WALKING STICK FOR THE VISUALLY CHALLENGED USING

INFRARED DISTANCE SENSOR

AINI FARIZA BINTI MOHD MUSTAFA

Submitted to the Faculty of Electrical Engineering

in partial fulfilment of the requirement for the degree of

Bachelor in Electrical Engineering (Medical Electronic)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

MAY 2009

ii

iii

To my beloved mother, father, brothers and sisters

iv

ACKNOWLEDGEMENT

First and foremost, I would like to express my gratitude to my supervisor, Dr.

Rubita Binti Sudirman for the guidance and support given to me during the progress

of this project. Your patience and enthusiasm to help me to complete this project are

much appreciated.

My appreciation also goes to all my members for their love, supports and

ideas which are really encourage me to finish my final year project. Nevertheless, my

thankfulness is also to the technicians of Medical Electronic Laboratory (MEP) who

always lend their hands preparing the equipments I needed in the lab. I also want to

express my gratitude for my friends and those who involve directly and indirectly in

this project.

v

ABSTRACT

Blindness is not a new phenomenon in the society. It is a condition of lacking

visual perception and always described as severe visual impairment with residual

vision. The legally blind people are those who have the visual acuity of 20/200 or

(6/60). It means that a blind person needs to stand within 20 feet (6 meters) to see an

object which someone with normal visual acuity can see from 200 feet (60 meters)

away. The legally blind people has trouble seeing things which other people take for

granted, like road signs, traffic lights, and so forth. They are more prone to falls and

other accidents because they cannot clearly discern their surrounding environment.

The visually challenged people or the blind people are always trying their best to be

normal and comfortable in surroundings. However their life and activities are greatly

restricted by loss of eyesight. Many people with serious visual impairments can

travel independently, using a wide range of tools and techniques. They are taught

how to travel safely, confidently, and independently in the home and the community.

They can find the way easily if they are familiar with an environment or route. The

most important mobility aid used by them is a walking stick or also known as

walking cane. The conventional walking stick employed by the visually challenged

people is actually not efficient to detect the object in front of the user. They can only

detect the object that is being hit by the walking stick. A walking stick for the

visually challenged people using the infrared distance sensor will become a great

help to them because this kind of walking stick is able to detect the object in the

specific range. In this project the distance range used is 10cm to 80 cm. When an

object is detected, sound alarm from a buzzer will alert the user about the object and

the person can avoid the object safely without hitting the object. As the distance of

the object and the user is closer, the loudness of the buzzer is increasing. The user is

able avoid the obstacles better using the newly designed walking stick.

vi

ABSTRAK

Cacat penglihatan bukanlah satu fenomena baru dalam masyarakat. Ia

merupakan suatu keadaan penglihatan yang tidak jelas dan disifatkan sebagai

kerosakan visual teruk. Orang buta adalah mereka yang mempunyai ketajaman

penglihatan 20/200 atau (6/60). Ini bermakna seorang buta perlu berdiri pada jarak 20

kaki (6 meter) untuk melihat objek yang orang normal dapat lihat dengan jelas pada

200 kaki (60 meter). Orang buta mengalami kesukaran untuk melihat objek, tanda

jalan, lampu isyarat dan lain-lain. Mereka lebih mudah mengalami kemalangan

kerana mereka tidak boleh melihat dengan jelas keadaan di sekeliling. Orang buta

selalu mencuba yang terbaik untuk berjalan seperti orang normal dan berada dalam

keadaan selesa di persekitaran. Bagaimanapun aktiviti mereka sangat terhad

disebabkan kehilangan penglihatan. Orang buta boleh bergerak bebas menggunakan

pelbagai peralatan berjalan dengan teknik tertentu. Mereka telah diajar untuk

mengembara dengan selamat, yakin dan bebas di rumah dan persekitaran. Mereka

dapat mencari jalan dengan mudah jika telah biasa dengan sesuatu persekitaran atau

laluan. Pergerakan dari satu tempat ke tempat yang lain adalah penting dan bantuan

yang digunakan adalah sebatang tongkat. Tongkat konvensional yang digunakan

tidak efisyen untuk mengesan objek yang berada di depan pengguna. Mereka hanya

boleh mengetahui terdapat objek di depan mereka dengan mengesannya dengan

tongkat. Sebatang tongkat untuk orang buta yang menggunakan pengesan jarak

inframerah akan menjadi alat bantu yang penting buat mereka kerana tongkat ini

dapat mengesan objek dalam julat jarak tertentu. Dalam projek ini, julat jarak yang

digunakan adalah dari 10cm sehingga 80 cm. Apabila suatu objek dikesan, bunyi

buzer akan kedengaran untuk menarik perhatian pengguna dan pengguna dapat

mengelak objek tersebut tanpa perlu mengetuk objek dengan tongkat. Semakin dekat

jarak objek dengan pengguna, bunyi buzer menjadi semakin kuat. Pengguna dapat

bergerak dengan lebih bebas dan lebih baik dengan menggunakan tongkat baru ini.

vii

TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION OF THESIS ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xiv

LIST OF APPENDICES xvi

1 INTRODUCTION

1.1 Background 1

1.2 Problem Statement 2

1.3 Objective of Project 3

1.4 Scope of Work 3

1.5 Outline of Thesis 3

1.6 Summary of Works 4

viii

2 THEORY AND LITERATURE REVIEW

2.1 Introduction 5

2.2 Medical Information of Blindness 5

2.2.1 Process of Vision 6

2.2.2 Visual Acuity 7

2.2.3 Causes 9

2.2.3.1 Cataracts 9

2.2.3.2 Glaucoma 10

2.2.3.3 Macular Degeneration 10

2.2.3.4 Diabetic Retinopathy 10

2.2.3.5 Retinitis Pigmentosa 11

2.3 Tools 11

2.3.1 Mobility 12

2.3.2 Communication 14

2.4 Infrared Light 15

2.5 Types of Distance Sensor 16

2.5.1 Infrared Proximity Sensor 16

2.5.2 Capacitive Proximity Sensor 17

2.5.3 Inductive Proximity Sensor 19

2.5.4 Acoustic Proximity Sensor 20

2.6 Infrared Distance Sensor 21

2.6.1 Reflection 22

2.6.2 Line detection 22

2.6.3 Triangulation 23

2.7 Sharp Infrared Rangers 23

2.7.1 IR-LED 24

2.7.2 Light Dependent Resistor Strip 25

2.7.3 Charge-coupled Device 27

2.7.4 Types of Sharp Infrared Distance Sensor 31

2.8 Schmitt Trigger 32

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3 METHODOLOGY

3.1 Introduction 36

3.2 Block Diagram 37

3.3 Design and Specification 37

3.3.1 Sharp GP2Y0A21YK0F

Infrared Distance Sensor 38

3.3.2 Schmitt Trigger Circuit 40

3.3.3 Buzzer 41

3.3.4 Long stick 42

4 RESULT AND DISCUSSION

4.1 Introduction 44

4.2 Schmitt Trigger Circuit Calculations 44

4.3 Experiment: Determine the Relationship

between the Distance of Object from

Infrared Distance Sensor and the Output

Voltage 46

4.3.1 Procedures 47

4.3.2 Experimental Result Analysis 47

4.4 Walking Stick with R Distance Sensor Model 49

5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 52

5.2 Recommendation 53

REFERENCES 54

APPENDICES 56

x

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Project Schedule for Semester 1 4

