e-Caneintranet.dei.uminho.pt/gdmi/galeria/temas/pdf/42976.pdf · 2010. 4. 26. · University of...

University of Minho, Portugal

Engineering School

e-Cane

Electronic Cane Development

A thesis presented

by

António Rafael Cardoso Costa

Submitted to the University of Minho in order to obtain the degree of

Master in Electronics Engineering

Department of Industrial Electronics

University of Minho, Portugal

October 2009

i

“The rung of a ladder was never meant to rest upon, but only to hold a man's foot long

enough to enable him to put the other somewhat higher”. (Thomas Huxley)

iii

Dissertation conducted under the

scientific supervision of Prof. Filomena

Soares, Associate Professor at the

Department of Industrial Electronics of

the University of Minho.

v

Resumo

Da colaboração entre a Universidade do Minho e a APPACDM (Associação

Portuguesa de Pais e Amigos do Cidadão Deficiente Mental) surgiu a ideia do

desenvolvimento deste projecto, com a finalidade de melhorar a qualidade de vida de

pessoas cegas e portadoras de deficiência mental.

A bengala é utilizada como auxiliar de pessoas cegas nos seus movimentos

diários, tendo demonstrado ser uma grande ajuda para a independência e confiança dos

mesmos. Este método tem como grande vantagem o baixo custo de aquisição

comparativamente com outros auxiliares tais como, por exemplo, o uso de cães guias.

No entanto, apresenta algumas desvantagens, nomeadamente a impossibilidade da

detecção de obstáculos a partir de uma determinada distância, ou a partir de uma certa

altura.

Este projecto é dedicado ao desenvolvimento de uma bengala de baixo custo, à

qual serão adicionados sensores de ultra-sons, capazes de ultrapassar as limitações da

bengala normal. Como o público-alvo são pessoas cegas com deficiência mental, é

também objectivo do projecto desenvolver uma pulseira que receba a informação

proveniente dos sensores e vibre quando detecta obstáculos. Assim, o utilizador pode

distinguir o lado esquerdo do lado direito – competência frequentemente não adquirida

pelo utilizador – através da vibração, tanto do punho da bengala como da pulseira.

Utiliza-se o microcontrolador ATMEGA16, que efectua o processamento dos

sinais provenientes dos sensores, a activação do micro motor existente na bengala e a

activação do módulo de rádio frequência. Este, por sua vez, faz activar o micro motor

existente na pulseira.

Encontra-se concluído e operacional, em laboratório, o primeiro protótipo da

bengala electrónica. O protótipo final e o teste em ambiente real serão realizados num

futuro próximo.

vii

Abstract

From the collaboration between the University of Minho and APPACDM

(Portuguese Association of Parents and Friends of Mentally Retarded Citizens) arose

the idea of developing this project, with the purpose to improve the quality of life of

blind people with mental disability.

The white cane is the most common method used to assist blind people in their

daily movements. It has proved to be a great help to their independence and confidence.

Its low cost is an advantage regarding other processes, such as the use of guide dogs.

However, this method has some disadvantages, such as the impossibility of detecting

obstacles from a certain distance or above a certain height.

This project is dedicated to the development of a low cost cane equipped with

ultrasonic sensors, capable of overcoming the limitations of the white cane. Since the

target group is blind people with mental disabilities, it is also an objective of the project

to develop a bracelet that receives the information from the sensors. This bracelet will

warn the user of the presence of an obstacle on the left side. To the right side and front,

the warning signal will be at the cane. This enables the user to start distinguishing the

left side from the right side – a competence not acquired by some blind people with

mental disabilities – through the vibration of both the cane and the bracelet.

In order to control the system, an ATMEGA16 microcontroller is used. It

processes the signals coming from the sensors and the warning signals, activates the

micro motor implemented on the cane and also activates the RF module, which will

activate the micro motor in the bracelet.

The first laboratory prototype is complete and operational. The final prototype

and the tests in a real environment will be performed in the near future.

ix

Acknowledgements

I would like to express my sincere thanks to my supervisor, Prof. Filomena Soares

for the guidance and support all along the development of this project. With her critical

opinion but also with her confidence on my work, this project was successfully

accomplished.

To APPACDM, in particular to Dr. Fátima Moreira and Dr. Dora Ribeiro for their

help in the understanding of the mind of blind people with mental disabilities and for

the great opportunity of working on this project.

I would like to say thanks to Ricardo Freitas for his great contribution to this

project and also for his friendship through the years. I also wish to thank Nuno Brito

and Paulo Ribeiro for their help.

To my friends, for their friendship and for being with me at the good times and bad

times on my life. They were always there to help me overcoming innumerous

difficulties and, for that, I will always be grateful.

To the technical staff for their cooperation, providing help and access to the

facilities of the Department of Industrial Electronics.

Last but not least, I would like to thank my parents, my brothers and my sister in

law, for their encouraging support, as well as financial support, during my studies. They

are and they will always be a model for me to follow.

xi

Index

1 Introduction ............................................................................................................. 21

1.1 Motivation ........................................................................................................ 22

1.2 Overview of similar projects ............................................................................ 22

1.3 Aim of the project ............................................................................................ 23

1.4 Project Milestones ............................................................................................ 24

1.5 Thesis outline ................................................................................................... 25

1.6 References ........................................................................................................ 26

2 State of the Art ........................................................................................................ 27

2.1 Blindness and existing solutions ...................................................................... 28

2.1.1 Mobility and blind people......................................................................... 28

2.1.2 Mobility techniques .................................................................................. 29

2.1.3 Mobility, without auxiliary methods ........................................................ 29

2.1.3.1 Reference and information points ..................................................... 29

2.1.3.2 Tactile movement .............................................................................. 30

2.1.3.3 Mobility plans ................................................................................... 30

2.1.4 Auxiliary help methods ............................................................................ 30

2.1.4.1 Human ............................................................................................... 30

2.1.4.2 White cane ......................................................................................... 31

2.1.4.3 Guide dogs......................................................................................... 33

2.1.4.4 Electronic Instruments....................................................................... 34

2.2 Electronic tools available ................................................................................. 35

2.2.1 The Laser Cane ......................................................................................... 35

2.2.2 The Ultra Cane.......................................................................................... 36

2.2.3 Mowat Sonar ............................................................................................ 38

2.2.4 K-Sonar ..................................................................................................... 38

2.2.5 The Polaron .............................................................................................. 39

2.2.6 The GuideCane ......................................................................................... 40

2.2.7 Hand Guide ............................................................................................... 40

2.2.8 WalkMate ................................................................................................. 41

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2.2.9 Laser Long Cane ....................................................................................... 41

2.3 References ........................................................................................................ 44

3 Background ............................................................................................................. 47

3.1 Sensors ............................................................................................................. 48

3.1.1 Ultrasonic Sensors .................................................................................... 48

3.1.1.1 Principle of operation ........................................................................ 48

3.1.1.2 Distance measurement....................................................................... 49

3.1.1.3 Benefits.............................................................................................. 50

3.2 Ultrasonic SRF02 ............................................................................................. 50

3.3 Microcontroller ................................................................................................ 51

3.3.1 Atmega16 pin description ......................................................................... 52

3.3.2 ADC – Analog to digital converter .......................................................... 53

3.3.2.1 Operation ........................................................................................... 54

3.3.2.2 Starting a conversion ......................................................................... 54

3.4 Antenna ............................................................................................................ 55

3.4.1 RF – Radio Frequency .............................................................................. 55

3.4.2 RF module ................................................................................................ 56

3.5 References ........................................................................................................ 56

4 e - Cane development .............................................................................................. 57

4.1 e - Cane Project overview ................................................................................ 58

