automatic speed limiter

8/3/2019 Automatic Speed Limiter

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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.


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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


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CHAPTER 2

TRANSMITTER SECTION

Fig 1.1 Detailed Block Diagram


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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


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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.


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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.


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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


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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


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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


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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.


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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.


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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


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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


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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


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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.


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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.


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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


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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


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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


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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.


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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


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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


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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.


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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


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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.


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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.


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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

automatic speed limiter

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