Pulsed Fibre Optic Light Source for Optical Tomography

Pulsed Fibre Optic Light Source
for Optical Tomography
By
Qasim Humayoun
000894986
Submitted in Partial Fulfilment of the
Requirements for the Degree of
BEng (Hons) Electrical and Electronics Engineering
Technology
Supervisor: Robert Jenner
Electronic, Electrical and Computer Engineering
Faculty of Engineering and Science
30 September 2016

ii
Abstract
This project focuses around the implementation and design of a pulsed visible LED light
source that is can be used for one of the widely demanded tomographic technique, optical
tomography. The product consists of array of 16 visible LEDs so that it is can be used for
imaging related applications. Due to the physical dimensions of the visible LEDs, it is not an
effective method to be used for imaging purposes, this is mainly due to the reason the beam
will not be able to obtain the levels of resolution that is suitable for such applications. A very
effective way to overcome this issue was to develop a remote light source and guide the ray
into an array of fibre optic; the small size of the optic cable higher levels of resolution, levels
of resolution that is adequate for imaging purposes can be achieved. The fibre will then feed
the beam of light through a transparent section of a pipeline for imaging applications. The
intensity of the visible LEDS can vary if required. The product will provide a constant light
or pulsed light at user defined speeds.

iii
Acknowledgements
This research was supported by University of Greenwich. I thank my colleagues B. Gaire, L.
Sherif and J. Kabano who provided insight and expertise that greatly assisted the research,
although they may not agree with all of the interpretations/conclusions of this paper. On top
of that I would like to thank my supervisor R. Jenner who provided great support, made sure I
was moving in the right direction and for comments that greatly improved the manuscript. I
thank the technicians for assistance with ordering the components. And my colleagues A.
Ayeni and Ubon who provided their technical knowledge.
All the people mentioned above were a great support and helped in shaping the outcome of
the entire project.

iv
Table of Contents
CHAPTER 1 INTRODUCTION. .......................................................................................... 1
1.1 OVERVIEW .............................................................................................................. 1
1.2 AIMS AND OBJECTIVES ............................................................................................ 2
1.3 LITERATURE REVIEW................................................................................................ 4
1.3.1 Background ....................................................................................................... 4
1.3.2 Benefits of using pulses of light.......................................................................... 5
1.3.3 Does Optic fibre help with resolution?................................................................ 6
CHAPTER 2 DESIGN......................................................................................................... 7
2.1 PRODUCT REQUIREMENT ......................................................................................... 7
2.2 SELECTION OF COMPONENTS AND MATERIALS ........................................................... 7
2.2.1 Micro-controller based timing circuit................................................................... 8
2.2.2 Emitters ........................................................................................................... 12
2.2.3 Preparation of Optical Fibre ............................................................................. 13
2.3 ANALYSIS.............................................................................................................. 16
2.4 DESIGN SOLUTION ................................................................................................. 17
CHAPTER 3 IMPLEMENTATION..................................................................................... 20
3.1 BUILDING THE LIGHT PROJECTION CIRCUIT .............................................................. 20
3.2 BUILDING THE MICRO-CONTROLLER TIMING BASED CIRCUIT ...................................... 22
3.3 BUILDING THE PROTOTYPE..................................................................................... 23
3.4 CHANGING THE PLATFORM ..................................................................................... 24
3.5 CONFIGURING DE0 BOARD..................................................................................... 25
3.6 BUILDING THE FINAL PROTOTYPE............................................................................ 29
3.7 COUPLING THE OPTIC FIBRE ................................................................................... 31
3.8 FINALIZING............................................................................................................ 33
CHAPTER 4 TESTING, RESULTS AND DISCUSSION ................................................... 34
4.1 TESTING WITH ARDUINO ........................................................................................ 34
4.2 RESULTS WITH ARDUINO........................................................................................ 35
4.3 TESTING THE VHDL CODE ..................................................................................... 37
4.4 TESTING/RESULTS OF THE LIGHT PROJECTION CIRCUIT............................................ 38
4.5 TESTING/RESULTS OF DIFFERENT CONFIGURATIONS................................................ 39
4.6 TESTING/RESULTS OF INDIVIDUAL LEDS (FINAL PROTOTYPE) ................................... 40
4.7 FINAL TESTING...................................................................................................... 41
CHAPTER 5 CONCLUSIONS .......................................................................................... 43
5.1 CONCLUSION ........................................................................................................ 43
5.2 REFLECTIONS AND FUTURE WORK ......................................................................... 44

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REFERENCES ................................................................................................................... 45
APPENDIX A GANTT CHART ........................................................................................... 47
APPENDIX B (DATASHEETS)........................................................................................... 48
APPENDIX C (VHDL CODE).............................................................................................. 50
APPENDIX D (PARTS LIST/BILL OF MATERIALS).......................................................... 55

1
Chapter 1 Introduction.
1.1 Overview
Started from the Greek words "tomos" which indicates slice and "graph" which means
picture, tomography can be characterized as a photo of a ‘slice’ of a process. Process
tomography is a “Tomographic” technology that involves the accomplishment of measuring
different signals sent from emitters and captured from the other end, the periphery of an
object with the help of sensors. This “object” placed in parallel to the sensors and emitters
can be in the form of a process vessel, human bones, process vessels and pipelines. The use
of tomography provides the user with a precise cross-section image of the subject placed in
between the sensors and emitters.
There are several diverse tomographic technologies, each offering an extensive variety of
applications. A few well known tomographic technologies are X-rays and CAT scans.
Using light techniques for gathering information in a similar way is among these diversities.
Optical Tomography has existed for many years. In early times it was used to provide visual
inspection for fermentation processes. Giving results in terms of clarity, colour and gas hold-
ups. This has been one of the main techniques for exploring the quality and state of the
fermentation process. However, in recent times many of the ways in which matter interacts
with light has been used to examine and learn the process parameters. Using the principles of
absorption, diffraction and reflection to provide the cross-section of the subject/container.
Figure 1.1. An array of eight transducer pairs. (Left) Top view. (Right) Front view
The figure above illustrates how the emitters, object and the detectors are positioned. The
emitters are placed around the cross-section of the object/container/pipe and detectors can be
found aligned on the same axis on the other side of the container/pipe. The beams of light
produced from the visible LED emitters are optically designed to frame a collimated beam
incident on the vessel containing the procedure of interest as seen on figure 1 (right)
Emitter Detector
Flow
Regime

2
Industrial areas have pipelines and containers that are fed with gases/liquids. These industries
provide its consumers with high quality products and in order to do that, they would very
much like to know what goes on inside these pipelines/containers and how gases/liquids
behave as they pass through them. It gives estimation where ordinary observing instruments
can't be worked, because of either the way of the regulation or the procedure in progress.
Optical tomography can be used to overcome this problem.
The motivation for this solution is that the use of optical tomography means that the
outcomes can create on-line query-able three dimensional information and visual
representations, considering a far more noteworthy level of comprehension of the procedure.
They are also quite non-intrusive and immune to electrical (background) noises. In monetary
terms, they are less expensive to use, as it comprises of just three imperative parts, the
controller, emitters and optic fibre link.
Because of the physical measurements of the visible LEDs, it is not a viable strategy to be
utilized for imaging purposes. This is predominantly because of the reason that the beam
won't have the capacity to acquire the levels of resolution that is suitable for such
applications. An exceptionally compelling approach to defeat this issue is to add a remote
light source and guide the beam into a variety of fibre optic; the little size of the optic link
more elevated levels of resolution that is sufficient for imaging purposes to be accomplished.
The fibre will then bolster the light emission through a straightforward area of a pipeline for
imaging applications.
These pulses of optical light from the emitters are then sent through a pipeline and are
recognised and received on the sensor side. On the off chance that the entire bundle (the
emitters with the sensors for the application) then it will be directed for finding the image for
that pipeline only. So instead, the source (emitter) is only to be planned and created and for
application purposes the industry can have diverse sensors for various pipelines/holders set-
up. The sensors will be characterized likewise, contingent on the material and its holder they
are utilizing it for and one and only emitter would be required. Along these lines they can
utilize the same heartbeat emitter for various parts in their ranges.
1.2 Aims and Objectives
Ultimately the main goal of this project was to build a pulsed fibre optic light source that will
be used for optical tomography. For the goal to be achieved the project will focus on a few
major aims.
1. Build an array of isolated light sources and guide the beams from the source through a
variety of optic fibre
2. Build a circuit/system that would provide variations of scan rates.
3. Build a circuit/system that would allow the user to control the intensity of the light
source
In order for the following aims to be achieved there are several objectives that had to be
completed. The entirety of the project was broken down into smaller fragments of objectives
and targets that were to be accomplished in a certain timeline. A Gantt chart was used to help

