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Eye controlled HMI
CHAPTER 1
INTRODUCTION TO EYE-HMI
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.
In this project our objective is 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. We will provide RF interface between
acquisition/processing part and application so that it’s easy to handle and easy to install in
homes and hospitals.
ECE, SBMSIT 1
Eye controlled HMI
ELECTRO-OCULOGRAPHY (EOG) PRINCIPLE
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.
Basically EOG is a bio-electrical skin potential measured around the eyes but first we have to understand eye itself:
Anatomy of the Eye
The main features visible at the front of the eye are shown in Figure .The lens,
directly behind the pupil, focuses light coming in through the opening in the centre of the
eye, the pupil, onto the light sensitive tissue at the back of the eye, the retina. The iris is
the coloured part of the eye and it controls the amount of light that can enter the eye by
changing the size of the pupil, contracting the pupil in bright light and expanding the
ECE, SBMSIT 2
Eye controlled HMI
pupil in darker conditions. The pupil has very different reflectance properties than the
surrounding iris and usually appears black in normal lighting conditions. Light rays
entering through the pupil first pass through the cornea, the clear tissue covering the front
of the eye. The cornea and vitreous fluid in the eye bend and refract this light. The
conjuctiva is a membrane that lines the eyelids and covers the sclera, the white part of the
eye. The boundary between the iris and the sclera is known as the limbus, and is often
used in eye tracking.
The light rays falling on the retina cause chemical changes in the photosensitive
cells of the retina. These cells convert the light rays to electrical impulses which are
transmitted to the brain via the optic nerve. There are two types of photosensitive cells in
the retina, cones and rods. The rods are extremely sensitive to light allowing the eye to
respond to light in dimly lit environments. They do not distinguish between colours,
however, and have low visual acuity, or attention to detail. The cones are much less
responsive to light but have a much higher visual acuity. Different cones respond to
different wavelengths of light, enabling colour vision. The fovea is an area of the retina of
particular importance. It is a dip in the retina directly opposite the lens and is densely
packed with cone cells, allowing humans to see fine detail, such as small print. The
human eye is capable of moving in a number of different manners to observe, read or
examine the world in front of them.
The Electrooculogram
The electrooculogram (EOG) is the electrical signal produced by the potential
difference between the retina and the cornea of the eye. 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
ECE, SBMSIT 3
Eye controlled HMI
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, four to five electrodes are employed to attain the EOG signals.
Figure 2 shows the electrode placement.
ECE, SBMSIT 4
Eye controlled HMI
1 & 4 for detecting vertical movement
2 & 3 for detecting horizontal movement
5 is for reference(can be omitted or place at
forehead).
Blink detection is by separate algorithm based on
EOG signals
Figure 2: electrode placements
Advantages of the EOG over other methods
The visual systems mentioned in our projet offer robust methods of eye tracking,
usually with very good accuracy. While in certain circumstances, visual methods may be
more appropriate, the electrooculogram offers a number of advantages. Some of the
reasons for favouring the EOG over other options
• Range
The EOG typically has a larger range than visual methods which are constrained
for large vertical rotations where the cornea and iris tend to disappear behind the eyelid.
Angular deviations of up to 80◦ can be recorded along both the horizontal and vertical
planes of rotation using electrooculography.
• Linearity
The reflective properties of ocular structures used to calculate eye position in
visual methods are linear only for a restricted range, compared to the EOG where the
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Eye controlled HMI
voltage difference is essentially linearly related to the angle of gaze for ±30◦ and to the
sine of the angle for ±30◦ to ±60◦
• Head Movements are Permissible
The EOG has the advantage that the signal recorded is the actual eyeball position
with respect to the head. Thus for systems designed to measure relative eyeball position
to control switches (e.g. looking up, down, left and right could translate to four separate
switch presses) head movements will not hinder accurate recording.
• Non-invasive
Unlike techniques such as the magnetic search coil technique, EOG recordings do
not require anything to be fixed to the eye which might cause discomfort or interfere with
normal vision. EOG recording only requires three electrodes (for one channel recording),
or five electrodes (for two channel recording), which are affixed externally to the skin.
• Obstacles in front of the eye
In visual methods, measurements may be interfered with by scratches on the
cornea or by contact lenses. Bifocal glasses and hard contact lenses seem to cause
particular problems for these systems. EOG measurements are not affected by these
obstacles.
• Cost
EOG based recordings are typically cheaper than visual methods, as they can be
made with some relatively inexpensive electrodes, some form of data acquisition card and
appropriate software.
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Eye controlled HMI
• Lighting Conditions
Variable lighting conditions may make some of the visual systems unsuitable or at
least require re-calibration when the user moves between different environments. One
such scenario which could pose problems is where the eye tracking system is attached to
a user.
• Eye Closure is Permissible
The EOG is commonly used to record eye movement patterns when the eye is
closed, for example during sleep. Visual methods require the eye to remain open to know
where the eye is positioned relative to the head, whereas an attenuated version of the
EOG signal is still present when the eye is closed.
• Real-Time
The EOG can be used in real-time as the EOG signal responds instantaneously to
a change in eye position and the eye position can be quickly inferred from the change.
The EOG is linear up to 30◦.
Limitations of EOG-Based Eye tracking
The measured EOG voltage varies for two reasons. Either the eye moves (which
we want to record), or baseline drift occurs (which we want to ignore). Baseline drift
occurs due to the following factors:
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Eye controlled HMI
• Lighting Conditions
The DC level of the EOG signal varies with lighting conditions over long periods
of time. When the source of the light entering the eye changes from dark conditions to
room lighting, as per studies it can take anywhere from between 29-52 minutes for the
measured potential to stabilise to within 10% of the baseline, and anywhere between 17-
51 minutes when the transition is from room lighting to darkness.
• Electrode Contact
The baseline may vary due to the spontaneous movement of ions between the skin
and the electrode used to pick up the EOG voltage. The mostly commonly used electrode
type is silver-silver chloride (Ag-AgCl). Large DC potentials of up to 50mV can develop
across a pair of Ag-AgCl electrodes in the absence of any bioelectric event, due to
differences in the properties of the two electrode surfaces with respect to the electrolytic
conduction gel. The extent of the ion movement is related to a number of variables
including the state of the electrode gel used, variables in the subject’s skin and the
strength of the contact between the skin and the electrode. Proper preparation of the skin
is necessary to maximize conduction between the skin and the conduction gel, usually by
brushing the skin with alcohol to remove facial oils.
• Artifacts due to EMG or Changes in Skin Potential
The baseline signal may change due to interference from other bioelectrical
signals in the body, such as the electromyogram (EMG) or the skin potential. EMG
activity arises from movement of the muscles close to the eyes, for example if the subject
frowns or speaks. These signals may be effectively rejected by careful positioning of the
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Eye controlled HMI
electrodes and through low pass filtering the signal. Skin potential changes due to
sweating oremotional anxiety pose a more serious problem.
• Age and Sex
sex have a significant effect on baseline voltage levels, although this should not
pose a problem if a system is calibrated initially for each particular user.
• Diurnal Variations
The baseline potential possibly varies throughout the day. Manual calibration is
often used to compensate for DC drift - the subject shifts his gaze between points of
known visual angle and the amplifier is balanced until one achieves the desired
relationship between voltage output and degree of eye rotation. With frequent re-
calibration, accuracies of up to ±30′ can be obtained. While manual calibration may be
acceptable practice in clinical tests that use the EOG, this restriction hinders the EOG
from being used independently as a control and communication tool by people with
disabilities.
