This document describes a project to control the speed of a DC motor using pulse width modulation (PWM) generated by an AT89C52 microcontroller. The document outlines the purpose, components, circuit diagram, programming, and workflow. Key components include an AT89C52 microcontroller, L293D motor driver, DC motor, voltage regulator, and buttons. PWM signals of varying duty cycles control the motor's speed. Code uses timers to generate PWM and buttons to select speed. The summary provides an overview of the goal and approach.

1. PREPARED BY
 DISHA MODI (100280111066)
 HARDIK JOSHI (100280111125)
 HARSHAL PATIL (100280111124)

2.  Introdution
 Purpose
 Aim
 Analysis
 User interface
 Hardware interface
 Software interface
 Programming used
 Working procedure
 Conclusion
 Cost of components used
 Bibliography
Table of Contents

3. 
Purpose:
 DC-Motor is a SISO(single input single output) device. Which
converts electrical energy to mechanical energy, means here it gives
variable speed according the change in supply voltage given to it and
this input voltage varies accordingly width of the pulses which is
generated by controller IC.
 DC motors have a long tradition of being used as adjustable speed
machines and a wide range of options have evolved for this purpose.
 For exa; Cooling blowers and inlet air flanges provide cooling air for
a wide speed range at constant torque , also in household appliences
like fan, mixer etc.
Aim: To control the speed of DC-Motor by
generating pulses of variable duty cycles using the
AT89C52 controller IC.

4. What is PWM(Pulse Width Modulation) ?
 Pulse Width Modulation – Using digital pulses to create some analog value other than
just ‘high’ and ‘low’ signal levels.
 Many digital systems are powered by a 5-Volt power supply, so if you filter a signal
that has a 50% duty cycle you get an average voltage of 2.5 Volts. Other duty cycles
produce any voltage in the range of 0 to 100% of the ‘high’ voltage, depending upon
the PWM resolution.
 The duty cycle is defined as the percentage of digital ‘high’ to digital ‘low’ signals
present during a PWM period.
Uses for PWM: 1) To digitally create an analog output voltage level for control
functions and power supply.
2) To digitally create analog signals for arbitrary waveforms, sounds, music and speech

5. List of components used:
 Controller IC AT89C52
 Motor driver IC L293D
 DC motor 150 rpm
 Voltage controller IC 7805
 Crystal oscillator (12Mhz)
 Bridge rectifier
 Pull up resistor
 Box, ceramic and electrolytic capacitor
 2 pin push button switches
 Connector pins and connecting wires
 Variable voltage adapter

6. 
 Features
 • Compatible with MCS-51™ Products
 • 8K Bytes of In-System Reprogrammable Flash Memory
 • Endurance: 1,000 Write/Erase Cycles
 • Fully Static Operation: 0 Hz to 24 MHz
 • Three-level Program Memory Lock
 • 256 x 8-bit Internal RAM
 • 32 Programmable I/O Lines
 • Three 16-bit Timer/Counters
 • Eight Interrupt Sources
 • Programmable Serial Channel
 • Low-power Idle and Power-down Modes
AT89C52 CONTROLLER IC

7. Description
The AT89C52 is a low-power,
high-performance CMOS 8-bit
microcomputer with 8K bytes of Flash
programmable and erasable read only
memory (PEROM). The device is
manufactured using Atmel’s high-density
nonvolatile memory technology and is
compatible with the industry-standard
80C51 and 80C52 instruction set and
pinout. The on-chip Flash allows the
program memory to be reprogrammed in-
system or by a conventional nonvolatile
memory programmer. By combining a
versatile 8-bit CPU with Flash on a
monolithic chip, the Atmel AT89C52 is a
powerful microcomputer which provides a
highly-flexible and cost-effective solution
to many embedded control.

