1. INTRODUCTION

One of the most promising renewable energy sources characterized by a huge potential of

conversion into electrical power is the solar energy. The conversion of solar radiation into

electrical energy by Photo-Voltaic (PV) effect is a very promising technology, being clean,

silent and reliable, with very small maintenance costs and small ecological impact. The

interest in the Photo Voltaic conversion systems is visibly reflected by the exponential

increase of sales in this market segment with a strong growth projection for the next decades.

According to recent market research reports carried out by European Photovoltaic Industry

Association (EPIA), the total installed power of PV conversion equipment increased from

about 1 GW in 2001up to nearly 23 GW in 2009.

The continuous evolution of the technology determined a sustained increase of the

conversion efficiency of PV panels, but nonetheless the most part of the commercial panels

have efficiencies no more than 20%. A constant research preoccupation of the technical

community involved in the solar energy harnessing technology refers to various solutions to

increase the PV panel’s conversion efficiency. Among PV efficiency improving solutions we

can mention: solar tracking, optimization of solar cells geometry, enhancement of light

trapping capability, use of new materials, etc. The output power produced by the PV panels

depends strongly on the incident light radiation.

The continuous modification of the sun-earth relative position determines a continuously

changing of incident radiation on a fixed PV panel. The point of maximum received energy is

reached when the direction of solar radiation is perpendicular on the panel surface. Thus an

increase of the output energy of a given PV panel can be obtained by mounting the panel on a

solar tracking device that follows the sun trajectory. Unlike the classical fixed PV panels, the

mobile ones driven by solar trackers are kept under optimum insolation for all positions of

the Sun, boosting thus the PV conversion efficiency of the system. The output energy of PV

panels equipped with solar trackers may increase with tens of percents, especially during the

summer when the energy harnessed from the sun is more important. Photo-Voltaic or PV cells,

known commonly as solar cells, convert the energy from sunlight into DC electricity. PVs

offer added advantages over other renewable energy sources in that they give off no noise

and require practically no maintenance. A tracking system must be able to follow the sun

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with a certain degree of accuracy, return the collector to its original position at the end of the

day and also track during periods of cloud over.

The major components of this system are as follows.

Light dependent resistor

Microcontroller.

Output mechanical transducer (stepper motor)

1.1 Background

A Solar Tracker is a device onto which solar panels are fitted which tracks the motion of the

sun across the sky ensuring that the maximum amount of sunlight strikes the panels

throughout the day. The Solar Tracker will attempt to navigate to the best angle of exposure

of light from the sun. This report aims to let the reader understand the project work which I

have done. A brief introduction to Solar Panel and Solar Tracker is explained in the Literature

Research section. Basically the Solar Tracker is divided into two main categories, hardware

and software. It is further subdivided into six main functionalities: Method of Tracker Mount,

Drives, Sensors, RTC, Motors, and Power Supply of the Solar Tracker is also explained and

explored. The reader would then be brief with some analysis and perceptions of the

information.

By using solar arrays, a series of solar cells electrically connected, a DC voltage is generated

which can be physically used on a load. Solar arrays or panels are being used increasingly as

efficiencies reach higher levels, and are especially popular in remote areas where placement

of electricity lines is not economically viable. This alternative power source is continuously

achieving greater popularity especially since the realisation of fossil fuels shortcomings.

Renewable energy in the form of electricity has been in use to some degree as long as 75 or

100 years ago. Sources such as Solar, Wind, Hydro and Geothermal have all been utilised

with varying levels of success. The most widely used are hydro and wind power, with solar

power being moderately used worldwide. This can be attributed to the relatively high cost of

solar cells and their low conversion efficiency. Solar power is being heavily researched, and

solar energy costs have now reached within a few cents per kW/h of other forms of electricity

generation, and will drop further with new technologies such as titanium oxide cells. With a

peak laboratory efficiency of 32% and average efficiency of 15-20%, it is necessary to

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recover as much energy as possible from a solar power system. This includes reducing

inverter losses, storage losses, and light gathering losses. Light gathering is dependent on the

angle of incidence of the light source providing power (i.e. the sun) to the solar cell’s surface,

and the closer to perpendicular, the greater the power. If a flat solar panel is mounted on level

ground, it is obvious that over the course of the day the sunlight will have an angle of

incidence close to 90° in the morning and the evening. At such an angle, the light gathering

ability of the cell is essentially zero, resulting in no output. As the day progresses to midday,

the angle of incidence approaches 0°, causing a steady increase in power until at the point

where the light incident on the panel is completely perpendicular, and maximum power is

achieved. As the day continues toward dusk, the reverse happens, and the increasing angle

causes the power to decrease again toward minimum again. From this background, we see the

need to maintain the maximum power output from the panel by maintaining an angle of

incidence as close to 0° as possible. By tilting the solar panel to continuously face the sun,

this can be achieved. This process of sensing and following the position of the sun is known

as Solar Tracking. It was resolved that real-time tracking would be necessary to follow the

sun effectively, so that no external data would be required in operation.