1.2 Project Schedule for Semester 2 4

2.1 Characteristic of Infrared LED 25

3.1 Specifications of Sharp GP2Y0A21YK0F 39

4.1 Distance versus Output Voltage 48

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LIST OF FIGURE

FIGURE NO. TITLE PAGE

1.1 The Conventional Walking Stick 2

2.1 Anatomy of Human Eye 6

2.2 Process of Vision 6

2.3 Snellen Chart 8

2.4 Folded Long Cane 13

2.5 Support Cane 13

2.6 A blind man with a Guide Dog 14

2.7 Capacitive Proximity Sensor Circuit 17

2.8 Capacitive Proximity Sensor 18

2.9 Inductive Proximity Sensor Circuit 20

2.10 Inductive Proximity Sensor 20

2.11 Object Detection Using IR Light 21

2.12 IR Reflection Sensor 22

2.13 Triangular IR Sensor 23

2.14 The Inner Workings of an LED 25

2.15 Light Dependent Resistor Symbol 26

2.16 Basic Structure of Light Dependent Resistor 27

xii

2.17 Light Dependent Resistors 27

2.18 The Anatomy of A Charge-coupled Device 28

2.19 CCD Photodiode Array Integrated Circuit 30

2.20 The Rangers of IR Detectors 31

2.21 Output Voltage to Distance Curve 32

2.22 Schmitt Trigger Symbol 33

2.23 A Single Input Schmitt Trigger Circuit 34

2.24 Hysteresis Curve 35

3.1 Block Diagram of the Walking Stick 37

3.2 Distance Sensor 38

3.3 Wires Connection of Sharp GP2Y0A21YK0F 38

3.4 Block Diagram of GP2Y0A21YK0F 39

3.5 Distance of Sharp GP2Y0A21YK0F vs Output Voltage 40

3.6 Schmitt Trigger Circuit 41

3.7 Buzzer 42

3.8 Polyvinyl Chloride (PVC) 43

4.1 The Experiment Flow Diagram 47

4.2 Graph of Distance versus Output Voltage 48

4.3 The Best Fit Curve to Represent the Data 49

4.3 The Walking Stick with IR Distance Sensor 50

4.4 The IR Distance Sensor 50

4.5 Battery and Buzzer 51

4.6 Switch 51

xiii

LIST OF SYMBOLS

Ω - Resistance

V - Voltage

THz - Frequency Terahertz (x1012

)

GHz - Frequency Gigahertz (x109)

cm - Centimeter (x10-2

)

mm - Millimeter (x10-3

)

µm - Micrometer (x10-6

)

nm - Nanometer (x10-9

)

≈ - Approximation

λ - Wavelength

xiv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Sharp GP2Y0A21YK0F Datasheet 56

B LM358N Datasheet 66

1

CHAPTER 1

INTRODUCTION

1.1 Background

More than 161 million people worldwide are visually impaired. Among them,

124 million have low vision and 37 million are blind. Another 153 million people

suffer from visual impairment due to uncorrected refractive errors such as near-

sightedness, far-sightedness or astigmatism. Virtually all these people could restore

normal vision with eyeglasses or contact lenses. More than 90% of the world's

visually impaired people live in low- and middle-income countries. Except in the

most developed countries, cataract remains the leading cause of blindness.

Blindness is a condition of lacking visual perception and it is always

described as severe visual impairment with residual vision. The blind people’s life

and activities are greatly restricted by loss of eyesight. They can only walk in fixed

routes that are significant in their lives, with blind navigation equipments and the

accumulated memories in their long-term exploration. This situation has resulted in

many difficulties to them in their normal work, lives, activities, and so on. Based on

the investigation about daily activity characteristics and modes of the blind, the study

found that the main difficulties encountered in a trip of the blind included walking on

the road, finding way, taking a bus and looking for usual life-arena.

Several devices have been developed for mobility and navigation assistance

of the blind and are typically known as travel aids or blind mobility aids. The most

successful and widely used travel aid is the long cane. The walking cane used by the

visually challenged people is a white cane with a red tip which is the international

2

symbol of blindness. It is used to detect obstacles on the ground, uneven surfaces,

holes, steps, and puddles. Blind pedestrians usually tap their cane on the ground, and

the resulting vibrations indicate the nature of the surface. Tapping also produces

sound, which is then reflected by nearby obstacles. Very skillful travelers are able to

detect these echoes and their direction of origin.

1.2 Problem Statement

Walking stick or walking cane is the most important equipment needed by the

blind people to help them walking. The conventional walking stick used by them

which is a long white cane that is relatively easy to use, light and not expensive.

However its range of detection is very limited and it is only used to detect the object

which is near to the user. The user has to tap the ground or the object to detect the

obstacle. The foremost disadvantage of the conventional cane, however, is its failure

to detect obstacles outside of its reach. Figure 1.1 shows the conventional walking

stick currently used by the blind people.

The visually challenged people can avoid the object better if the walking

stick can produces audible warning when there is an object in the specific range of

distance. This kind of travel aid is able to alarm them about the object in front of

them by producing sound when the distance sensor detects the object in the specific

distance range.

Figure 1.1 The Conventional Walking Stick

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1.3 Objective of Project

The objective of this project is to design a walking stick that produces sound

alarm to alert the blind people about an object in front of them within specific range.

1.4 Scope of Work

This project is focusing on the detection of object that is in front of the user

within the specific distance range which is depending on the type of distance sensor

used. In this project, an infrared (IR) distance sensor is going to be used. As the

object is closer to the sensor, the signal produced is increased as well. The signaling

mean of the walking stick is a buzzer which produces sound when the object is

detected. The strength of the sound is increasing as the object is getting closer to the

user.

1.5 Outline of Thesis

This thesis consists of five chapters. In first chapter, the introduction of this

thesis is discussed which includes the background, problem statement, objective,

scope of this project as well as summary of works. Chapter 2 described the theory

and literature reviews that have been done. The medical information about blindness,

the tools used by the blind people, various kind of distance sensor and the infrared

distance sensor will be explained in this chapter. In Chapter 3, the discussion on the

methodology of hardware implementation of this project is presented. The result and

discussion is presented in Chapter 4. Lastly, Chapter 5 draws the conclusion of this

project and recommendation that can be adopted in the future.

4

1.6 Summary of Works

Gantt charts shown in Table 1.1 and Table 1.2 illustrate the schedules of

works of the project that had been implemented in the first and second semester.

Table 1.1 Project Schedule for Semester 1

Week

Activities 1-3 4-6 7-9 10-12 13-15

1. Brief Idea

2. Literature Review

3. Multisim Simulation

4. Circuit Design

5. Report Preparation

6. Presentation

Table 1.2 Project Schedule for Semester 2

Week

Activities 1-3 4-6 7-9 10-12 13-15 16-18

1. Literature and

Theoretical Study

2. Construction of

Hardware

3. Modification and

Evaluation

4. Data analysis

5. Presentation

6. Report Writing

5

CHAPTER 2

THEORY AND LITERATURE REVIEW

2.1 Introduction

This chapter includes the study of medical information about blindness

disease such as the facts about the causes of this disease and also the aids used by

blind people. There are many types of infrared distance sensor which depend on their

range of detection and the theory of infrared light as well as the basic principle

infrared distance sensor explained in this chapter.

