i.MXS ARM BASED DIGITAL COMPASS

(UH) University of Hertfordshire
School of Electronic, Communication and Electrical
Engineering
BACHELOR OF ENGINEERING DEGREE WITH
HONOURS IN ELECTRICAL AND ELECTRONIC
ENGINEERING
Final Year Project Report
i.MXS ARM-BASED DIGITAL COMPASS
Report by:
Sheraz Khan Malik
Supervisor:
Kate Williams
APRIL 2008
DECLARATION STATEMENT
I certify that the work submitted is my own and that any material derived or quoted from the
published or unpublished work of other persons has been duly acknowledged (ref. UPR
AS/C/6.1, Appendix I, Section 2 – Section on cheating and plagiarism)
Student Full Name: Sheraz Khan Malik
Student Registration Number: 04106220
Signed: …………………………………………………
Date: 07 April 2008
School of Electronic, Communication and Electrical Engineering
BEng Final Year Project Report
ABSTRACT
This report holds the detailed information about how to design an i.MXS ARM BASED
DIGITALL COMPASS. To complete the task a Tahoe development platform was used which
was provided by the university. It operates with VS.NET Micro Framework software and runs
with an input of 5V. To achieve the compass characteristic a magnetic sensor was used
provided by the university. It was interfaced with the I2C bus on the Tahoe board, and to make
the compass fully working a programme code was developed using VS.NET Micro Framework
software with the help of sample codes. The output was obtained as a digital compass and to
make it look even better a GUI was created by making modifications to the same code.
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ACKNOWLEDGEMENTS
I would like to express my gratitute and appreciation to my project supervisor, Kate Williams for
encouraging me for my work with her advice and moral support.
I would also like to thank Mr John Willmort in Lab c-460, who provided peaceful working
environment, and helped me regarding general problems in the project lab.
Finally I would like to thank my parents as well as my friends Owais, Tafseer, Saad, Bilal and
Gurpreet who encouraged me throughout my project.
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TABLE OF CONTENTS
DECLARATION STATEMENT ........................................................................................................i
ABSTRACT .....................................................................................................................................i
ACKNOWLEDGEMENTS .............................................................................................................. ii
TABLE OF CONTENTS ................................................................................................................ iii
LIST OF FIGURES .........................................................................................................................v
GLOSSARY ................................................................................................................................... vi
1.
2.
3.
INTRODUCTION .................................................................................................................. 1
1.1
PROJECT AIM AND OBJECTIVE ................................................................................ 1
1.2
RESEARCH .................................................................................................................. 1
1.2.1
TAHOE DEVELOPMENT KIT ............................................................................... 1
1.2.2
TAHOE BOARD .................................................................................................... 2
1.2.3
SOFTWARE .......................................................................................................... 3
1.2.4
MAGNETIC SENSOR ........................................................................................... 5
HARDWARE ......................................................................................................................... 6
2.1
CMPS03 ........................................................................................................................ 6
2.2
I2C INTERFACING ....................................................................................................... 7
2.3
CONNECTING HARDWARE ............................................................................................ 9
CODING ............................................................................................................................. 12
3.1
Program.cs .................................................................................................................. 12
3.2
LCD.cs ......................................................................................................................... 14
3.2.1
Class Compass Element ....................................................................................... 15
3.2.2
Class Intro Screen ................................................................................................ 19
3.3
BusIO.cs ...................................................................................................................... 20
3.4
Sensor.cs .................................................................................................................... 22
4.
PROJECT TESTING AND WORKING ............................................................................... 24
5.
RESULTS AND DISCUSSION ........................................................................................... 27
6.
EVALUATION ..................................................................................................................... 29
7.
CONCLUSION & FURTHER DEVELOPMENT .................................................................. 30
REFERENCES ............................................................................................................................ 31
BIBLIOGRAPHY.......................................................................................................................... 32
APPENDIX.1 PROJECT CODE .................................................................................................. 33
Program.cs .................................................................................................................................. 33
LCD.cs ......................................................................................................................................... 34
BusIO.cs ...................................................................................................................................... 40
Sensor.cs .................................................................................................................................... 42
APPENDIX.2 SAMPLE CODE .................................................................................................... 44
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CMPS03Compass.cs .................................................................................................................. 44
I2CSlave.cs ................................................................................................................................. 48
Endianity.cs ................................................................................................................................. 52
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LIST OF FIGURES
Figure 1- Tahoe Board .................................................................................................................. 2
Figure 2- Block diagram Meridian CPU........................................................................................ 3