4.2 Ultrasonic sensors ............................................................................................ 59

4.3 Detection Methods ........................................................................................... 60

4.3.1 MA40A5 ................................................................................................... 61

4.3.1.1 Transmitter ........................................................................................ 61

4.3.1.2 Emitter Schematic ............................................................................. 62

4.3.1.3 Receptor ............................................................................................ 63

4.3.1.4 Block diagram ................................................................................... 63

4.3.1.5 Receiver circuit ................................................................................. 65

4.3.1.6 General Schematic............................................................................. 66

4.4 Components, Acronyms and Values ................................................................ 67

4.4.1 SRF02 Ultrasonic range finder ................................................................. 68

4.5 Microcontroller ................................................................................................ 69

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4.6 Bracelet ............................................................................................................ 70

4.7 Micro motor C-6070 ........................................................................................ 71

4.8 Antenna: RF module ........................................................................................ 71

4.9 Prototype .......................................................................................................... 72

4.10 References ........................................................................................................ 74

5 Software .................................................................................................................. 75

5.1 Compiler .......................................................................................................... 76

5.2 AVR Dragon .................................................................................................... 76

5.3 Microcontroller schematic ............................................................................... 77

5.4 Flowchart ......................................................................................................... 77

5.4.1 MA40A5 ................................................................................................... 78

5.4.2 SRF02 ....................................................................................................... 79

5.5 Implemented Functions in the microcontroller ................................................ 80

5.6 References ........................................................................................................ 81

6 Results ..................................................................................................................... 83

6.1 Experiments overview ..................................................................................... 84

6.2 Laboratory Results ........................................................................................... 84

6.2.1 Crosstalk Prevention ................................................................................. 85

6.2.2 Experiment 1 – Range of 30 centimeter ................................................... 86

6.2.3 Experiment 2 – Range of 1 meter ............................................................. 88

6.3 Bracelet laboratory tests ................................................................................... 91

6.4 Prototype experiment ....................................................................................... 92

7 Conclusions ............................................................................................................. 93

Appendix ........................................................................................................................ 97

Appendix A – Datasheets of the components used ..................................................... 99

Appendix B – PCB boards of the prototype ............................................................. 101

xv

Index of Figures

FIGURE 1: GENERAL VIEWS OF THE PROTOTYPE TRIAL CANE [3] ................................................................. 23

FIGURE 2: PARKING ON THE CURB ............................................................................................................... 28

FIGURE 3: HUMAN HELP ............................................................................................................................. 31

FIGURE 4: WHITE CANE ............................................................................................................................... 31

FIGURE 5: WHITE CANE MEASUREMENT ...................................................................................................... 32

FIGURE 6: GUIDE DOG ................................................................................................................................. 33

FIGURE 7: LASER CANE [6] ......................................................................................................................... 35

FIGURE 8: BRAIN CONNECTION [7] ............................................................................................................. 36

FIGURE 9: AVOIDING AN OBSTACLE ON THE RIGHT SIDE [11] ...................................................................... 37

FIGURE 10: DETECTING AN OBSTACLE ON THE LEFT SIDE [11] .................................................................... 37

FIGURE 11: MOWAT SONAR [12] ................................................................................................................. 38

FIGURE 12: K-SONAR [13] .......................................................................................................................... 39

FIGURE 13: POLARON [14] .......................................................................................................................... 39

FIGURE 14: THE GUIDE CANE [15] .............................................................................................................. 40

FIGURE 15: THE HAND GUIDE [17] ............................................................................................................. 41

FIGURE 16: THE WALKMATE [18] ............................................................................................................... 41

FIGURE 17: LASER LONG CANE [19] ........................................................................................................... 42

FIGURE 18: OBSTACLE DETECTION EXPLANATION ...................................................................................... 49

FIGURE 19: ATMEGS16 PINOUT .................................................................................................................. 52

FIGURE 20: ANTENNA: ELECTROMAGNETIC SCHEMATIC ............................................................................. 55

FIGURE 21: MICROCONTROLLER BLOCK DIAGRAM .................................................................................... 59

FIGURE 22: RANGE USING SENSORS ............................................................................................................ 60

FIGURE 23: LEFT DETECTION RANGE ........................................................................................................... 60

FIGURE 24: ULTRASONIC SENSORS ............................................................................................................. 61

FIGURE 25: ICM755 AS “ASTABLE OPERATION” ......................................................................................... 62

FIGURE 26: EMITTER ................................................................................................................................... 62

FIGURE 27: BLOCK DIAGRAM OF THE RECEPTOR ......................................................................................... 63

FIGURE 28: BAND PASS FILTER AND AMPLIFIER ......................................................................................... 64

FIGURE 29: INVERTER AMPLIFIER ................................................................................................................ 64

FIGURE 30: PEAK DETECTOR....................................................................................................................... 65

FIGURE 31: RECEIVER CIRCUIT .................................................................................................................... 65

FIGURE 32: ULTRASONIC SCHEMATIC ......................................................................................................... 66

FIGURE 33: SRF02 ULTRASONIC RANGE FINDER ......................................................................................... 68

FIGURE 34: SRF02 – I2C MODE .................................................................................................................. 69

FIGURE 35: PULSES GENERATED BY THE MICROCONTROLLER ..................................................................... 70

FIGURE 36: 3D BRACELET OVERVIEW ......................................................................................................... 71

FIGURE 37: CEBEK C-6070 .......................................................................................................................... 71

xvi

FIGURE 38: ANTENNA: (A) TRANSMITTER FM - RTFQ2; (B) RECEIVER FM - RRFQ2 ................................ 72

FIGURE 39: FIRST PROTOTYPE..................................................................................................................... 72

FIGURE 40: PROTOTYPE INSIDE VIEW .......................................................................................................... 73

FIGURE 41: BRACELET PROTOTYPE ............................................................................................................. 74

FIGURE 42: AVR DRAGON .......................................................................................................................... 76

FIGURE 43: MICROCONTROLLER MAIN CONNECTIONS ................................................................................. 77

FIGURE 44: MA40A5 FLOWCHART ............................................................................................................. 78

FIGURE 45: SRF02 FLOWCHART .................................................................................................................. 79

FIGURE 46 : WAVE FORM ON THE TERMINALS OF THE EMITTER ................................................................... 85

FIGURE 47: CROSSTALK PREVENTION ......................................................................................................... 85

FIGURE 48: DETECTION OF AN OBSTACLE (D = 30 CM) ................................................................................ 86

FIGURE 49: ECHO SIGNAL RECEIVED FROM THE OBSTACLE DETECTION (D=30 CM) ..................................... 86

FIGURE 50: ECHO SIGNAL RECEIVED AFTER THE FILTER AND THE AMPLIFIER (D=30CM) ............................. 87

FIGURE 51: ECHO SIGNAL RECEIVED AFTER THE DETECTION CIRCUIT (D=30CM) ........................................ 87

FIGURE 52: DETECTION OF AN OBSTACLE (D = 1M) ..................................................................................... 88

FIGURE 53: ECHO SIGNAL RECEIVED FROM THE OBSTACLE DETECTION (D=1 M) ......................................... 88

FIGURE 54: ECHO SIGNAL RECEIVED AFTER THE FILTER AND THE AMPLIFIER (D=1 M) ................................ 89

FIGURE 55: ECHO SIGNAL RECEIVED AFTER THE DETECTION CIRCUIT (D=1 M) ............................................ 90

FIGURE 56: RF TEST: A) TRANSMITTER WAVE; B) RECEIVER WAVE ........................................................... 91

FIGURE 57: PROTOTYPE FINAL TEST ............................................................................................................ 92

FIGURE 58: PEAK DETECTOR ....................................................................................................................... 92

xvii

Index of tables

TABLE 1: MOBILITY HELP ........................................................................................................................... 29

TABLE 2: COMPARISON OF THE MAIN AUXILIARY METHODS ....................................................................... 34

TABLE 3: CANES CHARACTERISTICS ............................................................................................................ 43

TABLE 4: MAJOR COMPONENTS LISTING AND ACRONYMS .......................................................................... 67

TABLE 5: RESISTOR VALUES........................................................................................................................ 67

TABLE 6: CAPACITOR VALUES..................................................................................................................... 68

xix

Nomenclature

Symbol Description Unit

d distance m

F frequency Hz

I current A

r radius meter

t time s

𝒕𝒕𝒓𝒂𝒏𝒔𝒎 Transmission time s

𝒕𝒓𝒆𝒄𝒆𝒑𝒕𝒊𝒐𝒏 Reception time s

T period s

v velocity of propagation m/s

Vamp Amplifier Output V

Vcc Operation Voltage V

Vdc DC voltage V

Vout Output voltage V

Vpp Peak to peak Voltage V

Acronyms

Symbol Description

ADC Analog- to-digital Converter

H High

I2C Inter-Integrated Circuit

L low

M medium

RX Ultrasonic Receiver

SRF02 Sensor Range Finder

SDA Serial Data

xx

SCL Serial Clock

TX Ultrasonic Transmitter

21

1 Introduction

Summary

This chapter provides the motivation to the development of this project.

