EYE CONTROLLED MOUSE USING
EMBEDDED SYSTEM
S.Mohamed Yousuf
C.Guru prasath
SYED AMMAL ENGINEERING
SYED AMMAL ENGINEERING
COLLEGE.
COLLEGE.
e-mail id – yousufrahan@gmail.com
ABSTRACT:
e-mail id –gurusuf@gmail.com
Many physically
nature of the recorded signal. Our choice
disabled individuals are deterred from
of an EOG over other possible methods
using computers due to their inability to
was selected based on the ease of usage
utilize a hand-controlled mouse. However,
and the low cost of production.
if directional discrimination of an icon can
be achieved, these individuals would be
OBJECTIVE:
able to take on the functions of a mouse
without the use of hands.
build a module that consists of an EOG
We implemented a module that
consist
of
The objective of this project is to
Electrooculogram
(EOG)
biopotential amplifier in order to obtain a
physiological signal due to eye movements
amplifier to control the mouse pointer in
the system monitor. This module will be
very useful for physically challenged
people.
and to use this signal to show directional DESIGN IMPLEMENTATION
discrimination. Our design can also be
DESIGN STAGES:
used as a model for future advancements
in
human-computer
interactions.
The EOG bio potential amplifier
should be capable of detecting frequencies
The first stage of our design is the
electrodes
signal is in the microvolt range (50-3500
µV). Therefore, when the DC offset is
removed, it will be challenging to obtain a
strong, usable signal given the minute
electrooculogram
(EOG)biopotential amplifier.
between dc-10 Hz, the range at which
most ocular movements operate. The EOG
and
Stages 2 and 3 encompass the
detection
of
horizontal
and
vertical
movements of the eye, respectively. The
second and third stages (for horizontal and
vertical
discrimination)
detect
lateral
movements at the periphery of each eye. The
hardware in these stages consists of the EOG
converters are used for horizontal and vertical
bio-potential
electrode outputs. For the microcontroller
amplifier.
The
filters
are
implemented using IC LM358.Two ICs are
part 8051 is used.
used in order to produce a six pole lowpass
The last and stage 5 is interfacing the whole
filter. The cutoff frequency of the filter is
circuit with system using the PS/2 mouse port
15Hz and roll off rate is 120dB/decade.
to access the mouse pointer by programming
Stage
4 consist of Analog to
Digital converter and microcontroller to
convert the analog signal into digital signal
and to send this digital signal to the system.
Analog to digital counter is implemented
using IC0809.Separate analog to digital
BLOCKDIAGRAM:
Fig:1 Design model
the microcontroller to synchronize with PS/2
port.
Design model:
eye rotates in its orbit. This potential can
be
1. Right upper electrode.
registered
in
electoretinogram
or
electrooculogram.
2. Left upper electrode.
The
3. Right lower electrode.
continuous
corneal-retinal
potential can be used to measure eye’s
position, this can be done by placing
4. Left lower electrode.
superficial electrodes in both sides of the
5. Right electrode.
eye (left and right) or in the top and
bottom and a third electrode on the
6. Left electrode.
forehead as a reference. This type of
MEASUREMENT
AND
ANALYSIS
OF ELECTROOCULOGRAPHY:
registration is called electrooculogram.
When the sight is centered, the dipole is
The eye is a seat of a steady
electric potential field that is quite
unrelated to light stimulation. In fact, this
symmetrically localized between the two
electrodes, so the output of the EOG is
zero.
field may be detected with the eye in total
When the person looks to the right
darkness and/or with the eyes closed.
the positive cornea gets closer to the left
Between the cornea and retina exists a
electrode that becomes more positive.
differential potential. This potential is
There is an almost linear relation between
because there are established ionic currents
the horizontal angle and the output of the
between
the
EOG, by approximately +30 degree or -30
photoreceptors and its base (darkness
degree from the visual arc. When the
currents).These currents relatively change
electrodes are located on the top and
when the photoreceptors are excited. This
bottom, the movements register vertically.
potential can be considered as an electric
The magnitude of this cornea-retinal
dipole which rotation center is in the
potential is in the range 0.05-3.5 mV.
external
segment
of
center of the eye and it rotates when the
Fig2:Section of Eye
It is not generated by excitable
electrodes were chosen because the half-
tissue but, rather, is attributed to the higher
cell potential was the closest to zero.
metabolic rate in the retina. The polarity of
Electrodes with the smallest amount of
this potential difference in the eyes of
half-cell potential are desirable because
invertebrates is opposite to that of
they cause the least amount of offset. By
vertebrates. This potential difference and
definition, the hydrogen electrode has a
the rotation of the eye are the basis for a
zero half-cell potential, but due to the
signal measured at a pair of surface
gaseous nature, they cannot be feasibly
electrodes. The signal is known as the
used. Although lead electrodes have a
electro-oculogram, (EOG).
lower half-cell potential than the Ag/AgCl
electrodes, lead is hazardous to the health
Ag-AgCl ELECTRODE:
and thus it is avoided. Thus our choice of
The electrodes were chosen with
the concern of protecting the eyes from
hazardous
elements.