Figure 3- IDE for VS.NET 2005 ................................................................................................... 4
Figure 5- I2C Bus Terminology ................................................................................................... 8
Figure 6- Project Hardware Components ................................................................................... 10
Figure 7- Project Block diagram ................................................................................................ 11
Figure 8- Class diagram for Program code ............................................................................... 12
Figure 9- Program.cs code for main window ............................................................................ 12
Figure 10- Program.cs code for button definitions .................................................................... 13
Figure 11- LCD.cs showing Private variables ........................................................................... 14
Figure 12- LCD.cs showing override event ................................................................................ 14
Figure 13- LCD.cs Reloading intro screen using else statement ............................................... 15
Figure 14- Compass Screen ...................................................................................................... 15
Figure 15- LCD.cs Compass screen display .............................................................................. 16
Figure 16 (a)- Picture used for angle and direction .................................................................... 16
Figure 16 (b)- Picture for analog compass display .................................................................... 16
Figure 17- LCD.cs Calculating screen centre points .................................................................. 17
Figure 18- LCD.cs array method for direction ............................................................................ 17
Figure 19- LCD.cs Calculating directions ................................................................................... 17
Figure 20- LCD.cs Drawing compass needle ............................................................................ 18
Figure 21- Intro screen for compass .......................................................................................... 19
Figure 22- LCD.cs Intro screen display ...................................................................................... 20
Figure 23- BusIO.cs Declaration of variables and constants ..................................................... 20
Figure 24- BusIO.cs Read operations ........................................................................................ 21
Figure 25- BusIO.cs Write operations ........................................................................................ 21
Figure 26- Sensor.cs showing address of register and sensor bus ........................................... 22
Figure 27- Sensor.cs Getting compass heading ........................................................................ 22
Figure 28- IDE showing debug window...................................................................................... 24
Figure 29- Compass intro screen displayed in LCD .................................................................. 25
Figure 30- Compass screen displayed on LCD ......................................................................... 25
Figure 31- Working compass intro screen ................................................................................. 27
Figure 32- Working compass screen display ............................................................................. 28
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GLOSSARY
ARM: It stands for Acorn RISC Machines, which is a 32 bit RISC (Reduced instruction set
computer) architecture developed by ARM Limited that is widely used by a number of
embedded designs.
i.MXS: It is the name of microprocessor designed by Freescale and operates at speed of
100MHz.
SDRAM: Synchronous Dynamic Random Access Memory, type of solid state computer
memory.
RISC: Stands for Reduced Instruction Set Computer
GUI: Graphical user interface. It allows people to interact with a computer and computer
controlled devices.
GPS: Global Positioning System is a navigation precise-positioning tool uses satellites to
determine position of the subject worldwide.
[1]
VS.NET: Visual Studio.NET is software based programming language also known as c-sharp, it
is used to develop console and GUI applications along with windows applications.
[2]
Console: Console application is a computer program designed to be used by the text only
computer interface.
[3]
SDK: Software development kit is a set of development tools which allow a user or a software
engineer to create applications for a specific software package.
Emulator: An emulator is the software used to perform emulation of the hardware used by a
system. Emulation is the simulation of silicon chips or integrated circuits used in a hardware
system using computer software.
[4]
SPI: Serial peripheral interface bus is a simple Master/Slave 4 wire protocol one for
synchronous clock (SCL), one for data transmitting, one for data receive and another for chip
select.
Chip Select: It is a control line that selects one chip out of several connected to the same
computer bus.
GPIO: General purpose input/output pins.
UART: Universal Asynchronous Receiver/Transmitter controller is the key component of the
serial communications subsystem of a computer. The UART takes bytes of data and transmits
the individual bits in a sequential fashion. At the destination, a second UART re-assembles the
bits into complete bytes.
[5]
IDE: Integrated development environment.
EEPROM: Electronically Erasable Programmable Read Only Memory.
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1. INRODUCTION
The project involves designing an i.MXS ARM Based Digital Compass. Digital compasses
have a great importance in today’s world. The modern technology has empowered mankind
to travel distant places. Compasses have played a vital role in many ways and are still being
used with a great importance. The people from the old age used different ways to direct them
towards their destinations. Compasses have made this job easier for today’s generation. They
are being used in aircrafts, robots, navigation systems, GPS receivers, sports watches,
submarines and etc.
This report contains various stages of work involved in designing the digital compass and all
the techniques and methodology used to achieve the required result.
1.1
PROJECT AIMS AND OBJECTIVES
The project aim was to design an I.MXS ARM Based Digital Compass with the help of the
provided Tahoe development kit and selecting a suitable magnetic sensor.
The objective of the project was to display output of the digital compass on the Tahoe board
by interfacing it with a suitable magnetic sensor, and using the VS.NET Micro Framework
software.
1.2
RESEARCH
The project research stage was to develop understanding for the steps involved in design and
working of digital compasses. The research process was carried out in order to understand
the working of the hardware as well as designing the software, which was achieved by using
internet and web based data. The main purpose of research stage was to get all the basic
information about the project and understand the steps involved in developing a digital
compass using the provided components.
1.2.1
TAHOE DEVELOPMENT KIT
The Tahoe development kit was provided by the university. The Tahoe platform provides an
ideal development system for Meridian CPU and .NET Micro Framework. The Tahoe platform
includes;




