Horizontal and vertical electrodes are placed across the eyes in horizontal and vertical position respectively in order to get left- right and up-down positions of eye ball as per Fig. 1. Ground electrode is placed on forehead and is connected to the DC ground of the electronics circuit. Signals from the electrodes are amplified and processed using instrumentation amplifier. Output of the instrumentation amplifier is given to 10 bit ADC of Microcontroller refer Table 1 for signal level. Initially operator has to look in forward direction to get reference signal value because reference signal may vary from operator to operator. For the operator to move in a required direction, he/she directs his/her eye in that direction and the acquired signal is compared with the reference signal registered in microcontroller at initialization of program. Decision is taken on the basis of profile of the signal and control signals are given to motors of the wheelchair to move in the desired direction. To stop the motors, operator has to look in upward direction and to start the motors, he/she has to look in downward direction Fig. 1. Placement of electrodes Table I Voltage for different eye positions Fig. 2. Output from instrumentation amplifier Schematic nstrumentation amplifier is used because signal from electrodes are of the order of 0.4mV to 1mV.Therefore signals from two electrodes are needed to be amplified and processed. Both op amp and differential amplifier are integrated in instrumentation amplifier (AD620) and its error is less than the circuit with op amp and differential amplifier used individually Fig. 4). Signal level at the output of instrumentation amplifier is measured by 10 bit ADC (Fig. 2). Average of every 64 samples is taken in ADC of microcontroller before decision making in order to reduce ripples and attain high accuracy. Fig. 4. Error comparison between AD620 and three op Amp IA Designs Fig. 6 Forward position detected on MATLAB When the operator moves his eyes in left direction, white pixels are decreased in sector 1, increased in sector 2 and remains constant in sector 3 . By this comparison with reference image, decision is taken to take a left turn similarly when the operator looks in right direction, white pixels are decreased in sector 3, increased in sector 2 and remains constant in sector | and decision is taken to move wheelchair in right direction. Fig. 5 Division reference and real time image into sectors. to motors of wheelchair. To stop and start the wheelchair, operator has to blink for two seconds. Fig. 8 Left position detected on MATLAB Table 2 Comparison of different models in terms of accuracy This research project is aimed at guiding the wheel chair in desired direction. Which was done by incorporating both E.0.G and camera interface on wheel chair prototype and accuracy is increased from 82% in camera interface to 92%. Considering the practical aspects of the project, it is proposed that camera and E.O.G. system should be connected to a single microcontroller unit for decision making. Also, obstacle sensors like ultra sound sensor, IR proximity sensor or infrared range sensor can be installed on the wheelchair to make sure that the operator does not collide with any obstacle .So, by combining both the technologies, wheelchair can be maneuvered by eye movements with high precision keeping in mind the safety of the operator Fig. 10 Flow diagram for implementation of eye controlled wheelchair with E.O.G. and camera interface.