ECE, SBMSIT 9
Eye controlled HMI
BLOCK DIAGRAM AND DESCRIPTION
Block Diagram of Eye controller Human Machine interface:
ECE, SBMSIT 10
Eye Movements
output
RF Interface RF RX Module
Application Part
Display Screen and
Device controller
Devices to be controlled by
eye movements
Graphics LCD
(MENU)
RF Interface RF TX Module
Acquisition and Processing Part
Electrodes near Eye to sense signal from eyes
EOG signals
Instrumentation AmplifierAnd active
filter
A/D Convertor
Embedded ControllerFor data
acquisition using I2C ADC
Processing for Eye Movement and Eye Blink
detections
Eye controlled HMI
DESCRIPTION
Acquisition Part
For four-five different electrodes two separate acquisition electronics is required
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.
ECE, SBMSIT 11
Eye controlled HMI
Active Filters and Gain Blocks:
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-40Hz. And
high pass filter to block DC and frequencies upto 0.1-0.3Hz. These filters and gain blocks
are implemented using LM324 Opamp.
Analog to Digital Convertor:
Final amplified and filtered analog output is converted into Digital signal using
I2C Based 4 channel A2D convertor-PCF8591 to save space as ADC0808 is little bigger
in size.
Acquisition and processing microcontroller:
This is 8051 class of microcontroller and it has to acquire signals from A/D
convertor for both chains up-down electrode chain and left-right electrode chain. As our
microcontroller is fast and powerful we will process the signal here itself and transmit
final eye move outputs to application part wirelessly.
Cmds sent:
01– CL: Right eye movement
02– CR: Left eye movement
03– CU: Up eye movement
04– CD: Down eye movement
05– BL: Blinking of eye
RF Transmitter:
Here we can use 315/433Mhz Tx modules along with HT640 Encoder to send eye
movement commands to the application part.
ECE, SBMSIT 12
Eye controlled HMI
Application Part
RF Receiver:
Wireless signals transmitted by our acquisition part are received in this section,
here we use 315/433Mhz Rx modules along with HT648 decoder. Output of RF receiver
goes to application part directly.
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 On-off alarm is generated to call assistance.
And assistant has to come and reset the alarm.
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.
ECE, SBMSIT 13
Eye controlled HMI
Many other applications are also possible like Computer Mouse interface, virtual
keyboard interface so disable can talk via this keyboard and send mails.
ECE, SBMSIT 14
Eye controlled HMI
BIO-POTENTIALS & ELECTRODES
Biopotentials
An electric potential that is measured between points in living cells, tissues, and
organisms, and which accompanies all biochemical processes. Also describes the transfer
of information between and within cells
ECE, SBMSIT 15
Eye controlled HMI
Mechanism behind Bio Potentials
• Concentration of potassium (K+) ions is 30-50 times higher inside as compared to
outside
• Sodium ion (Na+) concentration is 10 times higher outside the membrane than
inside
• In resting state the member is permeable only for potassium ions
Potassium flows outwards leaving an equal number of negative ions inside
Electrostatic attraction pulls potassium and chloride ions close to the
membrane
Electric field directed inward forms
Electrostatic force vs. diffusional force
Different Types of potentials are discussed here
The Membrane Potential
A potential difference usually exists between the inside and outside of any cell
membrane, including the neuron. The membrane potential of a cell usually refers to the
potential of the inside of the cell relative to the outside of the cell i.e. the extracellular
fluid surrounding the cell is taken to be at zero potential. When no external triggers are
acting on a cell, the cell is described as being in its resting state. A human nerve or
skeletal muscle cell has a resting potential of between -55mV and -100mV . This
potential difference arises from a difference in concentration of the ions K+ and Na+
inside and outside the cell. The selectively permeable cell membrane allows K+ ions to
pass through but blocks Na+ ions. A mechanism known as the ATPase pump pumps only
two K+ ions into the cell for every three Na+ cells pumped out of the cell resulting in the
outside of the cell being more positive than the inside. The origin of the resting potential
is explained in further detail in.
The Action Potential
ECE, SBMSIT 16
Eye controlled HMI
As mentioned already, the function of the nerve cell is to transmit information
throughout the body. A neuron is an excitable cell which may be activated by a stimulus.
The neuron’s dendrites are its stimulus receptors. If the stimulus is sufficient to cause the
cell membrane to be depolarised beyond the gate threshold potential, then an electrical
discharge of the cell will be triggered. This produces an electrical pulse called the action
potential or nerve impulse. The action potential is a sequence of depolarisation and
repolarisation of the cell membrane generated by a Na+ current into the cell followed by a
K+ current out of the cell. The stages of an action potential are shown in Figure
Figure 3.4: An Action Potential. This graph shows the change in membrane potential
as a function of time when an action potential is elicited by a stimulus.
• Stage 1 – Activation
When the dendrites receive an “activation stimulus” the Na+ channels begin to
open and the Na+ concentration inside the cell increases, making the inside of the cell
more positive. Once the membrane potential is raised past a threshold (typically around -
50mV), an action potential occurs.
• Stage 2 – Depolarisation
ECE, SBMSIT 17
Eye controlled HMI
As more Na+ channels open, more Na+ ions enter the cell and the inside of the
cell membrane rapidly loses its negative charge. This stage is also known as the rising
phase of the action potential. It typically lasts 0.2 - 0.5ms.
• Stage 3 – Overshoot
The inside of the cell eventually becomes positve relative to the outside of the
cell. The positive portion of the action potential is known as the overshoot.
• Stage 4 – Repolarisation
The Na+ channels close and the K+ channels open. The cell membrane begins to
repolarise towards the resting potential.
• Stage 5 – Hyperpolarisation
The membrane potential may temporarily become even more negative than the
resting potential. This is to prevent the neuron from responding to another stimulus during
this time, or at least to raise the threshold for any new stimulus.
• Stage 6
The membrane returns to its resting potential.
Propagation of the Action Potential
An action potential in a cell membrane is triggered by an initial stimulus to the
neuron. That action potential provides the stimulus for a neighbouring segment of cell
membrane and so on until the neuron’s axon is reached. The action potential then
propagates down the axon, or nerve fibre, by successive stimulation of sections of the
axon membrane. Because an action potential is an all-or-nothing reaction, once the gate
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Eye controlled HMI
threshold is reached, the amplitude of the action potential will be constant along the path
of propagation. The speed, or conduction velocity, at which the action potential travels
down the nerve fibre depends on a number of factors, including the initial resting
potential of the cell, the nerve fibre diameter and also whether or not the nerve fibre is
myelinated. Myelinated nerve fibres have a faster conduction velocity as the action
potential jumps between the nodes of Ranvier.
Synaptic Transmission
The action potential propagates along the axon until it reaches the axonal ending.
From there, the action potential is transmitted to another cell, which may be another nerve
cell, a glandular cell or a muscle cell. The junction of the axonal ending with another cell
is called a synapse. The action potential is usually transmitted to the next cell through a
chemical process at the synapse.