8. 
L293D Dual H-Bridge Motor Driver
 L293D is a dual H-Bridge motor driver, So with one IC we can interface two
DC motors which can be controlled in both clockwise and counter clockwise direction
and if you have motor with fix direction of motion the you can make use of all the four
I/Os to connect up to four DC motors.
 L293D has output current of 600mA and peak output current of 1.2A per channel.
Moreover for protection of circuit from back EMF output diodes are included within
the IC. The output supply (VCC2) has a wide range from 4.5V to 36V, which has made
L293D a best choice for DC motor driver.
 As you can see in the circuit, three pins are needed for interfacing a DC motor (A, B,
Enable). If you want the o/p to be enabled completely then you can connect Enable to
VCC and only 2 pins needed from controller to make the motor work.
 As per the truth mentioned in the image above its fairly simple to program the
microcontroller. Its also clear from the truth table of BJT circuit and L293D the
programming will be same for both of them, just keeping in mind the allowed
combinations of A and B.

9. A simple schematic for interfacing a DC motor using L293D is shown below.

10. ►Introduction
 Whenever a robotics hobbyist talk about making a
robot, the first thing comes to his mind is making the robot move on the
ground. And there are always two options in front of the designer whether to
use a DC motor or a stepper motor. When it comes to speed, weight, size,
cost... DC motors are always preferred over stepper motors.
 There are many things which you can do with
your DC motor when interfaced with a microcontroller. For example, you
can control the speed of motor, you can control the direction of rotation, you
can also do encoding of the rotation made by DC motor i.e. keeping track of
how many turns are made by your motors etc. So you can see DC motors are
no less than a stepper motor.

12. Voltage controller IC 7805
 The LM7805 of three-terminal positive voltage
regulators employ built-in current limiting,
thermal shutdown, and safe-operating area
protection which makes them virtually immune
to damage from output overloads.

13. Crystal Oscillator:
 A crystal oscillator is an electronic oscillator circuit that uses
the mechanical resonance of a vibrating crystal of piezoelectric material to
create an electrical signal with a very precise frequency.
 most common type of piezoelectric resonator used is the quartz crystal, but
other piezoelectric materials including polycrystalline ceramics are used in
similar circuit.
Here, we are using the 12MHz Crystal oscillator.
Bridge Rectifier:
 A rectifier is an electrical device that
converts alternating current (AC), which periodically
reverses direction, to direct current (DC), which flows
in only one direction. The process is known as
rectification.

14. Pull up resistors:
 Pull-up resistors are used in electronic logic circuits to ensure that inputs
to logic systems settle at expected logic levels if external devices are
disconnected or high-impedance.
 They may also be used at the interface between two different types of logic
devices, possibly operating at different power supply voltages.
 When the switch is open the voltage of the gate input is pulled up to the level
of 𝑉inWhen the switch is closed, the input voltage at the gate goes to ground.
 A pull-up resistor weakly "pulls" the voltage of the wire it is connected to
towards its voltage source level when the other components on the line are
inactive.
 When all other connections on the line are inactive, they are high-impedance
and act like they are disconnected. Since the other components act as though
they are disconnected, the circuit acts as though it is disconnected, and the pull-
up resistor brings the wire up to the high logic level.
 When another component on the line goes active, it will override the high logic
level set by the pull-up resistor. The pull-up resistor assures that the wire is at a
defined logic level even if no active devices are connected to it.

15.  General mini box cap: use for ( by passing, filtering frequency discrimination,
timing oscillation, pulse coupling etc...) this kind of capacitor will not pass
high AC current, it dominates micro AC signal.
Box capacitor:
Ceramic capacitor:
 A ceramic capacitor is a fixed capacitor with the
ceramic material acting as the dielectric. It is
constructed of two or more alternating layers of
ceramic and a metal layer acting as the electrodes.

