design and build a rotating led display

Rotating LED display Final Report Andre Bestbier

2015 16968107

i

Design and build a

rotating LED display

Mechatronic Project 478

Final Report

Mr A Bestbier

16968107

Supervisor: Mr WS Smit

2015


2015 16968107

i

Design and build a rotating

LED display

Mechatronic Project 478

Final Report

Mr A Bestbier

Student Number: 16968107

Supervisor: Mr WS Smit

23 October 2015


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Contents

List of figures ......................................................................................................... vi

List of tables........................................................................................................ viii

Executive Summary .............................................................................................. ix

ESCA Outcomes ..................................................................................................... x

Acknowledgements .............................................................................................. xii

1 Introduction ..................................................................................................... 1

1.1 Problem formulation ................................................................................ 1

1.2 Objectives ................................................................................................ 2

1.3 Motivation ............................................................................................... 2

2 Literature study .............................................................................................. 3

2.1 Physiological study .................................................................................. 3

2.2 Existing rotating displays ........................................................................ 4

2.3 Electromagnetic induction ....................................................................... 5

2.3.1 AC Generation ............................................................................. 5

2.3.2 Inductive coupling ....................................................................... 6

3 Quality function deployment ......................................................................... 7

3.1 Project requirements ................................................................................ 7

3.2 Engineering characteristics ...................................................................... 8

4 Concept generation and evaluation ............................................................... 9

4.1 Physical decomposition ........................................................................... 9

4.2 Conceptual solutions ............................................................................... 9

4.2.1 Spinning rod .............................................................................. 10

4.2.2 Motor ......................................................................................... 11

4.2.3 Communication ......................................................................... 11

4.2.4 Power transfer ............................................................................ 11

4.2.5 Processor .................................................................................... 13

4.2.6 Position sensor ........................................................................... 13

4.3 Final concept ......................................................................................... 14

5 AC generator design ..................................................................................... 15

5.1 Magnetic field design ............................................................................ 15

5.2 Generator structure design ..................................................................... 17

5.3 Testing of the AC generator .................................................................. 18


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6 Electronic circuit design ............................................................................... 20

6.1 Power supply ......................................................................................... 20

6.2 LED strip ............................................................................................... 21

6.3 Bluetooth module .................................................................................. 23

6.4 Photo interrupter .................................................................................... 23

6.5 Controller ............................................................................................... 24

6.6 Speed control ......................................................................................... 24

6.7 Testing of electronic subsystems ........................................................... 25

6.7.1 Power supply ............................................................................. 25

6.7.2 Photo interrupter ........................................................................ 25

6.7.3 Speed control ............................................................................. 26

7 Physical structure design.............................................................................. 27

7.1 Base design ............................................................................................ 27

7.2 Rod design ............................................................................................. 28

7.3 Assembly of the physical structure ....................................................... 29

7.4 Testing of the physical structure ........................................................... 30

8 Software ......................................................................................................... 31

8.1 Controlling shift registers ...................................................................... 32

8.2 Bluetooth setup and communication ..................................................... 33

8.2.1 Configuration in command mode .............................................. 33

8.2.2 Communication in data mode .................................................... 33

8.2.3 Data storage ............................................................................... 34

8.3 Sensor read and timing .......................................................................... 34

8.3.1 Reading sensor values ............................................................... 34

8.3.2 Timing the display ..................................................................... 34

8.4 User interface ........................................................................................ 35

8.4.1 Setting up the serial connection ................................................. 35

8.4.2 Graphical user interface ............................................................. 35

8.4.3 Input conversions ....................................................................... 36

9 Evaluation and recommendations ............................................................... 37

9.1 AC generator evaluation ........................................................................ 37

9.2 Electronic circuit evaluation .................................................................. 37

9.3 Physical structure evaluation ................................................................. 38

9.4 Software evaluation ............................................................................... 38

9.5 Overall evaluation and results ............................................................... 39

10 Conclusion ..................................................................................................... 41


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11 References ...................................................................................................... 42

Appendix A: Techno-economic analysis ....................................................... 44

A1. Time schedule ........................................................................................ 44

A2. Budget and actual costs ......................................................................... 44

A3. Technical impact ................................................................................... 46

A4. Return on investment ............................................................................. 46

A5. Potential for commercialization ............................................................ 46

Appendix B: Risk assessment ........................................................................ 47

Appendix C: Calculations .............................................................................. 49

C1. Engineering characteristics .................................................................... 49

C1.1 Display resolution ...................................................................... 49

C1.2 LED light intensity .................................................................... 49

C1.3 Minimum on time for LED ........................................................ 49

C1.4 Maximum time to switch LEDs................................................. 49

C1.5 Power need for spinning circuit ................................................. 50

C1.6 Motor torque .............................................................................. 50

C1.7 Power need for motor ................................................................ 52

C2. AC generator design .............................................................................. 52

C2.1 Designed induced voltage .......................................................... 52

C2.2 Actual induced voltage .............................................................. 52

C3. Electronic circuits .................................................................................. 53

C3.1 Smoothing capacitor .................................................................. 53

C3.2 Register shifting time ................................................................ 54

C3.3 LED resistor sizes ...................................................................... 54

C3.4 Actual motor torque ................................................................... 54

Appendix D: Data sheets ................................................................................ 55

D1. Photo interrupter .................................................................................... 55

D2. Voltage regulator ................................................................................... 56

D3. RBD LEDs ............................................................................................ 57

D4. Shift registers ......................................................................................... 58

Appendix E: Source code ............................................................................... 59

E1. loop() function ....................................................................................... 59

E2. displayFunction() function .................................................................... 60

E3. readSerial() function .............................................................................. 60

E4. shift() function ....................................................................................... 61


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E5. bluetoothSetup() function ...................................................................... 61

Appendix F: LED strip schematic diagram ................................................. 62

Appendix G: Detailed drawings .................................................................... 63

G1. Shaft layout drawing ............................................................................. 63

G2. Base layout drawing .............................................................................. 63

G3. Rod layout drawing ............................................................................... 65


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List of figures

Figure 1: Illusion of motion used in film industry [Eadweard Muybridge] .............................. 3

Figure 2: Path of vision from object to brain [Mike Wood] ...................................................... 3

Figure 3: Homemade rotating LED display [Vamsi Danda] ..................................................... 4

Figure 4: Rotating LED display kit [Beijiayue] ......................................................................... 5

Figure 5: AC generator principles [Wayne Storr] ...................................................................... 6

Figure 6: Diagram of electromagnetic coupling principles [A. Bestbier] ................................. 6

Figure 7: Physical decomposition of rotating LED display ....................................................... 9

Figure 8: Orientation concepts, A and B ................................................................................. 10

Figure 9: Two methods of power transfer [A Bestbier] ........................................................... 11

Figure 10: CAD model of generated concept rotating display ................................................ 14

Figure 11: AC generator design diagram ................................................................................. 15

Figure 12: Cross section of AC generator................................................................................ 16

Figure 13: Flux density plots of AC generator ........................................................................ 16

Figure 14: Manufactured shaft with copper coils .................................................................... 17

Figure 15: Sectioned CAD drawing of AC generator (left) and actual AC generator (right) . 18

Figure 16: Oscilloscope reading of generator output ............................................................... 19

Figure 17: Schematic diagram of the rectifier and regulator circuit ........................................ 20

Figure 18: Plot of voltage over the capacitor versus time ....................................................... 21

Figure 19: Schematic diagram of a section of LED strip......................................................... 22

Figure 20: LED strip PCB layout............................................................................................. 22

Figure 21: Front and back of manufactured PCB .................................................................... 22

Figure 22: Schematic diagram of photo interrupter ................................................................. 23

Figure 23: Schematic diagram of complete spinning circuitry ................................................ 24

Figure 24: Voltage levels of photo interrupter gate in operation ............................................. 25

Figure 25: Base CAD drawing ................................................................................................. 27

Figure 26: CAD design of the rod............................................................................................ 28

Figure 27: Exploded CAD assembly of display ...................................................................... 29

Figure 28: Completed rotating LED display ............................................................................ 30

Figure 29: Flow diagram of function sequence ....................................................................... 31

Figure 30: Flow diagram of shift() function ............................................................................ 32

Figure 31: Flow of information through the Bluetooth connection ......................................... 34

Figure 32: Flow diagram of the display‟s timing process........................................................ 35


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Figure 33: Graphical user interface screenshots ...................................................................... 36

Figure 34: "ABC" text displayed ............................................................................................. 39

Figure 35: "LED" text displayed .............................................................................................. 39

Figure 36: Picture of a house displayed ................................................................................... 40

Figure 37: Picture of a boat displayed ..................................................................................... 40

Figure 38: Gantt chart of the rotating LED display schedule .................................................. 44

Figure 39: Bar chart of actual an planned costs ....................................................................... 45

Figure 40: Diagram of spinning rod......................................................................................... 50

Figure 41: Diagram of rotating loop ........................................................................................ 51

Figure 42: Actual magnetic flux density plot of AG generator ............................................... 52

Figure 43: Plot of rectifier output versus time ......................................................................... 53

Figure 44: Schematic diagram of LED strip ............................................................................ 62


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List of tables Table 1: Engineering characteristics .......................................................................................... 8

Table 2: Evaluation of orientation concepts ............................................................................ 10

Table 3: Evaluation of orientation concepts ............................................................................ 12

Table 4: Processor evaluation .................................................................................................. 13

Table 5: Costs of purchases and manufacturing ...................................................................... 45

Table 6: Contact details in case of an emergency .................................................................... 48

Table 7: Forward voltage drops for LEDs ............................................................................... 54


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Executive Summary

Title of Project

Rotating LED display

Objectives

Design, build and test a rotating display prototype that relies on the “memory” of the human

eye to build up an image.

