Speed Control using PWM

1. SPEED CONTROL OF A DC MOTOR USING
MICROCONTROLLER 8051
A PROJECT REPORT
Submitted by
S. Kamal Viswanath (07241A0206)
M. Gowtham (07241A0203)
P. Ashok Kumar (06241A0205)
K. Rohit Naik (07241A0247)
in partial fulfillment for the award of the degree
of
Bachelor of Technology
IN
ELECTRICAL AND ELECTRONICS ENGINEERING
GOKARAJU RANGARAJU INSTITUTES OF ENGINEERING AND
TECHNOLOGY
JNTU HYDERABAD : 500085
January 2011

2. GOKARAJU RANGARAJU INSTITUTES OF
ENGINEERING AND TECHNOLOGY
BONAFIED CERTIFICATE
This is to certify that this project report “Speed Control of DC Motor using
microcontroller 8051” is the bonafied work of “Kamal Viswanath,
Gowtham, Ashok Kumar, Rohith Naik” who carried out the project under
my supervision.
SIGNATURE SIGNATURE
P.M. Sharma M. Chakravarthy
HEAD OF THE DEPARTMENT PROJECT GUIDE
ASSOCIATE PROFESSOR
ELECTRICAL AND ELECTRONICS ELECTRICAL AND ELECTRONICS
GRIET, GRIET,
BACHUPALLY, KUKATPALLY, BACHUPALLY, KUKATPALLY,
HYDERABAD-500 090. HYDERABAD-500 090.

3. ABSTARCT
The aim of developing this project is to
control the speed of DC motor. The main advantage in using a DC motor is that
the Speed-Torque relationship can be varied to almost any useful form. To
achieve the speed control an electronic technique called Pulse Width
Modulation is used which generates High and Low pulses. These pulses vary
the speed in the motor. For the generation of these pulses a microcontroller
(AT89c51) is used. As a microcontroller is used setting the speed ranges as per
the requirement is easy which is done by changing the duty cycles time period
in the program. This project is practical and highly feasible in economic point of
view, and has an advantage of running motors of higher ratings. This project
gives a reliable, durable, accurate and efficient way of speed control of a DC
motor.

4. CONTENTS
CHAPTER No. TITLE PAGE No.
ABSTRACT iii
1. INTRODUCTION 1
1.1 DC Motor 1
1.2 Pulse Width Modulation 3
1.3 Microcontroller 6
2. FLOW CHART 8
3. BLOCK DIAGRAM 9
4. CIRCUIT DIAGRAM 10
5. HARDWARE DESCRIPTION 11
6. SOFTWARE DESCRIPTION 12
7. DATA ACQUAINTED 14
8. DATA SHEETS 16
9. COMPONENTS LISTING 24
10. REFERENCES 24

5. INTRODUCTION
DC MOTOR
The device that converts electrical energy
into mechanical energy is called as a motor. The motor that utilizes a DC supply
to produce mechanical output is DC Motor. The advantages of using these types
of motors over conventionally used AC motors are stated below.
• DC motors have higher controller efficiency.
• DC motors have typical 98% efficiency.
• DC motors have better overload and peak voltage characteristics.
• The main advantage of using these DC motors ids that the speed-
torque characteristics can be varied to almost any useful form.
As a result of all these advantages these
motors have a wide range of applications in places where constant speed is to be
maintained at varying loads. Conveyor belts, elevators, cranes, ski lifts,
extruders, mixers, sewing machines are few such applications where DC motors
are used. So controlling the speed of a DC motor is a purposeful and required
place to work on. The various types of DC motors are

6. • Series field wound type
• Shunt field wound type
• Compound field wound type
For all these types of DC motor common methods of speed controls.
Speed control methods in a DC motor:
The motor speed can be controlled by
controlling armature voltage and armature current. It is obvious that speed
control is possible by varying
•Flux per pole ,Φ (Flux control)
•resistance Ra of armature circuit (Rheostatic Control)
•applied voltage V (Voltage Control)
The above methods have some demerits like a large amount of power is wasted
in the controller resistance. Hence, efficiency is decreased. It needs expensive
arrangement for dissipation of heat produced in the controller resistance. It
gives speeds below the normal speed. By these data that are acquainted we can
draw a conclusion that these electric and electromechanical methods are less
adaptive so electronic techniques are used for speed control. These methods
provide higher efficiency, greater reliability, quick response, higher efficiency.
One such technique is Pulse Width Modulation. We apply this technique in our
project so as to control the speed of the DC motor.