1- Tahoe Board.
1- USB cable.
A VS.NET 2005 installation disk.
SDK with customise emulator for .NET Micro Framework.
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1.2.2
BEng Final Year Project Report
TAHOE BOARD
The Tahoe board is a fully functional system allowing an infinite variety of expansion via
support for serial, SPI and I2C communications. Shown below is the Figure of the Tahoe
board.
[6]
Figure -1 Tahoe Board
The technical
[6]
[6]
specifications of the board are as follows;
Core:

Embedded Fusion Meridian CPU

It is a microprocessor mounted at the back of the Tahoe platform operates at
100MHz.

It has a 2MB flash and 8MB SDRAM.
GPIO:

Most pins are configurable as GPIO if not used for other purposes

Minimum of 16 GPIO Pins Available (up to 64)
Communication and expansion busses:

1x UART RS-232 DB9 connector

I2C for external peripherals

SPI Bus (can use GPIOs for ―chip selects‖ if required)

USB Function (for application download and debug)
Timers and clocks:

timer output

Optional input for programmable timer (can use internal clock)

Pulse width modulator (PWM)
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Power supply:



5V input
Allows powering direct from USB Function port (no additional supply needed)
3.3V outputs for peripherals.
Shown below is the block diagram for Meridian CPU;
Figure – 2 Block diagram for Meridian CPU
1.2.3
SOFTWARE
The software used for the project was VS.NET Micro Frame Work (Version 2005), the Tahoe
board is compatible with this software. The .NET Micro Framework
[7]
is Microsoft's latest
implementation of the .NET Common Language Runtime (CLR). The most notable aspect of
the .NET Micro Framework is that it does not need any underlying operating system. The
Micro Framework requires very little in the way of system resources thus reducing the overall
cost of a system. (The minimum memory resources are about 384K of FLASH/ROM and
256K of RAM) The Micro Framework first appeared in the MSN Direct Smart Personal Object
Technology (SPOT) watches and devices. In May of 2006 Microsoft announced it would make
the .NET Micro Framework available to the general embedded community through hardware
partners. The most noticeable use of the Micro Framework so far is the Windows
Sideshow compatible devices built into many new laptops for Windows Vista.
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The .NET Micro Framework
[7]
BEng Final Year Project Report
consists of two parts the Common Language Runtime and the
Core Libraries. The Common Language Run time is a system, designed by Microsoft that
executes Microsoft Intermediate Language or MSIL instructions. The software is provided with
an SDK called ―Tahoe SDK‖ that plugs directly into Visual Studio 2005 and applications can
be written directly in C# for CPUs with the .NET Micro Framework. The Core Libraries
provided in the SDK are an extended sub set of the framework available on the desktop. The
.NET Micro Framework adds many specialized components designed for small, low power
2
embedded systems like I C, and SPI.
[7]
The figure-3 shows a working view of the VS.NET 2005 software used in the project;
Figure – 3 IDE for VS.NET 2005
The Micro Framework
[7]
offers embedded systems developers a line of CPUs that essentially
directly execute MSIL. There is no need for low level assembly language or other proprietary
languages. You can use the standardized C# language to implement a complete embedded
system from handling interrupts to displaying a rich Graphical User Interface (GUI).
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1.2.4
BEng Final Year Project Report
MAGNETIC SENSOR
In the project one of the important tasks was to decide which magnetic sensor must be used
for compassing as there were a lot of magnetic sensors available in market. There was a
variety of magnetic sensors available for compassing depending upon their output including
1-axis, two-axis and three-axis magnetic sensors.
Magnetic sensors
[8]
detect changes, or disturbances, in magnetic fields that have been
created or modified, and from them derive information on properties such as direction,
presence, rotation, angle, or electrical currents. The output signal of these sensors requires
some signal processing for translation into the desired parameter. Although magnetic
detectors are somewhat more difficult to use, they do provide accurate and reliable data —
without physical contact.
A magnetic field is a vector quantity with both magnitude and direction. The scalar sensor
measures the field's total magnitude but not its direction. The omnidirectional sensor
measures the magnitude of the component of magnetization that lies along its sensitive axis.
The bidirectional sensor includes direction in its measurements. The vector magnetic sensor
incorporates two or three bidirectional detectors. Some magnetic sensors have a built-in
threshold and produce an output only when it is surpassed.
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2. HARDWARE
The hardware part of the project involved connecting the suitable magnetic sensor to the
Tahoe board. The selection of magnetic sensor was not an easy job as there were a lot of
varieties of magnetic sensor available. The selection criteria were based on the sensor
output, whereas the required output for sensor was to be digital, which means that an ADC
(Analog to Digital Converter) was also required as a part of hardware. As from the name it
suggests that an ADC converts an analog signal into digital signal.
The magnetic sensor chosen for this project was the CMPS03.
2.1
CMPS03
OVERVIEW:
The CMPS03 is a two-axis compass module (sensor board). It is called a compass module as