What (am I going to / did I) do that is new/unique?

The display will be durable and reliable, unlike previous attempts.

A unique user interface will be written to control the device wirelessly.

The display will not use slip rings to transfer power to the rotating circuitry; instead it will

use some kind of “wireless” power transfer method.

What are the (expected) findings?

The design and construction of a functioning rotating LED display prototype is the expected

end result.

A user must be able to control the image to be displayed by means of a user interface on a

personal computer.

A clear and stable image is expected to be displayed to the onlookers.

The display should be durable and reliable.

What value will/do the results have?

A working prototype will be built that can act as a stepping stone to a production model.

Subsystems developed during this project will be unique and possibly of value for future

projects.

The device will use electronics to demonstrate a physiological phenomenon in an

aesthetically pleasing and exciting way that will inspire people and capture the imagination.

If more than one student is involved, what part will/did I do?

No other students are involved.

Which aspects of the project will carry on after completion of my part?

The continuation of the project is not yet planned.

Future projects may be undertaken to optimise the display and to implement image

processing software to allow the user to display any image from the computer.


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ESCA Outcomes

1. Problem solving:

Analyses and defines the problem

Identifies the criteria for an acceptable solution

Identifies necessary information, engineering knowledge and

skills

Generates, analyses and evaluates possible approaches to

solution

Formulates and presents the solution in an appropriate form

Chapters

1.1

1.2, 3.1, 3.2

2

4.1, 4.2, 4.3

4.3

2. Application of scientific and engineering knowledge:

Mathematical and numerical analysis – models engineering

components

Communicates concepts, ideas and theories with the aid of

mathematics

Uses physical laws for the solution of engineering problems

Chapters

5.2, 6.1

2, 3, 5, 6

Appendix C

5

3. Engineering design:

Designs components, systems or products as part of the project

Plans and manages the design process

Acquires and evaluates knowledge: applies correct principles,

evaluates and uses design tools

Performs analysis, quantitative modelling and optimisation

Alternatives were critically considered, evaluated and solution was

found

Techno-economic analyses

Project‟s result is functional and utilises knowledge from the

applicable areas

Chapters

5, 6, 7, 8

4.3

2, 5, 6, 7, 8

5.2, 6.1

4

Appendix B

9.5

5. Engineering methods, skills and tools, Information Technology:

Uses appropriate engineering methods, skills and tools

Tests and assesses the results produced by the method, skill or tool

Creates computer applications as required by the discipline

Chapters

5.2, 5.4, 6.1, 6.2

5, 6, 7

8, Appendix D

6. Professional and technical communication:

Uses appropriate structure, style and language

Uses effective graphical support

Chapters

All chapters,

reports,

presentation

8. Individual, team and multidisciplinary working:

Identifies and focuses on objectives

Works strategically

Executes tasks effectively

Chapters

1.2

All chapters

9

9. Independent learning ability:

Applicable independent research was conducted and sensibly used

Sources and evaluates information

Accesses and applies knowledge acquired outside formal instruction

Chapters

2

References


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Department of Mechanical and Mechatronic

Engineering

Stellenbosch University

Declaration

I know that plagiarism is wrong.

Plagiarism is to use another's work (even if it is summarised, translated or rephrased) and

pretend that it is one's own.

This assignment is my own work.

Each contribution to and quotation (e.g. "cut and paste") in this assignment from the work(s)

of other people has been explicitly attributed, and has been cited and referenced. In addition

to being explicitly attributed, all quotations are enclosed in inverted commas, and long

quotations are additionally in indented paragraphs.

I have not allowed, and will not allow, anyone to use my work (in paper, graphics, electronic,

verbal or any other format) with the intention of passing it off as his/her own work.

I know that a mark of zero may be awarded to assignments with plagiarism and also that no

opportunity be given to submit an improved assignment.

I know that students involved in plagiarism will be reported to the Registrar and/or the

Central Disciplinary Committee.

Name: ..................................................

Student no: ..................................................

Signature: ..................................................

Date: ..................................................


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Acknowledgements

I would like to thank Mr Smit, supervisor of this project, for his guidance, leadership and

support.

I would also like to thank all the technical staff of the Electrical and Electronic Engineering

department who assisted me with the technical and practical aspects of the project, with

special thanks to Mr Petzer, Mr Brandt and Mr Pieterse.


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1 Introduction

The ability to transfer information and meaning is a central part of human existence. Since

the start of the electrical era a wonderful array of new ways of communication became

possible. Electrical screens form a major part of this revolution and there is a permanent need

for new and existing ways to display images electronically.

The purpose of this project is to investigate, design and build a display that relies on the

„memory‟ of the human eye in order to build up an image. The design consists of a spinning

rod with a strip of small and bright, tri-coloured light emitting diodes (LEDs) at the end. The

LEDs are turned on at the right moments to build up an image. A user is able to control the

image to be displayed through a user interface on a personal computer. This project will set

out to achieve the original objectives as described by the project definition and the study

leader.

This document is a design report. It will provide some technical background about the topic,

after which the design and manufacture procedure will be discussed. Lastly the rotating LED

display will be evaluated to see if it can display a clear and steady image in a reliable and

sustainable way.

1.1 Problem formulation

This project arose from the need to solve a complex problem. The problem can be broken

into its basic parts in order to obtain a better understanding of it. The need was initially stated

by the project supervisor, Mr Smit, as follows:

A display should be built.

The display should rely on the memory of the human eye to build up an image.

The design contains a thin, spinning rod with small and bright, tri-colour LEDs.

LEDs should be turned on at the right moments to build up the image.

Additional details about the problem were gained through discussions with the project

supervisor. Subsequent assumptions could be made about the problem, based on a

background of engineering knowledge and practical experience.

By compiling all these given and derived goals, a complete problem definition can be

formulated as follows:

Design and build a durable and reliable rotating LED display. The display should use the

memory of the human eye to build up an image by switching a strip of bright, tri-coloured

LEDs on and off while spinning them on a thin rod.


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1.2 Objectives

In order to solve the problem defined above, certain objectives need to be set. Achieving

these objectives will lead to a successful solution to the problem. The primary objective is to

design and build a rotating LED display. Being a complex problem it can be divided into

various secondary objectives. The following are the secondary objectives that guided this

project:

To do research and to obtain information concerning the principles and functionality of

the rotating LED display.

To design and construct a reliable and durable mechanical structure to support and spin

the LED rod.

To design and assemble an electronic circuit to control the LED display.

To design and implement a durable and effective way of powering the circuit.

To design and create a way to communicate with the rotating LED display in order to

send commands and telling it what to display.

To end up with a working prototype of a rotating LED display incorporating all the

above-mentioned features, as well as being more reliable and durable than current

models.

This report will discuss the above-mentioned objectives and document the design and

implementation processes that accompany each. These objectives also serve as a definition of

the project‟s scope. All tasks necessary to reach these objectives are within the project‟s

scope. Design philosophies that guided this project include design for durability, reliability,

simplicity and efficient use of space and material.

1.3 Motivation

The motivation behind this project is to push the boundaries of the electronic display as it is

known today. The driving force is innovation and the creation of a unique prototype to inspire

and capture the imagination of onlookers. The rotating LED display and related technology

have many uses, which justifies the money and time that will be spent on this project. The

display can be used in the fields of advertising, display signs, entertainment and aesthetics.

A unique attribute of this rotating display is the fact that its physical form is notably smaller

than its apparent size when spinning. This means that when not in use this display will

occupy a fraction of the space of a normal display, as well as use far less LEDs than a

stationary LED display. Modified versions of the rotating LED display can be used on a

variety of spinning structures, like wheels, fans and wind turbines.

The distinctive sub-systems, algorithms and features developed in this project will lead the

way in creating better rotating LED display in future and may lead to useful contributions to

other fields of technology as well. In order to create the display various unique systems will

be developed that will also make a contribution to other fields of technology. These one-of-a-

kind systems include the power supply used to power the spinning LEDs and the algorithms

used to control the LEDs.


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2 Literature study

2.1 Physiological study

The rotating LED display relies on the apparent “memory” of the human eye. This

phenomenon is not completely understood by scientists. Various attempts have been made to

explain this effect of which the most recent is called flicker fusion [1]

.*

Flicker fusion is also associated with the science of films, where a series of discrete images

displayed in quick succession will appear to the viewer as a single image [1]

. The black spaces

between successive images on a film reel is not perceived by the viewer, for a positive

afterimage of the previous image remains in vision [2]

. The illusion of movement, like in a

film, is part of the short-range apparent motion theory [3]

, but is not part of the scope of this

project, since only stationary images will be displayed. Figure 1 shows an example of a series

of images that will cause the illusion of fluid motion when displayed in quick succession.

Figure 1: Illusion of motion used in film industry [Eadweard Muybridge]

It is stated that flicker fusion is caused by a combination of physiological effects. The one of

interest to this study is the remnant of an image perceived by a viewer for a finite time after

the image has been removed. This is called a positive afterimage. It is believed that this is

caused by persisting activity in the occipital lobe of the brain because of retinal photoreceptor

cells sending neural impulses [2]

. The path of vision from object to brain which is responsible

for the afterimage effect is shown in Figure 2.

Figure 2: Path of vision from object to brain [Mike Wood]

* Sources are indicated by a number or name in square brackets. Refer to the number in the list of references.