Resting potential:
Nerve and muscle cells are encased in a semi-permeable membrane that permits
selected substances to pass through while others are kept out. Body fluids surrounding
cells are conductive solutions containing charged atoms known as ions. In their resting
state, membranes of excitable cells readily permit the entry of K+ and Cl- ions, but
effectively block the entry of Nu+ ions (the permeability for K+ is 50-100 times that for
Na+). Various ions seek to establish a balance between the inside and the outside of a cell
according to charge and concentration. The inability of Nu+ to penetrate a cell membrane
results in the polarization that is called as Resting Potential.
ECE, SBMSIT 19
Eye controlled HMI
EOG ELECTRODES
Because of the very low amplitude of the EOG, the electrodes represent the
weakest link in the entire recording system. The following properties are desirable in an
EOG electrode:
(a) Stable electrode potential: Spontaneous fluctuations of only 2 or 3mV in the potential
difference between an electrode and the surrounding electrolyte will produce artifacts
very much larger than the EOG.
(b) Equal electrode potentials: A small standing potential difference between a pair of
electrodes will not present major difficulties, apart from producing a temporary deflection
of the trace and possibly blocking of the amplifiers when the electrodes are first
connected to the recorder. However, if the current flow between the electrode varies
owing to changing contact resistances, artifact may result, As it is in practice never
possible to ensure that conventional electrodes are of equal potential, it follows that a
third desirable characteristic is constant electrode contact resistances
(c) Equal electrode resistances: EOG recording is bedeviled by electrical interference -
particularly from ac mains; there are generally unwanted changes in potential difference
between the subject and the ECG machine that are seen as common mode signals and can
he rejected by the use of differential amplifiers. Unequal electrode resistances, however,
unbalance the system and produce an out-of-phase component that will appear in the
tracing.
(d) Low electrode resistance: With modern amplifier design, it is now easy to ensure that
the electrode resistances are very much less than the input impedance so that as much as
possible of the ECG signal is applied at the input of the amplifier. The effects of unequal
electrode resistances are less marked when the actual values are low. In general when the
other criteria above are satisfied, the electrode resistance is to be less than 5k and
measurement of resistance provides a good check on the quality of electrode preparation
and application.
ECE, SBMSIT 20
Eye controlled HMI
The desirable characteristics above can generally be satisfied by the use of
nonpolarisable electrodes, so far as identical physical and chemical structure, securely
attached to skin that has first been cleaned and abraded to remove the outer layer which is
of high resistance.
TYPES OF ELECTRODES
Ag-AgCl electrodes and disposable electrodes were used when the data was
recorded from the frontal region. These electrode types that are used were shown in fig.
Figure: Different types of electrodes
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Eye controlled HMI
BIO-POTENTIAL AMPLIFIERS
Bio signals are recorded as potentials, voltages, and electrical field strengths
generated by nerves and muscles. The measurements involve voltages at very low levels,
typically ranging between 1 μV and 100 mV, with high source impedances and
superimposed high level interference signals and noise. The signals need to be amplified
to make them compatible with devices such as displays, recorders, or A/D converters for
computerized equipment. Amplifiers adequate to measure these signals have to satisfy
very specific requirements. They have to provide amplification selective to the
physiological signal, reject superimposed noise and interference signals, and guarantee
protection from damages through voltage and current surges for both patient and
electronic equipment. Amplifiers featuring these specifications are known as biopotential
amplifiers
. Basic requirements and features, as well as some specialized systems,
The basic requirements that a biopotential amplifier has to satisfy are:
the physiological process to be monitored should not be influenced in any way by
the amplifier
the measured signal should not be distorted
the amplifier should provide the best possible separation of signal and
interferences
the amplifier has to offer protection of the patient from any hazard of electrical
shock
the amplifier itself has to be protected against damages that might result from
high input voltages as they occur during the application of defibrillators or
electrosurgical instrumentation
A typical configuration for the measurement of bio potentials is shown in figure.
Three electrodes, two of them are picking up the biological signal and the third providing
the reference potential, connect the subject to the amplifier. The input signal to the
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amplifier consists of five components: (1) the desired biopotential, (2) undesired
biopotentials, (3) a power line interference signal of 50 Hz and its harmonics, (4)
interference signals generated by the tissue/electrode interface, and (5) noise. Proper
design of the amplifier provides rejection of a large portion of the signal interferences.
The main task of the differential amplifier as shown in Figure is to reject the line
frequency interference that is electrostatically or magnetically coupled into the subject.
The desired biopotential appears as a voltage between the two input terminals of the
differential amplifier and is referred to as the differential signal. . The line frequency
interference signal shows only very small differences in amplitude and phase between the
two measuring electrodes, causing approximately the same potential at both inputs, and
thus appears only between the inputs and ground and is called the common mode signal.
Strong rejection of the common mode signal is one of the most important characteristics
of a good biopotential amplifier.
Fig : Typical configuration for the measurement of biopotentials. The biological signal V
appears between the two measuring electrodes at the right and left arm of the patient, and
is fed to the inverting and the non-inverting inputs of the differential amplifier. The right
leg electrode provides the reference potential for the amplifier with a common mode
voltage Vc as indiacted.
common mode rejection ratio
CMRR of an amplifier is defined as the ratio of the differential mode gain over the
common mode gain. The output of a real biopotential amplifier will always consist of the
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Eye controlled HMI
desired output component due to a differential biosignal, an undesired component due to
incomplete rejection of common mode interference signals as a function of CMRR, and
an undesired component due to source impedance unbalance allowing a small proportion
of a common mode signal to appear as a differential signal to the amplifier. Since source
impedance unbalances of 5,000 to 10,000 Ω, mainly caused by electrodes, are not
uncommon, and sufficient rejection of line frequency interferences requires a minimum
CMRR of 100 dB, the input impedance of the amplifier should be at least 109 Ω at 60 Hz
to prevent source impedance unbalances from deteriorating the overall CMRR of the
amplifier. State-of-the-art biopotential amplifiers provide a CMRR of 120 to 140 dB.
In order to provide optimum signal quality and adequate voltage level for further signal
processing, the amplifier has to provide a gain of 100 to 50,000 and needs to maintain the
best possible signal-to noise ratio. The presence of high level interference signals not only
deteriorates the quality of the physiological signals, but also restricts the design of the
biopotential amplifier. In order to prevent the amplifier from going into saturation,
this component has to be eliminated before the required gain can be
provided for the physiological signal.
Fig :Schematic design of the main stages of a biopotential amplifier. Three electrodes
connect the patient
A typical design of the various stages of a biopotential amplifier is shown in above figure.
The electrodes which provide the transition between the ionic flow of currents in
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Eye controlled HMI
biological tissue and the electronic flow of current in the amplifier, represent a complex
electrochemical system. The electrodes determine to a large extent the composition of the
measured signal. The preamplifier represents the most critical part of the amplifier itself
since it sets the stage for the quality of the biosignal. With proper design, the preamplifier
can eliminate, or at least minimize, most of the signals interfering with the measurement
of biopotentials.
Instrumentation Amplifier
An important stage of all biopotential amplifiers is the input preamplifier which
substantially contributes to the overall quality of the system. The main tasks of the
preamplifier are to sense the voltage between two measuring electrodes while rejecting
the common mode signal, and minimizing the effect of electrode polarization over
potentials. Crucial to the performance of the preamplifier is the input impedance which
should be as high as possible. Such a differential amplifier cannot be realized using a
standard single operational amplifier (op-amp) design since this does not provide the
necessary high input impedance. The general solution to the problem involves voltage
followers, or noninverting amplifiers, to attain high
input impedances. A possible realization is shown in figure(a). The main disadvantage of
this circuit is that it requires high CMRR both in the followers and in the final op-amp.
