Vehicle Speed Mearurement System Final2

VEHICLE SPEED MEASUREMENT

SYSTEM

TABLE OF CONTENTSTopic Page No.

CERTIFICATE ....................................................................................................... 2

DECLARATION ..................................................................................................... 3

ACKNOWLEDGEMENT… .................................................................................... 4

ABSTRACT.............................................................................................................. 5

CHAPTER 1.INTRODUCTION.............................................................. ................ 6

1.1. The Basic Concept ....................................................................................... 7

1.2. Circuit Description...................................................................................... 8

1.3. Components List.......................................................................................... 10

CHAPTER 2.CONSTRUCTION AND WORKING

2.1. Construction………………………………………………………………... 12

2.2. PCB layout…………………………………………………………………. 13

2.3. PCB designing ………….…………………………………………………. 14

2.4. Coding………………………………………………………………………. 19

CHAPTER 3.Component Description

3.1. Resistance…………………………………………………………….....32

3.2.

Capacitor………………………………………………………………...33

3.3. Semiconductor Diode ………………………………………………….. 34

3.4. LED……………………………………………………………………. 35

3.5. Laser……………………………………………………………………..37

3.6 LDR ……………………………………………………………………...42

3.7 PIC16F877 Microcontroller…………………………………………….. 44

3.8.Voltage regulator IC 7805 ……………………………………………… 55

3.9 Transformer……………………………………………………………... 57

CHAPTER 4.CONCLUSION ……………………………….………………… 59

BIBLIOGRAPHY…………………………………………………………… ... 60

ABSTRACT

With the advent of modern era an exponential increase in the number of vehicle the

number of accident has risen alarmingly. One of the main reasons for such a rise is the

negligence of drivers especially on highway, where less traffic seemingly allow him to

take a negligent approach toward safety rules. Often high speeding vehicles pose a

danger to fellow commuter .This project aspire to solve such problem by measuring the

vehicle speed and then giving alarm in case of overspeed.

CHAPTER 1

INTRODUCTION

The system “Vehicle Speed Measurement System” has come into existence, to prevent

accidents that keep occurring due to speed violation, since the drivers tend to ignore their

speedometers. Speed measurement using a light barrier is achieved by using transmitter

and receiver. They are basically implemented on highways.

This speed checker will come handy for the highway traffic police as it will not only

provide a 16X2 LCD Module Display in accordance with a vehicle‘s speed but also

sounds an alarm if the vehicle exceeds the permissible speed for the highway.

The system basically comprises of two laser transmitter- Ultrasonic sensor pairs, which

are installed on the Highway 100m apart, with the transmitter and the sensor of each pair

on the opposite sides of the road.

1.1 BASIC CONCEPT

The system displays the time taken by the vehicle in crossing this 100m distance from

one pair to the other with a resolution of 0.01second, from which the speed of the vehicle

can be calculated as follows:

Speed (kmph) = Distance/Time

= 0.1km/{(Readingx0.01)/3600}

Or,

Reading = 3600/Speed (On display)

As per the above equation, for a speed of 40kmph the display will read 900(or 9seconds),

and for a speed of 60kmph the display will read 600 (or 6 seconds). Note that the LSB

of the display equals 0.01second and each succeeding digit is 10 times the preceding

digit. Then if the speed cross a prescribed limit through alarm we may know it.

.

.1.2 CIRCUIT DESCRIPTION

The circuit consists of major parts:

1) The power supply

2) The transmitter section :- ultrasonic sensor

3) The micro controller section

The power supply is used to convert to ac to dc via transformer, then with the help of

voltage regulator IC 7805 a 5 Volt dc supply and through IC 7806 a 6 volt dc supply is

obtain .The need of these supply arises due to the fact that every electronic component

either works on a 5 v and 6 v dc supply

The transmitter section consists of a two laser transmitters.

The receiver section consists of two ultrasonic detectors; these two detectors catch the

rays coming from the transmitter. When a object pass through the first pass it blocked

the light coming from the first transmitter which is noted by the first detector and when

the object passes through the second transmitter then the absence of light is obtained by

the second detector .Then the distance is calculated by the microcontroller .

The microcontroller is the main controlling section of the project. It performs a number

of functions. It is attached through the two photo detector through two forward bias

transistor which serves as amplifiers to amplify the current received.

The second function of microprocessor is to calculate speed of travelling vehicle with

help of elapse time measurement method.

This microcontroller is then attached to a buzzer which produces an alarm if the speed of

vehicle exceed a specified speed limit .Microcontroller is also interfaced with a 16X2

LCD Module display which shows the vehicle speed.

1.3 COMPONENT LIST:

1. Resistors (all ½ watt, ± 5% carbon)

Quantity Value

7 10K

6 1K

1 20K

2.Capacitors

Quantity Value

2 470uF,25V electrolytic

2 22 pF, 25V electrolytic

1 1000uF, 35V electrolytic

3. Integrated Circuits

Quantity Value

1 16X2 LCD Module display

1 PIC16f8777A

1 7805 , 5V regulator

4. Diodes

Quantity Value

2 IN4007, rectifier diode

3 Light Emitting Diode

2 Laser Diodes

5. Miscellaneous

Quantity Value

1 230V AC primary to 12-0-12V, 500mA

secondary transformer

1 4 MHz, Crystal Oscillator

2 Push-to-on switch

1 On/Off switch

2 Transistors

Ultrasonic Range Meter

The Ultrasonic Range Meter is an efficient way to measure the distance of unreachable

obstacles. It is based on sending sound waves through a specific medium and observing the

returning echoes to measure the distance from the device to the obstacle.

The device is divided into three parts, transmitter, receiver and the microcontroller. The

transmitter consists of an electronics circuitry which generates electrical signal .In addition, an

electromechanical transducer to convert electrical signal to physical form to drive through the

medium, which is air. The receiver also consists of an electronics circuitry which detects the

echoes bounced back from the obstacles. The microcontroller is programmed for selectivity

sequence and to calculate the time of flight of the signal to find the distance and display it.

The system architecture of the Ultrasonic Range Meter was built to be cheaper, requires less

power and delivers better performance. It can be reconfigured to adapt to a variety of pulsed

Ultrasonic systems.

Introduction

The main purpose of this project is to measure the distance to unreachable objects, obstacles or

places using a portable device.

0

Figure 2.1: The hand-held ultrasonic range meter device.

2.2 Motivation

The motivation of using this device is when construction engineers at any sites need to measure

distances to unreachable places in a quick and easy way using this device with high efficiency

and accuracy.

2.3 Characteristics

This device detects the distance to an object and shows the result in centimeters. This device is

activated by a trigger mechanism, pressing the trigger for one time will give us the distance to

an object if there was no error like poor aiming. The distance to an object is displayed using a

digital display with a high intensity in order to be seen in any lighting conditions.

It is a simple and portable device similar to a gun as shown in Figure 2.2 that uses a laser pointer

to aim at a specific area to get the reflection at the receiver side.

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Figure 2.2: Description of each part of the device.

2.4 Conclusion

In order to design and build a portable device, the weight of the device is a primary problem.

The technology of using ultrasonic to measure distances is in continuous progress, features have

been added to this technology to make it easy to use and more accurate by assigning more

challenging constraints. The constraints of our device are discussed in the next chapter.

3.1 Introduction

Defining the constraints of our device will help to design and then build the hand-held ultrasonic

range meter device. By defining these constraints, the problems will be clearer, the suitable

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solutions will become easier to find and those constraints will help to get the design needed

from the engineer.

3.2 Minimum target size and ultrasonic medium

The minimum target size is 40cm*40cm in order to get detection at the receiver side.

The ultrasonic medium is air.