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The flicker fusion threshold is the frequency at which a flickering light appears completely

steady to a human observer. This frequency is of utmost importance to this project, for it will

be the minimum frequency at which the display should rotate. effect. The human flicker

fusion threshold highly depends on the brightness of the light source and varies substantially

from one individual to another. It is usually taken at 15 to 20 Hz [4]

and modern movies are

recorded at 24 Hz. A display refresh rate of 60 Hz is used in CRT screens, which can cause a

faint flicker. Modern displays increase their refresh rate to up to 100 Hz to avoid flicker, but

most humans cannot detect flicker in refresh rates higher than 75 Hz [5]

.

2.2 Existing rotating displays

A study of the current state to rotating LED displays show that there are at present two

categories of LED displays.

On the one hand there is a series of home-built prototypes. These are built by hobbyists and

vary from very simple to quite advanced. Most of them use 8 LEDs and a single shift register

which is pre-programmed to display a fixed image. They also rely either on slip rings or a

battery to power the spinning circuitry. Overall these prototypes are poorly designed,

improvised and not especially durable. Figure 3 shows an example of such a home-made

rotating LED display from an online open source community. This display was built by

Vamsi Danda [6]

.

Figure 3: Homemade rotating LED display [Vamsi Danda]

On the other hand there are manufactured rotating LED displays. These come in kits which

can be assembled at home or can be bought pre-assembled. These designs are usually very

compact and consists of a single printed circuit board fixed to a motor. Many of these models

also rely on slip rings or batteries for power, but there are some displays that make use of

induction power of some sort. These displays can be very advanced: some have image

processing software and others can display images in three dimensions. Figure 4 on the next

page shows a rotating LED display kit made by Beijiayue and advertised on AliExpress [7]

.


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Figure 4: Rotating LED display kit [Beijiayue]

2.3 Electromagnetic induction

One of the unique challenges of this project is powering the rotating circuitry. As seen in the

literature study of existing rotating LED displays, the traditional way of powering the display

is through the use of slip rings or a battery. These methods do not comply with this project‟s

design goals of durability and reliability. Slip rings are susceptible to wear and batteries run

out of power. Therefore an alternative way to power the display needs to be researched.

This study focuses on the principles of electromagnetic induction with the aim of using it to

power the display being designed in this project.

Faraday‟s law of electromagnetic induction describes how a magnetic field will interact with

an electric circuit to induce an electromotive force (EMF) [8]

. According to this law, a EMF is

induced in a conductor that is placed in a changing magnetic field. It can be expressed by the

following equation:

.

The direction of the EMF is in such a way as to oppose the change which created it. This is

described by Lenz‟s law and is responsible for the negative sign in the equation [9]

. A

magnetic field, B, originates from electrical currents and magnetic materials and is measured

in Tesla. Magnetic flux, ɸB, is the surface integral of the magnetic field passing through a

surface. Permanent magnets are graded by their maximum energy product. This can be

related to the magnetic flux per unit volume of the magnet [10]

.

The following two applications of Faraday‟s law is of interest to this project.

2.3.1 AC Generation

Alternating current (AC) generation is an application of Faraday‟s law. A diagram illustrating

the basic principles of an AC generator is shown in Figure 5 on the next page. A changing

magnetic field can be achieved by moving the conductor within the magnetic field in such a

way that it will cut the magnetic lines of force. In this case to relative movement is achieved

by rotating the coil.


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Figure 5: AC generator principles [Wayne Storr]

2.3.2 Inductive coupling

Inductive coupling is the transfer of energy between two magnetically coupled coils that

resonate at the same frequency [11]

. A common practical example of inductive coupling is

found in a transformer. Alternating current through the transmitting coil creates a changing

magnetic field. This magnetic field induces voltage in the collector coil. Any energy passed

through the transmitting coil will oscillate and die away slowly. Because the receiver coil

resonates at the same frequency, it can pick up most of the energy before it is lost. Figure 6

shows a diagram of the principles of electromagnetic coupling. L1 and L2 are the coupled

coils. The AC current in the primary coil on the left side is generated and it then induces a

current to flow in the secondary coil on the right side. As seen in Figure 6, the coils do not

need to be in contact for power to be transferred.

Figure 6: Diagram of electromagnetic coupling principles [A. Bestbier]


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3 Quality function deployment

This chapter aims to establish the requirements of the project and then to relate these

requirements to engineering characteristics with quantitative parameters. This is an important

step leading to the generation of concepts. The goal of the engineering characteristics is

threefold: firstly to generate a list of well-defined specifications for the rotating LED display,

secondly to calculate or derive design goals for each of the specifications, and lastly to get a

sense of the relative importance of the different specifications, in order to see which carries

the most weight.

3.1 Project requirements

Requirements arise from the problem statement and a study of current technology in this

field. It is important to identify all the needs expressed, to ensure that they will be taken into

account when designing the rotating LED display. These are non-technical goals that are set

for this project. Here follow the main project requirements:

The display should spin faster than the human flicker fusion

The display should have enough LEDs to display text

The device should display text in a stationary and stable fashion

The device should fit on a standard desk of display cabinet

The spinning electronics should be powered “wirelessly”

The device should be durable and reliable

The device should be controllable by a user on a computer in the same room

The device should run smoothly and silently


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3.2 Engineering characteristics

The project requirements can be related to engineering characteristics containing measurable

design goals as shown in Table 1. Calculations regarding some of the values can be found in

Appendix C, as shown in the reference column. The relative importance is a percentage given

to each engineering characteristic, showing its importance relative to the others.

The engineering characteristics, design goals and the relative importance between them will

be used throughout the design process. They will act as guidelines when generating concepts

and criteria during the evaluation of these concepts. The final prototype will also be evaluated

using the following table as guideline:

Table 1: Engineering characteristics

Engineering characteristics Design goal Reference Relative

Importance

Spinning radius 100 mm 2%

Number of LEDs 16 6%

Display resolution 100x16 C1.1 5%

Light intensity > 200 mcd per LED C1.2 5%

Rotational speed 20 Hz 14%

Minimum on time for LEDs 5x10-4

s C1.3 8%

Maximum time to switch LEDs 5x10-6

s C1.4 10%

Voltage supply for spinning circuit > 5 V 12%

Current draw for spinning circuit ~ 0.54 A C1.5 9%

Power need for spinning circuit ~ 2.7 W C1.5 9%

Motor torque 0.0482 Nm C1.6 4%

Power need for motor 0.9644 W C1.7 6%

Lifetime > 500 h 3%

Components used Locally available 2%

Communication speed < 5 s per instruction 3%

Communication protocol Serial 2%


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4 Concept generation and evaluation

This project, being a complex engineering problem, consists of many subsystems working

together to form a whole. The method that will be used in this chapter consists of a physical

decomposition, finding various concepts for the basic structures, evaluating the solutions and

synthesizing these solutions to form a working design.

4.1 Physical decomposition

Breaking this complex problem into its basic elements will be the first step in finding the best

solution. Figure 7 shows a diagram of the physical decomposition of the rotating LED

display. At the top is the rotating LED display as a whole. It is then divided into four

characteristic parts and each part is divided into its basic elements. Element blocks marked

with blue on the diagram are areas where concepts need to be generated and evaluated.

Figure 7: Physical decomposition of rotating LED display

4.2 Conceptual solutions

Various solutions can be proposed for each of the physical units as marked with blue in

Figure 7. The function of these elements is known and their design goals have been identified

in Chapter 3. Possible solutions will be proposed in this section. These solutions originate

from the accumulated body of engineering knowledge supplemented by the knowledge

gained from the literature study. Where necessary, an analysis of strengths and weaknesses

will be done to identify the best solution to a problem. The following section will discuss

these solutions, evaluate them and identify the best one.


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4.2.1 Spinning rod

There are two possible orientations with regards to the spinning rod and the placement of the

LED as shown in Figure 8 . In orientation A the motor is placed on the x-z plane some

distance from the ground. The display turns around the y-axis and the spinning LEDs form a

circular shape. In orientation B the motor is placed on the ground and the shaft turns around

the z-axis. The spinning LEDs form a cylindrical shape.

Figure 8: Orientation concepts, A and B

The strengths and weaknesses of both conceptual orientations are shown in Table 2. Strengths

are highlighted with green and weaknesses with red.

Table 2: Evaluation of orientation concepts

Orientation A Orientation B

Easy to mount LEDs Square shaped display

Simple spinning rod Simple support structure

Complex support structure Capable of 360° display

Wedge shaped display Low center of gravity

High center of gravity Complex spinning rod

Susceptible for vibrations Bending moment on rod

Orientation B is chosen because of all the advantages listed in Table 2. The main

consideration is the centre of gravity and the complexity of the support structure. Vibrations

and imbalances are a major threat to the display. Orientation B allows the motor to be fixed

securely to a base and minimal support structures are needed. This orientation also enables a

square image to be displayed 360° around a vertical axis.


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4.2.2 Motor

An electric motor must be chosen to rotate the LED rod. A choice must be made between

brushed or brushless. Brushed motors are simpler to run than brushless for they are powered

by direct current (DC) and are cheaper. Brushless motors, on the other hand, have higher

torque for size ratios than brushed ones and are more durable [12]

. Since durability is one of

the design goals, the brushless motor is chosen. The brushless motor is also more compact

and easier to attach a shaft to, because of its outrunner form.

4.2.3 Communication

A method of communication needs to be established so that a user can send commands to the

display. Three options are considered for this: serial over USB, Bluetooth and Wi-Fi.

Serial communication over USB depends on a cable connection to transfer data. The

processor will be spinning along with the rest of the display. This means that the display will

have to be stopped to connect a cable and update the image. This is neither practical nor

efficient.

The solution is to use wireless communication. Bluetooth and Wi-Fi are two protocols used

to send data wirelessly via radio waves in the 2.4 GHz frequency range [13]

. Both of these

protocols will work for this device. Bluetooth is chosen, because it is intended for medium

speed and personal area networks over short distances such as the one that will be necessary

for this device.

