EEG for the braindead

I was hoping to start this blog yesterday but I couldn’t find the time coz I went for a rock show. This little project is a resurrected version of something similar I worked on a few years ago. A lot of my inspiration comes from the OpenEEG project. So, if you’re ready for the ride, let’s begin!

I hope to be able to provide a few useful guidelines to those who’d like to build a cheap and affordable EEG recording circuit for themselves. My idea is to build a basic EEG circuit based on the venerable INA118 (precision instrumentation amplifier) and then record the data output either through a :

a) RS232 serial port (optoisolation achieved using 6N139)

OR

b) Soundcard (signal is first FM modulated, optoisolated using CP Clare’s LOC 110 which is then fed into the Mic input and finally software demodulated into the original EEG signal )

One thing I definitely want is to have atleast 8 separate channels and I’m planning to employ Active electrodes (16 of them + 1 for the Right Leg Driver). The difference between a Passive and Active electrode is that the latter uses an op-amp combined with the electrode itself. This provides better readings and also better noise reduction. Now, the best part about this entire thing is that i plan on using ONLY ONE INA118 inst. amplifier for all 8 channels. This will be achieved by routing the signals from the active electrodes through an isolation analog multiplexer such as MAX4558.

It’s gonna take a while before i complete the entire thingamagic, but it’ll be worth it. If all works well, I’ll use this for my own neurofeedback training purposes.

Here’s a pic of the basic EEG circuit. What you’re looking at is the basic building block based on INA118 (the chip on the left) with a Right Leg Driver (RLD) running on TLC272 (to the right).

INA118 basic EEG circuit with RLD

Keep checking in every now and then. Once the circuit is completed, I will post the entire schematic. Will definitely keep you posted on any progress made in the meantime…

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~ by teknomage on November 11, 2007.

12 Responses to “EEG for the braindead”

  1. hi i am currently doing a very similar project… although i m stuck in programming the 8 input multiplexer….. any ideas?

  2. hi,
    I am working on similar project but instead of EEG i am working on ECG. I planning to add the right leg drive circuit to it. can u please help me with this issue
    Thanks in advance

  3. Hi GP!

    Sorry about the delay. I’m sure you’re aware that the whole purpose of including a RLD is to inject a small portion of the noise back into the body, so that when it is picked up by the Instrumentation Amplifier, the noise is supposed to suppressed even further. All this supposedly works in theory but it depends on quite a few variables… the impedance of the electrodes and its variations over time… the skin impedance as well as proper common mode rejection of the IA.

    First of all, which IA are your using? AD620 or the INA114 series?? If you take a look at the RDL circuit in the INA114 datasheet, that should give you a headstart. But quite frankly, in my experience, I’ve got wonderful results in my ECG readings WITHOUT the RDL circuit. So, try your circuit with and without the RDL and see how it performs either way.

    Let me know if you need any further assistance. I’ll be glad to help 🙂

    Sincerely,
    AJ

  4. sir ;
    please give me acircuit discription to construct eeg
    my e mail address is

    • Viraj, what the heck do you think is all the info pasted on this blog for?! Go through the blog properly and you will have all the information you need. Dont expect people to spoon-feed you!!!

  5. Hello dude

    Can you please provide a schematic of your circuit? It would be greatly appreciate.

    • Sigh! Can’t you guys look? The schematic is available on my blog itself. Just click the thumbnail to enlarge it.

  6. Bravo friend, nice work!

  7. Hi,
    I intend to build an active electrode based on the AD620. Where can I find a schematic of the best way to do it, using AD620 or a better instrumentation amplifier (e.g INA121 or 118)? Are you going to use an instrumentation amplifer to build your active electrodes?

    • Check out the active electrodes schematics on OpenEEG’s Active Electrodes page: http://openeeg.sourceforge.net/doc/hw/ae.html
      I tried to replicate Jarek’s circuit but my attempt was not successful. However, your mileage may vary, so just give it a shot. You will need to use high-accuracy, low drift OpAmps (not an IN amplifier) for your Active Electrodes, coz you want to first obtain an amplified version of the absolute (not differential) scalp voltages and later send them to your final IN amplifier board. I’m interested in how your experimentation turns out, so keep me posted, my friend…

  8. IS the EEG Schematic up to date as of 5 July 2010? What is the value of R!? Must be a potentiometer if for GAIN.

  9. Hi.. Great Work..
    I am student of B.sc and doing my BM engineering. Actually our group is working on EEG based project. I found your email address in the website of Adrian Mohan. Sir , our analog circuitry consist of:
    AD620
    Low pass of 25 Hz
    Amplifier of variable gain
    Notch
    Low pass of 25 Hz
    Actually we want to view our EEG signals on digital oscilloscope available in our labs. We are using 3 electrodes.
    1st at C3 position on scalp connected to pin 3 of Ad620
    2nd at earlobe connected to pin 2 of Ad620
    3rd at frontal bone connected to ground.
    but the problem is that we are not getting any signal, there is just noise on oscilloscope.
    We are using Agcl electrodes.
    Sir please any help or any advice will be greatly appreciated.
    We will be really thankfull to you.

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