Post on 06-Apr-2018
8/3/2019 Automatic Speed Limiter
1/28
1
CHAPTER 1
INTRODUCTION
1.1 NEED FOR SPEED LIMITING
In this modern day world, where the catch word is SPEED, from vehicles,
processors, working and people, SPEED LIMITING sounds odd. Speed breakers are
found in roads to control speed of vehicles on road. But they are not effective. Sign
Boards are placed by the road side in places like hospitals, educational institutions,
offices, etc. stating the speed of the vehicles. But people are seen exceeding the limit in
these places. The aim of this project is to limit the speed in such places.
1.2 THE WORKING
Speed limiting is achieved with the help of IR transmitters mounted in these
zones, where the speed code is to be followed. An array of IR LEDs is mounted on
archways, erected at the place where the zone is supposed to begin and end. Each vehicleis mounted with the limit sensor, which is capable of detecting the IR rays from the
archway. As the vehicle crosses the archway, the receiver section produces a
corresponding voltage which is given to a signal conditioning circuit. The output of the
signal conditioning circuit is given to the microprocessor, which is used to rotate a
stepper motor. The stepper motor rotation causes the restriction of air-fuel mixture into
the engine, thereby reducing speed.
8/3/2019 Automatic Speed Limiter
2/28
2
1.3BLOCK DIAGRAM
Fig.1.1 Block Diagram
The IR Transmitter is an IR LED.
The IR Receiver consists of Photo transistor and Signal conditioning circuits.
The Stepper Motor section consists of the microprocessor and the interfacing
cards together with the stepper motor.
The Carburetor Section consists of the vehicle fuel injection system and the
restricting valve.
IR
RECEIVER
STEPPER
MOTOR CARBURETOR
IRTRANSMITTER
8/3/2019 Automatic Speed Limiter
3/28
3
CHAPTER 2
TRANSMITTER SECTION
Fig 1.1 Detailed Block Diagram
8/3/2019 Automatic Speed Limiter
4/28
4
2.1 IR TRANSMITTER
The IR transmitter is nothing but an Infra Red LED (Light Emitting diode).
IR LED of wavelength 740 nm is being used here.
Fig 2.1 Infra Red LED
LEDs have several advantages over conventional incandescent lamps. For one
thing, they don't have a filament that will burn out, so they last much longer.
Additionally, their small plastic bulb makes them a lot more durable. They also fit more
easily into modern electronic circuits.
But the main advantage is efficiency. In conventional incandescent lamps, the
light-production process involves generating a lot of heat (the filament must be warmed).
This is completely wasted energy, unless the lamp is used as a heater, because a huge
portion of the available electricity isn't going toward producing visible light. LEDs
8/3/2019 Automatic Speed Limiter
5/28
5
generate very little heat, relatively speaking. A much higher percentage of the electrical
power is going directly to generate light, which cuts down on the electricity demands
considerably.
Up until recently, LEDs were too expensive to use for most lighting applications
because they're built around advanced semiconductor material. The price of
semiconductor devices has plummeted over the past decade, however, making LEDs a
more cost-effective lighting option for a wide range of situations. While they may be
more expensive than incandescent lights up front, their lower cost in the long run can
make them a better buy. In the future, they will play an even bigger role in the world of
technology.
The use of Infra-red LEDs has a very significant and distinct advantage over the
conventional optical ones, for the simple reason that if optical LEDs are used as
transmitters, the receivers to be used would then not only respond to the light from the
LED, but also to the ambient light present in the surrounding. If the receiver were to
respond to only the installed LED, then the circuitry would become more complex. Thus
the use of Infra-red LEDs is much more appropriate and also makes the design simple.
2.2 EXCITATION TO THE LED
The infra-red LED is excited with a pulse waveform. This pulse waveform is
obtained from a standard NE 555 IC, operating in the astable mode. The use of pulse
excitation for the LED has several advantages. Firstly, the IR rays from the LED are
more pronounced if the excitation is a pulse waveform. Secondly, if a pulse waveform is
used rather than a constant D.C. supply, the heating of the LED filament is reduced, as
current does not flow all the time, hence increasing the life-time of the LED.
