Neural Design Group N2

Da’Janel Roberts

Matthew Morgan

Jonathan James

Goals

Research EEG theory Replicate Brainmaster amplifier design. Determine whether the Brainmaster design

can actually measure brainwaves.

What is a brain wave?

The sum of the electrical activity of millions of neurons, located primarily in the cortex.

Measured by an electroencephalogram (EEG) via surface electrodes.

Classified according to three properties: Frequency Amplitude Shape

International 10/20 System of Electrode Placement

Most widely used method.

Electrodes are placed relative to the underlying area of cerebral cortex.

Letters correspond to brain lobe area.

The "10" and "20" refer to the 10% and 20% interelectrode distance. 

                                                                    

Types of Brain Waves

Five types of brain waves Alpha Beta Theta Delta Mu

Alpha Waves

8 – 13 Hertz Low amplitude Relaxation Reflecting

                                     

Beta Waves

14 – 30 Hertz Rapid oscillations with

small amplitudes Alertness Working

Theta Waves

4 – 7 Hertz Prominent when

dreaming or drowsy. Arise from emotional

stress such as frustration.

Delta Waves

Less than 3.5 Hertz Occur during deep

sleep or other non-attentive states of mind

Prominent when totally subconscious

Mu Waves

Resemble croquet wickets in shape

Associated with physical movements or the intentions to move.

EEG Amplifier Requirements

High Gain (80dB and up) Low Noise Bandwidth (.5Hz to 50Hz) Minimal cost

Current Technologies

Various technologies available: WaveRider Series Mindset BrainMaster

WaveRider Series

WaveRider Pro, 4 channels, $1700. WaveRider Jr., 2 channels, $950. CEO, 1 channel, $545. Pro version monitors brain waves (EEG), heart rate, muscle

tension (EMG), and skin resistance (GSR). .5 Hz – 40 Hz pass band, -72 db at 60 Hz. 8 bit A/D converter, 128 samples-per-second.

Mindset

Mindset, 16 channels, $2195-$4999. Different software sets: one for research and one for clinical

use. Uses 2 fourth-order Sallen-key active filters, 48db roll-off

per octave, 1.8 Hz - 36 Hz frequency pass band. 16 bit A/D converter, 1024 samples-per-second-per-channel

(programmable from 64).

BrainMaster

The BrainMaster was the design we decided to replicate.

Specifications: Gain : 20,000 (86dB) Bandwidth : 1.7Hz – 34Hz CMRR : 100dB

BrainMaster schematic

Assembling Design

Ordering parts: Adrian Smith from group N1 ordered the parts for the design.

Difficulties with the OP-90

-Only available in surface mount.

-Adrian had to order adapters. All parts arrived by March 15, 2002.

Replicating Design

Board completed the day after all the parts arrived.

Testing the BrainMaster

Initial inconsistencies:

-Sometimes the amplifier worked, and sometimes it didn’t.

-The problem turned out to be bad solder joints.

-The amplifier output became consistent after re-soldering the faulty joints.

Eyebrow Test

The electrodes were placed on the forehead high above the right eyebrow.

When the eyebrows were lifted and held up, the amplitude of the signal changed dramatically.

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Frequency Content

When the eyebrows were relaxed, the FFT of the output of the amplifier revealed a peak at 20 Hz. This could possibly correspond to a beta wave.

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Noise Problems?

Noise was generated by physically moving wires.

Also, there was some noise in the frequency response when the electrodes were shorted together.

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Matlab Processing

Matlab was used to clean up the noise in the signal so that we could better analyze it for brainwaves.

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Matlab FFT Analysis

The Matlab FFT analysis did not prove the existence of brainwaves.

The 20 Hz peak present in the oscilloscope FFT capture was not present in the Matlab analysis.

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Analysis

The output from the amplifier was not different for an aware subject and a tired subject.

If we were reading brainwaves, there should have been a visible change in the frequency analysis.

Conclusions

Energy exists at expected frequencies but data is insufficient to conclude it was due to brain waves.

Device could not be used as for EEG control.