3.3 Target range

The target range is the distance range between the person who is using the hand-held ultrasonic

range meter device and the targeted object. The target range consists of two boundaries, one is

the minimum distance limit and the other is the maximum distance limit. If the operator of the

hand-held ultrasonic range meter device exceeds these two boundaries, the hand-held

ultrasonic range meter device may not detect the distance or may display a false detection.

The target range is between 10 centimeters and 300 centimeters.

3.4 Range measurement accuracy

Each specific distance has an error percentage; the more samples sent the less the error is.

The range measurement accuracy is the accuracy of the distances measured between the

operator of the hand-held ultrasonic range meter device and the targeted object; it allows

knowing how much each distance is close to the real value of the distance. The range

measurement accuracy is +/- 3 cm. The less this value is, the more accurate distances would be

calculated by the hand-held ultrasonic range meter device.

3.5 The battery

A 9 V battery could be used to activate this device.

3.6 Weight and size

Our device would not exceed the weight 0.5 kilogram. This weight is acceptable for the operator

to carry the hand-held ultrasonic range meter device and to fix his arm while aiming at the

targeted object.

The area of the cover is 15cm x 7 cm, and the height is 8 cm.

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3.7 Budget

This hand-held ultrasonic range meter device is between 50 U.S dollars and 75 U.S dollars.

3.8 Time

The time estimated to accomplish the hand-held ultrasonic range meter device is one month

due to the changes in the constraints.

3.9 Number of engineers

The number of engineers working on the hand-held ultrasonic range meter device is three

engineers.

3.10 Conclusion

After discussing and choosing the constraints, the solutions for these sets of challenging

problems are to be discussed and solved physically and mathematically in the next chapter.

4.1 Introduction

To solve the problem of detecting the distance to an object, many solutions are presented. In this

chapter the solutions are discussed, all the advantages and disadvantages are shown. The

comparison between these solutions will help to determine which solution has more advantages

and satisfies the constraints at the same time.

4.2 Hand-held laser range meter device

4.2.1 Description

This device is characterized by its accuracy and portability; it uses a laser beam. The two

techniques might be used to measure the distance. There are two techniques that have been

used in order to measure distances, the time of flight technique and the triangulation technique.

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4.2.1.1 Time of flight measurement

Even the fastest photon requires a certain period of time to cover the distance from the sensor

to the target and back. This time is directly proportional to the distance traveled, taking into

account the velocity of light in the medium involved, which may be easily derived from the

velocity of light in a vacuum. The cost and complexity of this method depends upon the

precision and resolution required.

Data acquisition and analysis electronics must cope with ns and sub-ns time scales: decimeter

ranges may be easily resolved by nanosecond pulses but precision in the millimeter and sub-

millimeter range requires pulse lengths of a few tens of picoseconds and the associated

electronics. Clearly, a poorly resolved pulse will lead to uncertainty in the accuracy of the

measurement; the standard deviation in measured distance is proportional to the optical pulse

rise time and is inversely proportional to the signal-to-noise ratio. At ranges of a few kilometers

and above, a different problem arises; at such distances the amount of reflected photons which

reach the detector is very small. Signal intensity can be improved by optimum beam focusing at

the source, or by the use of a retro reflector mounted in the target.

4.2.1.2 Triangulation

Triangulation is the most commonly used method for distances of 10 meters or less. A laser or

LED is used to produce a collimated beam which then impinges on the surface of the target. The

target reflects light in many directions, some of the reflected light reaching the detector. The

position of the reflected light focused onto the detector depends on the distance between the

sensor and target. Detectors such as position sensitive detectors (PSD), diode arrays or CCD

arrays enable the reflected light to be detected with high spatial resolution and at high sampling

frequencies. The sensor-object distance is calculated trigonometrically and accuracies of better

than 0.5% are the norm.

5

Measurement times of less than 10 ms are common, allowing real-time study of moving or

vibrating objects. The light source should be compact and should produce an intense, small spot

of light with minimal divergence. Amplitude modulation is used in order to eliminate the effects

of stray (background) light.

Figure 4.1: Hand-held laser range meter device.

4.2.2 The advantages

As shown in Figure 4.1, the hand-held laser range meter device is a portable device.

It is characterized with its high accuracy and high precision. The laser beam consists of a small

beam width which reaches a long target range.

4.2.3 The disadvantages

The poor aiming on the targeted object causes a bad reflection of the laser and that would

display a false detection of the object’s distance that has been targeted.

The atmospheric conditions may affect the ranging capabilities of the hand-held laser range

meter device. The rain and snow reflect the laser beam and that may display a false detection of

the object’s distance.

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4.3 Hand-held ultrasonic range meter device

4.3.1 Description:

This device works on the same concept of the laser gun device but the difference is that it uses a

large beam width of ultrasonic waves as shown in Figure 4.2. The time of flight and triangulation

techniques might be used to measure the distance using ultrasonic waves.

Figure 4.2: Hand-held ultrasonic range meter device.

4.3.2 The advantages

The hand-held ultrasonic range meter device is a portable device as shown in Figure 4.2. The

hand-held ultrasonic range meter device is characterized with its precision and high accuracy.

Atmospheric conditions will not affect the capabilities of the device.

4.3.3 The disadvantages

The beam of the hand-held ultrasonic range meter device consists of a large beam width as

shown in Figure 4.2 and that may cause a false detection of the object’s distance at the receiver

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side because the beam may hit a group of objects placed near each others and the reflection of

the ultrasonic wave is caused by several objects. The object must be flat and not an absorber

and it should be normal to the direction of the ultrasonic wave. This device could be jammed

and is affected by interference.

4.4 Comparison

After looking at the advantages and the disadvantages, the best solution is to use the gun device

using laser beams. The beam width of the hand-held laser range meter device is smaller than

the beam width of the hand-held ultrasonic range meter device as shown in Figure 4.5; this

enables the operator of the hand-held laser range meter device to hit a specific object and get

less reading errors unlike other devices.

The comparison has shown that the hand-held ultrasonic range meter devices could be better in

some cases because it will not be affected by the atmospheric conditions. As shown in Table 4.1,

using a descending order from the best accuracy and precision of the devices to the worst, the

most accurate and precise is the hand-held laser range meter device. The second is the hand-

held ultrasonic range meter device. Depending on our constraints, our choice was to design an

ultrasonic range meter because of the budget and availability of the components.

Table 4.1: Solutions comparison with respect to its accuracy and precision.

Devices Hand-held laser

range meter

Hand-held ultrasonic

range meter

Accuracy High accuracy High accuracy

Precision High precision Precise

8

Figure 4.3: Beam width comparison of ultrasonic waves and laser beams.

4.5 Conclusion

Each solution has its advantages and disadvantages depending on the situation where the

device is used; the hand-held laser range meter device is a fast growing technology because of

its efficiency and its accuracy as well as the hand-held ultrasonic range meter device as shown in

Table 4.1. In the next chapter the design of the hand-held ultrasonic range meter device will be

implemented.

CHAPTER 5

All designs are based on specific constraints. The design of the hand-held ultrasonic range meter

device is based on measuring the distance using the time of flight technique. The process of this

design is more explained in details in the next section.

5.2 The overall system

The calculations are done by the following way. First of all, the device calculates the time that

the ultrasonic wave took to reach the targeted object and come back to the receiver. Thus, if we

need to calculate the time needed for the ultrasonic wave to reach the object from the device,

we divide the previous time we had by two. Second, the device multiplies the time by the speed

of sound (340 m/s) to get the distance between the device and the object. The time from

transmission of the pulse to reception of the echo is the time taken for the sound energy to

travel through the air to the object and back again. Since the speed of sound is constant through

air, measuring the echo reflection time lets you calculate the distance to the object using this

equation:

Distance = (s * t)/2 (in meters) (5.1)

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Where: s [m/s] is the speed of sound in air and t [s] is the round trip echo time.

