CHAPTER – 1

GENERAL OVERVIEW OF THE PROJECT

1.1 Introduction

Direct current (DC) motors have variable characteristics and are used

extensively in variable-speed drives. DC motor can provide a high

starting torque and it is also possible to obtain speed control over wide

range. Why do we need a speed motor controller? For example, if we

have a DC motor in a robot, if we just apply a constant power to each

motor on a robot, then the poor robot will never be able to maintain a

steady speed. It will go slower over carpet, faster over smooth flooring,

slower up hill, faster downhill, etc. So, it is important to make a controller

to control the speed of DC motor in desired speed.

DC motor plays a significant role in modern industrial. These are several

types of applications where the load on the DC motor varies over a speed

range. These applications may demand high-speed control accuracy and

good dynamic responses.

In home appliances, washers, dryers and compressors are good examples.

In automotive, fuel pump control, electronic steering control, engine

control and electric vehicle control are good examples of these. In

aerospace, there are a number of applications, like centrifuges, pumps,

robotic arm controls, gyroscope controls and so on.

By using NI LabVIEW as the motor controller, we can control a DC

motor for multiple purposes using only one software environment. We

can interface Arduino Uno with LabVIEW and use a DC motor driver

L293D as the sub controller, and an encoder of the motor as the sensor.

1.2 Objective of the Project

The main core of this project is to design a speed control system of DC

Motor by using PWM technique generated through Arduino. This system

will be able to control the DC motor speed at desired speed regardless the

changes of load. We can implement a low cost acquisition system

intended for control applications using the Arduino prototyping platform.

Arduino has become a popular open source single-board microcontroller

among electronic hobbyists, and it is gaining acceptance as a quick

prototyping tool for engineering and educational projects also. The

system meets the following requirements:

Suitable for educational purpose

Low cost: The components are affordable.

Easy to assembly due to the constitution of the

modules.

Able to run on different platforms: the overall system

can operate in different operating systems.

Open hardware and open source: This means that the

hardware and the software used has a public access. Anyone

can use it and improve it.

Suitable for control applications

Bidirectional: It is possible for data to be transmitted in both

directions via USB serial communication.

Wired / Wireless connection

Autonomous or dependent system

1.3 Organisation of the Project

The present report is organized in ten chapters. In general, all of them can

be read independently as self-contained entities. In first chapter, it discuss

about the objective and scope of this project as well as its application.

While

Chapter 2 will discuss more on theory and literature reviews that have

been done.

Chapter 3 will discuss about how to measure speed of DC motor and

speed controlling technique that can be used to control the speed of the

motor.

In Chapter 4 and Chapter 5 the discussion will be on L293D motor

driver and Encoder respectively.

Chapter 6 and Chapter 7 present the details of IR Sensors and PWM.

Chapter 8 and Chapter 9 deals with Arduino UNO and its interfacing

with LabVIEW.

Chapter 10 gives the conclusion of this project and future work that can

be done based on this work.

CHAPTER – 2

THEORY

This chapter will discuss about theory portion. It will discuss about

various hardware and software components used in the project. It will

also introduce the need of automation and Arduino platform.

A computer, using a control application done in LabVIEW, controls all

the system by cable or wireless. This control application display all the

data obtained from the acquisition system, and save it into a file

document in order to obtain a history of the measures.

In this project various sensors like Infrared sensors are used and there

data is gathered using Arduino microcontroller, control action can also be

done simultaneously like DC motor control using Pulse Width

Modulation as demonstrated further. Simple block to demonstrate is

shown in Figure 2.1 LabVIEW-Arduino Interaction with physical world.

Figure 2.1 LabVIEW-Arduino Interaction with physical world

2.1 Automation of DC Electrical Machines

In today’s world of changing technologies and the advent of

newness and innovations automation plays a major role.

Automation is in everything we see in the world today.

Automation is also present in things which are used in the day to

day life.

Similarly automation is also present in the field of electrical

engineering especially machines. In the discussion considered in

the report the automation of electrical machines mainly refers to

the automation of DC electrical machines that is DC motor, DC

generator, or the set of a motor generator which are tightly coupled

together.

The automation of DC electrical machines includes a same kit for

every test to be performed on the machines but only changing the

programming part.

The change in the programming part is done using very open and

compatible software called the LabVIEW (version 7.1) software

The DC motor can be controlled by using Arduino board (which

measures the speed ) and LabVIEW (which controls the speed)

2.2 Need for Automation

Automation is the use of control systems and information technologies

reducing the need for human intervention. In the scope of

industrialization, automation is a step beyond mechanization. Then it

provides the applications of automation in industries such as

manufacturing, agricultural, health care, distribution and logistics, cold

storage, retail, field service, government. Automation (including robotics,

industrial automation and computer numerical control), is the use of

control systems such as computers to control industrial machinery and

processes, replacing human operators. And also mechanization provides

human operators with machinery to assist them with the physical

requirements of work; automation greatly reduces the need for human

sensory and mental requirements as well. At first glance, automation

might appear to devalue labour through its replacement with less-

expensive machines; however, the overall effect of this on the workforce

as a whole remains unclear.

Today automation of the workforce is quite advanced, and continues to

advance increasingly more rapidly throughout the world and is

encroaching on ever more skilled jobs, yet during the same period the

general well-being and quality of life of most people in the world (where

political factors have not muddied the picture) have improved

dramatically. Automation is also being implemented in the manufacturing

industries where combining the wireless local area network (WLAN)

enabled handheld computers, bar code and thermal printing technologies

with applications from market-leading are done.

Advanced Automation is also used to streamline the entire

manufacturing processes. By creating a more seamless flow of

continuous, accurate documentation on materials, parts or machine

conditions, one will experience fewer errors and improve production.

Advanced Automation can help one error-proof one’s operations to

deliver better products faster, reduce waste, control costs and improve

customer service.

Hence, because of all these recompenses it can be confirmed that there is

a dire need for automation in any application, phase or any industry.

2.3 Data Acquisition System (DAQ) using Arduino

Considering small scale applications where accuracy and high speed is

not so important, industrial scale DAQ’s with high price tag is not

necessary. But instead a low cost micro controller like Atmel 328

(Arduino Uno) is enough to meet the requirement.

DC motor control using Pulse Width Modulation (PWM) signifies the

controllability of the Arduino hardware and LabVIEW software.

Graphical User Interface created by the LabVIEW is extremely pleasing

and user friendly. Various controls like PID controllers, analog and

digital filters etc. can be incorporated in the advance versions (PID block

is available in LabVIEW control system palette)

The control signals are fed into L293D motor IC which requires the

power required by the motor to run , the cycle can be varied from 0-100%

by controlling the user controlled interactive graphical data even the

motor direction is controlled from the front panel of the programme by

the user pc integrated with the system

Because the Arduino can't handle more than 40ma of current, you must

have an external power source to power it. This circuit enables you to use

a motor that is too big for the Arduino to handle, control direction of the

motor with a relay, and control the speed of the motor with a

potentiometer.

2.4 Basic Overview

The main overview of our project can be well explained with the help of

the figure shown below-

Figure 2.2 Basic Overview

Our Project is divided into two parts:

a) HARDWARE

b) SOFTWARE

The hardware part consist of following parts-

DC MOTOR

L293D DC MOTOR DRIVER

ENCODER

IR SENSOR

ARDUINO BOARD (FOR PWM GENERATION)

The software part consist of-

LAPTOP WITH LABVIEW SOFTWARE INSTALLED

The main challenge of our project is creating an interface control system

for motor operations, from small-scale models to large industrial

applications. Now we will try to explain components and software that

has been used in our project in the following chapters.

