An Exploration Into the Mysterious EEG
The electroencephalogram(EEG）is a test of the bio-electrical potentials generated by the cerebral cortex nerve cells in the electrical activity of the brain. It records the electric wave changes in the brain activity and can generally reflect the electrophysiology activity of the cerebral neurons in the cerebral cortex or on the surface of the scalp. Bio-electric phenomenon is one of the basic characteristics of life activities. All living creatures ranging from big whales to small bacteria have either strong or weak bio-electricity. In fact, the word ‘cell’ in English also means ‘battery’. Similar to micro batteries, the numerous cells are the source of bio-electricity. As there are many nerve cell activities existing in the human brain, the electrical rhythmic changes or rather the electrical oscillation is formulated. Such oscillation resembles waves when presented under scientific instruments. Therefore, we call the neural electrical oscillation in the brain as the EEG. To put it in a nutshell, the EEG is the bio-energy produced by the brain cells. Metaphorically speaking, it is the rhythm of the brain cells activity.
Features of the EEG
Modern scientific research prove that human brains produce their own EEG in at least four important separate wave bands when working, which can be detected by the electronic sensor.
The EEG is a set of spontaneous and rhythmic nerve-electric activities. Frequency ranges changing within 1-30 times can be grouped into four wave bands and they are δ（1－3Hz）、θ（4－8Hz）、α（8－13Hz）、β（14－30Hz). (Scholars have mixed views on how to mark the boundaries between every two wave bands. Some scholars think that frequency of the δ wave is less than 4Hz, θ wave is 4～8Hz，α wave is 8～12Hz，and β wave 12～35Hz. Some researchers even believe that there is an EEG larger than 35Hz and name it as the γ wave. People who live under such condition may be life-threatening.
Step 1: Control Theory 1. the EEG Sensor to Receive Signals
Signal amplification technique makes the original EEG signals clearer. Noise filtering technique can eliminate background noises released by muscles, pulses and the electrical equipment.Wave filter can remove disturbing noises ranging from 50-60Hz from power grids. In order to detect the EEG signals from interfering noises, we need a reference electrode and a electric circuit grounding system.Electric circuit grounding system enables the electrical pressure of human body equivalent of your headphone voltage. The reference electrode filters the surrounding noises through the common-mode rejection. The reference electrode and the circuit grounding system of the equipment are often connected through human ears. Therefore, you have to make sure connection in your ear region is sound when using the equipment.
Step 2: Control Theory 2. a Small Car Controlled by the EEG
By putting the EEG electrodes onto your forehead, you can send signals including those interfering ones in the surrounding environment to the sensor. Common-mode rejection algorithm is used to filter the interfering noises so as to detect the EEG signals. The signals are then transferred to the controller to make the small car move forward.
Step 3: Control Theory 3. Controlling Direction:
The left-right rotating mechanism is realized by the triaxial accelerometer. By judging the rotating speed of the car head, you can decide where it is heading. This triaxial I2C communication mode is simple and convenient. The whole size is also small (20*20mm), which can be easily controlled.
Step 4: Control Theory 4. Issues in the Debugging Process
1)Baud rate inaccuracy: the baud rate should be set as 57600
2) The EEG connection: clean with some alcohol and water to ensure sound connection between the electrodes and your skin.
3) Disturbances: computer power supply is not recommended for disturbances reduction in the surrounding environment.
4) Programming: efficiency and timelessness is relatively poor due to blockage in information receiving.
Step 5: Circuit Diagram-The Transmitting Circuit
By putting the EEG electrodes onto your forehead, you can send signals including those interfering ones in the surrounding environment to the sensor. Common-mode rejection algorithm is used to filter the interfering noises so as to detect brainwave signals. Brainwave signals are then transferred to the controller to make the small car move forward.
The left-right rotating mechanism is realized by the triaxial accelerometer. By judging the rotating speed of the car head, we can decide where it is heading.
Step 6: Receiving Circuit
This controller is one of the many sharp collisions and perfect combinations between Bluetooth 4.0 and Arduino, by inheriting all the functions of the RoMeo controller and adding on the Bluetooth 4.0 wireless communication technology. It is supported by thousands of open sources and can easily extend the Arduino module. This module integrates two paths DC motor and a wireless outlet, thus providing an easier way of starting a project. The circuit controls the motor's movement by receiving signals through the Bluetooth.