3
to keep track of the objectives to be completed within the timeline. For the venture to be
recorded "finished", the greater part of the goals are to be done. Below are some of the
objectives that helped in shaping the project. More detailed versions of the objectives were
arranged with further advancement in the outline territory of the venture.
Figure 1.2. Target list listing the fragments of objectives
All through undertaking these targets will function as a rule to advance in the project. The
destinations specified above are only a standard way to complete an undertaking in each of
the goals, it will be separated into further detail and set other point by point targets at each
strides.
Project Requirement
• Detailed examination of issue: Inspecting the problem at hand and finding a potential
solution for it. This objective looks at the project from a broader view and details the
essential issues at hand.
• Detailed specifications: listing all the specifications and using them to help in the
architecture and design of the project. The listing acts as a general checklist that the
design would have to fulfil to be considered as a plausible solution.
Architecture and Design
 Design tool selection: Different design tool selections such as matrix and Pugh table
will be used, in correlation with the specifications to help choose the most appropriate
design for the project.
 Design analysis: After the different designs are compared using the Design tool
selection, they would be analysed and the most appropriate design for the project will
be selected.
Project
Requirement
Architecture and
Design
Development
Testing
•Detailed examination of
issue
•Detailed specifcations
•Design tool selection
•Design analysis
•Implementation of selected
design
•Circuit design
•Fault Findings
•Compare expected results
with actual results
•final Evaluation

4
Development
 Implementation of selected design: After the analysing the design selection methods
and choosing the appropriate design. The process of putting the design into effect will
be carried out. This will help identify the components and the materials of the
product.
 Circuit design: After the selection of the materials and components, the circuit design
will be built and a physical model of the product will be created.
Testing
 Fault finding: After the circuit building, the design will be tested to find any possible
faults that might emerge in any of the components or materials. The faults might
originate from the wirings or might be in the form of semantic errors.
 Compare expected results with actual results: As the goal suggests, the final product
will be tested in several parameters and would be compared with the results that is to
be expected from each of the parameters. This involves the light intensity emitting
from the source, the variation of scan rates and its frequency.
 Final evaluation: After all the testing is done a final conclusion will be carried out to
see if the product as a whole is functional and is effective in delivering its purpose.
Following the straight path and completing the objectives along the journey will anchor the
odds of achieving the Aims of the project.
1.3 Literature review
1.3.1 Background
Optical tomography is a new technique that is used in medical imaging and industrial process
tomography. In 1943, Horecker [19] introduced the potential of using near infrared light as a
probing radiator. He realised that haemoglobin in blood is a good absorber of near infrared
light and the absorption of oxygenated and deoxygenated blood were found to be different.
Later in 1996, a project took place that dealt with developing a working system that used
optical light for medical imaging. It was later used in industrial process tomography system
to help in monitoring the periphery of industrial processes such as mixing tanks, oil pipelines
and fermentation processes. Optical tomography has become a very popular form of
tomography in industrial world, mainly due to its cheap and off-the-self components and its
ability to develop good quality images and provides the important flow information such as
velocity, concentration measurements and flow rates without invading the process/object.
Thus, as a result, cross-section images of these processes can generate better monitoring and
more effective utilization of applicable process capacity. Optical tomography can be a very
potential candidate in verifying and developing process theories and models, as well as
improving the current process instruments used.

5
1.3.2 Benefits of using pulses of light
S. Ibrahim [18] mentioned in one of his paper that in optical tomography, the alignment of
the emitters play an important role in determining if the design is fruitful or not. The light
from the source emitting from the source must be detected by the receivers on the opposite
end of the pipe. Many of the vessels and pipes in industries and manufacturers have very poor
transparency and are very opaque. Consequently, a great outline of optical windows is
required to guarantee the light generally gotten by the beneficiaries, ensuring that light is
received by the receivers. It is also a good idea of sending pulses of light from the source to
the receivers. Sending pulses rather than one continuous stream of light provides a higher
resolution of the cross-section of the object of interest. The receivers will be expecting the
pattern of pulses and will be prepared for the sequence, any disturbance within the pipeline
means that the receiver did not experience that pulse in the pattern and would use the
information to help better develop the final cross-section image of the vessel containing the
process of interest. It also eliminates the highly unusual behaviour of light and uses statistical
analysis from the pulses and uses the data to better predict the cross-section image and
provide the users with an accurate outcome.
Faramarzi [17]. Johansen, G [12] and Sakami. M [9] published their work which supported S.
Ibrahim’s [18] work. Both the papers were on similar terms but had different case studies.
Faramarzi and Sakami analysed the short-pulse laser propagation and in their conclusion they
mentioned that the pulses of light from the source helped in developing an image of better
quality, but unlike Ibrahim’s work, the images gathered from the individual pulses would be
stacked on top of each other (by a computer software), giving a very detailed outcome.
In 2006, Kunal Mitra [9] and few of his other colleagues performed an experiment that
supported Ibrahim’s [18], Faramarzi [17] and Sakami’s [9] work. His aim was to perform a
numerical analysis of short-pulse laser interacting with medium representing human tissue.
The experiment was performed with a time-resolved optical detection scheme; the scheme
would provide a computer (that would combine all the detections from the receivers and
“bind” them together, developing an image) with support to help predict the cross-section of
the image. Next, the same experiment was carried but without the use of the short-pulses and
the detection scheme. He came to conclusion that the short-pulses developed much better
images than the latter approach.
Figure 1.3. Kunal Mitra’s illustration fixating his results

6
The figure above shows the results of Kunal Mitra’s [10] experiment. The image on the right
involved the use of short-pulses. In terms of resolution the difference between them is by a
land slide.
1.3.3 Does Optic fibre help with resolution?
Earlier researches done by Khoo [4], Ruzairi [2], Hisyamuddin [5] and Sallehuddin [3] have
shown that the optic fibre cables used as a means of medium from the source to the object
aids in image construction.
The acquired concentration profile from the image reproduction is required together with the
velocity profile to finish the mass flow rate estimation in a ventilated conveying system.
Fundamentally, the principle of measurement in tomography is to acquire every single
possible combination of measurement from the sensor framework. The higher the
measurement acquired from the sensors, the resolution of the system would be better. By
utilizing the parallel projection, past explores have each confronted the issue of acquiring a
high resolution of their system. This is because the parallel projection technique confines the
number of measurements to the quantity of sensors being utilized. In a research done by Chan
[6], he implemented a fan beam projection technique (instead of a parallel projection) to
obtain flow representation using visible LED as the emitters, but the resolution and the
number of receiving sensors he used in his system were limited by the physical size of the
visible LEDs being used. Thus, his research focused in implementing the fan-beam projection
method by using optic fibre cables to act as a means to transport light from the visible LED to
the sensing side. Because of the sheer small size of the optical cables Chan [6] was able to
increase the number of sensors and the number of measurements taken, ultimately obtaining a
system with high resolution then before.
Figure 1.4. Fibre optic configuration
The figure above shows the configuration that Chan [6] used in his system to increase the
number of measurements taken, leading to high resolution.

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Chapter 2 Design
2.1 Product requirement
The problem at hand was to build a pulsed light source that can be used for optical
tomography. The product had array of visible LED emitters. Depending upon the size of the
pipe, a number of visible LEDs will be placed around the body of the pipe to develop a 3D
model of the inside process of the pipe. For this project 16 visible LED emitters are used.
These array of visible LEDs are controlled via a micro-controller (with timing based
capabilities) to allow for different scan rates to be selected, a system to control the intensity
of the visible LED emitters and a system to allow users to control with visible LED emitter to
use.
1. Micro-Controller: The controller should be able to drive the array of visible LEDs
effectively. Allow user control to vary the intensity of the LEDs, be able to provide
different pulse rate options for the emitting visible LEDs and provides user control to
switch any desired emitters or array of emitters.
2. Visible LEDs: There should be arrays of LEDs available to provide for an increased
number of measurements that can be taken to produce an image effectively. The
visible LEDs should have high intensity to be able to transfer light up to the vessel of
process. And should have fast timing rates to provide effectively for the different scan
rates. If the LEDs are not fast enough then the LEDs will not be able to keep up with
the pulses and would not light-up with high intensity, losing performance of the
overall product.
3. Optic Fibre: The optic fibre should be able to be fitted with the LEDs effectively and
is capable of accepting the incoming light from emitters. The cable should also be
able to transport the light effectively to the vessel of the process
2.2 Selection of components and materials
This section of the chapter mainly focuses on the different aspects of the project from which
the most appropriate components and materials will be selected, shaping the final design.

8
2.2.1 Micro-controller based timing circuit
Figure 2.1. Micro-controller – brainstorming Ideas
The figure above was the Brainstorming that was done for the selection of a Micro-controller.
The primary function that the micro-controller should be able to deliver is that it should be
able to drive an array of 16 LEDs. The controller acts as the backbone of the project and the
selection of the most appropriate controller will further shape the design of the product.
PIC series
Abdul Rahim [1] in his system used two different PIC (Programmable Interface Controller)
micro-controllers when designing an optical tomography system. His research compared two
microcontrollers PIC and ds-PIC (Digital Signalling-PIC) and concluded the benefits of using
each of the two micro-controllers.
PIC18F4520 is written in C language. It has a RAM of 21 bits and consists of 20 GPIO
(General Purpose Input/Output) that are able to operate in clock mode, this functionality will
the circuit to operate at different scan rates. PIC18 is one of the most popular in its family;
this is mainly due its fast performance and ease to interact with other PIC controllers.
Mircro-
controller?
Rasberry Pi
Arduino
De0
development
Board
PIC Series

9
Figure 2.2. PIC18 micro-controller
The figure above shows the Pin layout of PIC18. One of the disadvantages of PIC18 is that
the Program memory is not accessible and is only one time programmable.
The dsPIC30F6014A from the same family as the previous mentioned microcontroller. It also
uses C programming language and contains 66 I/O ports which is more than enough than
required and allows for further extension in the emitter.
Figure 2.3. DcPIC30 microcontroller
After using the two for the same task Abdul Rahim [1] came to a conclusion that in terms of
performance ds-PIC outperformed PIC18 and the usage for the optical tomography system
was better with ds-PIC, as it has 66 I/O pins. And the programming part for dsPIC is much
simpler and less troublesome than PIC18.