Table 5.1: The delay times of boundary range

Round trip echo

time

Distance

t = 588 us10 cm

t = 17.6 ms3 m

.

Figure 5.1: General block diagram.

5.2.1 Calculation of the distance to an object

The hand-held Ultrasonic Range meter device offers precise ranging information from roughly

10cm to 3 meters. The ranger works by transmitting a pulse of sound outside the range of

human hearing. This pulse travels at the speed of sound away from the ranger in a cone shape

and the sound reflects back to the ranger from any object/target in the path of this sonic wave.

The ranger pauses for a brief interval after the sound is transmitted and then awaits the

reflected sound in the form of an echo. The controller driving the ranger then requests a ping;

the ranger creates the sound pulse, and waits for the return echo. If received, the ranger reports

this echo to the controller and the controller can then compute the distance to the object based

on the elapsed time.

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The Pulse Trigger Input line should be held low and then brought high for a minimum of 100μsec

to initiate the sonic pulse. The pulse is generated on the falling edge of this input trigger. The

ranger’s receiver circuitry is held in a short blanking interval of 600 μsec to avoid noise from the

initial ping and then it is enabled to listen for the echo. The echo line is low until the receive

circuitry is enabled. Once the receive circuitry is enabled, the falling edge of the echo line signals

an echo detection or nothing if there is no reflection.

The long-range measurement is difficult a little. To measure the correct distance, the following

conditions are necessary.

The object must be perpendicular to the range meter.

The surface of the object must be flat.

There is not object which reflects the ultrasonic around.

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Figure 5.2: Theoretical graph of the pulses and its echo-reflection pulse.

5.3 Ultrasonic system

It consists of a transmitter and receiver pair on the device and a microcontroller with a digital

display. There are two different transducers for transmitter and receiver. The transmitter

transmits and the receiver waits for the reflected signals. The Figure 5.3 illustrates this system.

Figure 5.3: The overall design of the ultrasonic system.

5.3.1 Ultrasonic Transmitter

The transmitter consists of an electronics circuitry and an electromechanical transducer.

The electronic circuitry generates the required frequency electrical signal and the

electromechanical transducer converts that electrical signal into the physical form and activates

the open medium surface. This oscillating physical surface creates the ultrasonic Waves. The

oscillating surface creates a pressure variation and ultimately a pressure wave with a frequency

equal to that of the surface oscillation. The Figure 5.4 shows the generation of ultrasonic waves.

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Figure 5.4: The transmitter circuit design.

The transmitter was designed to oscillate at a resonant frequency of about 40 KHz. The 555

timer generates a 40 KHz sinusoidal ultrasonic wave. The frequency is calculated by using the

following formula:

F = 1.44 / 2 * R1 * C = 1.44 / 2 * 15.6 KΩ * 1nF = 46 kHz. (5.1)

This design of the transmitter was done in way to get the closest value to 40 KHz by adjusting

the resistor and the capacitor to the values shown in the Figure 5.4.

5.3.1.1 The 555 timer datasheet

The 555 monolithic timing circuits is highly stable controller capable of producing accurate time

delays, or oscillation .In the delay time of operation, the time is precisely controlled by one

external resistor and capacitor .For a stable operation as an oscillator, the free running

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frequency and the duty cycle are both accurately controlled with two external resistors and one

capacitor. As shown in Figure 5.5:

Figure 5.5: The 555 block diagram.

The Table 5.2 shows the datasheet of the 555 timer, the parameter rating and the units

characterized by each component.

Table 5.2: The datasheet of the 555 timer

Symbol Parameter Rating Unit

VCC Supply Voltage +16 V

Pd Maximum allowable power

dissipation 600 mW

TAOperating ambient

temperature range0 to 70 ºC

VTH (Vcc = 5v) Threshold voltage 3.33 V

VTRIG(Vcc = 5v) Trigger Voltage 1.67 V

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VRESET Reset Voltage 0.3 to 1.0 V

.5.3.2 Ultrasonic Receiver

The receiver also has the same configuration except that it has a receiver electronic circuitry and

a transducer, which converts the ultrasonic sound waves into an electrical signal. The sound

waves travel into the medium and are reflected by an object in the path of the waves. This

reflected wave is then sensed by the receiver, which actually calculates the time of flight of the

signal to find the distance. The Figure 5.6 illustrates the receiver circuit.

Figure 5.6: The receiver circuit design.

5.3.2.1 Basis of the operational amplifier

The operational amplifier is the amplifier with the very big voltage gain.

In case of TL082 to be using this time, at the specification, the voltage gain becomes 150V/mV. It

is the 15 V output in 0.1 mV of the input. To say becomes 150,000 times of gain. In case of the

15

operational amplifier, the value of the voltage gain doesn't have the relation too much. Anyway,

the fact that the voltage gain is big is important.

5.3.2.2 The Difference Gain amplification

There are positive input and negative input in the operational amplifier.

The voltage gain can be calculated by the following formula.

G = Vo/Vi = -(Rf/Ri) (5.2)

Figure 5.7: The difference gain amplification.

Using the voltage divider formula:

Vb = V1 * R2/(R1 + R2) (5.3)

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The current passing through Ri is the same current passing through Rf because the current

entering the negative input is negligible in μA (in the ideal operational amplifier, it is considered

zero) and this gives the following equation:

(Vi – Va) / Ri = (Va – Vo) / Rf (5.4)

Vo = (V1 * R2 * (Rf + Ri) / (R1 + R2) * Ri)– Vi * Rf / Ri (5.5)

5.3.2.3 Signal amplification circuit

The signal amplification circuit is illustrated below in the Figure 5.8.

Figure 5.8: The circuit of the signal amplification.

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The ultrasonic signal which was received with the reception sensor is amplified by 2500 times

(68dB) of voltage with the operational amplifier with two stages.

The voltage gain G is 100 times at the first stage (40dB) and 25 times (28dB) at the next stage.

Generally, the positive and the negative power supply are used for the operational amplifier.

The circuit this time works with the single power supply of +5 V. Therefore, for the positive input

of the operational amplifiers, the half of the power supply voltage is applied as the bias voltage

and it is made 2.5 V in the central voltage of the amplified alternating current signal.

When using the operational amplifier with the negative feedback, the voltage of the positive

input terminal and the voltage of the negative input terminal become equal approximately. So,

by this bias voltage, the side of the positive and the side of the negative of the alternating

current signal can be equally amplified. When not using this bias voltage, the distortion causes

the alternating current signal. When the alternating current signal is amplified, this way is used

when working the operational amplifier for the two power supply with the single power supply.

Using the formula in 5.1:

Vi is the input voltage at the ultrasonic transducer.

Vo1 is the output voltage of the first amplification stage.

Vo2 is the output voltage of the second amplification stage.

At minimum distance, d = 10 cm,

Vi max = 2.50004 V.

Vo1 = (5 * 47K * (100k + 1k) / (47k + 47k) * 1K) - 2.50004 * 100k / 1k = 2.496 V.

Vo2 = (5 * 47K * (100k + 3.9k) / (47k + 47k) * 3.9K) - 2.496 * 100k / 3.9k = 2.6 V.

At maximum distance, d = 3 m,

Vi max = 2.4999 V.

Vo1 = (5 * 47K * (100k + 1k) / (47k + 47k) * 1K) - 2.4999 * 100k / 1k = 2.46 V.