16.  An electrolytic capacitor is a type of capacitor that uses an electrolyte (an ionic
conducting liquid) as one of its plates to achieve a larger capacitance per unit
volume than other types, but with performance disadvantages.
 All capacitors conduct alternating current (AC) and block direct current (DC)
and can be used, amongst other applications, to couple circuit blocks allowing
AC signals to be transferred while blocking DC power, to store energy, and to
filter signals according to their frequency.
Electrolytic capacitor

17. 2 pin Push button switches:
 Miniature 2-PIN Single Pull Single Throw switches. These are high quality
momentary on switches. Perfect as a tactile reset switch. Mounts perfectly into
standard breadboards. Rated up to 50mA.
Power on/off switch
 This is a simple SPDT slide switch - great for use as
an ON/OFF button, or just as a general control switch.
The pins are spaced by 0.1", so it's breadboard friendly.
The switch is rated for 0.3A at 50VDC.

18. Connector pins and connecting wires:
This is a simple wire cable. Great for
jumping from one point to another point in circuit to
make connection between that two points.
Adaptor is just a power supply, it plugs
into the wall and converts AC current to a single DC
voltage in most cases. There are also adapters that
output a different AC voltage. Here, we are using the
5-12V DC variable voltage adapter.
Variable voltage adapter:

20. Programming used:
Code to control dc motor using pwm
#include <reg52.h>
sbit mybit=P2^0; //Positive of motor
sbit L293D_B=P2^1; //Negative of motor
sbit L293D_E=P2^2; //Enable of L293D
sbit sw1=P1^1; // switch for high speed
sbit sw2=P1^0; // switch for low speed
void delay(void);
void main()
{
sw1=1; // make switches as input
sw2=1;
while(1)
{
if (sw2==0)

21. {
mybit=1;
delay();
delay();
delay();
mybit=0;
delay();
}
if(sw1==0) //switch 1 is pressed
{
mybit=1;
delay();
mybit=0;
delay();
delay();
delay();
}
else
mybit=1;
}
}

22. void delay (void) // function to generate time delay using timer
{
unsigned char x,y;
TMOD=0x02; //timer 0 in mode 2
for(x=0;x<=20;x++)
for(y=0;y<=36;y++)
{
TH0=-23;
TR0=1;
while(TF0==0);
TR0=0;
TF0=0;
}
}

23. Waveform Generated for this program:
1.Output waveform for high speed-

24. 2. Output waveforms for low speed-

25. 
 Steps for operating user interface-
 Switch on the variable voltage adapter.
 Set the power supply of adapter to 12 volts.
 Slide the power on/off switch to on condition.
 Press reset button .
 Press switch 1 to getting high speed of motor.
 Press switch 2 to getting low speed of motor.
Working Procedure

26. 
 We can control DC-Motor by generating pulses of variable duty cycles
through controller IC AT89C52 efficiently.
 By increasing or decreasing pulse width, the controller regulates
energy flow to the motor shaft. The motor’s own inductance acts like a
filter, storing energy during the “on” cycle while releasing it at a rate
corresponding to the input or reference signal.
 By generating pwm we can reduces the damage done to the motor due
to excessive amount of current.
Conclusion:

27. Cost of components used:
Sr.No. Name of components quantity Price per piece Total
1. Controller IC AT89C52 1 80 80
2. Trainer board 1 135 135
3. Motor driver L293D IC 1 80 80
4. DC motor 150 rpm 1 250 250
5. Bridge rectifier ic 1 30 30
6. 7805 IC 1 10 10
7. Box, ceramic, electrolytic capacitor 10 5 50
8. Pull up resistor 3 15 45
9. adapter 1 120 120
10. Crystal oscillator 1 20 20
11. switches 4 5 20
12. Connecting pins & wires - 40 40

28. 
 1. The 8051 Microcontroller and Embedded Systems Using Assembly
and C,2/e by Muhammad Ali Mazidi, Janice Gillispie Mazidi and
Rolin McKinlay ( Second Edition , Pearson Education ).
 2. The 8051 Microcontroller & Embedded Systems using Assembly
and C By K. J. Ayala, D. V. Gadre (Cengage Learning , India Edition).
 3. 8051 Microcontrollers: MCS51 family and its variants by Satish
Shah, Oxford University Press.
Bibliography: