project report (cs499)-albert maira
TRANSCRIPT
UNIVERSITY OF DAR ES SALAAM
COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND COMPUTER SYSTEMS ENGINEERING
PROJECT REPORT CS499
PROJECT TITLE: MICROCONTROLLER BASED TAXI BILLING SYSTEM
A Project Report in Partial Fulfilment for the Award of Bachelor of Science in Computer Engineering & Information Technology
Name of Candidate: Maira, Albert M. Registration Number: 2006-04-05608 Supervisor: Dr. M.M. Kissaka Submission Date: 9th July 2010
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Table of Contents Content Page TABLE OF CONTENTS .............................................................................................................................. I DECLARATION ........................................................................................................................................ III ABSTRACT ................................................................................................................................................ IV ACKNOWLEDGEMENTS ......................................................................................................................... V LIST OF FIGURES .................................................................................................................................... VI LIST OF TABLES ...................................................................................................................................... VI LIST OF ABBREVIATIONS AND ACRONYMS .................................................................................VII CHAPTER 1 ................................................................................................................................................. 1 INTRODUCTION ........................................................................................................................................ 1
1.1 WHAT IS A TAXIMETER? ....................................................................................................................... 1 1.2 CURRENT SITUATION ............................................................................................................................ 1 1.3 PROBLEM STATEMENTS ........................................................................................................................ 2 1.4 OBJECTIVES .......................................................................................................................................... 2 1.5 SIGNIFICANCE OF THE PROJECT ............................................................................................................. 3 1.6 SCOPE OF THE PROJECT ......................................................................................................................... 3 1.7 METHODOLOGY .................................................................................................................................... 3
CHAPTER 2 ................................................................................................................................................. 5 LITERATURE REVIEW ............................................................................................................................ 5
2.1 MICROCONTROLLER ............................................................................................................................. 5 2.2 LCD ..................................................................................................................................................... 7 2.3 TAXIMETERS ......................................................................................................................................... 7
2.3.1 Mechanical taximeters ................................................................................................................. 7 2.3.2 Microprocessor taximeters .......................................................................................................... 8 2.3.3 Microcontroller taximeters .......................................................................................................... 9
2.4 DIGITAL LOGIC ..................................................................................................................................... 9 2.5 ODOMETRY ..........................................................................................................................................10 2.6 INTERRUPTS .........................................................................................................................................10
CHAPTER3 .................................................................................................................................................12 INITIAL DESIGN .......................................................................................................................................12
3.1 SYSTEM MODELLING ...........................................................................................................................12 3.1.1 System Requirements...................................................................................................................12 3.1.2 Block Diagram of the System ......................................................................................................12 3.1.3 System flow chart ........................................................................................................................13 3.1.4 Resource management ................................................................................................................15
3.2 COMPONENTS SELECTION ....................................................................................................................15 3.2.1 PIC16F877A microcontroller .....................................................................................................15 3.2.2 JHD162A DISPLAY ....................................................................................................................18 3.2.3 Keypad ........................................................................................................................................19 3.2.4 Pushbutton switch .......................................................................................................................20
CHAPTER 4 ................................................................................................................................................21 DEVICE CONFIGURATION ....................................................................................................................21
4.1 POWER CONFIGURATION ......................................................................................................................21
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4.1.1 Power-On Reset (POR) ...............................................................................................................22 4.1.2 MCLR Reset during normal operation ........................................................................................23 4.1.3 MCLR reset during sleep ............................................................................................................23 4.1.4 WDT reset (During normal operation) .......................................................................................24 4.1.5 WDT Wake-up (during SLEEP) ..................................................................................................24 4.1.6 Brown-out Reset (BOR) ..............................................................................................................24 Power Control/Status Register (PCON) ..............................................................................................25 Device Configuration Word Register ...................................................................................................26
4.2 OSCILLATOR CONFIGURATION .............................................................................................................27 4.3 INTERRUPT CONFIGURATION ...............................................................................................................29
4.3.1 INTCON register .........................................................................................................................30 4.3.2 OPTION_REG register ...............................................................................................................31 4.3.3 PIE1 register ...............................................................................................................................32 4.3.4 PIR1 register ...............................................................................................................................33 4.3.5 T1CON register ...........................................................................................................................34
4.4 I/O PORTS DIRECTION .........................................................................................................................36 4.4.1 Port A ..........................................................................................................................................36 4.4.2 Port B ..........................................................................................................................................37 4.4.3 Port C ..........................................................................................................................................38 4.4.4 Port D .........................................................................................................................................38 4.4.5 Port E ..........................................................................................................................................38
CHAPTER 5 ................................................................................................................................................40 SOFTWARE IMPLEMENTATION .........................................................................................................40
5.1 MAIN PROGRAM THREAD .....................................................................................................................41 5.1.1 Initialisation ................................................................................................................................41 5.1.2 Update LCD display....................................................................................................................42
5.2 DISTANCE COST ISR THREAD ..............................................................................................................42 5.3 TIME COST ISR THREAD.......................................................................................................................42
CHAPTER 6 ................................................................................................................................................43 HARDWARE IMPLEMENTATION ........................................................................................................43
6.1 POWER SUPPLY ....................................................................................................................................44 6.2 DEVICE INTERFACING ..........................................................................................................................46
6.2.1 Interfacing PIC16F877A and LCD screen ..................................................................................46 6.2.2 Interfacing PIC16F877A and Keypad.........................................................................................47 6.2.3 Interfacing PIC16F877A with sensor .........................................................................................47
6.3 RESET CIRCUIT .....................................................................................................................................48 6.4 CIRCUIT SIMULATION ..........................................................................................................................50
CHAPTER 7 ................................................................................................................................................52 CONCLUSION ............................................................................................................................................52
7.1 CHALLENGES .......................................................................................................................................52 7.2 SUCCESSES ..........................................................................................................................................52 7.3 FAILURES .............................................................................................................................................53 7.4 RECOMMENDATIONS ...........................................................................................................................53
REFERENCES: ...........................................................................................................................................54 APPENDIX A: APPLICATION SOFTWARE CODE. ...........................................................................55 APPENDIX B: PROJECT ACTIVITIES .................................................................................................59 APPENDIX C: PROJECT COSTS ............................................................................................................60
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Declaration Statement of Authorship and Originality I declare that this report and work described in it are my own work, with any contribution
from others expressly acknowledge and/or cited.
I declare that the work in this report was carried out in accordance with the regulations of
the University of Dar es Salaam and has not been presented to any other University for
examination either in Tanzania or overseas. Any views expressed in the report are those
of the author and in no way represent those of the University of Dar es Salaam.
Maira, Albert M.
SIGNED: …………………….
DATE: ……………………….
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Abstract Within our modern day towns and cities in Tanzania taxicabs are a common means of
transportation, but the billing of the taxicabs is currently done through negotiation
between the taxicab driver and a prospective customer. This situation can lead into
several inconveniences to both the taxicab driver and the customer.
This design project proposes a prototype microcontroller circuit that will enable to
implement a computerised billing mechanism to be used to automate the billing in
taxicabs.
In this design an external wheel revolution sensor is used to generate an interrupt to the
microcontroller each time the wheels make a single revolution; and from this interrupt,
distance travelled is deduced by using wheel dimensions (circumference). Also time
duration of the journey is obtained from an internal timer in the microcontroller which is
set to overflow after every two seconds; and from this interrupt, hiring time of the
journey is obtained for billing purposes.
Then finally, the microcontroller by using the predetermined billing rate which is based
on parameters of cost per 100metres distance and cost per 1minute time of the journey, it
calculates the cost (in T.Shs) incurred by the customer and displays it on the LCD screen.
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Acknowledgements The first and the foremost to be thanked is the almighty God, who gave me strength,
courage, and direction to perform this project. Secondly, I would like to acknowledge Dr.
M.M. Kissaka my supervisor for providing me assistance, guidance and constructive
criticism throughout the design of my project.
Also I would like to give my sincere thanks to all Electrical and Computer Systems
engineering (ECSE) department staffs for their constructive suggestions and help toward
my project.
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List of figures
Figure 1: System block diagram ....................................................................................... 13 Figure 2: System flow chart .............................................................................................. 14 Figure 3: Reset circuit ....................................................................................................... 23 Figure 4: PIC power stabilisation supply .......................................................................... 45 Figure 5: LCD Power stabilisation circuit ........................................................................ 46 Figure 6: Microcontroller reset circuit .............................................................................. 49 Figure 7: Taxicab choices ................................................................................................. 50 Figure 8: Taxicab billing ................................................................................................... 51 Figure 9: Display bill ........................................................................................................ 51
List of tables Table 1:PIC16F877A features .......................................................................................... 17 Table 2: Oscillator frequency configuration choices ........................................................ 28 Table 3: Recommended capacitors for crystal oscillator .................................................. 28 Table 4: Prescaler rate select bits ...................................................................................... 32 Table 5: Bill of materials (BOM) ...................................................................................... 49
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List of abbreviations and acronyms
ADC Analogue to digital converter
BOR Brown out reset
BOM Bill of materials
CMOS Complementary metal oxide semiconductor
CPU Central processing unit
EEPROM Electrically erasable programmable read only memory
EPROM Erasable programmable read only memory
ECSE Electrical and computer systems engineering
I/O ports Input or output port
ISR Interrupt service routine
LCD Liquid crystal display
LVP Low voltage programming
MCLR Master clear
MCU Microcontroller unit
MSSP Master Synchronous Serial Port
OST Oscillator start-up timer
OTP One time programmable
PIC® Programmable intelligent computer
POR Power on reset
PWRT Power up timer
RAM Random access memory
ROM Read only memory
ST Schmitt trigger
TTL Transistor-transistor logic
T.Shs Tanzanian shillings
WDT Watch dog timer
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Chapter 1
Introduction Microcontroller based taxi billing system is a computerised electronic billing system for
rented personal transportation services of a taxicab, which are commonly found within
our modern day towns and cities as one of transportation means.