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Vo2 = (5 * 47K * (100k + 3.9k) / (47k + 47k) * 3.9K) - 2.46 * 100k / 3.9k = 2.50156 V.

ΔVi = 2.50004 – 2.4999 = 0.04 mV.

A slight change in Vi formed a bigger change in Vo2.

Δ Vo2 = ΔVi * Gain = 0.04 * 2500 = 100 mV.

5.3.2.4 Data of the TL082 operational amplifier

As for TL082, the two operational amplifiers are enclosed with the one package.

Figure 5.9: Pin connections top view.

Table 5.3: The datasheet of the TL082 operational amplifier.

Symbol Symbol Value Unit

19

Supply VoltageVCC

VEE

+18

-18V

Differential Input Voltage VID ±30 V

Input Voltage Range VIDR ±15 V

Output Short Circuit Duration tSC Continuous

Power Dissipation

(Plastic Package)

PD

1/8JA

680

10

mW

mW/°C

Operating Ambient

Temperature RageTA 0 - +70 °C

Storage Temperature Range Tstg -65 - +150 °C

Slew rate SR 16 V/μs

Gain bandwidth product GBW 4 MHz

The magnitude of the input voltage must not exceed the magnitude of the supply voltage or

15V, whichever is less. The output may be shorted to ground or either supply. Temperature

and/or supply voltages must be limited to ensure that power dissipation ratings are not

exceeded.

For the 741 operational amplifier, GBW = 1 MHz, SR = 0.5 V/μs.

For the TL082 operational amplifier, GBW = 4 MHz, SR = 16 V/μs.

Vi(t) = 0.04 cos ( 40000 * 2 * Π * t) mV.

Vo(t) = 100 cos ( 40000 * 2 * Π * t) mV.

(Vo(t)) = 2 * Π * 40000 * 0.1 = 0.025 V/μs.′

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0.025 V/μs < 0.5 V/μs the 741 operational amplifier could be used.

0.025 V/μs < 16 V/μs the TL082 operational amplifier could be used.

The TL082 operational amplifier has a better slew rate.

For a 10% error in the frequency, F = 40000 * 0.9 = 36000 Hz.

The required gain bandwidth product for a gain = 2500 is,

GBW = 36000 * 2500 = 90 MHz > 4 MHz.

The signal amplification is split into two stages because of this gain bandwidth product.

The maximum gain G max = 4 MHz / 36000 Hz = 111.11.

The maximum gain is greater than the gain for the first stage 100 and the second stage 25.

5.3.3 Detection circuit

The detection is done to detect the received ultrasonic signal. It is the half-wave rectification

circuit which used the 1N4148 diodes.

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Figure 5.10: The detection circuit.

The DC voltage according to the level of the detection signal is gotten by the capacitor

behind the diode. The 1N4148 diode is used because it is a fast switching diode.

5.5 Power supply and battery

The Ultrasonic transmitter and receiver require four connections to operate. First there are the

power and ground lines. The Ultrasonic transmitter and receiver require a 5V power supply

capable of handling roughly 50mA of continuous output. The remaining two wires are the signal

wires, one to enable or disable the transmitter and the other to get the returned echo. The

microcontroller needs also a 5V to operate. This 5V power supply is got using a regulator. The

user can use a 12V DC power supply or a 9V battery to operate this device illustrated in Figure

5.13.

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Figure 5.13: The power supply circuit.

5.6 Ultrasonic sensors

A market survey has been done to select the best available ultrasonic proximity sensor available

at that time. The following are some of the sensors that have been considered for the

development of this system.

Table 5.5: The Ultrasonic sensor specifications.

Transducer Range Beam

angle

Measurement speed Frequency Sensitivity

SQ-40T/R 10 cm - 3 m 30º 20 ms 40 Khz high

SensComp

600

15 cm –10.7 m 15º 200 ms 50 Khz good

The ultrasonic transducers are optimized for 25 kHz, 32 kHz, 40 kHz or wide bandwidth

transducers. This project uses a 40 kHz transducer but it will still work with the others if the

appropriate changes to the software are being made. The receiver and generator circuits will

work as they are. The 40 kHz signal is easily generated by the microcontroller but detection

requires a sensitive amplifier and a peak detector. Transducers are devices that convert

electrical energy to mechanical energy, or vice versa. The transducer converts received echoes

into analog electrical signals that are output from the transducer. Ultrasonic transducers

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operate to radiate ultrasonic waves through a medium such as air. Transducers generally create

ultrasonic vibrations through the use of piezoelectric materials such as certain forms of crystals

or ceramic polymers. The overall capacitance of a transducer is dependent upon the area and

the thickness of the piezo material.

Ultrasonic transducers are available in various technical forms. Ultrasonic transducers are

typically formed of either piezoelectric elements or of micro-machined ultrasonic

transducer (MUT) elements. For industrial use, solid-state transducers are usually used,

because of their robustness. They basically include a piezoceramic device as an element

for converting between electric signals and acoustic signals and a resonant adapter layer,

with which the transfer of sound to the air is optimized. The piezoelectric elements

typically are made of a piezoelectric ceramic such as lead-zirconate-titanate (PZT), with a

plurality of elements being arranged to form a transducer. Piezoceramic ultrasonic

transducers are the transducers of choice for rugged, industrial applications because they

are efficient and environmentally robust. These sensors have been used in industry for

numerous applications; however have not been capable of short range object detection

until recently. A micro-machined ultrasonic transducer (MUT) is formed using known

semiconductor manufacturing techniques resulting in a capacitive ultrasonic transducer

cell that comprises a flexible membrane supported around its edges over a silicon

substrate. The membrane is supported by the substrate and forms a cavity. The MUT may

be electrically energized to produce an appropriate ultrasonic wave. Similarly, when

electrically biased, the membrane of the MUT may be used to receive ultrasonic signals

by capturing reflected ultrasonic energy and transforming that energy into movement of

the electrically biased membrane, which then generates a receive signal. Capacitive

micro-machined ultrasonic transducers (cMUTs) are tiny diaphragm-like devices with

electrodes that convert the sound vibration of a received ultrasound signal into a

modulated capacitance. For transmission the capacitive charge is modulated to vibrate the

diaphragm of the device and thereby transmit a sound wave. In general, ultrasonic

transducers are constructed by incorporating one or more piezoelectric vibrators which

are electrically connected to pulsing-receiving system. [3]

5.6.1 Electrostatic Ultrasonic Sensors

24

Electrostatic ultrasonic sensors operate similar to an electrical capacitor. These sensors usually

are composed of a fixed conductive plate and a free metallic surface coated with a layer of

insulation that separates the two plates.

When an electric potential is placed across the fixed conductive plate, the free metallic surface

is pulled against the fixed plate. When an oscillating electrical potential is applied to the fixed

plate, the free plate oscillates at a similar frequency thereby creating acoustic pressure waves.

When receiving an ultrasonic signal, the Electrostatic ultrasonic sensors produce a varying

capacitance created by the pressure waves hitting the free metallic surface.

5.6.2 Piezoelectric Ultrasonic Sensors

Piezoelectric ultrasonic Sensors are composed of a Piezo material and an acoustic surface. The

Piezo material can either be a crystal or ceramic. The Piezo material is attached to the acoustic

surface such that any physical changes in the geometry of the material will affect the acoustic

surface.

When an electrical potential is placed across the Piezo material, the geometry changes thereby

disturbing the acoustic surface.

When an oscillating electrical potential is placed across the Piezo material, the acoustic surface

generates an acoustic signal. When receiving an ultrasonic signal, the ultrasonic waves strike the

acoustic surface thereby compressing the Piezo material.

The Piezo material emits electrons when compressed thereby creating an electrical signal.