ECG
disposable
electrodes were used because of their easy
availability.
Silver/Silver-Chloride
electrodes takes into account a low cost
and proper signal pick-up.
To record the ECG, EEG, EMG, EOG, etc.
electrodes must be used as a transducers to
convert an ionic flow of current in the
setting the electrode back slightly from the
body to an electronic flow along a wire.
surface of the skin on a quantity of
Two
coupling jelly (electrolyte paste).
important
characteristics
of
electrodes are electrode potential and
contact impedance. Good electrodes will
have low stable figures for both of the
MEASURMENT
OF
ELECTROOCULOGRAPHY
above characteristics. Electrode potential
The acquisition system employs
arises because a metal electrode in contact
Ag – AgCl surface electrodes for signal
with an electrolyte (body fluids) forms a
pickup which requires application of
half cell with a potential dependent upon
sufficient electrolyte gel to reduce the skin
the metal in use and the ions in the
impedance. As we said earlier human eye
electrolyte.
can be described as a dipole with positive
All
electrodes
suffer
from
variations in contact resistance due to
movement, and the drying out of any
pole at cornea and negative pole with
retina. Two surface electrodes are placed
surrounding
coupling medium. This is improved by
Fig3: Formation of dipole moment due to eye ball movement
the
eye.
When the eye turns to right side,
electrode. Likewise when the eye turns to
right surface electrode becomes positive
left side, left surface electrode becomes
when compared with the other surface
positive than the other surface electrode.
Fig4: Typical EOG waveform
DESIGN
OF
ELECTRO-
owing
to
Rejection
OCULOGRAM AMPLIFIER
its
high
Ratio
Common
(CMRR).
Mode
Two
instrumentation amplifiers are employed
The first stage of any EOG
biopotential
amplifier
is
the
instrumentation amplifier which provides
the initial amplification while reducing the
effect of signals such as Power-line
interference and skin muscle artifacts
for this purpose, one for each of the two
channels. Since the EOG signal content
varies between DC and 10 Hz, a low pass
filter is used after the signal pickup stage,
with cutoff frequencies of 15 Hz as shown
in fig. 5.
Fig 5: EOG measurements
INSTRUMENTATION AMPLIFIER
required gain. Actually, this stage can be
implemented using IC 741.But, three ICs.
Here
instrumentation
we
use
amplifier.
AD620
The
main
objective of this stage is to eliminate the
So, we designed this filter part using IC
LM358. It has two comparators inside the
IC
dc drift between cornea and retina in our
eyes. It is a low power amplifier. If we use
ANALOG
IC741 we need three op amps, so we finish
CONVERTER:
TO
DIGITAL
it with this single op amp. It is also an 8pin
IC, but it consumes very low power.
The next stage is to convert the
Minimum CMRR value is 100dB, so it has
analog signals to digital signals. ADC
the greater tendency to eliminate the
0809 is used to do this operation. Since
common mode signal, so it provides
two analog signals are to be converted to
difference signal which we need exactly.
digital signals ADC 0809 is used which
has 2 channels. The ADC0809 data
The input current is 3mA.The
acquisition component is a monolithic
output of this amplifier is the difference
CMOS device with an 8-bit analog-to-
between
voltage
digital converter, 8-channel multiplexer
outputs. So this voltage contains the
and microprocessor compatible control
information of the eye movement.
logic. The 8-bit A/D converter uses
the
two
electrodes
LOW PASS FILTER
successive
approximation
the
conversion
technique.
Usually noise frequency is in the range of
features
high
KHz or MHz, but our signal is in the range
stabilized comparator, a 256R voltage
0-15Hz. But, the output voltage is very
divider with analog switch tree and a
low. So if noise interrupts, then the
successive approximation register. The 8-
information may lose. To avoid this, we
channel multiplexer can directly access
designed a low pass filter for 16Hz.It is a
any of 8-single-ended analog signals. The
six pole filter (Three second order filters
device eliminates the need for external
are cascaded). It provides 120dB/decade.
zero and full-scale adjustments.
a
The
as
impedance
converter
chopper
So the noise will be completely eliminated
at the end of this stage. Here feedback
resistors are adjusted to provide the
Easy
interfacing
to
microprocessors is provided by the latched
and decoded multiplexer address inputs
with an overload-protected 5V power
and latched TTL TRI-STATE outputs.
supply.