8/3/2019 Automatic Speed Limiter
6/28
6
2.3 NE-555
The 555 timer is a highly stable device for generating accurate time delay or
oscillation. Signetics Corporation first introduced this device as the SE555/NE 555 and it
is available in two packages styles, 8-pin circular style. To-99 can or 8-pin mini DIP or
as 14-pin DIP. A 8- pin mini DIP is used here.
The 555 timer can be used with supply voltage in the range of +5V to +18V and
can drive load upto 200 mA. It is compatible with both TTL and CMOS logic circuits.
Because of the wide range of supply voltage, the 555 timer is versatile and easy to use in
various applications
Fig 2.2 NE 555
2.4 INTERNAL CIRCUIT DIAGRAM
Referring to the fig 2.3, three 1K internal resistors act as voltage divider,
providing bias voltage of 2/3 Vcc to the upper comparator and 1/3 Vcc to the lower
comparator, where Vcc is the supply voltage. Since these two voltages fix the necessary
comparator threshold voltage, they also aid in determining the timing interval. It is
possible to vary time electronically too, by applying a modulation voltage to the controlvoltage input terminal (pin 5). As no such modulation is intended here, a capacitor of
0.01F is connected (As recommended by manufacturers) between control terminal and
ground to by-pass noise or ripple from the supply.
8/3/2019 Automatic Speed Limiter
7/28
7
Fig 2.3 Internal Circuit Diagram of NE555
In the standby state, the output of the control flip-flop is HIGH. This makes the
output LOW, because of power amplifier which is basically an inverter. A negative
going trigger pulse is applied to pin 2 and should have its dc level greater than the
threshold level of the lower comparator (i.e. Vcc/3). At the negative going edge of the
trigger, as the trigger passes through (Vcc/3), the output of the lower comparator goes
HIGH and sets the FF (Q=1, Q=0). During the positive excursion, when the threshold
voltage at pin 6 passes through (2/3) Vcc, the output of the upper comparator goes HIGH
and resets the FF (Q=0, Q=1).
The reset input provides a mechanism to reset the FF in a manner which overrides
the effect of any instruction coming to FF from lower comparator. This overriding reset
8/3/2019 Automatic Speed Limiter
8/28
8/3/2019 Automatic Speed Limiter
9/28
9
is high (equals Vcc) as Reset R=0, Set S=1 and this combination makes Q'=0 which has
unclamped the timing capacitor C.
When the capacitor voltage equals (to be precise just greater than), (2/3) Vcc the
upper comparator triggers the control flip-flop so that Q'=1. This in turn, makes
transistor Q1 on and capacitor C starts discharging towards ground through Rb and
transistor Q1 with a time constant RbC ( neglecting the forward resistance of Q1). Current
also flows into transistor Q1 through Ra. Resistors Ra and Rb must be large enough to limit
this current and prevent damage to the discharge transistor Q 1. The minimum value of Ra
is approximately equal to Vcc/0.2 where 0.2A is the maximum current through the on
transistor Q1.
During the discharge the timing capacitor C, as it reaches (to be precise is just less
than) Vcc/3, the lower comparator is triggered and at this stage S=1, R=0, which turns
Q'=0. Now Q=0 unclamps the external timing capacitor C. The capacitor C is thus
periodically charged and discharged between 2/3Vcc and 1/3Vcc respectively. The length
of time that the output remains HIGH is the time for the capacitor to charge from 2/3Vcc
to 1/3Vcc. It may be calculated as follows:
Fig 2.5 Timing Diagram
)1(/ RCt
ccc eVv
= Eqn 2.1
8/3/2019 Automatic Speed Limiter
10/28
10
The time t1 taken by the circuit to charge from 0 to (2/3) Vcc is,
RCt
eVVRCt
cccc
09.1
)1(3/2
1
/1
=
=
And the time t2 to charge from 0 to (1/3) Vcc is,
RCt
eVVRCt
cccc
405.0
)1(3/1
2
/2
=
=
So the time to charge from (1/3) Vcc to (2/3) Vcc is
CRRt
ttt
baHIGH
HIGH
)(69.0
21
+=
=
The output is low while the capacitor discharges from (2/3) Vcc to (1/3) Vcc and the
voltage across the capacitor is given by
)3/23/1 /1 RCtcccceVV =
Solving, we get
RCt 69.0=
So, for the given circuit,
CRt bLOW 69.0=
Eqn 2.2
Eqn 2.3
Eqn 2.4
Eqn 2.5
Eqn 2.6
Eqn 2.7
Eqn 2.8
Eqn 2.9
Eqn 2.10
8/3/2019 Automatic Speed Limiter
11/28
11
CHAPTER 3
RECEIVER SECTION
3.1 SENSOR
The receiver section uses an Infra-red sensor that is nothing but an Infra-red
sensitive photo transistor. The photo transistors base lead is kept open. In the normal
case, the photo-transistor is in the non-conducting state. When the transistor is exposed to
Infra-red rays, it drives the base and hence produces a base current. This causes the
transistor to go to the conduction state.
