i

TEMPERATURE BASED DC MOTOR SPEED CONTROL

GARY ROYSTON GEORGE

This thesis is submitted as partial fulfillment of the requirements for the award of the

Bachelor of Electrical Engineering (Electronics)

Faculty of Electrical & Electronics Engineering

Universiti Malaysia Pahang

NOVEMBER, 2010

ii

AUTHOR’S DECLARATION

I declare that this thesis entitled “TEMPERATURE BASED DC MOTOR SPEED

CONTROL” is the result of my own research except as cited in the references. The

thesis has not been accepted for any degree and is not concurrently submitted in

candidature of any other degree.

Signature : __________________

Name : GARY ROYSTON GEORGE

Date : 28th NOVEMBER 2010

iv

ACKNOWLEDGEMENT

First and foremost, I want to express my great deepest gratitude for my

supervisor, Miss Nor Laili Binti Ismail for her continued support, encouragement,

and guidance in overseeing the progress of my project from initial phase until it is

complete. Without her valuable advices and comments, this project would not have

been possible to finish.

My fellow postgraduate students should also be recognised for their support.

My sincere appreciation also extends to all my colleagues and others who have

provided assistance at various occasions. Unfortunately, it is not possible to list all of

them in this limited space.

Last but definitely not the least to my parent and my family, I would never

thank enough for their endless support and encouragement throughout my studies in

University Malaysia Pahang (UMP).

v

ABSTRAK

Kelajuan motor DC boleh dikawal dengan mengubah bekalan voltan antara

dua terminal motor DC dan ini boleh dilakukan melalui pelbagai cara. Projek ini

menggunakan kawalan kelajuan motor DC brushless melalui bacaan suhu daripada

sensor suhu analog. Microcontroller akan mengeluarkan isyarat pulse-width

modulation (PWM) dengan variasi duty cycle yang ditetapkan berdasarkan bacaan

suhu untuk mengawal kelajuan motor DC melalui MOSFET yang bertindak sebagai

suis yang hidup dan mati mengikut frekuensi PWM sebagai pacuan motor.

Microcontroller yang mengandungi pengubah analog kepada digital (ADC) dan

fungsi PWM akan digunakan dalam projek ini untuk berfungsi dengan sensor suhu

analog dan mengawal kelajuan motor DC brushless.

vi

ABSTRACT

The speed of a DC motor can be controlled by varying the supply voltage

across the two terminals of DC motor and there are many ways of doing so. This

project uses control logic for the brushless DC (BLDC) motor speed control which is

based on the ambient temperature readings of an analog temperature sensor. The

microcontroller will produce a pulse-width modulation (PWM) signal with variable

duty cycle based on the temperature data obtained to regulate the motor speed

through a MOSFET as switching component to turn ON and OFF at PWM frequency

which act as the motor drive. A microcontroller with analog to digital converter

(ADC) interface and PWM peripheral will be used in this project to communicate

with an analog temperature sensor and to regulate a brushless DC motor speed.