10
Arduino
Figure 2.4. Arduino Uno
An Arduino has 6 analogue input pins and 13 digital I/O pins from which only 6 are PWM
(Pulse-Width Modulation) these PWMs will make the emitters to pulse at different scan rates.
These micro-controllers are open-source, meaning that the components used in the controller
are obtained from off-the-self materials. They are programmed using C language and can be
programmed to provide the user with controls to select any single or groups of LEDs. From
looking that Figure 2.3 it can be seen that Arduino does not have enough pins to control 16
LEDs. But because of its vast functionality it can effectively operate with LEDs Drivers,
these will be able to drive the required number of emitters. Because it has PWM’s it will be
also be able to make the LEDs to pulse at different scan rates.
Raspberry Pi (model 2)
Figure 2.5. Raspberry Pi 2
A raspberry pi is a single-board computer. They operate on Python buy also support C and
C++ languages. Raspberry Pi 2 consists of 20 GPIO and similar to Arduino can be
programmed to control the 16 LED emitters. They are very cost effective and are very
compact in terms of size.

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De0 Development board
Figure 2.6 De0 Board
These are development board that can be used for a variety of functions it consists of 36
GPIO pins and can be programmed to control the LED emitters. Unlike Arduino and
Raspberry Pi, De0 uses Hardware Description Languages (HDL). They come with built-in
switches that can be programmed to control the LED emitters. HDL is naturally parallel and
assignments can be both parallel and sequential. All the other micro-controllers mentioned
before operate using programming language, which can only handle sequential instructions.
However, De0 boards are not compact in size and can be very expensive unlike the other
micro-controllers.
The mentioned micro-controllers will now be compared with each other against some
parameters that will help in selection of the perfect microcontroller for the project.
Table 2.1. Comparison of micro-controllers
Micro-controller Cost Size Functionality Ease in
programming
PIC series *** ***** ** **
Arduino **** **** *** ***
Raspberry Pi **** **** *** **
De0 board ** *** ***** ****
From looking at the table Arduino was selected as the micro-controller. This is mainly due to
its compact size and inexpensive off-the-self components. Arduino fulfils the requirement to
be used for the project. It can be programmed to control the intensity of the LEDs. However
because it does not have enough pins to control the 16 LEDs, a LED driver has to be used to
drive the required number of LEDs. TLC5940 chip is one of the most popular LED driver
that is used to control large number of LEDs and works very effectively with Arduino.

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2.2.2 Emitters
Emitters are the main optical sensors in the project and were carefully selected to satisfy the
requirements and characteristics of the hardware system of the project. The requirements for
the projects hardware system was that the emitters must have a very fast setting time when it
is being derived by a pulse rate. The reason for the fast setting time is that when the visible
LED is in operation and are being used in its pulse modes, the visible LED will not be able to
“Keep-up” with fast changes of digital HIGHs and LOWs (On’s and Off’s) and will reduce in
intensity, lowering the performance of the overall product.
There are three emitters that can be selected for the Optical fibre Process Tomography
(OFPT) system visible LEDs, Infrared and laser diodes. Looking at the requirements of the
project, it has already been established that the emitters are going to be visible LED driven.
Thus narrowing the search down to that type of emitters. Visible LEDs are very cost effective
and more user friendly compared to the other types of emitters. Besides, the output power of
visible LEDs is linearly proportional to driving the current. Linearity can play an important
characteristic to light sources in analogue applications which is accentuated in the usage of
the OFPT sensors. For any open debates questioning the use of visible LEDs for the hardware
system. In terms of linearity and cost visible LEDs are a better choice than laser diodes.
Problem with using LED
However, visible LEDs are not without weaknesses. One of the major issue of using visible
LED as a transmitter for the system is that because it operates as a visible light with the
wavelength ranging from 380nm to 700nm, the results in the tomography sensors that would
be used with the OFPT light source system is going be greeted with unwanted noise from the
surrounding environment. Most of the light used in our daily life is visible or white light such
as florescent light or incandescent light which have a peak radiant power of about 380nm.
This can easily affect the light received by the photo-receivers that would be used in the
sensing part of the system, making the projects OFPT light source system impractical and
expendable.
Potential solution
The most suitable and appropriate way to reduce the unwanted noise is to use a visible LED
that emits a light with a wavelength above the radiant power of household lights. This
criterion’s narrow down the search for the selection of the appropriate visible LED emitter for
the projects OPFT light source system.
The visible LED that is to be selected has to have high intensity, fast setting time when driven
by a pulse and above 380nm.
Looking at all the criterion the most appropriate visible LED was chosen that fulfilled all the
requirements. A Cree C503 series –Green colour LED was selected for the project. The
visible LED consists of a 5mm round shape and provides trustworthy performance and a
stable Lumen yield. The visible LEDs were manufactured using “optical-graded” epoxy
resin, offering moisture and temperature resistance for outdoor use.

13
Figure 2.7. Cree c503 series High Intensity Green LED
The figure above illustrates the actual size and shape of the LED. The lens of the LED is
clear and colourless, preventing any coloured lens to reduce the intensity of the LED.
Table 2.2. Parameters of selected LED
Requirements Met (), Not met (×) Evidence
High Intensity Met () The LED operates at a Luminous
intensity of 100 candela
Dominant wavelength Met () Because it a Green coloured LED
it has a dominant wavelength of
535nm
fast setting time Met () The LED is highly stable and
provides effective outcome during
different scan rates
The table above looks up the LEDs parameters and provides evidence that the requirements
asked by the projects light source system has been met.
2.2.3 Preparation of Optical Fibre
In utilizing optical fibre for tomography imaging, the basic optical transmitter converts
electrical info signals into adjusted light for transmission over an optical fibre. Also, the light
beam emitting from the source will be received by the receiving sensors via the optic fibre
cables.

14
Figure 2.8. Fibre optic configuration, similar to Chan’s system
The figure above illustrates how the fibre optic cable is configured. The Transmitter is
directly connected to the fibre optic cable which is then fed to the pipeline containing the
process of interest. With respect to the visible LEDs little physical size, it is trusted that
utilizing fibre optic will permit a higher number of optical sensors to be introduced, thus
achieving high level of resolution measurement in the tomography. Optical fibres provide
high bandwidth which allows measurements to be executed on fast flowing particles.
As stated earlier in the report (page 6), the optical fibre cables are used together with the
selected emitters to increase the level of resolution. It would be of good choice of selecting a
single core fibre optic cable made of polymer, having a core diameter of 1.00mm instead of a
fibre optic cable made of glass. This is because the former approach is easier to install and
affordable and as the core is plastic based rather than glass based, terminating the cable will
be much easier. The requirements for the selection of optic fibre will be very strict as it holds
the bridge that links the projects OFPT light source system to other receiving systems and
would be hindered useless if the bridge is not complete.
Figure 2.9. The selected fibre optic cable
Fibre Optic
Transmitter
MATERIAL FLOW
THROUGH PIPELINE

15
The figure above shows the fibre optic cable that was selected to for the system, completing
the bridge and potentially increasing the resolution. The acrylic optical fibre cable is made
with the polymer material mentioned earlier and is suited to for development and design of
short distance links. The cable is matched for visible light having a wavelength of 400nm to
700nm, within the limit of the LED that was selected. The cable is highly durable and heat
resistant. Its internal core has a diameter of 1mm and has an outer diameter of 2.2 mm.
The fibre optic cable has a numerical aperture of 0.47 and an acceptance angle of 56 degrees,
as calculated using the Core refractive index and clad refractive index. The numerical
aperture will determine the acceptance cone of the fibre cable. It determines how much light
can be collected by the optic fibre cable. Equation 2.1 (below) gives the formula to calculate
the numerical aperture for the optic cable. Equation 2.2 (below) gives the formula that can be
used to calculate the numerical aperture and Figure 2.10 shows the acceptance angle of the
selected optic fibre cable. The total receiving angle of the optic fibre cable is twice the
acceptance angle and in this case is 112 degrees.
-(n2)(n1)
22
(Eq: 2.1)
asin=NA  (Eq: 2.2)
Where:
n1 = core refractive index
n2 = clad refractive index
NA = numerical aperture of the fibre optic
Ɵa = acceptance angle of the fibre cable
(Note: numerical aperture is a measure of how much light can be collected by the optic fibre.
Acceptance angle is the max angle of a light beam hitting the fibre core (along its axis) which
allows the beam to be guided by the core. Core refractive index is the refraction of light when
it hits the core of the fibre cable. Clad refractive index causes the light to be restricted to the
core of the optic fibre cable.)
Figure 2.10. the acceptance angle of an optic fibre cable