Microcontrollers are virtually everywhere in our modern society such that they can be
found in practically every digital electronic device that furnishes an independent
functionality to it’s user be it at home, industry or office. For example we can find
microcontrollers in our televisions, fridges, microwave ovens, personal computers and
printers.
1.1 What is a taximeter? A taximeter is a device that indicates the amount to be charged for use of a taxi by using
a predetermined rate or rates based on distance travelled, time elapsed or a combination
of both.
Taximeters arose out of a need to automate the taxi fare since in our present day society
we tend to seek efficiency and quality in our lives, with minimum resources in terms of
cost and time through the use automatic or semi-automatic mechanisation.
1.2 Current situation The current situation found in our Tanzanian towns and cities is that; billing for rented
transportation services is conducted through negotiation by word of mouth between the
taxicab driver and the customer. So only until the cost has been agreed between the two
parties the journey can begin.
There is no clear billing structure used to arrive at the cost rather billing is assumed
depending on the case by case basis and bargain power of the parties, this design project
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will address this shortage by proposing a microcontroller based billing system which uses
billing structure based on the measured distance and time to determine the cost.
1.3 Problem statements Due to the use of negotiation caused by a lack of clear billing structure the present
situation has several problems which lead into inconveniences to both the taxicab driver
and the customer as well;
Lack of clear billing structure for taxicabs which causes price bargains between
taxicab driver and customer causes wastage of time.
Difficulties might arise to people who are new into town since they can be caught
at a disadvantage in bargains, since they cannot estimate the destination distance
and thus reasonable cost.
Difficulties to foreigners who cannot speak the local language Swahili during
price negotiation.
1.4 Objectives Due to the aforementioned problems of the present situation this design project will
address the situation by proposing a microcontroller billing system whose main objective
is to computerise and thus automate the billing system of rented transportation services of
the taxicab by achieving the following specific objectives.
To design a microcontroller circuit that is capable of measuring time and
distance.
To design a microcontroller circuit that calculates the cost by using time and
distance as the billing parameters.
To design a microcontroller circuit that displays the measured distance, time and
cost on the alphanumeric LCD screen.
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1.5 Significance of the project Upon its completion, the project will come up with the circuit that will be able to measure
the distance travelled and hiring time of the journey then system will automatically
calculate the fare. The circuit will provide a means of standardising the taxicab billing so
that it can be justly to both the taxicab driver and to the customer.
1.6 Scope of the project This project is undergraduate final year project performed in partial fulfilment for the
award of Bachelor of Science in Computer Engineering and Information Technology.
The project is a design-implement based project that will use microcontroller, revolution
sensor, and LCD display to build a circuit that will automatically measure distance
covered and hiring time to calculate cost. Only a prototype will be accomplished, mainly
for proof of concept purposes and its industrial application may not be feasible at this
stage.
1.7 Methodology Since the system to be designed is an embedded electronics application then both
principles of hardware and software design methodologies are adopted in order to
accomplish the intended designed system then the following development approach will
be used.
Literature review in design, interfacing and practical limitations and challenges of
microcontroller systems.
Functional requirements elicitation from the users of the proposed system.
System requirements identification.
System plan design and circuit simulation.
Implementation of system plan and circuit on to a breadboard prototype circuit.
Testing of prototype to ascertain that the requirements have been met and to
account for the subtle practical challenges.
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The current situation has been outlined in this chapter together with its associated
problems and a design methodology has been identified as an approach to achieve the
design goals and solve the present problems. So the next chapter is about literature
review on the different implementation of taximeters together with associated
technologies so as to achieve an efficient and useful design in this project.
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Chapter 2
Literature review This is the chapter that gives some information on various technologies to be used in the
construction of this design project
2.1 Microcontroller A microcontroller is a single chip, self contained computer which incorporates all the
basic components of a much familiar personal computer but on a much smaller scale.
That’s why microcontrollers are often referred to as single chip devices or single chip
computers. The main consequence of the microcontroller’s small size is that its resources
are far more limited than those of a personal computer microprocessor.
In functional terms, a microcontroller is a programmable single chip which controls a
process or system. Microcontrollers are typically used as embedded controllers where
they control part of a larger system such as an appliance, automobile device, scientific
instrument or a computer peripheral to name a few. In this design a microcontroller will
be used to control a process that is the billing process.
Physically, a microcontroller is an integrated circuit with pins. The pins present on a
microcontroller are used for power, ground, oscillator clock signals, I/O ports, interrupt
request signals, reset and control pins. In contrast the pins present on a microprocessor
are most often memory bus signals (rather than I/O ports).
A typical microcontroller has the following building parts
CPU: this is a part that does all the computing and supervisory functions within a
microcontroller as it; fetches, decodes and executes program instructions and
directs the flow of data to and from memory. The CPU performs the calculations
as required by program instructions and places the results of these calculations
into memory space.
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ROM: this is a non-volatile memory used for storage of program codes and data
in the microcontroller. The microcontroller uses ROM memory space to store
program instructions so that they can not be affected by loss of power.
RAM: this is the data memory used to store all of the program variables, thus it is
used to read and write data values as a program runs. RAM uses volatile memory
(hence when the power is off its contents are lost) type of technology whose
access time does not depend on the spatial locality of the given memory address.
I/O PORTS: these are the pins used to provide communication access to/from the
microcontroller and other electronic peripheral devices and systems.
Just as any other computer architecture microcontrollers are of two basic types;
Harvard architecture microcontroller: in this architecture the microcontroller
uses separate memory space for program instructions and data. This allows two
or more internal data buses which allow simultaneous access to both instructions
and data. for example the CPU fetches instruction on the program memory bus if
fetched instruction requires an operation on data memory the CPU can fetch the
next program instruction while it uses the data bus for it’s data operation this
gives high throughput and speeds up execution time, but at the cost of more
hardware complexity as this architecture requires much more internal buses for
data and program instruction. In this design a microcontroller with Harvard
architecture will be used due to good performance.
Von Neumann architecture microcontroller: in this microcontroller architecture
there is a single common memory space where both program instructions and
data are stored, thus there is a single data bus which fetches both instructions and
data. Each time the PU fetches a program instruction it may have to perform one
or more read/write operations to data memory space. It must wait until these
subsequent operations are complete before it can fetch and decode the next
program instruction. The advantage of this architecture lies in its simplicity and
economy.
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2.2 LCD LCDs are alphanumeric displays which are commonly used in microcontroller circuit
applications due to their advantages of low cost and low power consumption. And thus
are ideal in low power battery operated portable devices. There are basically two types of
LCDs as far as the interface technique is concerned namely parallel and serial LCDs.
Parallel LCDs are connected to the microcontroller I/O pins using four or eight data wires
and data is transferred from the microcontroller to the LCD in parallel form either one
nibble at a time if four data wire mode or one byte if eight data wire mode is used. This
has the advantage of being economical and with better performance.
Serial LCDs are connected to the microcontroller using only one data line and data is
transferred to the LCD using the standard RS232 asynchronous data communication
protocols. Serial LCDs are easier to use but they usually cost more than the parallel ones
due to presence of serial controller chip such as RS232.however they have an advantage
that only one wire is used to interface them to a microcontroller, thus saving the number
of I/O pins required.
In this design a parallel LCD with eight data wires will be used due to better performance
and relatively smaller cost as compared to serial LCD.
2.3 Taximeters Apart from the microcontroller approach chosen in this design there are other two more
methods which can be used to provide a billing mechanism of taxicabs.
2.3.1 Mechanical taximeters These were the early means of constructing taximeters by using the mechanical
computing gears to transduce the distance covered into billing cost.
The mechanical taximeters have the following advantages
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They have good temperature performance.
They are immune from electrical and electromagnetic interference.
The mechanical taximeters have the following disadvantages
They are heavy and bulky.
They are difficulty to calibrate accurately on a timely basis.
They suffer from poor accuracy.
They lack adequate resolution.
They have limitations on the number of optional rates.
They have limited feature capability.
They do not take advantage of available electronic technology.
The process of calibrating mechanical taximeters to new fare rates is awkward
and expensive as it usually requires change in computing gears.
Mechanical computing gears with time are subject to corrosion and wear and this
introduces errors in fare calculations.
In general the use of mechanical taximeters does not provide much room for flexibility in
the billing requirements and it does not fit well with present day ubiquitous electronics
technologies which are much more efficient and cheap.
2.3.2 Microprocessor taximeters These are taximeters which use the general purpose microprocessor as the computing
engine of the billing system of taximeter.
The advantages of microprocessor taximeters are
They have high performance.
They are easy to interface to other intelligent peripherals and systems.
However the microprocessor taximeters have the following disadvantages
They have poor temperature performance.
They have high cost.
They are susceptible from electrical and electromagnetic interference.
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They have high power requirements.
In general the use of general purpose microprocessor in taximeters is uneconomical as the
microprocessors have so many capabilities (which must be paid for at a high cost), but
which are not normally needed in the operation of taximeters.
2.3.3 Microcontroller taximeters These are taximeters which use a dedicated processor of the microcontroller to provide a
computing mechanism for billing system of taximeter. This is the preferred choice in this
design due to the following advantages
They are cheap in cost.
They are flexible in providing the billing options.
They have adequate performance for taximeter application.
They have good resolution.
