Wireless Eye Movement Controlled Human Machine
Interface
.
OBJECTIVE
To design a Human Machine interface, which can be controlled using EOG
Signals and final output is to be used to move cursor on the Graphic Display which has
several buttons and each button on clicking by blinking of eyes activated corresponding
appliance or action.
INTRODUCTION AND BACKGROUND
Bio-based human computer interface (HCI) has the potential to enable severely
disabled people to drive computers directly by bioelectricity rather than by physical
means. A study on the group of persons with severe disabilities shows that many of them
have the ability to control their eye movements, which could be used to develop new
human computer interface systems to help them communicate with other persons or
control some special instruments. Furthermore, this application of EOG-based HCI could
be extended to the group of normal persons for game or other entertainments. Nowadays,
some methods which attain user’s eye movements are developed.
Electro-oculography (EOG) is a new technology of placing electrodes on user’s
forehead around the eyes to record eye movements. EOG is a very small electrical
potential that can be detected using electrodes. Compared with the EEG, EOG signals
have the characteristics as follows: the amplitude is relatively high (15-200uV), the
relationship between EOG and eye movements is linear, and the waveform is easy to
detect. Considering the characteristics of EOG mentioned above, EOG based HCI is
becoming the hotspot of bio-based HCI research in recent years.
The electrooculogram (EOG) is the electrical signal produced by the potential
difference between the retina and the cornea of the eye[1]. This difference is due to the
large presence of electrically active nerves in the retina compared to the front of the eye.
Many experiments show that the corneal part is a positive pole and the retina part is a
negative pole in the eyeball. Eye movement will respectively generates voltage up to
16uV and 14uV per 1° in horizontal and vertical way. The typical EOG waveforms
generated by eye movements are shown in Figure 1.
In Figure 1, positive or negative pulses will be generated when the eyes rolling
upward or downward. The amplitude of pulse will be increased with the increment of
rolling angle, and the width of the positive (negative) pulse is proportional to the duration
of the eyeball rolling process.
METHODOLOGY
In our HCI system, three to five electrodes are employed to attain the EOG
signals. Figure 2 shows the electrode placement.
1 & 4 for detecting vertical movement
2 & 3 for detecting horizontal movement
5 is for reference.
Or only 1&2 with reference electrode can also be
used.
Blink detection is by separate algorithm based on
EOG signals
Figure 2: electrode placements
Outputs of electrodes are amplified and filtered this is our front end electronics
after that using A/D convertor signal is digitized and this completes our Acquisition of
Signal part. Now we combine all acquire signals from all electrodes and send them via
RF interface for future Pre and post processing of signals and finally Eye movements and
Eye blink events are extracted and sent as commands to drive cursor on screen which is
part of application part, buttons one the cursors are clicked using eye moments and eye
blink and designated action is completed but application circuit.
BLOCK DIAGRAM / PROCESS
Acquisition Part
Electrodes
near Eye to
sense signal
from eyes
EOG signals
Instrumentation
Amplifier
And active
filter
A/D
Convertor
Embedded
Controller
For data
acquisition and
transmission
wirelessly
RF Interface RF/
Zigbee Module
Application Part
Devices to be
controlled by
eye
movements
Display
Screen and
Device
control
interace
Eye
Movements
output
Embedded
Microcontroller
or PC to
process EOG
signal
Preprocessing
and processing
for Eye
Movement and
Eye Blink
detections
Processing Part
DESCRIPTION
Acquisition Part
For five different electrodes five separate acquisition electronics is there
Electrodes:
First thing to interface to body is Electrodes here we are using reusable electrodes to
connect electronics with human body and these electrodes will pickup signals which
corresponds to eye movements signals mixed with some others signals which are noise
for us.
We are going to use Ag-AgCl electrodes as they are low cost and easily available.
Instrumentation Amplifier:
Signals from electrodes are received and sent to Instrumentation Amplifier.
An instrumentation amplifier is a type of differential amplifier that has been outfitted
with input buffers, which eliminate the need for input impedance matching and thus make
the amplifier particularly suitable for use in measurement and test equipment. Additional
characteristics include very low DC offset, low drift, low noise, very high open-loop