16
2.3 Analysis
After the selection of potential components and materials analysis will be carried out to see if
the overall requirements are being met
Table 2.3. Design Specification checklist
Parameter Requirement Met (), Not met (×)
or to be Met (//)
Evidence
LEDs There should be
arrays of LEDs to
provide for
increased number
of measurements
that can be taken
that can be taken
to produce an
image effectively
Met () As established in the
report earlier, 16 LEDs
will be used for the
projects OTPT light
source
The LEDs would
have high
intensity
Met () The LEDs has an
intensity of 100 cd
Fast timing rates
to provide for the
different scan
rates
Met () The LED is highly stable
and provides effective
outcome during different
scan rates
Micro-
controller
To be able to
drive the Array of
LEDs effectively
Met () A LED Driver will be
used with Arduino Uno
to control the selected
array of LEDs
Allow user control
to vary the
intensity of the
LEDs
Met () Arduino can be
programmed effectively
to fulfil the requirement
Be able to provide
different scan
rates for the
emitting LEDs
Allow user control
to switch any
desired
emitter/array of
emitters
Optic Fibre Can be fitted with Met () For more details please

17
cable LEDs refer to chapters “2.4 and
3.7” of the report
Be capable of
accepting the
incoming light
from emitters
Met () The cable has an
acceptance angle greater
than the viewing angle of
the LED
Be able to
transport the light
effectively to the
process of interest
Met () The cable made of
polymer and is ideal for
design and
implementation of short
distance links
From the above table it can be seen that all of the requirements were met, except for the
requirement stating if the optic fibre can be fitted with LEDs, which was accomplished later
in the project. Comparing the components next to their requirements identified that the main
aim of the project can be achieved if no trial error takes place during the implementation of
the project.
2.4 Design solution
Now that all the components are identified and the requirements are met, the physical design
can now be started. Before the implementation of the product can be started, a solution for the
design has to be established. This “established” outline arrangement will shape how the
physical item will look like as it will distinguish which wire goes where and what component
goes where.
Before the final design will be created the different components will need a way to be
collaborated with each other and should be able to work in unison with each other. Starting
from the micro-controller, the TLC5940 LED driver chip has to be connected with the micro-
controller and the LED. The reason for using the TLC LED driver chip is the Arduino UNO
does not have enough PWM (Pulse-Width-Modulation) pins available. The PWM is a method
of getting analogue results with digital means. The PWM will help in controlling the intensity
of the LEDs and in making them pulse, but with lack of PWM pins means that the desired
number of emitters cannot be installed. One solution for this problem is to use the TLC LED
driver chip. This chip uses only a few pins from the Arduino and can drive up to 8 LEDs. The
chip can be daisy-chained, connecting more chips to the chip that is already connected with
the Arduino to increase the number of connected LEDs.

18
Figure 2.11. Circuit diagram
The figure above shows the circuit diagram of how the LEDs were connected with the
Arduino via the TLC chip. The blue, red and purple wires on the right hand side are all
connected to the pins on the Arduino board. In case of daisy-chaining the second chip with
the first one, the red and the green wires (clock and latch signal respectfully) will be extended
parallel to connect to the second chip. The figure below gives a better illustration of how the
daisy chaining will take place.
Figure 2.12. Daisy-chaining the chips
TLC5940
TLC5940
TLC5940

19
The Red wire is connected to Pin 9 on the Arduino board. Pin 9 on the board supports PWM
and will help in controlling the intensity and scan rates. The blue wire will be connected to
pin 12 which will support serial data input and the green wire can be connected to any of the
Arduino’s Digital pins.
Now that the relation between the Arduino and the LEDs are established the coupling
between the fibre optic cable and the LEDs can be designed. Any signal that is lost due to
improper coupling between the optic fibre cable and the sensors can result in inaccurate data
acquisition. In order to prevent this problem of transmission loss due to the coupling between
the LED emitters and the fibre optic cables, custom-made “Caps” can be used. From the data
sheet it was established that the physical size of the selected LED is 5 mm and the outer
diameter of the chosen fibre optic cable is 2.2 mm. the custom-made “Cap” will have an
opening of about 5 mm ( 0.05 mm) and another opening of about 2.2 mm ( 0.05 mm). The
LED will be placed in the 5 mm hole and the terminating end of the fibre optic will be placed
in the 2.2 mm hole. When in operation the emitting light will be forced to escape from the 2.2
mm hole that was made, minimizing any loss that can occur between the coupling of the LED
and the fibre optic cable.
Figure 2.13 Coupling between the LED emitter and fibre optic
The figure above illustrates how the coupling between the visible LED emitter and the fibre
optic cable is carried out. As it can be seen that only space for the light emitted from the
visible LED can escape the cap from only the 2.2 mm hole, forcing the light to go through the
fibre optic cable with minimum loss of light in the coupling.
Now that the design for the coupling between the visible LED and fibre optic has been
created, the overall hardware design can also be created and the implementation of the design
can be carried out.
Optic
Fibre
Custom-made
Cap
LED
5.00mmhole
2.2 mm
hole

20
Figure 2.14.Topology of the hardware construction
The above shows a topology of the hardware construction that was done. The Host computer
was used to upload the written code and supply the micro-controller with power. The Micro-
controller would then be uploaded with the code which would then be used to control the
light projection circuit, giving options for different scan rates, intensity control and switch the
desired LED/array of LEDs either on or off. The emitters will then project light onto the fibre
optic cable which will be used to guide the light to the vessel of process.
Chapter 3 Implementation
3.1 Building the light projection circuit
As mentioned earlier in the design section, 16 visible LEDs are going to be used. The LEDs
will be arranged in a 4*4 network.
A resistor of 150 Ω is connected to the LEDs. The resistor value was calculated using
equation 3. From looking at the visible LED’s datasheet it was established that the current
suitable for providing the highest intensity is 30 mA with a voltage of 5 V.
R
V
=I (Eq: 3.1)
Where:
I = Current (Amps)
V = Voltage (V)
R = Resistor (Ω)
Host computer Microcontroller
Light
projection
circuit
Transmitter Fibre Optic cable

21
From the equation the resistor value provided was approximately 167 Ω, however a 167 Ω is
not available in the real world and the closest resister to that value is 150 Ω. This supplies the
LEDs a bit more current (33 mA) but still within the acceptable range.
Figure 3.1 light projection circuit
From above it can be seen that the LEDs on each breadboard are evenly spaced, making it
easier to distinguish between the different arrays and LEDs. When in operation, the user can
easily recognise which LED is switched on by pinpointing it location, the LED number
represents the X-axis and the Array number represents the Y-axis. An example can be seen
on Figure 3.1, the highlighted LED can easily be distinguished using it co-ordinates (Array 4,
LED 2).
The vertical connectors on the sides and the middle of the breadboards are connected with
each other. These will be later connected to the GND (ground) pin and 5 V pin on the
Arduino.
The LEDs were obtained from RS-components. The initial LED that was selected from the
design has an intensity of 100 cd. The reason for choosing 100 cd was to provide high
intensity and still be high after travelling through the optic fibre cables (experiencing loss in
intensity). However, the LED that was available with the largest candela that also fitted the
LEDs
1 2 3 4
Arrays
1234
(Array 4, LED 2)

22
other criterions was 90.5 cd. All other LEDs that were above 90.5 cd were not “through-
hole”, had larger forward operating voltage and required special switches to operate. Thus the
LED with the 90.5 cd was chosen.
3.2 Building the micro-controller timing based circuit
After the light projection circuit was built, the micro-controller timing based circuit was
build. Irrelevant to the title of the sub-chapter, the micro-controller timing based circuit was
to configure the already build-Arduino Uno, making it suitable to drive all the 16 visible LED
emitters.
Figure 3.2. Micro-controller timing based circuit
The image above shows the micro-controller connected with the TLC LED driver chip. It can
be seen that only one TLC chip was used. This is because when buying the LED driver, the
chip was also available with a 16 pin LED driving capabilities. This reduced some wiring in
the overall circuit as there was no need for daisy-chaining of the TLC chip.
The 16 wires will be connected to a couple of actuator switches. These actuators came in
groups of 8 switches and made the overall product look cleaner as they were suitable to be
placed on a breadboard.
The TLC5940 Led driver chip was obtained from Amazon. The initial idea was to buy two
TLC chip with 8 LED driving capabilities and connect them together through daisy-chaining.
But upon searching for the component, a TLC chip with 16 LED driving capabilities was
discovered. The micro-controller on the other was obtained from Amazon as well. The
controller uses an ATmega328 chip. This chip is the heart of Arduino and the programming
code that would be written is uploaded onto this chip. If the testing goes well and no the

23
prototype works effectively, the ATmega328 chip would be removed from the Arduino or a
separate ATmega328 would be obtained and implemented with the prototype. This is because
the Arduino consists of many other components that are not being fully utilised with the
project and can be removed to make the overall size of the product more compact and easier
to use.
3.3 Building the prototype
The Micro-controller and the light projection circuit were connected to tighter via an actuator
switch. The actuator switch will be used to turn on or off the desired LED.
Figure 3.3. Building initial prototype
The image above shows the initial prototype that was build. The prototype does not have any
circuit to make the visible LEDs pulse at different scan rates or any circuit to vary the
intensity of the visible LEDs.
The prototype was then tested in terms of functionality of the actuators to see if all the LEDs
turn on and off effectively and to test the intensity of the LEDs. More details of the testing
can be seen on chapter 4.
After testing it was discovered that the intensity of the LEDs were not as high as expected.
Later some more testing was carried out to find any faults or the reason for the dimness of the
LEDs (The details of these testing can be seen in chapter 4). It was discovered that the LED