2.5 About LabVIEW

Lab VIEW is a graphical programming environment used by millions of

engineers and scientists to develop sophisticated measurement, test, and

control systems using intuitive graphical icons and wires that resemble a

flowchart. It offers unrivalled integration with thousands of hardware

devices and provides hundreds of built-in libraries for advanced analysis

and data visualization – all for creating virtual instrumentation. The

LabVIEW platform is scalable across multiple targets and OSs, and, since

its introduction in 1986, it has become an industry leader. The

programming that is done in this Lab VIEW software is mainly Graphical

Programming that is Program with drag-and-drop, graphical function

blocks instead of writing lines of text. The representation is mainly

Dataflow Representation which is easily developed, maintain, and

understand code with an intuitive flowchart representation.

Lab VIEW is the centre piece of graphical system design and provides

engineers and scientists with the tools you need to create and deploy

measurement and control systems. We can get more done in less time

with LAB VIEW through its unique graphical programming environment;

built-in engineering-specific libraries of software functions and hardware

interfaces; and data analysis, visualization, and sharing features. We can

bring your vision to life with Lab VIEW. Through a world-class

ecosystem of partners and technology alliances, a global and active user

community, and consistent annual releases, you can have the confidence

to continually innovate. Lab VIEW makes complex control simple and

accessible.

Lab VIEW makes me better because code reuse saves time and effort

because one of the most efficient ways to shorten development time is

through code reuse. By taking advantage of existing code, whether it has

already been written or is part of a resource library, developers and

domain experts can focus on their applications rather than committing

valuable time and resources to programming. Lab VIEW is an ideal

platform for prototyping, designing, and deploying high-quality products

to market fast. We can use one development environment to quickly

iterate on your embedded hardware and software designs and then reuse

the best parts in a final product.

Lab VIEW removes the need to abstract those into procedural code. Our

whiteboard diagram becomes your code. Also, we have all of the

functions at your fingertips to easily deal with the complex web of

sensors, multiple-linked actuators, and dynamic real-time control.

LabVIEW reduces the time to test these products by helping you develop

a flexible and efficient system that synchronizes multiple measurements

and analysis within your software. This results in faster inspection times

across I/O. The Lab VIEW development environment provides the ability

to build programs graphically by using intuitive icons and wires that

resemble a flowchart. Because Lab VIEW requires us to base the

structure of the program around the flow of data, we are encouraged to

think in terms of the problem you need to solve as well as conceptualize

our application in a parallel view and not sequential.

CHAPTER – 3

DC MOTOR

The input is electrical energy (from the supply source), and the output is

mechanical energy (to the load).

DC motors consist of one set of coils, called armature winding, inside

another set of coils or a set of permanent magnets, called the stator.

Applying a voltage to the coils produces a torque in the armature,

resulting in motion.

3.1 Constructional Features

A DC motor relies on the fact that like magnet poles repels and unlike

magnetic poles attracts each other. A coil of wire with a current running

through it generates a electromagnetic field aligned with the centre of the

coil. By switching the current on or off in a coil its magnet field can be

switched on or off or by switching the direction of the current in the coil

the direction of the generated magnetic field can be switched 180°.

A simple DC motor typically has a stationary set of magnets in the stator

and an armature with a series of two or more windings of wire wrapped in

insulated stack slots around iron pole pieces (called stack teeth) with the

ends of the wires terminating on a commutator. The armature includes the

mounting bearings that keep it in the centre of the motor and the power

shaft of the motor and the commutator connections. The winding in the

armature continues to loop all the way around the armature and uses

either single or parallel conductors (wires), and can circle several times

around the stack teeth. The total amount of current sent to the coil, the

coil's size and what it's wrapped around dictate the strength of the

electromagnetic field created.

The sequence of turning a particular coil on or off dictates what direction

the effective electromagnetic fields are pointed. By turning on and off

coils in sequence a rotating magnetic field can be created. These rotating

magnetic fields interact with the magnetic fields of the magnets

(permanent or electromagnets) in the stationary part of the motor (stator)

to create a force on the armature which causes it to rotate. In some DC

motor designs the stator fields use electromagnets to create their magnetic

fields which allow greater control over the motor. At high power levels,

DC motors are almost always cooled using forced air.

Figure 3.1 DC Motor

3.2 Basic principle of operation

If electrical energy is supplied to a conductor lying perpendicular to a

magnetic field, the interaction of current flowing in the conductor and the

magnetic field will produce mechanical force (and therefore, mechanical

energy).

3.3 Commutation Action

The commutator allows each armature coil to be activated in turn. The

current in the coil is typically supplied via two brushes that make moving

contact with the commutator. Now, some brushless DC motors have

electronics that switch the DC current to each coil on and off and have no

brushes to wear out or create sparks.

Different number of stator and armature fields as well as how they are

connected provide different inherent speed/torque regulation

characteristics. The speed of a DC motor can be controlled by changing

the voltage applied to the armature. The introduction of variable

resistance in the armature circuit or field circuit allowed speed control.

Modern DC motors are often controlled by power electronics systems

which adjust the voltage by "chopping" the DC current into on and off

cycles which have an effective lower voltage.

Since the series-wound DC motor develops its highest torque at low

speed, it is often used in traction applications such as electric

locomotives, and trams. The DC motor was the mainstay of electric

traction drives on both electric and diesel-electric locomotives, street-

cars/trams and diesel electric drilling rigs for many years. The

introduction of DC motors and an electrical grid system to run machinery

starting in the 1870s started a new second Industrial Revolution. DC

motors can operate directly from rechargeable batteries, providing the

motive power for the first electric vehicles and today's hybrid cars and

electric cars as well as driving a host of cordless tools. Today DC motors

are still found in applications as small as toys and disk drives, or in large

sizes to operate steel rolling mills and paper machines.

If external power is applied to a DC motor it acts as a DC generator, a

dynamo. This feature is used to slow down and recharge batteries on

hybrid car and electric cars or to return electricity back to the electric grid

used on a street car or electric powered train line when they slow down.

This process is called regenerative braking on hybrid and electric cars. In

diesel electric locomotives they also use their DC motors as generators to

slow down but dissipate the energy in resistor stacks. Newer designs are

adding large battery packs to recapture some of this energy.

Figure 3.2

The above figure shows the workings of a brushed electric motor with a

two-pole rotor (armature) and permanent magnet stator. "N" and "S"

designate polarities on the inside face of the magnets; the outside faces

have opposite polarities. The + and -signs show where the DC current is

applied to the commutator which supplies current to the armature coils.

Figure 3.3

3.4 Speed Measurement of DC Motor

To start with this project, we need a device that will measure the speed of

the motor shaft. There are several methods which can use to measure the

speed of motor. Here, we will only discuss about speed measurement by

using tachometer and encoder.

3.4.1 Speed Measurement of DC Motor using Tachometer

Tachometer is an instrument that measure speed motor based on concept

of back EMF induced in motor when it is running. The EMF is voltages

appear on the commutator segments caused by rotated in the magnetic

field by some external force.