7. PWM
Pulse width modulation (PWM) is a method for binary signals generation,
which has 2 signal periods (high and low). The width (W) of each pulse varies
between 0 and the period (T). The main principle is control of power by
varying the duty cycle. Here the conduction time to the load is controlled. Let
for a time t1, the input voltage appears across the load i.e. ON state and for t2
time the voltage across the load is zero.
• The average voltage at output is given by
Va = 1/T ∫ vodt = t1/T Vs = ft1 Vs = kVs
• the average load current Ia = Va/R = kVs/R where,
T is the total time period =t1+t2,
k = t1/T is the duty cycle.
• The rms value of output voltage is V0 = ( i/T ∫ V0
2
dt ) ½
= k Vs
• The output power and is given by
Pi = 1/T ∫v0idt = 1/T ∫ v0
2
/R dt = kVs
2
/R

8. • The duty cycle can be varied from 0 to 1 by varying t1, T or f. Therefore,
the output voltage V0 can be varied from 0 to Vs by controlling k, and the
power flow can be controlled.
• As the time t1 changes the width of pulse is varied and this type of
control is called pulse width modulation (PWM) control.
For better understanding of PWM these diagrammatic representations can be
used. These figures represent the waveforms obtained as output at different
voltage requirements.
High Speed Signal (90%): The green part of the signal represents the ON
time and the white part of it represents time when it is not receiving any voltage.
Signal with half voltage (50%):

9. Signal with low voltage (10%):
Advantages of PWM :
The main advantage of PWM is that power loss in
the switching devices is very low. When a switch is off there is practically no
current, and when it is on, there is almost no voltage drop across the switch.
Power loss, being the product of voltage and current, is thus in both cases close
to zero. PWM works also well with digital controls, which, because of their
on/off nature, can easily set the needed duty cycle. Using pulse width
modulation has several advantages over analog control. Using PWM to dim a
lamp would produce less heat than an analog control that converts some of the
current to heat. Also, if you use PWM, the entire control circuit can be digital,
eliminating the need for digital-to-analog converters. Using digital control lines
will reduce the susceptibility of your circuit to interference. Finally, motors may
be able to operate at lower speeds if you control them with PWM. When you
use an analog current to control a motor, it will not produce significant torque at
low speeds. The magnetic field created by the small current will be too weak to
turn the rotor. On the other hand, a PWM current can create short pulses of
magnetic flux at full strength, which can turn the rotor at extremely slow
speeds.
The technology has become more pervasive as low cost
microcontrollers incorporate PWM control. Microcontrollers offer simple

10. commands to vary the duty cycle and frequencies of the PWM control signal.
PWM is also used in communications to take advantage of the higher immunity
to noise provided by digital signals. So by getting these pulses generated by a
microcontroller we can increase the efficiency, accuracy and thus the reliability
of the system. The most commonly used microcontroller is 8051 that has been
used in this project for production of pulses.
MICROCONTROLLER
A microcontroller (abbreviated µC, uC or MCU) is a
small computer on a single integrated circuit containing a processor core,
memory, and programmable input/output peripherals. This programmes
memory in the form of NOR flash or OTP ROM is also often included on chip,
as well as a typically small amount of RAM.
Advantages of Microcontroller
Microcontrollers are widely used in today’s control systems for the following
reasons:
• Design and Simulation – Because you are programming with software,
detailed simulations may be performed in advance to assure correctness
of code and system performance.
• Flexibility – Ability to reprogram using Flash, EEPROM or EPROM
allows straightforward changes in the control law used.
• High Integration – Most microcontrollers are essentially single chip
computers with on-chip processing, memory, and I/O. Some contain
peripherals for serial communication and reading analog signals (with an

11. analog-to-digital converter or ADC). This differentiates a microcontroller
from a microprocessor. Microprocessors require that this functionality be
provided by added components.
• Cost – Cost savings come from several locations. Development costs are
greatly decreased because of the design/flexibility advantages mentioned
previously. Because so many components are included on one IC, board
area and component savings are often evident as well.
• Easy to Use – Just program and go! While in the past, programming has
often involved tedious assembly code, today C compilers are available for
most microcontrollers. Microcontrollers often only require a single 5V
supply as well which makes them easier to power and use.
8051 is also one such microcontroller with certain features like
• An 8-bit ALU.
• Harvard memory architecture – the external program memory and data
memory have separate address spaces from 0x0000 and separate
controlsignal(s).
• 8-bit internal data bus width and 16-bit internal address bus – Harvard
memory architecture
• CISC (Complex Instruction Set Computer)
• Special function registers (SFRs) –PSW(processor status word), A
(accumulator),B register, SP (stack pointer) and registers for serial IOs,
timers, ports and interrupt handler.
• on-chip RAM of 128 bytes.
• 32 bytes of RAM also used as four banks of registers. Each register-set
thus eight registers.
• External data/stack memory can be added upto 64 kB in most of the
version. In certain 8051 enhancements, this limit enhanced to 16 MB.
After acquiring the data about microcontroller,
DC motor and PWM technique we can get into designing a circuit that uses
these units in controlling the speed of a DC motor

12. FLOW CHART
Start
Check if both switches are open
No
Yes
Decrease speed
Speed Required
80%
No
Speed Required
50%
No
Close S1&S2