vii

TABLE OF CONTENTS

CHAPTER ELEMENTS PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vii

LIST OF FIGURES x

LIST OF APPENDICES xii

LIST O LIST OF ABBREVIATION xiii

CHAPTER 1 INTRODUCTION

1.1 Background of Study 1

1.2 Problem Statement 2

1.3 Project Objective 2

1.4 Project Scope 3

1.5 Thesis outline 4

viii

CHAPTER 2 LITERATURE REVIEW

2.1 Analog to Digital Converter (ADC) 5

2.2 Pulse Width Modulation (PWM) 5

2.3 PIC 16F877 Microcontroller 7

2.4 MOSFET switching applications 8

2.4.1 Turn-On procedure 9

2.4.2 Turn-Off procedure 11

2.5 MOSFET Driver 14

2.6 LM35 precision centigrade temperature sensor 16

2.7 DC-DC boost converter 16

CHAPTER 3 METHODOLOGY

3.1 Theory of operation 19

3.2 System Operation Flowchart 21

3.3 Design hardware 22

3.4 Sensor and microcontroller interfacing 22

3.5 Principle of operation for controlling

DC motor speed using PWM 27

3.6 DC motor speed control and LED

signal behavior by PIC 27

3.7 DC motor speed control by a power MOSFET 33

ix

3.8 PWM control using transistor at low side drive 33

3.9 DC-DC Boost Converter simulation 34

3.9.1 Pulse-width modulation simulation setting 36

3.9.2 Voltage output simulation setting 37

CHAPTER 4 RESULTS AND DISCUSSIONS

4.1 PROTEUS ISIS Professional v7.6 SP4

simulation for PIC16F877 interfacing with

LM35 temperature sensor and 14-pins LCD display 38

4.2 DC motor speed control and LED simulation 39

4.3 DC-DC Boost Converter simulation by

PSpice OrCAD Capture v9.1 41

4.4 Hardware 44

4.4.1 Hardware overview 44

4.4.2 Oscillator result on output PWM signal

for motor control 47

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS

5.0 Conclusion 52

5.1 Future Recommendation 53

x

REFERENCES 54

APPENDICES A: INSTRUCTION SOURCE CODE 57

B: DATASHEET 61

xi

LIST OF FIGURES

FIGURE TITLE PAGE

1 Examples of PWM duty cycle square waves 6

2 Pin diagram for PIC16F877A microcontroller 8

3 Simplified clamped inductive switching model 9

4a MOSFET turn-on diagram 9

4b MOSFET turn-on time intervals 10

5a MOSFET turn-off diagram 12

5b MOSFET turn-off time intervals 12

6 Direct gate drive circuit 15

7 Typical DC-DC boost converter 17

8 Design flowchart 21

9 Circuit design for the hardware 22

10 Schematic circuit for sensor, lcd and microcontroller

interface 23

11a Source code 24

11b Source code (continued) 24

12 LM35, PIC16F877 and external crystal, LCD display,

LED, MOSFET and 12V DC motor interface

simulation. 28

13 Definition and variables for PWM and LED

xii

output program 29

14 PWM duty cycle and LED behavior program 30

15 Low side drive circuit 34

16 DC-DC boost converter schematic by PSpice OrCAD

Capture v9.1 software 34

17 A running simulation with a voltage/level marker at

the generated PWM signal 36

18 Simulation setting; Transient analysis, runtime

until 1ms 36

19 A running simulation with a voltage/level marker at the

output voltage 37

20 Simulation setting; Transient analysis, runtime

until 0.1s 37

21 A running simulation at temperature of 28°C set on

LM35 38

22 LM35, PIC16F877 and external crystal, LCD display,

LED, MOSFET and 12V DC motor interface

simulation 39

23 A running simulation at a temperature below 25°C.

The output LED is low and DC motor is not running

(duty cycle = 0) 40

24 Simulation at temperature between 25°C and 41°C.

The motor is running at 65.5% motor speed and the

LED is blinking. 40

25 Simulation at temperature higher than 41°C.

Duty cycle is 100%, drive DC motor to a full speed.

The output LED is high. 41

26 Graph of transient analysis for PWM simulation between

0s to 1ms (PWM duty cycle is 25%) 41

27 Graph of transient analysis between 50ms until 100ms 42

28 PW of VPULSE is reduced to 8µs 42

29 Graph of transient analysis between 50ms until 100ms 43

xiii

30 Simulation using a larger capacitor (2.2mF) and PW is

adjusted to 8.5µs 43

31 Graph of transient analysis between 0s to 100ms 44

32 Hardware circuit 45

33 DC-DC boost converter circuit 46

34 LCD display 30°C temperature reading and the motor

is running 46

35 PWM input into IRF 540N MOSFET at 26°C 47

36 PWM input into IRF 540N MOSFET at 28°C 47

37 PWM input into IRF 540N MOSFET at 30°C 48

38 PWM input into IRF 540N MOSFET at 32°C 48

39 PWM input into IRF 540N MOSFET at 34°C 49

40 PWM input into IRF 540N MOSFET at 36°C 49

41 PWM input into IRF 540N MOSFET at 38°C 50

42 PWM input into IRF 540N MOSFET at 40°C 50

43 PWM input into IRF 540N MOSFET at 42°C 51

LIST OF TABLES

TABLE TITLE PAGE

1 Temperature reading and calculated PWM duty cycle,DC motor speed and LED signal behavior. 32

2 Hardware label 45

3 Temperature reading with theoretical calculated PWM

duty cycle and oscillator result on hardware testing

duty cycle. 51

xiv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Instruction Source Code 57

B1 Datasheet for PIC 16F877 62

B2 Datasheet for LM 35 66

B3 Datasheet for LM 7805 72

B4 Datasheet for TO-220 package 77

B5 Datasheet for IRF540N 78

LIST OF ABBREVIATION

DC Direct Current

PIC Programmable Interface Controller

PWM Pulse Width Modulation

ADC Analog to Digital Converter

RPM Revolutions per Minute

LCD Liquid Crystal Display

xv

MOSFET Metal–Oxide–Semiconductor Field-Effect Transistor

PCB Printed Circuit Board

CICM Continuous Inductor Current Mode

DICM Discontinuous Inductor Current Mode

PFC Power Factor Correction

EMI Electromagnetic Interference

CHAPTER 1

INTRODUCTION

1.1 Background of study

The speed of a DC motor can be varied by many methods and one of them

is by using Programmable Interface Controller (PIC) to produce Pulse Width

Modulation (PWM) signal with variable duty cycle. But, in terms of varying a DC

motor speed, there are options of doing it manually or automatically. By manually

means that the input data that is to be sent to the microcontroller to determine output

voltage supply to the motor by PWM method is determined by the user. But in

automatic control to vary a DC motor speed, the input data is not based on online

data input from the user, but from programmed code to control the output voltage

supply to the motor through PWM by variable input data obtained by sensor

interfacing.