24
driver chip was taking too much current away from the Arduino and not providing enough to
the LEDs. Upon looking at the chips datasheet and surfing through some forum related to the
chip, it was discovered that the chip is not powerful enough to be used for a LED with such
high requirements.
A different driver chip was used to see if there was any difference in the intensity of the
LEDs. A 74HC595 shift register chip this time. However, it was also not able to supply the
required results and was very adamant when trying to configure the chip with the Arduino. It
took more pins then the TLC and required daisy-chaining. The main issue was that when
daisy-chained, it didn't permit the user to program the second chip independently and had a
cascading impact when programming the primary chip. In other words, if did not consider the
second chip as an isolated chip and when programming, the two chips had to be considered as
a single chip. This implied if the client switches on the first LED of the first chip they are
consequently switching on the first LED of the second chip.
Conclusion, the results did not vary. Due to lack of time and the deadlines getting closer, one
solution for the problem was to completely change the micro-controller and eliminate the
need for any LED driver chips. Looking back at table 2.1, the comparison between micro-
controllers, it can be seen that the DE0 board offers high level of functionality and has more
than enough GPIO (General Purpose Input/Output) pins to provide for the 16 visible LEDs.
Also the fact that it was already available from the university made it usable at the spot,
rather than wasting time in ordering any other micro-controller. However, the size of the
overall product would be compromised, the De0 board, in size, is larger than the Arduino
board, but at the given circumstances and lack of time, the sheer size of the overall product
had to be sacrificed to make the project work.
3.4 Changing the platform
As the De0 board was already available from the university is made it a lot easier to find a
solution as soon as possible. The De0 board offers two 36 GPIO pins, which is more than
enough for the 16 visible LEDs. The De0 board also comes with already installed switches
which can be used to control the pulse rates of the LEDs.
Keeping the design of the overall project the same. It has to be amended to be able to operate
effectively on a different platform, which in this case in the De0 development board. Before
implementing the development board to the light projection circuit, it was tested using a few
visible LEDs to see if it was able to deliver the expected results effectively, (the results can
be seen in chapter 4). The results from the testing were very sufficient and adequate enough
to be used for the final product.
As mentioned before the topology and the design of the hardware construction was not
changed but rather amended to be used on a different platform. Instead of Arduino the De0
board will be used and the LED driver chip will be removed from the prototype.

25
3.5 Configuring De0 board
Before the final prototype can be build and the light projection circuit connected with the
micro-controller, the De0 board had to be configured. Before it could be connected with the
projection circuit it had to be programmed. The programme would mention the 16 LEDs, the
different buttons to make them pulse at different scan rates. The mentioned ports (leds) in the
code will then be assigned onto the specific GPIO pins. The visible LEDs will be then
connected to its respective GPIO pins. It involved a lot of testing phases to obtain the most
appropriate configuration (more detail can be seen about the testing on chapter 4).
Before the actual hardware configuration of the De0 board was done, a sample code was
written for it. The sample code was written in VHDL (VHSIC-Very High Speed Integrated
Circuit Hardware Description Language). This sample code would allow user control to
switch any LED on or off and also provided with a scan rate of 50 Hz. The testing of the
sample code can be seen in chapter 4 of the report. Also the complete sample code as well as
the complete final code can be found in the Appendix section of the report.
The code below shows a small section of the code that will be discussed, explaining the
different part of the code.
ENTITY testing_led IS
PORT
(
clk_slow : IN STD_LOGIC;
blinker : IN STD_LOGIC;
global_reset : IN STD_LOGIC;
led0 : OUT STD_LOGIC;
led15 : OUT STD_LOGIC
);
END ENTITY testing_led;
the “clk_slow” is the scan rate of 50 Hz, the “blinker” is the switch that would assign all the
LEDs to “clk_slow” (the scan rate) if it is switched on. The “global_reset” is a safety switch
that was added to turn all the LEDs off in case of any technical issues or any risk of hazard.
All the LEDs listed from “led0” to “led15” are the actual visible LEDs that it would be
assigned to.

26
The De0 board consists of an already build-in clock that operates at 50 MHz, this 50 MHz
clock was used for the different scan rates for the LED. The method from which this was
achieved was by writing another piece of code which “divided” the 50 MHz clock, reducing
its frequency and making it slower so that it can be used for the different scan rates.
The piece of code below shows the process from which the clock division was achieved.
clk_timer: PROCESS (clk, reset)
BEGIN
IF reset = '1' THEN
Counter <= (OTHERS => '0');
ELSIF (clk 'EVENT AND clk ='1') THEN
Counter <= counter + 1;
END IF;
clk_out <= counter (22);
END PROCESS clk_timer;
The clock division is dependent upon the original 50 MHz clock from the board. The
“counter” would keep counting up as the original clock experiences a rise in clock edge.
When the “counter” reaches 22 it will then change the state of the “clk_out”, this “clk_out” is
then assigned to the “clk_slow” as seen from the previous piece of code.
Figure 3.4. Clock divider simulation
The figure above illustrates how a clock divider works. The first wave is the 50 MHz clock.
The wave below it is half of 50 MHz and would only change in state when the second change
is experienced in the 50 MHz clock. The last wave is half of the wave in the middle and
would only change in state with every third change in the 50 MHz clock.
After the clock divider code was written the two pieces of code where then brought together
to work in correlation with other in a new file of code. This new file made the two pieces of
code to work together and would later be used for the selection of the different scan rates.
Every 2nd
change will cause the second wave to
change its state

27
After the overall code was written, the LEDs and the other inputs and outputs mentioned in
the code were then assigned to the respective GPIO pins of the De0 board.
Figure 3.5. Pin assignment
The figure above shows the pin assignment for each of the nodes mentioned in the sample
code. The second column indicates if the specific code was either an input or and output and
the third column is the location of the pins that the specific nodes are assigned to. A table was
created to help assign the appropriate I/O to its respective pins. The table can be found in the
appendix along with the distribution of the GPIO headers.
Now that the code is written and the pins assigned, the configuration of the hardware can now
be implemented. When using the Arduino, the testing was done after whole prototype was
built as seen in figure 3.3. A lot of time was wasted to try built the circuit that was never
deemed to work in the first place, so to save some time, the De0 will first be tested using only
a single LED and a single switch to find the configuration that works effectively. This
configuration will then be implemented to all the LEDs and the switches.
Several configurations were tried before the ultimate configuration was figured out. The
initial configuration was that the anode (positive) side of the LED were connected to the
GPIO pins on the board and the cathode (negative) side of the LED was connected to ground
with a 150 Ω resistor in between. When voltage was applied to the GPIO pin the LED did not
light to the required intensity. It was discovered that the GPIO pins only supplied a voltage of
3.3 V. the LED is supposed to be supplied at least 4 V.
Thus the configuration was changed again. The final configuration that was tried was the
“golden ticket”, the anode side of the LED was connected to the 5 V pin on the De0 board
with the resistor in between and the cathode side of the LED was connected to the GPIO pin.
When the LED is supposed to light the GPIO pin would be programmed to go grounded (0

28
V) completing the circuit and lighting up the LED. (Note: the sample had to be amended
every time to fit the configuration that was implemented).
Figure 3.6. Final configuration
The figure above shows the final configuration that was selected for the new and improved
prototype. Another problem that was being faced was with the switch that made the LED
pulse at the scan rates. One end of the switch went to ground and the other end of the switch
was connected to the GPIO switch. Several configurations were tried with making the switch
work effectively, but all the configurations that were tries did not work. All of them had the
same issue, whenever the user comes close to slide the switch the user’s hands acts as a
parasitic capacitance (unwanted capacitance) to the wire, making it go high and affecting the
outcome. The reason for this unwanted capacitance was that when the switch was off, the
wire connected to the GPIO pin was not grounded and was open to any voltage that was
being experienced. A simple solution to this was to take add a high value resistor and connect
it parallel with the GPIO pin.

29
Figure 3.7. Scan rate’s switch configuration
The above figure explains how the configuration was made for the switch that provided the
scan rate.
Now that the configuration of the De0 board is done, the sample code written, configuration
for the LED and the switches established. The project is now ready to be taken to the next
step with the implementation of the second prototype.
3.6 Building the final prototype
One of the main problems that could alter the sails of the project is the components and the
wires that make the project whole and bridge the connection between the light projection
circuit and the micro-controller. The components can get faulty or the wires can be damaged
from continuous usage. These would affect the final outcome from the prototype and would
cast a very tedious barrier to carry out the fault finding if required.
Thus, before the construction of the final prototype began, all the visible LEDs on the light
projection circuit were supplied with 5 V to see if they are all still operation and there are no
faulty resistors, LEDs or wiring present.
Connected to
ground
Connected to
GPIO pin
Connected to
ground and is
parallel

30
Figure 3.8. De0 configuration circuit
The figure above shows the final configuration that is done for the micro-controller. The
GPIO pins are connected to two 8 actuator switches. The other end of these actuators will be
connected to the light projection circuit that was build. Another actuator with 4 switches is
also connected to the GPIO pins of the De0 board. These 4 switches will be used to make the
visible LEDs pulse at different scan rates.
The master reset or “global_reset” is assigned to the switch that is already installed on the
De0 board. Later on four more switches that are installed on the De0 board will be used to
control Arrays of LEDs. From these four switches the user will be able to switch groups of
four LEDs together. When the product is used in application, it could get time consuming to
switch all the LEDs one by one, by adding these four switches. The user can control 4 LEDs
at a time.
It is now time to bring the two circuits, the micro-controller and the light projection, together
to work in unison. The sample code was used as a frame to write the final code which was
used with the prototype. The code was compiled and simulated to see if there were any
semantic or systematic errors in them. As each of the LEDs was connected with the De0
board were tested to see if it operates efficiently and copes with the different controls.
As mentioned before the topology of the hardware was not changed, it was only altered to
make it adaptable with the change in the micro-controller and the configurations. So far the
development board has shown good promise so far and hopefully will be the “ONE” to make
the project working.

