EEG Schematic
Alright, so here it is! Finally, after all that experimentation, it all boils down to this. As of now, this schematic incorporates only ONE EEG channel measured by an INA118, which is then fed to an inverting amplifier followed by a Fliege Filter (cut off frequency is set at 33.86 Hz). I previously used a dual supply to power the circuit, but with the help of TLE2426, I’ve been able to use just a single +5V supply (which comes from a 7805 connected to a 9V battery). If you have any questions at all, feel free to post here or email me at: 
EEG schematic
For the electrodes, I got good results by replacing the gel layers in medical electrodes (already used) with sponges soaked in warm saline water.
Future plans:
- Precision analog multiplexer to expand this circuit into 8 or more EEG channels
- Using this circuit for neuro feedback – specifically Alpha & Theta training
In case you’d like to read more about creating your own EEG circuit, check out Solson’s EEG page. He’s got some neat info on his EEG hardware as well as on Neuro-feedback.
By the way, I’ve also been working on a circuit that kinda replicates the results that you can get from Dr. Robert Becker’s Brain Tuner. You can read more about the Brain Tuner here. basically incorporates Cranial Electro Stimulation at very low currents. In my version of this device, I’ve programmed a PIC 16F628A to generate specific sinewave frequencies (very low Hz) followed by a low DC current that suddenly switches polarity at the required moment to place the user in a light alpha state. More on this later…
i saw your EEG schematic online and it generated few questions in my mind. does your EEG circuit gives you specific wave(for e.g. alpha,gamma,delta etc.,)?or it is a combination of all the signals?i would also like to know about one of your circuit element,7805T(IC).i know it is IC but what it does and where did you get it from.i could not find 7805T anywhere. i will really appriciate your help.please respond to this as i might have further questions.
thank you
Hi Matin! The eeg circuit just amplifies what comes straight from the scalp… so, all the various brainwave patterns are present together, depending on the cut-off freq of your high pass filter. The readings are logged by a Serial Data Logger (i’ll post the schematic for that later on) and fed to the serial port of a computer. I’ve written a software that displays the waveform of the actual readings and I’ve almost completed coding an FFT frequency analyzer which will clearly show the intensity levels for each integer frequency commonly associated with the brainwave frequency ranges. Hope this answers your questions…
I’ve been trying for months to get something like this working for neurofeedback. I know it should not take me months, but hey, I wouldn’t be trying to do neurofeedback if I could turn one round in a day or two.
Anyway, glad I found another circuit.
EKG was easy, the instrument amps I’ve tried (INA126 and INA129) both plugged straight into the PIC ADC. I used a body reference to amp for the INA126, and I’m using a TLC272 DRL with the INA129. I’m not convinced it’s much “better” than just using connecting a reference electrode, but I prefer having ONE differential reference and ONE DRL.
(just to clarify, without the DRL, the reference pin on the instrument amp has an electrode too – but then I needed another to ground – I might have done something wrong… anyway…)
Your circuit looks much nicer (read: I have lots of these parts so I don’t need to shop)
My first question, what gain resistor did you use on your instrument amp?
Secondly, why are the TLC272 marked as three individual parts if the TLC272 is dual? Or is that just a quirk of your schematic program?
Also, to make two channels, you could tie X input pin on INA[a] to X input on INA[b]? So that you could have channel one, channel two, reference and DRL/VGND… a total of four electrodes?
And finally, when I MultiSim the filter, (I want to squash 50hz), I don’t get a most ideal response… could I do the filtering digitally? Or is the signal liable to clip?
Sorry if I’ve been a nuisance. I really would like to get this thing working so I can (fingers crossed) abate my need for ADHD medication.
Thank you, I really appreciate your efforts so far
What is the gain resistor u used in ur submitted schematic diagram
Hi there, I vary the gain resistor between 100 to 470 ohms. Depends on how good the readings are…
It looks like you have done a great job on the schematic! I’m having trouble reading the one on this website. Would it be possible to send me a larger image?
Thanks!
Rob
Operator error – I didn’t click on the schematc…
Rob
did it give output ?
i didnt found ic 7805t in multisim 10.1
is those component available ,can i buy it?
thank you for that great effort