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2. LITERATURE RESEARCH

This chapter aims to provide a brief knowledge of Solar Panel, Solar Tracker and the

components which made up Solar Tracker.

2.1 Technology of Solar Panel

Solar panels are devices that convert light into electricity. They are called solar after the sun

because the sun is the most powerful source of the light available for use. They are

sometimes called photovoltaic which means "light-electricity". Solar cells or PV cells rely on

the photovoltaic effect to absorb the energy of the sun and cause current to flow between two

oppositely charge layers. A solar panel is a collection of solar cells. Although each solar cell

provides a relatively small amount of power, many solar cells spread over a large area can

provide enough power to be useful. To get the most power, solar panels have to be pointed

directly at the Sun. The development of solar cell technology begins with 1839 research of

French physicist Antoine-Cesar Becquerel. He observed the photovoltaic effect while

experimenting with a solid electrode in an electrolyte solution. After that he saw a voltage

developed when light fell upon the electrode.

According to Encyclopaedia Britannica the first genuine for solar panel was built around

1883 by Charles Fritts. He used junctions formed by coating selenium (a semiconductor) with

an extremely thin layer of gold. Crystalline silicon and gallium arsenide are typical choices of

materials for solar panels. Gallium arsenide crystals are grown especially for photovoltaic

use, but silicon crystals are available in less-expensive standard ingots, which are produced

mainly for consumption in the microelectronics industry. Norway’s Renewable Energy

Corporation has confirmed that it will build a solar manufacturing plant in Singapore by 2010

- the largest in the world. This plant will be able to produce products that can generate up to

1.5 Giga watts of energy every year. That is enough to power several million households at

any one time. Last year the world as a whole produced products that could generate just 2

GW in total.

2.2 Evolution of Solar Tracker

Since the sun moves across the sky throughout the day, in order to receive the best angle of

exposure to sunlight for collection energy. A tracking mechanism is often incorporated into

the solar arrays to keep the array pointed towards the sun. A solar tracker is a device onto

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which solar panels are fitted which tracks the motion of the sun across the sky ensuring that

the maximum amount of sunlight strikes the panels throughout the day. When compare to the

price of the PV solar panels, the cost of a solar tracker is relatively low. Most photovoltaic

solar panels are fitted in a fixed location- for example on the sloping roof of a house, or on

framework fixed to the ground. Since the sun moves across the sky though the day, this is far

from an ideal solution. Solar panels are usually set up to be in full direct sunshine at the

middle of the day facing South in the Northern Hemisphere, or North in the Southern

Hemisphere. Therefore morning and evening sunlight hits the panels at an acute angle

reducing the total amount of electricity which can be generated each day.

Fig 2.1 Sun’s apparent motion

During the day the sun appears to move across the sky from left to right and up and down

above the horizon from sunrise to noon to sunset. Figure 2.1 shows the schematic above

of the Sun's apparent motion as seen from the Northern Hemisphere. To keep up with

other green energies, the solar cell market has to be as efficient as possible in order not to

lose market shares on the global energy marketplace. The end-user will prefer the

tracking solution rather than a fixed ground system to increase their earnings because:

The efficiency increases by 30-40%.

The space requirement for a solar park is reduced, and they keep the same

output.

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The return of the investment timeline is reduced.

The tracking system amortizes itself within 4 years.

In terms of cost per Watt of the completed solar system, it is usually cheaper

to use a solar tracker and less solar panels where space and planning permit.

A good solar tracker can typically lead to an increase in electricity generation

capacity of 30-50%.

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3. PROJECT DESCRIPTION3.1 Block Diagram

Fig 3.1 Block Diagram of Project3.2 Schematic Diagram

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Fig 3.2 Schematic Diagram of Project

3.3 printed circuit board

Almost all circuits encountered on electronic equipment (computers, TV, radio, industrial

control equipment, etc.) are mounted on printed circuit boards. Close inspection of a PCB

reveals that it contains a series of copper tracks printed on one or both sides of a fiber glass

board. The copper tracks form the wiring pattern required to link the circuit devices

according to a given circuit diagram. Hence, to construct a circuit the necessity of connecting

insulated wires between components is eliminated, resulting in a cleaner arrangement and

providing mechanical support for components. Moreover, the copper tracks are highly

conductive and the whole PCB can be easily reproduced for mass production with increased

reliability.

1) Types of PCB

PCB's can be divided into three main categories:

Single-sided

Double-sided

Multi-layered.

Single-sided PCB

A single-sided PCB contains copper tracks on one side of the board only, as shown in Figure

3.3. Holes are drilled at appropriate points on the track-so that each component can be

inserted from the non-copper side of the board, as shown in Figure 3.4. Each pin is then

soldered to the copper track.

