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!
Step 1: Parts
- 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.
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
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
- 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.
- 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