EEGs are a noninvasive way to look into your brain. While the brain is extremely complex, areas of it can lock into circular firing patterns, resulting in telltale brain waves that one can observe with the right equipment. Intensity of these waves change depending on your internal state. The waves we will be most easily able to distinguish are alpha and beta waves -- alpha waves occur at around 8-12 Hz and when measured from the frontal lobe provide an estimate of how relaxed a person is, while beta waves are around 12-30 Hz and correspond to how much a person is concentrating or how alert they are.
The concentration of each wave can also tell more specific things about your thought patterns depending on where you measure them from. For example, alpha concentrations on the left motor cortex increase when you think about moving your right hand. Regardless of where you're taking measurements, looking at the concentrations of waves in real time - a process called biofeedback - can give you much greater control over them.
This tutorial is an in-depth guide on how to make your own simple EEG circuit. Along with monitoring brain wave concentration, the final circuit can also be used as an ECG, as a way to see your heartbeat trace. The circuit will use 3 electrodes - 2 to measure a voltage difference across your scalp, and one as a reference to ground. Depending on how many parts you already have, the circuit could only set you back around $10.
The aim for this project is to be easily available and understood by people of every technology background. For those electronically savvy, I will include up front a finalized schematic so you can jump right into making it yourself. For those that want more guidance, I will include a detailed description / explanation of every section of the circuit, showing you what it does and why you need it.
Then, I'll move onto the software (Processing based), which is a very important piece in actually interpreting the raw data you receive.
So - let's start!
The concentration of each wave can also tell more specific things about your thought patterns depending on where you measure them from. For example, alpha concentrations on the left motor cortex increase when you think about moving your right hand. Regardless of where you're taking measurements, looking at the concentrations of waves in real time - a process called biofeedback - can give you much greater control over them.
This tutorial is an in-depth guide on how to make your own simple EEG circuit. Along with monitoring brain wave concentration, the final circuit can also be used as an ECG, as a way to see your heartbeat trace. The circuit will use 3 electrodes - 2 to measure a voltage difference across your scalp, and one as a reference to ground. Depending on how many parts you already have, the circuit could only set you back around $10.
The aim for this project is to be easily available and understood by people of every technology background. For those electronically savvy, I will include up front a finalized schematic so you can jump right into making it yourself. For those that want more guidance, I will include a detailed description / explanation of every section of the circuit, showing you what it does and why you need it.
Then, I'll move onto the software (Processing based), which is a very important piece in actually interpreting the raw data you receive.
So - let's start!
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Signing UpStep 1: Parts
I purchased most of my parts from Digikey (and Amazon). Their layout might seem slightly intimidating at first glance, but they seem like the cheapest place to get parts. And they have the USPS first class shipping option ( < $3 for small orders, choose this! It will save you a lot.), meaning you don't have to spend the same amount on parts as shipping, as it is on some websites.
Chips:
- 1x Instrumentation Amplifier - AD620AN - This is the most expensive, and most important part. While technically you can make your own instrumentation amplifier from 3 op-amps, I could never get my own to give me good results. Precision cut resistors in this ensure that it'll do its job.
- 2x Quad Op-Amp - TL084CN - Any Op-Amp will do. You need 5 single amps, this one just includes 4 in each chip.
Capacitors:
I would strongly suggest buying a capacitor bundle from ebay or the like, espcecially if you plan on ever doing some other sort of electronic project. One bundle and you're basically set for life. Regardless, whether you buy them in a pack or individually, make sure to include these capacitors :
- 1x 10 nF, ceramic
- 1x 20 nF, ceramic
- 1x 100nF, tantalum
- 5x 220nF, tantalum
- 1x 1uF, electrolytic
- 2x 10uF, electrolytic
Resistors:
Same as capacitors, I suggest a bundle. This is a very good one, has all the values you need (minus the potentiometer). The individual values you'll need, though, are:
- 1x 1kΩ Potentiometer - via Digikey - very useful to adjust your gain on the fly.
- 2x 12Ω
- 1x 220Ω
- 1x 560Ω
- 2x 22kΩ
- 1x 47kΩ
- 2x 100kΩ
- 2x 180kΩ
- 1x 220kΩ
- 2x 270kΩ
- 1x 1MΩ
Connectors:
- A breadboard to wire everything on. This one is large enough, and comes with useful jumper wires. I suggest saving the jumper wires specifically for connecting the various stages of the design. This will make it very modular, and easy to reorganize/reorder if you end up needing to.
- Wires for everything else. I like that pack, since it's pre-cut and keeps your board tidy. You can also get plain wire and cut it yourself.
- 3.5mm audio cable.
- 2x 9V batteries for power.