Fig 3.1 Operation of the Sensor
In the ideal case, the output is 5V. But due to the inherent conduction resistance
of the photo-transistor, the output is typically 1.2V. This voltage is then fed to an
amplifier stage.
8/3/2019 Automatic Speed Limiter
12/28
12
3.2 SIGNAL CONDITIONING
Fig 3.2 Amplification of the signal
The amplifier stage is essentially an Operational amplifier, in the non-inverting
configuration. The gain of the Operational amplifier is governed by the following
equation
)/1( ifio RRVV += Eqn 3.1
The objective of the signal conditioning circuit is to give a 5V output. Hence the
gain is adjusted so that the output is nearly 5V. This gives us the ratio Rf /Ri to be 4
(approximately). The resistor values are chosen as Ri equal to 1K and Rf equal to 4.7
K.
The output of the signal conditioning circuit is given as input to the
microprocessor stage.
8/3/2019 Automatic Speed Limiter
13/28
13
CHAPTER 4
MICROPROCESSOR
The overall objective of the microprocessor section is to acquire the output from
the signal conditioning stage and detect the entry and exit of the vehicle into or out of the
zone. After the detection, the microprocessor and the associated interface unit should run
the stepper motor either in the forward direction or reverse direction depending on
whether it has detected an entry or an exit of the vehicle.
4.1 INTERFACING TECHNIQUE
The output from the signal conditioning circuit is either a HIGH (5V) or a LOW
(0V). Whenever the vehicle enters or leaves the speed restricted zone, the signal
conditioning circuit yields a HIGH output. Whether the vehicle enters or leaves the zone
is indicated by a flag value which is included in the assembly program in the
microprocessor.
When the vehicle enters the speed limited zone, the flag is SET to a value of 1.
When the vehicle leaves the zone, the flag value is RESET to 0.
The output from the signal conditioning circuit is given as an interrupt to Port A
(which is configured in the program, as an input port) of the 8255 IC of the
microprocessor. While the microprocessor program is executing, If and When a HIGH
appears at PORT A and the flag value is 0, then it indicates that the vehicle is just
entering the zone. Hence the stepper motor needs to be rotated in the forward direction.
This is accomplished by transferring the execution control of the microprocessor program
to a subroutine that makes the stepper motor to rotate in the forward direction for a
specified angle. When a HIGH appears at PORT A and the flag value is 1, it indicates
that the vehicle is just leaving the zone. Hence the stepper motor needs to be rotated in
the reverse direction. This is accomplished by transferring the execution control of the
8/3/2019 Automatic Speed Limiter
14/28
14
microprocessor program to a subroutine that makes the stepper motor to rotate in the
reverse direction for the same angle as before.
4.2 CODE
MAIN SUBROUTINE
Table 4.1 Main routine
LABEL MNEMONICS COMMENT
MVI A, 00 Initialize flag to 0
STA 4200MVI A, 9C Configuring Port A as input
portOUT 0F
LOOP XRA A Clear the accumulator
IN 0C Get input from Port A
CPI 50
JC LOOP Wait for HIGH
LDA 4200 Check flag value
CPI 00
JZ FORW Call subroutine FORWJMP REV Call subroutine REV
8/3/2019 Automatic Speed Limiter
15/28
15
FORWARD SUBROUTINE
Table 4.2 Forward Sub-routine
LABEL MNEMONICS COMMENT
FORW MVI C,80START LXI H, LOOK UP
MVI B,04
REPT MOV A,M
OUT C0
DCR C
JZ END
LXI D, 0303
DELAY NOP
DCX D
MOV A,EORA D
JNZ DELAY
INX H
DCR B
JNZ REPT
JMP START
LOOK UP DB 09 05 06 0A (Data in reverse order in case of
REV)END XRA A
MVI A,01 SETS THE FLAG (RESETS the
FLAG In case of REV)
STA 4200
JMP LOOP
8/3/2019 Automatic Speed Limiter
16/28
16
4.3 PARALLEL PORT CONNECTORS (P4)
Fig 4.1 Parallel Port Connectors
Connector Used:
26 pin IDC male connector.