This project uses control logic for the DC motor speed control which is

based on the ambient temperature readings of an analogue temperature sensor. The

microcontroller will produce a PWM signal with variable duty cycle based on the

temperature data obtained to regulate the motor speed. A PIC with analogue input

2

and PWM peripheral will be used in this project to communicate with an analogue

temperature sensor and to regulate a brushless DC motor (BLDC motor) speed.

1.2 Problem Statement

Generally, temperature controlled DC motor speed is applicable in cooling

fan speed control. It is necessary to control the fan speed to reduce noise produced by

the fan and improving the fan reliability. The noise levels produced by a cooling fan

are in fact can reach 70 dB. Since fan noise increases exponentially to the fan

rotation speed, reducing revolutions per minute (RPM) by a small amount potentially

means a reduction in fan noise. This must be done cautiously, as excessive reduction

in speed may cause components to overheat and be damaged. If done properly fan

noise can be drastically reduced. The control of the fan speed is obtained by a closed-

loop system, which is using temperature sensor as a feedback of the system. A

controlled fan speed in accordance to temperature does as well reduce the power

consumption of the fan itself.

1.3 Project Objective

i. Build the hardware that consists of PIC microcontroller, an analogue

temperature sensor, N-Channel MOSFET, a 12V BLDC motor, an LCD

display to display ambient temperature, and a DC-DC boost converter to

boost 9Vdc to 12Vdc to supply the BLDC motor.

3

ii. Design source code for the PIC programming to interface with the analogue

temperature sensor and the LCD display to display ambient temperature

reading and such that it meet the required conditions for the BLDC motor

speed control based on ambient temperature reading. Another PWM program

also required to drive an N-channel MOSFET of the boost converter.

1.4 Project Scope

i. Use PROTEUS ISIS Professional v7.6 SP4 software to design and simulate

hardware schematic of PIC microcontroller interfacing with an analogue

temperature sensor, LCD display, an N-channel MOSFET and a BLDC

motor. Simulation must be done with a complete function of .hex file for the

microcontroller.

ii. Use PSpice OrCAD Capture v9.1 software to design and simulate a DC-DC

boost converter to boost a 9Vdc supply to 12Vdc.

iii. Use MicroCode Studio 4.0.0 PICBASIC PRO v2.6 to design source code for

the PIC and converting the .pbp file to .hex file.

iv. Build the hardware that consists of PIC microcontroller, an analogue

temperature sensor, N-Channel MOSFET, a 12V BLDC motor, an LCD

display to display ambient temperature, and a DC-DC boost converter to

boost 9Vdc supply to 12Vdc.

4

1.4 Thesis Outline

This thesis contains 5 chapters that include Chapter 1: Introduction, Chapter 2:

Literature reviews, Chapter 3: Methodology, Chapter 4: Results and discussions,

Chapter5: Conclusion and recommendations. Each chapter will contribute to explain

different focus and discussion relating with the corresponding chapter’s heading.

Chapter 1 contains introduction which presents the overviews of the project

that is constructed. It consists of project background, objective, problem statement

and project scope.

Chapter 2 contains literature review which discuss about the reference taken

for this project completion.

Chapter 3 discuss about the methodology in this project which consists of

method used to undertake simulations, experiments, hardware development and

testing.

Chapter 4 contains result and discussions focused on the analysis of the result

acquired and discussed the outcome obtained.

Chapter 5 contain conclusion and recommendations for this project.

CHAPTER 2

LITERATURE REVIEW

2.1 Analog to Digital Converter (ADC)

Analog to digital converter converts a continuous quantity to a discrete

digital/binary-coded number [1]. An ADC is an electronic device that converts an

input analog voltage (or current) to a digital number proportional to the magnitude of

the voltage or current [1]. In this project, variable voltage output from an analog

temperature sensor is converted to a digital value through an ADC pin of the PIC.

The ADC is by means of interfacing the analog temperature sensor with PIC.

Definition of port and bit needed for the operation must first be included in PIC

program to enable the function of the ADC.