Piezoelectric materials vibrate in response to alternating voltages of certain frequencies applied

across the material. Piezoelectric elements are similar to common analog capacitors in that

piezo elements generally include two electrodes separated by a piezoelectric material that

functions as a dielectric, shown in Figure 5.14 and the sensitivity with respect to frequency is

described in Figure5.15.[3]

25

Figure 5.14: The SQ-40T/R ultrasonic transducer.

Figure 5.15: The sensitivity of the SQ-40T/R with respect to the frequency.

26

5.7 The schematic of the ultrasonic range meter design:

The functionality of this system can be divided into three main parts as shown in Figure

5.27; the transmitter, the receiver, the microcontroller and the digital display.

The transmitter, enabled via the microcontroller, is designed to activate a 555 oscillator with a

frequency of 40 KHz. The width of the pulse is 0.1 ms, every 40 ms a pulse is transmitted.

One of the most important and sophisticated part of the device is the receiver.

The receiver consists of a signal amplification stage and peak detection stage.

The signal is amplified by a gain of 2500 in order to reduce the noise effect.

In order to reduce the cost of the power supply of the device, the +/- Vcc was avoided and 0-5 V

power supply was used in the design of the signal amplification stage.

The peak detection is used to transform the signal into a pulse.

The microcontroller controls all the parts in the device and performs all the arithmetic

calculations of the distance and displays it on the 7-segment digital display. This process of

distance calculation is continuously repeated as long as the device is turned on.

The laser pointer on the device is used to pinpoint the target in order to get less error caused by

the malfunction use of the device.

The program used in the PCB design is ExpressPCB which is a professional program.

The design of the PCB is splitted into two PCB circuits as shown in Figures 5.28, 5.29; one for the

transmitter and receiver and the other for the microcontroller with transistors used to enable

the 7-segment display.

27

Figure 5.16: The overall schematic of the Ultrasonic range meter.

Figure 5.17: The printed circuit board diagram of the microcontroller.

6.1 Factors affecting the performance of Ultrasonic sensors

Position/distance measurement using ultrasonic sensors is based on the principle of measuring

the time of flight of the ultrasonic waves in a particular medium. There are number of factors

28

which affect the accuracy of measurement and therefore should be taken into consideration

while designing the ultrasonic sensing system. The following are some of the factors.

6.1.1 Radiation pattern:

All ultrasonic sensors have their specific radiation pattern associated with it.

This acoustic radiation pattern is a function of spatial angle called beam angle. Beam angle, Ω

is defined as the total angle between the points at which the sound power reduces to half its

peak value, commonly known as 3 dB points.

The spot diameter of the beam can be formulated as.

D = 2R tan (0.5 Ω) (5.6)

Where, D = spot diameter in centimeters.

R = target range in centimeters.

Ω = beam angle in degrees.

At minimum range, R = 10 cm and Ω = 30º.

D = 2 * 10 * tan (15º) = 5.358 cm.

At maximum range, R = 300 cm and Ω = 30º.

D = 2 * 300 * tan (15º) = 160.769 cm.

Radiation pattern consists of a main lobe and side lobes. Radiation power is dominant mainly in

the front region of the sensor, so as to say that the main lobe is directly in front of the sensor,

followed by side lobes sidewise with null region in between these lobes.

Radiation pattern is mainly determined by factors such as the frequency of operation and the

size, shape and acoustic phase characteristics of the vibrating surface. The beam pattern of the

transducer is independent of its nature as a transmitter or receiver.

29

In most of the application, side lobes are suppressed and narrow beams are used. This

suppression is achieved by the processing system and so, the radiation pattern of the transducer

may not be same as the radiation pattern of the whole ultrasonic sensing system. The

narrowness of the beam pattern is a function of the diameter of the radiating surface to the

wavelength of the sound at the operating frequency. As the D/λ ratio increases, beam narrows

out whereas as D/λ ratio decreases, beam broadens. For most of the application narrow beam is

desired and therefore D/λ ratio should be more. The following Figures 6.1, 6.2 show the

radiation pattern, its main lobe and side lobes with the relative attenuation.

Figure 6.1: Geometric approximation of the ultrasonic beam width.

30

Figure 6.2: Beam pattern with respect to amplitude.

6.1.2 Frequency, wavelength and attenuation:

The frequency of the ultrasonic sensing system is determined by the resonant frequency of the

ultrasonic transducer. The selection of this transducer is made considering number of factors

such as transducer size, measurement resolution, measurement range, background noise and

attenuation. The wavelength of the ultrasonic wave can be found out with the following

formula,

λ = C/f (6.1)

Where λ is the wavelength, C is the velocity of sound equal to 340 m/s at 20º C and f is the

frequency equal to 40 KHz.

C, velocity of sound varies with variation in temperature, pressure, medium type, humidity, air

turbulence, conventional currents. So before calculating the wavelength, the speed of sound is

required to be calculated.

λ = 340/40 = 8.5 mm.

6.2 Environmental factors:

The attenuation of sound power depends on the speed of sound, which depends on many

environmental factors like temperature, medium, pressure, humidity, acoustic interference,

radio frequency interference.

6.2.1 Temperature

The velocity of sound in a medium varies with temperature. So, the time taken by the sound to

echo back to the receiver will vary and since this time of flight is proportional to the measured

31

distance. The measured distance will vary with the variation in temperature. Thus the variation

in temperature introduces errors in the measurement.

The sound wave propagation speed in the air depends on the temperature. So, to measure the

distance more correctly, it is necessary to revise according to the temperature. The sound wave

propagation speed can be calculated using one of the two formulas.

V = 331.5 + 0.6 * T [ m/sec ] (6.2)

T : The temperature (°C)

Table 6.1: The speed of sound at each temperature.

Temperature (°C) in air Speed of sound (m/sec)

-10 325.5

0 331.5

10 337.5

20 343.5

30 349.5

40 355.5

50 361.5

32

300

310

320

330

340

350

360

370

-10 0 10 20 30 40 50

Temperature ºC

Spee

d of

sou

nd m

/s

Figure 6.3: Graph of speed with respect to temperature

In this project, the speed of sound used in this program is 340 m/s because this speed is relative

to the temperature 20 ºC which is an average value. A temperature sensor could be added to

this project with a small manipulation to the program, in order to use the right speed value. In

this way, this device would be used in all atmospheric conditions. [4]

6.2.2 Pressure and humidity

As the pressure reduces, the density of particle in the medium decreases thus providing less and

less resistance to the traveling wave. Although slightly pressure effects the velocity of sound

wave, humidity which is defined as the moisture content in the medium basically has a very little

effect on the velocity of sound but it actually effect the radiating surface. The acoustic pressure

p must satisfy the three-dimensional wave equation.

(6.3)

6.2.3 Medium

33

Velocity of sound depends on the kind of medium the sound travels. Sound speed varies with

different medium. The Table 6.2 summarizes some of the medium with the sound velocity in it.

Table 6.2: The ultrasonic wave speed through different mediums

Medium Speed, m/s at 10°C

Air 331.5

Ammonia 414.8

Argon 301.9

Carbon Dioxide 257.8 (low frequency)

Carbon Disulfide 184.7

Carbon Monoxide 337.1

Chlorine 205.4

Ethylene 313.9

Helium 969.8

Hydrogen 1269.4

Illuminating Gas 490.4

Methane 431.9

Neon 434.9

Nitric Oxide 324.9

Nitrogen 334.06

Nitrous Oxide 261.8

Oxygen 317.2

34

.

6.2.4 Acoustic Interference

If the environment contains number of objects that generates background noise and if this

background noise falls in the sensitive frequency of the receiver of the ultrasonic sensing

system, it will result in erroneous measurement.