13 pins arranged in two rows.
Pin to pin pitch distance = 2.54 mm.
8/3/2019 Automatic Speed Limiter
17/28
17
Signal Description
Table 4.3 Signal Description
PIN DETAILS PIN DETAILS
1 PA0 14 PB52 PA1 15 PB6
3 PA2 16 PB7
4 PA3 17 PC0
5 PA4 18 PC1
6 PA5 19 PC2
7 PA6 20 PC3
8 PA7 21 PC4
9 PB0 22 PC5
10 PB1 23 PC6
11 PB2 24 PC712 PB3 25 GND
13 PB4 26 VCC
Signal Definition
PA0-PA7 = Port A I/O lines
PB0-PB7 = Port B I/O linesPC0-PC7 = Port C I/O lines
The peripheral interface IC 8255 should be configured before using it for I/O
operation. The mode control word to configure Port A as input is 9C.
8/3/2019 Automatic Speed Limiter
18/28
18
The following are the I/O addresses of 8255
Table 4.4 I/O Addresses of 8255
IC NO. Function Address
U3 Control Register 0FU3 Port A 0C
U3 Port B 0D
U3 Port C 0E
4.4 STEPPER MOTOR INTERFACING
The Stepper Motor is interfaced to the Microprocessor by the add-on card VBMB-
013A and the motor is made to run at constant speed.
VBMB-013A board is a microprocessor based stepper motor controller capable of
demonstrating the various modes of stepper motor operations. This board supports
stepper motor, ranging from 2 to 2Kg with operating voltages 6, 12 & 24V.The supply is
given externally.
Stepper motor requires logic signals of relatively high power. In this board the
silicon Darlington pair (TIP 122) transistors are used to supply that required power. The
driving pulses are generated by the interface circuit. The input for the interface circuit is
TTL pulses generated under software control using a microprocessor trainer kit. The TTL
level of pulse sequence from the data bus is translated to high voltage output pulses using
a buffer 7407 with open collector.
The Darlington pair transistor (TIP 122) drives the stepper motor as they withstand
higher current. A 220 ohm resistor and an IN4148 diode are collected between the power
supply and Darlington pair collector for supporting fly back current.
The data lines D0-D3 and D4-D7 are used to drive the 8 TIP 122 available on
this board. The four collector points of each TIP 122 are brought to two 5 pin connectors
8/3/2019 Automatic Speed Limiter
19/28
19
P2 & P3 to connect two different stepper motors. With this board it is possible to connect
stepper motor of torque ranging from 2 to 20Kg with operating voltage of 12, 24 & 6V.
Fig 4.2 Connection between a VBMB-13A Board to Microprocessor
Fig 4.3 Connection between a VBMB-13A to Power Supply
8/3/2019 Automatic Speed Limiter
20/28
20
CHAPTER 5
AUTOMOBILE SECTION
The end objective of speed limiting in the vehicle is accomplished in thecarburetor of the automobile. Here, the air-fuel mixture that is being injected into the
engine is limited. A valve is fitted to the outlet of the carburetor. The stepper motor is
coupled to the stem of the valve. In the normal case (when the vehicle is outside the
zone), the valve is fully open. The forward rotation of the stepper motor closes the valve
to a certain extent, thereby limiting the amount of combustion mixture that enters the
engine, which in turn limits the speed of the vehicle. The reverse rotation of the stepper
motor restores the valve to its normal position.