With the input buffers working at unity gain, all the common-mode rejection must be
accomplished in the output amplifier, requiring very precise resistor matching.
Additionally, the noise of the final op-amp is added at a low signal level, decreasing the
signal-to-noise ratio unnecessarily. The circuit in Fig(b) eliminates this disadvantage. It
represents the standard instrumentation amplifier configuration. The two input op-amps
provide high differential gain and unity common-mode gain without the requirement of
close resistor matching.
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Eye controlled HMI
Fig :Circuit drawings for three different realizations of instrumentation amplifiers for
biomedical applications. Voltage follower input stage (a), improved, amplifying input
stage (b) 2 op-amp version (c).
1
21 21
R
RG
3
42 R
RG
The preamplifier, often implemented as a separate device which is placed close to
the electrodes or even directly attached to the electrodes, also acts as an impedance
converter which allows the transmission of even weak signals to the remote monitoring
unit. Due to the low output impedance of the preamplifier, the input impedance of the
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Eye controlled HMI
following amplifier stage can be low, and still the influence of interference signals
coupled into the transmission lines is reduced.
We are using AD620 its specification and details can be found in datasheet.
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Eye controlled HMI
ACQUISITION FRONT END
Electrodes capture the biopotentials from the body but these signals are very
weak and very noisy so there is invariable need of advance acquisition system which
comprises of precision instrumentation amplifier, active filters, multiple gain block and
for interfacing to ADC we have to do dc shifting(or clamping) of signal followed by
clipping to avoid any residual negative voltages.
Circuit is given below:
Figure: Acquisition circuit diagram (same is for up-down and left-right).
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Eye controlled HMI
In above circuit diagram IA AD620 is set for gain of 50, which is followed by low
pass filter and high pass filter together the made band pass filter and we are getting
frequencies 0.5 to 4Hz at output, this is amplified buy gain block 1 which has variable
gain now our signal range is few mv, we need one more gain block followed by active
low pass filter to reject all high frequency noises above 3Hz and some gain also can be
provided if required at this stage. After this we have dc level shifter and clipper ckt to
ensure only positive voltages are going to ADC.
Similar circuit is there for up-down but only we have to adjust the again using
variable resistor and dc level shift voltage. Both the final outputs are fed to I2C based 4
channel ADC PCF8591, left right signal is fed to ch0 and up-down signal is fed to ch1.
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Eye controlled HMI
I2C Based serial ADC PCF8591
Introduction to I2C Protocol:
Name I2C is shorthand for a standard Inter-IC (integrated circuit) bus.
Philips originally developed I2C for communication between devices inside of a
TV set. Examples of simple I2C-compatible devices found in embedded systems include
EEPROMs, thermal sensors, and real-time clocks.
The main objective behind the invention of I2C bus is to establish a simple low
pin count bus that can connect different ICs on a circuit board of Television or Radio.
Later I2C grew beyond the limits of TV and Radio and now it can be found in almost
every computer motherboards and other embedded devices. I2C can also be used for
communication between multiple circuit boards in equipments with or without using a
shielded cable depending on the distance and speed of data transfer.
Standard I2C devices operate up to 100Kbps, while fast-mode devices operate at
up to 400Kbps. A 1998 revision of the I2C specification (v. 2.0) added a high-speed mode
running at up to 3.4Mbps. Most of the I2C devices available today support 400Kbps
operation. Higher-speed operation may allow I2C to keep up with the rising demand for
bandwidth in multimedia and other applications.
I2C is appropriate for interfacing to devices on a single board, and can be stretched
across multiple boards inside a closed system, but not much further. An example is a host
CPU on a main embedded board using I2C to communicate with user interface devices
located on a separate front panel board. A second example is SDRAM DIMMs, which
can feature an I2C EEPROM containing parameters needed to correctly configure a
memory controller for that module.
ECE, SBMSIT 30
Eye controlled HMI
I2C is a two-wire serial bus, as shown in Figure 1. There's no need for chip select or
arbitration logic, making it cheap and simple to implement in hardware.
The two I2C signals are serial data (SDA) and serial clock (SCL). Together, these
signals make it possible to support serial transmission of 8-bit bytes of data-7-bit device
addresses plus control bits-over the two-wire serial bus. The device that initiates a
transaction on the I2C bus is termed the master. The master normally controls the clock
signal. A device being addressed by the master is called a slave.
In a bind, an I2C slave can hold off the master in the middle of a transaction using
what's called clock stretching (the slave keeps SCL pulled low until it's ready to
continue). Most I2C slave devices don't use this feature, but every master should support
it.
The I2C protocol supports multiple masters, but most system designs include only
one. There may be one or more slaves on the bus. Both masters and slaves can receive
and transmit data bytes.
Each I2C-compatible hardware slave device comes with a predefined device
address, the lower bits of which may be configurable at the board level. The master
transmits the device address of the intended slave at the beginning of every transaction.
Each slave is responsible for monitoring the bus and responding only to its own address.
This addressing scheme limits the number of identical slave devices that can exist on an
I2C bus without contention, with the limit set by the number of user-configurable address
bits (typically two bits, allowing up to four identical devices).
ECE, SBMSIT 31
Eye controlled HMI
Communication
As you can see in Figure 2, the master begins the communication by issuing the start
condition (S). The master continues by sending a unique 7-bit slave device address, with
the most significant bit (MSB) first. The eighth bit after the start, read/not-write (),
specifies whether the slave is now to receive (0) or to transmit (1). This is followed by an
ACK bit issued by the receiver, acknowledging receipt of the previous byte. Then the
transmitter (slave or master, as indicated by the bit) transmits a byte of data starting with
the MSB. At the end of the byte, the receiver (whether master or slave) issues a new ACK
bit. This 9-bit pattern is repeated if more bytes need to be transmitted.
In a write transaction (slave receiving), when the master is done transmitting all of
the data bytes it wants to send, it monitors the last ACK and then issues the stop condition
(P). In a read transaction (slave transmitting), the master does not acknowledge the final
byte it receives. This tells the slave that its transmission is done. The master then issues
the stop condition.
I2C offers good support for communication with on-board devices that are
accessed on an occasional basis. I2C's competitive advantage over other low-speed short-
distance communication schemes is that its cost and complexity don't scale up with the
number of devices on the bus. On the other hand, the complexity of the supporting I2C
software components can be significantly higher than that of several competing schemes
(SPI and MicroWire, to name two) in a very simple configuration. With its built-in
addressing scheme and straightforward means to transfer strings of bytes, I2C is an
elegant, minimalist solution for modest, "inside the box" communication needs.
ECE, SBMSIT 32
Eye controlled HMI
Advantages of I2C
• Only two bus lines are required to establish full-fledged bus.
• Each slave device connected is uniquely addressable using slave addresses
• Can choose a short 7 bit addressing or 10 bit addressing (which can accommodate
large number of devices on the same bus, but less popular).
• No strict baud rate specified since the clock is driven directly by the master.
Supports up to 3.4 Mbits/sec transfer speeds.
• True multimaster support with up to 8 masters in a single bus system.
• Very simple protocol which can be emulated by microcontrollers without
integrated I2C peripheral device. And its Inexpensive
Limitations of I2C
• 7 bit addressing supports only a very small number of devices.