it is SOC (system on a chip) itself. The compass
[9]
uses the Philips KMZ51 magnetic field
sensor, which is sensitive enough to detect the Earth’s magnetic field. The output from two of
them mounted at right angles to each other is used to compute the direction of the horizontal
component of the Earth’s magnetic field. The compass also has an ADC which converts the
analog signal into digital signal. Shown below is the figure for CMPS03 showing direction for
its true north and its connections;
[9]
Figure – 4 CMPS03 (connections)
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PIN CONNECTIONS:
Pin 1 +5 V. The compass module requires a 5v power supply at a nominal 15mA.
There are two ways of getting the bearing from the module. A PWM signal is available on pin
4, or an I2C interface is provided on pins 2, 3.
[9]
Pin 2, 3 are an I2C interface and can be used to get a direct readout of the bearing. If the I2C
interface is not used then these pins should be pulled high (to +5v) via a couple of resistors.
Around 47k is ok, the values are not at all critical.
[9]
Pin 4. The PWM signal is a pulse width modulated signal with the positive width of the pulse
representing the angle. The pulse width varies from 1mS (0°) to 36.99mS (359.9°) – in other
words 100uS/° with a +1mS offset. The signal goes low for 65mS between pulses, so the
cycle time is 65mS + the pulse width - i.e. 66ms-102ms. The pulse is generated by a 16 bit
timer in the processor giving a 1uS resolution. It was to be made sure that the I2C pins, SCL
and SDA, were connected to the 5v supply if PWM was used, as there are no pull-up resistors
on these pins.
[9]
Pin 5 is used to indicate calibration is in progress (active low). An LED can be connected from
this pin to +5v via a 390 ohm resistor if user wishes.
[9]
Pin 6 is one of two ways to calibrate the compass, the other is writing 255 (0xFF) to the
command register. The calibrate input has an on-board pull-up resistor and can be left
unconnected after calibration.
[9]
Pins 7 and 8 are left unconnected as they have on board pull-up resistors.
Pin 9 is ground 0V power supply.
2.2
I2C INTERFACING
The I2C bus is a two wired bus serial data line (SDA) and serial clock line (SCL), usually to
interact within small number of divisions. It can operate at different speeds 100kbps (standard
mode), 400kbps (fast mode) and 3.4Mbps (high speed mode).The data transfer in I2C bus is
bi-directional and is 8-bit oriented and is in form of serial data.
On an I2C-bus any I2C device can be attached and every device can talk with any master,
passing information forward and backward.
Each device
[10]
has a unique 7-bit I2C address so that the master knows specifically whom
they are communicating with. Typically the four most significant bits are fixed and assigned to
specific categories of devices.
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The three less significant bits are programmable through hardware address pins allowing up
to eight different I2C address combinations and therefore allowing up to eight of that type of
device to operate on the same I2C-bus. These pins are held high to VCC (1) or held low to
GND (0). 7-bit addressing allows up to 128 devices on the same bus but some of these
addresses are reserved for special commands so the practical limit is around 120.
[10]
Shown below is the diagram of the I2C bus terminology;
Figure – 5 I2C Bus Terminology
[10]
Master device controls the SCL, starts and stops the data transfer and controls the
addressing of the other devices.
Slave device itself is addressed by the Master. In case of the data transmitting and receiving
that Master-transmitter sends data to the slave-receiver and the Master-receiver requires data
from the Slave-transmitter.
The data bits are transferred after start condition. The data transmission is byte oriented
where;
1 byte = 8bit + one acknowledge bit
The most significant bit (MSB) always comes first. During the first byte transfer Master is
transmitter and address slave is receiver.
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I2C communication Protocol with the Compass module is same as the popular EEPROM’s.
The compass module has a 16 byte array of registers, some of which double up as 16bit
registers are as follows;
Register
Function
0
Software Revision number
1
Compass Bearing as a byte, i.e. 0-255 for a full circle
2, 3
Compass Bearing as a word, i.e. 0-3599 for a full circle, representing 0-359.9
degrees.
4, 5
Internal Test - Sensor1 difference signal - 16 bit signed word
6, 7
Internal Test - Sensor2 difference signal - 16 bit signed word
8, 9
Internal Test - Calibration value 1 - 16 bit signed word
10, 11
Internal Test - Calibration value 2 - 16 bit signed word
12
Unused - Read as Zero
13
Unused - Read as Zero
14
Unused - Read as Undefined
15
Command Register
Table showing functions of compass module registers.
Register 0 is
[9]
the Software revision number (8 at the time of writing). Register 1 is the
bearing converted to a 0-255 value. This may be easier for some applications than 0-360
which requires two bytes. For better resolution registers 2 and 3 (high byte first) are a 16 bit
unsigned integer in the range 0-3599. This represents 0-359.9°. Registers 4 to 11 are internal
test registers and 12, 13 are unused. Register 14 is undefined. There is no need to read them
it would do nothing but waist the I2C bandwidth. Register 15 is used to calibrate the compass.
2.3
CONNECTING HARDWARE
The hardware connections were made according to the provided data sheet of the compass
module and the user manual given with the Tahoe board. The equipment used for the
hardware connections were as follows;