Electrode Supplies:
- Ambu Neuroline Cups seem to be the most cost-effective method, found here. Thanks to user jonencar for the link in the comments.
- electrode gel
Chips:
- 1x Instrumentation Amplifier - AD620AN - This is the most expensive, and most important part. While technically you can make your own instrumentation amplifier from 3 op-amps, I could never get my own to give me good results. Precision cut resistors in this ensure that it'll do its job.
- 2x Quad Op-Amp - TL084CN - Any Op-Amp will do. You need 5 single amps, this one just includes 4 in each chip.
Capacitors:
I would strongly suggest buying a capacitor bundle from ebay or the like, espcecially if you plan on ever doing some other sort of electronic project. One bundle and you're basically set for life. Regardless, whether you buy them in a pack or individually, make sure to include these capacitors :
- 1x 10 nF, ceramic
- 1x 20 nF, ceramic
- 1x 100nF, tantalum
- 5x 220nF, tantalum
- 1x 1uF, electrolytic
- 2x 10uF, electrolytic
Resistors:
Same as capacitors, I suggest a bundle. This is a very good one, has all the values you need (minus the potentiometer). The individual values you'll need, though, are:
- 1x 1kΩ Potentiometer - via Digikey - very useful to adjust your gain on the fly.
- 2x 12Ω
- 1x 220Ω
- 1x 560Ω
- 2x 22kΩ
- 1x 47kΩ
- 2x 100kΩ
- 2x 180kΩ
- 1x 220kΩ
- 2x 270kΩ
- 1x 1MΩ
Connectors:
- A breadboard to wire everything on. This one is large enough, and comes with useful jumper wires. I suggest saving the jumper wires specifically for connecting the various stages of the design. This will make it very modular, and easy to reorganize/reorder if you end up needing to.
- Wires for everything else. I like that pack, since it's pre-cut and keeps your board tidy. You can also get plain wire and cut it yourself.
- 3.5mm audio cable.
- 2x 9V batteries for power.
Electrode Supplies:
- Ambu Neuroline Cups seem to be the most cost-effective method, found here. Thanks to user jonencar for the link in the comments.
- electrode gel
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http://www.radio-electronics.com/info/circuits/opamp_notch_filter/opamp_notch_filter.php
For the electrodes, did some searching around for a more cost-effective option and found these:
Ambu Neuroline Cup
$7.50 for a pack of 10! They are "Single patient use", and intended to be disposed of after each use in medical environments. This is mainly for purposes of sterilization; for our purposes, however, we should be able to get extended use. :)
Can pick them up directly from Ambu in the US; King Medical is a good option for Canadian DIY.
Picked these up for my first attempt at the EEG circuit and should be giving them a try in the next few days. Will post how it goes.
1. i replaced those tantalum capacitors with electrolytic ones of the same value ...will it affect the circuit operation??
2. The power line frequency over here is 50 hz....so,whats the new value of resistors and capacitors?
Plz help.....
I think what I'll do is ignore the amplifier and use the components to make another set of ~ 30 Hz Low Pass filters.
Did you have to do much processing of data in your program? I'm applying more filtering in LabVIEW, including the 50 Hz Notch filters. I see some changes when messing around with the electrodes but am waiting on the electrode gel to take proper readings.
What sort of environment did you take your readings in? Do you have any screen shots of the sort of readings you got from your system?
Thanks for your quick response to my other queries. Much appreciated. I'll let you know the outcome of the alternative implementation!
Besides that, once I got the time signal in I just took the FFT of it and displayed that to see the various frequency bands. On step 10 there's a picture of the time data (after the quick digital filtering) that I got in, with the FFT beneath it.
Firstly, it looks like you had a myDAQ available to you but instead you used the sound card of your PC to acquire the signals. Was there a particular reason for this? I am trying to use the myDAQ analogue input channels of the myDAQ to acquire a differential signal from the circuit.
Secondly, I'm not having much luck with the 60 Hz notch filters. I've put the design into multisim and the response is very different from what you've shown in LabVIEW. Instead of the 60 Hz frequency cut off, I am seeing attenuation of all frequencies below 84 Hz and above 2 kHz. It's a long shot but I was wondering whether you came across any similar issues with your circuit that may help me resolve this problem?
The notch filter just has the amplifier for some fine tuning, it's not really necessary. I can't help much with the frequency response being distorted for the notch filters, though. That was one part I didn't do a multisim simulation beforehand: I built it and tested it with the myDAQ, and the results were what I wanted. Try a T-Notch: if it works, then that's great. Let me know if it does!
Seriously, well done.
would it work with AD620NB instead of AD620AN?
also is would be awesome to make it standalone, with a lcd (arduino - raspberry pi?)
Thanks
please correct me if i am wrong.
thank you