It has the intention to demonstrate the need for this project, showing its

motivation and aim. It also explains the method used during the development.

Finally, the thesis outline is presented.

1.1 Motivation

1.2 Overview of similar projects

1.3 Aim of the project

1.4 Project milestones

1.5 Thesis outline

CHAPTER 1 – INTRODUCTION ELECTRONIC CANE DEVELOPMENT

22

1.1 Motivation

From the collaboration between the University of Minho (Guimarães, Portugal)

and APPACDM (Portuguese Association of Parents and Friends of Mentally Retarded

Citizens, located in the city of Braga), which aims to help and integrate people with

difficulties, emerged the idea of developing an electronic cane that will facilitate the

mobility of blind people, in particular of one of its students who also has a mental

disability, which restricts her from certain tasks.

The project and the development of this cane took place at the University of

Minho, in its Department of Industrial Electronics.

1.2 Overview of similar projects

Many projects were and are being developed around the world with the aim to

assist the locomotion of blind people. Canes using sensors to detect an obstacle is one of

those. The idea of this kind of technology has arisen primarily in Germany and then it

has been “imported” to countries such as United Kingdom, Brazil, Canada and United

States.

Brazil has been developing a walking stick with electronic sensors. On the

presence of an obstacle, a warning device that vibrates at a distance of at least one meter

and a half is switched on. It can detect obstacles on the waist line or 70 cm above the

shoulders. These sticks were tested in more than 30 users, with good results [1].

In Brazil it is possible to find another stick, similar to the previous one, but with

the ability of distinguishing colors. This project was developed by the Inaciana’s

Educational Foundation, an Electronic Engineering school. The device is able to emit a

beep every time an obstacle is detected, reducing the frequency of the beeps as the

obstacle gets closer [2].

In Canada and United States there are also references to the development of this

type of technology. A walking stick with the same characteristics of the referred above

was developed and implemented. In [3], beyond the images of the prototype, the authors

present all the cane characteristics, using schemes and illustrative texts. Figure 1 shows

the prototype.

ELECTRONIC CANE DEVELOPMENT CHAPTER 1 – INTRODUCTION

23

Figure 1: General views of a prototype trial cane [3]

In Portugal it is also possible to purchase a cane, the Ultra Cane, with similar

characteristics, such as the use of ultrasonic sensors to detect obstacles and vibrating

signals, at a cost of 800€ [4]. That purchase can be made on the site of Ataraxia [5].

1.3 Aim of the project

The aim of the e-Cane project is the development of a low cost cane with

ultrasonic sensors to detect obstacles both on right/front and left side of the user. As

seen in section 1.2, some projects are being developed in this area. However their

purpose is to help a restricted group: blind people. The target group of the e-Cane

project is broader: blind people with mental disability. The e-Cane aims at enabling a

superior independence of these individuals. The integration of the sensors in the cane

provides a correct detection of obstacles.

Considering the cognitive development of the first user (she does not distinguish

left from right positions), the use of a bracelet in the left wrist was foreseen. The

bracelet will give the user information corresponding to the detection of an obstacle in

the left side. So, she will be able to gradually start distinguishing the left side from the

right side. This will happen because when an obstacle is detected, the warning signal

will be on the cane or on the wrist, depending on the location of the obstacle.


24

1.4 Project Milestones

The work consists of the design of an electronic cane. It requires selecting

sensors, a board capable of performing data acquisition, a microcontroller, micro motors

and a bracelet.

Several tasks were performed:

a) Literature review of sensors.

b) Sensor selection.

Ultrasonic sensors were chosen, due to their projection on the environment and

the range they can achieve both on the horizontal or vertical axis.

c) Sensor hardware development.

Sensor hardware (transmitter and receiver) has to be implemented, taking into

account the characteristics and working conditions of the ultrasonic sensors chosen. All

the tests were performed using the equipment available at the laboratory, such as an

oscilloscope, a function generator and a power supply.

d) Microcontroller programming.

The information acquired by the sensors has to be processed. A program was

written (in C language) in order to manage this information, activating the

microcontroller pins according to the information received. If an obstacle appears in the

front/right side of the user the microcontroller will activate a micro motor on the cane

and, if the obstacle is at the left side, it will activate a micro motor on the bracelet by

sending a signal through an antenna.

ELECTRONIC CANE DEVELOPMENT CHAPTER 1 – INTRODUCTION

25

e) Bracelet development.

As mentioned before, an antenna is required to send the information to the

bracelet. So, a radio frequency module has to be chosen and implemented. It is essential

that the module has the characteristics needed for this project, such as small size and

low power requirement.

f) Tests and adjustments.

1.5 Thesis outline

This document is divided in 7 chapters.

Chapter 1 presents the motivation and purpose of this project. An explanation of

what to expect from it is given and similar projects are presented. It also contains the

project milestones, making an overview of the several tasks to be performed.

Chapter 2 makes reference to some problems of the daily routine of blind people. It

also contains information about some techniques used to help this target group, like the

white cane, the guide dogs and ETA’s (Electronic Travel Aids). Information about

similar projects is also presented.

Chapter 3 details the theoretical elements used in the development of the electronic

cane.

Chapter 4 examines the hardware part of the design, explaining all the processes

used in the development of the cane. It makes reference to the sensors, in particular to

the transmitter and the receiver. It also contains information about the microcontroller

used and the development of the bracelet.

Chapter 5 has an explanation of the software used in the development of the cane,

using flowcharts and texts.


26

Chapter 6 contains the laboratory results and their discussion, using images from an

oscilloscope which were taken from all the processes used during the e-Cane

development.

Chapter 7 presents all the conclusions that were achieved during the e-Cane

development and also the future implementations of the project.

All the datasheets used and some illustrated pictures showing the PCB boards

(separated by processes) are presented in the appendix.

1.6 References

[1].[Online] [Cited: October 25, 2008.] http://www.lerparaver.com/node/577.

[2].[Online] [Cited: October 25, 2008.]

http://sentidos.uol.com.br/canais/materia.asp?codpag=10718&cod_canal=11.

[3]. Hoyle, BS; Fowler, JM; Waters, DA; Withington, DJ, Development of the

Electronic Guide Cane for Enhanced Primary Mobility for the Vision Impaired Euro-

Assist-CVHI 2004 Conference and Workshop on Assitive Technologies for Vision and

Hearing Impairment, 2004.

[4].[Online][Cited:November10,2008.]

http://www.megaserafim.pt/index.php?page=shop.product_details&category_id=53&fly

page=shop.flypage&product_id=86&option=com_virtuemart&Itemid=26

[5].[Online] [Cited: November 10, 2008.] http://www.ataraxia.pt/produtos.php?id=6001

http://www.ataraxia.pt/produtos.php?id=6001

27

2 State of the Art

Summary

This chapter starts with a little overview of some similar projects of “electronic

canes”, making also reference to blindness and associated problems.

The research clarifies certain aspects of the project development and it helps to

identify the innovation of the e-Cane project compared to the existing ones.