The magnitude of the EMF is given by [3.1],

EMF = KE φ N [3.1]

Where, KE = a constant based on motor construction

φ = magnetic flux

N = speed of motor (in rpm)

The actual relationship between motor speed and EMF follows and is

derived from Equation [3.2],

N= EMF/ KE φ [3.2]

Thus, the motor speed is directly proportional to the EMF voltage ad

inversely proportional to the field flux. For permanent magnet DC motor,

when the EMF measured is increases, the speed of the motor is also

increases with the gain. So, the speed of motor can be measured by

measuring the back EMF using tachometer.

3.4.2 Speed Measurement of DC Motor using Encoder

The best way to measure speed is to fit an optical encoder. This shines a

beam of light from a transmitter across a small space and detects it with a

receiver the other end. If a disc is placed in the space, which has slots cut

into it, then the signal will only be picked up when a slot is between the

transmitter and receiver. As shown in below figure a a disk with number

of slot is placed between a photo transmitter like Infrared LED and photo

detector like photodiode or phototransistor.

The output of photo detector is then given to squaring circuit. This will

have an output which swings to +5v when the light is blocked, and about

0.5 volts when light is allowed to pass through the slots in the disc.

Figure 3.4 Encoder Wheel

The frequency of the output waveform is given by,

= (N * Rpm)/ 60 [3.3]

Where, = frequency of output waveform

Rpm = speed in revolutions per minutes

N = number of slots at disc

So, from Equation 3.3, the speed of DC motor in rpm is given by,

Rpm = * 60 / N [3.4]

3.5 Speed Controlling of DC Motor

For precise speed control of servo system, closed-loop control is

normally used. The speed, which is sensed by analog sensing

devices (e.g., tachometer), is compared with the reference speed

to generate the error signal and to vary the armature voltage of

the motor. There are several controllers that can used to control

the speed of the motor such as by using thyristor, phase-locked-

loop control, chopper circuit, Fuzzy Logic Controller, PWM

technique and etc. Here Speed Control through PWM technique

is discussed.

3.5.1 Speed Control of DC motor using PWM technique

Figure 3.5 Simple Motor Circuit

Let us consider a simple circuit that connects a battery as power supply

through a switch MOSFET (Metal-Oxide-Semiconductor Field Effect

Transistor) as shown in Figure 3.5. When the switch is closed, the motor

sees 12 Volts, and when it is open it sees 0 Volts. If the switch is open for

the same amount of time as it is closed, the motor will see an average of 6

Volts, and will run more slowly accordingly.

This on-off switching is performed by power MOSFETs. A MOSFET

(Metal-Oxide-Semiconductor Field Effect Transistor) is a device that can

turn very large currents on and off under the control of a low signal level

voltage.

The average of voltage that supply to DC motor is given by,

= ( /T ) * [3.5]

Where, = average voltage supply to DC motor

= time ON of switches

T = period of PWM

( /T ) = DC, duty cycle

Figure 3.6 PWM signal and average voltage

As the amount of time that the voltage is on increases compared with the

amount of time that it is off, the average speed of the motor increases and

vice versa.

The time that it takes a motor to speed up and slow down under switching

conditions is depends on the inertia of the rotor (basically how heavy it

is), and how much friction and load torque there is.

If the supply voltage is switched fast enough, it won’t have time to

change speed much, and the speed will be quite steady. This is the

principle of switch mode speed control.

Thus the speed is set by PWM – Pulse Width Modulation.

CHAPTER – 4

L293D MOTOR DRIVER

Now we will discuss the dc motor driver L293D which is basically

driving the dc motor either in clockwise direction or anticlockwise

direction according to the logics which had been provided by the

microcontroller connected to that driver.

Generally, even the simplest robot requires a motor to rotate a wheel or

performs particular action. Since motors require more current then the

microcontroller pin can typically generate, you need some type of a

switch (Transistors, MOSFET, Relay etc.,) which can accept a small

current, amplify it and generate a larger current, which further drives a

motor. This entire process is done by what is known as a motor driver.

Figure 4.1

Motor driver is basically a current amplifier which takes a low-current

signal from the microcontroller and gives out a proportionally higher

current signal which can control and drive a motor. In most cases, a

transistor can act as a switch and perform this task which drives the motor

in a single direction.

Turning a motor ON and OFF requires only one switch to control a single

motor in a single direction. What if we want your motor to reverse its

direction? The simple answer is to reverse its polarity. This can be

achieved by using four switches that are arranged in an intelligent manner

such that the circuit not only drives the motor, but also controls its

direction. Out of many, one of the most common and clever design is a

H-bridge circuit where transistors are arranged in a shape that resembles

the English alphabet "H”.

4.1 H-Bridge Circuit

Figure 4.2 H-Bridge Circuit

As we can see in the image, the circuit has four switches A, B, C and D.

Turning these switches ON and OFF can drive a motor in different ways.

1. Turning on Switches A and D makes the motor rotate clockwise

2. Turning on Switches B and C makes the motor rotate anticlockwise

3. Turning on Switches A and B will stop the motor (Brakes)

4. Turning off all the switches gives the motor a free wheel drive

5. Lastly turning on A & C at the same time or B & D at the same

time shorts your entire circuit. So, do not attempt this.

An H-bridge motor driver IC is used to control the motor. L293D is a 16-

bit IC, with 2-channel motor control or in other words, we can control

and move two motors using this IC both in clockwise and anti-clockwise

direction. Each channel has a separate enable pin, 2 input pins, 2 ground

pins, and 2 output pins.

We will use only one channel. There is one supply voltage pin and a logic

reference voltage pin. Output-1 and output-2 will be plugged to positive

and negative terminal of the DC motor.

Figure 4.3 L293D Driver IC

H-bridges can be built from scratch using relays, MOSFETs, field effect

transistors (FET), bi-polar junction transistors (BJT), etc. But if our

current requirement is not too high and all we need is a single package

which does the job of driving a small DC motor in two directions, then all

we need is a L293D IC. This single inexpensive package can interface not

one, but two DC motors. L293, L293B and few other versions also does

the same job, but pick the L293D version as this one has an inbuilt fly

back diode which protects the driving transistors from voltage spikes that

occur when the motor coil is turned off.

The L293 and L293D are quadruple high-current half-H drivers. The

L293 is designed to provide bidirectional drive currents of up to 1 A at

voltages from 4.5 V to 36 V. The L293D is designed to provide

bidirectional drive currents of up to 600-mA at voltages from 4.5 V to 36

V. Both devices are designed to drive inductive loads such as relays,

solenoids, dc and bipolar stepping motors, as well as other high-

current/high-voltage loads in positive-supply applications.

All inputs are TTL compatible. Each output is a complete totem-pole

drive circuit, with a Darlington transistor sink and a pseudo-Darlington

source. Drivers are enabled in pairs, with drivers 1 and 2 enabled by

1,2EN and drivers 3 and 4 enabled by 3,4EN.When an enable input is

high, the associated drivers are enabled and their outputs are active and in

phase with their inputs. When the enable input is low, those drivers are

disabled and their outputs are off and in the high-impedance state. With

the proper data inputs, each pair of drivers forms a full-H (or bridge)

reversible drive suitable for solenoid or motor applications. On the L293,

external high-speed output clamp diodes should be used for inductive

transient suppression. A VCC1 terminal, separate from VCC2, is

provided for the logic inputs to minimize device power dissipation.

The L293and L293D is characterized for operation from 0°C to 70°C.