This error is more pronounced when the amplitude/power of the background noise is more then

the echo itself resulting in very low SNR (signal to noise ratio), which is undesirable. Typically,

the background noise is less at higher frequency and so narrow beam angles works best in an

area where background noise is high.

6.2.5 Radio Frequency Interference

Radio frequency signal present in the environment also affects the ultrasonic sensing system.

6.3 Target Consideration

The principle of ultrasonic sensing is based on transmission of sound wave followed by the

reflection of the echo. These echoes are summed up at the receiver. The return echo is a

function of target distance, geometry, surface, size, composition, orientation of object/sensor

etc.

6.3.1 Composition

Some of the objects are good reflector and some are good absorber. So the amount of echo

returned back depends on the kind of material the object is composed of. This finally effects the

35

measurement as it varies from object to object for the same fix distance of the target from the

sensor. The object must not be composed of soft surfaces that absorb most of the sound energy.

6.3.2 Size and shape

Size and shape affects the amount of echo reflected back to the receiver. For example, for large

planner object (object size >> beam size) almost all the ultrasonic wave will be reflected back to

the receiver. Whereas in case where the object is very small as compared to the beam size, then

part of the ultrasonic sound wave will be reflected to the receiver and the rest will be lost. The

shape determines the angle at which the ultrasonic wave will be reflected. Common to all

ultrasonic ranging systems is the problem of ultrasonic reflection. With light waves, our eye can

see objects because the incident light energy is scattered by most objects, which means that

some energy will reach our eye, despite the angle of the object to us or to the light source. This

scattering occurs because the roughness of an object's surface is large compared to the

wavelength of light 550 nm. Only with very smooth surfaces such as a mirror does the

reflectivity become highly directional for light rays. Ultrasonic energy has wavelengths much

larger 6.35 mm in comparison. Therefore, ultrasonic waves find almost all large flat surfaces

reflective in nature. The amount of energy returned is strongly dependent on the incident angle

of the sound energy.

Figure 6.4 shows a case where a large object is not detected because the energy is reflected

away from the receiver.

36

Figure 6.4: Undetected large object due to reflection.

6.3.3 Position and Orientation

If the size of object is small as compared to the beam size, then the measurement depends on

the position of the object in the beam region. When object is on the main lobe axis, the

reflected echo reaching to the receiver will be very strong and if it is out of axis, the reflected

echo will be weak.

Although the basic range formula is accurate, there are several factors when considering the

accuracy of the result. Since the speed of sound relies on the temperature, a 10N temperature

difference may cause the range to be in error by 1%.

Geometry also affects range in two major ways. The range equation assumes that the sonar

beam width is negligible. An object may be off center, but normal to the transmitted beam. The

range computed will be correct, but the X-component may be in error. Using the formula: X = R

* sin f (6.4)

At a range of 9 meters and a beam width of 30N, the X component would be 2.33 meters off

center. Figure 6.5 illustrates this.

37

Figure 6.5: Object offset due to ultrasonic beam width.

Another geometric effect is shown in Figure 6.6. When the object is at an angle to the receiver,

the range computed will be to the closest point on the object, not the range from the center line

of the beam. This is called cosine error.

Figure 6.6: Range error due to angle between object and sonar.

38

6.4 Power of the detected signal

We need to calculate the power of the detected laser beam in order to detect the reflection at

the receiver in a maximum distance range. Power of the detected signal is calculated by the

following way:

Pdet = Pult * є * δ * S / (4 * π * R²) (6.5)

Pult is the power of the emitted ultrasonic wave.

S is the object target area that reflected the echo.

R is the distance between the device and the target.

є is the target response to the ultrasonic wave.

δ is the geometric form-factor for propagation of the ultrasonic wave and the response signal

through the ambient media (air, water …).

6.5 Noise

The output of the sensor involves noise, which is primarily introduced because of the

uncertainty of the echo which might comes back from the false object/target. Also the

attenuation of the sonic burst depends on the position of the object/target in the lobe region.

6.6 Errors

In general it is desired to develop the worst case analysis to permit the design of the hand-held

ultrasonic range meter device capable of operation under all conditions with a minimum error

(maximum acceptable error is +/- 3 cm). The errors associated with both calculations and

measurements can be characterized with regard to their accuracy and precision as shown in

Figure 6.7. Accuracy refers to how closely a computed or measured value agrees with the true

39

value. Precision refers to how closely individual computed or measured values agree with each

other.

Figure 6.7: (a) The samples are inaccurate and imprecise. (b) The samples

are accurate and imprecise. (c) The samples are inaccurate and

precise. (d) The samples should be accurate and precise in order

to get the acceptable error.

6.6.1 Truncation errors

The truncation errors are those that result from using an approximation in place of an exact

mathematical procedure.

For a distance that is being measured, the hand-held ultrasonic range meter device showed a

distance R but the real distance was R +/- 3 cm. This means that the error is at its maximum.

40

At a minimum distance range, with the distance equal to 10 cm.

T1 is the real time of the real distance for the echo to propagate, get reflected by the targeted

object then get back to the receiver.

T1 = (0.1 m * 2) / 340 m/s = 588 μs.

T2 is the time captured by the microcontroller for the echo to propagate, get reflected by the

targeted object then get back to the receiver.

T2 = (0.12 m * 2)/ 340 m/s = 705 μs.

Truncation error = ((T2 – T1)/T2) * 100 = 16.6 %. (6.6)

At a maximum distance range, with the distance equal to 300 cm.

T1 is the real time of the real distance for the echo to propagate, get reflected by the targeted

object then get back to the receiver.

T1 = (3 m * 2) / 340 m/s = 17.6 ms.

T2 is the time captured by the microcontroller for the echo to propagate, get reflected by the

targeted object then get back to the receiver.

T2 = (3.07 m * 2)/ 340 m/s = 18.05 ms.

Truncation error = ((T2 – T1)/T2) * 100 = 2.54 %. (6.7)

6.6.2 Cosine error

41

The effect attributable to cosine error occurs with ultrasonic when the position of this ultrasonic

range meter device is not in true alignment with the target. Since the distance to be determined

is relative to the position of the object with respect to the position of the device, any deviation

from true alignment results in an increase in the distance displayed.

CHAPTER 2

CONSTRUCTION AND WORKING

2.1 CONSTRUCTION

Assemble the circuit on a PCB. An actual-size, single-side PCB layout for speed checker

is shown in fig. and its component in other one. Before operation using a multi meter

check whether the power supply output is correct. If yes, apply power supply to the

circuit by flipping switch S3 to ‘on’. In the circuit use long wires for connecting the two

LDRs, so that you can take them out of the PCB and install on one side of the highway,

100metres apart.

42

Install the two laser transmitters (such as laser torches) on the other side of the highway

exactly opposite to the ultrasonic . Reset the circuit by pressing switch S2, so the display

shows ‘0000.’ Using switch S1, select the speed limit (say, 60 kmph) for the highway.

When any vehicle crosses the first laser, ultrasonic will trigger IC. The output of IC goes

high for the time set to cross 100 meters with the selected speed (60 kmph) and LED1

glows during this period. When the vehicle crosses the second laser light, the output of

IC2 goes high and Led2 glows for this period. Buzzer sounds an alarm if the vehicle

crosses the distance between the lasers set ups at more than the selected speed (lesser

period than preset period). The counter starts counting when the first laser beam is

intercepted and stops when the second laser beam is intercepted.

The time taken by the vehicle to cross both the laser beams is displayed on the LCD

display. For 40kmph speed setting, with timer frequency set at 100Hz, if display count is

less than ‘600,’ it means that the vehicle has crossed the speed limit (and simultaneously

the buzzer sounds). Reset the circuit for monitoring the speed vehicle.