5.1 CARBURETOR PRINCIPLE
The carburetor is a device which mixes air and fuel for an internal-combustion
engine. Carburetors are still found in small engines and in older or specialized
automobiles such as those designed for stock car racing. However, most cars built since
the early 1980s use computerized electronic fuel injection instead of carburetion. The
majority of motorcycles still are carbureted due to lower weight and cost.
The carburetor works on Bernoulli's principle: the fact that moving air has lower
pressure than still air, and that the faster the movement of the air, the lower the pressure.
Generally, the throttle or accelerator does not control the flow of liquid fuel. Instead, it
controls the amount of air that enters the carburetor. Faster flows of air and more air
entering the carburetor draws more fuel into the carburetor due to the partial vacuum that
is created.
BERNOULLIS PRINCIPLE
Bernoulli's principle states that in fluid flow, an increase in velocity occurs
simultaneously with decrease in pressure. This principle is a simplification of Bernoulli's
equation which states that the sum of all forms of energy in a fluid flowing along an
enclosed path is the same at any two points in that path. It is named after the Dutch/Swiss
8/3/2019 Automatic Speed Limiter
21/28
21
mathematician/scientist Daniel Bernoulli, though it was previously understood by
Leonhard Euler and others. For a mathematical formulation, see Bernoulli's equation. In a
fluid flow with no viscosity, and therefore one in which a pressure difference is the only
accelerating force, it is equivalent to Newton's laws of motion. It is important to note that
the only cause of the change in fluid velocity is the difference in pressures either side of
it. It is very common for the Bernoulli Effect to be quoted as if it states that a change in
velocity causes a change in pressure. The Bernoulli principle does not make this
statement and it is not the case.
A common model used to demonstrate the Bernoulli Effect is a convergent,
divergent nozzle also called a venturi. This is simply a large diameter tube feeding into a
smaller diameter tube and then further feeding into another larger tube. Venturis are
easier to understand when considering a gas rather than a liquid, but the functions for
either are much the same. In order for any gas flow to occur it is essential that the exit
pressure is lower than the entry pressure for this system. This pressure difference causes
the fluid to accelerate from the intake larger tube into the smaller tube. The stored spring
energy available to the fluid because of the pressure difference results in the fluid not
only expanding as it goes from higher to lower pressure, but effectively overshooting in
its expansion as a result of the mass of the gas particles and compressibility of the gas,
springing apart beyond the point where all the forces would be balanced. Before the fluid
can spring back, there is more fluid behind it, also at this lower pressure. This first
sample of fluid then has no pressure difference either side of it to cause it to spring back.
This part of the fluid then remains at a lower pressure until it merges with the slower
fluid in the exit tube. The pressure in the exit tube will be higher than that in the smaller
middle tube, and so the fluid moving from the smaller to larger tube is slowed down by
this pressure difference.
8/3/2019 Automatic Speed Limiter
22/28
22
Fig 5.1 The Venturi in a Carburetor
5.2 OPERATION
Inside a carburetor is a venturi, Fig 5.1. The venturi is a restriction inside the
carburetor that forces air to speed up to get through. A river that suddenly narrows can be
used to illustrate what happens inside a carburetor. The water in the river speeds up as it
gets near the narrowed shores and will get faster if the river narrows even more. The
same thing happens inside the carburetor. The air that is speeding up will cause
atmospheric pressure to drop inside the carburetor. The faster the air moves, the lower the
pressure inside the carburetor.
Most motorcycle carburetor circuits are governed by throttle position and not by
engine speed. There are five main metering systems inside most motorcycle carburetors.
These metering circuits overlap each other and they are:
pilot circuit
throttle valve
needle jet and jet needle
main jet
choke circuit
8/3/2019 Automatic Speed Limiter
23/28
23
The pilot circuit has two adjustable parts, fig 5.2. The pilot air screw and pilot jet. The air
screw can be located either near the back side of the carburetor or near the front of the
carburetor. If the screw is located near the back, it regulates how much air enters the
circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it
is turned out, it opens the passage more and allows more air into the circuit which results
in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will
be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned
more than two turns out for best idling, the next smaller size pilot jet will be needed.
Fig. 5.2 Pilot Circuit
The pilot jet is the part which supplies most of the fuel at low throttle openings. It
has a small hole in it which restricts fuel flow though it. Both the pilot air screw and pilot
jet affects carburetion from idle to around 1/4 throttle.