2.2 Pulse Width Modulation (PWM)

6

Pulse width modulation (PWM) is a technique for controlling analog

circuits with a processor's digital outputs [2]. PWM is a way of digitally encoding

analog signal levels. Through the use of high-resolution counters, the duty cycle of a

square wave is modulated to encode a specific analog signal level. The PWM signal

is still digital because, at any given instant of time, the full DC supply is either fully

on or fully off. The voltage or current source is supplied to the analog load by means

of a repeating series of on and off pulses. The on-time is the time during which the

DC supply is applied to the load, and the off-time is the periods during which that

supply is switched off. Given a sufficient bandwidth, any analog value can be

encoded with PWM [2]. For fully off the duty cycle used will be 0% and 100% for

fully on. The duty cycle is independent of the frequency of the PWM signal and the

same type of waveform will be observed for a specific duty cycle [3].

Figure 1: Examples of PWM duty cycle square waves [3].

From Figure 1, the digital signal (solid line) is at a constant frequency while

the pulse width is changed (modulated). The dotted line represents the average

signal (if the digital signal is converted to an average). The duty cycle represents the

amount of time that the signal is high compared to the amount of time that the signal

is low [3].

7

2.3 PIC 16F877 Microcontroller

All single cycle instructions except for program branches which are two

cycle, the operating speed is 20 MHz and clock input is 200 ns instruction cycle It is

having up to 8K x 14 words of FLASH Program Memory, up to 368 x 8 bytes of

Data Memory (RAM) and up to 256 x 8 bytes of EEPROM Data Memory [4].

PIC is a family of RISC (Reduced Instruction Set Computer)

microcontroller manufactured exclusively by Microchip. PICs are faster, more

reliable (high noise immunity) and code-efficient than 8051s. PIC is having an

internal memory and it can be extended by using I2C protocol. PIC will operate with

50 nano-Amps in sleep mode, and has a variety of sleep modes to further conserve

power. Atmel’s ATmega165P AVR controller Consumes 100nano-Amps in Power

Down mode PIC to be fully operable with any supply rated between 2V to 5.5V. For

battery-powered projects PICs are most suitable [4].

Many microcontrollers include on-chip PWM units. PIC 16F877 has two,

each of which has a selectable on-time and period. The duty cycle is the ratio of the

on-time to the period while the modulating frequency is the inverse of the period. To

start PWM operation, the data sheet suggests the software should [5]:

Set the period in the on-chip timer/ counter that provides the modulating

square wave.

Set the on-time in the PWM control register.

Set the direction of the PWM output, which is one of the general-purpose I/O

pins.

Start the timer.

Enable the PWM controller.

This 40-pin PIC microcontroller unit is chosen for its suitability for this

project. It has what are needed for this project; support ADC which is to be use to

receive analog voltage value from the analog temperature sensor and the PWM

8

peripheral that produces PWM signal with various duty cycle determined by the PIC

source code [5].

Figure 2: Pin diagram for PIC16F877 microcontroller [5].

The PIC microcontrollers are very easy to use with PWM as they have built

in PWM generators. What need to be done is to set up the relevant control registers

[5].

2.4 MOSFET switching applications

To investigate the actual switching behavior of the MOSFET transistors, the

parasitic inductances of the circuit will be neglected. The following descriptions

relate to clamped inductive switching because most MOSFET transistors and high

9

speed gate drive circuits used in switch mode power supplies work in that operating

mode [7].

Figure 3: Simplified clamped inductive switching model [7].

2.4.1 Turn-On procedure

The turn-on event of the MOSFET transistor can be divided into four

intervals as depicted in Figure 4a and Figure 4b.

Figure 4a: MOSFET turn-on diagram [7].

10

Figure 4b: MOSFET turn-on time intervals [7].

For the first step the input capacitance of the device is charged from 0V to

VTH. During this interval most of the gate current is charging the CGS capacitor. A

small current is flowing through the CGD capacitor too. As the voltage increases at

the gate terminal and the CGD capacitor’s voltage has to be slightly reduced [7]. This

period is called the turn-on delay, because both the drain current and the drain

voltage of the device remain unchanged. Once the gate is charged to the threshold

level, the MOSFET is ready to carry current. In the second interval the gate is rising

from VTH to the Miller plateau level, VGS,Miller. This is the linear operation of the

device when current is proportional to the gate voltage. On the gate side, current is

flowing into the CGS and CGD capacitors just like in the first time interval and the VGS

voltage is increasing. On the output side of the device, the drain current is increasing,

while the drain-to-source voltage stays at the previous level (VDS, OFF). Until all the

current is transferred into the MOSFET and the diode is turned-off completely to be