2.2 PCB LAYOUT

43

2.3 PCB DESIGNING

Printed circuit board is a piece of art. The performance of an electronics circuit depends

upon layout and design of PCB. Various steps in design of PCB are explained.

44

The general consideration while artwork is discussed below:

PCB is used to rout electrical current & signal through copper track, which are firmly

bounded to an insulating base. The material used for PCB is paper phenolic which is less

costly & used in consumer electronics circuits. Paper phenolic is more resistant to

moisture but difficult to machined drill as glass epoxy.

Rules for Layout

PCB interconnects various electronic components by an interconnection. The general

considerations are:

1. Mechanical considerations, size shape, mounting PCB etc.

2. User system considerations whether for consumer or laboratory or industry.

3. Electrical & electronic parameters such as impedance, gain, electromagnetic

coupling etc.

4. Ease of maintenance.

Designing

Now-a-days PCB has become an important factor during designing various circuits.

Advantages of PCB over normal wiring:

1. PCB is necessary for interconnecting a large no. Of component in very small area

with minimum parasitic wiring effect.

2. PCB is suitable for the mass production with less chance of wiring effect.

3. Wiring is avoided.

4. Servicing is easier.

5. By using PCB, electronic equipment becomes more reliable, small in size & less

costly.

6. Small component are easily mounted on PCB.

7. Construction is neat, small & truly a work of art.

45

2.3.1 Production of PCB manually

To prepare the PCB manually following procedure is accepted:

1. Measure the dimension of components such as resistor, capacitor or diodes.

2. Measure the proper space between terminals of active components such as

transistor, IC’s etc.

3. Decide high density or low-density circuit. Use vertical mounting wherever

possible.

Measure the dimension of components and spacing between terminals of IC’s. Draw the

layout as in artwork using trace paper & carbon paper. Draw the image of figure.

Then cake holes into PCB by using drill machines (after etching is done). Avoid drilling

before etching.

After drying pen ink, keep PCB in FeCl3 solution & add some HCI for faster etching.

After drilling the PCB, draw layout using etching pen of good quality & leave it drying.

During etching unwanted copper is dissolved FeCl3 solution & wanted copper tracks are

saved below ink.

Procedure

The procedure of making of PCB consists of following steps:

(I) Drawing of the lay out.

(II) Printing of PCB

(III) Etching of PCB

Drawing of the layoutWith the circuit diagram and the entire component at hand, we draw a complete lay out

plan on a graph paper. We should care regarding location shape utilization and we keep

the line on the other side as for as possible, we trace the complete layout on a trace paper.

Printing of PCB

46

We cut the referred size of PCB using hawk saw and file. Now we put carbon paper on it.

Since the tracing paper transparent we can now reproduce carbon paint over the carbon

surface by using ball pen over it.

Etching of PCB

Etching is a process of attacking & removing the unprotected & unwanted copper from

PCB to yield desired conductor pattern. The most common etchant used in industry is

ferric chloride. Theoretically any one of following solution can used to etch the board:

1. Ammonium persulphate.

2. Cupric acid

3. Cupric chloride

4. Ferric chloride

Method of etching includes tray rocking, tank etching & spray etching. Out of these, tray

rocking is simplest one. These consist of a tray of Pyrex glass attached to a power-

rocking table, if power-rocking table is not available, rocking of tray with etching

solution can be done manually also.

Ferric chloride crystals of 500 gm. are mixed in water to make a total solution of 1 liter

Cupric & ferric ions precipitate out of solution the room of sludge that tends to settle at

bottom of etching bath. Ideal etch condition requires that etchant be heated to a

temperature between 60-70 degrees.

The PCB is immersed in etchant solution width copper side up in the tray. Only one

board should be etched at a time, as the table is rocked the unprotected copper dissolves.

When etching is completed the board is rinsed under water &then allowed to dry. Using

lacquer thinner or acetic acid or petrol removes the resist material. After the resist has

been removed, clean the copper. After the board is inspected & inspected & approved, it

is ready for whole drilling, component mounting then for soldering.

47

Soldering Technique

Soldering

Soldering is a process for the jointing metal parts with the addition of solder where the

melting temperature is solvated below that of material joined.

Selection of Proper Soldering Iron

There should be a proper soldering iron for each type of job, as we know that metal is a

very good conductor of neat therefore when soldering on a metal, chassis of heavy iron is

used.

But it will not practical to use such type of iron on a PCB used in project because heat

dissipation on the other side could damage a PCB a low wattages (35w)’ soldering iron is

used for this purpose.

Selection of solder

Selection of proper solder wire for the job is the major consideration in the making of

good soldering connections it should be of low melting temperature metal consisting

basically of fin and load with varying amount of other metal such as a antimony and

cadmium to give alloys various physical purpose in the process of joining of two metal

together the solder detach a small amount of surface of each at temperature below there

melting point the action of melting solder on metal is similar to the action of water on salt

generally the composition used fro the solder in 60% tin and 40% lead.

Flux

The application of a proper flux is a necessary link in the soldering chain the metal we

commonly used in electronics is usually converted with a fine non-metallic film called

“oxide”. The major function of the flux is to deal with the metal oxide.

Soldering Technique

48

1. Proper iron should be selected or a special job. A side tipped, high voltage is

necessary when soldering on a metal chassis pen. For PCB repairing a low

wattage pencil iron should be recommended tip of which should be narrow.

2. The iron tip should be kept clean, when iron is used continuously. It is exposed to

air and the tip may become oxidized oxidization can be prevented by keeping the

tip may clean at all the time.

3. When the iron is turned, the tip should be whipped removed any excessive metal

solder. A ray should never be used to write the tip because it may have small

deposit of carbon instead of a commercial tip cleaner.

4. The area to be soldered should clean at all the time. It may look clean. A thin

oxide film may be present and prevent proper soldering only or greasily deposit or

small bit or large material should be cleaned, that may be embedded on the

surface to be soldered purpose.

5. A flat face of a well-sheeted iron should be applied against the surface to be

soldered. This should be heated to a high temperature enough to melt the solder.

6. The solder should be removed first and when the iron on junction should be

distributed or more any portion of it.

7. When the surface is sufficiently heated, the solder is applied to the deposit and not

to melt and flow freely towards the iron.

8. The area around the junction should be checked to any excess solder on tinning

plate, which can cause shorts.

9. The excess of solder should be removed and cleaned.

49

CHAPTER3

COMPONENT DESCRIPTION

3.1 RESISTOR

Resistor is a component of an electric circuit that resists the flow of direct or alternating

electric current. Resistors can limit or divide the current, reduce the voltage, protect an

electric circuit, or provide large amounts of heat or light.

An electric current is the movement of charged particles called electrons from one region

to another. The amount of resistance to the flow of current that a resistor causes depends

on the material it is made of as well as its size and shape. Resistors are usually placed in

electric circuits, which are devices formed when current moves through an electrical

conductor.

When a voltage, or electric potential, is applied to opposite ends of a circuit, it causes

current to flow through the circuit. As the current flows, it encounters a certain amount of

resistance from the conductor and any resistors in the circuit. Each material has a

characteristic resistance. For example, wood is a bad conductor because it offers high

resistance to the current; copper is a better conductor because it offers less resistance. In

any electric circuit, the current in the entire circuit is equal to the voltage across that

circuit divided by the resistance of the circuit. Resistors are often made to have a specific

value of resistance so that the characteristics of the circuit can be accurately calculated.