The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially
affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various
8/3/2019 Automatic Speed Limiter
24/28
24
sizes and the size is determined by how much cutaway from the backside of it, fig 5.3 is.
The larger the cutaway, the leaner the mixture (since more air is allowed through it) and
the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on
them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a
3.0mm cutaway, while a 1 will have a 1.0mm cutaway (which will be richer than a 3).
Fig 5.3 The Slide Cutaway
The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet
needle is a long tapered rod that controls how much fuel can be drawn into the carburetor
venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the
mixture since the thicker taper will not allow as much fuel into the venturi as a leaner
one. The tapers are designed very precisely to give different mixtures at different throttle
openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves
and holds it from falling or moving from the slide. The clip position can be changed to
make an engine run richer or leaner, fig 5.4. If the engine needs to run leaner, the clip
would be moved higher. This will drop the needle farther down into the needle jet and
cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and themixture will be richer.
The needle jet is where the jet needle slides into. Depending on the inside diameter
of the needle jet, it will affect the jet needle. The needle jet and jet needle work together
to control the fuel flow between the 1/8 thru 3/4 range. Most of the tuning for this range
is done to the jet needle, and not theneedle jet.
8/3/2019 Automatic Speed Limiter
25/28
25
Fig 5.4 Jet Needle
5.3 FUEL INJECTION CONTROL
The main jet controls fuel flow from 3/4 through full throttle, fig 5.5. Once the
throttle is opened far enough, the jet needle is pulled high enough out of the needle jet
and the size of the hole in the main jet begins to regulate fuel flow. Main jets have
different size holes in them and the bigger the hole, the more fuel that will flow (and the
richer the mixture). Higher the number on the main jet, the more fuel that can flow
through it and the richer the mixture.
Fig 5.5 Main Jet and Fuel Flow
8/3/2019 Automatic Speed Limiter
26/28
26
A tap like restriction is placed in the outlet stream of the carburetor. This valve is
coupled to the stepper motor. When the stepper motor rotates in the forward direction, the
valve restricts the flow of the air-fuel mixture to some extent and so the speed is limited.
When the stepper motor reverses direction, the valve opens and so normal flow is
resumed.
8/3/2019 Automatic Speed Limiter
27/28
27
CHAPTER 6
CONCLUSION
The project has so far introduced the concept of a speed limit in critical zones like
hospitals, educational institutions, etc. By this, the project offers a wide range of
prospects for the future. This technique can be made generic to suit all kinds of places of
vehicular traffic and can be made global. The concept of a nominal speed limit in such
critical zones can be extended to traffic-dependent speed limits in various zones. For
example, highways can have maximum speed limit, arterial roads in cities can have a
moderate speed limit, while congested roads can have minimum speed limit. This can be
realized by using transmitters of different wavelengths in the different zones. The signal
conditioning needs minimal modification to accomplish this logic.
If this is realized, it will result in great reduction of accidents on roads and regular
movement on traffic on all kinds of roads. Also, the need for traffic regulating personnel
on the roads would then become antiquated.
For realizing multiple speed zones, transmitters with different wavelengths can be
used. The wavelength content can be decoded by the sensor with appropriate filter
circuits. A simple circuit to realize this logic could be a phase locked loop without
feedback. This can give a voltage proportional to the frequency of the transmitter. Then
this voltage can be conditioned and given to the microprocessor. The assembly program
needs a slight modification to implement the new logic.
8/3/2019 Automatic Speed Limiter
28/28
28
BIBLIOGRAPHY
1. Gaonkar R.S Microprocessor Architecture Programming and application
Wiley Eastern Ltd., New Delhi, 1995.
2. Roy Choudhury and Shail Jain, Linear Integrated Circuits Gupta & Co.,
(1995).
3. Sergio Franco, Design with Operational Amplifiers and Analog Integrated
Circuits, 2nd Edition Tata McGraw Hill, New Delhi, 1997.
4. S. Tomweather, Automotive Electronics Tata McGraw Hill Publishers, New
Delhi, 1999.
5. Web Reference wikipedia.org, carbresearch.com