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Fig 3.3 Printed circuit board

Fig 3.4 Single sided PCBDouble-sided PCB

Double-sided PCBs have copper tracks on both sides of the board. The track layout is

designed so as not to allow shorts from one side to another, if it is required to link points

between the two sides, electrical connections are made by small interconnecting holes which

are plated with copper during manufacture.

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Fig 3.5 Double sided PCBMulti-layer PCB

In multi-layer PCBs, each side contains several layers of track patterns which are insulated

from one another. These layers are laminated under heat and high pressure. A multi-layer

PCB is shown in Figure 3.6

Fig 3.6 Multi layered PCB2) MAKING A PCB

PCB's commonly available on the market are not particular circuits, but are available as

copper clad boards. In other words, the whole area of one or both sides of the board is coated

with copper. The user then draws his track layout on the copper surface, according to his

circuit diagram. Next, the untraced copper area removed by a process called etching. Here,

the unused copper area is dissolved away by an etching solution and only the required copper

tracks remain. The board is then cleaned and drilled at points where each device is to be

inserted. Finally, each component is soldered to the board.

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The etching process depends on whether board is of plain or photo-resist type. These are

treated separately in the following section.

a) Making a PCB out of a plain copper clad board

Equipment required

The following items are required:

A single-sided copper clad board.

Ferric chloride solution, which is the etching liquid.

An etch-resist pen is with its ink resisting to ferric chloride.

A PCB eraser.

Track layout design

The first step is to draw the track layout on the plain copper clad board, according to the

circuit to be implemented which turns on an LED when the push-button is pressed. The lines

joining different components will form the track layout on the PCB. Each component is

inserted from the non-copper side of the board and its leads appear on the copper side. For

example, when viewing the component side, the base of the BC109 transistor appears to the

right of the collector, while from the track side, it appears at the left of the collector.

b) Making a PCB out of a photo resist board

Equipment required

Photo-resist board

Ferric chloride solution as etchant

A white board marker

Transparent polyester film for use as drafting sheet

Sodium hydroxide solution as developer

Ultra-violet exposure unit

Track layout design

Using the same principles outlined in section a track layout is drawn to scale on the

transparency using the white board' marker. It may be useful to insert graph paper below the

transparent sheet for accurate dimensioning of the layout.

Photo-etching

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The principle behind photo-etching is to place the transparency over the copper clad and to

expose it to UV radiation, hence leaving the track regions intact and softening unused areas.

First, the protective plastic film is removed from the board. The traced transparency is then

placed over the board, being careful to ensure that the copper side of the design faces

upwards. The combination is next placed in a UV exposure unit, with the transparency facing

the fluorescent tubes inside the unit. At the track regions, UV radiation is prevented from

reaching the board, and hence the photo sensitive remains hardened in these regions. After an

exposure of about 5 minutes the board can be removed. The PCB is then placed in a solution

of caustic soda which dissolves away any unhardened photo-sensitive area. After a few

minutes of development time, the track layout is apparent. The board is finally removed and

rinsed in cold water.

Final etching

After having allowed the tracks to harden for about half an hour, the unmarked copper area is

etched by ferric chloride solution.

3) The following points should be noted:

It is a good idea to draft the track layout on graph paper before drawing the final

layout on the copper clad.

Use an etch resist pen to draw the track layout on the copper clad (the latter must be

cleaned initially).

The following lead spacing can be used as a rule of thumb: allow 10 mm for a 1/4 W

resistor, 8 mm for a signal diode, 4 mm for LED's and ceramic capacitors. The lead

spacing may also be measured before drawing.

Terminals for the power supply input leads must also be included on the layout.

The arrangement of components must be well planned so as to minimize the amount

of cooper clad board required.

Allow the ink to dry before etching.

4) Etching

The copper clad is now ready to be etched. If the etchant is available in powder form, it needs

to be mixed with water in anon-corrodible container. A powder to water ratio of 2:5 by mass

is about right. Etching time may vary between 10 to as long as 90 minutes, depending on the

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concentration and temperature of the etchant. The process can be accelerated by warming the

solution and by frequently agitating the etching bath. The ferric chloride solution gradually

dissolves any untraced copper area. When etching is complete, only the track layout remains

on the board. The latter is then removed the bath and rinsed with clean water. The etch resist

ink is finally rubbed away with a PCB eraser, or with very fine grain sand paper.

Making a PCB out of a photo-resist copper clad board

The photo-resist board consists of a single or double sided copper clad coated with a light-

sensitive and the latter is protected with a plastic which should be removed before use. Its

advantage over the plain copper clad board is that the track layout does not need to be drawn

directly on the board.

The use of etch-resist transfers

The use of pens to design track layouts may not give neat result, even when using a ruler. For

instance, it may be difficult to draw tracks with the same line Width or to draw well aligned

terminals for IC's and discrete devices, Etch-resist PCB symbols and tracks are available for

direct transfer to the copper clad or to the transparency. Transfer is by rubbing down the

relevant symbol with a soft pencil.