50

Resistors are designed to have a specific value of resistance. Most resistors used in

electric circuits are cylindrical items a few millimeters long with wires at both ends to

connect them to the circuit. Resistors are often color coded by three or four color bands

that indicate the specific value of resistance. Some resistors obey Ohm’s law, which

states that the current density is directly proportional to the electrical field when the

temperature is constant. The resistance of a material that follows Ohm’s law is constant,

or independent of voltage or current, and the relationship between current and voltage is

linear.

3.2 CAPACITOR

Capacitor, or electrical condenser, is a device used for storing an electrical charge. In its

simplest form a capacitor consists of two metal plates separated by a non-conducting

layer called the dielectric. When one plate is charged with electricity from a direct-

current or electrostatic source, the other plate will have induced in it a charge of the

opposite sign; that is, positive if the original charge is negative and negative if the charge

is positive. The electrical size of a capacitor is its capacitance, the amount of electric

charge it can hold.

Capacitors are useful when direct current must be prevented from entering some part of

an electric circuit. Fixed-capacity and variable-capacity capacitors are used in

conjunction with coils as resonant circuits in radios and other electronic equipment.

51

Large capacitors are also employed in power lines to resonate the load on the line and

make it possible for the line to transmit more power.

Capacitors are produced in a wide variety of forms. Air, mica, ceramics, paper, oil, and

vacuums are used as dielectrics, depending on the purpose for which the device is

intended.

3.3 SEMICONDUCTOR DIODE

Circuit Diagram

Diode is a electronic device that allows the passage of current in only one direction. The

diodes, most commonly used in electronic circuits today are semiconductor diodes. The

52

simplest of these, the germanium point-contact diode, dates from the early days of radio,

when the received radio signal was detected by means of a germanium crystal and a fine,

pointed wire that rested on it. In modern germanium (or silicon) point-contact diodes, the

wire and a tiny crystal plate are mounted inside a small glass tube and connected to two

wires that are fused into the ends of the tube.

3.4 LED

A diode is an electronic component through which current passes in only one direction.

Light-emitting diodes (LEDs) are semiconductors that produce light when current passes

through them. They are used in many common devices, such as the tuning indicator on a

radio. An arrangement of seven LEDs in the shape of an ‘8’ can be used to display any

number from 0 to 9. This arrangement is often used on calculators and digital watches.

Light-Emitting Diode (LED), device that emits visible light or infrared radiation when an

electric current passes through it. LEDs are made of semiconductors, or electrical

conductors, mixed with phosphors, substances that absorb electromagnetic radiation and

re-emit it as visible light. When electrical current passes through the diode the

semiconductor emits infrared radiation, which the phosphors in the diode absorb and

53

reemit as visible light. The visible emission is useful for indicator lamps and

alphanumeric displays in various electronic devices and appliances. Devices such as

remote controls and cameras that focus automatically use infrared LEDs, which emit

infrared radiation instead of visible light.

Light-emitting diodes use the properties of electroluminescence, in which certain

substances emit electromagnetic radiation when excited by the flow of an electric current,

and fluorescence, in which some substances absorb wavelengths of electromagnetic

radiation other than visible light and re-emit the radiation as visible light. When charged

particles such as electrons pass through certain semiconductors, they boost to higher

orbits one or more electrons in some of the atoms in the semiconductor. When these

electrons fall back to lower orbits, the atom emits infrared radiation. When this radiation

strikes a phosphor atom, electrons in the phosphor atom jump to higher orbits. The

phosphor atom emits visible light when the electrons fall back to a lower orbit.

54

3.8 VOLTAGE REGULATOR IC 7805

LM78XX Series Voltage Regulators

General Description

The LM78XX series of three terminal regulators is available with several fixed output

voltages making them useful in a wide range of applications. One of these is local on card

regulation, eliminating the distribution problems associated with single point regulation.

The voltages available allow these regulators to be used in logic systems,

instrumentation, Hi-Fi, and other solid state electronic equipment. Although designed

primarily as fixed voltage regulators, these devices can be used with external components

to obtain adjustable voltages and currents.

The LM78XX series is available in an aluminum TO-3 package which will allow over

1.0A load current if adequate heat sinking is provided. Current limiting is included to

limit the peak output current to a safe value. Safe area protection for the output transistor

is provided to limit internal power dissipation. If internal power dissipation becomes too

high for the heat sinking provided, the thermal shutdown circuit takes over preventing the

IC from overheating.

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Considerable effort was expanded to make the LM78XX series of regulators easy to use

and minimize the number of external components. It is not necessary to bypass the

output, although this does improve transient response. Input bypassing is needed only if

the regulator is located far from the filter capacitor of the power supply. For output

voltage other than 5V, 12V and 15V the LM117 series provides an output voltage range

from 1.2V to 57V.

Features

Output current in excess of 1A

Internal thermal overload protection

No external components required

Output transistor safe area protection

Internal short circuit current limit

Available in the aluminum TO-3 package

Voltage Range

LM7805C -5V

LM7812C -12V

LM7815C -15V

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3.9 TRANSFORMER

MUTUAL INDUCTANCE

When current flows through a coil, magnetic field is induced around the coil. When A.C.

Supply is given to coil, then since there is positive and negative half cycles in a A.C.

cycle. So there magnetic fields also attains maximum and minimum values. If we place

another coil in the magnetic fields of first coil then their produces a voltage in expound

coil. Transformer works on that principle.

Coil L1 is connected to A.C. source. This coil is called primary coil. When alternating

current flows through the coil then there induces a alternating magnetic field. In a half

cycle the direction of current through the coil is as shown by arrow, this current makes

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North Pole of upper end of coil L1. As the value of current increases, the magnetic field

cut the turns of coil L2. Due to this there produces a induced Electromagnetic force (emf)

and thus current flows though the load resistance, in this way due to flow of terminating

current in coil L1 there an alternating current flows through coil L2 also.

In transformer both coils are wounded is opposite direction to each other. Here current

starts to flow from upper end of coil L1. This current causes upper end positive. The

induced magnetic field produced produces current in secondary coil L2 and so there

voltage induces. The positive end of induces. The positive end of induced voltage in

secondary is at upper end of secondary and negative end is at lower end of coil. In that

type of transformer the secondary voltage in 180 out of phase with primary voltage. This

relationship is known as signal inversion.

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After completion of first half cycle, the current flow through coil L1 stops for a moment

since at this time input is passing through 180. As current decreases, magnetic fields in

L1 become eliminate. Later on current through coil L1 decrease, there current through

coil L1 also decreases. In next half cycle the current through coil L1 reverses its

direction. Due to this there produces opposite polarity magnetic field through around the

coil. Again this field cuts the turns of coil L2 and produced EMFF in L2. The polarity is

reversed, so polarity of induced voltage in coil L2 in also reversed. In this way in this half

cycle also there current flows through the secondary.

CHAPTER 4

CONCLUSION

The monitoring of speed of the vehicles on the highway is necessary and this model

presents a simple and economical solution to this problem. However there are several

advancements that can be made. One of it is the use of microcontrollers.

We can also use a GSM modem to inform the administering authorities regarding any

over speeding vehicles. In this case the modem will enable the system to send a message

regarding the vehicles identity to the required person on the mobile.

Another system which is being used practically in this field is the Doppler radar. This

system is based on the phenomenon of Doppler Shift to measure to speed of the vehicle.

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Bibliography

BOOK REFERENCES

1. Boylestad , Robert L. and Nashelsky Louis, Electronic Devices and Circuit

Theory, Pearson Education, 2002.

2. Mano Morris M., Digital Design ,Prentice Hall India, New Delhi, 2002.

3. Sedra Adel S. and Smith Kenneth C., Microelectronic Systems,Oxford University

Press,2006.

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WEBSITE REFERENCES

www.geocities.com

www.efymag.com

www.google.com

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