2.2 Medical Information of Blindness

Human eye is an organ which gives the sense of sight, allowing people to

observe and learn more about the surrounding world. Eyes are used in almost every

activity in daily life, whether reading, working, watching television, writing a letter,

driving a car, and in countless other ways. The eye allows human to see and interpret

the shapes, colors, and dimensions of objects in the world by processing the light

they reflect or emit. The eye is able to detect bright light or dim light, but it cannot

sense an object when light is absent. Anatomy of human eye is shown in Figure 2.1

which can help to understand the structure of the eye.

6

Figure 2.1 Anatomy of human eye

2.2.1 Process of Vision

Human can see the objects surround them by the process of vision which can

be explained by referring to Figure 2.2 below.

Figure 2.2 Process of vision

7

Light waves from an object which is in this case is a woman, enter the eye

first through the cornea, the clear dome at the front of the eye. The light then

progresses through the pupil, the circular opening in the center of the colored iris.

Fluctuations in incoming light change the size of the eye’s pupil. When the light

entering the eye is bright enough, the pupil will constrict, due to the pupillary light

response. Initially, the light waves are bent or converged first by the cornea, and then

further by the crystalline lens that is located immediately behind the iris and the

pupil, to a nodal point located immediately behind the back surface of the lens. At

that point, the image becomes reversed (turned backwards) and inverted (turned

upside-down).

The light continues through the vitreous humor, the clear gel that makes up

about 80% of the eye’s volume, and then, ideally, back to a clear focus on the retina,

behind the vitreous. The small central area of the retina is the macula, which

provides the best vision of any location in the retina. If the eye is considered to be a

type of camera, the retina is equivalent to the film inside of the camera, registering

the tiny photons of light interacting with it. Within the layers of the retina, light

impulses are changed into electrical signals. Then they are sent through the optic

nerve, along the visual pathway, to the occipital cortex at the posterior of the brain.

Here, the electrical signals are interpreted by the brain as a visual image.

2.22 Visual Acuity

Visual acuity often is referred to as Snellen acuity. Snellen Chart and the

letters are named for a 19th-century Dutch ophthalmologist Hermann Snellen (1834–

1908) who created them as a test of visual acuity. The illustration of Snellen Chart is

shown in Figure 2.3. A person’s visual acuity is an indication of the clarity or

clearness of the vision. It is a measurement of how well a person sees. The word

“acuity” comes from the Latin “acuitas”, which means sharpness. The reason that the

number “20” is used in visual acuity measurements is because, in the United States,

the standard length of an eye exam room that is, the distance from the patient to the

8

acuity chart is about 20 feet. In Great Britain, where meters are used instead of feet, a

typical eye exam room is about 6 meters long. Therefore, instead of using 20/20 for

normal vision, a notation of 6/6 is used in Britain.

Figure 2.3 Snellen Chart

In order to be considered legally blind, someone must have vision of 20/200

(6/60) in the person’s best eye with correction, or have a visual field which is limited

to 20 degrees or less, in contrast with the 180 degree visual field enjoyed by people

with healthy eyes. This definition means that it is possible for someone to be able to

see and to still be considered blind in the eyes of the law. Visual acuity is expressed

in a format which compares someone's vision to “normal” vision when viewing an

object at a set distance in feet or meters. If the second number is smaller, it means

that someone has visual acuity which is better than normal, because that person can

stand further away from an object and still see it clearly, while if the second number

is larger, it means that visual acuity is worse, because the person needs to stand

closer to an object to see it.

In the case of someone with 20/200 (6/60) vision, a person needs to stand

within 20 feet (6 meters) to see an object which someone with normal visual acuity

can see from 200 feet (60 meters) away. This has obvious consequences, as it means

9

that a legally blind person has trouble seeing things which other people take for

granted, like road signs, traffic lights, and so forth. People who are legally blind are

also more prone to falls and other accidents because they cannot clearly discern their

surrounding environment. A person with 20/20 (6/6) vision, for example, would

notice a crack in the sidewalk and avoid it, but a legally blind individual might not be

able to clearly see the crack, or might not understand what the visual disturbance

meant, so the person could trip and fall.

2.2.3 Causes

Serious visual impairment has a variety of causes such as due to diseases,

injuries, genetic defects and poisoning. The biggest factor that contributes to

blindness is disease and malnutrition. According to World Health Organization

(WHO) estimates in 2002, the most common causes of blindness around the world

are:

cataracts (47.9%)

glaucoma (12.3%)

age-related macular degeneration (AMD) (8.7%)

corneal opacity (5.1%)

diabetic retinopathy (4.8%)

2.2.3.1 Cataracts

Opacities and clouding of the eye's lens, known as cataracts, may form and

block the passage of light through the eye. Some people are born with cataracts, but

the incidence increases with age. They are not painful; in fact the only symptom is

blurred, dimmed or double vision. Not all require surgery, but those large enough to

cause serious visual problems require surgical removal of the lens, implantation of an

intraocular lens and corrective glasses or contact lenses.

10

2.2.3.2 Glaucoma

Perhaps one in every seven or eight cases of blindness is due to this disorder,

in which the transparent fluid inside the forward part of the eye does not drain

normally and excess pressure is built up within the eye. If the pressure is not

controlled, the delicate structure of the eye is increasingly damaged, resulting in

blurred vision, a narrowed field of sight and eventually total blindness. Early

symptoms may include blurred vision, halos around lights and reduced side vision. In

the acute type, there is great pain as eye pressure rises quickly from blocked drainage

canals. In the more common chronic type there is no pain and vision loss is gradual.

Many cases are controlled very well by medication, but surgery is sometimes

necessary.

2.2.3.3 Macular Degeneration

As the inner surface or lining at the back of the eye, the retina functions a

little like the film in a camera. The macula is the part of the retina which forms the

center of the picture and the sharpest image. Degeneration or breakdown of the retina

may occur, especially with increased age. The disorder may be slow or rapid, but

peripheral vision usually remains good. Magnifiers may help, and a few people may

be helped by laser treatment to seal off blood vessels which have grown beneath the

retina or to repair the macular's weak spots by removing worn-out tissue and

allowing new tissue growth.

2.2.3.4 Diabetic Retinopathy

The increased lifespan of diabetics has increased the incidence of this

disorder. Changes in the tiny blood vessels of the diabetic's retina can cause

blindness. Abnormal blood vessels are formed, some may burst and the retina may

11

even break loose from the back of the eye. Laser treatments to seal blood vessels or

reattach the retina may help if undertaken early. Some diabetics, incidentally, do not

experience vision loss.

2.2.3.5 Retinitis Pigmentosa

Frequently beginning as what is called "night blindness," this condition brings

degeneration of the retina and the choroid or a related vascular area, usually

involving an abnormal development of excess pigment. It is hereditary, with a variety

of patterns of inheritance and development. The most common pattern of

development is as follows: At approximately age ten or twelve, the youngster begins

to experience some difficulty in seeing at night and in poorly lighted areas. The

visual field also begins to narrow, frequently resulting in what is commonly termed

"tunnel vision" although he may not realize this at first. The visual loss is

progressive, so that the individual is usually legally blind by young adulthood and

slowly loses more and more vision thereafter. Many adults with retinitis pigmentosa

have a very tiny field of vision in which they see well under a good light but which is

so small as to be of little use. Total blindness often results and there is no known

treatment.

2.3 Tools

There are many useful tools or aids to be used by blind people to help them to

perform their daily activities. Most tools are designed for the visually challenged

people assist them in mobility and communication.