2.4 Digital logic When a pin on a microcontroller port is configured as the input line, the microcontroller
can read the electrical voltage present on that input pin to determine its logical binary
value (0 or 1). Similarly when the pin is configured as the output pin, the microcontroller
can raise the voltage on that pin to +5 V by placing logical binary 1 at the bit location on
the port. Placing a binary 0 at the bit location will output a zero voltage.
In the TTL logic electronic family; electrically a binary 1 is equal to a positive voltage
level between 2V and 5V. A binary 0 is equal to a voltage of 0 to 0.8V. The voltage value
between 0.8 and 2V are undefined.
While in CMOS logic family, the input voltage within 1.5V (0 to 1.5V) of ground are
considered as the binary 0 while the input voltage within 1.5V to +5V supply are
considered as the binary 1. The main advantage of CMOS logic devices is their low
power requirements as compared to TTL based devices or other logic families. This is the
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main reason CMOS logic has become the dominant form of logic used for large complex ICs.
Thus for this design CMOS based electronic devices will be used.
2.5 Odometry Odometry is the technique of measuring distance travelled by a vehicle, generally by
measuring wheel revolutions. A pushbutton switch in this design will be used to measure
angular displacement of a wheel. By knowing the wheel dimensions (i.e. circumference)
it is not difficult to calculate the actual distance moved this is a simple technique but, it
can take no account of wheel slippage, or inaccuracies in wheel dimensions due to
change in tyre pressure or other parts of the measurement chain.
2.6 Interrupts Interrupts are a mechanism of a microcontroller which enables it to respond to some
events at the moment when they occur, regardless of what microcontroller is doing at the
time. This is a very important part in this design, because it provides connection between
a microcontroller and environment which surrounds it. Generally, each interrupt changes
the program flow, interrupts it and after executing an interrupt subprogram (interrupt
routine) it continues from that same point onwards.
There are basically two types of interrupts namely;
Hardware interrupts these are interrupts that are initiated by a peripheral hardware
module event for example the timer module could issue an interrupt on overflow
to the central processing unit.
Software interrupts are software instructions that make calls to interrupt-handler
routines. Software interrupts are not often used in smaller microcontrollers, but
they are very common in microprocessor architectures as trap handlers.
In typical microcontroller architecture there are multiple hardware interrupt sources and
when an interrupt request is acknowledged the execution jumps to the handler, the
address the program jumps to is known as the interrupt vector.
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Depending on the architecture of the microcontroller the interrupts can be either be
vectored or non vectored interrupts. For vectored interrupts architectures this address is
specified by the application while for non-vectored architectures a specific address is
used by the processor.
The midrange PIC16FXXX MCU architecture (to be used in this project) uses non-
vectored approach; whereby whenever an interrupt occurs the program goes to constant
ISR address constant at 0004h. Thus it is the duty of the programmer to test which
specific interrupt indeed occurred (i.e. by testing specific interrupt flag bits) and take
appropriate action accordingly. Some processors with vectored interrupt approach (e.g.
high end architecture devices PIC24FXXX) have multiple interrupt vectors for handling
multiple interrupt sources with different interrupt handlers at programmer specified
memory location.
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Chapter3
Initial Design This chapter will give information about the modelled building blocks required the
system it will also explain how different system parts and components are chosen as
building components of the design depending on their features and characteristics.
3.1 System Modelling This section will elaborate on the model of the design, to implement a microcontroller
circuit that acts as a taximeter by taking into consideration the user requirements and the
needed hardware
3.1.1 System Requirements The following user general requirements have been identified
The user interface must be simple.
The contact area of push buttons should be at least 50 mm 2 .
The energy source must be provided by a car.
It must be able to show distance travelled, hiring time and cost.
The cost of production should be low.
The software architecture must be modular.
The design should include the possibility of being used as a development board
for new modules.
User needs to be able to reset the system to give a new billing instance.
3.1.2 Block Diagram of the System The designed system will include the following building blocks
Keypad: this is used to capture user settings.
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Wheel revolution sensor: this is a digital switch that triggers a wheel revolution
interrupt to a microcontroller each time it is triggered by a wheel revolution.
LCD screen: this is the display used to show the measured distance, time and
calculated cost.
Microcontroller: this is the workhorse of the system and performs all the decision
making and computations.
Keypad Microcontroller
Revolution sensor
Display
Figure 1: System block diagram
3.1.3 System flow chart The system flow chart in this design utilises three asynchronous program threads;
namely, the main program, wheel revolution sensor ISR and the timer1 overflow ISR.
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Start
Disable time interrupt
Save main program registers to be affected
Increment seconds time counter
Update display
Is the stop key pressed?
Restore main program registers
Enable time counter interrupt
Is 60 seconds reached?
Increment cost due to minute
time
Yes
Reset seconds counter
No
Yes
No
Yes
Disable sensor interrupt
Save main program registers to be affected
Increment distance metres counter
Is 100 metres reached?
Yes
Increment cost due to 100 metres
distance
Reset hundred metres counter
No
Restore main program registers
Enable sensor interrupt
Return Return
Wait for START key
Is the start key pressed?
No
Check keypad status for pressed key
Initialisation
Figure 2: System flow chart
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3.1.4 Resource management In the restricted environment of a microcontroller the memory requirements needs to be
taken into consideration early from the design stage so that a microcontroller with
sufficient resources for the design can be selected.
Variable or Module Resources (bytes) Real time clock 10 User settings 20 Stack 100 Local variables 200 Total RAM estimate 330 Constants 10 Interrupt service routines 300 Initialisation 100 Display 400 Keypad decode 100 Total ROM estimate 910
3.2 Components selection This section give information about the components selected to provide building blocks
from the functional and system requirements identified.
3.2.1 PIC16F877A microcontroller This is the preferred microcontroller choice in this design due to the following
advantages of Microchips PIC microcontroller family products:
The availability of excellent low-cost and free development tools.
The largest and strongest user Internet based community of probably any silicon
chip family.
An outstanding distributor network with a wide variety of parts available in very
short notice.
A wide range of devices with various features that just about guarantees that there
is a microcontroller suitable for any application.
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Microchip's efforts at continually improving and enhancing the PIC MCU family
based on customer's needs.
High-Performance RISC CPU which means all instructions are single-cycle
except for program branches which needs two instruction cycles.
It has enhanced flash program memory (EEPROM) package with typical 100,000
erase/write cycle.
It has Data EEPROM memory with a typical 1,000,000 erase/write cycle.
Data EEPROM Retention time of at least 40 years.
It has a Low-power CMOS Technology with a fully static design and a wide
operating voltage range (2.0V to 5.5V).
Internal Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable
operation
Programmable code protection capability.
Power saving Sleep mode ability.
Selectable oscillator options.
These strengths have contributed to the Microchip PIC8-bit MCU being the second most
popular microcontroller product in the world today (1as of 2010). This is up from the
twentieth position in 1995.
1 www.microchip.com
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The PIC16F877A microcontroller belongs in a midrange family of microchip’s
microcontroller products. It is a 40 pins flash based 8-bit CMOS microcontroller with the
following main features
Table 1:PIC16F877A features
The other important features of PIC16F877A which are important in this design include
It contains internal 16bit TIMER1 which can be used to monitor the elapsed time
for billing purposes. This timer will cause an interrupt each moment it overflows
and it’s interrupt on overflow can be monitored for elapsed time for billing.
It has PORTB 0 external interrupt which can be used to monitor the wheel
revolution sensor interrupt, such that each moment the PORTB 0 changes from
low to high by an external sensor; an interrupt for a wheel revolution will be
generated.
The PORTB 0 has internal pull capability which means the pins on this port can
be configured to be internally tied to logic HIGH by being internally connected to
V dd , and thus when they change to logic LOW via a grounding switch caused by
Key Features PIC16F877A Operating Frequency DC – 20 MHz Resets (and Delays) POR, BOR (PWRT, OST)
Flash Program Memory (14-bit words) 8K
Data Memory (bytes) 368 EEPROM Data Memory (bytes) 256 Interrupts 15 I/O Ports Ports A, B, C, D, E Timers 3 Capture/Compare/PWM modules 2 Serial Communications MSSP, USART Parallel Communications PSP 10-bit Analogue-to-Digital Module 8 input channels Analogue Comparators 2 Instruction Set 35 Instructions Packages 40-pin PDIP 44-pin PLCC 44-pin TQFP 44-
pin QFN
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an external event such as key press an appropriate action can be taken due to this
external interrupt by a microcontroller.
Brown-out detection circuitry for Brown-out Reset (BOR) which has the ability of
detecting the unsafe operation voltage and will reset the MCU should it detect
anomalous power state.
3.2.2 JHD162A DISPLAY This is a liquid crystal display with two rows (lines) and sixteen columns (characters)
alphanumeric characters display capability which will be used to provide the graphical
user interface to the users, by displaying visual information about available choices, time,
distance and cost of the journey.
JHD162A contains HD44780U internal display controller which is capable of accepting
data sent in either 4bit two operations or 8bit one operation ,so that it is capable of
interfacing with both 4bit or 8bit microprocessor cores. Since in this design an 8bit mode
will be used because the PIC16F877A microcontroller has an 8bit data processing core,
in addition to that so as to achieve better performance an 8bit mode is preferred as few
operations will be needed which consequently give short execution time as compared to
4bit mode which needs twice as much operations and thus time to display the same
number of characters.
When the JHD162A display is not enabled, data lines are in tri-state mode which means
they are in a state of high impedance (i.e. they appear as if they are disconnected) and
this means they do not interfere with the operation of the microcontroller when the
display is not being addressed.