4. COMPONENTS DESCRIPTION

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4.1 Solar Tracker

Solar Tracker is basically a device onto which solar panels are fitted which tracks the motion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. After finding the sunlight, the tracker will try to navigate through the path ensuring the best sunlight is detected. The design of the Solar Tracker requires many components. The design and construction of it could be divided into six main parts that would need to work together harmoniously to achieve a smooth run for the Solar Tracker, each with their main function. They are:

Methods of Tracker Mount

Methods of Drives

Sensor and Sensor Controller

Motor and Motor Controller

Tracker Solving Algorithm

Data Acquisition/Interface Card

4.2 Methods of Tracker Mount

1. Single axis solar trackers

Single axis solar trackers can either have a horizontal or a vertical axle. The horizontal type is

used in tropical regions where the sun gets very high at noon, but the days are short. The

vertical type is used in high latitudes where the sun does not get very high, but summer days

can be very long. The single axis tracking system is the simplest solution and the most

common one used.

2. Double axis solar trackers

Double axis solar trackers have both a horizontal and a vertical axle and so can track the

Sun's apparent motion exactly anywhere in the World. This type of system is used to control

astronomical telescopes, and so there is plenty of software available to automatically predict

and track the motion of the sun across the sky. By tracking the sun, the efficiency of the solar

panels can be increased by 30-40%.The dual axis tracking system is also used for

concentrating a solar reflector toward the concentrator on heliostat systems.

4.3 Methods of Drive

1. Active Trackers

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Active Trackers use motors and gear trains to direct the tracker as commanded by a

controller responding to the solar direction. Light-sensing trackers typically have two photo

sensors, such as photodiodes, configured differentially so that they output a null when

receiving the same light flux. Mechanically, they should be omnidirectional and are aimed 90

degrees apart. This will cause the steepest part of their cosine transfer functions to balance at

the steepest part, which translates into maximum sensitivity.

2. Passive Trackers

Passive Trackers use a low boiling point compressed gas fluid that is driven to one side or the

other by solar heat creating gas pressure to cause the tracker to move in response to an

imbalance.

4.4 Sensors

A sensor is a device that measures a physical quantity and converts it into a signal which can

be read by an observer or by an instrument.

1. Light Dependent Resistor

Light Dependent Resistor is made of a high-resistance semiconductor. It can also be referred

to as a photoconductor. If light falling on the device is of the high enough frequency, photons

absorbed by the semiconductor give bound electrons enough energy to jump into the

conduction band. The resulting free electron conducts electricity, thereby lowering resistance.

Hence, Light Dependent Resistors is very useful in light sensor circuits. LDR is very high-

resistance, sometimes as high as 10MΩ, when they are illuminated with light resistance drops

dramatically.

A Light Dependent Resistor is a resistor that changes in value according to the light falling on

it. A commonly used device, the ORP-12, has a high resistance in the dark, and a low

resistance in the light. Connecting the LDR to the microcontroller is very straight forward,

but some software ‘calibrating’ is required. It should be remembered that the LDR response

is not linear, and so the readings will not change in exactly the same way as with a

potentiometer. In general there is a larger resistance change at brighter light levels. This can

be compensated for in the software by using a smaller range at darker light levels.

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Fig 4.1 Light Dependent Resistor2. Photodiode

Photodiode is a light sensor which has a high speed and high sensitive silicon PIN

photodiode in a miniature flat plastic package. A photodiode is designed to be responsive to

optical input. Due to its water clear epoxy the device is sensitive to visible and infrared

radiation. The large active area combined with a flat case gives a high sensitivity at a wide

viewing angle. Photodiodes can be used in either zero bias or reverse bias. In zero bias, light

falling on the diode causes a voltage to develop across the device, leading to a current in the

forward bias direction. This is called the photovoltaic effect, and is the basis for solar cells -

in fact a solar cell is just a large number of big, cheap photodiodes. Diodes usually have

extremely high resistance when reverse biased.

Fig 4.2 different type of photo diodes

4.5 Motor

Motor is use to drive the Solar Tracker to the best angle of exposure of light. For this section,

we are using stepper motor.

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Stepper Motor

Features

Linear speed control of stepper motor

Control of acceleration, deceleration, max speed and number of steps to move

Driven by one timer interrupt

Full - or half-stepping driving mode

Introduction

This application note describes how to implement an exact linear speed controller for stepper

motors. The stepper motor is an electromagnetic device that converts digital pulses into

mechanical shaft rotation. Many advantages are achieved using this kind of motors, such as

higher simplicity, since no brushes or contacts are present, low cost, high reliability, high

torque at low speeds, and high accuracy of motion. Many systems with stepper motors need

to control the acceleration/deceleration when changing the speed. This application note

presents a driver with a demo application, capable of controlling acceleration as well as

position and speed.

