What is EEG
Electroencephalography or EEG henceforth, is a method of measuring brain activity. It works by measuring the voltage between two points on the skull, typically using electrodes, probes henceforth. This is the technology that you might recognize from the sci-fi brain to computer interfaces or from a sleep lab. This fundamentally works by picking up on the electrical signals from different parts of your brain which can be used to determine the rough state of that area of the brain.
Analog and Digital Converters
One major component of EEG is the process of converting the analog data captured by the probes into digital signals that can be handled by the brain. Computers work using a binary system to represent data, high voltage or low voltage, the voltage points are discrete. The values coming from the brain are continuous. Therefore, some process must occur to turn analog voltage levels into digital values. These devices can be found in many different products, including but not limited to: Modern Voltmeters, Oscilloscopes, and Digital Cameras. We will call these converters A->D for shorthand. An everyday example of this is the old AM (Analog) vs the newer FM (Digital) Radios, you might have noticed that AM gets more noisy and quieter as you get further from the station (In this case, the Brain), while FM stays just as clear and loud as long as it plays.
Why those converters are so expensive
Analog to Digital converters aren't actually hugely expensive, but the ones used for EEG are very expensive for a number of reasons:
- In the Industry Standard configuration, they have to work at very low voltages
- Crosstalk can occur simply by having other wires to the signal
- Involves quantization of the input, so it necessarily introduces a small amount of error or noise, which takes good engineering to fix
Electronic component reference
| Component | Description |
|---|---|
| Multiplexer (HW-178) |
Analog switch that connects one input selected from several inputs to a single output. |
| Instrumental Amplifier (AD620) |
Boosts the EEG signals up so they are more noise tolerant (because the signal is more powerful) |
| Microcontroller (Arduino Due) |
Relatively expensive single-board computer that can run code and output faster than most others available. |
| Microcontroller (ESP8266) |
Relatively cheap single-board computer that runs very fast, but with limited output options. |