4.2.4 Power transfer

Two options to supply power to the spinning circuit were discussed in the literature study,

namely AC generation and inductive coupling. Both are based on the principles of

electromagnetic induction. These two options lead to the following two conceptual power

supplies shown in Figure 9:

Figure 9: Two methods of power transfer [A Bestbier]

Induction coupling AC generation

Magnets

Rotating coil

Primary coil

Secondary coil


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Each method of power transfer will lead to a different direction of the structures design. For

the AC generator, some kind of structure needs to surround a rotating shaft to create a

stationary magnetic field. A shaft will connect the motor to the spinning rod. This shaft will

contain copper coils and will rotate inside the magnetic field. For the inductive coupling

method, there will be a stationary coil just above the motor and a spinning coil on the rotating

rod. The stationary coil will be connected to a AC power source and will induce voltage in

the coil spinning along with the rotating display. The strengths and weaknesses of both power

transfer methods are shown in Table 3. Strengths are highlighted with green and weaknesses

with red.

Table 3: Evaluation of orientation concepts

AC generation Inductive coupling

High power transfer No magnets needed

Harnesses spinning motion Simple design

Robust Lighter

No additional circuitry needed Distance reduces power transfer

Well known and understood

principle

Additional circuitry needed to

generate AC current

Extra hardware needed LED control circuit needs to be

tuned to resonate at specific

frequency

Extra torque needed to rotate shaft Interference with motor coils

Both types of energy transfer methods evaluated in Table 3 have their strengths and

weaknesses. There is no obvious choice. Since the main consideration for the choice of power

supply is power transfer, AC generation is a more suitable option to supply power to the

rotating display. Its higher power transfer in relation to inductive coupling is especially

attractive in this application.

The stationary magnetic field of the generator can by produced by permanent magnets or by

current carrying coils. Permanent magnets are preferred for this function, because they are

smaller and can produce a stronger magnetic field in this case. Furthermore, coils will need

an additional electric circuit to power them.


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4.2.5 Processor

A variety of programmable microcontrollers are available that will work for this project. A

few of the options will be investigated in order to choose the best one. Processors are

evaluated in terms of speed, size, pins, memory and ease of use. Table 4 shows the results.

Table 4: Processor evaluation

Processor Arduino Pro

Mini [14]

MSP430

LaunchPad [15]

Renesas rl78g13 [16]

Pic 18f4680 [17]

Speed 16 MHz 16 MHz 32 MHz 40 MHz

I/O Pins 20 14 52 20

Memory 32 kB 16 kB 512 kB 64 kB

Size 33x18 mm 55x70 mm 30x100 mm 36x8 mm

Stand-alone Yes Yes Yes No

Ease of use Medium Easy Hard Hard

After an analysis of all the available options it is decided to use the Arduino Pro Mini. It is

the smallest of the options that can operate without supporting hardware. This is important,

because space- and weight-carrying capability is limited on the spinning part of the display. It

is very versatile and relatively easy to install and program. There are abundant open source

libraries available and this device is easily connected to various peripheral devices. A 10-bit

analog-to-digital converter will be very helpful when reading outputs from sensors.

4.2.6 Position sensor

A sensor is needed to sense the angular position of the rotating rod. This sensor will have to

be able to alert the microcontroller each time the rod passes a specific position. Two sensors

are considered for this task: firstly, a photo interrupter, using an infrared emitter and receiver,

and secondly, a hall effect sensor that varies its output relative to a magnetic field. The photo

interrupter is chosen, because it has a fast enough switching time of 0.1 μs, as shown by its

datasheet [Appendix D1], and because it will not be affected by the magnetic field of the

induction power supply.


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4.3 Final concept

The top-down decomposition is followed by bottom-up synthesis. All the parts chosen by the

various evaluation processes will be combined to form the final design for a working rotating

LED display prototype. The final prototype consists of a LED strip in a vertical position,

fixed to a thin rod. The rod is connected to a brushless motor via a shaft. The shaft holds a

number of copper coils which rotate inside a magnetic field, forming an AC generator. An

Arduino Pro Mini aided by a photo interrupter sensor will control the LEDs. A user will

communicate with the rotating display through a Bluetooth connection. Figure 10 shows a

CAD model of the concept generated in this chapter.

Figure 10: CAD model of generated concept rotating display

Some of the chosen subsystems will need further development and design in order to be fully

functional. This chapter selects all the physical parts. In the chapters to follow these parts will

be designed. The design process will be similar for all the subsystems. Each subsystem will

be divided further into its basic parts. These parts will be designed and developed. Finally the

various parts will be tested and integrated. The chapters to follow will document the design of

the AC generator, electronic circuits, physical structure and software respectively.

Upright rod

orientation

Photo

interrupter

Brushless

motor

Arduino Pro Mini &

Bluetooth module

AC generator

Base structure


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5 AC generator design

An AC generator was chosen for the transfer of power to the rotating circuitry. This chapter

aims to design the AC generator. Figure 11 shows a diagram of the basic layout of the AC

generator.

Figure 11: AC generator design diagram

The spinning circuitry containing the processor, LEDs and Bluetooth module needs to be

supplied with 5 V DC. The AC generator supplies power to a power supply subsystem

containing a current rectifier and a 5 V voltage regulator. The exact characteristics of the

power supply is not yet known, so certain assumptions will be made. Assume a voltage drop

over the current rectifier of 1.4 V and a output ripple voltage of 0.2 V. If the regulator needs a

minimum of 5 V, the AC generator must generate a sine wave with a minimum peak voltage

of . It has also been established that the shaft will rotate at 20 Hz.

5.1 Magnetic field design

N38 neodymium rear-earth permanent magnets were selected to provide a stationary

magnetic field. Neodymium magnets are used, because it is the strongest type of permanent

magnet that is commercially available [18]

. Eight Neodymium bar magnets will be arranged in

four sets of two at opposite sides of the rotating shaft to create the magnetic field.

The goal is to get as many flux linkages between the coils and the magnetic field. To achieve

this, the magnetic flux density between the magnets needs to be as high as possible. A

laminated ring of high permeability will complete the path of the flux around the outside of

the shaft. The use of laminations reduces eddy currents [19]

. Minimizing air gaps will

strengthen the magnetic intensity.

Rotating shaft

Stationary magnet Stationary magnet

Copper coils

Coil ends powering

display Display attach here

Motor attach here


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In order to calculate the flux density, the structure of the shaft, magnets and laminated ring

needs to be modelled. Finite Element Method Magnetics (FEMM) [20]

is an open source

software that analyses the magnetic characteristics of structures. FEMM will be used to aid

the design of the AC generator. The main goal of this simulation is to calculate the average

flux density that passes through the coils as the shaft rotates. Figure 12 shown a cross section

through the AC generator. This is also the view that will be modelled using FEMM.

Figure 12: Cross section of AC generator

A FEMM simulation was run using the properties as shown in Figure 12 and with the shaft in

two positions of rotation. Figure 13, A and B show the results in the form of a colour-coded

flux density plot.

Figure 13: Flux density plots of AC generator

From Figure 13 it is seen that the average flux density through the coils of the AC generator

is 1.2 Tesla. This property is used to calculate the EMF generated by the generator. On the

basis of Faraday‟s equation, as shown in the literature study, the following formula can be

derived to express the EMF in terms of the field density, rotation speed, number of coils and

coil area.

A B

1018 Steel

Magnetisation direction

Stationary magnet (N38) Air gap

Copper coils (SWG 14)

Rotating shaft (1018 Steel)

Holes for bolts


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Equation 1: Faraday's law to calculate induced voltage

Certain assumptions must be made since all the variables are not known. With the surface

area of the coil as 0.00045 m2 and the number of coils as 150, the induced EMF is predicted

have a peak voltage of 10.1788 V. Step-by-step calculations are included in Appendix C2.

This is within the range of the voltage regulator and it allows for some voltage drop to occur

when the signal is rectified.

5.2 Generator structure design

By means of these assumed and calculated parameters a final design can be made of the AC

generator. The shaft will connect the rotating rod to the motor and will have slots machined

into it to hold the copper coils. Insulated copper wire with a 0.2 mm diameter will be used to

wind two coils of 100 turns each onto the shaft. Figure 14 shows the manufactured shaft with

the copper coils. Detailed drawings can be found in the Appendix G and the drawing pack

included in the project file.

Figure 14: Manufactured shaft with copper coils

The outer ring of the generator is built up out of discs laser cut from 0.6 mm thick mild steel

sheets. These discs are stacked and bolted together. Protrusions on the top and bottom discs

hold the magnets in place and the bottom disc has holes to fix it to the base. A 3D-printed

bearing housing is bolted on the top disk and holds a bearing to locate the shaft concentrically

inside the ring structure. Figure 15 on the next page shows a sectioned CAD drawing of the

AC generator next to the manufactured version.

𝐸𝑀𝐹 𝑁𝑑 𝐵𝑑𝑡

𝐸𝑀𝐹 𝑁𝑑(𝐵 𝐴)

𝑑𝑡

𝐸𝑀𝐹 𝑁 (𝐵 𝐴) 𝜔


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Figure 15: Sectioned CAD drawing of AC generator (left) and actual AC generator

(right)

5.3 Testing of the AC generator

The AC generator was constructed as designed and it was tested to see if it performs as

predicted. The two main concerns with regards to the generator are the physical structure and

the power transfer capabilities. This section describes the testing procedure and the results.