Fig 4.3 Stepper Motors

Theory

Stepper motor

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This application note covers the theory about linear speed ramp stepper motor control as well

as the realization of the controller itself. It is assumed that the reader is familiar with basic

stepper motor operation, but a summary of the most relevant topics will be given.

Bipolar vs. Unipolar stepper motors

The two common types of stepper motors are the bipolar motor and the Unipolar motor. The

bipolar and unipolar motors are similar, except that the Unipolar has a centre tap on each

winding as shown in Figure 4.4

Fig 4.4 Bipolar and Unipolar stepper Motor

Unipolar stepper motor

Stepper motors are very accurate motors that are commonly used in computer disk drives,

printers and clocks. Unlike dc motors, which spin round freely when power is applied,

stepper motors require that their power supply be continuously pulsed in specific patterns.

For each pulse the stepper motor moves around one step often 15 degrees giving 24 steps in a

full revolution.There are two main types of stepper motors - Unipolar and Bipolar. Unipolar

motors usually have four coils which are switched on and off in a particular sequence.

Bipolar motors have two coils in which the current flow is reversed in a similar sequence.

Each of the four coils in a Unipolar stepper motor must be switched on and off in a certain

order to make the motor turn. Many microprocessor systems use four output lines to control

the stepper motor, each output line controlling the power to one of the coils. As the stepper

motor operates at 5V, the standard transistor circuit is required to switch each coil. As the

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coils create a back emf when switched off, a suppression diode on each coil is also required.

The table below show the four different steps required to make the motor turn.

Table 4.1 Unipolar stepper motor operation

Step Coil 1 Coil 2 Coil 3 Coil 41 1 0 1 02 1 0 0 13 0 1 0 14 0 1 1 01 1 0 1 0

Look carefully at the table 4.1 and notice that a pattern is visible. Coil 2 is always the

opposite or logical NOT of coil 1. The same applies for coils 3 and 4. It is therefore possible

to cut down the number of microcontroller pins required to just two by the use of two

additional NOT gates. Fortunately the Darlington driver IC ULN2003 can be used to provide

both the NOT and Darlington driver circuits. It also contains the back emf suppression diodes

so no external diodes are required.

Bipolar Stepper motor

The bipolar stepper motor has two coils that must be controlled so that the current flows in

different directions through the coils in a certain order. The changing magnetic fields that

these coils create cause the rotor of the motor to move around in steps.

The bipolar motor needs current to be driven in both directions through the windings, and a

full bridge driver is needed as shown in Figure 4.5 (a). The centre tap on the Unipolar motor

allows a simpler driving circuit shown in Figure 4.5 (b), limiting the current flow to one

direction. The main drawback with the Unipolar motor is the limited capability to energize all

windings at any time, resulting in a lower torque compared to the bipolar motor. The

Unipolar stepper motor can be used as a bipolar motor by disconnecting the centre tap.

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(a) (b)

Fig 4.5 Bipolar and Unipolar drivers with MOS transistorsImplementation

A working implementation written in C is included with this application note. Full

documentation of the source code and compilation information is found by opening the

‘readme.html’ file included with the source code. The demo application demonstrates linear

speed control of a stepper motor. The user can control the stepper motor speed profile by

issuing different commands using the serial port, and the AVR will drive the connected

stepper motor accordingly. The demo application is divided in three major blocks, as shown

in the block diagram in Figure 4.6. There is one file for each block and also a file for UART

routines used by the main routine.

Fig 4.6 Block diagram of demo application

Main c has a menu and a command interface, giving the user control of the stepper motor by

a terminal connected to the serial line. Speed controller c calculates the needed data and

generates step pulses to make the stepper motor follow the desired speed profile. Smdriver.c

counts the steps and outputs the correct signals to control the stepper motor.

Timer interrupt

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The timer interrupt generates the step pulses calls the function Step Counter ( ) and is only

running when the stepper motor is moving. The timer interrupt will operate in four different

states according to the speed profile shown in Figure 4.7 and this behaviour is realized with a

state machine in the timer interrupt shown in Figure 4.8.

Fig 4.7 Operating states for different speed profile parts

Fig 4.8 State machine for timer interrupt

When the application starts or when the stepper motor is stopped the state-machine remains

in the state STOP. When setup calculations are done, a new state is set and the timer interrupt

is enabled. When moving more than one step the state-machine goes to ACCEL. If moving

only 1 step, the state is changed to DECEL. When the state is changed to ACCEL, the

application accelerates the stepper motor until either the desired speed is reached and the state

is changed to RUN, or deceleration must start, changing the state to DECEL. When the state

is set to RUN, the stepper motor is kept at constant speed until deceleration must start, then

the state is changed to DECEL.It will stay in DECEL and decelerate until the speed reaches

zero desired number of steps. The state is then changed to STOP.