12

2.3.1 Mobility

Many people with serious visual impairments can travel independently, using

a wide range of tools and techniques. The blind people are taught how to travel

safely, confidently, and independently in the home and the community. They can find

the way easily if they are familiar with an environment or route.

Tools such as the walking cane can be a great help to them to move freely.

The mobility canes are often made from aluminium, graphite-reinforced plastic or

other fibre-reinforced plastic, and they can come with a wide variety of tips

depending upon user preference. Mostly the cane used by the visually challenged

people is a white cane with a red tip which is the international symbol of blindness.

However there are at least five different varieties of this tool, each serving a slightly

different need. The types of blind people’s walking cane are long cane, “kiddie”

cane, identification cane and support cane.

A long cane is used to extend the user's range of touch sensation. This

traditional white cane, also known as a Hoover cane, after Dr. Richard Hoover, is

designed primarily as a mobility tool used to detect objects in the path of a user. Cane

length depends upon the height of a user, and traditionally extends from the floor to

the user's sternum. Some organizers favor the use of much longer canes It is usually

swung in a low sweeping motion, across the intended path of travel, to detect

obstacles. Figure 2.4 shows a folded long cane which is used by the blind people.

Other type of cane used by blind people is “kiddie” cane which works in the

same way as the long cane, but is specially designed to be used by blind children.

The identification (ID) cane is used primarily to alert others as to the carrier’s visual

impairment. It is often lighter and shorter than the long cane, and is more limited as a

mobility tool. The support cane is usually used by elders to support their weight,

warn of changes in depth, and identify them as visually impaired. Some support cane

users are younger people with additional problems that affect body balance. Figure

2.5 shows the image of a support cane.

13

Figure 2.4 Folded long cane.

Figure 2.5 Support Cane

Besides the walking cane, some people employ guide dogs to assist in

mobility. Guide dogs are assistance dogs trained to lead blind or vision impaired

people around obstacles. Figure 2.6 illustrates a blind man with a guide dog that

guides him to move from one place to another place. The guide dogs are trained to

navigate around various obstacles, and to indicate when it becomes necessary to go

up or down a step. The guide dogs have to be professionally trained to guide the

14

blind person so that the blind people will not have problems to give instructions to

the dogs. However, the helpfulness of guide dogs is limited by the inability of dogs to

understand complex directions. They are also partially (red-green) color blind and are

not capable of interpreting street signs.

Figure 2.6 A blind man with a guide dog

2.3.2 Communication

The Braille system is an important aid used by the visually challenged people

as a communication tool. This method is widely used by them to read and write.

Braille was devised in 1821 by Louis Braille, a Frenchman. At the age of three, he

became totally blind and needed a lot of help from family and friends to carry on

with his lesson. When he grew up, Braille was determined to make learning easier for

blind children by enabling them to read and write.

Every letter is represented by a different arrangement of 6 raised dots. Just six

dots are the basis of the whole system arranged in two parallel lines of three, in a cell

of 7 mm x 4 mm. These dots derive a combination of 63 different patterns forming

26 alphabet letters, 10 punctuation, figures and abbreviations.

15

There are a number of different versions of Braille:

Grade 1, which consists of the 26 standard letters of the alphabet and

punctuation. It is only used by people who are first starting to read Braille.

Grade 2, which consists of the 26 standard letters of the alphabet, punctuation

and contractions. The contractions are employed to save space because a

Braille page cannot fit as much text as a standard printed page. Books, signs

in public places, menus, and most other Braille materials are written in Grade

2 Braille.

Grade 3, which is used only in personal letters, diaries, and notes. It is a kind

of shorthand, with entire words shortened to a few letters.

Braille has been adapted to write in many different languages and is also used for

musical and mathematical notations.

2.4 Infrared Light

The electromagnetic spectrum encompasses a continuous range of

frequencies or wavelengths of electromagnetic radiation, ranging from long

wavelength with low energy radio waves to short wavelength with high frequency,

high-energy gamma rays. The electromagnetic spectrum is traditionally divided into

regions of radio waves, microwaves, infrared radiation, visible light, ultraviolet rays,

x rays, and gamma rays. Infrared (IR) radiation lies between the visible and

microwave portions of the electromagnetic spectrum. The infrared part of the

electromagnetic spectrum covers the range from roughly 300 GHz (1 mm) to 400

THz (750 nm). It can be divided into three parts:

Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm).

Mid-infrared, from 30 to 120 THz (10 to 2.5 μm).

Near-infrared, from 120 to 400 THz (2,500 to 750 nm).

16

Near infrared light is closest in wavelength to visible light and far infrared is

closer to the microwave region of the electromagnetic spectrum. The longer, far

infrared wavelengths are about the size of a pin head and the shorter, near infrared

ones are the size of cells, or are microscopic. Far infrared waves are thermal. The

heat from sunlight, a fire, a radiator or a warm sidewalk is far infrared type. The

temperature-sensitive nerve endings in human skin can detect the difference between

inside body temperature and outside skin temperature. Near infrared waves are non-

thermal. These shorter wavelengths of near infrared are the ones used by television’s

remote control.

2.5 Types of Distance Sensor

Distance sensors or proximity sensor open or close an electrical circuit when

they make contact with or come within a certain distance of an object. Proximity

sensors are most commonly used in manufacturing equipment, robotics, and security

systems. There are four basic types of proximity sensors which are infrared,

capacitive, inductive and acoustic Proximity sensors are widely used in

manufacturing processes, for example, to measure the position of machine

components. They are also used in security systems, in applications such as detecting

the opening of a door, and in robotics, where they can monitor a robot or its

components' nearness to objects and steer it accordingly.

2.5.1 Infrared Proximity Sensor

Infrared proximity sensors work by sending out beams of invisible infrared

light. A photodetector on the proximity sensor detects any reflections of this light.

These reflections allow infrared proximity sensors to determine whether there is an

object nearby. As proximity sensors with just a light source and photodiode are

17

susceptible to false readings due to background light, more complex switches

modulate the transmitted light at a specific frequency and have receivers which only

respond to that frequency. Even more complex proximity sensors are able to use the

light reflected from an object to compute its distance from the sensor.

2.5.2 Capacitive Proximity Sensor

Capacitive proximity sensors sense target objects due to the target's ability to

be electrically charged. Since even non-conductors can hold charges, this means that

just about any object can be detected with this type of sensor. Figure 2.7 shows the

circuit of capacitive proximity sensor.

Figure 2.7 Capacitive Proximity Sensor Circuit

Inside the sensor is a circuit that uses the supplied DC power to generate AC,

to measure the current in the internal AC circuit, and to switch the output circuit

when the amount of AC current changes. Unlike the inductive sensor, however, the

AC does not drive a coil, but instead tries to charge a capacitor. Capacitors can hold a

charge because when one plate is charged positively, negative charges are attracted

18

into the other plate, thus allowing even more positive charges to be introduced into

the first plate. Unless both plates are present and close to each other, it is very

difficult to cause either plate to take on very much charge. Only one of the required

two capacitor plates is actually built into the capacitive sensor.

The AC can move current into and out of this plate only if there is another

plate nearby that can hold the opposite charge. The target being sensed acts as the

other plate. If this object is near enough to the face of the capacitive sensor to be

affected by the charge in the sensor's internal capacitor plate, it will respond by

becoming oppositely charged near the sensor, and the sensor will then be able to

move significant current into and out of its internal plate.

Capacitive proximity sensors sense distance to objects by detecting changes

in capacitance around it. A radio-frequency oscillator is connected to a metal plate.