The first test was to see if all the components of the generator fit together as planned. During

the assembly of the parts it was noted that the magnets are bigger than initially expected. The

sets of 2 magnets each did not fit into the allocated space provided, and interfered with the

shaft‟s rotation. A magnet was removed from each set to prevent this interference, leaving

only four magnets to produce the magnetic field. This resulted in a weaker magnetic field.

FEMM simulation predicts that the magnetic flux density will drop 54.17%, from 1.2 T to

0.55 T. Recalculating the induced EMF of this reduced magnetic field results in a peak EMF

of 4.665 V. EMF calculations and the magnetic flux density plot can be seen in Appendix

C2.2.


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To test the power transfer capacity of the generator, the ends of the spinning coil was

connected to an oscilloscope by means of a slip ring. The motor was powered up and a

voltage reading was made. Figure 16 shows a screenshot of the oscilloscope reading.

Figure 16: Oscilloscope reading of generator output

The signal seen in Figure 16 is as expected. The high frequency noise in the signal is due to

uneven contact made by the slip ring. The signal is that of an alternating voltage supply. The

peaks of the signal are somewhat more pointed due to the shape of the coils and the magnetic

field. The peak EMF is about 4 V which is significantly lower that initially planned. This is

primarily caused by the weaker magnetic field and also to some extent by losses in the system

due to inefficiencies ignored by the calculations.

The measured reduced peak EMF (Figure 16) is 14.25% smaller than the calculated peak

EMK (Appendix C2.2). Assuming that this trend will continue when the magnetic field

increased, the peak EMF when using all eight magnets will be ( ) . This is more than the minimum required peak voltage for the power supply.


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6 Electronic circuit design

In this chapter the design of the electronic system of the rotating display will be described..

This system can be subdivided into five subsystems: power supply, LED strip, Bluetooth

module, photo interrupter, controller and speed control.

6.1 Power supply

The AC generator is designed to output a sine wave of amplitude 10.1788 V at 20 Hz. This

signal needs to be converted to a steady 5 V direct current to supply power to the rest of the

electronics. A two-step power supply is designed to achieve this.

Step one is needed to supply the voltage regulator with its minimum input voltage of 5 V as

indicated by the datasheet [Appendix D2]. The generated AC signal is passed through a full

bridge diode rectifier. Four 1N007 diodes are used along with a capacitor to smooth out the

signal to a maximum ripple voltage of 0.2 V. In Appendix C3.1 the size of the capacitor is

calculated to be 220 μF.

Step two is needed to regulate the voltage to a steady 5 V to be used by the rest of the

electronic components. The voltage regulator will supply an output voltage of 5 V with a

tolerance of 4% as indicated by its datasheet (Appendix D2). A schematic diagram of the

rectifier circuit and the regulator in shown in Figure 17.

Figure 17: Schematic diagram of the rectifier and regulator circuit

LT SPICE is free software [21]

used to draw and simulate electronic circuits. This tool is used

to simulate the output of step one of the power supply, the diode bridge, and plot the voltage

over the smoothing capacitor. A voltage versus time graph in the circuit is shown in Figure

18 on the next page. It is seen from this figure that the ripple voltage is within the desired

range of 0.2 V. This signal can now be passed through the voltage regulator and be

reregulated to a steady 5 V to be used by the electronic components of the rotating display.


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Figure 18: Plot of voltage over the capacitor versus time

6.2 LED strip

The display will consist of a strip of 16 red, green and blue (RGB) LEDs. An output is

needed to control each colour of each LED, which means that 48 channels are needed to

control the whole strip. A series of six serial-in, parallel-out, 8-bit registers will be used to

control the LEDs. This setup makes it is possible to control 48 channels using only three

digital output pins of the controller.

74HC4094 shift registers Appendix D4 are used for two main reasons. Firstly, they have data

and storage registers, meaning new data can be shifted while the old data are still available on

the parallel output pins [datasheet in Appendix D.4]. This means that the LEDs can be

switched on and off more quickly. Secondly, they will allow for a total shifting time of

5.0526x10-7

s as calculated in Appendix C3.2. This is fast enough to satisfy the design goal

set in Chapter 3.

By using the recommended current for the LEDs [datasheet in Appendix D3] the required

resistances can by calculated as shown in Appendix C3.3. The standard resistor value of

120 Ω is used for the red LEDs and 82 Ω for green and blue LEDs. Figure 19 shows a

schematic diagram of a section of the LED strip circuit drawn with Eagle PCB free

software[22]

. Only two of the shift registers are shown to illustrate the connections between

them. The complete schematic can be seen in Appendix F.


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Figure 19: Schematic diagram of a section of LED strip

Common anode RGB LEDs will be used, which means that the LED will light up if the

corresponding pin on the shift register is pulled low. The display will be powered by the 5V

power supply.

To reduce the size of the LED strip a printed circuit board (PCB) will be designed to hold the

components. Furthermore, surface-mount (SMD) resistors and shift registers will be used. A

5-pin header will be used to supply power and connect the LED strip to the controller. Eagle

PCB‟s free software [22]

is used to design the PCB layout that is shown in Figure 20. This

layout is designed to be manufactured with a milling machine. Design considerations for

milling include the thickness of copper tracks, distance between tracks and the reduction of

the number of vias.

Figure 20: LED strip PCB layout

Figure 21 shows the front and back of the completed PCB with soldered components.

Figure 21: Front and back of manufactured PCB


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6.3 Bluetooth module

Bluetooth was chosen during the concept generation phase as the preferred method of

communication between the display and a computer. A variety of similar Bluetooth modules

are available on the market. The Bluetooth Mate Silver module was chosen, because it is

designed specifically to work with the Arduino Pro range of controllers [23]

. This module acts

as a serial pipe, replacing the RX and TX wires of a serial cable. Data received through the

RX pin are passed out through Bluetooth and data received through Bluetooth are passed out

through the TX pin. The module is powered from the 5 V power supply and connects to two

I/O pins of the controller.

6.4 Photo interrupter

A photo interrupter was chosen for position sensing. The photo interrupter consists of an

infrared emitter on one end and an infrared detector on the other. Figure 22 shows a

schematic diagram of the photo interrupter.

Figure 22: Schematic diagram of photo interrupter

If the gap between the emitter and detector is open, the detector gate lets current through and

Analog out equals 5 V (Vcc). If the gap is blocked, the detector gate is closed and Analog out

equals ground. Analog out is connected to an analog pin of the Arduino and this pin will read

the analog level. 1k Ω resistors will be used to limit the current through the emitter and

detector. The resistor in series with the detector also acts as a pull-down resistor. An analog

signal is used, because the voltage change at Analog out is not discrete, but continuous. The

microcontroller will analyse this analog signal and decide if the gate is open or closed.


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6.5 Controller

An Arduino pro mini will be used to control the display. This development board is based on

the ATmega328 integrated microcontroller. The board is supplied with 5V from the power

supply and is used to communicate with the LED strip, Bluetooth module and photo

interrupter sensor. The controller, power supply and Bluetooth module are soldered to a

prototyping board and wires are used to connect the LED and photo interrupter circuit. Figure

23 shows a schematic diagram of the complete spinning circuitry.

Figure 23: Schematic diagram of complete spinning circuitry

The microcontroller can be programmed through a serial over USB connection to a computer

with supporting software. The microcontroller board does not include an USB-to-Serial

converter. An FTDI device like the FT232RL can be used to provide this conversion. An

alternative way to program the microcontroller is by using another Arduino product with an

onboard USB-to-Serial converter. For this project an Arduino Uno is used. The ATmega IC is

removed from the DIP socket on the Uno and the RX, TX, ground and reset pins of the Uno

is connected to the corresponding pins on the Arduino Pro Mini. The Uno is then connected

to the computer by means of a USB cable. The Arduino Pro mini can now be programmed

via the Uno.

6.6 Speed control

A brushless motor was chosen during the concept generation phase. Specifications for

selecting the correct brushless motor include the physical shape and size, torque, speed and

availability. The motor must be able to overcome the inertia of the spinning structure and the

counter torque of the AC generator. The required torque was calculated during the setting up

of the engineering characteristics in Chapter 3. RC Hobby SA is a local distributor of motors

and motor accessories. The 5010-620 KV model is chosen for this device. It meets the torque

and speed requirements and the flat outrunner shape is ideal for use in this design.


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An electronic circuit is needed to control the brushless motor. The motor needs three phase

power which will be supplied by an electronic speed controller (ESC). The supplier suggests

a 10 ESC for the selected motor [24]

. The RCTimer 12 A ESC with SimonK firmware is

chosen, because it has the correct current rating and is locally available. The ESC is supplied

with 12 V by a bench power supply. A pulse width modulated (PWM) signal is sent to the

ESC to control the speed of the motor. A programmable microcontroller will be used to

generate the PWM signal.

6.7 Testing of electronic subsystems

Tests were carried out to check if the various electrical subsystems perform as designed. This

section describes these tests and shows the results.

6.7.1 Power supply

The power supply was built and tested to see if it can regulate a signal similar to the one that

the AC generator is designed to generate. The rectifier was built and connected to a signal

generator set to generate a 20 Hz sine wave of amplitude 10.1788 V to simulate the AC

generator output. It was found that the power supply functions as designed and outputs a

steady 5 V signal.

6.7.2 Photo interrupter

The photo interrupter‟s analog out signal was tested to determine the voltage levels

corresponding to the different states of the gate. The sensor was wired up as designed and the

voltage of Analog out was measured while the gate was opened and closed. It was seen that

1.73 V corresponds to an open gate, and 0.01 V to a closed one. Figure 24 shows a graph

plotted of the voltage on Analog out versus time as the gate was opened and closed.