JHD162A display has 16pin connector for interfacing the display to a microcontroller
V ss this is the 0V grounding pin.
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V dd this is the pin which is connected to the positive power supply, the
manufacturer’s recommended supply is 5V,however the module can be operated
as low as 3V or as high as 6V.
V ee this is the pin used to control the contrast of the display and thus should be
connected to a variable voltage supply or it can be connected to ground if
contrast adjustment is not needed.
RS this is the register select pin when it is low data transferred to the display is
treated as commands on the other hand when RS is high a character can be
transferred to or from the module.
WR / Pin this is the pin which is pulled low in order to write commands or
character data to the LCD module, also when this pin is high character data or
status information can be read from the module. This pin is usually connected to
ground because we normally write to the LCD module rather than read from it.
EN pin this is an enable pin which is used to initiate the transfer of commands or
data between LCD module and microcontroller. when writing to the display data
is transferred only on the high to low transition of this pin .when reading from the
display data becomes available after the low to high transition of the enable pin
and this data remains valid so long as the enable pin is high.
Pins 7 to 14 are eight data bus lines (D 0 to D 7 ) and will be used to transfer
display characters to the LCD module.
Pin 15 provides an anode connection pin for LED backlight.
Pin 16 provides a cathode for LED backlight.
3.2.3 Keypad This is the twelve button 4×3 switch matrix keypad which allows the microcontroller to
capture user settings and supervisory commands from the user. Functionally the keypad
is simply a set of switches connected in a row and column arrangement and accessed by a
scanning routine.
20
If the row inputs (A, B, C, D) are all set high initially and no button is pressed all the
column outputs (1, 2, 3) will be high (i.e. pulled up to 5V). However if a logical LOW is
output on each row in turn and a button pressed that LOW will appear at the column
output and thus can be read into the PIC, the combination of active row and column
identifies the pressed key by the microcontroller.
3.2.4 Pushbutton switch This is a device which enables the wheel revolution to be sensed by a microcontroller, the
main interest here is not to switch directly a voltage or current but rather to convert the
switch position in to a logic level that can be read by a microcontroller port.
This is achieved in this design by internally puling up the PORTB 0 to V dd such that
when this push button is pressed due to wheel revolution the PORTB 0 will go LOW and
this will generate an external interrupt on the microcontroller.
The pushbutton switch is chosen in this design due its following features
It is simple to interface with the microcontroller since it is a passive sensor which
means it does not require any signal conditioning mechanism.
It is very economical as compared to other active sensors such as optoelectronic
sensors which contain transduction mechanism to transform optical signal in to
electrical signal.
It does not require any analogue to digital conversion.
21
Chapter 4
Device configuration This is the section which describes the design of the system by first describing the
various configuration registers together with the justification of the configured choice.
Because within any electronic device the configuration registers are the most important
registers since they determine the overall behaviour of the electronic device which in this
case is the PIC16F877A microcontroller unit.
The device configuration relevant to this design has four main distinct categories namely
Power configuration
Oscillator configuration
Interrupts configuration
I/O ports configuration
4.1 Power configuration This is an important configuration with in a microcontroller as it determines the power
status and behaviour of the microcontroller during initialisation and operation. It achieves
this by controlling the PWRT and OST modules.
PWRT module is the timer that provides a fixed 72 ms nominal time-out during power-up
(that is from the POR). Because Power-up Timer operates on an internal RC oscillator the
chip is kept in RESET as long as the PWRT is active (i.e. first 72msec after power up).
This power up timer delay allows V dd to rise to an acceptable safe level. A configuration
bit with in CONFIGURATION WORD REGISTER<3> provides the option of enabling
or disabling the PWRT.
OST module is the module that is intended to keep the chip in Reset until the crystal
oscillator is stable The Oscillator Start-up Timer (OST) provides a delay of 1024
oscillator cycles (from OSC1 input) after the PWRT delay is over (i.e. if PWRT is
22
enabled). This helps to ensure that the crystal oscillator or resonator has started and has
stabilised. The OST time-out is invoked only for XT, LP and HS modes and only on
Power-on Reset or wake-up from Sleep.
The PIC16F877A differentiates between various kinds of RESET conditions
Power-on Reset (POR)
MCLR Reset during normal operation
MCLR Reset during SLEEP
WDT Reset (during normal operation)
WDT Wake-up (during SLEEP)
Brown-out Reset (BOR)
4.1.1 Power-On Reset (POR) A Power-on Reset pulse is generated on-chip when V dd rise is detected (in the range of
1.2V - 1.7V). To take advantage of the POR, I tie the MCLR pin through a resistor (so
as to protect the MCU from spurious voltage spikes) to V dd . This will eliminate external
RC components usually needed to create a Power-on Reset.
From the device datasheet a maximum rise time for PIC16F877A V dd is 10µseconds.
Now when the device starts normal operation (i.e. exits the RESET condition), device
operating parameters (voltage, frequency, current and temperature) must be met with in
10µseconds to ensure smooth operation. If these conditions are not met, the device must
be held in RESET until the operating conditions are met. Brown-out Reset is be used to
meet the start-up conditions since it is the one which controls the power-up start timer
(PWRT).
23
4.1.2 MCLR Reset during normal operation This is the master clear of the device which can be triggered by setting the MCLR low
and it will reset the device into an initial known safe state by clearing the entire RAM and
starting program execution all over again.
PIC16F877A devices have an internal noise filter in the MCLR reset path the filter which
will detect and ignore small pulses. From the datasheet PIC16F877A requires the low
pulse width to be at least 2µseconds to have a valid reset signal.
2Figure 3: Reset circuit
4.1.3 MCLR reset during sleep This is the reset condition which wakes up the microcontroller from sleep by driving the
MCLR low. The external MCLR Reset will cause a device Reset. And all other events
will be considered a continuation of program execution before entering the initial sleep
state and thus cause a “wake-up”.
2 Microcontroller compiled tips n tricks pp24- Microchip cooperation
24
The TO and PD bits in the Status register can be used to determine the cause of device
Reset. The PD bit, which is set on power-up, is cleared when Sleep is invoked. The TO
bit is cleared if a WDT time-out occurred and caused wake-up.
4.1.4 WDT reset (During normal operation) The Watchdog Timer is a free running, on-chip RC oscillator which does not require any
external components. This RC oscillator is separate from the RC oscillator of the
OSC1/CLKI pin.
If this timer is enabled and it has not been reset within a specific amount of time it will
timeout cause a reset situation on the microcontroller. But in this design this timer is
disabled because its reset functionality is not needed.
4.1.5 WDT Wake-up (during SLEEP) During normal operation, a WDT time-out generates a device Reset (Watchdog Timer
Reset). Also if the device is in Sleep mode, a WDT time-out causes the device to wake-
up and continue with normal operation (Watchdog Timer Wake-up).
Because the WDT clock is independent from the external or internal system clock, then
this means that the WDT will run even if the external clock on the OSC1/CLKI and
OSC2/CLKO pins of the device has been stopped, for example, by execution of a SLEEP
instruction. The TO bit in the Status register will be cleared upon a Watchdog Timer
time-out.
4.1.6 Brown-out Reset (BOR) The configuration bit, BODEN, can enable or disable the Brown-out Reset circuit. If V dd
falls below V BOR (about 4V) for longer than T BOR (about 100μsec) the brown-out
situation will reset the device. On the other hand if V dd falls below V BOR for less than
25
T BOR , a RESET may not occur. This feature will be implemented so as to have a reliable
microcontroller system which is intelligent enough to shut down when supplied power
falls below optimal operating values.
Once the brown-out occurs, the device will remain in Brown-out Reset until V dd rises
above V BOR . The Power-up Timer then keeps the device in RESET for T PWRT (about
72msec). If V dd should fall below V BOR during power-up timer (T PWRT ), the Brown-out
Reset process will restart when V dd rises above V BOR with the Power-up Timer Reset.
The Power-up Timer is always enabled when the Brown-out Reset circuit is enabled,
regardless of the state of the PWRT configuration bit.
The above configurations choices are controlled and/or monitored by the microcontroller
by using the following two registers;
Power control/status registers (PCON)
Configuration word register
Power Control/Status Register (PCON) The Power Control/Status Register, this is an important register with in the
microcontroller used to indicate the power status during transitioning from powering up
or reset condition. The power status indicated enables the programmer to take appropriate
action.
PCON Register Bit# 7 6 5 4 3 2 1 0 0 0 0 0 0 0 POR BOR . 7-2: Unimplemented bits (read as ‘0’) 1: POR : Power-on Reset Status bit
1 = No Power-on Reset occurred 0 = A Power-on Reset occurred (must be set in software after a Power-on Reset occurs)
26
0: BOR : Brown-out Reset Status bit 1 = No Brown-out Reset occurred 0 = A Brown-out Reset occurred (must be set in software after a Brown-out Reset or Power-on Reset occurs)
Bit 0 is Brown-out Reset Status bit this bit is unknown on a Power-on Reset. It is
recommended to the user to set it and check its status on subsequent RESETS to see if bit
BOR cleared, indicating a BOR occurred. However when the Brown-out Reset is
disabled, the state of the BOR bit is unpredictable and is, therefore, not valid at any time.
Bit 1 is POR (Power-on Reset Status bit). It is cleared on a Power-on Reset and unaffected
otherwise. The user must set this bit following a Power-on Reset.
Device Configuration Word Register The device configuration register bits allow each user to customize certain aspects of the
device to the needs of the application. When the device powers up, the state of these bits
determines the modes that the device uses. These bits are mapped in program memory
location 2007h. This location is not accessible during normal device operation (can be
accessed only during programming mode).