4.2 Pin Configuration of L293D DC Motor Driver

Figure 4.4 Pin Diagram

4.3 Pin Description

Enable pins: These are pin no. 1 and pin no. 9. Pin no. 1 is used

to enable Half-H driver 1 and 2 (H bridge on Left side). Pin no. 9 is

used to enable H-bridge driver 3and 4. (H Bridge on right side).

The concept is simple, if you want to use a particular H bridge you

have to give a high logic to corresponding enable pins along with

the power supply to the IC. This pin can also be used to control

speed of the motor using PWM technique.

VCC1 (Pin 16): Power supply pin. Connect it to 5V supply.

VCC2 (Pin 8): Power supply for motor. Apply +ve voltage to it

as per motor rating. If you want to drive your motor at 12V, apply

12V on this pin. It is also possible to drive motor directly on a

battery, other than the one used for supplying power to the circuit,

just connect +ve terminal of that battery to VCC2 pin and make

GND of both the batteries common. (MAX voltage at this pin is

36V).

GND (Pins 4, 5, 12, 13): Connect them to common GND of

circuit.

Inputs (Pins 2, 7, 10, 15): These are input pins through which

control signals are given by microcontrollers or other circuits/ICs.

For example, if on pin 2 (Input of 1st half H driver) we give Logic

1 (5V), we will get a voltage equal to VCC2 on corresponding

output pin of 1st half H driver i.e. pin no. 3. Similarly for Logic 0

(0V) on Pin 2, 0V on Pin 3 appears.

Outputs (Pin 3, 6, 11, 14): Outputs pins. According to input

signal output signal comes.

4.4 L293D Driver Circuit

Figure 4.5 Driver Circuit

OPERATION OF L293d DC MOTOR DRIVER:

CLOCKWISE ROTATION :

INPUT 2 is made low and a PWM signal is generated on INPUT 1 pin.

ANTICLOCKWISE DIRECTION :

INPUT 2 is made high and a PWM is generated on INPUT1 PIN.

There are 2 enable pins on L293dD IC : Pin 1 and pin 9 for being able to

drive the motor. It is like a switch.

For driving the motor with left H-bridge we need to enable pin 1 high and

for right H-bridge you need to make pin 9 high.

Pin 16,Vcc-5 volts supply, for pin 1 and 2 to make them high.

4.5 L293D Logic Table

Let a motor is connected on left side output pins (pin 3, 6)

For rotating the motor in clockwise direction the input pins has to be

provided with logic 1angd logic 0

• Pin 2=logic1 and Pin 7=logic 0 (clockwise direction).

• Pin 2=logic0 and Pin 7=logic 1(anticlockwise direction).

• Pin 2=logic0 and Pin 7=logic 0 (idle).

• Pin 2=logic1 and Pin 7=logic 1 (idle).

Vcc=5 volts for its internal operation.

Vss (V) supply=9 volts.

The maximum Vss motor supply = 36 volts.

Maximum current=600 mA (0.6 amperes).

1A 2A 1Y 2Y Motor 1

Logic 0 Logic 0 0 0 Stop

Logic 1 Logic 0 12 V 0 Clockwise

Logic 0 Logic 1 0 12 V Anticlockwise

Logic 1 Logic 1 12 V 12 V Brake

Table 4.1 Logic Table

This is how the device driver L293D device driver works and how we

have connected the device driver is explained in this chapter in detail.

This driver is also very helpful in our project and it basically provides the

platform that how the speed of dc motor can be controlled in a very

simple way.

CHAPTER – 5

ENCODER

5.1 What is encoder?

An encoder is a device which converts a mechanical information of a

shaft or position into an electrical signal

Figure 5.1

5.2 How is this accomplished?

As the code disc rotates, it shutters light from the LED and is received

and transmitted as square\sine waveforms

Figure 5.2

4.3 Types of Encoder

Rotary

Linear

Now let’s see the difference between them-

ROTARY LINEAR

Convert angular position into Analog or

Digital signal

Convert linear movement to Analog or

Digital signal

Encodes for rotary motion and measuring

angle, speed or velocity

Encodes for measuring distance travelled,

positioning, location.

Table 5.1 Difference between Rotary and Linear Encoder

A shafted rotary encoder is built so that the rotor portion of the encoder is

a short shaft that is usually attached through a flexible coupling to the

shafts of various motion control equipment. The body of the shafted

rotary encoder is commonly fixed by a rigid mounting bracket.

Rotary encoders are used in many applications that require precise shaft

unlimited rotation—including industrial controls, robotics, special

purpose photographic lenses, computer input devices (such as optic

mechanical mice and trackballs), controlled stress rheometers, and

rotating radar platforms.

Figure 5.3

Rotary Encoders are basically of two types

Absolute, and

Incremental (relative).

The output of absolute encoders indicates the current position of the shaft,

making them angle transducers. The output of incremental encoders

provides information about the motion of the shaft, which is typically

further processed elsewhere into information such as speed, distance, and

position.

4.4 Absolute Rotary Encoder

An "absolute" encoder maintains position information when power is

removed from the system. The position of the encoder is available

immediately on applying power. The relationship between the encoder

value and the physical position of the controlled machinery is set at

assembly; the system does not need to return to a calibration point to

maintain position accuracy.

An absolute encoder has multiple code rings with various binary

weightings which provide a data word representing the absolute position

of the encoder within one revolution. This type of encoder is often

referred to as a parallel absolute encoder.

4.4.1 Construction

Digital absolute encoders produce a unique digital code for each distinct

angle of the shaft. They come in two basic types: optical and mechanical

Mechanical absolute encoders: A metal disc containing a set of

concentric rings of openings is fixed to an insulating disc, which is rigidly

fixed to the shaft. A row of sliding contacts is fixed to a stationary object

so that each contact wipes against the metal disc at a different distance

from the shaft. As the disc rotates with the shaft, some of the contacts

touch metal, while others fall in the gaps where the metal has been cut

out. The metal sheet is connected to a source of electric current, and each

contact is connected to a separate electrical sensor. The metal pattern is

designed so that each possible position of the axle creates a unique binary

code in which some of the contacts are connected to the current source

(i.e. switched on) and others are not (i.e. switched off).

Because brush-type contacts are susceptible to wear, encoders using

contacts are not common; they can be found in low-speed applications

such as manual volume or tuning controls in a radio receiver.

Optical absolute encoders : The optical encoder's disc is made of glass

or plastic with transparent and opaque areas. A light source and photo

detector array reads the optical pattern that results from the disc's

position at any one time.This code can be read by a controlling device,

such as a microprocessor or microcontroller to determine the angle of the

shaft.

The absolute analog type produces a unique dual analog code that can be

translated into an absolute angle of the shaft.

4.5 Incremental Rotary Encoder

An incremental rotary encoder provides cyclical outputs (only) when the

encoder is rotated. They can be either mechanical or optical. The

mechanical type requires debouncing and is typically used as digital

potentiometers on equipment including consumer devices. Most modern

home and car stereos use mechanical rotary encoders for volume control.

Due to the fact the mechanical switches require debouncing, the

mechanical type are limited in the rotational speeds they can handle. The

incremental rotary encoder is the most widely used of all rotary encoders

due to its low cost and ability to provide signals that can be easily

interpreted to provide motion related information such as velocity.

The fact that incremental encoders use only two sensors does not

compromise their accuracy. One can find in the market incremental

encoders with up to 10,000 counts per revolution, or more.

There can be an optional third output: reference or "index", which

happens once every turn. This is used when there is the need of an

absolute reference, such as positioning systems. The index output is

usually labelled Z.

The optical type is used when higher speeds are encountered or a higher

degree of precision is required.

Incremental encoders are used to track motion and can be used to

determine position and velocity. This can be either linear or rotary

motion. Because the direction can be determined, very accurate

measurements can be made.

Figure 5.4 Incremental Encoder

4.6 DC Motor with Encoder

Figure 5.5

We are using a dc motor on which encoder is mounted and the

connections are made by connecting the wires to the Arduino board.

Colour of wire Function

Brown Motor power

(connected to one

Motor Terminal)

Blue Motor power

(connected to other

Motor Terminal)

Green Encoder ground

Black Encoder Vcc (5 volts)

Red Encoder A output

Purple Encoder B output

Table 5.2 Wire Functions

CHAPTER – 6

INFRARED SENSORS

6.1 Introduction

An infrared sensor is an electronic instrument that is used

to sense certain characteristics of its surroundings by either

emitting and/or detecting infrared radiation. It is also

capable of measuring heat of an object and detecting

motion. Infrared waves are not visible to the human eye.

In the electromagnetic spectrum, infrared radiation is the

region having wavelengths longer than visible light

wavelengths, but shorter than microwaves. The infrared

region is approximately demarcated from 0.75 to 1000µm.

The wavelength region from 0.75 to 3µm is termed as

near infrared, the region from 3 to 6µm is termed mid-

infrared, and the region higher than 6µm is termed as far

infrared.

Infrared technology is found in many of our everyday

products. For example, TV has an IR detector for

interpreting the signal from the remote control. Key

benefits of infrared sensors include low power

requirements, simple circuitry, and their portable feature.

A wheel speed sensor used with an IR sensor is a type of

tachometer which measures speed with the help of optical

properties. It is a sender device used for reading the speed

of a vehicle's wheel rotation this wheel is embedded over

the shaft of motor and an aluminium strip is places over its

outer surface and when the wheel rotates then the IR

sensor senses the light emitted from this strip and counts

the number of pulses which is nothing but the speed of

motor.

6.2 Types of Infra-Red Sensors

Infra-red sensors are broadly classified into two types:

Thermal infrared sensors – These use infrared energy as heat.

Their photo sensitivity is independent of wavelength. Thermal

detectors do not require cooling; however, they have slow response

times and low detection capability. They have been used

extensively for sensing and detecting purpose.

Figure 6.1 Thermal Infrared Sensor

Quantum infrared sensors – These provide higher detection

performance and faster response speed. Their photo sensitivity is

dependent on wavelength. Quantum detectors have to be cooled so

as to obtain accurate measurements. The only exception is for

detectors that are used in the near infrared region. These sensors

are mainly used for speed detection and control.

6.3 Working Principle

A typical system for detecting infrared radiation using infrared

sensors includes the infrared source such as blackbody radiators,

tungsten lamps, and silicon carbide. In case of active IR sensors,

the sources are infrared lasers and LEDs of specific IR wavelength

Next is the transmission medium used for infrared transmission,

which includes vacuum, the atmosphere, and optical fibers.

Figure 6.2 Basic Design of IR Sensor

Thirdly, optical components such as optical lenses made from

quartz, CaF2, Ge and Si, polyethylene Fresnel lenses, and Al or Au

mirrors, are used to converge or focus infrared radiation.

Likewise, to limit spectral response, band-pass filters are ideal.

Finally, the infrared detector completes the system for detecting

infrared radiation. The output from the detector is usually very

small, and hence pre-amplifiers coupled with circuitry are added

to further process the received signals.

6.4 Applications

The following are the key application areas of infrared sensors:

Tracking and art history

Climatology, meteorology, and astronomy

Thermography, communications, and alcohol testing

Heating, hyper spectral imaging, and night vision

Biological systems, photo bio modulation, and plant health

Gas detectors/gas leak detection

Water and steel analysis, flame detection

Anaesthesiology testing and spectroscopy

Petroleum exploration and underground solution

CHAPTER – 7

PULSE WIDTH MODULATION

Pulse Width Modulation, or PWM, is a technique for getting analog

results with digital means. Digital control is used to create a square wave,

a signal switched between on and off. This on-off pattern can simulate

voltages in between full on (5 Volts) and off (0 Volts) by changing the

portion of the time the signal spends on versus the time that the signal

spends off. The duration of "on time" is called the pulse width. To get

varying analog values, we change, or modulate, that pulse width. If we

repeat this on-off pattern fast enough with an LED for example, the result

is as if the signal is a steady voltage between 0 and 5v controlling the

brightness of the LED.

PWM has several uses:

Dimming an LED

Providing an analog output; if the digital output is filtered,

It will provide an analog voltage between 0% and 100%.

Generating audio signals.

Providing variable speed control for motors.

Generating a modulated signal, for example to drive an infrared

LED for a remote control.

Figure 7.1 PWM Generation

7.1 Principle

Pulse-width modulation uses a rectangular pulse wave whose pulse width

is modulated resulting in the variation of the average value of the

waveform. If we consider a pulse waveform f(t), with period T, low value

y_{min}, a high value y_{max} and a duty cycle D, the average value of

the waveform is given by:

∫ ( )

As f(t) is a pulse wave, its value is y_{max} for 0<t<D. T and y_{min}

for D.T <t<T. The above expression then becomes:

(∫

∫

)

= ( )

= + (1 - D)

This latter expression can be fairly simplified in many cases where

y_{min}=0 as =D. y_{max}. From this, it is obvious that the average

value of the signal ( ) is directly dependent on the duty cycle D.

A simple method to generate the PWM pulse train corresponding to a

given signal is the intersective PWM: the signal (sine wave) is compared

with a saw tooth waveform. When the latter is less than the former, the

PWM signal (magenta) is in high state (1). Otherwise it is in the low state

(0). When the value of the reference signal is more than the modulation

waveform, the PWM signal (magenta) is in the high state, otherwise it is

in the low state.

7.2 Applications of PWM :

Telecommunications: In telecommunications, PWM is a form of

signal modulation where the widths of the pulses correspond to

specific data values encoded at one end and decoded at the other.

Pulses of various lengths (the information itself) will be sent at

regular intervals (the carrier frequency of the modulation).

Figure 7.2

Voltage regulation: PWM is also used in efficient voltage

regulators. By switching voltage to the load with the appropriate

duty cycle, the output will approximate a voltage at the desired

level. The switching noise is usually filtered with an inductor and a

capacitor.

One method measures the output voltage. When it is lower than the

desired voltage, it turns on the switch. When the output voltage is

above the desired voltage, it turns off the switch.

Audio effects and amplification: PWM is sometimes used in

sound (music) synthesis, in particular subtractive synthesis, as it

gives a sound effect similar to chorus or slightly detuned oscillators

played together. (In fact, PWM is equivalent to the difference of

two saw tooth waves with one of them inverted.) The ratio between

the high and low level is typically modulated with a low frequency

oscillator. In addition, varying the duty cycle of a pulse waveform

in a subtractive-synthesis instrument creates useful tumbrel

variations. Some synthesizers have a duty-cycle trimmer for their

square-wave outputs, and that trimmer can be set by ear; the 50%

point (true square wave) was distinctive, because even-numbered

harmonics essentially disappear at 50%. Pulse waves, usually 50%,

25%, and 12.5%, make up the soundtracks of classic video games.

A new class of audio amplifiers based on the PWM principle is

becoming popular. Called "Class-D amplifiers", they produce a

PWM equivalent of the analog input signal which is fed to the

loudspeaker via a suitable filter network to block the carrier and

recover the original audio. These amplifiers are characterized by

very good efficiency figures (≥ 90%) and compact size/light weight

for large power outputs. For a few decades, industrial and military

PWM amplifiers have been in common use, often for driving servo

motors. Field-gradient coils in MRI machines are driven by

relatively high-power PWM amplifiers.

Electrical: SPWM (Sine–triangle pulse width modulation) signals

are used in micro-inverter design (used in solar or wind power

applications). These switching signals are fed to the FETs that are

used in the device. The device's efficiency depends on the

harmonic content of the PWM signal. There is much research on

eliminating unwanted harmonics and improving the fundamental

strength, some of which involves using a modified carrier signal

instead of a classic saw tooth signal in order to decrease power

losses and improve efficiency. Another common application is in

robotics where PWM signals are used to control the speed of the

robot by controlling the motors.

7.3 Modes of Operation

The different modes of operation are given as following :

Normal mode

Clear timer on compare(CTC) match mode

Phase correct PWM mode

Fast PWM mode

7.3.1 Normal Mode

The simplest mode of operation is the Normal mode (WGM01:0).In this

mode the counting direction is always up(incrementing),and no counter

clear is performed. The counter simply overruns when it passes its

maximum bit value(TOP=0xFF) and then restarts from the

bottom(0x00).In normal operation the timer/Counter Overflow

Flag(TOV0) will be set in the same timer clock cycle as the TCNT0

becomes zero. The TOV0 Flag in the case behaves like a ninth bit, except

that it is only set, not cleared. However, combined with the Timer

Overflow interrupt that automatically clears the TOv0 flag, the timer

resolution can be increased by software. The output compare unit can be

used to generate interrupts at some given time. Using the output compare

to generate waveforms in Normal mode is not recommended, since this

will occupy too much of the CPU time.

7.3.2 CTC Mode

In Clear Timer on compare or CTC mode (WGM01:0=2), the OCRO

register is used to manipulate the counter resolution. In CTC mode the

counter is cleared to zero when the counter value(TCNT0) matches the

OCR0.The ORC0 defines the top value for the counter, hence also its

resolution. This mode allows greater control of the Compare Match

output frequency. It also simplifies the operation of counting external

events. The counter value (TCNT0) increases until a Compare Match

occurs between TCNT0 and OCR0 and then counter (TCNT0) is cleared.

An interrupt can be generated each time the counter value reaches the

TOP value by using the OCF0 flag. If the interrupt is enabled, the

interrupt handler routine can be used for updating the TOP value.

However, changing TOP to a value close to BOTTOM when the counter

is running with none or a low presale value must be done with care since

the CTC modes does not have the double buffering feature. If the new

value written to ORC0 is lower than the current value of TCNT0, the

counter will miss the Compare Match. The counter will then have to

count to its maximum value (0xFF) and wrap around starting at 0x00

before the Compare Match can occur. For generating a waveform output

in CTC mode, the OC0 output can be set to toggle its logical level on

each Compare Match by setting the Compare Output mode bits to toggle

mode(COM01:0=1).The OC0 value will not be visible on the port pin

unless the data direction for the pin is set to output. The waveform

generated will have maximum frequency of fOC0=f_I/O/2 when OCR0 is

set to zero (0x00).

7.3.3 Fast PWM Mode

The fast PWM mode provides high frequency PWM wave for generation

options. The fast PWM differs from other PWM options by its single

slope operation. The counter counts from BOTTOM to maximum the

starts from bottom .In non-inverting compare output mode; the output

compare (OC0) is cleared on the compare match between TCNT0 and

OCR0, and set at BOTTOM.

In inverting compare output mode, the output is set on compare match

and cleared at BOTTOM. Due to single slope operation, the operating

frequency of fast PWM can be twice as high as phase correct PWM mode

that uses dual slope operation. This high frequency makes the fast PWM

well suited for power regulation, rectification and DAQ applications.

High frequency allows physically small sized external components (coils,

capacitors), and therefore reduces total system cost. In fast PWM mode,

the counter is incremented until the counter value matches the MAX

value. The counter is then cleared at the following timer clock cycle.

The Timer/Counter overflow flag(TOV0) is set each time the counter

reaches MAX. If the interrupt enabled, the interrupt handler routine can

be used for updating the compare value. In fast PWM mode, the compare

unit allows generation of PWM waveforms on the OC0 pin. Setting the

COM01:0 bits to two will produce a non-inverted PWM and an inverted

PWM output can be generated by setting the COM01:0 to three. The

actual OC0 value only be visible on the port pin is set as output. The

PWM waveform is generated by setting (or clearing) the OC0 register at

the Compare Match between OCR0 and TCNT0 and clearing (or setting)

the OC0 Register at the timer clock cycle the counter is cleared (changes

from MAX to BOTTOM.

7.3.4 Phase Correct PWM

The phase correct PWM mode (WGM01:0) provides a high resolution

phase correct PWM waveform generation option. The phase correct

PWM mode is based on a dual slope operation. The counter counts

repeatedly from BOTTOM to MAX and then from MAX to BOTTOM.

In non-inverting Compare output mode, the output compare (OC0) is

cleared on the compare match between TCNT0 and OCR0 while up-

counting, and set on the compare match while down-counting. In

inverting Output compare mode, the operation is inverted. The dual slope

operation has lower maximum operation frequency than single slope

operation. However, due to the symmetric feature of the dual-slope PWM

modes, these modes are preferred for motor control applications.

CHAPTER – 8

ARDUINO UNO

The Arduino Uno is a microcontroller board based on the ATmega328. It

has 14 digital input/output pins (of which 6 can be used as PWM

outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB

connection, a power jack, an ICSP header, and a reset button. It contains

everything needed to support the microcontroller; simply connect it to a

computer with a USB cable or power it with a AC-to-DC adapter or

battery to get started.

The Uno differs from all preceding boards in that it does not use the FTDI

USB-to-serial driver chip. Instead, it features the Atmega16U2

(Atmega8U2 up to version R2) programmed as a USB-to-serial converter.

"Uno" means one in Italian and is named to mark the upcoming release

of Arduino 1.0. The Uno and version 1.0 will be the reference versions of

Arduino, moving forward. The Uno is the latest in a series of USB

Arduino boards.

Figure 8.1 Arduino Uno R3 Front Side

8.1 Summary

Microcontroller ATmega328

Operating Voltage 5V

Input Voltage

(recommended)

7-12V

Input Voltage (limits) 6-20V

Digital I/O Pins 14 (of which 6 provide PWM output)

Analog Input Pins 6

DC Current per I/O Pin 40 mA

DC Current for 3.3V Pin 50 mA

Flash Memory 32 KB (ATmega328) of which 0.5 KB used by boot loader

SRAM 2 KB (ATmega328)

EEPROM 1 KB (ATmega328)

Clock Speed 16 MHz

8.2 Power

The Arduino Uno can be powered via the USB connection or with an

external power supply. The power source is selected automatically.

External (non-USB) power can come either from an AC-to-DC adapter

(wall-wart) or battery. The adapter can be connected by plugging a

2.1mm center-positive plug into the board's power jack. Leads from a

battery can be inserted in the Gnd and Vin pin headers of the POWER

connector.