1-Soldering iron.

6- Coloured wires.

2- Connecting headers.
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The compass module was not directly soldered on the I2C bus of the Tahoe board. Two
headers were used in order to prevent direct contact of the soldering iron to the Tahoe board
and the compass module (sensor board). Different coloured wires were used to differentiate
the connections. Initially all the wires were soldered on to the connecting headers in order to
avoid any damage to the sensor board or the Tahoe board. Red coloured wire was used for
5V connection and black for the 0V ground. Pin1 +5V of the sensor board was connected to
the +5V on the I2C bus and Pin9 0V ground was connected to the 0V ground of the I2C bus.
Pins 2 (SCL) and 3 (SDA) of the compass module were connected to the SCL and SDA pins
of the I2C bus on the Tahoe board. Yellow colour wire was used for SCL and purple colour
wire was used for SDA. Pink and brown coloured wires were used for pin 5 and 6 but they
were left un-connected according to the given connections. The pin 6 was to be calibrated but
it was left un-connected as the calibration was done through the software.
Shown below is the picture of all the hardware components involved;
Figure – 6 Project Hardware components
It was made sure that all the connections were accurate according to the data sheet before
powering the board as it could result in damaging the board. Extra care was taken while
handling the compass module as it was sensitive to static charge. In order to avoid that anti
static wrist band was used which was provided in the laboratory to avoid the hazard of static
charge.
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Shown below is the block diagram of the project hardware part, showing all the connections
from the sensor board to the I2C bus on the Tahoe board.
Figure – 7 Project Block Diagram
Problems faced during the hardware connection were as follows;

Lose connection due to weak soldering.

An inverted connection, SDA of the sensor board was connected to the SCL of the
Tahoe board.