2.1 Blindness and existing solutions

2.2 Electronic tools available

CHAPTER 2 – STATE OF THE ART ELECTRONIC CANE DEVELOPMENT

28

2.1 Blindness and existing solutions

Is considered a Visual Disability when a person has an injure on the visual

system that provokes a total loose or in part of the vision. It can be caused by a disease,

malformation, poor nutrition or trauma. This impairment causes a reduction or loss of

some abilities, such as to recognize faces or places and to walk safely [1].

2.1.1 Mobility and blind people

To blind people, the daily routines, as walking safely in the streets avoiding the

obstacles, can be a hard work. Obstacles as in Figure 2, are an example of what blind

people face up every days on the streets.

Figure 2: Parking on the curb

People with visual impairments can travel independently using different tools

and techniques. Orientation and mobility specialists are trained to teach those people

how to move securely and autonomously. They also can learn how to travel on specific

routes that they may use often [1].

ELECTRONIC CANE DEVELOPMENT CHAPTER 2 – STATE OF THE ART

29

2.1.2 Mobility techniques

Nowadays, we are able to find some ways to help the movement of the blind

people. They can be divided in two groups: one of them without using mobility

auxiliary help and the other one using it [2]. Table 1 presents some of the differences.

Table 1: Mobility help

In the following sub-chapters these mobility items are explained in detail.

2.1.3 Mobility, without auxiliary methods

In this chapter it will be explained the different methods used to help blind

people without a mobility auxiliary method.

2.1.3.1 Reference and information points

The reference and information points support the orientation of the blind people.

A reference point is defined as an object, sound, smell or tactile indicator that is

exclusive of the place that the blind is moving. To be permanent in time, space and

easily accessible, it is the one of the characteristics that this kind of objects need to

have.

In contrast, a point of information is any auditory stimulation or tactile, which

gives information useful to his movement.


30

In the case of reference points it is only need one point to determinate where the

person is, and in the case of information points it is necessary an aggregation of them

[2].

2.1.3.2 Tactile movement

This technique consists on walking parallel to a wall or any other guide surface.

This has the purpose to avoid shocks to obstacles low placed, such as, chairs or tables.

At the same time this has the aim to facilitate the location of points of reference or

information on the wall that are essential to improve the blind movement [2].

2.1.3.3 Mobility plans

The mobility plans are an addition to the correctly movement of the blind

people. They are produced in different materials that can be distinguished by touch what

has the aim to help to produce a mental image of the spaces. Mobility plans can be

made using methods such as sound or it can be writing in Braille.

Its development is complex because a lot of restrictions have to be considered, in

order to the person distinguish them. Considering that the touch has different

characteristics comparing to the vision, a proper training is necessary for a correct

reading of the plans [2].

2.1.4 Auxiliary help methods

It will be consider as auxiliary help methods those that are constantly in “touch”

with the user, therefore an explanation of some of them is described below.

2.1.4.1 Human

This technique helps the blind people to walk safely in all kind of places that can

be known or not by him, using the help of another person (Figure 3). The human helper

has to remain a little in front and the blind has to hold the person above the elbow.

During the movement they have to be always in touch in order to avoid obstacles.


31

Figure 3: Human Help

2.1.4.2 White cane

Tools like white cane with a red tip1 can be used to improve mobility, Figure 4.

The white cane has to be sweeping the area in front describing a semi-circle that covers

a space between the two shoulders of the person [3].

For detecting obstacles with the white cane, the blind person has always to touch

the obstacle, and he/she does not know in advance the presence of it. Sometimes he is

not able to detect the obstacle, for example a truck, because the cane will pass under it

and the blind can accidently go against the higher part of the truck and gets hurt [3].

Figure 4: White cane

1 Red tip - International symbol of blindness


32

The white cane has some advantages which are described below [3] [4]:

It helps to find curbs, stairs, stuffs parked in the way and things that the user

needs to find (when properly used);

It do not need a hand contact to detect obstacles;

It can be used on different temperature or weather conditions;

No maintenance (virtually).

However it has some disadvantages like:

Limited range (limited to its size);

Does not provide protection against collision to the upper part of the body;

Discrimination;

Danger of tripping pedestrians in congested areas.

As seen in Figure 5, the white cane only provides a distance measure of its

dimension. Thus, the development of this electronic cane using sensors will offer a

larger sensing area.

Figure 5: White cane measurement


33

2.1.4.3 Guide dogs

Instead of the cane some people use guide dogs to assist them in mobility

(Figure 6). These dogs are trained to go around obstacles and to indicate the presence of

a step, for example.

Figure 6: Guide dog

The guide dogs are considered efficient helpers to assist blind people on their

movements; however the maintenance in terms of supplies and treatments eventually

necessary can be expensive. They also have the disadvantage of the impossibility to not

enter in some locals, such as hotels or banks for example [3].

It can be concluded that guide dogs have good advantages to the user, such as:

Psychological, social and physiological benefits;

Companionship;

Reduction of anxiety, depression and loneliness;

In order to avoid obstacles, the dog plan another route directing the blind

through it [3].

On the other hand, they also have some disadvantages:

Extra time and energy needs of the dog;

Some places deny access to its facilities;

Training sessions every time a new dog is necessary [3].


34

2.1.4.4 Electronic Instruments

Electronic instruments bring advantages to the movement of the blinds, for

example:

Independent travel;

To receive advanced knowledge about obstacles;

Reduce the fear of collisions;

No entrance restrictions on restaurants, hospitals, churches, taxis and

buses.

In order to choose between the three most important methods of helping blind

people, a comparison table was made (Table 2).

Table 2: Comparison of the main auxiliary methods2

Cost Independence Efficiency Maintenance

Psychological,

social and

physiological

benefits

Entrance

restrictions

White

Cane L M M L M L

Guide

Dogs H H H H H H

Electronic

Cane M H H M M L

It can be concluded through the analysis of the table 2, that the guide dogs are

good helpers to blind people. However the electronic cane brings more benefits to the

user, as it is less expensive, has less maintenance costs and do not have any restrictions

in attending social events.

2 Considering L - low; M - medium ; H- high


35

2.2 Electronic tools available

Over the years some electronic tools were developed in many different countries.

Called ETAs (Electronic Travel Aids), this kind of tools can be used by themselves or

combined with primary aids, such as the guide dog or long canes. Some of those tools

are presented in the next sections [5].

2.2.1 The Laser Cane

Developed in Honolulu3 (United States) and called “The Laser Cane” [6] (Figure

7), it is able to detect obstacles in a range of 12 feet 4 (3.66 meters) in front of the user.

With the objective to warn the user when an obstacle is detected it has two different

methods: audible or a vibrating. The user can choose to use both methods at the same

time or the audible sound can be switched off, using only the vibrating one. The audible

method is consisted of “go, do not go” information sent to the user.

Figure 7: Laser Cane [6]

3 Honolulu is the capital and most populous census-designated place (CDP) in the U.S. state of Hawaii

4 1 feet is equal to 0.3048 meters

http://en.wikipedia.org/wiki/State_capitalhttp://en.wikipedia.org/wiki/Census-designated_placehttp://en.wikipedia.org/wiki/U.S._statehttp://en.wikipedia.org/wiki/Hawaii


36

2.2.2 The Ultra Cane

From the collaboration between Sound Foresight and the University of Leeds in

United Kingdom, has arisen the idea of a “Bat cane” [7] [8]. Recently it was called “The

Ultra Cane”, being able to detect obstacles during the movement of the blind and when

an obstacle is detected, it warns the user. To detect obstacles it emits an ultrasonic wave

and receives the echo signal from the detection (when occurs an obstacle detection).

Buttons incorporated on the handle have the property to vibrate and to warn the

user how far away is from the obstacle. This method helps the user to have a better

acknowledgement of the environment around him and to improve his reaction to avoid

obstacles.

The adaptation to the Ultra Cane is not a problem and if the blind has already

used a white cane the adaptation should be easier. The feedback that the user gets

through the vibration signal at the handle, helps to build a subconsciously map of the

environment, what in a near future makes easier to move on those places.