gain, very high common-mode rejection ratio, and very high input impedances.
Instrumentation amplifiers are used where great accuracy and stability of the circuit both
short- and long-term are required.
We are using AD620 which is precision Instrumentation amplifier.
Active Filters:
Opamp based Active filters are used we have low pass filter so that only eye signals are
going future in the circuit, cutoff frequency for this filter is 20Hz.
All above are required separately for each electrode i.e we need four such chains.
Analog to Digital Convertor:
Final amplified and filtered analog output is converted into Digital signal using
ADC0808 8bit-8Channel A/D convertor, or we can also try I2C Based 4 channel A2D
convertor to save space as ADC0808 is little bigger in size.
Acquisition microcontroller:
This is 8051 microcontroller and it has to acquire signals from A/D convertor for all
electrodes, make them data packets and transmit it via RF interface with proper protocol.
We intend to use low pin count device to save space as complete acquisition part is body
mounted. For example AT89c4051 and AT89c2051 are only 20 pin devices.
RF Trasmitter:
Here we can use 433Mhz modules or Zigbee interface to transfer our digitized eye signals
from each electrodes for future processing to main processing circuit.
Processing Part
RF Receiver:
Wireless signals transmitted by our acquisition part are received in this section and these
data packets contain digitized signals of all electrodes in each frame. Now these are
future processed to extract eye movements.
Signal Processing:
In this part we process the signals received from acquisition part using P89V51RD2,
ATMEGA128, equivalent or high end processor, here amplitude, durations, frequencies
etc various attributes are processed and eye movements are extracted from the signals,
this block gives UART ASCII output as follows:
R – Right eye movement
L – Left eye movement
U – Up eye movement
D – Down eye movement
B – Blinking of eye
Application Part
Display and appliance controller:
This is a again a microcontroller which receives eye movements signals (R L U D B) as
described above via UART interface. We are using P89V51RD2 from NXP (Philips), this
microcontroller is connected to Graphic LCD which is displaying Cursor and 4 buttons
1. TV
2. FAN
3. Lights
4. Alarm
Using eye movements a cursor is controlled and using blink click operation is done each
button is toggle button i.e. if appliance is on it will become off and vice versa. But alarm
button is different when clicked a 30sec alarmed is generated to call assistance.
Now this controller is also connected to relay board so button action is converted into
relays getting switch off and on. And hence appliances are getting turned on and off.
Many other applications are also possible like Computer Mouse interface, virtual
keyboard interface so disable can talk via this keyboard and send mails.
REQUIREMENTS AND SPECIFICATION
Hardware Requirements:
Hardware components:
XBEE 2.4GHZ -Series 2 - Transceiver - 100mtr
Mesh network
RF Transmitter and receiver - 433 MHz / 100mts range
ENCODER & DECODER BRDS - WITH HT 640 648
4 CH RELAY BOARD - Transistor Based
GRAPHIC DISPLAY - 128X64
HT 640 - 8 BIT ENCODER
HT 648 - 8 BIT DECODER
ADC 00809 - 8 BIT 8 CH
LM324 – OPAMP / INA (Instrumentation amplifier) AD620
555 – timer
If required ADC0820 or I2C based ADC
Power Supply
Buzzer and Cables
Body Mounted Embedded System
Embedded controller to control display and appliances
Embedded system for Processing of EOG signals (OR to be done in Matlab/C with PC
interface one for input EOG signal and one for ouput eye movement ouput )
Finally Electrodes and Medical Accessories
PC Requirements:
Pentium 4 PC or higher
OS: Win XP or higher.
Minimum 1GB RAM.
Software: KEIL/ SDCC/ Matlab
Specifications of HMI System:
Detection of Eye movements and eye blink at minimum 5sec with 1Sigma accuracy.
EXPECTED OUTPUT AND CONCLUSION
Intermediate Output of the system is Eye movements and Eye Blinking Commands in
UART interface commands are in ASCII code
U - Eye up movement detected
D - Eye down movement detected
L - Eye Left movement detected
R - Eye Right movement detected
B - Eye Blink detected
Above o/p is sent to application part which interprets and move cursors accordingly and
button are clicked using same o/p and corresponding relay is toggled hence appliance is
controlled.
REFERENCES

http://en.wikipedia.org/wiki/Eye_tracking

IEEE Paper: EOG signal detection for home appliances activation

Human-Computer Systems Interaction: Backgrounds and Applications By
Zdzislaw S. Hippe, Juliusz L. Kulikowski

Hand book Of Biomedical Instrumentation By Khandpur.

Fun n' Games By Panos Markopoulos, Boris de Ruyter, Wijnand Ijsselsteijn.

Intelligent wearable interfaces By Yangsheng Xu, Wen J. Li, Ka Keung Caramon
Lee