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4.6 Microcontroller

A microcontroller is a single chip that contains the processor, non-volatile memory for the

program, volatile memory for input and output, a clock and an I/O control unit also called a

computer on a chip, billions of microcontroller units are embedded each year in a myriad of

products from toys to appliances to automobiles. For example, a single vehicle can use 70 or

more microcontrollers. The following picture describes a general block diagram of

microcontroller.

Features

High-performance, Low-power AVR 8-bit Microcontroller

Advanced RISC Architecture

131 Powerful Instructions – Most Single-clock Cycle Execution

32 x 8 General Purpose Working Registers

Fully Static Operation

Up to 16 MIPS Throughput at 16 MHz

On-chip 2-cycle Multiplier

High Endurance Non-volatile Memory segments

16K Bytes of In-System Self-programmable Flash program memory

512 Bytes EEPROM

1K Byte Internal SRAM

Write/Erase Cycles: 10,000 Flash/100,000 EEPROM

Data retention: 20 years at 85°C/100 years at 25°C

Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program

True Read-While-Write Operation

Programming Lock for Software Security

JTAG Interface

Boundary-scan Capabilities According to the JTAG Standard

Extensive On-chip Debug Support

Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG

Interface

Peripheral Features

Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes

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One 16-bit Timer/Counter with Separate Prescalers, Compare Mode, and

Capture

Mode

Real Time Counter with Separate Oscillator

Four PWM Channels

8-channel, 10-bit ADC

8 Single-ended Channels

7 Differential Channels in TQFP Package Only

2 Differential Channels with Programmable Gain at 1x, 10x, or 200x

Byte-oriented Two-wire Serial Interface

Programmable Serial USART

Master/Slave SPI Serial Interface

Programmable Watchdog Timer with Separate On-chip Oscillator

On-chip Analog Comparator

Special Microcontroller Features

Power-on Reset and Programmable Brown-out Detection

Internal Calibrated RC Oscillator

External and Internal Interrupt Sources

Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down,

Standby

and Extended Standby

I/O and Packages

32 Programmable I/O Lines

40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF

Operating Voltages

2.7 - 5.5V for ATmega16L

4.5 - 5.5V for ATmega16

Speed Grades

0 - 8 MHz for ATmega16L

0 - 16 MHz for ATmega16

Power Consumption @ 1 MHz, 3V, and 25°C for ATmega16L

Active: 1.1 mA

Idle Mode: 0.35 mA

Power-down Mode: < 1 μA

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ATmega16:

The ATmega16 is a low-power, high-performance advance RISC8-bit microcontroller with

32K bytes of in-system programmable Flash memory. The on-chip Flash allows the program

memory to be reprogrammed in-system or by a conventional non-volatile memory

programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a

monolithic chip, the Atmel ATmega16 is a powerful microcontroller, which provides a highly

flexible and cost-effective solution to many, embedded control applications. The ATmega16

provides the following standard features:32K bytes of Flash, 1024 byte of EEPROM & 2KB

INTERNAL S RAM ,32 I/O lines, Watch dog timer, two data pointers, two 16-bit

timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip

oscillator,8-channel 10 bit ADC and clock circuitry. The Idle Mode stops the CPU while

allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning.

The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other

chip functions until the next interrupt.

Fig 4.9 Pin diagram of ATmega16

Overview-

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The ATmega16 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced

RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega16

achieves throughputs approaching 1 MIPS per MHz allowing the system designed to

optimize power consumption versus processing speed.

Pin Descriptions

VCC Digital supply voltage

GND Ground

Port A (PA7 - PA0) Port A serves as the analog inputs to the A/D Converter. Port A also

serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pin scan

provide internal pull-up resistors. The Port A output buffers have symmetrical drive

characteristics with both high sink and source capability. When pins PA0 to PA7are used as

inputs and are externally pulled low, they will source current if the internal pull-up resistors

are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the

clock is not running.

Port B (PB7 - PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors.

The Port B output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port B pins that are externally pulled low will source current if

the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition

becomes active, even if the clock is not running.

Port C (PC7 - PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors.

The Port C output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port C pins that are externally pulled low will source current if

the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition

becomes active, even if the clock is not running. If the JTAG interface is enabled , the pull-up

resistors on pins PC5 (TDI), PC3 (TMS) and PC2 (TCK) will be activated even if a reset

occurs.

Port D (PD7 - PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors.

The Port D output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port D pins that are externally pulled low will source current if

25

the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition

becomes active, even if the clock is not running.

RESET Reset Input. A low level on this pin for longer than the minimum pulse length will

generate a reset, even if the clock is not running.

XTAL1 Input to the inverting Oscillator amplifier and input to the internal clock operating

circuit.

XTAL2 Output from the inverting Oscillator amplifier.

AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. It should be

externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be

connected to VCC through a low-pass filter.

AREF AREF is the analog reference pin for the A/D Converter.

