

what was the intended use of building the EEG? Biomedical is where my interest are in electronics and am curious to know what your project is

-Derek

EEG know how

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