The configuration bits can be programmed (read as '0') or left un-programmed (read as
'1') to select various device configurations. The ability to change these settings once they
have been programmed depends on the memory technology and the package type.
For Read Only Memory (ROM) devices, these bits are specified at time of ROM code
submittal and once the device is masked may not be changed for those devices (would
require a new mask code).For One Time Programmable (OTP) devices, once these bits
are programmed (’0’), they may not be changed. For windowed EPROM devices, once
these bits are programmed (’0’), the device must be UV erased to return the configuration
word to the erased state. UV erasing the device also erases the program memory. For
Flash devices, these bits may be erased and reprogrammed.
27
In this design due to advantage of flexibility in prototyping the flash memory device is
used. The program word register is then programmed as;
Bit# 13 12 11 10 9 8 7 6 5 4 3 2 1 0 1 1 1 1 1 1 0 1 1 1 0 0 0 1 Bit#
13: Flash memory code protection is DISABLED
12: Unimplemented bit (recommended to read as 1)
10-9: WRT flash program memory write is DISABLED as the result the unprotected
memory location can be written by EECON control
8: CPD data EE memory code protection is DISABLED
7: LVP: low voltage in circuit serial programming is DISABLED as the result
RB3 is digital I/O and high voltage programming must be used on MCLR pin for
downloading application code to the chip.
6: BOREN brown-out reset control bit is ENABLED
5-4: Unimplemented manufacturer recommends to read as ‘1’
3: PWRTEN power up timer control bit is ENABLED
2: WDTE watch dog timer control bit is DISABLED
1-0: FOSC1:FOSC0 oscillator selection bits crystal (resonator) oscillator XT mode
selected
4.2 Oscillator configuration PIC16F877A device can have up to four different oscillator modes. The user can program
up to two device configuration bits (FOSC1 and FOSC0) in order to select one of these
FOUR oscillator modes by either selecting
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Table 2: Oscillator frequency configuration choices Configuration bits FOSC1:FOSC0
OSC Mode
OSC Feedback Inverter Gain
Comment
11 RC — Least expensive solution for device oscillation (only an external resistor and capacitor is required). Most variation in time-base. Device’s default mode.
10 HS High Gain High frequency application. Oscillator circuit’s mode consumes the most current of the three crystal modes.
01 XT Medium Gain
Standard crystal/resonator frequency. Oscillator circuit’s mode consumes the middle current of the three crystal modes.
00 LP Low Gain Low power/frequency applications. Oscillator circuit’s mode consumes the least current of the three crystal modes.
In XT, LP or HS modes, a crystal or ceramic resonator is connected to the OSC1/CLKIN
and OSC2/CLKOUT pins to establish oscillation. The PIC16F876 oscillator design
requires the use of a parallel cut crystal. Use of a series cut crystal may give a frequency
out of the crystal manufacturer’s specifications. When in XT, LP or HS modes, the
device can have an external clock source to drive the OSC1/CLKIN pin.
In this design a XT mode is preferred since it requires the optimum current out of the
three possible crystal oscillator modes which is crucial since the source of power will
come from dry cell batteries. In addition to that, also due to small frequency of XT mode
the effects of the electromagnetic interference are minimal, this is important so as to
minimize the interference to the electronics systems of the taxicab.
Table 3: Recommended capacitors for crystal oscillator
Oscillator type Crystal Freq. Cap. Range C1 Cap. Range C2 LP 32 kHz 33pF 33 pF
200 kHz 15 pF 15 pF XT 200 kHz 47-68 pF 47-68 pF
1MHz 15 pF 15 pF 4 MHz 15 pF 15 pF
HS 4 MHz 15 pF 15 pF 8 MHz 18-33 pF 15-33 pF 20 MHz 15-33 pF 15-33pF
29
In this design a clock rate of 1MHz ( 610 Hz) is chosen because a 2second interval
interrupt is desired from an internal 16bit TIMER1 which has the maximum pre-scale
value of 1:8
Then
1 instruction takes 6104 ÷ sec = 4μsec
Selecting the prescale value of 1:8 then the counter increments every:
8×4μsec= 32μsec
For the 16bit TIMER1 counter to overflow it will have to reach 65536 in
65536×32μ = 2.097seconds ≈ 2seconds
Then after every 2 seconds an interrupt will be received by the microcontroller with a
1MHz clock, this interrupt will be used to monitor the time of the journey for billing
purposes.
4.3 Interrupt Configuration PIC16F877A microcontroller can have many sources of interrupt. These sources
generally include one interrupt source for each peripheral module, though some modules
may generate multiple interrupts (such as the USART module). The interrupts supported
by PIC16F877A microcontroller are:
INT Pin Interrupt (external interrupt)
TMR0 Overflow Interrupt
PORTB Change Interrupt (pins RB7:RB4)
Comparator Change Interrupt
Parallel Slave Port Interrupt
USART Interrupts
Receive Interrupt
Transmit Interrupt
A/D Conversion Complete Interrupt
Data EEPROM Write Complete Interrupt
Timer1 Overflow Interrupt
30
Timer2 Overflow Interrupt
CCP Interrupt
SSP Interrupt
In this design I will use only two interrupt sources namely; TIMER1 OVERFLOW
INTERRUPT for managing the billing time and PORTB0/INT EXTERNAL
INTERRUPT from the pushbutton switch which is used to monitor the distance covered.
There are five registers used in the control and status of the two interrupts required in this
design. The registers needed to be configured for the interrupts are
INTCON register
OPTION_REG register
PIE1 register
PIR1 register
T1CON register
4.3.1 INTCON register The INTCON Register is a readable and writable register, which contains various enable
and flag bits for the TMR0 register overflow, RB Port change and External RB0/INT pin
interrupts.
Bit# 7 6 5 4 3 2 1 0 1 1 0 1 0 T0IF INTF RBIF Bit#
7: GIE: Global Interrupt Enable bit is ENABLED; this implies all unmasked
interrupts are enabled.
6: PEIE: Peripheral Interrupt control bit is ENABLED; this implies all unmasked
peripheral interrupts are enabled
5: T0IE: TMR0 Overflow Interrupt Control bit is DISABLED
4: INTE: RB0/INT External Interrupt Control bit is ENABLED
3: RBIE: RB Port Change Interrupt Control bit is DISABLED
31
2: T0IF: TMR0 Overflow Interrupt Flag bit
1 = TMR0 register has overflowed (must be cleared in software)
0 = TMR0 register did not overflow
1: INTF: RB0/INT External Interrupt Flag bit
1 = The RB0/INT external interrupt occurred (must be cleared in software)
0 = The RB0/INT external interrupt did not occur
0: RBIF: RB Port Change Interrupt Flag bit
1 = At least one of the RB7:RB4 pins changed state; a mismatch condition will
continue to set the bit. Reading PORTB will end the mismatch condition and
allow the bit to be cleared (must be cleared in software).
0 = none of the RB7:RB4 pins have changed state
4.3.2 OPTION_REG register The OPTION_REG Register is a readable and writable register, which contains various
control bits to configure the TMR0 prescaler/WDT postscaler (single assignable register
known also as the prescaler), the External INT Interrupt, TMR0 and the weak pull-ups on
PORTB.
Bit# 7 6 5 4 3 2 1 0 0 1 0 0 1 1 1 1 Bit# 7: RBPU : PORTB Pull-up control bit is ENABLED.
6: INTEDG: Interrupt Edge Select bit Interrupt ON RISING EDGE (↑) of RB0/INT
pin is selected
5: T0CS: TMR0 Clock Source Select bit unimplemented (read as ‘0’)
4: T0SE: TMR0 Source Edge Select bit unimplemented (read as ‘0’)
3: PSA: Prescaler Assignment bit is reserved for WDT instead of TMR0
2-0: PS2:PS0: Prescaler Rate Select bits 1:128
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Table 4: Prescaler rate select bits Bit Value TMR0 Rate WDT Rate 000 1:2 1:1 001 1:4 1:2 010 1:8 1:4 011 1:16 1:8 100 1:32 1:16 101 1:64 1:32 110 1:128 1:64 111 1:256 1:128
4.3.3 PIE1 register The PIE1 register contains the individual control bits for the peripheral interrupts
Bit#
7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 1 Bit# 7: PSPIE: Parallel Slave Port Read/Write Interrupt Control bit is DISABLED.
6: ADIE: A/D Converter Interrupt Control bit is DISABLED
5: RCIE: USART Receive Interrupt Control bit is DISABLED
4: TXIE: USART Transmit Interrupt Control bit is DISABLED
3: SSPIE: Synchronous Serial Port Interrupt Control bit is DISABLED
2: CCP1IE: CCP1 Interrupt Control bit is DISABLED
1: TMR2IE: TMR2 to PR2 Match Interrupt Control bit is DISABLED
0: TMR1IE: TMR1 Overflow Interrupt Control bit is ENABLED
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4.3.4 PIR1 register The PIR1 register contains the individual flag bits for the peripheral interrupts. Bit# 7 6 5 4 3 2 1 0 PSPIF PSPIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF Bit#
7: PSPIF: Parallel Slave Port Read/Write Interrupt Flag bit
1 = A read or a write operation has taken place (must be cleared in software)
0 = No read or write has occurred.
6: ADIF: A/D Converter Interrupt Flag bit
1 = An A/D conversion completed
0 = The A/D conversion is not complete
5: RCIF: USART Receive Interrupt Flag bit
1 = The USART receive buffer is full
0 = The USART receive buffer is empty
4: TXIF: USART Transmit Interrupt Flag bit
1 = The USART transmit buffer is empty
0 = The USART transmit buffer is full
3: SSPIF: Synchronous Serial Port (SSP) Interrupt Flag
1 = The SSP interrupt condition has occurred, and must be cleared in software
before returning from the Interrupt Service Routine. The conditions that will set
this bit are:
• SPI
- A transmission/reception has taken place.