When the plate nears an object, the radio frequency changes, and the frequency

detector sends a signal telling the switch to open or close. These proximity sensors

have the disadvantage of being more sensitive to object that conduct electricity than

to objects that do not conduct electricity. Figure 2.8 illustrates the capacitive

proximity sensor used in industry field.

Figure 2.8 Capacitive Proximity Sensor

19

2.5.3 Inductive Proximity Sensor

Inductive proximity sensors sense distance to objects by generating

magnetic fields. They are similar in principle to metal detectors. A coil of wire is

charged with electrical current, and an electronic circuit measures this current. If a

metallic part gets close enough to the coil, the current will increase and the

proximity sensor will open or close the electrical circuit accordingly. Inductive

proximity sensors operate under the electrical principle of inductance. Inductance is

the phenomenon where a fluctuating current, which by definition has a magnetic

component, induces an electromotive force (EMF) in a target object. To amplify a

device’s inductance effect, a sensor manufacturer twists wire into a tight coil and

runs a current through it.

An inductive proximity sensor has four components; the coil, oscillator,

detection circuit and output circuit. The oscillator generates a fluctuating magnetic

field the shape of a doughnut around the winding of the coil that locates in the

device’s sensing face. When a metal object moves into the inductive proximity

sensor’s field of detection, Eddy circuits build up in the metallic object, magnetically

push back, and finally reduce the Inductive sensor’s own oscillation field. The

sensor’s detection circuit monitors the oscillator’s strength and triggers an output

from the output circuitry when the oscillator becomes reduced to a sufficient level.

The main disadvantage of inductive proximity sensors is that they can only detect

metallic objects. Figure 2.9 and 2.10 show the images of inductive proximity sensor.

20

Figure 2.9 Inductive Proximity Sensor Circuit

Figure 2.10 Inductive Proximity Sensor

2.5.4 Acoustic Proximity Sensor

Acoustic proximity sensors or Ultrasonic (US) sensors are similar in principle

to infrared models, but use sound instead of light. They use a transducer to transmit

inaudible sound waves at various frequencies in a preset sequence, then measure the

length of time the sound takes to hit a nearby object and return to a second transducer

on the switch. Essentially, acoustic proximity sensors measure the time it takes for

sound pulses to "echo" and use this measurement to calculate distance, just like

sonar.

21

2.6 Infrared Distance Sensor

Infrared sensors are widely used as a distance or proximity sensors and for

obstacle avoidance in robotics. They offer lower cost and faster response times than

ultrasonic (US) sensors. IR sensors are almost exclusively used as proximity

detectors in mobile robots. The walking stick is designed using an infrared distance

sensor which is used to detect the object and a buzzer to alert the user. The infrared

distance sensor detects the object that is within the specific distance range of the

sensor.

Referring to Figure 2.11, the basic idea is to send infra red light through IR-

LEDs, which is then reflected by any object in front of the sensor. Another IR-LED

is used to detect the reflected IR light. There are three categories of IR distance

sensor which are reflection, line detection, and triangulation.

Figure 2.11 Object Detection Using IR Light

22

2.6.1 Reflection

This type of IR distance sensor uses an IR-LED and IR-diode or

phototransistor. When an object is close to the sensor it reflects the light emitted by

the LED to the IR-diode. When referring to Figure 2.12, by using modulated IR-light

(A) and filtering (B) the input signal of the IR-diode leads to better results as these

blocks much of other IR-light. There are ICs that contain a modulator, IR-diode and

filter-circuit.

Figure 2.12 IR reflection sensor

2.6.2 Line detection

This type of IR distance sensor has similar setup as the reflection IR-sensor,

but aimed downwards to detect lines on the ground. This sensor makes use of the

difference in reflection between a white background and a black line. More advanced

robots use multiple line detection sensors to follow a line more cleanly.

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2.6.3 Triangulation

Infrared triangulation sensors consist of an IR-LED and an IR-sensitive LDR

strip. They combined with built-in optical lenses, and the reflected beam's position on

the LDR depends on how far the object is. By referring to Figure 2.13, a pulse of

light with wavelength range of 850nm +/-70nm is emitted and then reflected back or

not reflected at all. When the light returns it comes back at an angle that is dependent

on the distance of the reflecting object. Triangulation works by detecting this

reflected beam angle by knowing the angle, distance can then be determined.

Figure 2.13 Triangular IR Sensor

2.7 Sharp IR Rangers

Sharp has a family of sensors that use triangulation principle for measuring

distance. They consist of an IR-LED, an IR-sensitive LDR strip and a small linear

Charge Couple Device (CCD) array to compute the distance and presence of objects

in the field of view. The basic principle is that a pulse of IR light is emitted by the

emitter. This light travels out in the field of view and either hits an object or just

24

keeps on going. In the case of no object, the light is never reflected and the reading

shows no object. Referring to Figure 2.13, if the light reflects off an object, it returns

to the detector and creates a triangle between the point of reflection, the emitter, and

the detector.

2.7.1 IR- LED

A light-emitting diode (LED) is an electronic light source. LED consists of a

chip of semiconducting material impregnated, or doped, with impurities to create a p-

n junction. As in other diodes, current flows easily from the p-side, or anode, to the

n-side, or cathode, but not in the reverse direction. Charge-carriers which are

electrons and holes flow into the junction from electrodes with different voltages.

When an electron meets a hole, it falls into a lower energy level, and releases energy

in the form of a photon.

The wavelength of the light emitted, and therefore its color, depends on the

band gap energy of the materials forming the p-n junction. In silicon or germanium

diodes, the electrons and holes recombine by a non-radiative transition which

produces no optical emission, because these are indirect band gap materials. The

materials used for the LED have a direct band gap with energies corresponding to

near-infrared, visible or near-ultraviolet light. Figure 2.14 shows the LED operations.

LED development began with infrared and red devices made with gallium

arsenide. Advances in materials science have made possible the production of

devices with ever-shorter wavelengths, producing light in a variety of colors. Most

materials used for LED production have very high refractive indices. This means that

much light will be reflected back in to the material at the material/air surface

interface. Therefore Light extraction in LEDs is an important aspect of LED

production, subject to much research and development. Table 2.1 shows the

wavelength range, voltage drop and material used in infrared LED.

25

Figure 2.14 The inner workings of an LED

Table 2.1 Characteristic of Infrared LED

Color Wavelength [nm] Voltage [V] Semiconductor Material

Infrared λ > 760 ΔV < 1.9 Gallium Arsenide (GaAs)

Aluminium Gallium

Arsenide (AlGaAs)

2.7.2 Light Dependent Resistor (LDR) Strip

A light dependent resistor (LDR) or photoresistor or cadmium sulfide (CdS)

cell is a resistor whose resistance decreases with increasing incident light intensity. It

can also be referenced as a photoconductor. The photodetector is a resistive

transducer whose resistance changes as a function of external light. The best known

and easiest-to-use type of light-sensitive device (photodetector) is the light-dependent

resistor or LDR which uses the symbol shown in Figure 2.15. A photoresistor is

made of a high resistance semiconductor. If light falling on the device is of high

enough frequency, photons absorbed by the semiconductor give bound electrons

26

enough energy to jump into the conduction band. The resulting free electron (and its

hole partner) conduct electricity, thereby lowering resistance.