One of the headers was damaged with the soldering iron, which was then replaced
with a new one.
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3. CODING
This section of the report contains the detailed explanation of the programe code developed
for the project. For complete copy of the code as well as the sample code please refer to the
Appendix. The programe code was developed by looking at different examples of basic clanguage code regarding compassing and the sample code provided with the sensor board.
The programe code was divided into four main classes. The class diagram shown below
gives an overview about overall working of the programe code.
Figure – 8 Class diagram for Programe code
3.1
Program.cs
The Program.cs class runs the main window application and also checks for the button
definitions.
Figure – 9 Program.cs code for main window
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It shows in figure-9, that this class allows to initiate and run the main window application. The
main window application is like a starting point for the class.
Figure – 10 Program.cs code for button definitions
The above figure-10 is showing the button definition part of the class Program.cs. In this part
of Program.cs the buttons on the Tahoe board are accessed with the help of the program
code. It shows that the functioning button is the ―Select‖ button which is named as SW7, and
in the programe code it shows that it checks for all the buttons and gets value ―True‖.
Whereas on button SW7 it gets ―False‖ this allows it to jump towards the next step. It is not
necessary to define all the buttons. Only the required button can also be defined but it is done
for demo purposes.
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3.2
BEng Final Year Project Report
LCD.cs
The LCD.cs class inherits window class which is inbuilt class of the SDK. This class is
responsible to show any button activity and show different images and text (GUI) to be
displayed on the screen. The LCD class is further divided into two sub classes for different
screens. LCD class is important class as it holds all the GUI elements and is responsible to
show all the text and image activity.
Figure – 11 LCD.cs code showing Private variables
In figure-11 the LCD class window is defining variables, which give the font size, background
colour and create a new intro screen on the LCD of the Tahoe board. The
intro.StartRendering allows the text to be printed on the screen.
Figure – 12 LCD.cs code showing override event
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The figure-12 shows the override event for the button activity using ―if/else‖ statements. The
override event is used in order to make changes into the start rendering event. The start
rendering event has a default method of printing text. Override event provides user to play
with the start rendering function and change it as required. It shows that the override event
detects the button action and responds accordingly if the rite button is pressed it will exit the
intro screen and load the compass view screen.
Figure – 13 LCD.cs Reloading intro screen using else statement
In above figure-13 it is showed that if the wrong button is pressed the program will invalidate
the compass view screen and load the intro screen again using the ―else‖ statement.
The LCD class has further two sub classes explained below.
3.2.1
Class Compass Element
The class compass element displays the compass reading and compass screen on to the
LCD of the Tahoe board. In this class the different images are displayed on to the compass
screen. The compass screen obtained is shown below;
Figure – 14 Compass Screen
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Figure – 15 LCD.cs code compass screen display
The figure-15 shows how to display any bitmap image. Any Bitmap file can be displayed using
these lines of code; any bitmap file present in the resource folder of the programe can be
displayed by using this part of the program code. The picture format can be Bitmap as well as
JPEG. The above piece of code is simply accessing the bitmap files from the resources and
displaying them as image on the LCD for compass and angle. The images used are shown
below,
Figure – 16(a) Picture used for angle and direction
The figure-16(a) shows the picture used to display the angle of the compass as well as the
direction.
Figure – 16(b) Picture for analog compass display
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The picture (figure-16(b)) was used for analog compass display with the help of the program
code explained above and showed in figure-15. Both these images (16a, 16b) were displayed
on the screen but before doing that the centre points of the screen were calculated which can
be shown in the figure-16 below.
Figure – 17 LCD.cs Calculating screen centre points
The compass direction was displayed by using array method. The compass direction was
divided in 16 directions between 0’ to 360’which gives a value of 22.5.That means the
compass direction must change after every 22.5’ degrees. The array was assigned with 16
numbers.
Figure – 18 LCD.cs array method for direction
The process was very simple. On getting the angle value from the sensor board, the value
was then divided with the calculated value 22.5. It gives a number between 1- 16 and
depending on the number the array displays the direction. The figure-18 below shows the
piece of code for the process explained.
Figure – 19 LCD.cs Calculating directions
The last two lines of the code in figure-19 are drawing text for angle and direction on the
screen with a selected green colour and also calculating the points where the text should be
displayed or in other words the parameters for the text and angle. The direction calculation
can be shown for example if we assume the angle value to be 45’ degrees.
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We have;
Calculated value for directions = 22.5
=2
Hence the calculated direction will be NE (North East) as it is the 2
nd
number direction from
the left hand side if you see figure-17. The calculated value is passed to array and the string
then display’s the direction that comes on that number which is 2. So that means the
compass should be pointing at NE (North East) at an angle of 45’ degrees.
Figure – 20 LCD.cs Drawing Compass needle
The program code shown in above figure-20 is drawing the compass needle. The compass
needle was drawn using the Math function for drawing vector. North was used to calibrate the
compass it was given an off -set value of 90. So the default position of the compass angle
was 90.The compass needle was to be drawn according to the clock radius of the blue circle
in the compass picture shown in figure-16(b). It was approximately 50 pixels.
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The value of the clock radius was first defined at the top of the program code in Private
variables. The compass needle was then drawn by taking Cos and Sine of the compass
angle. Initially it resulted in a big value giving the compass needle an abnormal length. To
avoid this calculated value was then divided by 1000 to get it to unity. As we know that the
value for Sine and Cos is between 0-1, after that it was then multiplied by 50 (clock radius),
which controlled the length of the compass needle according to the clock radius of the blue
circle.
To obtain the full length of the compass needle the same code was used by adding a
negative sign to it which gave a compass needle of similar length but on the opposite
direction. To differentiate the opposite side its colour was changed to black
3.2.2
Class Intro Screen
As from the name it shows that this class is responsible for loading the intro screen onto the
LCD screen of the Tahoe board. The same lines of code were used for this class as
discussed before in figure-15. Shown below is the picture of the intro screen of the compass.
Figure – 21 Intro Screen for compass
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Figure – 22 LCD.cs Intro Screen display
The exact same code was used to display the intro screen elements. The pictures were
accessed through the resource files and were displayed by using the program code in figure21.
3.3
BusIO.cs
The BusIO.cs class is responsible for I2C communication protocol between the software and
the hardware. The class allows the software to communicate with the I2C bus of the Tahoe
board. This class manipulates the functionality of the I2C slave class which is provided with