Superior Collicolus is a part of the human brain that receives information from

its senses – vision, hearing and touch (Figure 8). For blind people this part only receives

information from two senses: hearing and touch. So, it emits a vibrating signal to the

finger when an obstacle is detected. This has the aim to let the user free to listen to all

the other sounds around him. The vibrating signal at the finger has the purpose to help

the user to create a spatial map which will be very useful at the daily routines [7] [8].

Figure 8: Brain Connection [7]


37

The Ultra Cane can also be found in Portugal at the website of Ataraxia [9],

having a commercial cost of 800€ [10]. In addition, the website gives access to the

characteristics of the cane in question and also to a video [11], which illustrates how to

use it. The video shows a virtual demonstration of the ultra cane being taken by a man

who is able to avoid numerous obstacles in his way, with confidence and no fear. A

voice of a woman explain that with two buttons the user is able to know which side the

obstacle is, being that way capable to turn for the correctly place in order to avoid it.

In Figure 9, the ultra cane is detecting the presence of an obstacle on the right

side of the user, and indicates to the user that he needs to avoid it by changing his

course to the left side.

Figure 9: Avoiding an obstacle on the right side [11]

In the opposite to the previous figure, Figure 10 has the obstacle on the left side

of the user. The ultra cane detects the presence of it, but it sends the “information” to

the user that he does not need to avoid it, because is far way and he can pass over

without crash.

Figure 10: Detecting an obstacle on the left side [11]


38

2.2.3 Mowat Sonar

This ETA (Figure 11) uses ultrasonic sensors to determinate the distance to the

obstacles, warning the user by a vibrating signal. The frequency of the warning signal

became higher when the obstacle approaches to the user. This device can be worn on the

chest or on the hand held. When walking on a hallway, the user points the device to the

side wall and has to move away to where the low-high frequency transitions occur,

being that way moving in a safe zone without obstacles. Mowat has a wide beamwidth,

which has the disadvantage of poor bearing resolution [12].

Figure 11: Mowat Sonar [12]

2.2.4 K-Sonar

The K – sonar (Figure 12) is an ultrasonic sensing device that combined with the

long cane increases the independence of blind people. Using this device, it is possible to

perceive all the surroundings that otherwise could not be possible to. The K–sonar

improves the safety and reduces the stress, motivating blind people to move into

unknown places [13].

K-sonar works using ultrasonic sensors to detect obstacles. The sonar

information is gathered and it provides a mental map of objects both in front and sides

of the user. When an object is detected, an audio warning signal is switched on and it

varies according to how far way the obstacle is, indicating that way the distance to the

obstacles, what may increase the reaction to avoid it. The user listens to these sounds

through miniature earphones [14].


39

Figure 12: K-sonar [13]

2.2.5 The Polaron

It is an electronic device to help blind people and it can be used on the hand or at

the chest (Figure 13). It uses ultrasonic sensors to detect obstacles within four, eight or

sixteen feet. The Polaron can be used combined to a long cane or with a guide dog,

which permits the user to move securely and efficiently. When an obstacle is detected

the warning signal is given by a vibration or by a sound signal. The user is able to

choose both notifications signals and to change the volume, by the use of a switch

located on the control side of the device. When used in the chest, a miniaturized

vibrator located at the neck indicates the presence of an obstacle [14].

Figure 13: Polaron [14]


40

2.2.6 The GuideCane

This electronic device (Figure 14) is based on ultrasonic sensors and has the aim

to help blind people. It has the property to completely avoid obstacles and training is

not required, given that the process is totally instinctive, since it preserves position

information by merging odometry, compass, and gyroscope data [15] [16].

Figure 14: The Guide Cane [15]

2.2.7 Hand Guide

The Hand Guide (Figure 15) in order to detect obstacles uses infrared

technology which permits a range detection of four feet. The user is able to choose

from two warnings methods: sound or a vibration signal that increases when an obstacle

becomes closer to him. Together with the white cane it is able to provide a good

identification of gasps and steps, while the Hand Guide permits a higher “view” of

barriers, such as the signs on the roads [17].


41

Figure 15: The Hand Guide [17]

2.2.8 WalkMate

The WalkMate (Figure 16) was produced by Safe Tech International, Inc.

[1993], and it can be worn at the waist level (suspended from the neck loop), or it may

be handheld [18].

The user can choose between a vibrating or a sound as warning signal, when as

obstacle appears in its way. It has two working zones: 7 feet (2.13m) and 4 feet (1.22m).

If an object is detected at the range zone of 7 feet, a slowly pulse (about 4 pulses per

second) will be switched on (beep or vibration). A rapid beep or a vibration with a

higher frequency is triggered when the obstacle becomes closer [18].

Figure 16: The Walkmate [18]

2.2.9 Laser Long Cane

The Laser Long Cane (Figure 17) is able to avoid possible collisions, using a

laser system. The electronic utensils and the power supply necessary to the properly

work of the system are integrated in the handle. The cane emits a laser signal that on the

presence of an obstacle is reflected and received again at the cane. It advertises the user

by a vibrating warning signal at the handle. It is also able to detect obstacles beyond the


42

head and the chest area. The possibility to combine with diversity long canes is also an

advantage of this device [19].

Figure 17: Laser Long Cane [19]

After the analysis of the characteristics of all the projects equivalents to the

e-Cane, it can be conclude that they all have several points in common. Except for the

Hand Guide, Laser Cane and the Laser Long Cane, they all use ultrasonic sensors to

detect obstacles and all have similar warning methods. Table 3 shows a comparison of

the main characteristics of the projects described above.


43

Table 3: Canes characteristics

Cane Sensor type Range Warning method

Min Max vibrate audible

Laser Cane Laser 0 3.66 m x x Guide Cane Ultrasonic 2 cm 4 m x Hand Guide Infrared 0 1.23 m x x

K-Sonar Ultrasonic 1.83 m 4.88 m x

Laser Long Cane Laser 0 1.45 m x Mowat Sensor Ultrasonic 1 m 4 m x

Polaron Ultrasonic 1.23 m 4.88 m x x Ultra Cane Ultrasonic 2 m 4 m x Walk Mate Ultrasonic 1.22 m 2.13 m x x

New e-Cane Project

Ultrasonic 0.18 m 2 m x

Comparing the working range of the canes, most of them have a larger distance;

however it was thought that more than 2 meters could be confusing for the user. Since

the target group shows mental disability, with a range higher than 2 meters, more

obstacles could be detected, that might not be necessary to detect. For example, walking

into a shopping would be very difficult, because the walls would be constantly detected

by the cane, what would confuse the user.

It can be assumed, by Table 3, that the e-Cane is a similar project. However it

has the advantage of using a different method to warn the user when an obstacle is

detected in the left side, by using a bracelet. This difference makes the e-Cane a better

choice, since it will help a larger group of users.

Regarding costs, the e-Cane is a low cost equipment for helping blind people

with mental impairments.


44

2.3 References

[1].[Online] [Cited: November 5, 2008.]

http://www.acapo.pt/information.asp?op=cegueira.

[2].Manuel Bueno Martín and Salvador Toro Bueno. Deficiência Visual, Aspectos

Psicoevolutivos e Educativos . s.l. : Santos Livros Editora 2003.

[3].[Online] [Cited: January 15, 2009.] http://www.livingblind.com.


http://www.lerparaver.com/mobilidade_comportamentos.htm.

[5].Kay, L., Electronic Aids for Blind Persons: an Interdisciplinary Subject, IEEE

Proceedings, Vol. 13 1, N. 7,1984 pp. 559-576.

[6].[Online] [Cited: December 10, 2008.]

http://www.eyeofthepacific.org/electronic%20aids.htm.

[7].[Online] [Cited: November 10, 2008.] http://www.batcane.com

[8].Nikhil Ichalkaranje,A. Ichalkaranje,L. C. Jain, Intelligent paradigms for assistive

and preventive healthcare, Springer 2006, Vol. 19.