LDR operation relies on the fact that the resistance of cadmium sulphide

(CdS) film varies with the intensity of the light falling on its face; the resistance is

very high under dark conditions, and low under bright conditions. Figure 2.16 shows

the LDR’s basic construction, which consists of a pair of metal film contacts

separated by a snack-like track of cadmium sulphide film designed to give the

maximum possible contact area with the two metal films. The structure is housed in a

clear plastic case that gives free access to external light.

Practical LDRs are sensitive, inexpensive and readily available devices with

good voltage and power handling capabilities, similar to those of a normal resistor.

They are available in several sizes and package styles. The most popular size having

a face diameter of roughly 10 mm. Normally such a device has a resistance of several

mega ohms under dark conditions, falling to about 900 Ω at a light intensity of 100

Lux (typical of a well lit room) or about 30 Ω at 8000 Lux (typical of bright sunlight)

Figure 2.15 Light Dependent Resistor Symbol

27

Figure 2.16 Basic Structure of Light Dependent Resistor

Figure 2.17 Light Dependent Resistors

2.7.3 Charge-coupled Device

A charge-coupled device (CCD) is a two-dimensional grid of semiconductor

capacitors that can transfer charge between each other. While the term is widely used

for image sensors, it actually describes the process by which the charges are

transferred through the capacitors towards the grid edge. The concept of digital

photography was first developed in 1961 at the Jet Propulsion Laboratory, but it

wasn't until 1969 that the first CCD was invented at Bell Labs. Commercial CCDs

28

started appearing during the early 1970s, and one of the first uses was in camcorders.

CCDs are semiconductors made using photolithography techniques, similar to those

used to make transistors and integrated circuits. Chemical layers are deposited on a

silicone wafer and then etched away to build up the channels and gates that form the

capacitors and diodes. Many layers are required to make one CCD, and many CCDs

are made on one wafer at the same time, which are later separated and mounted in

case. The schematic diagram illustrated in Figure 2.18 shows various components

that comprise the anatomy of a typical CCD.

Figure 2.18 The anatomy of a charge-coupled device

Fabricated on silicon wafers much like integrated circuit, CCDs are processed

in a series of complex photolithographic steps that involve etching, ion implantation,

thin film deposition, metallization, and passivation to define various functions within

the device. The silicon substrate is electrically doped to form p-type silicon, a

material in which the main carriers are positively charged electron holes. Multiple

dies, each capable of yielding a working device, are fabricated on each wafer before

being cut with a diamond saw, tested, and packaged into a ceramic or polymer casing

with a glass or quartz window through which light can pass to illuminate the

photodiode array on the CCD surface.

29

When a ultraviolet, visible, or infrared photon strikes a silicon atom resting in

or near a CCD photodiode, it will usually produce a free electron and a "hole" created

by the temporary absence of the electron in the silicon crystalline lattice. The free

electron is then collected in a potential well located deep within the silicon in an area

known as the depletion layer, while the hole is forced away from the well and

eventually is displaced into the silicon substrate. Individual photodiodes are isolated

electrically from their neighbors by a channel stop, which is formed by diffusing

boron ions through a mask into the p-type silicon substrate.

The principal architectural feature of a CCD is a vast array of serial shift

registers constructed with a vertically stacked conductive layer of doped polysilicon

separated from a silicon semiconductor substrate by an insulating thin film of silicon

dioxide by referring to Figure 2.19. After electrons have been collected within each

photodiode of the array, a voltage potential is applied to the polysilicon electrode

layers termed as gates to change the electrostatic potential of the underlying silicon.

The silicon substrate positioned directly beneath the gate electrode then becomes a

potential well capable of collecting locally-generated electrons created by the

incident light. Neighboring gates help to confine electrons within the potential well

by forming zones of higher potentials, termed as barriers, surrounding the well. By

modulating the voltage applied to polysilicon gates, they can be biased to either form

a potential well or a barrier to the integrated charge collected by the photodiode.

The most common CCD designs have a series of gate elements that subdivide

each pixel into thirds by three potential wells oriented in a horizontal row. Each

photodiode potential well is capable of holding a number of electrons that determines

the upper limit of the dynamic range of the CCD. After being illuminated by

incoming photons during a period termed as integration, potential wells in the CCD

photodiode array become filled with electrons produced in the depletion layer of the

silicon substrate. Measurement of this stored charge is accomplished by a

combination of serial and parallel transfers of the accumulated charge to a single

output node at the edge of the chip. The speed of parallel charge transfer is usually

sufficient to be accomplished during the period of charge integration for the next

image.

30

Figure 2.19 CCD Photodiode Array Integrated Circuit

After being collected in the potential wells, electrons are shifted in parallel,

one row at a time, by a signal generated from the vertical shift register clock. The

electrons are transferred across each photodiode in a multi-step process. This shift is

accomplished by changing the potential of the holding well negative, while

simultaneously increasing the bias of the next electrode to a positive value. The

vertical shift register clock operates in cycles to change the voltages on alternate

electrodes of the vertical gates in order to move the accumulated charge across the

CCD.

After traversing the array of parallel shift register gates, the charge eventually

reaches a specialized row of gates known as the serial shift register. Here, the packets

of electrons representing each pixel are shifted horizontally in sequence, under the

control of a horizontal shift register clock, toward an output amplifier and off the

chip. The entire contents of the horizontal shift register are transferred to the output

node prior to being loaded with the next row of charge packets from the parallel

register. In the output amplifier, electron packets register the amount of charge

produced by successive photodiodes from left to right in a single row starting with

the first row and proceeding to the last. This produces an analog raster scan of the

photo-generated charge from the entire two-dimensional array of photodiode sensor

elements.

31

Their main use is in photography, where CCD image sensors are found in

virtually all digital cameras and scanners. Astronomers were early adopters of CCDs

because they are up to one hundred times more sensitive than photographic film.

However, they need to be cooled to temperatures well below zero to reduce thermally

generated charges that cause errors. CCDs are also used in other fields such as

electron microscopy, spectroscopy, and fluoroscopy. They can also be found in night

vision equipment.

2.7.4 Types of Sharp Infrared Distance Sensor

Sharp has manufactured variety types of infra-red distance sensors. These

distance sensors boast a small package, very little current consumption, and a variety

of output options. Figure 2.20 helps to characterize each type by minimum and

maximum ranges, as well as whether the sensor returns a varying distance value or a

Boolean detection signal.

Figure 2.20 The ranges of IR detectors

32

The output of these infrared distance sensor is non-linear with respect to the

distance being measured because of some basic trigonometry within the triangle from

the emitter to reflection spot to receiver.

Figure 2.21 Output Voltage to Distance Curve

The graph in Figure 2.21 shows typical output from these detectors. The

output of the infrared distance sensors within the stated range which is from 10 cm to

80 cm is not linear but rather somewhat logarithmic. This curve will vary slightly

from one infrared distance sensor to another distance sensor. The other thing to

notice in the above graph is that once the object is in the distance range less than

10cm, the output drops rapidly and starts to look like a longer range reading.

2.8 Schmitt Trigger

In electronics, a Schmitt Trigger is a comparator that incorporates positive

feedback. When the input is higher than a certain chosen threshold, the output is

high; when the input is lower than chosen threshold, the output is low; when the

input is between the two, the output retains its value. The trigger is so named because

the output retains its value until the input changes sufficiently to trigger a change.

33

This dual threshold action is called hysteresis, and implies that the Schmitt trigger

has some memory.