31
Figure 3.9. Final prototype
From the above figure it can be seen that the prototype works perfectly. A potentiometer was
used to control the intensity of the LEDs. The potentiometer has a max resistance of 100 Ω
and is connected between the LEDs and the 5 V supply. The positions were the LED switch
and the scan rate controller are placed are marked and can clearly be seen from the figure.
Because the LEDs are all connected to the same 5 V supply the voltage across each LEDs are
a bit smaller, this was tested individually for each of the LEDs. A simple for is would be to
add extra battery cells to the 5 V supply.
3.7 Coupling the optic fibre
Referring back to table 2.3. It can be seen that one of the requirements, “Can the optic fibre
be fitted with the LEDs?” was marked as To Be Met. Well…. This is where it will be deemed
“MET”.
Looking at the datasheets for the LEDs and the fibre optic cable. It was established that the
size of the LED is 5 mm and the size of the cable is 2.2 mm. one potential solution was
demonstrated in chapter 2.4. To use a custom made sort-of-Cap to cover the LED and
connect the optic cable. The “Cap” would have width of 5.5 mm, height of 3 mm and
thickness of 5.5 mm. the Cap would be made out of PVC and would be made using 3D
printing. Holes would later be drilled on the two ends of the cylinder, one would have a
diameter of 5.1 mm and the other would have a diameter of 2.4 mm. however, before the
modelling of the Cap had begun, it was discovered that the 3D printers available in the
university were not so accurate and would not be capable of creating the Cap with the exact
requirements.
Intensity
controllerScan rate
controller
LED
controller

32
Thus, a different solution was founded. A heat shrink connection tubes could also be used to
make the coupling different the optic fibre and the LED. A heat shrink connection tubes are
shrinkable plastic tubes that are used as a means of protecting or connecting different wires
together. When heat is applied to the plastic tube it will shrink in size and will attain that size
till its end. A normal heat shrink connection tube shrinks to one third of its original size.
Figure 3.10. Coupling of LED and optic fibre.
The figure above shows how the coupling between the optic fibre cable and the LED was
done using the heat shrink connection tube. The tube was heated until it could not shrink
anymore and the two were tightly fitted together.
Both the LED and the optic cable had the resistivity to stand the temperature that was used to
make the connection tubes shrink, about 90 degree Celsius. The fibre optic cable that was
bought came in the length to 20 m. for each of the LEDs about 15 cm to 25 cm of the cable
was cut, which was about 5 m in total that was used for the project.

33
3.8 Finalizing
Figure 3.11. Final product
The figure above shows the final prototype of the project. The De0 is connected to the LEDs
via the switches. Another actuator is connected to the De0 that provided 4 switches which
were assigned to provide the user to choose from different scan rates of 50 Hz, 100 Hz, 200
Hz, 400 Hz and 800 Hz. The last scan rate was assigned to a switch which is already installed
on the De0 board.
Figure 3.12. Array of LEDs
The figure above shows the array of 16 LEDs that are guided through optic cable and aligned
parallel to each other. When used in operation these ends will be placed around the pipeline
and collected by the receiver on the opposite end.

34
Chapter 4 Testing, Results and Discussion
4.1 Testing with Arduino
As mentioned earlier the whole project was based on an Arduino platform but due to
unforeseen circumstances the prototype was not able to deliver the expected outcome. From
the data sheet of the selected visible LED it was established that to achieve the max intensity
from the LED it needs to be supplied with a voltage of 4 V and a current of 30 mA (this does
not take into account the other factors that would affect with the brightness of the LED and
would only consider the factors that can be controlled and varied which in this case is the
voltage and the current being supplied).
When the initial prototype (Figure 3.3) was operational and the demo code was uploaded to
the Arduino. The expected intensity was not achieved and thus after that prototype was then
tested against a single visible LED that was taken from the prototype and placed on a separate
breadboard with the TLC chip. This was done to minimise the number of wiring that was
present in the initial prototype and make the testing of the LEDs easier.
Below is the test code that was to test the intensity of the LED
#include "Tlc5940.h"
void setup()
{
Tlc.init (0); // initialise the chip and set all
channels to an off position
}
void loop()
{
Tlc.set (0, 4095); // set LED to highest brightness
Tlc.update (); // update the TLC with the mentioned instructions
}
The “# include tlc5940.h” is the TLC5940 library that was downloaded from the Arduino
website and placed within the library of the Arduino sketch. This was done to make the
TLC5940 chip programmable within the sketch. The function of the code above is very
simple and makes the LED that is connected to the TLC chip to light up to its brightest
intensity.

35
Figure 4.1. Testing single LED with Arduino
The figure above shows the configuration that was done using only one LED to test its
intensity.
4.2 Results with Arduino
The intensity of the LED is dependent upon the current and the voltage being supplied to it.
So to measure the intensity the current and the voltage is to be measured. A simple
multimeter was used to measure both the voltage and the current. The table below shows the
results of the measurements being compared to the expected values.
Table 4.1. Results with Arduino
Parameter Ideal results Expected results Actual results
Voltage (V) 4 3.2 2.0
Current (mA) 30 25 15
Because of the tolerance in the components and the resistance existing in the wires, the
expected results were smaller than the ideal results. As it can be seen the actual results are
significantly smaller than the expected results. The LED lighted up very dimly.

36
But there could be fault in any of the wiring that might be cause for the actual results to be
smaller than the expected results. All the wires were later changed and the parameters were
measured again but the results were still the same.
Figure 4.2. Testing using different configuration
During the testing of finding any faults in the circuit many minor changes were made and the
different configurations were tested with the same parameters. Later on the LED was directly
connected to the Arduino via a resistor, as shown in the figure above. When the LED was
directly connected it lit very brightly and when tested against the parameters, it gave the
results that were expected from it.
Upon looking at the chips datasheet and surfing through some forum related to the chip, it
was discovered that the chip is not powerful enough to be used for a LED with such high
requirements. Thus because of this the chip had to be changed, that was the initial idea
anyways. The chip that replaced the TLC5980 was a 74HC595 chip. However, it was also not
able to supply the required results and was very stubborn when trying to configure the chip
with the Arduino. It took more pins then the TLC and required daisy-chaining. The main
issue was that when daisy-chained, it did not allow the user to programme the second chip
separately and had a cascading effect when programming the first chip. Simply, if did not
consider the second chip as an isolated chip and when programming the two chips had to be
considered as a single chip. This meant that switching one LED on chip-1 also switched on a
LED connected to chip-2.

37
Thus, as mentioned in chapter 3, the whole platform was changed and moved to the De0
development board.
4.3 Testing the VHDL code
As mentioned, before the configuration of the De0 could be started a sample code had to be
written to make the micro-controller usable with the LEDs and the switches. Some pieces of
the sample code can be seen at chapter 3.5. The code was written in an application by the
name of “Quartus 2” using VHDL and the simulation for the code was done using Modelsim.
The code was first compiled to look for any syntax error within the code. After the
compilation was done the code was then tested in the simulation to search for any semantic
errors that might exist.
The simulation graph shows the wave in Nano seconds and the unit cannot be changed, sod
for the purpose of doing the simulation the scan rate was made a lot faster than the previous
50 Hz that was assigned in the sample code. (Note: the scan rate was only changed for testing
purposes. It will then be changed back to its original 50 Hz speed when used in the actual
physical hardware)
Figure 4.3. Simulation results.
NOTE: the LED nodes mentioned in the code are connected to the cathode (negative) side of
the LED, they would have to be switched off (LOW state) to turn the LEDs on. So in the
simulation, if the LEDs nodes are HIGH the LEDs do not light up and if the LED nodes are
LOW then the LED would operate
Table 4.2. LED pins connection state
Anode side Cathode side Outcome
HIGH HIGH No light
HIGH LOW Light
Safety Switch 50 MHz clock
Pulse control
switch
Pulsing at
25 MHz

38
The anode side of the LED is already connected to a voltage of 5 V. in the coding it’s the
Cathode side that are altering. And when it goes LOW the circuit is complete.
Referring back to figure 4.3. The first wave is the safety switch, when it is on, no LEDs
would light. The second wave is the original 50 MHz clock of the board. When the “blinker”
switch, wave three is switched on, the LEDs start to pulse at a scan rate of 25 MHz. This
confirms that the sample experienced no semantic errors and is liable to be used for the final
product.
4.4 Testing/Results of the light projection circuit
One of the main problems that could alter the sails of the project is the components and the
wires that make the project whole and bridge the connection between the light projection
circuit and the micro-controller. The components can get faulty or the wires can be damaged
from continuous usage. These would affect the final outcome from the prototype and would
cast a very tedious barrier to carry out any fault finding when required.
Thus, before the construction of the final prototype began, all the visible LEDs on the light
projection circuit were supplied with 5 V to see if they are all still operation and there are no
faulty resistors, LEDs or wiring present.
All the LEDs were grounded and the De0 was used to supply the light projection circuit with
the 5 V. a wire was taken from the boards 5 V pin and was connected to multi-meter. The
multi-meter would then bridge the gap the gap between the LED and 5 V supply. If the LED
or the wire connected to the LED is faulty it would not light up and no readings would be
seen on the multi-meter. However, if the LED and its connection is fault free it would light
up and its current would be experienced by the multi-meter.
Figure 4.4. Testing individual LEDs

