1. Different types of normal brain waves
Beta waves occur at a frequency of 13 to 30 cycles per second. They are usually associated with anxiety, depression, or the use of sedatives.
Alpha waves occur at a frequency of 8 to 12 cycles per second in a regular rhythm. They are present only when you are awake but have your eyes closed. Usually they disappear when you open your eyes or start mentally concentrating.
Theta waves occur at a frequency of 4 to 7 cycles per second. They are most common in children and young adults.
Delta waves occur at a frequency of 0.5 to 3.5 cycles per second. They generally occur only in young children during sleep.

2. EEG measurement setup
10-20 Lead system is most widely clinically accepted
Certain physiological features are used as reference points
Allow localization of diagnostic features in the vicinity of the electrode
Often a readily available wire or rubber mesh is used
Brain research utilizes even 256 or 512 channel EEG hats

3. Electrodes – Basics High-quality biopotential measurements require
Good amplifier design
Use of good electrodes and their proper placement on the patient
Good laboratory and clinical practices
Electrodes should be chosen according to the application
Basic electrode structure includes:
The body and casing
Electrode made of high-conductivity material
Wire connector
Cavity or similar for electrolytic gel
Adhesive rim
The complexity of electrode design often neglected

4. Electrodes - Basics Skin preparation by abrasion or cleansing
Placement close to the source being measured
Placement above bony structures where there is less muscle mass
Distinguishing features of different electrodes:
How secure? The structure and the use of strong but less irritant adhesives
How conductive? Use of noble metals vs. cheaper materials
How prone to artifact? Use of low-junction-potential materials such as Ag-AgCl
If electrolytic gel is used, how is it applied? High conductivity gels can help reduce the junction potentials and resistance but tend to be more allergenic or irritating
Baseline drift due to the changes in junction potential or motion artifacts Choice of electrodes
Muscle signal interference  Placement
Electromagnetic interference  Shielding

5. Ag-AgCl, Silver-Silver Chloride Electrodes
The most commonly used electrode type
Silver is interfaced with its salt silver-chloride
Choice of materials helps to reduce junction potentials
Junction potentials are the result of the dissimilar electrolytic interfaces
Electrolytic gel enhances conductivity and also reduces junction potentials
Typically based on sodium or potassium chloride, concentration in the order of 0.1 M weak enough to not irritate the skin
The gel is typically soaked into a foam pad or applied directly in a pocket produced by electrode housing
Relatively low-cost and general purpose electrode
Particularly suited for ambulatory or long term use

6. Gold Electrodes Conductive polymer electrodes
Very high conductivity  suitable for low-noise meas.
Inertness  suitable for reusable electrodes
Body forms cavity which is filled with electrolytic gel
Compared to Ag-AgCL: greater expense, higher junction potentials and motion artifacts
Often used in EEG, sometimes in EMG
Conductive polymer electrodes
Made out of material that is simultaneously conductive and adhesive
Polymer is made conductive by adding monovalent metallic ions
Aluminum foil allows contact to external instrumentation
No need for gel or other adhesive substance
High resistivity makes unsuitable for low-noise meas.
Not as good connection as with traditional electrodes

7. Metal or carbon electrodes
Other metals are seldom used as high-quality noble metal electrodes or low-cost carbon or polymeric electrodes are so readily available
Historical value. Bulky and awkward to use
Carbon electrodes have high resistivity and are noisier but they are also flexibleand reusable
Applications in electrical stimulation and impedance plethysmography
Needle electrodes
Obviously invasive electrodes
Used when measurements have to be taken from the organ itself
Small signals such as motor unit potentials can be measured
Needle is often a steel wire with hooked tip

8. Current technique of BCI
Input
Output

9. Categories of BCI 2. Steady state visual evoke potentials (SSVEP)
Based on EEG signal :
1. Event–related de-synchronization / synchronization (ERD/ERS)
2. Steady state visual evoke potentials (SSVEP)
3. P300 component of event related potentials (ERPs)
4. Slow cortical potentials (SCPs)

10. Different features of each BCI system [2]

11. Steady-state Visual Evoked Potential
(SSVEP)
SSVEP is an EEG signal response to the flickering visual stimulus with a frequency higher than 6 Hz [1]

12. Journal: Development of a Low-Cost FPGA-Based SSVEP BCI Multimedia Control System [1]
User target:
patients suffering from severe motor disabilities, such as amyotrophic lateral scleroses (ALS), spino-cerebellar ataxia (SCA), and other paralyzed patients, may have limited motion while constrained on a hospital bed

13. System configuration

14. Acquisition module
Pre amplifier: Instrumentation amplifier, INA 128, (Gain setting, Gain: 1000)

15. ADC Module MicroChip MCP3201
the 8-pin dual in-line package (DIP) with serial control interface [serial peripheral interface (SPI)] devices,.
The resolution and maximum sampling rate of the ADC are 12 b and 100 k samples/s.

16. Signal Processing

17. Data flickering, segmenting and averaging

18. Hardware System

19. Result

20. References
[1] Kuo-Kai Shyu; Po-Lei Lee; Ming-Huan Lee; Ming-Hong Lin; Ren-Jie Lai; Yun-Jen Chiu, "Development of a Low-Cost FPGA-Based SSVEP BCI Multimedia Control System," Biomedical Circuits and Systems, IEEE Transactions on , vol.4, no.2, pp.125,132, April 2010 [ 2] Danhua Zhu, Jordi Bieger, Gary Garcia Molina, and Ronald M. Aarts, “A Survey of Stimulation Methods Used in SSVEP- Based BCIs,” Computational Intelligence and Neuroscience, vol. 2010, Article ID , 12 pages, 2010