The goal of this project was to build an affordable EEG device to monitor and record brainwaves. One big limitation of the commercial systems I looked at is the fact that they're wired to a sensor box which interfaces by another wire to the computer. This means the subject is tethered to the experimenter, making it difficult to perform experiments in a natural setting. One of my design criteria was for the headset to be highly portable, allowing data acquisition in nearly any environment.
The other drawback of the majority of extant commercial systems is their high cost, many ranging in the thousands of dollars. I aimed to design a system that could be built an order of magnitude cheaper, making it affordable to curious self-experimenters and amateur scientists. Of course this tradeoff limited the complexity of the design, and I eventually settled on building a single electrode system.
During my research I discovered the article How to Hack Toy EEGs | Frontier Nerdswww.frontiernerds.com/brain-hack, in which they discovered that an off-the-shelf toy called "MindFlex Dual" contained two headsets (one for each player) that embed a commercial EEG chip from a company called NeuroSky. This game was not a huge commercial success, and at the time I began construction could be purchased for around $60. This was substantially less than even a single chip ordered from NeruoSky would cost, and you got two of them. The headset exterior could also be reused in my design, providing me with a fabric electrode, straps, and two chambers that sit just over each ear containing my custom circuitry and batteries.