• Different devices from different manufacturers come with hard coded slave
address or address will be configurable in a small range only. This can lead to
address clashes sometimes.
• No automatic bus configuration or plug and play
Applications of I2C
• I²C is appropriate for peripherals where simplicity and low manufacturing cost are
more important than speed. Common applications of the I²C bus are:
• Reading configuration data from SPD EEPROMs on SDRAM, DDR SDRAM,
DDR2 SDRAM memory sticks (DIMM) and other stacked PC boards
• Supporting systems management for PCI cards, through an SMBus 2.0
connection.
• Accessing NVRAM chips that keep user settings.
ECE, SBMSIT 33
Eye controlled HMI
• Accessing low speed DACs and ADCs.
• Changing contrast, hue, and color balance settings in monitors (Display Data
Channel).
• Changing sound volume in intelligent speakers.
• Controlling OLED/LCD displays, like in a cellphone.
• Reading hardware monitors and diagnostic sensors, like a CPU thermostat and fan
speed.
• Reading real time clocks.
• Turning on and turning off the power supply of system components.
• A particular strength of I²C is that a microcontroller can control a network of
device chips with just two general-purpose I/O pins and software.
• Peripherals can also be added to or removed from the I²C bus while the system is
running, which makes it ideal for applications that require hot swapping of
components.
Characteristics Of The I2C-Bus
The I2C-bus is for bidirectional, two-line communication between different ICs or
modules. The two lines are a serial data line (SDA) and a serial clock line (SCL). Both
lines must be connected to a positive supply via a pull-up resistor. Data transfer may be
initiated only when the bus is not busy.
Bit transfer
One data bit is transferred during each clock pulse. The data on the SDA line must
remain stable during the HIGH period of the clock pulse as changes in the data line at this
time will be interpreted as a control signal.
ECE, SBMSIT 34
Eye controlled HMI
Start and stop conditions
Both data and clock lines remain HIGH when the bus is not busy. A HIGH-to-LOW
transition of the data line, while the clock is HIGH, is defined as the start condition (S). A
LOW-to-HIGH transition of the data line while the clock is HIGH, is defined as the stop
condition (P).
Acknowledge
The number of data bytes transferred between the start and stop conditions from
transmitter to receiver is not limited. Each data byte of eight bits is followed by one
acknowledge bit. The acknowledge bit is a HIGH level put on the bus by the transmitter
whereas the master also generates an extra acknowledge related clock pulse.
A slave receiver which is addressed must generate an acknowledge after the
reception of each byte. Also a master must generate an acknowledge after the reception of
each byte that has been clocked out of the slave transmitter. The device that
acknowledges has to pull down the SDA line during the acknowledge clock pulse, so that
the SDA line is stable LOW during the HIGH period of the acknowledge related clock
pulse. A master receiver must signal an end of data to the transmitter by not generating an
ECE, SBMSIT 35
Eye controlled HMI
acknowledge on the last byte that has been clocked out of the slave. In this event the
transmitter must leave the data line HIGH to enable the master to generate a stop
condition.
Out of various devices we are using I2C Serial ADC (Analog to Digital
Convertor) for acquiring EOG signals.
ECE, SBMSIT 36
Eye controlled HMI
I2C Based Serial ADC PCF8591:
An analog-to-digital converter (ADC) is a device which converts a continuous
quantity to a discrete time digital representation. An ADC may also provide an isolated
measurement. The reverse operation is performed by a digital-to-analog converter (DAC).
Typically, an ADC is an electronic device that converts an input analog voltage or
current to a digital number proportional to the magnitude of the voltage or current.
Various ADC are available with serial and parallel interfacing. To save the pin
count and board space we have decided to use serial ADC, again in serial ADC we have
SPI interface and I2C interface, we have choose I2C serial ADC as it requires only 2
lines for interfacing and data rates are sufficient for most of the system. In our project we
are using PCF8591 from Philips which is I2C serial ADC/DAC chip.
PCF8591 Description:
The PCF8591 is a single-chip, single-supply low power 8-bit CMOS data
acquisition device with four analog inputs, one analog output and a serial I2C-bus
interface. Three address pins A0, A1 and A2 are used for programming the hardware
address, allowing the use of up to eight devices connected to the I2C-bus without
additional hardware. Address, control and data to and from the device are transferred
serially via the two-line bidirectional I2C-bus.
The functions of the device include analog input multiplexing, on-chip track and
hold function, 8-bit analog-to-digital conversion and an 8-bit digital-to-analog
conversion. The maximum conversion rate is given by the maximum speed of the I2C-
bus.
Features:
• Single power supply
ECE, SBMSIT 37
Eye controlled HMI
• Operating supply voltage 2.5 V to 6 V
• Low standby current
• Serial input/output via I2C-bus
• Address by 3 hardware address pins
• Sampling rate given by I2C-bus speed
• 4 analog inputs programmable as single-ended or differential inputs
• Auto-incremented channel selection
• Analog voltage range from VSS to VDD
• On-chip track and hold circuit
• 8-bit successive approximation A/D conversion
• Multiplying DAC with one analog output.
Applications:
• Closed loop control systems
• Low power converter for remote data acquisition
• Battery operated equipment
• Acquisition of analog values in automotive, audio and TV applications.
•
ECE, SBMSIT 38
Eye controlled HMI
Block Diagram:
Pin Description and Pin Diagram:
FUNCTIONAL DESCRIPTION
ECE, SBMSIT 39
Eye controlled HMI
Addressing
Each PCF8591 device in an I2C-bus system is activated by sending a valid
address to the device. The address consists of a fixed part and a programmable part. The
programmable part must be set according to the address pins A0, A1 and A2. The address
always has to be sent as the first byte after the start condition in the I2C-bus protocol. The
last bit of the address byte is the read/write-bit which sets the direction of the following
data transfer .
Control byte
The second byte sent to a PCF8591 device will be stored in its control register and
is required to control the device function. The upper nibble of the control register is used
for enabling the analog output, and for programming the analog inputs as single-ended or
differential inputs. The lower nibble selects one of the analog input channels defined by
the upper nibble. If the auto-increment flag is set, the channel number is incremented
automatically after each A/D conversion.
ECE, SBMSIT 40
Eye controlled HMI
A/D conversion
The A/D converter makes use of the successive approximation conversion
technique, the on-chip D/A converter and a high-gain comparator are used temporarily
during an A/D conversion cycle. An A/D conversion cycle is always started after sending
a valid read mode address to a PCF8591 device. The A/D conversion cycle is triggered at
the trailing edge of the acknowledge clock pulse and is executed while transmitting the
result of the previous conversion.
Once a conversion cycle is triggered an input voltage sample of the selected
channel is stored on the chip and is converted to the corresponding 8-bit binary code.
Samples picked up from differential inputs are converted to an 8-bit twos complement
code. The conversion result is stored in the ADC data register and awaits transmission.
If the auto-increment flag is set the next channel is selected. The first byte
transmitted in a read cycle contains the conversion result code of the previous read cycle.
ECE, SBMSIT 41
Eye controlled HMI
After a Power-on reset condition the first byte read is a hexadecimal 80. The maximum
A/D conversion rate is given by the actual speed of the I2C-bus.