the SDK. This class performs the read/write operation on the required registers.
Figure – 23 BusIO.cs Declaration of variables and constants
All the variables and constants are defined in this piece of programe code shown in figure-23.
The values used are default values. The register 1 is used as it gives compass bearing as a
byte, i.e. 0-255 for a full circle. The register numbers used for I2C communication are 2 and 3
as explained above that these registers get compass bearing as a word, i.e. 0-3599 for a full
circle, representing 0’-359.9’ degrees in angle.
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Figure – 24 BusIO.cs Read operations
In the above (figure-24) part of the program code the BusIO class is to read any port on the
I2C bus of the Tahoe board. Execute method will read bytes on the I2C bus and returns the
number of bytes successfully on the bus.
Figure – 25 BusIO.cs Write operations
In figure-25 the program code writes the port on the I2C bus. The Execute method here will
write bytes on the I2C bus and returns the number of bytes successfully on the bus. The
process taking place in this part of code is similar to the one explained for code in figure-24
the only difference is that this time the code is performing the write operation instead of read
operation.
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3.4
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Sensor.cs
The sensor class implements the functionality of the sensor board to read the compass
values in degrees.
Figure – 26 Sensor.cs showing address of register and sensor bus
This part of the program code (Figure-26) assigns address to the sensor bus. The address
used is 60 as it was the default address given for the sensor board. In the next step the
compass heading is taken from the register 2. As explained above the register 2 and 3 get
compass bearing as a word i.e. 0-3599 for a full circle representing 0’- 359.9’ degrees of
angle.
Figure – 27 Sensor.cs getting compass heading
This section of program code (Figure-27) gets the Azimuth value from the sensor board and
then reads the register value when it is high into the data buffer. The next step it shows that
the byte order is set using Big Endian.
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The Big Endian means the big end first, which means that the high order bytes are stored first
into the low memory location. Then it converts the receiving bytes into float (decimal) type and
returns the value to the calling function. If the condition is not satisfied then it uses the ―else‖
statement to display an error message.
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4. PROJECT TESTING AND WORKING
This section of the report contains the project testing on hardware as well as software basis,
and the problems faced during the software and hardware testing.
The hardware was tested with the help of software. All the communication and expansion
buses of the Tahoe board were tested at very initial stage to confirm that the board itself was
working perfectly. This was done by running default test programs provided with the software
for the each communication bus. It helped in understanding the nature of the hardware as
well as the software. In hardware there were problems faced during testing of the SPI bus it
kept on showing error messages which was then rectified by making changes to the test
program code. It helped in understanding the debugging process which later on helped in
software testing. After connecting the sensor board with Tahoe board the software was then
tested before the final testing of the whole project.
The software testing was carried throughout the program code development process. Initially
there were errors in the program code. Debugging was carried out constantly to make sure
that the program code was correctly working before testing it with the hardware.
The debugging process helped in error diagnosis and also helped in understanding the csharp language limitations.
Figure – 28 IDE showing debug window
After completing the testing process for hardware and software the whole project was then
tested to get the required results.
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The hardware was connected to the PC/Laptop with the help of provided USB cable. As soon
as the cable is plugged in the power light of the Tahoe board turns green (on). The software is
then run. Once the debug button is pressed the program code is build and debugged
completely. After completing the debug process the intro screen appears on the LCD of the
Tahoe board telling the user to press button SW7 to start.
Figure – 29 Compass intro screen displayed on LCD
As soon as the user hits the SW7 button or the select button on the Tahoe board it moves on
to the next screen which is the compass screen. The compass screen displays angle
measured by the sensor board and the directions calculated through the program code. It also
displays the compass needle which changes direction with respect to the changing angle. The
angle changes with the change in direction of sensor board i.e. right or left. Shown below is
the picture of the compass screen displaying angle, direction and compass needle.
Figure – 30 Compass screen displayed on LCD
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The direction name and compass needle direction showed in figure-30 is correct with respect
to the angle measured by the sensor board. It can be proved as follows;
Number of compass direction = 360 / 16 = 22.5
Angle measured by the sensor board = 119.8
Direction appearing on the display = ESE (East South East)
Measured angle / compass direction = 119.8 / 22.5 = 5.3, Approx 5
Whereas the divided direction names are;
N,NNE,NE,ENE,E,ESE,SE,SSE,S,SSW,SW,WSW,W,WNW,NW,NNW,N
th
Hence out of these directions starting from 0, ESE is the 5 number direction which has been
displayed on the LCD screen and even the compass needle is pointing towards the same
direction.
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5. RESULTS AND DISCUSSION
This section of the report contains all the results obtained at the testing and implementation
stage f the project. The results obtained were as expected and were satisfying the objective of
the project.
Figure – 31 Working Compass intro screen
The figure-29 is showing the picture of the whole project running and displaying the intro
screen, which shows that the software and the hardware are working correctly. Also it can be
seen that the sensor board is connected to the Tahoe board. The button labelled as SW7 is
the select button which allows the user to move on to compass screen by pressing it. These
pictures were taking at the project demonstration time.
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Figure – 32 Working Compass screen displayed
Figure-30 shows the working display of the project as Digital Compass. It can be seen that
the angle is displayed in degrees and the name of the direction is also displayed. Also the
compass needle is pointing in the direction displayed.
From the results it can be seen that the project was a success in terms of achieving the
required task. It meets the brief of, developing an i.MXS ARM Based Digital Compass device
that directs the user towards the wanted direction based on its true north. The results also
justify all the details explained above in the report regarding the project.
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6. EVALUATION
The projects meets the requirements for i.MXS ARM Based Digital Compass. Project was
completed within the specified time without facing any high level difficulties. The project
satisfies the requirement of an i.MXS ARM Based Digital Compass. The device created can
be used in different applications such as aircrafts, robots, Navigation systems, GPS receivers
and etc.
Although the project did not exactly followed the time plan provided in the feasibility study,
due to some delays in the progress but it was completed before the given time.
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7. CONCLUSION & FURTHER DEVELOPMENT
The project satisfied the requirements of an i.MXS ARM Based Digital Compass. This project
helped in improving learning skills and provided a chance of enhancing knowledge. It helped
in understanding the basic concepts of digital compasses, and the background knowledge
about the magnetic sensors and their operations. It also improved the skills in learning csharp programming language.
The projects requirements were;