Schmitt trigger has been in use for many years, having been originally

invented by an American scientist named Otto Schmitt. In terms of the fact that the

Schmitt trigger has hysteresis, the circuit symbol for one of these circuits

incorporates the hysteresis symbol into it. According to Figure 2.22, all Schmitt

triggers use this symbol. Schmitt-trigger buffers are categorized in three

configurations:

• Fixed threshold voltages with non-inverted outputs

• Fixed threshold voltages and inverted outputs

• Variable threshold voltages with non-inverted outputs

Figure 2.22 Schmitt Trigger Symbol

The benefit of a Schmitt trigger over a circuit with only a single input

threshold is greater stability and noise immunity. With only one input threshold, a

noisy input signal near that threshold could cause the output to switch rapidly back

and forth from noise alone. A noisy Schmitt Trigger input signal near one threshold

can cause only one switch in output value, after which it would have to move beyond

the other threshold in order to cause another switch. Figure 2.23 below show a single

input Schmitt trigger circuit.

34

Figure 2.23 A single input Schmitt trigger circuit

Schmitt triggers are typically built around comparators, connected to have

positive feedback instead of the usual negative feedback. For this circuit the

switching occurs near ground, with the amount of hysteresis controlled by the

resistances of R1 and R2. The comparator gives out the highest voltage it can, +Vcc,

when the non-inverting (+) input is at a higher voltage than the inverting (-) input,

and then switches to the lowest output voltage it can, −Vcc, when the positive input

drops below the negative input. For very negative inputs, the output will be low, and

for very positive inputs, the output will be high, and so this is an implementation of a

"non-inverting" Schmitt trigger.

For instance, if the Schmitt trigger is currently in the high state, the output

will be at the positive power supply rail (+Vcc). V+ is then a voltage divider between

Vin and +Vcc. The comparator will switch when V+=0 (ground). Current conservation

shows that this requires

Vin/R1 = −Vcc/R2 (2.1)

Hence, Vin must drop below − (R1/R2) Vcc to get the output to switch. Once the

comparator output has switched to –Vcc, the threshold becomes + (R1/R2) Vcc to

switch back to high.

35

Figure 2.24 Hysteresis curve

So this circuit creates a switching band centered around zero with trigger

levels, lower trigger point voltage (VLTP) and upper trigger point voltage (VUTP). The

input voltage must rise above the top of the band, and then below the bottom of the

band, for the output to switch on and then back off. If R1 is zero or R2 is infinity, i.e.

an open circuit, the band collapses to zero width, and it behaves as a standard

comparator.

36

CHAPTER 3

METHODOLOGY

3.1 Introduction

Walking stick for the visually challenged using infrared distance sensor

utilizes Sharp infrared distance sensor, Schmitt trigger circuit, and a buzzer to be

integrated in a long stick. The first step that is taken is to determine the appropriate

range to be used. The detection range is the range where the infrared distance sensor

is able to detect the object. If the object is out of the range, the IR emitter will not be

able to reach the object and certainly it is impossible to receive the reflected signal

from the object by the IR detector. On the other hand, if the object’s position is

within the specific range of IR distance sensor, the IR emitter will be able to send the

IR light to the object and the object’s reflected IR light will be sent to the IR detector.

In this project, a Sharp GP2Y0A21YK0F infrared distance sensor with

detection range 10 cm to 80 cm is used. The signaling element that is applied in this

invention to warn the user is a buzzer. This component will produce sound that can

be heard by the blind people. The loudness of the sound is depending on the distance

between the object and the IR distance sensor. When the distance is closer, the sound

generated is louder.

37

3.2 Block Diagram

Figure 3.1 is the block diagram of the walking stick with IR distance sensor

which has several stages. The object is detected by an IR distance sensor and the

output voltage is produced. The Schmitt trigger circuit is connected to a buzzer

which will produces sound to warn the user.

Figure 3.1 Block diagram the walking stick

3.3 Design and Specification

In order to design a walking stick that can help the visually challenged person

to walk, an infrared red distance sensor with a specific range is used to detect the

obstacle in front of the user and a buzzer to generate sound to warn them.

38

3.3.1 Sharp GP2Y0A21YK0F Infrared Distance Sensor

Figure 3.2 Distance sensor

Sharp GP2Y0A21YK0F is an infrared distance sensor, composed of an

integrated combination of position sensitive detector (PSD), infrared emitting diode

(IRED) and signal processing circuit. The variety of the reflectivity of the object, the

environmental temperature and the operating duration are not influenced easily to the

distance detection because of adopting the triangulation method. This device outputs

the voltage corresponding to the detection distance. So this sensor can also be used as

a proximity sensor.

Figure 3.3 Wires connections of Sharp GP2Y0A21YK0F

39

Referring to Figure 3.3, the sensor has three wires which should be connected

to the following locations:

Signal (red) to a buzzer.

5 V (yellow) to a VIN set to 5 V.

Ground (black) to a ground.

Figure 3.4 Block diagram of GP2Y0A21YK0F

Figure 3.4 shows the block diagram of distance sensor GP2Y0A21YK0F

which include voltage regulator, oscillation circuit, output circuit, LED drive circuit,

LED, PSD and signal processing unit. Table 1 shows about the features of Sharp

GP2Y0A21YK0F.

Table 3.1 Specifications of Sharp GP2Y0A21YK0F.

Feature Specification

Distance measuring range 10 to 80 cm

Package size 29.5×13×13.5 mm

Consumption current Typ. 30 mA

Supply voltage 4.5 to 5.5 V

40

The Sharp distance sensors are a popular choice for many projects that

require accurate distance measurements. This IR distance sensor is more economical

than sonar rangefinders, yet it provides much better performance than other IR

alternatives. The detection range of this version is approximately 10 cm to 80 cm (4"

to 32") and a plot of distance versus output voltage is shown below. The output

voltage of IR distance sensor is decreasing as the distance is increasing.

Figure 3.5 Distance of Sharp GP2Y0A21YK0F versus output voltage

3.3.2 Schmitt Trigger

Figure 3.6 illustrates the Schmitt trigger which makes use of positive

feedback to largely eliminate the multiple transitions. The voltage at the non-

inverting input, V+, determines the threshold voltage. The key point is that because

of the positive feedback provided by the 100 kΩ resistor in the above circuit, the

41

value of the threshold voltage V+ will depend on the output state Vout. The equation

to obtain threshold voltage is as the following:

(3.1)

Figure 3.6 Schmitt trigger circuit

When Vout = +5 V then +V ≈ 0.5 V and when Vout = 0 V then V ≈ 0 V. This means

that there are two different thresholds in the circuit, the one which determines when

the output will switch from "high" to "low" is equal to +0.5 V while the one which

determines when the output will switch from "low" to "high" is equal to 0 V.

3.3.3 Buzzer

The signaling element used to alert the user is a buzzer. Figure 3.7 shows the

buzzer used to give alarm to the user. The user is able to estimate the distance of

object from the strength of sound produced by the buzzer. The loudness of the sound

produced by the buzzer is depending on the input voltage given to it. The buzzer is

42

buzzing stronger when the input voltage supplied is higher. In this project, the output

voltage of IR distance sensor is supplied to the buzzer, for that reason the volume of

the buzzer is depending on the distance of the IR distance sensor with the object.

Figure 3.7 Buzzer

3.3.4 Long stick

The long stick is the most popular navigational aid for the blind. It is

relatively easy to use, light and not expensive. In this project, a white Polyvinyl

Chloride (PVC) pipe with length about 100 cm is used as a stick. PVC has its own

advantages to make it a very suitable material to be used as the walking stick

compared too other material like wood and aluminium. The main strong points are:

• Good compromise impact / rigidity.