Before above steps always we have to send channel selection control byte as write
command, steps are as follows:
o Start
o Address with Write cmd(0)
o Control byte with channel no(00 , 01 , 10 , 11)
o Stop
We are using P89V51RD2 to acquire and process the data and final eye
movement cmd is send via RF Tx module using Ht640 encoder, at receiving end after RF
Rx module data goes to decoder HT648 and then to Application Microcontroller all
interfacing is described in following chapters.
MICROCONTROLLER P89V51RX2
Computer in its simplest form needs at least 3 basic blocks: CPU, I/O and the
RAM/ROM. The integrated form of CPU is the microprocessor. As the use of
microprocessors in control applications increased, development of microcontroller unit or
ECE, SBMSIT 42
Eye controlled HMI
MCU took shape, wherein CPU, I/O and some limited memory on a single chip was
fabricated. Intention was to reduce the chip count as much as possible. We decided to use
P89V51RXX series of Microcontroller.
The P89V51RB2/RC2/RD2 are 80C51 microcontrollers with 16/32/64 kB flash
and 1024 B of data RAM. A key feature of the P89V51RB2/RC2/RD2 is its X2 mode
option. The design engineer can choose to run the application with the conventional
80C51 clock rate (12 clocks per machine cycle) or select the X2 mode (six clocks per
machine cycle) to achieve twice the throughput at the same clock frequency. Another way
to benefit from this feature is to keep the same performance by reducing the clock
frequency by half, thus dramatically reducing the EMI.
The flash program memory supports both parallel programming and in serial ISP.
Parallel programming mode offers gang-programming at high speed, reducing
programming costs and time to market. ISP allows a device to be reprogrammed in the
end product under software control. The capability to field/update the application
firmware makes a wide range of applications possible. The P89V51RB2/RC2/RD2 is also
capable of IAP, allowing the flash program memory to be reconfigured even while the
application is running.
Features of P89V51RXX:
80C51 CPU Core
5 V operating voltage from 0 MHz to 40 MHz
16/32/64 kB of on-chip flash user code memory with ISP and IAP
Supports 12-clock (default) or 6-clock mode selection via software or ISP
SPI and enhanced UART
PCA with PWM and capture/compare functions
Four 8-bit I/O ports with three high-current port 1 pins (16 mA each)
Three 16-bit timers/counters
Programmable watchdog timer
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
ECE, SBMSIT 43
Eye controlled HMI
TTL- and CMOS-compatible logic levels
Brownout detection
Low power modes
o Power-down mode with external interrupt wake-up
o Idle mode
DIP40, PLCC44 and TQFP44 packages
Block Diagram:
Pin Diagram:
ECE, SBMSIT 44
Eye controlled HMI
Pin description of P89CV51RXX
Port 0: Port 0 is an 8-bit open drain bidirectional I/O port. Port 0 pins that have ‘1’s
written to them float, and in this state can be used as high-impedance inputs. Port 0 is also
the multiplexed low-order address and data bus during accesses to external code and data
memory. In this application, it uses strong internal pull-ups when transitioning to ‘1’s.
Port 0 also receives the code bytes during the external host mode programming, and
outputs the code bytes during the external host mode verification. External pull-ups are
required during program verification or as a general purpose I/O port.
Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 pins are
pulled high by the internal pull-ups when ‘1’s are written to them and can be used as
inputs in this state. As inputs, Port 1 pins that are externally pulled LOW will source
current (IIL) because of the internal pull-ups. P1.5, P1.6, P1.7 have high current drive of
ECE, SBMSIT 45
Eye controlled HMI
16 mA. Port 1 also receives the low-order address bytes during the external host mode
programming and verification.
Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins are
pulled HIGH by the internal pull-ups when ‘1’s are written to them and can be used as
inputs in this state. As inputs, Port 2 pins that are externally pulled LOW will source
current (IIL) because of the internal pull-ups. Port 2 sends the high-order address byte
during fetches from external program memory and during accesses to external Data
Memory that use 16-bit address (MOVX@DPTR). In this application, it uses strong
internal pull-ups when transitioning to ‘1’s. Port 2 also receives some control signals and
a partial of high-order address bits during the external host mode programming and
verification.
Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins are
pulled HIGH by the internal pull-ups when ‘1’s are written to them and can be used as
inputs in this state. As inputs, Port 3 pins that are externally pulled LOW will source
current (IIL) because of the internal pull-ups. Port 3 also receives some control signals
and a partial of high-order address bits during the external host mode programming and
verification.
PSEN: Program Store Enable is the read strobe for external program memory.
Reset: While the oscillator is running, a HIGH logic state on this pin for two machine
cycles will reset the device.
External Access Enable: EA must be connected to VSS in order to enable the device to
fetch code from the external program memory. EA must be strapped to VDD for internal
program execution.
ECE, SBMSIT 46
Eye controlled HMI
Address Latch Enable: ALE is the output signal for latching the low byte of the
address during an access to external memory. This pin is also the programming pulse
input (PROG) for flash programming.
Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock
generator circuits.
Crystal 2: Output from the inverting oscillator amplifier.
VCC: Supply voltage.
GND: Ground.
The additional feature of Port3
ECE, SBMSIT 47
Eye controlled HMI
CHAPTER
RF INTERFACING
For transmission of data/Cmds from one point to another point wirelessly we need
to have RF interface, RF interfacing requires 4 parts:
1> RF Transmitter Module
2> RF Receiver Module
3> Transmitter Encoder
4> Receiver Decoder
RF Transmitter Module ST433/315
The STT-433/315 is ideal for remote control applications where low cost and
longer range is required. The transmitter operates from a 1.5-12V supply, making it ideal
for battery-powered applications. The transmitter employs a SAW-stabilized oscillator,
ensuring accurate frequency control for best range performance. Output power and
harmonic emissions are easy to control, making FCC and ETSI compliance easy. The
manufacturing-friendly SIP style package and low-cost make the STT-433/315 suitable
for high volume applications.
Features
433.92/315 MHz Frequency
Low Cost
1.5-12V operation
11mA current consumption at 3V
Small size
4 dBm output power at 3V
ECE, SBMSIT 48
Eye controlled HMI
Applications
Car security system
Sensor reporting
Automation system
Remote Keyless Entry (RKE)
Remote Lighting Controls
On-Site Paging
Asset Tracking
Wireless Alarm and Security Systems
Long Range RFID
Automated Resource Management
Note: 3pin RF Tx module is having helical wire antenna
RF Receiver Module STR-433/315
The STR-433/315 is ideal for short-range remote control applications where cost
is a primary concern. The receiver module requires no external RF components except for
the antenna. It generates virtually no emissions, making FCC and ETSI approvals easy.
The super-regenerative design exhibits exceptional sensitivity at a very low cost. The
manufacturing-friendly SIP style package and low-cost make the STR-433/315 suitable
for high volume applications.
ECE, SBMSIT 49
Eye controlled HMI
Features
Low Cost
5V operation
3.5mA current drain
No External Parts are required
Receiver Frequency: 433.92/315 MHZ
Typical sensitivity: -105dBm
IF Frequency: 1MHz
Applications: Same as Transmitter Module
ECE, SBMSIT 50
Eye controlled HMI
Note: 3pin RF Rx module is having helical wire antenna
Transmitter Encoder HT12E (212 series)
The 212 encoders are a series of CMOS LSIs for remote control system
applications. They are capable of encoding information which consists of N address bits
and 12-N data bits. Each address/data input can be set to one of the two logic states. The
programmed addresses/ data are transmitted together with the header bits via an RF or an
infrared transmission medium upon receipt of a trigger signal. The capability to select a
TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the
application flexibility of the 212 series of encoders. The HT12A additionally provides a
38kHz carrier for infrared systems.