39
From the above figure the current reading can be seen on the multi-meter, 31 mA and the
LED is lit, indicating that the LED is fault-free for the moment and is liable to be used for the
project. The same test was done for each of the 16 visible LEDs individually.
In total, 4 LEDs were discovered to have been faulty. These faulty components were removed
and replaced with the extra LEDs that were available.
4.5 Testing/Results of different configurations
As mentioned before when building the configuration of the De0 board, several
configurations were tried. Below are some of the configurations that were tested and lead to
the final “golden” configuration.
Table 4.3. Finding the golden nugget (configurations)
Configuration Voltage
applied
Anode
side
Cathode
side
Resistor
(Ω)
Voltage
at LED
(V)
Current
at LED
(mA)
1 5 V Connected
to GPIO
Grounded 150 2.5 18
2 6.5 V Connected
to GPIO
Grounded 150 2.5 18
3 5 V Connected
to 5 V
Connected
to GPIO
150 3 18.6
4 6.5 V Connected
to 5 V
Connected
to GPIO
150 3.34 30
5 5 V Connected
to 5 V
Connected
to GPIO
51 3.36 25
6 5 V Connected
to 5 V
Connected
to GPIO
35 3.4 31
In the first two configurations even though the voltage supplied was 5 V and 6.5 V, it did not
affect the voltage that was supplied to the LED pins. The voltage that was supplied to the
GPIO pins was 3.3 V and could not be changed. Thus leading to configurations 3 and 4.
The difference in the readings from configuration 2 to 3 can be seen clearly in the table. The
voltage increased by 0.5 V and the current was increased by 0.6 mA. In configuration 4 an
extra battery cell was added and the voltage applied was increased to 6.5 V. This
configuration gave readings that were expected since the very beginning of the testing trials.

40
In configuration 5 the voltage was brought back to its normal value, 5 V and the resistor was
decreased to one third of the original value that was calculated. The current decreased but the
voltage at the LED was constant. Looking at all the results of the voltage and current,
Equation 3.1 was used again to find a new resistor value that would give a current of 30 mA.
In the golden configuration, the resistor that was used was 35 Ω. It did not exactly give a
current of 30 mA but 28 mA was good enough.
4.6 Testing/Results of individual LEDs (final prototype)
Because all the LEDs in the light projection circuit were connected to the same 5 V source.
The voltage across each of the LEDs was reduced. Each of these LEDs were tested in terms
of voltage and current. The table below shows the results of the parameters for the individual
emitters.
The current should be 30 mA and the voltage should be 3.4 V.
Table 4.4. Results of individual LEDs
LED Voltage (V) Current
(mA)
LED Voltage (V) Current
(mA)
1 3.01 20 9 2.98 19
2 2.99 19 10 2.97 19
3 2.98 18 11 3.00 20
4 3.20 21 12 2.96 19
5 2.64 17 13 2.78 18
6 2.89 18 14 3.21 21
7 3.21 20 15 3.01 20
8 2.45 16 16 3.01 20
From the above table it can be seen clearly that none of the LEDs come close to the expected
results. A simple solution for this problem was that a couple more battery cells were added to
the 5 V supply. Increasing the supply to a total of 8 V. All the components were suitable to be
used with 8 V supply and worked efficiently.
Intensity Test
The intensity for the LEDs was also tested. From figure 3.9, it can be seen that a
potentiometer was used to control the intensity of the LEDs. The potentiometer was

41
connected between the light projection circuit and the voltage supply source. The
potentiometer that was used at the start caused some issues. The LEDs would just go off or
would go extremely dim. Upon looking at the data sheet of the potentiometer it was
discovered that it had a resistance of 10 KΩ and turning it even a bit would cause the
resistance to reach more than 500 Ω. The potentiometer was then changed and was replaced
with another potentiometer that had a max resistance of 100 Ω.
4.7 Final Testing
Now that the final prototype has been built and the coupling of the fibre optic cables and the
LEDs established. The only that’s left to do is to test the product to see if it is adequate
enough to guide the visible beams to a medium.
One of the topics that can be seen emerging throughout in this report is the intensity of the
LEDs. The whole Arduino platform was changed because the desired intensity was not
achieved. When building the final prototype the intensity of the LEDs were measured by
measuring the voltage and current it receives. The reason for the strictness of the intensity is
that, when the product is in operation, the visible beam will emit from the light projection
circuit through the 15 cm -25 cm fibre optic cable and through the medium just so that it can
cast a shadow of the internals of the medium. If the intensity was not that high there would
have been no light experienced by any receivers on the other end of the container.
A transparent bottle was used as a medium for the test and a Lux-meter was used to test the
intensity of the LED. There were a total of three tests that were done. During the tests all
other lights were turned off and all the tests were performed in a dark room. This was done to
minimize any background visible light that might interfere with the readings on the lux-
meter. The tests that were done were:
Test 1
The first test was to test the intensity of the emitters through the optic fibre cable. There was
no medium placed in this test. This test was done to see if the lux-meter fluctuates as the
distance between the fibre cable and the lux-meter changes. This test also provided a frame of
reference when doing tests 2 and 3.
Table 4.5. Lux reading, no medium.
Distance (cm) Lux-meter reading (LUX)
0 25
3 15
10 8

42
From the above, the results that provide with a good frame of reference. Now that there are
values that can be used for comparison. Test 2 can be carried out
Test 2
In test 2, a bottle was used as a medium. The bottle was placed in between the optic fibre
cable and the Lux-meter. The bottle has a diameter of approximately 7 cm. the bottle was
empty and had no fluid or gas flowing through it. The reading that the lux-meter experienced
was 12 lux.
Test 3
Test 3 was done using the same bottle but this time the bottle was filled with water. This test
was carried out to see how the readings would change when there’s a fluid passing through
the medium. The reading that the lux-meter experienced was 5 lux.
(A lux is a unit of light measurement that takes the area into account. It is equal to one lumen
per square metre)
Table 4.6. Overall test results
Test Medium Distance (cm)
Lux-meter reading
(lux)
1 None 7 13.5
2 Empty bottle 7 12
3
Bottle filled with clear
water
7 5
From the above table it can be seen that the lux reading goes down. If the diameter of the
bottle is greater than 7 than the readings will goes even more down. Thus, it can be said that
the product is suitable to be used for a pipeline or container that has a length or diameter of 7
cm or less, if it is more than that then any receivers placed on the other end may not capture
any light or experience very little.

43
Chapter 5 Conclusions
5.1 Conclusion
Now that the final prototype had been built and tested effectively at different stages against
several parameters using various techniques. Let’s look at the projects aims and objectives
again to see if there’s any criteria that still has to be met.
The ultimatum aim of this is to build and design a pulsed fibre optic light source that is going
to be used for optical tomography. For the goal to be achieved the project had focused on a
few major aims that shaped the final product, leading to the success of the project.
1. Build an array of isolated light sources and guide the beams from the source through a
variety of optic fibre
2. Build a circuit/system that would provide variations of scan rates.
3. Build a circuit/system that would allow the user to control the intensity of the light
source
Looking the aims listed above we can be finalised that all the Aims of the product are met.
The isolated light source has been referred as the light projection circuit that was built. The
coupling between the LED and the optic fibre cable was done to make the cable suitable
enough to guide the beams of light from the source.
The micro-controller, De0, was used to provide the users with variable scan rates to choose
from. 5 different scan rates were provided with frequencies of 25 Hz, 50 Hz, 100 Hz, 200 Hz
and 400 Hz.
From the same circuit that was used to provide the different scan rates, the micro-controller
was also programmed to allow users to control the intensity of the LEDs and allow users to
switch any desired LED or Array of LEDs.
The initial idea from the very beginning was to use an Arduino as the micro-controller. The
project was based on an Arduino platform. However, due to unforeseen circumstances the
whole platform had to be changed. The LED driver chip that was used with the Arduino took
a lot of current away from the LEDs. Ironically, the LED driver chip was not able to drive
any of the LEDs effectively. Thus the platform was changed from Arduino to De0
development board. An Arduino Mega could have also been used, as it provided more pins
than Arduino UNO, enough pins to be used for the project. But under the circumstances and
the deadlines dawning in, the De0 was used. It filled the entire criterion’s that were expected
for the project and was already available to be used. However, the sheer size of the project
had to be sacrificed as the De0 board is larger than Arduino. The De0 board worked very
efficiently in delivering the requirements. A worthwhile sacrifice made for the greater good.