[9].[Online] [Cited: November 10, 2008.] http://www.ataraxia.pt/produtos.php?id=6001

[10].[Online][Cited:November10,2008.]

http://www.megaserafim.pt/index.php?page=shop.product_details&category_id=53&fly

page=shop.flypage&product_id=86&option=com_virtuemart&Itemid=26


http://www.batcane.com/ultracane_demonstrator.htm

[12].Mark M. Uslan,American Foundation for the Blind,Alec F. Peck,William R.

Wiener , Access to mass transit for blind and visually impaired travelers, American

Foundation for the blind, July 1990, pp.148-149

[13].[Online] [Cited: November 15, 2008.] http://www.batforblind.co.nz .

[14]. José Mira, José Ramón Álvarez, Mechanisms, symbols, and models underlying

cognition, Springer, June 2005


http://www.eyeofthepacific.org/electronic%20aids.htm .


http://www.engin.umich.edu/research/mrl/00MoRob_22.html.

http://www.batcane.com/http://www.batforblind.co.nz/


45

[17].[Online] [Cited: November 17, 2008.] http://www.nfbcal.org/nfb-rd/1405.html .


http://www.tiflotecnia.com/produtos/fichas_tecnicas/ft_handguide.pdf .

[19].William R. Wiener and Richard L. Foundations of orientation and Mobility, 2nd

edition Bruce B. Blash. s.l. : Welsh Editors 1997.

[20].[Online] [Cited: January 25, 2009.]

http://www.ddaware.co.uk/index.php?option=com_content&view=article&id=54&Itemi

d=75

http://www.ddaware.co.uk/index.php?option=com_content&view=article&id=54&Itemid=75http://www.ddaware.co.uk/index.php?option=com_content&view=article&id=54&Itemid=75


46

47

3 Background

Summary

Some clarifications regarding the working functionalities of the devices used in

this project are explained in this chapter.

3.1 Sensors

3.2 Sensor SRF02

3.3 Microcontroller

3.4 Antenna

CHAPTER 3 – BACKGROUND ELECTRONIC CANE DEVELOPMENT

48

3.1 Sensors

A sensor allows analyzing the surroundings, which might be temperature, light or

even the measurement of distances. These sensors can be classified as transducers. A

transducer transforms one type of energy into another, for example light, heat or

movement into electric energy.

During the years, the expansion of this technology has resulted in numerous

profits, such as the chance to amplify the efficiency on the operation of an engine, the

realization of investigations with greater precision on less time and even the

measurement of distances in order to avoid, for instance, collision with obstacles.

3.1.1 Ultrasonic Sensors

The ultrasonic sensor or sonar (an acronym for SOund Navigation And Ranging),

emits waves impossible to hear to humans, checking the reflection on a surface or object

present in its course [1].

Ultrasonic sensors sense targets made of almost any material; they are able to detect

clear, transparent and shiny targets as easily as dark and opaque materials [1].

3.1.1.1 Principle of operation

These types of sensors are based on a transmitter which transmits a small tone

and a receiver that collect the echo that occurs when an object reflects [2]. For

measurements of distances (d), it is calculated the time among the transmitted and the

received sound wave.

As illustrated in Figure 18, an ultrasonic wave is sent (in green), which in the

presence of an object (in blue) is reflected in the form of an echo (in orange), returning

to the receptor.

ELECTRONIC CANE DEVELOPMENT CHAPTER 3 - BACKGROUND

49

Figure 18: Obstacle detection explanation

3.1.1.2 Distance measurement

The sensor generates an ultrasonic pulse which propagates through the

transmission and is echoed by a reflection surface, as seen in Figure 18. So the distance

can be estimated using the formula:

𝑑 = 𝑣𝑡 (eq. 1)

In equation 1, 𝑣 is the velocity of propagation of the ultrasonic wave and 𝑡 is the

time elapsed between the transmission and the reception of an energy pulse. Besides the

time of transmission it must be taken into account the time to receive the echo.

Theoretically this time is equal to the transmission one (equation 2). So in equation 1 to

calculate the distance traveled by the wave it has to be taken into account the two

equations. Therefore, in order to determinate the distance of detection for obstacles,

equation 2 has to be divided by two (equation 3).

𝑡 = 𝑡𝑡𝑟𝑎𝑛𝑠𝑚 + 𝑡𝑟𝑒𝑐𝑒𝑝𝑡𝑖𝑜𝑛 𝑎𝑛𝑑 𝑡𝑡𝑟𝑎𝑛𝑠𝑚 = 𝑡𝑟𝑒𝑐𝑒𝑝𝑡𝑖𝑜𝑛 (eq. 2)


50

𝑑𝑜𝑏𝑠𝑡𝑎𝑐𝑙𝑒 =1

2× 𝑣𝑡 (eq. 3)

For example, if the obstacle is in a range of 1 meter, the distance calculated will

be 2 meters (1 meter for the transmission wave and 1 meter for the echo received).

As the sensor will be operating generally in air, the propagation speed of the

pulses in the air is 346 meters per second (25 ºC) [3].

3.1.1.3 Benefits

Ultrasonic sensors have some benefits, such as [4]:

Excellent suppression of the background with a trustworthy detection;

Detection by ultrasound without direct contact with the object and also

measuring the distance to it;

Highly accurate measurements;

Large scanning ranges;

Low cost;

No central blind spot;

Quality beam characteristics;

Low power requirement, good for a battery based system [4].

3.2 Ultrasonic SRF02

The SRF02 is a single transducer ultrasonic rangefinder in a small footprint PCB.

It operates using both I2C and Serial interfaces. Serial interface is a standard TTL level

UART format at 9600 baud, 1 start, 2 stop and no parity bits. It permits to be connected

directly to the serial ports on any microcontroller. SRF02 has new commands such as

the fact to include the ability to send an ultrasonic burst on its own without a reception

cycle or to perform a reception without the preceding burst. The minimum detection


51

range of this sensor is around 15 cm (6 inches) and it has the ability give distance

information in µs, cm or inches.

It can operate in two modes: I2C mode and Serial Mode as seen before. To use

serial mode the “Mode” pin has to be connected to 0V (Ground) and to the mode I2C it

has to left unconnected or tied to +5Vcc.

Inter-Integrated Circuit (I2C) was invented by Philips and usually is used to join

low-speed peripherals to a motherboard, embedded system or cellphone. Serial Data

(SDA) and Serial Clock (SCL) are the only two bidirectional open-drain lines, pulled up

with resistors. In general it is used voltages around +5V or +3.3V, however systems

with higher or lower voltages are allowed [5].

3.3 Microcontroller

The microcontroller used to the development of this project was the ATmega16. It

is a common low-power CMOS 8-bit based on the AVR enhanced RISC architecture. It

executes powerful instructions in a single clock cycle, what makes the ATmega16 to

achieve throughputs approaching 1 MIPS per MHz, allowing the system to optimize

power consumption versus processing speed, (datasheet annexed) [6].


52

3.3.1 Atmega16 pin description

A detailed description of ATmega16 (Figure 19) is presented in the next sub-

chapters.

Figure 19: ATmegs16 Pinout

VCC - Digital supply voltage; GND – Ground

The information about the pins of the microcontroller ATMEGA16 presented

below was transcribed from the datasheet annexed.

An explanation of the Port A and Port B is given and for the rest of the ports

they can be consulted at the datasheet annexed.

Port A (PA7 to PA0)

Port A serve as the analog inputs to the A/D Converter and an 8-bit bi-

directional I/O port, if the A/D Converter is not used. Port pins can give internal pull-up

resistors (selected for each bit). The Port A output buffers have symmetrical drive

characteristics with both high sink and source capability. The Port A pins are tri-stated

when a reset condition becomes active, even if the clock is not running.


53

Port B (PB7 to PB0)

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected

for each bit). The Port B output buffers have symmetrical drive characteristics with both

high sink and source capability. The Port B pins are tri-stated when a reset condition

becomes active, even if the clock is not running.

RESET

These pin corresponds to Reset Input. A low level on it terminal for more than

the minimum pulse length will generate a reset, even if the clock is not operating.