Features
Operating voltage 2.4V~5V for the HT12A 2.4V~12V for the HT12E
Low power and high noise immunity CMOS technology
ECE, SBMSIT 51
Eye controlled HMI
Low standby current: 0.1_A (typ.) at VDD=5V
HT12A with a 38kHz carrier for infrared transmission medium
Minimum transmission word
Four words for the HT12E
One word for the HT12A
Built-in oscillator needs only 5% resistor
Data code has positive polarity
Minimal external components
Pair with Holtek’s 212 series of decoders
18-pin DIP, 20-pin SOP package
Applications
Burglar alarm system
Smoke and fire alarm system
Garage door controllers
Car door controllers
Car alarm system
Security system
Cordless telephones
Other remote control systems
ECE, SBMSIT 52
Eye controlled HMI
Block diagram and Pin Diagram:
ECE, SBMSIT 53
Eye controlled HMI
ECE, SBMSIT 54
Eye controlled HMI
ECE, SBMSIT 55
Eye controlled HMI
Flow chart and application circuit of HT12E working:
ECE, SBMSIT 56
Eye controlled HMI
ECE, SBMSIT 57
Eye controlled HMI
Receiver Decoder HT12D (212 series)
The 212 decoders are a series of CMOS LSIs for remote control system
applications. They are paired with Holtek’s 212 series of encoders (refer to the
encoder/decoder cross reference table). For proper operation, a pair of encoder/decoder
with the same number of addresses and data format should be chosen. The decoders
receive serial addresses and data from a programmed 212 series of encoders that are
transmitted by a carrier using an RF or an IR transmission medium. They compare the
serial input data three times continuously with their local addresses. If no error or
unmatched codes are found, the input data codes are decoded and then transferred to the
output pins. The VT pin also goes high to indicate a valid transmission. The 212 series of
decoders are capable of decoding information that consists of N bits of address and 12_N
bits of data. Of this series, the HT12D is arranged to provide 8 address bits and 4 data
bits, and HT12F is used to decode 12 bits of address information.
Features
Operating voltage: 2.4V~12V
Low power and high noise immunity CMOS technology
Low standby current
Capable of decoding 12 bits of information
Binary address setting
Received codes are checked 3 times
Address/Data number combination
HT12D: 8 address bits and 4 data bits
HT12F: 12 address bits only
Built-in oscillator needs only 5% resistor
Valid transmission indicator
Easy interface with an RF or an infrared transmission medium
Minimal external components
Pair with Holtek’s 212 series of encoders
18-pin DIP, 20-pin SOP package
ECE, SBMSIT 58
Eye controlled HMI
Applications
Burglar alarm system
Smoke and fire alarm system
Garage door controllers
Car door controllers
Car alarm system
Security system
Cordless telephones
Other remote control systems
Block Diagram and Pin Diagram:
ECE, SBMSIT 59
Eye controlled HMI
ECE, SBMSIT 60
Eye controlled HMI
Operation
The 212 series of decoders provides various combinations of addresses and data
pins in different packages so as to pair with the 212 series of encoders. The decoders
receive data that are transmitted by an encoder and interpret the first N bits of code period
as addresses and the last 12_N bits as data, where N is the address code number. A signal
on the DIN pin activates the oscillator which in turn decodes the incoming address and
data. The decoders will then check the received address three times continuously. If the
received address codes all match the contents of the decoder’s local address, the 12_N
bits of data are decoded to activate the output pins and the VT pin is set high to indicate a
valid transmission. This will last unless the address code is incorrect or no signal is
received. The output of the VT pin is high only when the transmission
is valid. Otherwise it is always low.
Output Type
The 212 series of decoders, the HT12F has no data output pin but its VT pin can
be used as a momentary data output. The HT12D, on the other hand, provides 4 latch type
data pins whose data remain unchanged until new data are received.
ECE, SBMSIT 61
Eye controlled HMI
Flow Chart and Application Circuit
The oscillator is disabled in the standby state and activated when a logic “high”
signal applies to the DIN pin. That is to say, the DIN should be kept low if there is no
signal input
ECE, SBMSIT 62
Eye controlled HMI
Flow Chart:
Transmitter Module Interfacing
This is complete data transmission module, Microcontroller first send data to data
lines of encoder, address lines of encoder are hardwire, after giving data microcontroller
enables TE pin of encoder in order to start encoding process and at Dout pin of encoder
serial encoded data is coming this serial encoded data contains not only data but it
ECE, SBMSIT 63
EncoderHT12E
Microcontroller
TX RF Module
Data line
Transmit Enable
Microcontroller
DecoderHT12D
RX RF Module
Data line
VTValid
Eye controlled HMI
contains module address and sync bits, this signal is fed to RF Tx module which does
OOK modulation and transmits data wirelessly.
Receiver Module Interfacing
This is complete data Reception module; RF Rx module receives the wireless bit
stream this is fed to Decoder which first compares the address and sync if all is ok then it
compares data two times if both are same then only it enables VT pin (Valid
Transmission) and latch the output at data lines, when new data is received VT goes low
and then again with same logic it is set to high if same new data is received two times.
Rising edge of VT indicates new data has come falling edge of VT indicates data has
stopped or new data is going to come. We can read data at both edges. This can work in
two modes polling VT mode and Interrupt Mode in which VT is connected to INT0 pin of
MCU.
ECE, SBMSIT 64
Eye controlled HMI
ACQUISITION AND PROCESSING SYSTEM
Acquisition front end system will interface to the body get the EOG signal,
amplify it, filter it and pre process it to suit to ADC PCF8591 I2C Based 4 Channel ADC.
Left-right signal is given to channel 0 and up-down signal is given channel-1, this ADC is
interfaced to Microcontroller P89V51RD2 which is having I2C communication routines.
The microcontroller reads the data from ADC using I2C protocol and starts processing.
Once data is processed and if any eye movement was there it will conclude which eye
movement was made and decodes which command is given using eye. After decoding it
sends the command via RF transmitter module using HT12E Encoder.
Circuit diagram is given below:
ECE, SBMSIT 65
Eye controlled HMI
Figure: Acquisition and processing part
Processing of data to decode the eye movements:
Basically we get digital data from ADC for each channel, first we are checking for
straight sight to avoid noise and electrode not in use case. This we are doing by checking
that signal is not varying much it’s in some band near center. After the if signal goes up
for sufficient time > 200ms then its right eye movement in case of L-R and Up movement
in case of U-D, but if signal goes down then its left or down depending on which channel
you are processing. Any of the case if it come back before sufficient time then movement
is ignored but in case of up down, if signal is up for >50ms to <100ms then its consider as
blink movement.
Flow chart is for above processing is given below:
ECE, SBMSIT 66
Eye controlled HMI
We have looked in straight direction and signals are stabilized, now its turn to give
commands using eye movements.
Following are the follow charts to detect left, right, up, down and blink eye movements.
Figure: Flow chart for Left-Right Detection
ECE, SBMSIT 67
Eye controlled HMI
Figure: Flow chart for up-down and blink detections.
