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:

teknomage's EEG schematic

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…

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~ by teknomage on August 15, 2008.

36 Responses to “EEG Schematic”

  1. 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

  2. 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…

  3. 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 :-)

  4. 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…

  5. 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

  6. Operator error – I didn’t click on the schematc…

    Rob

  7. 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

  8. Interesting EEG. Thanks for showing the details. I’m looking at mapping the EEG of a person using a bone stimulator to show how they work.

  9. hi Mertin., your work is out of the ordinary and shall i need the exact output in measuremet of volts??
    Thank u – Victor

    • hi Victor, My name’s not Martin… i think you’ve mistaken my name for the person who posted the first comment here. But it’s no big deal. As for your question, it’d be better to display your measurements as microvolts…

  10. sir, i was designing an eeg sleep detector…my question is, how can i design an eeg circuit to define the alpha and theta frequency ??

    • You’ll have to either use very narrow filter bands to separately measure those frequency ranges… OR you could program your PIC to filter them for you… OR better yet, program the filters into your interface software.

      • sir, can u help me where can i get coding for my PIC…for my eeg circuit,the output from eeg circuit act as input to the PIC..i used PIC16F877A

  11. Hi there, outstanding work, about the Brain Tuner, have you ever got the chance to finish that project, will you post it here. Thanks

    • Hi Will, thank you for the compliment, although I really can’t take all the credit. I shelved the Brain Tuner project quite a few months ago and instead, I’m going back to the basics with Dr. Becker’s early works and experiments. You can see what I’ve been upto lately over here: electrobody.wordpress.com

  12. Sir why there is a need of TLE-2426, from the circuit operation point of view?
    What can we do if it is unavailable.?

    • Thats the chip which provides a virtual ground, so that entire circuit can work on a single battery. Otherwise, you would need to modify the entire circuit to work with a dual supply (e.g. +5V 0 -5V)

  13. hi… i am a student of engineering from india. i have taken the designing of eeg as my project. can u send me the circuit diagram of eeg so that i can implement it in hardware???

    • Prateek, please use your brains and CLICK the schematic image on the blog’s main page!!!

  14. Thankyou sir…… is there any alternativve for TLE2426 ???

  15. Sir,
    I am doing a final year project on “BRAIN MACHINE INTERFACE”. I found your circuit schematic very helpful, but I need the specifications of the electrodes. If you could guide me in selecting proper electrodes to analyza alpha, beta, delta & theta waves.
    Thank you

  16. teknomage if you are looking in on this page there is a Bob beck brain tuner page .

    http://www.rubysemporium.org/brain_tuner.html

    http://www.rubysemporium.org/brain_tuner_schem.html

    I built this, works really well.

  17. hi… i m rajesh from B.E.(biomedical ) sir i have to interface 21 eeg signals to computer at a time so plz tel me about the interfacing..

    • hi, well first of all, you have a couple of things to consider… one is the EEG frontend and second is the actual digital interfacing to the PC. So, for 21 EEG signals, are you planning to build 21 separate EEG circuits for the frontend and then feed them to the microprocessor and then to the PC via the serial port or USB? This will be the more expensive option but it’ll make things simpler for interfacing later on… OR your other option is to build only ONE single EEG measuring circuit and then use a multiplexer to scan through all your 21 channels, and then feed it to the uP to be sent to your PC. For this, you will need to get a couple of high-precision, low DC offset analog multiplexer… Someone has already worked on a circuit like this, but I’ll have to search around for the link and post it here. If not, then you’ll have to figure out a way to minimize noise from the multiplexer as well as the required clock to drive it… Hope this helps for now.

  18. hi sir,
    this is baji studying b.tech. i want to do a project “operating a computer with brain instructions”. can u plz tel me is this EEG schematic useful for me to give instructions to computer?
    plz reply soon…………….

  19. hi,
    i want to know why you have inverting amplifier after INA 118 and why not put it after low pass filter. help me

  20. hey i am sumukh from India i am doing a BCI project , and i am done with my hardware part and now i want know can i use eegprobe ,after getting the signals i want to process in matlab. please reply me.

  21. Sir,I want to design an equipment which shows the output of both EEG and ECT,for that how can i design an EEG preamplifier circuit??

  22. Ic not avaible

  23. Hello Teknomage!
    I am a student in a university in technology and science. I need your help.
    Can you send me the schematic of EEG 1 chanel you made and the informations
    about data? I extremly need to finish my work. Especially in amplier.
    My email: haquoctubk@gmail.com
    I look forward your reply early.
    Thank you!

    • Hullo Ha Quoc, the schematic is already on my blog. Just click the image in the top post and you’ll get it…

  24. hi sir

    i’m an engenier student , i found your work
    awesome !! :Dand for my finely project i have to interface 20 EEG signals to computer at the same time using a multiplexer ! can you you please help me to design the PCB ?!! thnx

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