XTAL1

This pin corresponds to the Input of the inverting Oscillator amplifier and input

to the internal clock operating circuit.

XTAL2

This the Output from the inverting oscillator amplifier.

AVCC

The supply voltage pin for Port A and the A/D Converter is the AVCC. It has to

be connected to VCC, even if the ADC is not used. During the use of the ADC, this pin

should be connected to VCC using a low pass-filter.

AREF

AREF is the analog reference pin for the A/D Converter [5].

3.3.2 ADC – Analog to digital converter

The ATmega16 has incorporated a 10-bit successive approximation ADC. This

is connected to an 8-channel Analog Multiplexer which permits an 8 single-ended

voltage inputs constructed from the pins of PortA. The device also supports 16

differentials voltage input combinations: ADC0, ADC1, ADC2 and ADC3.


54

A Sample and Hold circuit is also able on the ADC which make certain that the

input voltage to the ADC is held at a constant level during the conversion [6].

3.3.2.1 Operation

Through successive approximations the ADC switches an analog input voltage

to a 10-bit digital value. GND will be minimum value considered and the maximum

value is the voltage on the AREF pin minus 1 LSB. The analog input channel and

differential gain are selected by writing to the MUX bits in ADMUX.

The information from the ADC is a 10-bit result and it is presented in the ADC

Data Registers: ADCH and ADCL.

If the result is no more than 8-bits precision and left adjusted, it is sufficient to

read ADCH. Otherwise, ADCL should be read first, then ADCH, to make sure that the

content of the Data Registers are from the same conversion. Once ADCL is read, ADC

access to Data Registers is blocked. The ADC has its own interrupt which can be

triggered when a conversion completes. When ADC access to the Data Registers is

forbidden to read the ADCH and ADCL, otherwise the interrupt will trigger even if the

result is lost [6].

3.3.2.2 Starting a conversion

To start a single conversion a logical one has to be written on the ADC Start

Conversion pin, ADSC. This bit keeps in high level as long as the conversion is in

progress and it will be cleared by hardware when the conversion is completed [6].


55

3.4 Antenna

An antenna (Figure 20) is a transducer able to transmit or receive

electromagnetic waves. They convert electromagnetic waves into electrical currents or

vice versa. An antenna is used in systems such as radio and television broadcast, point-

to-point radio communication, wireless LAN, radar and space exploration [7].

An antenna is considered simply as an arrangement of one or more conductors.

In the process of transmission, a voltage is applied on the terminal of the antenna and an

alternating current is created, which causes the conductors to radiate an electronic field.

In the reception process the opposite happens: an electromagnetic field from a different

source provokes an alternating current in the conductors and an equivalent voltage at the

antenna’s terminals is created [7].

Figure 20: Antenna: Electromagnetic schematic

3.4.1 RF – Radio Frequency

Radio frequency (RF) is a rate of oscillation of an electromagnet radiation in the

range of about 3 Hz to 300 GHz. This range matches to the frequency of alternating

current electrical signals employed to create and identify radio waves. [8].

http://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/w/index.php?title=Electromagnet_radiation&action=edit&redlink=1http://en.wikipedia.org/wiki/Hzhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Electrical_signalhttp://en.wikipedia.org/wiki/Radio_waves


56

3.4.2 RF module

The concept for RF module can be considered simple. It is the join of a

transmitter and a receiver part which permit the user to simply send serial data, control

robots and other wireless information. Combining the RF receiver and the RF

transmitter a link very consistent can be produced and a transfer of wireless data can be

established, not including any additional work processor. These have usually low power

requirements, ideal to be feeding by batteries [9], being one of the requirements of the

e-Cane project.

3.5 References


http://www.maxwellbohr.com.br/downloads/Tutorial%20Eletronica%20-

%20Aplicacoes%20e%20funcionamento%20de%20sensores.pdf .

[2].[Online] [Cited: November 6, 2008.] http://www.honeywell-

sensor.com.cn/prodinfo/sensor_ultrasonic/technical/98ib81.pdf .

[3].C. Baukal Jr., The John Zink Combustion Handbook (Industrial Combustion Series),

CRC Ed, 2001.


http://www.sick.com.br/br/produtos/sensoresindustriales/sensoresultrasom/pt.html.

[5]. Paret, D. e Fenger. C.; “The I2C Bus from Theory to Practice”, Wiley and

Sons.1997

[6].[Online] [Cited: June 20, 2009.] http://www.atmel.com/

[7].John Volakis, Antenna Engineering Handbook, Fourth Edition, McGraw-Hill

Professional, Wiley June 2007.

[8].Devendra Misra, Radio-frequency and microwave communication circuits: analysis

and design, 2 nd Edition 2004.

[9].[Online] [Cited: February 20, 2009.] http://www.tato.ind.br/files/TXMRXM.pdf .

http://www.maxwellbohr.com.br/downloads/Tutorial%20Eletronica%20-%20Aplicacoes%20e%20funcionamento%20de%20sensores.pdfhttp://www.maxwellbohr.com.br/downloads/Tutorial%20Eletronica%20-%20Aplicacoes%20e%20funcionamento%20de%20sensores.pdfhttp://www.sick.com.br/br/produtos/sensoresindustriales/sensoresultrasom/pt.htmlhttp://www.atmel.com/http://www.amazon.com/exec/obidos/search-handle-url/ref=ntt_athr_dp_sr_1?%5Fencoding=UTF8&sort=relevancerank&search-type=ss&index=books&field-author=John%20Volakishttp://www.tato.ind.br/files/TXMRXM.pdf

57

4 e - Cane development

Summary

In this chapter, the design and the development of the e-Cane are explained and all

the devices used in the prototype are detailed.

4.1 e - Cane Project overview

4.4 Components, Acronyms and values

4.2 Ultrasonic sensors

4.3 Detection Methods

4.5 Microcontroller

4.6 Bracelet

4.7 Micro motor C-6070

4.8 Antenna: RF module

CHAPTER 4 – E-CANE DEVELOPMENT ELECTRONIC CANE DEVELOPMENT

58

4.1 e - Cane Project overview

In the e-Cane development some requirements were defined: it should be a low-

cost prototype, it should have low power consumption and it should have small

dimensions, in order to have a portable system to insert both in the cane and the

bracelet.

The project initially began with a research regarding electronic schemes to drive

the sensors MA40A5.

Given that the reference voltage should have values that could be provided by a

small battery, some of the electronic configurations could only be used for laboratory

tests. Circuits with voltage reference between - 15 V and +15 V or between -18V and

18V are very commons; however it can only be applied in laboratory tests. Since the

project has the aim to be portable, it could not operate within these values.

A scheme with reference voltage between 0V and 9V was tested and

implemented. Since the portable system should be small, in order to detect obstacles on

the left side, another sensor was chosen. It should be a sensor that had already

incorporated all the associated electronics in a small size. So, the sensor SRF02 was

chosen, tested and incorporated on the prototype.

Using the microcontroller ATMEGA16 to control and activate all the processes, a

C programming in language C was developed.

After testing the sensors and the programming, other search was made. The

warning system using micro motors both on the wrist and cane had to be tested as well

as the RF modules, with the purpose to promote the communication between the

microcontroller and the bracelet.

The Block Diagram (Figure 21) shows an overview of the main processes of the

project.

ELECTRONIC CANE DEVELOPMENT CHAPTER 4 – E-CANE DEVELOPMENT

59

Figure 21: Microcontroller Block Diagram

As illustrated in Figure 21 the microcontroller ATmega16 can be considered as

the center of the all development, being responsible for:

- Sending a square wave to the sensor MA40A5 (activation of the sensor);

- Making operate the SRF02;

- Receive the signals from the detections;

- Switching on the micro motor;

- Sending information through the RF module in order to switch on the micro

motor at the bracelet.

4.2 Ultrasonic sensors

In order to make a distinction between both left and right/front side of the user, it

was necessary to use two ultrasonic sensors. At the beginning it was thought to use two

MA40A5 sensors; however its implementation would have physical dimensions that

would exceed the space available on the cane.