Alternate Functions of Port A

Port A has an alternate function as analog input for the ADC as shown in Table 4.2. If some

Port A pins are configured as outputs, it is essential that these do not switch when a

conversion is in progress. This might corrupt the result of the conversion.

Table 4.2 Port A Pins Alternate Functions

Port Pin Alternate Function

PA7 ADC7 (ADC input channel 7)

PA6 ADC6 (ADC input channel 6)

PA5 ADC5 (ADC input channel 5)

PA4 ADC4 (ADC input channel 4)

PA3 ADC3 (ADC input channel 3)

PA2 ADC2 (ADC input channel 2)

PA1 ADC1 (ADC input channel 1)

PA0 ADC0 (ADC input channel 0)

The alternate pin configuration of Port B is as follows:

• SCK – Port B, Bit 7

26

SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled

as a Slave, this pin is configured as an input regardless of the setting of DDB7. When the SPI

is enabled as a Master, the data direction of this pin is controlled by DDB7. When the pin is

forced by the SPI to be an input, the pull-up can still be controlled by the PORTB7 bit.

• MISO – Port B, Bit 6

MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as

a Master, this pin is configured as an input regardless of the setting of DDB6. When the SPI

is enabled as a Slave, the data direction of this pin is controlled by DDB6. When the pin is

forced by the SPI to be an input, the pull-up can still be controlled by the PORTB6 bit.

• MOSI – Port B, Bit 5

MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as

a Slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is

enabled as a Master, the data direction of this pin is controlled by DDB5. When the pin is

forced by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit.

• SS – Port B, Bit 4

SS: Slave Select input. When the SPI is enabled as a Slave, this pin is configured as an input

regardless of the setting of DDB4. As a Slave, the SPI is activated when this pin is driven

low. When the SPI is enabled as a Master, the data direction of this pin is controlled by

DDB4. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by

the PORTB4 bit.

• AIN1/OC0 – Port B, Bit 3

AIN1, Analog Comparator Negative Input Configure the port pin as input with the internal

pull-up switched off to avoid the digital port function from interfering with the function of

the analog comparator. OC0, Output Compare Match output: The PB3 pin can serve as an

external output for the Timer/Counter 0 Compare Match. The PB3 pin has to be configured as

an output to serve this function. The OC0 pin is also the output pin for the PWM mode timer

function.

27

• AIN0/INT2 – Port B, Bit 2

AIN0, Analog Comparator Positive input Configure the port pin as input with the internal

pull-up switched off to avoid the digital port function from interfering with the function of

the Analog Comparator. INT2, External Interrupt Source 2: The PB2 pin can serve as an

external interrupt source to the MCU.

• T1 – Port B, Bit 1

T1, Timer/Counter1 Counter Source.

• T0/XCK – Port B, Bit 0

T0 Timer/Counter 0 Counter Source XCK USART External Clock. The Data Direction

Register DDB0 controls whether the clock is output DDB0 set or input DDB0 cleared. The

XCK pin is active only when the USART operates in Synchronous mode.

The alternate pin configuration of Port C is as follows:

• TOSC2 – Port C, Bit 7

TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set one to enable asynchronous

clocking of Timer/Counter2, pin PC7 is disconnected from the port, and becomes the

inverting output of the Oscillator amplifier. In this mode, a Crystal Oscillator is connected to

this pin, and the pin cannot be used as an I/O pin.

• TOSC1 – Port C, Bit 6

TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set one to enable asynchronous

clocking of Timer/Counter2, pin PC6 is disconnected from the port, and becomes the input of

the inverting Oscillator amplifier. In this mode, a Crystal Oscillator is connected to this pin,

and the pin cannot be used as an I/O pin.

• TDI – Port C, Bit 5

TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data

Register. When the JTAG interface is enabled, this pin cannot be used as an I/O pin.

28

• TDO – Port C, Bit 4

TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register.

When the JTAG interface is enabled, this pin cannot be used as an I/O pin. The TD0 pin is

tri-stated unless TAP states that shifts out data are entered.

• TMS – Port C, Bit 3

TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller

state machine. When the JTAG interface is enabled, this pin cannot be used as an I/O pin.

• TCK – Port C, Bit 2

TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface

is enabled, this pin cannot be used as an I/O pin.

SDA – Port C, Bit 1

SDA, Two-wire Serial Interface Data: When the TWEN bit in TWCR is set one to enable the

Two-wire Serial Interface, pin PC1 is disconnected from the port and becomes the Serial

Data I/O pin for the Two-wire Serial Interface. In this mode, there is a spike filter on the pin

to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open

drain driver with slew-rate limitation. When this pin is used by the Two-wire Serial Interface,

the pull-up can still be controlled by the PORTC1 bit.