The design of the ADC0809 has
The standard PS/2 mouse interface
been optimized by incorporating the most
supports
desirable
(right/left)
aspects
of
several
A/D
the
following
movement,
inputs:
Y
X
(up/down)
conversion techniques. The ADC0809
movement, left button, middle button, and
offers high speed, high accuracy, minimal
right button. The mouse reads these inputs
temperature dependence, excellent long-
at a regular frequency and updates various
term accuracy and repeatability, and
counters and flags to reflect movement and
consumes minimal power. These features
button states.
make
this
device
ideally
suited
to
The standard mouse has two
applications from process and machine
control to consumer and automotive
counters that keep track of movement: the
X-movement counter and the Y-movement
applications.
counter. These are 9-bit 2's complement
PS/2 INTERFACE AND PROTOCOL
values
and
each
has
an
associated
overflow flag. Their contents, along with
The
PS/2
mouse
interface
originally appeared in IBM's "Personal
System/2" computers in the late 80's. It
still remains a widely-supported interface
for the sake of constantly maintaining
backward compatibility.
The PS/2 mouse interface uses a
bidirectional serial protocol to transmit
movement and button-position data to the
computer's auxiliary device controller
(keyboard controller). The computer, in
turn, may send a number of commands to
the mouse to set the report rate, resolution,
reset the mouse, disable the mouse, etc.
The computer also provides the mouse
the state of the three mouse buttons, are
sent to the host in the form of a 3-byte
movement data packet (as described in the
next section.) The movement counters
represent the amount of movement that has
occurred since the last movement data
packet was sent to the host (i.e., they do
not represent absolute positions.)
When the mouse reads its inputs, it
records the current state of its buttons and
checks for movement. If movement has
occurred it increments (for +X or +Y
movement) or decrements (for -X or -Y
movement) its X and/or Y movement
counters. If either of the counters has
overflowed,
it
sets
the
appropriate
overflow flag. PS2 ports use synchronous
these are large margins both this works
serial signals to communicate between the
good since this is a synchronous port (this
keyboard or mouse to the computer
also helps cut on the cost of high precision
clocks). The data line transition is made on
Data transmission from the mouse
to the computer is done with, each clock
period is usually between 70 to 150
microseconds (10 to 25 microseconds for
transitions and 30 to 50 microseconds for
the falling edge of the clock signal and is
usually sampled when the clock is low.
Each data packet is composed of 11 bits, 1
start bit (which is low), 8 data bits, 1 odd
parity bit and 1 stop bit (high).
high or low state), some may feel that
MOVEMENT DATA PACKET:
The standard PS/2 mouse sends movement/button information to the host using the
following 3-byte packet
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Byte1 Y overflow X overflow Y sign bit X sign bit Always 1 Middle Btn Right Btn Left Btn
Byte 2 X Movement
Byte3 Y Movement
MOUSE
RESOLUTION
AND
TRACKING RATE
tracking rate of 102 inches per second and
for 400 CPI mouse only 25.2 inches per
second.Bi-directional
transmission
is
The standard PS/2 mouse (with
controlled by the CLK and DATA lines.
Logitech mouse) defaults to 160 CPI and
Both are fed by an open collector device
can be switched to 40, 80, 160 or 320 CPI
which let either host or mouse force the
with software. Microsoft mouse driver for
line to "0". During non-transmission, CLK
Windows 3.x and Windows 95 defaults to
is at "1" and DATA can be at "0" or "1".
160 counts per inch. The maximum
tracking rate for PS/2 mouse is 40
report/second * 255 counts per report =
10200 counts per second. For 100 CPI
mouse this would indicate maximum
The
host
can
inhibit
mouse
transmission by forcing CLK to "0". If the
host inhibits the mouse while it is
transmitting,
the
byte
must
be
retransmitted (if the inhibit state arrived
Sending data: Check that both
before the 11th clock).There is a simple
clock and data are high. Pull down data for
description in old IBM PS/2 model 50/60
start bit, and start clocking.
technical reference. The mouse interface is
the same as the keyboard interface. The
Intel 8042 supports two channels, one for
APPLICATION OF EOG SIGNAL:
Computer mouse control.
keyboard and one for the auxiliary device
(mouse, trackball, touchpad). Pin 1 is the
Robotics.
data, pin3 ground, pin 4 +5V and pin 5
Guidance of a wheelchair.
clocks.
Receiving data: Check "clock". If
inactive, there is a bit on the "data" line.
Each transmission unit is one start bit,
eight data bits, odd parity and one stop bit.
Start bits are low, stop bits high. Each
clock active or inactive period is 30 to 50
microseconds. Data transition to falling
edge of clock is 5 to 25 microseconds.
CONCLUSION:
The paper includes various applications
Computer
mouse
control,
Robotics,
Guidance of a wheelchair. The paper will
be very much useful to the handicapped
people to operate their pc using their eyes
alone.