So, two different kinds of ultrasonic sensors were used: the MA40A5 and the

SFR02 to detect obstacles both left and right side, as explained in the next section. The

first one was used to detect obstacles both at front and right side of the user, and the

second one to detect obstacle on the left side of the user.


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4.3 Detection Methods

Using the sensors integrated with the cane both on the front/right and left, a large

range compared to the normal use of the white cane is achieved. As it is possible to see

in Figure 22, the expected range (d) from the use of the sensors MA40A5 increases,

giving to the user a better perspective of what to expect.

Figure 22: Range using sensors

Therefore using the sensor SRF02 the confidence also increases (Figure 23),

because the user has a greater sense of the space, since the obstacles on the left side will

also be detected. As a result, the user is able to produce a mental map of the spaces and

on a near future may move in these places with more independence.

Figure 23: Left detection range


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As in Figure 23, two different distances, d1 and d2, are used. This was designed

so that the movement of the left arm does not interfere with the detection of obstacles,

since the reading could be obstructed by this movement. If that happens the user of the

cane could be misled because the arm would be constantly detected by the sensor and

therefore they would be alerted to the presence of obstacles, which were not there. In

the tests d1 was considered as 40 cm and d2 as 110 cm, making a total range of 150 cm.

An explanation of each sensor is given in the next sections.

4.3.1 MA40A5

The ultrasonic sensors chosen to read the signals coming from both front and right

side of the user were the MA40A5 (Figure 24). They have a working range of 0.6 to

20ft (18 cm to 6m) with a nominal frequency of 40 KHz (datasheet in appendix A).

Figure 24: Ultrasonic Sensors

The sensor consists of a transmitter and a receiver part explained below.

4.3.1.1 Transmitter

The first part of the schematic consists of an oscillator, responsible for creating

one signal with the frequency of 40 KHz to be sent to the ultrasonic emitter.

The oscillator consists of an ICM755, a CMOS timer that provides a

significantly improved performance over the standard NE/SE555. It is also a stable

controller capable of producing accurate time delays or frequencies. To produce a

square wave with the required frequency, it was used the configuration shown in Figure

25.


62

Figure 25: ICM755 as “Astable operation”

In this circuit the frequency is given by the equation:

F= 1

ln 2 𝑅𝐴+2𝑅𝐵 ∗𝐶1 (eq. 4)

4.3.1.2 Emitter Schematic

Using equation 4, the emitter schematic was developed and it is presented in

Figure 26. The potentiometer (R5) was used, in order to calibrate the circuit to produce

the frequency of 40 KHz.

Figure 26: Emitter


63

The tests made to this circuit are presented in Section 6.1.

4.3.1.3 Receptor

The receiver part is more complex than the transmitter part, because the strength of

the echo received can be very weak, being proportional to the distance. In other words,

if the sensor detects an obstacle further away from the receiver, the signal received will

be weak. Therefore, it was necessary to reinforce the signal and also to filter it, in order

to extract the desired information.

4.3.1.4 Block diagram

In order to understand the implemented project, a block diagram was developed

(Figure 27).

Figure 27: Block diagram of the Receptor

A detailed description of the processes is presented below,

Bandpass filter and amplifier- Since the entire system operates at 40

KHz, a bandpass filter is implemented to separate out the unnecessary frequency,

components or noise (Figure 28).


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Figure 28: Band Pass Filter and Amplifier

At the first and second stage the gain is given by equation 5, which refers to the

inverse amplifier gain (Figure 29). Therefore, the gain of the two stages is 330 times (33

times at the first stage and 10 times at the second one).

After this process the output (Vamp) is connected to the peak detector.

Figure 29: Inverter amplifier

Peak Detector - The peak detector sense the received ultrasonic signal. It

is half-wave rectification circuit with diodes. The DC voltage according to the level of

the detection signal is output to the capacitor. The circuit implemented is shown in

Figure 30.


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Figure 30: Peak Detector

Comparator – The output of the peak detector is connected to an input of

the microcontroller. The ADC in the microcontroller, as explained in section 3.3.2, can

read this information. So, connecting it to the input ADC0 existing in the

microcontroller and by software, it can be compared the value read to the reference

value. If the value read is higher than the reference value, an obstacle was detected, and

the microcontroller will set on the micro motor implemented in the cane.

4.3.1.5 Receiver circuit

The receiver circuit consists of the combinations of the band pass filter with the

peak detector, as seen in Figure 31.

Figure 31: Receiver circuit


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The experiments made during the development of the receiver part, can be seen

in section 6, where the illustrations of the tests are presented and explained.

4.3.1.6 General Schematic

The final schematic of the sensor consists of the combination of the two parts

explained before (Figure 32).

Figure 32: Ultrasonic Schematic

The circuit has a power supply between 0V (V-) and 9V (V+). The 7809

(Voltage regulator) is responsible to sustain that voltage. As it is possible to see in

Figure 32, the circuit is divided in three main parts:

(1) Emitter

(2) Receptor (Band pass filter and Amplifier)

(3) Peak Detector


67

After some tests, the implementation was possible as can be seen in chapter 6 at

the laboratory results.

4.4 Components, Acronyms and Values

The major components used in the e - Cane development are listed in Table 4,

including all the acronyms employed.

The electronic components, such as resistors and capacitors, used in the

development of the cane are illustrated in the tables 5 and 6.

Table 4: Major Components listing and Acronyms

Components Type Acronym

Ultrasonic Transmitter MA40A5S Tx

Ultrasonic Receiver MA40A5R Rx

Ultrasonic range finder SRF02 SRF02

Op-amp LM358N IC4

Diode 1N5819 D

Voltage Regulator 7809 IC1

Comparator LM311 LM311

555 Timer ICM755 IC3

Transistor 2N3904 Q1

RF Module RRFQ2/RTFQ2 RRFQ2/RTFQ2

Table 5: Resistor values

Resistor Value Resistor Value

R1 1KΩ R7 10 KΩ

R2 560 Ω R8 330KΩ

R3 10 KΩ R9 100KΩ

R4 10 KΩ R10 10 KΩ

R5 20 KΩ R11 10 KΩ

R6 10 KΩ


68

The resistors, R1- R5, were used at the emitter part (Figure 26) of the sensor

development. In the process of Band Pass Filter and Amplifier (Figure 28), the resistors

R6 – R11 were used.

Table 6: Capacitor values

Capacitor Value

C1 1 nF

C2 1 nF

C3 1 nF

C4 1 nF

C5 10 nF

The C1 value was used at the emitter part of the development of the sensor

MA40A5 (Figure 26). The capacitors, C2 and C3, were used on the process of Filtering

and Amplifying of the echo signal (Figure 28) and C4 was used at the peak detector

(Figure 30). The last capacitor C5 was used in the final schematic of the sensor (Figure

32).

4.4.1 SRF02 Ultrasonic range finder

The sensor SRF02 was used to detect the obstacles on the left side of the user as

explained in section 4.3. The choice of this sensor was made taking into account its

characteristics. Since that it already has all the processes of the block diagram of the

section 4.3.1.4 in a small size, it could be easily integrated to the cane without exceed

the space available at the prototype (Figure 33).

Figure 33: SRF02 ultrasonic range finder


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In order to read the distance measure and adjust the sensor by the use of a

computer the mode I2C was selected (Figure 34). This mode was chosen because of the

characteristics seen in 3.2.

The "Mode" pin should be left unconnected, since it has an internal pull-up

resistor. The SCL and SDA lines should have a pull-up resistor to +5v somewhere on

the I2C bus and it is suggested to use resistors of 1.8kΩ [1] [2].

Figure 34: SRF02 – I2C Mode

4.5 Microcontroller

The microcontroller is responsible to generate and send the pulses that activate the

transmitter part of the sensor. It works like a switch (on - off), that will permit to

receive, during the “off time”, an echo signal coming from the obstacle (when detected).

As explained in section 3.1.1.2, the distance is given by equation 2:

𝑑 = 1

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