Not necessarily a disease, just a wrong way of thinking. And I've been posting from a nook, which was screwed up and couldnt view the thread (it said it didnt exist.) Now that someone finally emailed me, I can upload the files! What do you think the email was listed for?
This is just the first page, designs for an active electrode circuit for the EEG. It is a type of high-Z operational amplifier filter called a "Butterworth filter." I've listed the part numbers, circuit diagrams and even pictures of how to wire the circuit. You can also look up the datasheet of the integrated circuit, and there are a few different kinds. I already finished a model that uses a surface mount IC, so its small enough to fit on the head of a quarter.
Basically, it works like this; The filter is designed to have a maximum frequency response in the center of the human brainwave frequencies. Im posting this without really reading the specs, but I believe its around 16 cycles per second. I am also using very sensitive feedback resistors, so the response of the filter is very sharp. Every time the frequency increases or decreases by 50% past the center point (16 cycles, if I remember right), the signal fades one-half, so that it is nearly unresponsive at higher frequencies. This is because the main concern in designing a portable EEG is that wires tend to pick up a charge in an electric field of any sort. If the wires arent all properly shielded, it will saturate the output with the hum from powerline fields. Anyone interested in designing a EEG should also consider a 60 Hz notch filter to block out the mains hum.