Figure 24: Voltage levels of photo interrupter gate in operation


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6.7.3 Speed control

The ESC system was tested to see how to motor responds. A test was done to calibrate the

ESC and to determine in what range the PWM needs to be generated. Code was written for an

Arduino Uno microcontroller to generate a PWM signal. The signal has a frequency of 50

Hz, an amplitude of 5 V and a pulse width that can be varied by entering a period. The motor

was connected and the pulse width varied to see how the motor responds.

The test showed that the ESC operates with a PWM signal from 1.4 ms to 1.8 ms. The ideal

PWM signal was found by flashing the microcontroller‟s on-board LED at 20 Hz and varying

the speed of the motor until the flashing LED was observed to flash in a stationary position.

The ideal PWM signal pulse width period was found to be 1.71 ms.


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7 Physical structure design

In this chapter the design of a physical structure for the display will be described. The

structure will consist of two parts. The one part will be standing on the floor, the base, and

the other part will be rotating with the shaft of the motor, the rod.

7.1 Base design

The function of the base is to support all the other components in a stable way and to provide

attachment for the motor and generator. It is to have holes at the bottom, so that it can be

fixed to a flat surface. The other main consideration is that it should be strong enough the

withstand the forces acting on it without losing structural integrity.

Another aspect that will influence the design of the base is the manufacturing method. Two

methods are considered for this, namely 3D-printing and welding. 3D-printing is a very

affordable, practical and accurate type of modern rapid manufacturing. It is ideal for this

application, since intricate designs can be achieved with relative ease. Welding, on the other

hand, is limited in accuracy and needs to be done by a skilled technician. For these reasons

3D-printing is chosen as manufacturing method.

Design for 3D-printing entails the use of stress relief gaps to prevent warping and fillets to

avoid sharp edges. Figure 25 shows a CAD drawing of a shape that will realise the functional

requirements using the design guidelines for 3D-printing. A detailed drawing can be found in

Appendix D2.

Figure 25: Base CAD drawing

Acrylonitrile butadiene styrene (ABS) plastic will be used for the base material. It is

relatively strong and mildly flexible, which is good for vibration absorption [25]

.


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7.2 Rod design

The function of the rod is to support the spinning circuitry and to hold the LED strip in the

correct position. The rod is made out of aluminum channel. Aluminum is chosen, because is

strong and light. The channel shape improves the strength and stiffness of the rod. The

desired shape is achieved by cutting and bending the channel. Holes are drilled to attach the

electronic circuits. Figure 26 shows a CAD design of the rod. Detailed drawings can be seen

in Appendix D3.

Figure 26: CAD design of the rod

It is important for the rod to be balanced around its axis. This will allow for smooth spinning

and will minimise vibrations. Most of the weight will be on the LEDs‟ side of the rod, so a

counterweight is added to balance the rod. To determine the weight of the counterweight, a

simple experiment was done. The rod was placed on a narrow edge with the hole for the shaft

in the middle. The counterweight was moved outward from the center until the rod balanced

on the narrow edge. The counterweight was then fixed in this position.


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7.3 Assembly of the physical structure

The motor and generator are screwed to the base. The shaft is screwed onto the motor and the

bearing is fitted on top of the shaft. The LED PCB, controller circuit and photo interrupter

circuit is bolted into the rod. Lastly, the rod is bolted on top of the shaft. A bracket is bolted

to the generator‟s bottom plate to line up with the gap in the photo interrupter and this will

serve as the zero position indicator of the display. The ESC circuit is connected to the motor

and the bench power supply. Figure 27 shows an exploded CAD assembly of the display to

illustrate how the physical structure fits together with some of the other components.

Figure 27: Exploded CAD assembly of display

Base

Shaft

AC generator

Rod

Counterweight

Spinning circuitry

PCB

LED strip

Motor


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7.4 Testing of the physical structure

The success of the physical structure lies in its ability to hold all the other components

together and support the entire rotating LED display. By assembling the various parts it is

possible to see if the rod and base function as designed. Figure 28 shows a photo of the

completed device. The base is bolted to a wooden plank to secure it.

Figure 28: Completed rotating LED display


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8 Software

This chapter concerns the development of the software to control the display. The same

modular approach for designing the hardware is also followed when designing the software.

The software can be divided into two main categories: Microcontroller software and user

interface software.

The microcontroller functions include controlling the shift registers, communication through

Bluetooth, reading from the sensor and timing the LED output. All these functions are done

by the on-board microcontroller. An open-source IDE specially developed by Arduino is used

to write C++ code and upload it to the microcontroller [26]

. The IDE enables the programmer

to develop code in a simplified environment by only writing a setup() function and a loop()

function along with any custom functions in an .ino file. This file is compiled, linked with

standard libraries and then uploaded to the microcontroller.

The user interface software is written using open course software called Processing [27]

. This

software will run on a personal computer (PC) loaded with a Windows 8 operating system.

Source code of the functions described in this chapter can be found in Appendix E. Headings

in the appendix will correspond with headings used in this chapter. Figure 29 shows a flow

diagram that illustrates the sequence in which functions are called in the microcontroller and

how events trigger certain actions. The individual functions will be discussed in the following

sections and reference can be made to this diagram to see how the different functions fit

together.

Figure 29: Flow diagram of function sequence


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8.1 Controlling shift registers

The first function of the microcontroller is to shift bits to the shift registers. Code is written to

control the three pins connected to the LED PCB, namely data, clock, and strobe. This

process happens in the Shift() function on the Arduino Pro Mini. This function receives an

array of 48 binary integers as a parameter and then shifts the array to the registers. A one will

result in a high logic level and a zero to a low logic level on the corresponding register pin.

The shift registers used are serial-in/parallel-out registers, meaning that the data pin will send

a signal containing serial information to the registers. Data is shifted through the registers on

each positive edge of the clock pin. The registers are latched, meaning that shifting happens

while the strobe pin is low and data is transferred to the pins of the register when the strobe

pin is high. The shiftOut() function in the Arduino library is used to control the data and

clock pins. The array is divided into six sets of eight bits and these sets are shifted one by one

to the registers. As the next set is shifted, the previous set moves to the next register. The

Figure 30 shows an diagram of how this process works.

Figure 30: Flow diagram of shift() function


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8.2 Bluetooth setup and communication

After the hardware hook-up of the Bluetooth Mate Silver (Bluetooth module) is done as

described in chapter 6, the software setup can be done. Detailed information regarding the use

of the module can be found in the device‟s user manual. The Bluetooth module has two

communication modes: command mode and data mode. Firstly command mode will be used

to configure the device and secondly data mode to receive data during normal operation [28]

.

8.2.1 Configuration in command mode

The firmware on the Bluetooth module can be configured in command mode through a serial

connection with the microcontroller. The Arduino SoftwareSerial library is used to establish a

serial connection between the microcontroller and the Bluetooth module via pins 2 and 3 on

the microcontroller. This frees up the physical UART of the microcontroller for use when

communicating with the PC of uploading code to the controller. To enter command mode the

string “$$$” is sent to the module.

The default baud rate of the Bluetooth module is 115200 bps. This baud rate will be reduced

to 9600 bps each time the Bluetooth module is powered up, because 115200 bps can

sometimes be too fast for the Software Serial connection. The command “U,9600,N”

temporarily changes the baud rate to 9600 bps with no parity. The device name will be

changed once off to “LED_Display” by sending the command “SN,LED_Display”.

The Bluetooth device is paired to the PC by powering up the Bluetooth module and then

using the PC to check for available Bluetooth devices. The PC is paired with “LED_Display”

using the default PIN for the Bluetooth module, 1234. PC com Port 5 is identified at the

Bluetooth communication port of the PC and will be accessed by the interface software.

8.2.2 Communication in data mode

To send data between the Bluetooth device and PC a serial terminal is opened to the

Bluetooth communication port of the PC, com port 5. As soon as a connection is made to a

paired device, the Bluetooth module enters data mode and acts as a serial pipeline. The

module passes all data received through Bluetooth to the microcontroller via the RX/TX

connection.

The user interface software will send a series of bytes that represents the desired image that

should be displayed. As soon as the microcontroller detects that there is serial data available

from the Bluetooth module, it calls the readSerial() function. This function receives data one

byte at a time through the SoftwareSerial connection with the Bluetooth module. The

function stores these bytes in variables that can be sent to the shift registers as needed. The

Bluetooth module idles until a new data is sent from the PC, and then the process is repeated.

Figure 31 on the next page shows a diagram adapted from the Bluetooth Mate Silver‟s user

manual that depicts the flow of information through the Bluetooth connection.


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Figure 31: Flow of information through the Bluetooth connection

8.2.3 Data storage

The data received by the microcontroller, through the Bluetooth connection, need to be stored

in a way that can be shifted to the registers when needed. This conversion is done in the

serialRead() function. The data is received byte by byte, with each byte representing the state

of one shift register for one 100th

of a rotation. The bytes are received and stored in a 6 by

100 array 2 dimensional (2D) array. This array contains display information of one complete

rotation.

8.3 Sensor read and timing

8.3.1 Reading sensor values

The photo interrupter is connected to analog pin A0 of the microcontroller as described in the

hardware setup in chapter 6.4. The ATmega328 integrated circuit of the microcontroller has

an on-board analog-to-digital (A/D) converter with a 10-bit resolution, meaning it can return

integers from 0 to 1023. During the testing of the photo interrupter in Chapter 6, it was seen

that the Analog out signal was 1.73 V when the gate is open, and 0.01 V when closed. The

A/D converter will convert these analog voltage levels to 354 and 2 respectively.

A function, readSensor(), is written to read the value from the sensor. A simple if() statement

can be coded to check if the digitalised voltage level is within a certain range and thereby

determining the status of the photo interrupter gate.

