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Inexpensive EEG Devices?
Rustcycle akss: "To extend prior music generation experimentation, I'm interested in creating music via genetic algorithms using neurofeedback to assign fitness values. Does anyone have a recommendation for EEG systems that are affordable outside research institutions? What's the best system under $2k? Ideally I'd want a multi-sensor system so I could do sonification experiments to 'hear' correlated data from different regions, but I'd settle for a one or two sensor system for initial experimentation — so long as there are drivers for Mac / Linux. How safe / unsafe is the OpenEEG route?"
Under $2000? I would be surprised if there was a system that cheap. I think your best bet is to build you own differential amplifiers with a couple of opamps.
I see the glass as full with a FoS of 2.
My senior design team from College actually went ahead and tried to build the machine featured on OpenEEG. In my experience, we were not capable of getting a signal with a high enough resolution of detecting anything other than "ACTIVE" or "NOT-SO-ACTIVE". But the circuitry provided does ..work... after a bit of tinkering. The resistor values are very important. Try to be as exact as possible. Also, shield everything you can from inteference. You'd be surprised how much interference the power lines in your house emit. It will be about around 60Hz, and periodic, if you are picking it up. The DRL portion of the circuit helps to reduce it.
As for analyzing the data it produces, that also becomes difficult. "ACtivity" on an EEG signal could be as small as a uV. Sample it as fast as you can. We used a PIC processor to sample.
Also, muscle signals can drown out the electrodes, try not to move.
Seriously, the subject MUST have full galvanic isolation from the power lines. The reason for this is that in every day life your skin provides a surprising amount of resistance and thus protection from shock. What is safe, 48 VDC, can kill an electrically compromised subject. When you put electrodes on the skin you create a low impedance path into the body. The typical solution for this is to use optical isolation. Check out Dallas/Maxim Semi and others for off the shelf solutions. DO NOT hook someone up to an oscilloscope - one leak in a transformer and they are dead. The other solution is to use batteries, but you have to be careful to limit the available voltage and current from a battery source.