• I2C Slave
- A transmission/reception has taken place.
• I2C Master
- A transmission/reception has taken place.
- The initiated START condition was completed by the SSP module.
- The initiated STOP condition was completed by the SSP module.
- The initiated Restart condition was completed by the SSP module.
34
- The initiated Acknowledge condition was completed by the SSP module.
- A START condition occurred while the SSP module was idle (Multi-Master
system).
- A STOP condition occurred while the SSP module was idle (Multi-Master
system).
0 = No SSP interrupt condition has occurred
2: CCP1IF: CCP1 Interrupt Flag bit
Capture mode:
1 = A TMR1 register capture occurred (must be cleared in software)
0 = No TMR1 register capture occurred
Compare mode:
1 = A TMR1 register compare match occurred (must be cleared in software)
0 = No TMR1 register compare match occurred
PWM mode:
Unused in this mode
1: TMR2IF: TMR2 to PR2 Match Interrupt Flag bit
1 = TMR2 to PR2 match occurred (must be cleared in software)
0 = No TMR2 to PR2 match occurred
0: TMR1IF: TMR1 Overflow Interrupt Flag bit
1 = TMR1 register overflowed (must be cleared in software)
0 = TMR1 register did not overflow
4.3.5 T1CON register This is the register which is used to configure the Timer1 peripheral. Timer1 module is a
16-bit timer/counter consisting of two 8-bit registers (TMR1H and TMR1L) which are
readable and writable. The TMR1 Register pair (TMR1H:TMR1L) increments from
0000h to FFFFh and rolls over to 0000h.
The TIMER1 Interrupt, if enabled, is generated on overflow which is latched in the
TMR1IF interrupt flag bit. This interrupt can be enabled/disabled by setting/clearing the
TMR1IE interrupt enable bit.
35
TIMER1 can operate in one of three modes, the operating mode is determined by clock
select bit, TMR1CS (T1CON<1>), and the synchronization bit, T1SYNC.the three
possible operation modes are
As a synchronous timer
As a synchronous counter
As an asynchronous counter
In timer mode, TIMER1 increments every instruction cycle while in counter mode, it
increments on every rising edge of the external clock input on pin T1CKI.
TIMER1 can be turned on and off using theTMR1ON control bit (T1CON<0>). TIMER1
also has an internal “reset input”, which can be generated by a CCP module.Timer1 has
the capability to operate off an external crystal. When the Timer1 oscillator is enabled
(T1OSCEN is set), the T1OSI and T1OSO pins become inputs. That is, their
corresponding TRIS values are ignored.
In this design the TIMER1 will be used as a synchronous timer to provide an interrupt
after every 2 seconds.
Bit# 7 6 5 4 3 2 1 0 0 0 1 1 0 1 0 1 Bit# 7-6: Unimplemented (read as ‘0’)
5-4: T1CKPS1:T1CKPS0: Timer1 Input Clock Prescale Select bits 1:8 ENABLED
11 = 1:8 Prescale value
10 = 1:4 Prescale value
01 = 1:2 Prescale value
00 = 1:1 Prescale value
3: T1OSCEN: Timer1 Oscillator Control bit is DISABLED this implies then the
counter increment on every prescaled instruction cycle
36
2: SYNCT1 : Timer1 External Clock Input Synchronization Control bit is
DISABLED; then synchronization is ignored since an internal oscillator is used
which needs no synchronization
1: TMR1CS: Timer1 Clock Source Select bit internal clock is used
0: TMR1ON: Timer1 On CONTROL bit is ENABLED
4.4 I/O Ports Direction The PIC16F877A has three input/output ports namely A, B and C which allows the
microcontroller to monitor and control other devices, each port has a corresponding
PORT register and TRIS data direction register.
PORT register is the latch for the data to be output. When the PORT is read, the device
reads the levels present on the I/O pins (not the latch). This means that care should be
taken with read-modify-write commands on the ports and changing the direction of a pin
from an input to an output.
TRIS register is used to control the data direction, for most ports, the I/O pin’s direction
(input or output) is controlled by this data direction register, that is the TRIS<x> bit
controls the direction of PORT<x> pin. A ‘1’ in the TRIS bit corresponds to that pin
being an input, while a ‘0’ corresponds to that pin being an output. However this
configuration can be overridden when peripheral is enabled at multiplexed general I/O
port the functionality of the I/O pins may change to accommodate the requirements of the
peripheral module
4.4.1 Port A PORTA is a 6-bit wide, bi-directional port, only PORTA<4> pin is a Schmitt Trigger
input and an open drain output. All other PORTA port pins have TTL input levels and
full CMOS output drivers. All pins have data direction bits (TRIS registers) which can
configure these pins as either output or input.
37
Setting a TRISA register bit puts the corresponding output driver in a hi-impedance
mode. Clearing a bit in the TRISA register puts the contents of the output latch on the
selected pin(s). In this design the PORTA is unused, left for further improvement of the
design hence the TRIS register is left programmed as
Bit# 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 0
4.4.2 Port B PORTB is an 8-bit wide, bi-directional port the appropriate register for direction of data
is TRISB at address 86h; each of the PORTB pins has a weak internal pull-up resistor
(i.e. resistor that defines the line to logic HIGH). A single control bit in OPTION_REG
can turn on all the pull-ups this is performed by clearing bit RBPU (OPTION<7>). The
weak pull-up is automatically turned off when the port pin is configured as an output and
the pull-ups are disabled on a Power-on Reset so we need to enable it at initialisation
routine just after the device powers up.
Four of the PORTB pins, RB7:RB4, have an interrupt on change feature. Only pins
configured as inputs can cause this interrupt to occur (i.e., any RB7:RB4 pin configured
as an output is excluded from the interrupt on change comparison). The input pins (of
RB7:RB4) are compared with the old value latched on the last read of PORTB. The
“mismatch” outputs of RB7:RB4 are OR’ed together to generate the RB Port Change
Interrupt with flag bit RBIF (INTCON<0>).
RB0/INT is an external interrupt input pin and is configured using the INTEDG bit
(OPTION_REG<6>) in this design this will be used to monitor an interrupt from wheel
revolution sensor, then the TRIS register for port B becomes.
Bit# 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 1
38
4.4.3 Port C PORTC is an 8-bit bi-directional port. Each pin is individually configurable as an input or
output through the TRISC register. PORTC pins have Schmitt Trigger input buffers and it
will be used to provide interface to the 4×3 keypad, then the TRIS register for port C is
programmed as.
Bit# 7 6 5 4 3 2 1 0 1 1 1 1 1 0 0 0
4.4.4 Port D PORTD is an 8-bit port with Schmitt Trigger input buffers. Each pin is individually
configurable as an input or output. PORTD can also be configured as an 8-bit wide
microprocessor port (Parallel Slave Port) by setting control bit, PSPMODE (TRISE<4>).
In such a mode, the input buffers are TTL, however this design will use this port as a
normal I/O port with 8bit parallel data bus to the LCD screen
Bit# 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 0
4.4.5 Port E PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7) which are
individually configurable as inputs or outputs. These pins have Schmitt Trigger input
buffers. The PORTE pins become the I/O control inputs for the microprocessor port when
bit PSPMODE (TRISE<4>) is set.
In this mode, the user must make certain that the TRISE<2:0> bits are set and that the
pins are configured as digital inputs. Also, ensure that ADCON1 is configured for digital
I/O. In this mode, the input buffers are TTL. The TRISE register also controls the Parallel
Slave Port operation.
39
PORTE pins are multiplexed with analogue inputs. When selected for analogue input,
these pins will read as ‘0’s. TRISE controls the direction of the RE pins, even when they
are being used as analogue inputs. The user must make sure to keep the pins configured
as inputs when using them as analogue inputs.
In this design this port is left unused for further improvement of the design, and thus the
TRISE register is programmed as;
Bit# 7 6 5 4 3 2 1 0 0 0 0 0 0 0 0 0
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Chapter 5
Software implementation Although microcontrollers have been traditionally been programmed using the assembly
language of the target device in this implementation a high level language will be used
because high-level languages offer several desirable advantages for this design project as
compared to the assembly language:
It is easier to develop programs using a high-level language.
Program maintenance is much easier if the program is developed using a high-
level language.
Testing a program developed in a high-level language is much easier.
High-level languages are more user-friendly and less prone to making errors.
It is easier to document a program developed using a high-level language.
In addition to the above advantages, high-level languages also have some disadvantages.
For example, the length of the code in memory is usually larger when a high-level
language is used, and the programs developed using the assembly language usually run
faster than those developed using a high-level language.
The application software code was implemented by using MikroC MikroElektronika
cooperation C compiler for Microchip PIC microcontroller’s version: 8.0.0.0. This high
level language C compiler was chosen for software implementation due to its following
advantages
The C compiler (MikroC) is well documented in a downloadable user manual.
Includes a good range of peripheral driver libraries, including CAN, Ethernet, and
graphical LCD drivers as part of a comprehensive I/O library.
The packages are oriented toward the educational and hobby market, offering
additional features designed to assist the beginner in developing C applications.
The pseudo code derived from the modelled system flow chart in chapter2 has the
following sequence of activities.
41
1. Program initialises.
2. User prompted for choice from available options.
3. IF start key chosen continue to step4 ELSE go back to step2.
4. Update the display screen.
5. Check for keypad status.
6. IF stop key is pressed from keypad stop and wait for start key press
ELSE go back to step4.