8.3.2 Timing the display

The photo interrupter gate will open and close once per rotation of the display. This will

happen when the rod passes the zero position, marked by a protrusion from the base which

obstructs the infra-red beam of the photo interrupter. This indicates that a new rotation has

begun and it triggers a series of events regarding the timing of the display.

The time that the loop() function takes to complete once is used as an unit of time to assist in

the timing of the display. A period counter is created that increments each time the loop()

function is completed. Each time the photo interrupter is triggered, the period counter is

divided by 100 (amount of horizontal pixels) to get the period of a pixel after which the

period counter is zeroed. A loop counter simultaneously counts the loop() function repetitions


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until it reaches the period of a pixel. When this happens the next pixel is displayed. This

process is repeated until all 100 horizontal pixels are displayed and then gets repeated when

the photo interrupter is triggered again. Figure 32 shows a flow diagram of the timing

process.

Figure 32: Flow diagram of the display’s timing process

8.4 User interface

A user interface is coded in Processing and runs on the PC. The function of the interface is to

allow the user to send commands, telling the display what to display. It contains code for

setting up the serial connection, creating the graphical user interface (GUI) and converting

the user input to serial data. Source code for the interfacing software can be found in the

project file.

8.4.1 Setting up the serial connection

When the user interface program is launched, a serial terminal is opened to the Bluetooth

communication port of the PC, com port 5. A Processing library for serial communication

will be used to send the user input from the PC to the Bluetooth module. Data is written to

this serial port, byte by byte, at a rate of 9600 bps. This is the rate at which the Bluetooth

module is configured to work.

8.4.2 Graphical user interface

A GUI is coded to allow the user to communicate with the device in a logical and simple

way. This interface will consist of a window with a series of buttons, tabs and text areas. The

controlP5 Processing library, written by Andreas Schlegel, is used to create the interface.

The user is able to input text by typing in a textbox, or to draw an image on a blank surface.

This text or image is then converted to an array of bytes and sent through the serial port when


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the user presses the “Send” button. Other inputs include selecting a colour, clearing the

display, reconnecting to the display, and quitting the interface program. Figure 33 shows a

screenshot of the two input methods available in the user interface program.

Figure 33: Graphical user interface screenshots

8.4.3 Input conversions

A 2D array of integers is created to represent the state of the display. The array contains 48

rows and 100 columns. One column of 48 elements, represents the state of the LEDs during

one 100th

of a rotation. A 1 represents off and a 0 represents on. The input from the user is

always converted by the backend of the interface software to this 2D array, regardless of the

input method. When the user presses “Send”, the elements of the 2D array are grouped

together in bytes with each bit representing an integer of the original array. This conversion

results in an array of 6 rows and 100 columns. The bytes are then sent one by one to the serial

port and will be received by the serialRead() function.


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9 Evaluation and recommendations

After the completion of the project the rotating LED display is evaluated. The different

subsections of the display will first be evaluated individually and then comments will be

made about the device as a whole. The performance is measured against the design goals set

in Chapter 3. The results of the project will also be discussed in this chapter.

9.1 AC generator evaluation

The results of the tests on the AC generator in Chapter 5 show a reduction in the voltage

generated. An actual peak voltage of 4.6653 V instead of the designed peak voltage of

10.1788 V is achieved. This is less than the minimum of 6.6 V needed to power the spinning

circuitry.

Therefore the design of the AC generator does not meet the requirements and does not

function as needed. This is due to the fact that less magnets were used than planned. To a

lesser extent it is also due to the fact the inefficiencies were not taken into proper account. To

solve this problem, the space for magnets can be enlarged and an efficiency factor can be

used. It will also help if more power supply prototypes can be built and tested. The use of

inductive coupling should also be considered in greater detail.

Furthermore, with regards to the shaft that forms part of the AC generator: The shaft, that

connects the motor to the spinning rod, is not concentric enough to allow for smooth spinning

at high speeds. The misalignment causes a vibration when the motor speeds up. This means

that the display cannot be spun at its optimal rate of 20 Hz. This reduces the POV effect by a

small margin. These misalignments can be prevented by placing a narrower concentricity

tolerance on the threaded holes at the top and bottom of the shaft when it is sent to be

manufactured. A tolerance of 0.05 mm should be sufficient to prevent the vibration at 20 Hz.

9.2 Electronic circuit evaluation

The different elements of the spinning circuit were tested and every one of them functioned

as designed. The minimum light intensity per LED is 800 mdc (Appendix D3) which is more

than the design goal of 200 mdc. The switch time for the LED strip is 5.9526x10-7

s as

calculated in Appendix 3.2, which is less than the design goal of 5x10-6

s.

The only alteration needed is the addition of a 9V battery to supply power instead of the

dysfunctional AC generator. The battery is connected to the voltage regulator.

An improvement can be made to the LED strip. Surface mount RGB LEDs can be used

instead of the through-hole type. By doing this and compacting the component placement, it

is possible to reduce the size of the LED strip PCB. This will lead to weight reduction and a

better-looking design.


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During the testing of the ESC it was found that the motor loses speed after some time,

although the PWM signal stays constant. This is due to the fact that the motor operates on the

threshold of its minimum speed. To prevent the speed loss from happening, a motor with a

smaller motor constant (Kv) can be selected. A motor with a Kv of 360 will be more suitable

for steady operation at 20 Hz.

To counter this loss of speed, a potentiometer is added to the microcontroller to allow the

user to manually vary the speed of the motor. The user can compensate for the loss of speed

over time by turning the potentiometer, thereby changing the PWM signal sent to the ESC.

9.3 Physical structure evaluation

The only problem encountered with regards to the physical design was the manufacture of the

base. The large flat bottom part of the base warped when the plastic cooled. This warping of

the plastic can be prevented by changing the form of the flat, bottom part of the base from a

square to a circle. More stress relief gaps can also be added. A 3D-printing technique called

rafting can also be used to prevent this warping. It is recommended that the use of a welded

steel base also be investigated. A steel base will be more rigid and vibration-resistant. The

increased weight will also anchor the display.

9.4 Software evaluation

Two comments can be made regarding the software of the project: firstly about the

communication time between the PC and the Bluetooth device, and secondly about the

software on the microcontroller.

The time it takes the computer to send 100 horizontal pixels worth of information to the

computer is 6.734 s. This is more than the design goal of 5 s. Communication time can be

reduced by choosing a higher baud rate. A baud rate of 38400 bps will shorten the time

substantially.

Although the microcontroller has 32 Kb of flash memory, only 2 Kb of that memory is

available for the storage of global variables. This causes a problem when an attempt is made

to create an array of 48 times 100 elements. As a result of this limitation the number of pixels

is reduced to 70x16. It is possible to work around this problem by storing the incoming serial

data as a long data type instead of an int data type.


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9.5 Overall evaluation and results

At the end it is possible to integrate all the subsystems to form a functioning rotating LED

display. The various parts are assembled with screws, bolts and nuts. The spinning electrical

parts are connected to each other and the motor is connected to a 12 V power supply through

the ESC. After the software is flashed to the microcontroller, the device is ready to be tested.

Test messages “ABC” (Figure 34) and “LED” (Figure 35) are sent to the display individually

via the text interface, after which a drawn picture of a house (Figure 36) and a boat (Figure

37) is sent via the draw interface. It can be noted that the images displayed by the device are

clear and stable and similar to the commands sent by the user.

Figure 34: "ABC" text displayed

Figure 35: "LED" text displayed


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Figure 36: Picture of a house displayed

Figure 37: Picture of a boat displayed


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10 Conclusion

This project aimed to achieve the original objectives as described by the project definition

and by the study leader: to design and build a display that relies on the „memory‟ of the

human eye in order to build up an image. The report documented the design and construction

of such a device.

Knowledge gained from the project problem statement and a literary study led the way to

generating various conceptual solutions to the different subsystems of the rotating LED

display. The best solution was chosen and synthesised to a final concept. The parts of the

final concept were designed, manufactured and constructed.

The evaluation of the various subsystems and the device as a whole led to the following

conclusions:

The mechanical structure designed, is strong and rigid enough to support the device. The

electronic circuit designed to control the LEDs functioned as planned with no alterations

from the initial design. The power transfer subsystem did not deliver enough power to the

spinning circuit because of variance in procured parts. This issue was bypassed by the

addition of a battery. The communication subsystem worked as planned, although a bit more

slowly. The data received are accurate and reliable each time. An intuitive and effective user

interface is used to send commands to the display.

The end product is a working prototype of an rotating LED display. The images displayed are

clearly visible in a stable position. The images also represent the user‟s commands

accurately. Because of the functioning prototype, this project can be labelled as a success.


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pcb-design-software/about-eagle/. [Accessed September 2015].

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bluesmirf?_ga=1.36124195.247628218.1442428181. [Accessed October 2015].

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Appendix A: Techno-economic analysis

A1. Time schedule

Figure 38 shows a Gantt chart of the baseline schedule (gray) set up during the planning

phase and the actual schedule (blue). In average activities took longer, which meant that tasks

had to be overlapped more. The testing and debugging phases started later and took longer

than expected due to the complicated nature of integrating the subsystems. All milestones

were reached on time. In total, the project was completed in less time than planned for.

Planned project hours: 563

Actual project hours: 533

Figure 38: Gantt chart of the rotating LED display schedule

A2. Budget and actual costs

Figure 39 on the next page shows a bar chart comparing the planned and actual cost of the

student‟s own time for different phases of the project. At the start the cost was lower than

higher than planned and towards the end the actual costs became lower. In total the cost for

the student‟s own time is less than planned. This is because to project was completed in less

time than planned for.