13.
Stop
BLOCK DIAGRAM

14. CIRCUIT DIAGRAM

15. HARDWARE DESCRIPTION

16. The components are connect on a
Printed Circuit Board as per the given connection details in the circuit diagram.
The functioning of the circuit can be explained with respect to the action format
that occurs in the circuit. As the supply is switched ON and both the switches
are open the switching supplies ideally 5V is given to the microcontroller.
Suppose if the any of the switch is closed the supply gets directly shorted with
the ground. This indicates the microcontroller about the switch positions and
thus generates the signal as per the given program for the respective switches
position. The transistor used allows current to conduct through it when ever a
positive pulse is given at its base that is given by the microcontroller
inaccordance with the program. As the transistor is forward biased the supply
that is used to run the motor gets connected with the motor terminals and motor
starts running. As soon as the 0 voltage is encountered the NPN transistor used
goes into reverse bias and stops its conduction so the motor’s armature supply
gets disconnected till the base current is 0 volts. By this we can deduce that the
speed of the motor is directly dependent on the supply given by microcontroller
to the base which indeed depends on the program written. So the speeds of
working of the circuit depends on the number of switches used, for instance in
the above circuit two switches are used so the number of speed levels are 22
= 4.
So the number of speed levels for X switches will be 2X
. So the speed of the
motor can be varied in steps.
SOFTWARE DESCRIPTION
#include<reg51.h>
These are the ports from where
the microcontroller gets the
information about the switch
positions.

17. sbit SW_1 = P2^6; //connecting switch 1 to the port 2 ,pin 6.
sbit SW_2 = P2^7; // connecting switch 1 to the port 2 ,pin 7.
sbit MTR = P1^0; // from this pin we get the signal that is to be fed to the base
void main()
{ int x;
while(1)
{
if(SW_1==0 & SW_2==0)
{ This condition is stated when both the switches are
closed in this position the supply from the switches is
shorted into the ground terminal so microcontroller
doesn’t get any voltage so the switches are considered
as 0’s. At this condition the program is written so that
the output signal given by the microcontroller should
have 150 machine cycles of ON state and 600 machine
cycles of OFF state.
MTR=1;
for(x=0;x<150;x++);
MTR=0;
for(x=0;x<600;x++);
}
if(SW_1==0 & SW_2==1)
{ This condition is stated when the switch1 is closed and
switch 2 is open in this position the supply from the
switch1 is shorted into the ground terminal so
microcontroller doesn’t get any voltage so the switch
is considered as 0. Similarly switch 2 is open and
supply is sent to microcontroller so it is considered
1.At this condition the program is written so that the
output signal given by the microcontroller should have
300 machine cycles of ON state and 300 machine
cycles of OFF state.
MTR=1;
for(x=0;x<300;x++);
MTR=0;
for(x=0;x<300;x++);
}
if(SW_1==1 & SW_2==0)
{ This condition is stated when the switch2 is closed and
switch 1 is open in this position the supply from the
switch2 is shorted into the ground terminal so
microcontroller doesn’t get any voltage so the switch
is considered as 0. Similarly switch 1 is open and
supply is sent to microcontroller so it is considered
1.At this condition the program is written so that the
output signal given by the microcontroller should have
600 machine cycles of ON state and 150 machine
MTR=1;

18. for(x=0;x<600;x++);
MTR=0;
for(x=0;x<150;x++);
}
if(SW_1==1 & SW_2==1)
In this condition both the switches are open so
they are stated as 1’s and in this condition the
motor runs at full speed.
{
MTR=1;
}
}
}
DATA AQUAINTED
Condition 1 when both the switches are open:

19. Voltage Speed
4.3V 860 rpm
Condition 2 when switch SW1 is
closed:
Voltage Speed Average speed
4.3V 860rpm
3.6V 720rpm
790 rpm
Condition 3 when switch SW2 is closed:

20. Voltage Speed Average speed
4.3V 860rpm
3.9V 780rpm
820 rpm
Condition 4 when both the switches are
closed:
Voltage Speed Average speed
4.3V 860rpm
3.3V 660rpm
760 rpm

21. COMPONENT LIST
Name of the
Component
Make Value Number
AT89C51
Micro Controller
ATMEL 1
Resistors R1,R2 10KΩ 2
Capacitors C1,C2 1nF 2
Capacitor C3 1mF 1
Diode D1 IN4004 1
Transistor T1 TIP122 1
Switches SW1,SW2 2
DC Motor AMETECK 12Volts 1
DC Adapter Q1(C) 12 Volts 1
DC Adapter Q2(C) 5 Volts 1
Crystal Oscillator X1 12MHz 1
REFERENCES
• Books on DC motors: Driving DC Motors by G.
MAIOCCHI, DC Motors and drives by BL. THERAJA.
• Books on PWM technique: Pulse Width Modulated
Power supplies by VALTER QUERCIOLI.
• Books on Microcontroller: The 8051
microcontroller and embedded systems by JANICE GILLISPIE MAZIDI.