• Good weathering (experience of more than 40 years).

• Very low maintenance.

• High thermal and acoustical insulation.

• High dimensional stability.

• Good Fire resistance.

• Good surface aspect with wide range of colours and appearances.

• No moisture absorption.

• Very good chemical resistance.

• Possibility to be welded.

43

The components are placed in the PVC pipe and a separated handle is made

for the user to hold the walking stick. The length of the stick is different for different

person depending on the height of the user. The ergonomic factor is important to

ensure that the user is comfortable to use the walking stick. Figure 3.8 below

illustrates the PVC pipe used as the walking stick.

Figure 3.8 Polyvinyl Chloride (PVC) pipe

44

CHAPTER 4

RESULT AND DISCUSSION

4.1 Introduction

An experiment is conducted for this project where the relationship between

the distance of object from Sharp GP2Y0A21YK0F infrared distance sensor and the

output voltage produced is obtained. The calculation Schmitt trigger circuit,

procedures and the result will be discussed in following sections.

4.2 Schmitt Trigger Circuit Calculations

Schmitt Trigger uses positive feedback with a loop-gain greater than unity to

produce a bistable characteristic. Positive feedback occurs because the feedback

resistor is connected between the output and non-inverting input terminals. Voltage

V+ in terms of the output voltage, can be found by using a voltage divider equation to

yield the value of V+ for the circuit used in this project

45

(4.1)

Voltage does not remain constant; rather, it is a function of the output voltage.

Input signal VI is applied to the inverting terminal. To determine the voltage

characteristic, we assume that the comparator is in one state, namely VO = VU, which

is upper state. Then

(4.2)

As long as the input signal is less than V+ , the output remains in its upper state. The

crossover voltage occurs when VI = V+ and is defined as VUTP.

(4.3)

When VI is greater than VUTP, the threshold at the inverting terminal is greater

than that at the non-inverting terminal. The differential input voltage (VI-VUTP) is

amplified by the open-loop gain of the comparator, and the output switches to its

lower state or VO = VL. Voltage V+ then becomes

(4.4)

46

Since VL < VU, the input voltage VI is still greater than V+, and the output

remains in its lower state as VI continues to increase. Considering the transfer

characteristic when VI decreases, as long as VI is larger than V+ = [R1/(R1+R2)] VL,

the output remains in its low saturation state. The crossover voltage now occurs when

VI = V+ and is defined as VLTP.

(4.5)

As VI drops below this value, the voltage at the non-inverting terminal is

greater than that at the inverting terminal. The differential voltage at the comparator

terminals is amplified by the open-loop gain, and the output switches to its upper

state, or VO = VU. As VI continues to decrease, it remains less than V+; therefore VO

remains in its upper state.

4.3 Experiment: Determine the Relationship between the Distance of Object

from Infrared Distance Sensor and the Output Voltage

An experiment is conducted to determine the relationship of distance of

object from IR distance sensor and the output voltage produced. The procedures of

the experiment and the analysis of result obtained from the experiment will be

discussed in the next sections.

47

4.3.1 Procedures

Figure 4.1 The experiment flow diagram

1) The circuit is connected as in Figure 4.1

2) An object is placed at distance 10 cm from the IR distance sensor.

3) The output voltage produced is recorded in Table 4.1.

4) Step 3 and 4 are repeated by increasing the distance of object from the IR

distance sensor.

4.3.2 Experimental Result Analysis

The data from the experiment are recorded in Table 4.1. The relationship

between the distance of object from IR sensor with the output voltage is determined

by looking the graph of distance versus output voltage in Figure 4.2.

48

Table 4.1 Distance versus output voltage

Table 4.1 shows the output voltage produced when the distance of object

from Sharp GP2Y0A21YK0F infrared distance sensor is altered in the range of 10

cm to 80 cm. The highest output voltage obtained is 2 V when the distance of object

is 10 cm and when the distance is 80 cm, output voltage produced is 0 V.

The graph of distance of object versus output voltage is shown in Figure 4.2.

The output voltage is decreasing when the distance of object from IR distance sensor

is increasing. The sound of buzzer is also decreasing when the distance is increasing.

Figure 4.2 Graph of distance versus output voltage

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Figure 4.3 shows the graph of distance versus output voltage with the best-fit

curve which gives the best fit equation to represent the data for Table 4.1. The best fit

equation is

y = 0.0005x2 – 0.0773x + 2.8017 (4.6)

Figure 4.3 The best fit curve to represent the data

4.4 Walking Stick with IR Distance Sensor Model

Figure 4.3 shows the walking stick that has IR distance sensor which can

detect the object in front of the user. In Figure 4.4, the infrared distance sensor is

placed at the lower part of the stick. The 9V battery with its holder and buzzer are

placed at the back of the walking stick as shown in Figure 4.5. The battery holder is

placed near the handle so that the user can replaced the battery easily while the

buzzer is placed at the upper part of the stick so that the user can hear the sounds of

buzzer better. A switch is placed near the handle like in Figure 4.6 for the user to

easily turn on/off the buzzer.

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Figure 4.4 The walking stick with IR distance sensor

Figure 4.5 The IR distance sensor

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Figure 4.6 Battery and buzzer

Figure 4.7 Switch

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CHAPTER 5

CONCLUSION AND RECOMMENDATION

5.1 Conclusion

Visually challenged people are a group of people who have problem to see.

Those who have the visual acuity of 20/200 are considered as legally blind. These

blind people employ many tools to help to perform their daily activities such as

Braille system which greatly useful for them to read and communicate. Other aids

used by them are the tools for mobility such as walking stick and guide dog. The

main tool used is walking stick or also known as walking cane which can help them

to detect object in front of them and avoid it.

The conventional walking stick is limited in range because the stick only

detects the object when the stick taps the object or ground. A walking stick with a

distance sensor can help them to avoid the obstacles better without tapping the object

or ground. Sharp GP2Y0A21YK0F infrared distance sensor is consumed to detect

the object within the distance range of 10 cm to 80 cm because it is small in size and

very efficient in detecting the object. A buzzer is employed as the signaling element

which generates sound when the object is sensed by the IR distance sensor. As the

object is getting closer to the IR distance sensor, the sound produced is becoming

louder. The sound of buzzer is depending on the output voltage of IR distance sensor

by varying the distance between object and the sensor.

The data taken from the experiment show that the output voltage of IR

distance sensor is decreasing when the distance between object and IR distance

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sensor is increasing which in turn the sound volume of the buzzer is also decreasing.

In conclusion, the objective of this project is successfully achieved because a walking

stick for the visually challenged using infrared distance sensor is successfully created

to detect the object in front of the user within the specific distance range which can

help them in mobility.

5.2 Recommendation

Even though the model of walking stick with IR distance sensor is

functioning as expected, there are some small imperfections that can be fixed. The

size of IR distance sensor is too big to be implanted in the walking stick. It would be

great if the size of the sensor is fit to be placed inside the walking stick. The walking

stick used in this project is unfolded. The user will have difficulties to bring and keep

the walking stick especially in crowded place. Besides that, the buzzer can be

replaced by a vibrator which vibrates to alert the user. The blind people are able to

feel the vibration by their touch sense. The deaf-blind people also can use the

vibrating walking stick to help them move from one place to another.

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