44
Just like the micro-controller there were several changes that had to be made, each a new
lesson learned. For example, the original idea for the coupling of the optic cable and the LED
was to use custom-made caps, but the 3D printers available were not accurate enough to print
the caps with the required dimensions. Upon further research to look for a replacement, heat
shrink connector tubes were discovered that worked perfectly in coupling the optic cable and
LEDs.
Apart from the mentioned, there were several other barriers that had to faced, getting the
“golden” configuration to get the highest brightness, fault testing off each components and
wires, finding the right components and so on. Each of these barriers was new lessons that
helped shape the project to a success. It thought that even though there is a barrier the best
option would be to look around the barrier rather than to try to knock it off.
5.2 Reflections and Future Work
In reflection, if there was more time available the final product would have been made more
user friendly. The circuit would have been moved to a PCB board if there was more time
available. If would not have affected the performance of the product in any way but would it
easier to carry and easier to use. As a recommendation, if someone tries to make this project
or if the project is carried out again, it is very advisable to read the datasheet from the
beginning and make sure that the components can be collaborated with its neighbouring
components.
What could have been done differently?
Before the construction of the initial prototype had started, the datasheets for each of the
components could have been looked to see if it could have supported other components. After
the initial prototype was constructed and during the testing part it was discovered that the
LED driver chip was not able to drive the LEDs in the first place. All the time that was
wasted in constructing the prototype could have been saved it its datasheet had been read in
advance.
Future work
The product could be moved to a PCB board, the PCB board can be designed and printed out
and the components would be soldered onto it. All the components used are suitable to be
used on a PCB board so no new components would need to be bought. The product has only
16 visible LEDs and can be used for pipeline and container having a diameter and length of 7
cm or less. The LEDs can be changed with another LED that has a higher intensity and more
LEDs can be added, so that it can be used for pipelines that has a diameter greater than 7 cm.
also the product does not consider the receiving side of the tomography, it can be further
developed so that it can be used with any kind of receivers that have photodiodes as their
detectors. A cover can also be designed and printed to house the product.

45
References
[1] Rahim, R., Rahiman, M., Chen, L., San, C. and Fea, P. (2008). Hardware Implementation
of Multiple Fan Beam Projection Technique in Optical Fibre Process Tomography. Sensors,
8(5), pp.3406-3428.
[2] Ruzairi A.R. (1993) A Tomography Imaging System for Pneumatic Conveyors Using
Optical Fibres. Ph.D. Thesis. Sheffield Hallam University
[3] Sallehuddin I. (2000). Measurement of Gas Bubbles in a Vertical Water Column Using
Optical Tomography. Ph.D. Thesis. Sheffield Hallam University
[4] Khoo B.F. (2002). Optical Fibre Sensors for Process Tomography. B.Sc.
Thesis. Universiti Teknologi Malaysia
[5] Hisyamuddin S. (2001). Sistem Tomografi Optik Berkejituan Tinggi. B.Sc.
Thesis. Universiti Teknologi Malaysia
[6] Chan K.S. (2002). Time Image Reconstruction for Fan Beam Optical Tomography
System. M.Sc. Thesis. Universiti Teknologi Malaysia
[7] Rahim, R. (2004). Optical tomography system for process measurement using light-
emitting diodes as a light source. Optical Engineering, 43(5), p.1251-1257.
[8] Williams R.A. (1995) Principles, techniques and applications. Editors. Process
Tomography. pp. 3–12.
[9] Sakami, M., Mitra, K. and Vo-Dinh, T. (2002). Analysis of short-pulse laser photon
transport through tissues for optical tomography. Optics Letters, 27(5), p.336.
[10] Pal, G., Basu, S., Mitra, K. and Vo-Dinh, T. (2006). Time-resolved optical tomography
using short-pulse laser for tumor detection. Appl. Opt., 45(24), p.6270.
[11] Zhang, W. (2001). VHDL Tutorial: Learn by Example. [Online] Esd.cs.ucr.edu.
Available at: http://esd.cs.ucr.edu/labs/tutorial/ [Accessed 18 Mar. 2016].
[12] Johansen, G. and Wang, M. (2008). Industrial Process Tomography. Measurement
Science and Technology, 19(9), p.090101.
[13] Williams, R. and Beck, M. (1995). Process tomography. Oxford: Butterworth-
Heinemann.

46
[14] Idroas, M., Rahim, R., Green, R., Ibrahim, M. and Rahiman, M. (2010). Image
Reconstruction of a Charge Coupled Device Based Optical Tomographic Instrumentation
System for Particle Sizing. Sensors, 10(10), pp.9512-9528.
[15] Schleicher, H. (2016). Optical Tomography - Helmholtz-Zentrum Dresden-Rossendorf,
HZDR. [Online] Hzdr.de. Available at:
https://www.hzdr.de/db/Cms?pOid=12075&pNid=3018 [Accessed 15 Mar. 2016].
[16] Arduino.cc. (2016). Arduino - ShiftOut. [Online] Available at:
https://www.arduino.cc/en/Tutorial/ShiftOut [Accessed 5 Mar. 2016].
[17] Faramarzi, m. (2012). A REVIEW ON APPLICATIONS OF OPTICAL
TOMOGRAPHY IN INDUSTRIAL PROCESS. 1st ed. [ebook] Johor: Universiti Teknologi
Malaysia, pp.767-781. Available at:
http://www.academia.edu/5418078/A_REVIEW_ON_APPLICATIONS_OF_OPTICAL_TO
MOGRAPHY_IN_INDUSTRIAL_PROCESS [Accessed 18 Feb. 2016].
[18] M. T. M. Khairi, S. Ibrahim, M. A. M. Yunus, and M. Faramarzi. A review on
APPLICATIONS OF OPTICAL TOMOGRAPHY IN INDUSTRIAL PROCESS. 2012.
Control and Instrumentation Department, Faculty of Electrical Engineering. Universiti
Teknologi Malaysia.
[19] Elizabeth M. C. Hillman. (2002). Experimental and theoretical investigations of near
infrared tomographic imaging methods and clinical applications. . Ph.D. Thesis. Department
of Medical Physics and Bioengineering University College London.

48
Appendix B (Datasheets)
Datasheet for LEDs
Datasheet for TLC5940 LED driver chip

49
Datasheet for Actuator switches
Datasheet for Optic fibre cable

50
Appendix C (VHDL Code)
Below is the code that was written for the scan rates
IBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY clk_div IS
PORT
(
reset, clk : IN STD_LOGIC;
clk50 : OUT STD_LOGIC;
clk1500 : OUT STD_LOGIC
);
END ENTITY clk_div;
ARCHITECTURE timer OF clk_div IS
SIGNAL counter : std_logic_vector(35 DOWNTO 0);
BEGIN
clk_timer: PROCESS(clk, reset)
BEGIN
IF reset = '1' THEN
counter <= (OTHERS => '0');
ELSIF (clk 'EVENT AND clk ='1') THEN
counter <= counter + 1;
END IF;
clk50 <= counter(24);
END PROCESS clk_timer;
END ARCHITECTURE timer;

51
Below is the code that was written for the LEDs
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
ENTITY testing_led IS
PORT
(
clk_slow_50 : IN STD_LOGIC;
blinker50 : IN STD_LOGIC;
array_switch1 : IN STD_LOGIC;
global_reset : IN STD_LOGIC;
led15 : OUT STD_LOGIC
);
END ENTITY testing_led;
ARCHITECTURE rtl OF testing_led IS
SIGNAL led_s : STD_LOGIC_vector(0 TO 15);

52
BEGIN
process( global_reset,
array_switch1, array_switch2, array_switch3,
array_switch4 )
begin
if(global_reset = '1') then
led_s <= "1111111111111111";
elsif (global_reset = '0') then
if(blinker50 ='1') then
led_s(0) <= clk_slow_50;
ELSIF (blinker100 = '1') THEN

53

54
ELSIF (blinker50 = '0' AND blinker100 = '0' AND blinker200 = '0' AND
blinker400 = '0' AND blinker1500 = '0') THEN
led_s(0) <= '0';
led_s(1) <= '0';
led_s(2) <= '0';
led_s(3) <= '0';
led_s(4) <= '0';
led_s(5) <= '0';
led_s(6) <= '0';
led_s(7) <= '0';
led_s(8) <= '0';
led_s(9) <= '0';
led_s(10) <= '0';
led_s(11) <= '0';
led_s(12) <= '0';
led_s(13) <= '0';
led_s(14) <= '0';
led_s(15) <= '0';
END IF;
END IF;
END PROCESS;
led0 <= led_s(0);
led1 <= led_s(1);
led2 <= led_s(2);
led3 <= led_s(3);
led4 <= led_s(4);
led5 <= led_s(5);
led6 <= led_s(6);
led7 <= led_s(7);
led8 <= led_s(8);
led9 <= led_s(9);
led10 <= led_s(10);
led11 <= led_s(11);
led12 <= led_s(12);
led13 <= led_s(13);
led14 <= led_s(14);
led15 <= led_s(15);
END ARCHITECTURE rtl;

55
Appendix D (Parts list/Bill of Materials)
Part No # Component Quantity Price (£)
1 Visible LEDs 25 3.70
2 Heat shrink connectors 20 4.27
3 Actuator switches 4 3.56
4 Jumper Cables 40 5.29
5 Optic Fibre 1 (20 meters) 23.49
6 Potentiometer 1 10.00
7 De0 board 1 Available from Uni
Total - - 50.31

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