In this design the modelled system flow chart of the application program has three
parallel threads that implements the above pseudo code namely
Main program thread block.
TIMER1 overflow interrupt time cost ISR thread.
PORTB 0 external interrupt distance cost ISR thread.
5.1 Main program thread The main program block has three functionalities
It initialises the microcontroller to an initial state by clearing executing the
initialisation routine.
It updates the display screen by executing the update display routine.
It checks the keypad for pressed key options and takes appropriate action
according to the captured user choice.
5.1.1 Initialisation In this stage the main program sets the configuration registers with appropriate values
and ensures that the microcontroller is within a desirable initial state for safe and reliable
operation of the microcontroller. In this routine the configuration registers are
programmed with the desired values and the program global variables are initialised to
their default values.
42
5.1.2 Update LCD display In this stage the main program updates the alphanumeric display with the values of time,
distance and cost. To not interfere with the display controller (HD44780) operation
interrupts are temporarily disabled during this procedure and the numeric values are first
converted into string character buffer before being sent to the display, since the display
controller is character based.
5.2 Distance cost ISR thread This is the interrupt service routine for handling the PORTB 0 external interrupt; it
achieves this by adding the metres counter to itself and then checks to see this running
sum if it has reached 100metres (0.1km), so that the cost can be calculated (i.e. billing in
this design is by each 0.1km covered distance).
Then the 100metres counter is checked if it has reached 1000metres (1km) so that the
kilometres distance counter can be updated and 100metres counter reset. Then the
function is implemented as.
5.3 Time cost ISR thread This is the interrupt service routine for handling the TIMER1 overflow interrupt which
occurs after every 2 seconds. In this routine the seconds counter is monitored if it has
reached one minute so that the billing cost can be calculated. (i.e. billing is by each
elapsed minute).
43
Chapter 6
Hardware implementation
This is the section which describes the hardware modules interconnection implementation
scheme so as to achieve a working system by using the Proteus professional version 7.2
Labcenter electronics.
Proteus VSM is an interactive electronics design package from Labcenter Electronics that
allows analogue, digital, and microprocessor circuits to be subjected to virtual testing
before the creation of a PCB layout for the construction of real hardware. ISIS is the
schematic capture package, and ARES is the layout package.
The circuit is entered directly onto the schematic by selecting components from a library
of parts, which have associated mathematical models (e.g., V= IR for a resistor). When
completed, the wiring schematic is converted to a set of nodes connected by components,
represented by a set of simultaneous equations derived from the model for each
component. The network is solved for any given set of inputs and the outputs are
displayed via active on-screen components, virtual instruments, or charts.
The microcontroller is simulated on the basis of its internal architecture and the specific
program being executed, which must be attached to complete the model. In our case, the
program is written in C and the HEX byte file produced by the compiler is attached to the
MCU. This file contains the program machine code and some additional information to
help with debugging the program. ISIS allows the source code and variables to be
displayed so that the program operation can be studied step by step and any functional
errors corrected.
44
6.1 Power supply In this design since the electronics components used all use 5v supply voltage hence the
V dd is tied to the voltage supply with a decoupling capacitor. The decoupling capacitor is
used to minimize the effects of rapid changes in power demands by devices in the circuit
(including the PIC16F877A). A decoupling capacitor can be thought of as a filter that
smoothes out the rough spots of the power supply and provides additional current for
high load situations on the circuit.
For this design tantalum decoupling capacitors at 5 volts, I use parts that are rated at 16
volts (which is a de-rated value less than one third of the rated value). When tantalum
capacitors are first powered up in an application, voltage spikes (which are caused by
power supply start up and current transients with in chips) can cause them to develop
"pin-hole" breakthroughs in the dielectric, which can cause the plates to touch.
3When the plates touch, heat is generated by the short circuit, which boils away more
dielectric. This process snowballs until the part explodes or catches fire. By derating the
capacitor values, the dielectric layer is thicker, minimizing the opportunity for pinholes to
develop.
Decoupling capacitors are to be placed across V dd and V ss of LCD and MCU, because
these are the components in this design which can develop significant current transients.
This does complicate the wiring somewhat, but does make a more reliable
microcontroller circuit.
From PIC16F877A datasheet the maximum current into V dd pin 250 mA and maximum
current out of V ss pin 300 mA. To be on the safe side current in to V dd is de-rated by
40%, then I dd = 150mA. Now to protect the microcontroller from voltage spikes I allow
0.5V to drop across the protection resistance such that i have V dd =4.5V.
Then from Ohm’s law the protection resistance is obtained as:
3 PIC microcontrollers, programming and customising pp70 by Myke Predko
45
Ω≅Ω=== 3.33333.3250
5.0mAv
ivr
Then by using the standard resistor value i have R PIC = 3.3Ω with I dd at 150mA
AFPIC 87716
ddV
ssV
0.1µF
5V DC SUPPLY
3.3Ω
Figure 4: PIC power stabilisation supply
Similarly from LCD screen datasheet the maximum supply current is 3mA then derating
this by 40% i have 1.8mA, and by allowing 0.5V to drop across the protection resistor the
value of protective resistor for display is obtained as;
By ohm’s law
Ω≅Ω≡== 27078.2778.15.0mAv
ivr
46
Then using the standard value I have R LCD =270Ω with the I dd at 1.8mA
ddV
ssV
0.1µF
5V DC SUPPLY
270Ω
AJHD162
Figure 5: LCD Power stabilisation circuit
6.2 Device interfacing
6.2.1 Interfacing PIC16F877A and LCD screen From the system modelling the PIC16F877A will be interfaced with 8-data wires using a
PORTD (i.e. data port) and the control from PORTB (i.e. control port) of microcontroller.
And from PIC16F877A device data sheet the maximum supply voltage for logic (i.e.
control and data port signals) is given by
V OH = V dd - 0.7V with I (max)OH =3mA
47
Since in this design chosen V dd is 4.5V this means the PORTB and PORTD output
logical high voltage will be 3.8V at a maximum operational current of 3mA.
Now from the LCD display datasheet the maximum input current value for the each data
pin of LCD module is 3mA and logical high voltage ranges from 2.2V to V dd (i.e. 2.2V
to 4.5V) and then this means the LCD module can be safely directly connected to the
microcontroller without any protection resistors.
6.2.2 Interfacing PIC16F877A and Keypad The PIC16F877A will be connected to the 4×3 keypad by using the first seven pins of
PORTC, since the keypad is just a set of matrix switches with the column configured as
outputs and rows configured as inputs. Such that the keypad scanning routine pulls up
one column at a time and reads the corresponding rows.
From the PIC16F877A datasheet the maximum output high voltage is obtained as above
to be 3.8V at a maximum current of 3mA, this will be the output high voltage for the
keypad columns that is PORTC pin 4 to 6.
Now since the keypad will be scanned within the same PORTC at pins 0 to 3 and
PORTC has Schmitt triggered I/O buffers then the input high voltage needs to be from
0.8 V dd to V dd that is from 3.8V to 4.5V (with V dd =4.5V). From the above paragraph i
have deduced that the output from the keypad column will be 3.8V, and then this means
this will be enough to trigger a Schmitt buffer input of rows at the maximum input
current of 25mA. This implies the keypad can be directly connected to the
microcontroller since their logical levels are compatible.
6.2.3 Interfacing PIC16F877A with sensor The wheel revolution sensor (pushbutton switch) will be connected at PORTB 0 , since
the internal pull up on PORTB has been enabled in this design, this means the input ports
48
of PORTB have been internally tied to V dd .which makes the job of this pushbutton is just
to bring logical low voltage to the PORTB 0 and this shall cause an external interrupt on
the rising edge of PORTB 0 .
Since the PORTB 0 has a Schmitt trigger buffer this implies the logical low is from V ss
to 0.2 V dd that is from 0V to 0.9V (with V dd =4.5V), this is achieved by directly tying
the PORTB 0 via a pushbutton switch.
6.3 Reset circuit This is the circuit which is used to restart program execution of the microcontroller that is
when a reset occurs the program counter is loaded with instruction at 0000h.this could be
useful in case the system is stuck. In this reset circuit the reset occurs when a reset
pushbutton is pressed.
To prevent the device from resetting several times during power up transitioning the
coupling capacitor is provided in this circuit so as to eliminate the effect of harmful
power transients that could set and reset the microcontroller several times when the
power is initially applied.
From the RC charging equation
)1( / RCtddc eVV −−=
For V c to reach 99% of V dd five time constants are essential this time will be enough to
allow the power to stabilise
i.e. t=5τ=5RC= 5×39kΩ×0.1µΩ =19.5msec
Then 19.5msec after power up the system will be stable and ready for operation.