The board can operate on an external supply of 6 to 20 volts. If supplied

with less than 7V, however, the 5V pin may supply less than five volts

and the board may be unstable. If using more than 12V, the voltage

regulator may overheat and damage the board. The recommended range is

7 to 12 volts.

The power pins are as follows:

VIN - The input voltage to the Arduino board when it's using an

external power source (as opposed to 5 volts from the USB

connection or other regulated power source). You can supply

voltage through this pin, or, if supplying voltage via the power

jack, access it through this pin.

5V - This pin outputs a regulated 5V from the regulator on the

board. The board can be supplied with power either from the DC

power jack (7 - 12V), the USB connector (5V), or the VIN pin of

the board (7-12V). Supplying voltage via the 5V or 3.3V pins

bypasses the regulator, and can damage your board. We don't

advise it.

3V3 - A 3.3 volt supply generated by the on-board regulator.

Maximum current draw is 50 mA.

GND - Ground pins.

IOREF - This pin on the Arduino board provides the voltage

reference with which the microcontroller operates. A properly

configured shield can read the IOREF pin voltage and select the

appropriate power source or enable voltage translators on the

outputs for working with the 5V or 3.3V.

8.3 Memory

The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also

has 2 KB of SRAM and 1 KB of EEPROM (which can be read and

written with the EEPROM library).

8.4 Input and Output

Each of the 14 digital pins on the Uno can be used as an input or output,

using pinMode(), digitalWrite(), and digitalRead() functions. They

operate at 5 volts. Each pin can provide or receive a maximum of 40 mA

and has an internal pull-up resistor (disconnected by default) of 20-50

kohms. In addition, some pins have specialized functions:

Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX)

TTL serial data. These pins are connected to the corresponding

pins of the ATmega8U2 USB-to-TTL Serial chip.

External Interrupts: 2 and 3. These pins can be configured to

trigger an interrupt on a low value, a rising or falling edge, or a

change in value.

PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the

analogWrite() function.

SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins

support SPI communication using the SPI library.

LED: 13. There is a built-in LED connected to digital pin 13.

When the pin is HIGH value, the LED is on, when the pin is LOW,

it's off.

The Uno has 6 analog inputs, labelled A0 through A5, each of which

provide 10 bits of resolution (i.e. 1024 different values). By default they

measure from ground to 5 volts, though is it possible to change the upper

end of their range using the AREF pin and the analogReference()

function. Additionally, some pins have specialized functionality:

TWI: A4 or SDA pin and A5 or SCL pin. Support TWI

communication using the Wire library.

There are a couple of other pins on the board:

AREF: Reference voltage for the analog inputs. Used with

analogReference().

Reset: Bring this line LOW to reset the microcontroller. Typically

used to add a reset button to shields which block the one on the

board.

8.5 Communication

The Arduino Uno has a number of facilities for communicating with a

computer, another Arduino, or other microcontrollers. The ATmega328

provides UART TTL (5V) serial communication, which is available on

digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the board channels

this serial communication over USB and appears as a virtual com port to

software on the computer. The '16U2 firmware uses the standard USB

COM drivers, and no external driver is needed. However, on Windows, a

.inf file is required. The Arduino software includes a serial monitor which

allows simple textual data to be sent to and from the Arduino board. The

RX and TX LEDs on the board will flash when data is being transmitted

via the USB-to-serial chip and USB connection to the computer (but not

for serial communication on pins 0 and 1).

A Software Serial library allows for serial communication on any of the

Uno's digital pins.

The ATmega328 also supports I2C (TWI) and SPI communication. The

Arduino software includes a Wire library to simplify use of the I2C bus

8.6 Programming

The Arduino Uno can be programmed with the Arduino software

(download). Select "Arduino Uno from the Tools > Board menu

(according to the microcontroller on your board).

The ATmega328 on the Arduino Uno comes preburned with a bootloader

that allows you to upload new code to it without the use of an external

hardware programmer. It communicates using the original STK500

protocol (reference, C header files).

We can also bypass the bootloader and program the microcontroller

through the ICSP (In-Circuit Serial Programming) header.

The ATmega16U2 (or 8U2 in the rev1 and rev2 boards) firmware source

code is available. The ATmega16U2/8U2 is loaded with a DFU

bootloader, which can be activated by:

On Rev1 boards: connecting the solder jumper on the back of the

board (near the map of Italy) and then resetting the 8U2.

On Rev2 or later boards: there is a resistor that pulling the

8U2/16U2 HWB line to ground, making it easier to put into DFU

mode.

We can then use Atmel's FLIP software (Windows) or the DFU

programmer (Mac OS X and Linux) to load a new firmware. Or we can

use the ISP header with an external programmer (overwriting the DFU

bootloader).

8.7 USB Overcurrent Protection

The Arduino Uno has a resettable polyfuse that protects your computer's

USB ports from shorts and overcurrent. Although most computers

provide their own internal protection, the fuse provides an extra layer of

protection. If more than 500 mA is applied to the USB port, the fuse will

automatically break the connection until the short or overload is removed.

8.8 Physical Characteristics

The maximum length and width of the Uno PCB are 2.7 and 2.1 inches

respectively, with the USB connector and power jack extending beyond

the former dimension. Four screw holes allow the board to be attached to

a surface or case. Note that the distance between digital pins 7 and 8 is

160 mil (0.16"), not an even multiple of the 100 mil spacing of the other

pins.

CHAPTER – 9

PWM GENERATION USING ARDUINO

9.1 Secrets of Arduino PWM

Pulse-width modulation (PWM) can be implemented on the Arduino in

several ways. This article explains simple PWM techniques, as well as

how to use the PWM registers directly for more control over the duty

cycle and frequency. This article focuses on the Arduino models, which

use the ATmega168 or ATmega328.

Briefly, a PWM signal is a digital square wave, where the frequency is

constant, but that fraction of the time the signal is on (the duty cycle) can

be varied between 0 and 100%.

Figure 9.1 PWM generation with different duty cycle

9.2 Simple Pulse Width Modulation with analogWrite

The Arduino's programming language makes PWM easy to use; simply

call analogWrite(pin, dutyCycle), where dutyCycle is a value from 0 to

255, and pin is one of the PWM pins (3, 5, 6, 9, 10, or 11). The

analogWrite function provides a simple interface to the hardware PWM,

but doesn't provide any control over frequency. (Note that despite the

function name, the output is a digital signal, often referred to as a square

wave.)

Probably 99% of the users can stop here, and just use analogWrite, but

there are other options that provide more flexibility.

9.3 Bit-banging Pulse Width Modulation

We can "manually" implement PWM on any pin by repeatedly turning

the pin on and off for the desired times. e.g.

void setup()

{

pinMode(13, OUTPUT);

}

void loop()

{

digitalWrite(13, HIGH);

delayMicroseconds(100); // Approximately 10% duty cycle @1KHz

digitalWrite(13, LOW);

delayMicroseconds(1000 - 100);

}

This technique has the advantage that it can use any digital output pin. In

addition, we have full control the duty cycle and frequency.

One major disadvantage is that any interrupts will affect the timing,

which can cause considerable jitter unless you disable interrupts.

A second disadvantage is we can't leave the output running while

the processor does something else.

Finally, it's difficult to determine the appropriate constants for a particular

duty cycle and frequency unless you either carefully count cycles, or

tweak the values while watching an oscilloscope.