Planned cost of the student‟s own time: R197 050.00

Actual cost of the student‟s own time: R186 550.00


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Figure 39: Bar chart of actual an planned costs

Table 5 shows the cost of purchases items and manufacturing processes. These costs is more

than planned for due to insufficient information about the exact parts and manufacturing

processes needed while doing the planning.

Table 5: Costs of purchases and manufacturing

The total actual cost can be calculated by adding the cost of the student‟s own time, the cost

of purchased items and the cost of manufacturing processes. The rotating LED display project

was completed under budget.

Planned total cost: R198 910.00

Actual total cost: R189 777.00


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A3. Technical impact

The technical value of this project lies in the unique combination of purchased and

manufactured components. The way the subsystems were designed and integrated enriches

the current body of knowledge in the field of rotating LED displays. This document, along

with the developed prototype, can serve as a valuable stepping stone to future research in this

field.

A4. Return on investment

The investment for the sponsor is the intellectual property generated by the research and the

opportunity to continue the research in this field. The bulk of the project‟s expenses was used

for the concept generation, evaluation, planning and developing stages. The expense on

manufacturing processes and the procurement of components was minimal. Consequently,

the return on investment for the projects sponsor is high.

A5. Potential for commercialization

If there is a market for rotating LED displays, this prototype will be an excellent candidate to

server as a stepping stone towards a production model.


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Appendix B: Risk assessment

Appendix B documents the risk assessment for this project. This assessment takes into

account all laboratory or experimental setups and includes safety measures, safety procedures

and emergency evacuation procedures. Guidelines will be given to ensure safe conditions at

all times. These guidelines can be found on the department of Mechanical and Mechatronic

Engineering‟s website in the document: Safety procedures for laboratory setups. Sections of

Appendix B are copied directly from this document and credit goes to the writers of the

document and Stellenbosch University.

This project will make use of the Mechatronic laboratory for experimental setups to test the

various subsystems of the rotating LED display. The tests include the testing of the electronic

speed control and the AC generator.

Risks include:

Being hit by the spinning structure

Fingers, hair or loose clothes being entangled in the spinning structure

The spinning structure disintegrating and objects flying through the air at high speeds

Electric shock

People at risk:

Person who is going to use the setup

People who are in close proximity to the setup

Safety procedures and steps to minimise risk:

Wear protective eyewear

Keep hands clear of spinning structure

Fasten hair and do not wear loose clothing

Ensure that all parts of the structure is fastened securely before staring up the motor

Incorporate a safety stop switch

Ensure that all wires are isolated

Keep fluids away from the setup

Always wear shoes in the laboratory

Disconnect device from power when working on it


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Emergency procedure:

The standard procedures of the laboratory used should be followed. The individual

conducting the experiment should familiarize himself/herself with the locations of emergency

exits, fire extinguishers and first aid kits. Table 6 can be referred to in the case of an

emergency.

Table 6: Contact details in case of an emergency


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Appendix C: Calculations

C1. Engineering characteristics

C1.1 Display resolution

Therefore the resolution is chosen as 100 wide by 16 high

C1.2 LED light intensity

Standard LEDs available from China Young Sun LED technology have a luminous intensity

of between 180 and 200 candela. The aim is to use LED brighter than this.

C1.3 Minimum on time for LED

The minimum on time for a LED in 0.5ms. Shift registers must be able to keep up with this

speed .

C1.4 Maximum time to switch LEDs

The maximum allowable time to switch the LEDs to a new state must be so that it does not

interfere with the image displayed.

A maximum switch time goal is set to be 1% of the minimum on time for any LED.


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C1.5 Power need for spinning circuit

Assume that only 5V components will be used in the rotating circuit. By analyzing standard

components it is possible to estimate the current draw of the spinning circuit.

C1.6 Motor torque

The motor must have enough torque to overcome the inertia of the spinning rod and the

counter torque due to the magnetic field. Torque to overcome friction forces is assumed to be

insignificant.

Torque to overcome inertia of spinning rod:

The spinning rod is modeled mathematically. Figure 40 shows the a diagram of the rod.

Masses are handled as point loads and lengths and masses are conservative estimations.

Figure 40: Diagram of spinning rod


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Torque to overcome magnetic field of AC generator:

The fundamental principles of a rotating loop is used to estimate the counter torque induced

by the AC generator. Figure 41 shows a diagram of a rotating loop. The parameters are

estimated while keeping in mind the physical size of the device. The magnetic field is

calculated as shown in Appendix C3.

Figure 41: Diagram of rotating loop


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C1.7 Power need for motor

If the motor produces a torque of 0.0482 Nm and turns at an angular velocity of 20 Hz

the power output of the motor can be calculated as:

C2. AC generator design

C2.1 Designed induced voltage

C2.2 Actual induced voltage

The FEMM analysis of the AC generator is repeated with the reduced number of magnets.

Figure 42 shows the actual magnetic flux density plot of the generator. It can be seen from

the figure that the average density is about 0.55 T. All the other parameters are the same as

designed.

Figure 42: Actual magnetic flux density plot of AG generator


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C3. Electronic circuits

C3.1 Smoothing capacitor

A ripple voltage of 0.2 V is chosen to lower the minimum peak voltage required without

needing to use an unnecessary large capacitor. The resistance of the spinning circuit was

measured. 1N007 diodes are used with a forward voltage drop of 0.7 V. Figure 43 shown a

plot of voltage versus time of the rectifier output in blue.

Figure 43: Plot of rectifier output versus time

Use the standard value higher than 200μF to ensure ripple is smaller than 0.2V.

Choose C = 220μF.


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C3.2 Register shifting time

The time that it takes to shift a complete set of LED state data through the shift registers is to

be calculated. 48 bits of data are to be shifted. 74HC4094 are used.

74HC4094 register capabilities:

C3.3 LED resistor sizes

All LEDs are connected to 5V and require a forward of 20mA. The forward voltage drop

varies for different colours. Table 7 from the LED data sheet shows the forward voltage

drops. Resistors are placed in series with the LEDs to regulate current. Resistor values are to

be calculated.

Table 7: Forward voltage drops for LEDs

A standard value of 120Ω is chosen for the red LEDs and 82Ω for the green and blue LEDs.

Slightly lower resistances are chosen to allow a larger than normal current to flow.

This will increase the brightness of the LEDs. The low duty cycle will prevent current

damage.

C3.4 Actual motor torque

The motor draws 0.75 A at 12V when spinning at 1200 rpm with its normal operating load.

The power and torque developed are to be calculated.


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Appendix D: Data sheets

D1. Photo interrupter


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D2. Voltage regulator


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D3. RBD LEDs


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D4. Shift registers


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Appendix E: Source code

E1. loop() function

//-------------------------------------------- CHECK BLUETOOTH -----------------------------------

if (bluetooth.available())

{

serialFlag = 1;

readSerial(); //Read and store tha data

}

//-------------------------------------------- CHECK INTERRUPT -----------------------------------

//Positive spike from the photo interruptor - zero position reached

if (analogRead(A0) < 100 && gateFlag == 0 && serialFlag == 0)

{

digitalWrite(ledPin, HIGH);

period = periodCount; //Calculate the periode

periodCount = 0; //Reset the period timer

gateFlag = 1;

dispFlag = 1;

}

else if (analogRead(A0) > 100 && gateFlag == 1 && serialFlag == 0)

{

digitalWrite(ledPin, LOW);

gateFlag = 0;

}

//------------------------------------------- CHECK DISPLAY STATUS -------------------------------

if (dispFlag == 1 && serialFlag == 0)

{

displayFunction(); //Display the next coulomb of the image

}

//------------------------------------------ LOOP() FUNCTION COUNTER ------------------------

if (periodCount < 1000)

{

periodCount++; //Increment the loop counter

}

}


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E2. displayFunction() function

void displayFunction()

{

if (loopCount == (period / 100)) //Calculate pixel period

{

shift(val[pixelCount]); //Shift the next coulomb of if the image

pixelCount++;

if (pixelCount == x) //If the while image has been displayed

{

pixelCount = 0

dispFlag = 0;

shift(zero);

}

loopCount = 0;

}

loopCount++;

}

E3. readSerial() function

void readSerial()

{

if (count6 < 6)

{

val[countX][count6] = ((int)bluetooth.read());

count6++;

}

if (count6 == 6)

{

countX++;

count6 = 0;

}

if (countX == x)

{

countX = 0;

count6 = 0;

serialFlag = 0;

digitalWrite(ledPin, HIGH); //On-board LED indicate when upload is done

delay(50);

digitalWrite(ledPin, LOW);

}

}


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E4. shift() function

void shift(int val[])

{

digitalWrite(latchPin, LOW);

shiftOut(dataPin, clockPin, MSBFIRST, val[0]); //Shift value to register 6






digitalWrite(latchPin, HIGH);

}

E5. bluetoothSetup() function

void bluetoothSetup()

{

bluetooth.begin(115200); // The Bluetooth Mate defaults to 115200bps

bluetooth.print("$"); // Print three times individually

bluetooth.print("$");

bluetooth.print("$"); // Enter command mode

delay(100); // Short delay, wait for the Mate to send back CMD

bluetooth.println("U,9600,N"); // Temporarily Change the baud rate to 9600, no parity

bluetooth.begin(9600); // Start Bluetooth serial at

}


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Appendix F: LED strip schematic diagram

Fig

ure 4

4: S

chem

atic d

iagra

m o

f LE

D strip


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Appendix G: Detailed drawings

G1. Shaft layout drawing

G2. Base layout drawing


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G3. Rod layout drawing

design and build a rotating led display

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