These commands are sent via RF Tx module at application part end there is RF
Rx module which receives the commands and send it to application controller which then
drives the cursor and operates buttons on Graphic LCD
ECE, SBMSIT 68
Eye controlled HMI
Graphics LCD JHD12864
JHD12864J is a light weight, low power consumption liquid crystal graphic
display. The module measures 54.0x50.0mm only. Supply voltage is 5V matching the
voltage for most microcontrollers. The LCD controller is Samsung KS0108B.
This LCD has 20 line interfacing which are described below:
Pin Description
Symbol Level Function
Vss 0V Ground
Vdd +5V Power supply for logic
Vo - Operating voltage for LCD (contrast adjusting)
RS H/L Register selection H:Display data L:Instruction code
R/W H/L Read/Write selection H:Read operation L:Write Operation
E H,H-
>L
Enable Signal.Read data when E is high,Write data at the falling
Edge of E
DB0 H/L Data bit 0
DB1 H/L Data bit 1
DB2 H/L Data bit 2
ECE, SBMSIT 69
Eye controlled HMI
DB3 H/L Data bit 3
DB4 H/L Data bit 4
DB5 H/L Data bit 5
DB6 H/L Data bit 6
DB7 H/L Data bit 7
CS1 H select the right half of display the CS1 bit is set
CS2 H select the left half of display the CS2 bit is set
/RST L Reset signal, active low
Vout -10V Output voltage for LCD driving
LEDA +5V Power supply for LED back light
LEDB 0V GND for LED back light
The display is split logically in half. It contains two controllers with controller #1 (Chip
select 1) controlling the left half of the display and controller #2 (Chip select 2)
controlling the right half. Each controller must be addressed independently. The page
addresses, 0-7, specify one of the 8 horizontal pages which are 8 bits (1 byte) high. A
drawing of the display and how it is mapped to the refresh memory is shown below
.
ECE, SBMSIT 70
Eye controlled HMI
Block Diagram of GLCD:
ECE, SBMSIT 71
Eye controlled HMI
Following are display control Instruction which MCU has to give while
interfacing to GLCD module:
ECE, SBMSIT 72
Eye controlled HMI
Basic interfacing diagram with MCU:
ECE, SBMSIT 73
Eye controlled HMI
Algorithm and flowchart for GLCD interfacing
1.Send the display off command 3eh
2. Send the display on command 3fh
3.If required you can use 11xx xxxx instruction to set the display line start
4. Set the Y-adddress to first coloumn 40h
5.Set the X-address to first page 0B8h
6.Blank the Display( clear all 128x64 pixels)
ECE, SBMSIT 74
Eye controlled HMI
Application Part
Application part consists of Graphics LCD, P89V51RD2 microcontroller, RF
receiver module with decoder HT12D, ULN2008 high current Darlington driver for
controlling high current devices or relays.
Eye Movements commands are sent to application part via RF transmitter, the RF
receiver receives the data and HT12D does channel decoding and give digital data to
MCU and with VT pin signal it gives indication that data is received. Which trigger the
ECE, SBMSIT 75
Eye controlled HMI
interrupt and in ISR we are read output of encoder into the MCU, and data is decoded for
cursor commands and blinks (clicks). According to commands cursor is move on the
screen but menu is only visible after 4 blinks. After moving to cursor to required button 2
blinks are required to click the button and designated operation is performed after 2blinks
are received.
This microcontroller control the graphic lcd, it prints messages on screen, it
creates menu on screen with 4 buttons and one cursor, for each cursor command cursor on
screen is moved using creating the new cursor at new position and removing old cursor.
4 devices are connected at four MCU pins, and this pins goes to input of
ULN2803 so devices using voltages 5-12V and current upto 400-500mA can be
controlled directly and high current and high voltages devices can be controlled via
relays.
Buzzer and FAN in our demo project are duty cycle, we duty cycle FAN to save
power and Buzzer is duty cycled so that patient does not have to activate buzzer again and
again till someone comes and attain him. Buzzer is made off by a buzzer reset switch.
Circuit diagram and flowcharts are given in following pages
Flow chart for Application
ECE, SBMSIT 76
Eye controlled HMI
ECE, SBMSIT 77
Eye controlled HMI
Circuit for Application part:
ECE, SBMSIT 78
Eye controlled HMI
Software and hardware requirements
Software and Hardware requirements along with component list
PC Requirements:
Pentium 4 PC or higher OS: Win XP or higher.Minimum 1GB RAM.Software: KEIL, Flash Magic and HyperTerminal
Hardware components:
RF Transmitter and receiver – 315/433 MHz
ENCODER & DECODER BRDS - WITH HT12E 648
RELAY BOARD - Transistor Based
GRAPHIC DISPLAY - 128X64
HT12E - 4 BIT ENCODER
HT12D - 4 BIT DECODER
LM324– OPAMP X2
INA (Instrumentation amplifier) AD620 X2
I2C based ADC PCF8591
Power Supply 9V DC adapter, and 9V Batteries X378L05, 79L05
FAN, Buzzer and Cables
P89V51RD2 and General Purpose MCU Board X2
Finally Electrodes and Medical Accessories
ECE, SBMSIT 79
Eye controlled HMI
Applications and Future work
Applications
Applications are not only limited to disable persons although this technology is most
useful for them:
Control of House hold appliances and Emergency call Bell.
A screen is provided with some buttons on that disable person move the cursor with eye
movement/ or cursor is slowly moving and to click a button he/she blinks the eye two
times and whatever button is meant for its executed, it can be turning on & off light
lights, calling assistance using bell etc.
Speech system for disable
this system enables disable person to talk via computer which has a special application
running having on screen keyboard, a text box not only this it as prediction of text logic
as he/she is trying to type by using eye movements on on screen keyboard system provide
predicted text in the drop down of text box which one can select to speed
text entry process
Email facility for disable
like previous application it has all interfaces and along with that email client is there
which sends email to fixed address or address can be typed via eye movement or selected
from address book again using eye signals only.
Eye movement controlled wheel chair
Wheel chair can go forward, backward, turn left and right using eye movements of the
disable person sitting on it.
US army is doing research on eye movement based Air craft and tank controls
ECE, SBMSIT 80
Eye controlled HMI
Hands free mouse using eye movement controller very useful specially in gaming
TV operation channel up & down volume up & down, turn on and off TV using
eye movements very useful for disables
Eye movements controlled mp3 player when ur hands are busy you can use this
system to play/pause, track change, and volume up&down using eye movements
ECE, SBMSIT 81
Eye controlled HMI
CONCLUSION
EXPECTED OUTPUT AND CONCLUSION
Intermediate Output of the system is Eye movements and Eye Blinking Commands
CU - Eye up movement detected
CD - Eye down movement detected
CL - Eye Left movement detected
CR - Eye Right movement detected
BL - 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/device is operated and hence
appliance is controlled using eye movements, in this project we have successfully
controlled appliances using eye movement.
Achievement:
Detection of Eye movements and eye blink at minimum 10sec rate with 1Sigma accuracy.
ECE, SBMSIT 82
Eye controlled HMI
REFERENCES
http://en.wikipedia.org/wiki/Eye_tracking
The 8051 Microcontroller, Kenneth J Ayala
C and the 8051, Thomas W. Schultz
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
Manuals in keil software
I2C-bus specification (version 2.1), from NXP semiconductors (Philips).
Datasheets of all the IC’s used in the system
ECE, SBMSIT 83