To design an i.MXS ARM Based Digital Compass.

To display digital compass output on the Tahoe board using magnetic sensor and
VS.NET Micro Framework software.
The project achievements were;

An i.MXS ARM Based Digital Compass was designed.

The output of Digital compass was displayed on LCD of Tahoe board using sensor
board and VS.NET Micro Framework software.
For future development it was decided that an off-set window will be introduced in the digital
compass. The output window will allow any user to set their true north according to their
requirement.
For example if a user thinks that the true north showed by the compass has an error of about
5 degrees. The user will press the selected button for the off-set window. A new screen will
appear asking the user to enter off-set value. This off set window will appear after the second
screen which is the compass screen or it could be accessed any time while the compass is
running by pressing the selected button. After entering the off-set value the user will be able
set the true north as required.
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REFERENCES
Reference
Number
Reference Link
[1]
http://scign.jpl.nasa.gov/learn/gps1.htm
[2]
http://en.wikipedia.org/wiki/Vs.net
[3]
http://en.wikipedia.org/wiki/Console_application
[4]
http://www.mameworld.net/easyemu/emuwhatis.htm
[5]
http://www.freebsd.org/doc/en_US.ISO8859-1/articles/serial-uart/index.html
[6]
http://www.embeddedfusion.com/uploadedFiles/products/TahoeDetailSheet.pdf
[7]
http://www.embeddedfusion.com/default.aspx?id=76
[8]
http://www.sensorsmag.com/articles/0399/0399_18/
[9]
http://www.robot-electronics.co.uk/htm/cmps3tech.htm
[10]
http://www.nxp.com/products/interface_control/i2c/facts/
[11]
http://www.robot-electronics.co.uk/acatalog/examples.html
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BIBLIOGRAPHY
BOOKS
TITLE
AUTHOR
1
Visual C# 2005 a developer’s notebook.
JESSE LIBERTY
2
Programming C# Jesse Liberty
JESSE LIBERTY
3
Professional C# 2005 with .NET 3.0
CHRISTIAN NAGEL
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APPENDIX.1
BEng Final Year Project Report
PROJECT CODE
Program.cs
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LCD.cs
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BusIO.cs
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Sensor.cs
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APPENDIX.2
BEng Final Year Project Report
SAMPLE CODE
The part of the sample code
[11]
used has been highlighted.
CMPS03Compass.cs
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I2CSlave.cs
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Endianity.cs
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