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…
Unlocking the secrets of the mind... 
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
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.
Interesting! Do you have a webpage sharing your work on this bone stimulator?
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…
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
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
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)
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!!!
Thankyou sir…… is there any alternativve for TLE2426 ???
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
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.
hey John, sorry I took so long to reply. Thanks for the links, really appreciate it! 🙂
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.
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…………….
hi,
i want to know why you have inverting amplifier after INA 118 and why not put it after low pass filter. help me
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.
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??
Ic not avaible
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…
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
Hi Ibrahim, sorry I cant help you with the actual design. You’ll have to do your own research and a LOT of experimentation to get a multiplexed EEG to work. I do remember seeing something of the same that was attempted by some of the guys from the OpenEEG group. Check this out:
http://www.jhansmann.de/eeg/EEG_input_mux/index.html
I also came across a webpage long ago which detailed a similar project by a bunch of college kids but cant find that link right now. As a note to some of the challenges you might face in your quest, check this out too: http://ilo.technologypublisher.com/technology/11471#.UXZ9iyKHOFc
hello sir, i am searching a circuit for signal (movement related potential) from spine (between L3-S1). i want to ask that will this designed circuit work for spinal signal?
Hey bro, I’m a brasillian electronics engennier, and i’m confused about the gain resistor. I saw it’s value on the coments, but is it connected to the shields os the electrodes? ‘Cause there are lines coming out by the two sides of the resistor, in the direction of the shields. Are they connected or what? Thanks ;D
hello sir I am kindly asking if u can give me your advice on this.Is it possible to use the above circuit to interface it with biomedical sensor pads to measure EEG level for sleep detection
Sure, it should work, you might need to experiment on your own to match the input impedances.
I feel so much happier now I uneasrtdnd all this. Thanks!
HI Artie, I know this comes as a LATE reply, but I’m glad my blog was helpful to your EEG experimentation in any little way 🙂
Hello! I built this circuit for Ecg . Can I ask you some questions? From what I understand I can see the set of waves coming from the scalp … I could not add a filter / selector so that I can distinguish different types of wave? Also I ask you where I can find the scheme of an interface to connect to a PC via a serial or USB cable?
Hello Luca, I’m glad my schematic is useful to you. But are you using it for ECG or EEG? ECG doesnt require as much gain and filtering as EEG does. For EEG real-time analysis, if you want to break down the incoming neural data, then you need to setup filters for each of the bands that you’re looking for. But honestly, it would be much better and EASIER if you were to implement these filters using a software-based approach. When I first started working on this circuit more than a decade ago, I didnt have many options, so I had to build everything from scratch. But nowadays, you get convenient kits that’ll make your work a whole lot easier. For the EEG A/D aspect, I suggest you look for a USB data logger, that can sample @ 128-256 Hz atleast. Back then, I personally built a PIC18F2550 USB HID oscilloscope for this purpose (you can search for its schematic). Otherwise if you prefer using Arduino, then check out this Arduino-based data logger:
But for ECG, if you’re not concerned about losing the ELF frequency components, then you can simply feed the output of the EEG circuit directly to your soundcard and use a DAW like Audition or Audacity to record your heartbeat. Since it’s stereo, you can record upto 2 channels at a time. You can then analyze the incoming data as sound even at the lowest sampling rate of 11025 Hz. You can also use a software called Win Oscilloscope to view the incoming ECG data via your soundcard. You have lots of possible options available to you nowadays. All the best to you!
Hi Teknomage! Thank you very much for your reply. But before going on I wanted to first understand if the circuit I built works. I used a 330 ohm gain resistor on Ina118. I used 3 integrated TS272 instead of TLC 272 … are they the same? Also trying with a multimeter I find 1 volt output, both with the electrodes connected or disconnected. In your opinion is it regular or is there something wrong? Thanks and a big greeting Luca
Hello Luca, a gain resistor of 330 ohms would set the INA’s gain to approx 150x. And sure, you could use TS272 as a dual opamp, although they’re not low-noise precision opamps like the TLC272, which are more suited to such bio-medical applications. As for the 1V DC offset you are seeing at the output, you’d have to be more specific… are you seeing this 1V from the INA118 differential output, or at the opamp outputs? If it’s the latter, then it’s somewhat fine because what you are seeing should be the DC biasing that is being employed from the TLE2426, although I’d say that offset should be closer to 2-2.5V instead of only 1 Volt. You need to check your circuit once again and make sure everything is in order.
Hello.
I am working towards implementing some sort of EEG design with the purpose of trying to find out what is happening in my head over time periods ranging up into several hours. I am aiming for at least 8 channels.
(I’m not yet sure about if I want to go into training my self with feedback in anyway whatsoever and if I am only wanting to be able to observe brainwave patters in a way which allows me to pair segments of the plots to recollections of the time those where recorded then the design aught to be very much simpler).
If you wouldn’t mind me asking you a couple of questions:
The raw signal entering the first amplifier will contain many frequencies including noise signals and 50/60Hz interference, from my research I find that I can use a combination of high-pass filter, low-pass filter and notch filter(for the 50/60Hz) to clean up what is picked up by the EEG channel so that what’s left is only all the relevant frequencies depicting what is going on inside of the brain, at that point all that’s left is to separate the frequencies and plot them in a suitable format for the users consumption or analysis.
But given the power of PC’s today and software such as Matlab, wouldn’t it be much cheaper and easier to simply digitize the raw EEG signal with as much details as possible/feasible, transfer it to a PC and use Matlab(or other software) to clean up the now digital data and then analyse the signal content?
Or can analog filter do things digital filters can’t?(in practical and real-world situations)
At some level this all comes down to whether or not I actually need a real-time design, which would take me longer to achieve, cost me more money and be a lot harder to do.
I would really appropriate your thoughts about what I have written about.
Yes of course David, if you want to save time and cost on developing your 8-channel EEG, then software-based filters will do the trick. Honestly, there’s very little that digital filters cant do in comparison to analog filters, it’s got more to do with tradeoffs in the filter order versus other factors. But if you’re not too concerned about real-time filtering, then digital filters will work. The only disadvantage I see is that if the power-hum overcomes the EEG signal from each channel, then it is quite likely to saturate the limited sampling bit range. If you are using active electrodes with your EEG circuit, then you can actually eliminate a good deal of the power-mains ‘hum’ at 50/60 Hz (depending on where you’re located), as long as you match the instrumentation amplifiers for each channel precisely.
Then, you can send your raw EEG data straight to an ADC or you could cheat by using an Arduino or Seed, transmit the data to your PC and then post-process the signal with your preferred DSP toolbox or language. Am sure you’re already familiar with higher-order filters, so implement a good low-pass filter from 1 to 45 hz or so, and a Notch filter at 50/60 Hz. All the best!
could not read your email address. please commensurate written! Thanks!