9.4 Using the ATmega PWM registers directly

The ATmega328P chip has three PWM timers, controlling 6 PWM

outputs. By manipulating the chip's timer registers directly, you can

obtain more control than the analogWrite function provides.

9.5 The Atmega 328 timers:

The ATmega328P has three timers known as Timer 0, Timer 1, and

Timer 2. Each timer has two output compare registers that control the

PWM width for the timer's two outputs: when the timer reaches the

compare register value, the corresponding output is toggled. The two

outputs for each timer will normally have the same frequency, but can

have different duty cycles (depending on the respective output compare

register).

Each of the timers has a prescaler that generates the timer clock by

dividing the system clock by a prescale factor such as 1, 8, 64, 256, or

1024. The Arduino has a system clock of 16MHz and the timer clock

frequency will be the system clock frequency divided by the prescale

factor. Note that Timer 2 has a different set of prescale values from the

other timers.

The timers are complicated by several different modes. The main PWM

modes are "Fast PWM" and "Phase-correct PWM", which will be

described below. The timer can either run from 0 to 255, or from 0 to a

fixed value. (The 16-bit Timer 1 has additional modes to supports timer

values up to 16 bits.) Each output can also be inverted.

The timers can also generate interrupts on overflow and/or match against

either output compare register, but that's beyond the scope of this article.

Timer Registers Several registers are used to control each timer. The

Timer/Counter Control Registers TCCRnA and TCCRnB hold the main

control bits for the timer. (Note that TCCRnA and TCCRnB do not

correspond to the outputs A and B.) These registers hold several groups

of bits:

Waveform Generation Mode bits (WGM): these control the overall

mode of the timer.(These bits are split between TCCRnA and

TCCRnB.)

Clock Select bits (CS): these control the clock prescaler

Compare Match Output A Mode bits (COMnA): these

enable/disable/invert output A

Compare Match Output B Mode bits (COMnB): these

enable/disable/invert output B

The Output Compare Registers OCRnA and OCRnB set the levels at

which outputs A and B will be affected. When the timer value matches

the register value, the corresponding output will be modified as specified

by the mode.

The bits are slightly different for each timer. Timer 1 is a 16-bit timer and

has additional modes. Timer 2 has different prescaler values.

9.6 Fast PWM

In the simplest PWM mode, the timer repeatedly counts from 0 to 255.

The output turns on when the timer is at 0, and turns off when the timer

matches the output compare register. The higher the value in the output

compare register, the higher the duty cycle. This mode is known as Fast

PWM Mode. There are two outputs for two particular values of OCRnA

and OCRnB. Note that both outputs have the same frequncy, matching

the frequency of a complete timer cycle.

9.7 Fast PWM Mode

The following code fragment sets up fast PWM on pins 3 and 11 (Timer

2). To summarize the register settings, setting the waveform generation

mode bits WGM to 011 selects fast PWM. Setting the COM2A bits and

COM2B bits to 10 provides non-inverted PWM for outputs A and B.

Setting the CS bits to 100 sets the prescaler to divide the clock by 64.

(Since the bits are different for the different timers, consult the datasheet

for the right values.) The output compare registers are arbitrarily set to

180 and 50 to control the PWM duty cycle of outputs A and B. (Of

course, you can modify the registers directly instead of using pinMode,

but you do need to set the pins to output.)

pinMode(3, OUTPUT);

pinMode(11, OUTPUT);

TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM21) |

_BV(WGM20);

TCCR2B = _BV(CS22);

OCR2A = 180;

OCR2B = 50;

On the Arduino, these values yield:

Output A frequency: 16 MHz / 64 / 256 = 976.5625Hz

Output A duty cycle: (180+1) / 256 = 70.7%

Output B frequency: 16 MHz / 64 / 256 = 976.5625Hz

Output B duty cycle: (50+1) / 256 = 19.9%

The output frequency is the 16MHz system clock frequency, divided by

the prescaler value (64), divided by the 256 cycles it takes for the timer to

wrap around. Note that fast PWM holds the output high one cycle longer

than the compare register value.

9.8 Phase-Correct PWM

The second PWM mode is called phase-correct PWM. In this mode, the

timer counts from 0 to 255 and then back down to 0. The output turns off

as the timer hits the output compare register value on the way up, and

turns back on as the timer hits the output compare register value on the

way down. The result is a more symmetrical output. The output

frequency will be approximately half of the value for fast PWM mode,

because the timer runs both up and down.

Example:

The following code fragment sets up phase-correct PWM on pins 3 and

11 (Timer 2). The waveform generation mode bits WGM are set to to 001

for phase-correct PWM. The other bits are the same as for fast PWM.

pinMode(3, OUTPUT);

pinMode(11, OUTPUT);

TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM20);

TCCR2B = _BV(CS22);

OCR2A = 180;

OCR2B = 50;

On the Arduin, these values yield:

Output A frequency: 16 MHz / 64 / 255 / 2 = 490.196Hz

Output A duty cycle: 180 / 255 = 70.6%

Output B frequency: 16 MHz / 64 / 255 / 2 = 490.196Hz

Output B duty cycle: 50 / 255 = 19.6%

Phase-correct PWM divides the frequency by two compared to fast

PWM, because the timer goes both up and down. Somewhat surprisingly,

the frequency is divided by 255 instead of 256, and the duty cycle

calculations do not add one as for fast PWM. See the explanation below

under "Off-by-one".

CHAPTER – 10

CONCLUSION AND FUTURE SCOPE

With the very basic concept of PWM, H-bridge and ARDUINO, the

direction and the speed of the motor can be controlled. It is practical and

highly feasible method according to economic point of view, reliability

and accuracy. It is programmable one therefore it can control various

motors.

The speed sensing is done using encoder and proximity IR sensor and the

controlling is done using LabVIEW interface for ARDUINO (LIFA).

The thesis provides a cost effective means of employing powerful

programming tool for various applications using prototyping board

ARDUINO. The potential of this method will be extended for various

other engineering applications in the near future.

10.1 Applications

Because the hardware required is low cost and general user

protocols potential applications is limited to the user.

In educational institutions this apparatus can be modified to

function as a Remote Virtual Lab.

Small scale industries can employ this method of control if

accuracy and speed is of less importance (since Arduino

microcontroller has certain limitations over speed i.e. clock

frequency)

In a large scale farming for collecting data from hundreds of

sensors like temperature and humidity sensors and then taking

collective decision over a period of time for control action like

sprinkler operation, can be implemented effectively and

economically using Arduino and LabVIEW.

Easy to assemble because of its constitution of modules and hence

it is able to run on different platforms and therefore it has a lot of

scope in the home automation system

It is possible to control the motor in both the directions so the data

can be transmitted in serial / parallel form using USB so it has its

application in wireless telecommunication networks.

10.2 Future Scope

Arduino is a type of special purpose microprocessor that has replaced

many hardware components such as timers and drum sequencers used

in relay logic. So with the help of this type of controller for DC machines

various industrial needs could be fulfilled which requires feedback and

control action.

The DC motor controller which has been developed is an extensive tool

for the automation system which is practiced in practically type of

manufacturing and assembly process. Some of the larger processes

include electrical power generation, oil refining, chemicals, steel mills,

plastics, cement plants, fertilizer plants, pulp and paper mills, automobile

and truck assembly, aircraft production, glass manufacturing, natural

gas separation plants.