49
AFPIC 87716
MCLR1.8kΩ
0.1µF
39kΩ
5V
RE
SE
T
Figure 6: Microcontroller reset circuit
From the above identified hardware requirements the following is a summary of required materials for prototype implementation
Table 5: Bill of materials (BOM) Quantity: References Value 1 RESISTOR1 39kΩ 1 RESISTOR2 1.8kΩ 2 CAPACITOR1, CAPACITOR2 15pF 1 CAPACITOR3 0.85nF 1 CAPACITOR4 0.1µF 1 LCD DISPLAY JHD162A 1 KEYPAD 4 × 3 1 MICROCONTROLLER PIC16F877A 1 PARALLEL CUT CRYSTAL OSCILLATOR 1MHz 1 LCD PROTECTION RESISTOR 270Ω 1 PIC PROTECTION RESISTOR 3.3Ω 1 MINI-PUSH BUTTON SWITCH SENSOR
50
6.4 Circuit Simulation The design schematic was developed in ISIS professional release 7.1 and the application
is simulated here for a typical routine of steps that occurs in the system;
Step1: User prompted for choice
RA0/AN02
RA1/AN13
RA2/AN2/VREF-/CVREF4
RA4/T0CKI/C1OUT6
RA5/AN4/SS/C2OUT7
RE0/AN5/RD8
RE1/AN6/WR9
RE2/AN7/CS10
OSC1/CLKIN13
OSC2/CLKOUT14
RC1/T1OSI/CCP2 16
RC2/CCP1 17
RC3/SCK/SCL 18
RD0/PSP0 19
RD1/PSP1 20
RB7/PGD 40RB6/PGC 39RB5 38RB4 37RB3/PGM 36RB2 35RB1 34RB0/INT 33
RD7/PSP7 30RD6/PSP6 29RD5/PSP5 28RD4/PSP4 27RD3/PSP3 22RD2/PSP2 21
RC7/RX/DT 26RC6/TX/CK 25RC5/SDO 24RC4/SDI/SDA 23
RA3/AN3/VREF+5
RC0/T1OSO/T1CKI 15
MCLR/Vpp/THV1
MICROCONTROLLER
PIC16F877A
1 2 3
4 5 6
7 8 9
0 #
1 2 3
A
B
C
D
KEYPAD4 BY 3
C1
15p
C2
15p
OSCILLATOR1MHz
VDD
R139k
C30.85n
R22k
SENSORC4100n
PROTECTION RESISTOR280
D7
14D
613
D5
12D
411
D3
10D
29
D1
8D
07
E6
RW
5R
S4
VS
S1
VD
D2
VE
E3
LCD1LM016L
Figure 7: Taxicab choices
51
Step2: System goes in to continuous billing loop when start key is pressed to update display and while checking for stop key.
RA0/AN02
RA1/AN13
RA2/AN2/VREF-/CVREF4
RA4/T0CKI/C1OUT6
RA5/AN4/SS/C2OUT7
RE0/AN5/RD8
RE1/AN6/WR9
RE2/AN7/CS10
OSC1/CLKIN13
OSC2/CLKOUT14
RC1/T1OSI/CCP2 16
RC2/CCP1 17
RC3/SCK/SCL 18
RD0/PSP0 19
RD1/PSP1 20
RB7/PGD 40RB6/PGC 39RB5 38RB4 37RB3/PGM 36RB2 35RB1 34RB0/INT 33
RD7/PSP7 30RD6/PSP6 29RD5/PSP5 28RD4/PSP4 27RD3/PSP3 22RD2/PSP2 21
RC7/RX/DT 26RC6/TX/CK 25RC5/SDO 24RC4/SDI/SDA 23
RA3/AN3/VREF+5
RC0/T1OSO/T1CKI 15
MCLR/Vpp/THV1
MICROCONTROLLER
PIC16F877A
1 2 3
4 5 6
7 8 9
0 #
1 2 3
A
B
C
D
KEYPAD4 BY 3
C1
15p
C2
15p
OSCILLATOR1MHz
VDD
R139k
C30.85n
R22k
SENSORC4100n
PROTECTION RESISTOR280
D7
14D
613
D5
12D
411
D3
10D
29
D1
8D
07
E6
RW5
RS
4
VSS
1
VDD
2
VEE
3
LCD1LM016L
Figure 8: Taxicab billing
Step3: When destination is reached and the user presses STOP button (#key) to stop billing here the cost is displayed and the system waits for start key for new billing.
RA0/AN02
RA1/AN13
RA2/AN2/VREF-/CVREF4
RA4/T0CKI/C1OUT6
RA5/AN4/SS/C2OUT7
RE0/AN5/RD8
RE1/AN6/WR9
RE2/AN7/CS10
OSC1/CLKIN13
OSC2/CLKOUT14
RC1/T1OSI/CCP2 16
RC2/CCP1 17
RC3/SCK/SCL 18
RD0/PSP0 19
RD1/PSP1 20
RB7/PGD 40RB6/PGC 39RB5 38RB4 37RB3/PGM 36RB2 35RB1 34RB0/INT 33
RD7/PSP7 30RD6/PSP6 29RD5/PSP5 28RD4/PSP4 27RD3/PSP3 22RD2/PSP2 21
RC7/RX/DT 26RC6/TX/CK 25RC5/SDO 24RC4/SDI/SDA 23
RA3/AN3/VREF+5
RC0/T1OSO/T1CKI 15
MCLR/Vpp/THV1
MICROCONTROLLER
PIC16F877A
1 2 3
4 5 6
7 8 9
0 #
1 2 3
A
B
C
D
KEYPAD4 BY 3
C1
15p
C2
15p
OSCILLATOR1MHz
VDD
R139k
C30.85n
R22k
SENSORC4100n
PROTECTION RESISTOR280
D7
14D
613
D5
12D
411
D3
10D
29
D1
8D
07
E6
RW5
RS
4
VSS
1
VDD
2
VEE
3
LCD1LM016L
Figure 9: Display bill
52
Chapter 7
Conclusion In the course of working on this project many things came up, both positive and negative,
however to a good extent things have been under control and the system was successful
designed. The design worked fine under the emulation environment. However during
implementation several challenges were encountered.
7.1 Challenges Numerous challenges were encountered during the project work implementation firstly
was parts availability because initially I had planned to use a four line display screen but
had to settle with two line display.
Secondly, parts cost affordability; the real world commercial taxi meters use optical
sensors or Hall Effect sensors for rotation detection, due to design budget constraint, I
had to use the pushbutton switch which is not durable, since it will wear out in a very
short time when implemented on the real world situation.
Thirdly, was the difficulty of obtaining the microcode programmer since there was none
within our department then I had to borrow the one from electronics science department
this caused many unnecessary hustles and wasted much valuable time during design
testing.
7.2 Successes The system plan was successfully designed, simulated and then tested on the breadboard
hardware prototyping circuit, so I could claim that my project objectives have been duly
met.
53
7.3 Failures Although I have been able to model and finally design the prototype; I have failed to
come up with quantifiable data and/or mathematical model that justifies by how much my
proposed system will reduce the inconveniences suffered by the customers and taxicab
drivers due to the present situation.
7.4 Recommendations The following are my recommendations for the improvement of the proposed
microcontroller based TAXI billing system for future works.
1. Sensor improvement: The design could be improved by replacing the pushbutton
switch with the optocoupler as a wheel revolution sensor. Because an Optocoupler
is a device that combines a LED and photo-transistor in the same case so when a
light beam is interrupted (e.g. by a spoke on the wheel) a revolution will be
sensed each time the light is interrupted, and the transistor will produce a pulse. In
this design this implementation was not used due to prohibitive cost of
optocoupler sensors.
2. Statistical records: Keeping statistical records by the microcontroller could
improve the financial management usefulness of the system to the users; this
could be achieved by attaching to the microcontroller retrievable special flash
memory to be used to store a billing log file so that it can be used for later
auditing and printing.
3. The government revenue authority (i.e. TRA) can use taximeters to increase the
source of revenues from taxi businesses by charging value added tax (VAT) on
taxicab business transactions.
54
References: Ball, S.R (2006),”Embedded Microprocessor systems - real world design”, Newnes press, New York, 2nd edition. Di Jasio et al (2008);” PIC Microcontrollers (know it all)”, Newnes press, Burlington, M.A, Gardner Nigel (1998); “An introduction to programming the microchip PIC in C”, Character Press Ltd, U.K. Hitachi cooperation (2000);”LMO41L display datasheet” Ibrahim, Dogan (2006); “Microcontroller Based Digital Control”. John Wiley and Sons. Iovine, John (2000); “PIC Microcontroller Project Book.” McGraw Hill, Inc. Sanchez, Julio, and Maria P Canton (2007); “Microcontroller Programming”. CRC press Nagy, C. (2003);”Embedded Systems Design using the TI MSP 430 series”,Newnes press, Burlington M.A. MikroElektronika cooperation (2006); “mikroC Users Manual” Microchip technology (2001);” PIC16F87XA datasheet” Microchip technology (2001);”PIC Microcontrollers midrange MCU Family Reference Manual” Microchip technology incorporated (2009);”Microchip Compiled Tips N’ Tricks Guide” Steiner Jack (1980); “Taximeter – US Patent 4205388” Wilmshurst, T. (2001). “An Introduction to the Design of Small-Scale Embedded Systems”. Palgrave. World Wide Web resources http:// www.microchip.com/forums http:// www.edaboard.com/forums
55
Appendix A: Application software code.
56
57
58
59
Appendix B: PROJECT ACTIVITIES
60
Appendix C: project costs S/N DESCRIPTION QUANTITY UNIT COST
(TSHS) TOTAL COST (TSHS)
1 Stationery: Plain papers (A4) 1 rim 7,000/= 7,000/= Marker pen 2 500/= 1,000/= Blue pen 1 dozen 300/= 3600/= Pencil 5 100/= 500/= Office file 1 2,500/= 2,500/= 2 Transport cost 30,000/= 3 Internet access 30,000/= 4 Printing expenses 100 pages 100/= 10,000/= 5 Binding costs 2 reports 3,000/= 6,000/= 6 Device and components:
Resistors/Capacitors pack Micro-controller Prototype board LCD Connecting wires
1 1 1 1
15,000/= 30,000/= 6,000/=
30,000/= 5,000/=
15,000/= 30,000/= 6,000/=
30,000/= 5,000/=
7 Miscellaneous expenses 30,000/= TOTAL 206,600/=