Da’Janel Roberts Matthew Morgan Jonathan James 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 The AD620 is an integrated instrumentation amplifier made by Analog Devices. It is an extremely high quality device --- good price The amplifier IC-2 is used to provide an integrator, used as a low-pass filter developing the reference for IC-1. 1st stage - This results in a baseline-correction that produces a low-frequency cutoff at 1.6 Hz. It also allows the output of IC-1 to operate near its center, providing good linearity. The input amplifier IC-1 is an Analog Devices AD620 instrumentation amplifier, set up with a gain of 50 2nd stage - The second stage provides a gain of 390 and a frequency response to 34 Hz. R10 is where to select the gain you want, or to put a potentiometer for adjustable gain. To apply this circuit, you need three (3) body connections, to get one channel. Two of the electrodes are the inputs: one is "active", or Grid 1, and the is "indifferent," or Grid 2. These would be somewhere on the head, where you want to record from. They would tend to be on one side of the head, and be considered a pair. The amplifier is creating a differential reading between them, with a gain of 10,000. Any signal that is common to them, is "bucked out" by the common-mode rejection ratio, which will be near 100dB. The third lead is the "ground return," and can be on the forehead, an earlobe, or even another part of the body. You could also test the amplifier by trying to get your heartbeat (EKG) recorded from one hand to another, for example, too. However, if this lead touches "real" ground, e.g. a waterpipe, the circuit will fail to operate, since the AGND level will be "shorted" to ground.

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.

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.

Noise Problems? Noise was generated by physically moving wires. Also, there was some noise in the frequency response when the electrodes were shorted together.

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

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.

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.