• SCL – Port C, Bit 0

SCL, Two-wire Serial Interface Clock: When the TWEN bit in TWCR is set one to enable

the Two-wire Serial Interface, pin PC0 is disconnected from the port and becomes the Serial

Clock I/O pin for the Two-wire Serial Interface. In this mode, there is a spike filter on the pin

to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open

drain driver with slew-rate limitation. When this pin is used by the Two-wire Serial Interface,

the pull-up can still be controlled by the PORT C0 bit.

4.7 LCD Display

A Liquid Crystal Display is an electronic device that can be used to show numbers or text.

There are two main types of LCD display, numeric display and alphanumeric text displays.

The display is made up of a number of shaped ‘crystals’. In numeric displays these crystals

are shaped into ‘bars’, and in alphanumeric displays the crystals are simply arranged into

patterns of ‘dots’. Each crystal has an individual electrical connection so that each crystal can

29

be controlled independently. When the crystal is ‘off’ i.e. when no current is passed through

the crystal, the crystal reflect the same amount of light as the background material, and so the

crystals cannot be seen. However when the crystal has an electric current passed through it, it

changes shape and so absorbs more light. This makes the crystal appear darker to the human

eye - and so the shape of the dot or bar can be seen against the background. It is important to

realise the difference between a LCD display and an LED display. An LED display often

used in clock radios is made up of a number of LEDs which actually give off light and so can

be seen in the dark. An LCD display only reflect slight, and so cannot be seen in the dark.

The dot-matrix liquid crystal display controller and driver LSI displays alphanumeric,

characters, and symbols. It can be configured to drive a dot-matrix liquid crystal display

under the control of a 4 or 8-bit microprocessor. Since all the functions such as display RAM,

character generator, and liquid crystal driver, required for driving a dot-matrix liquid crystal

display are internally provided on one chip, a minimal system can be interfaced with this

controller/driver. A single HD44780U can display up to two 8-character lines 16 x 2. A 16 x

2 line LCD module to display user information.

Fig 4.10 2 x16 LCD Display

4.8 TRANSFORMER:

A transformer is a device that transfers electrical energy from one circuit to another through

inductively coupled conductors - the transformer's coils or windings. Except for air-core

transformers, the conductors are commonly wound around a single iron-rich core, or around

separate but magnetically coupled cores. A varying current in the first or primary winding

creates a varying magnetic field in the core of the transformer. This varying magnetic field

induces a varying electromotive force or voltage in the secondary winding. This effect is

called mutual induction.

30

Fig 4.11 Transformer

If a load is connected to the secondary circuit, electric charge will flow in the secondary

winding of the transformer and transfer energy from the primary circuit to the load connected

in the secondary circuit. The secondary induced voltage VS, of an ideal transformer, is scaled

from the primary VP by a factor equal to the ratio of the number of turns of wire in their

respective windings:

N s

N p=

V s

V p

By appropriate selection of the numbers of turns, a transformer thus allows an alternating

voltage to be stepped up - by making NS more than NP or stepped down, by making it.

BASIC PARTS OF A TRANSFORMER

In its most basic form a transformer consists of:

A primary coil or winding.

A secondary coil or winding.

A core that supports the coils or windings.

Refer to the transformer circuit in figure as you read the following explanation: The primary

winding is connected to a 50-hertz ac voltage source. The magnetic field builds up and

collapses about the primary winding. The expanding and contracting magnetic field around

the primary winding cuts the secondary winding and induces an alternating voltage into the

winding. This voltage causes alternating current to flow through the load. The voltage may be

stepped up or down depending on the design of the primary and secondary windings.

31

THE COMPONENTS OF A TRANSFORMER

Two coils of wire are wound on some type of core material. In some cases the coils of wire

are wound on a cylindrical or rectangular cardboard form. In effect, the core material is air

and the transformer is called an air-core transformer. Transformers used at low frequencies,

such as 50 hertz and 400 hertz, require a core of low-reluctance magnetic material, usually

iron. This type of transformer is called an iron-core transformer. Most power transformers are

of the iron-core type. The principle parts of a transformer and their functions are: The core,

which provides a path for the magnetic lines of flux. The Primary winding, this receives

energy from the ac source. The secondary winding, this receives energy from the primary

winding and delivers it to the load. The enclosure, this protects the above components from

dirt, moisture, and mechanical damage.

4.9 BRIDGE RECTIFIER

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave

rectification. This is a widely used configuration, both with individual diodes wired as shown

and with single component bridges where the diode bridge is wired internally.

Basic operation

According to the conventional model of current flow originally established by Benjamin

Franklin and still followed by most engineers today, current is assumed to flow through

electrical conductors from the positive to the negative pole. In actuality, free electrons in a

conductor nearly always flow from the negative to the positive pole. In the vast majority of

applications, however, the actual direction of current flow is irrelevant. Therefore, in the

discussion below the conventional model is retained. In the diagrams below, when the input

connected to the left corner of the diamond is positive, and the input connected to the right

corner is negative, current flows from the upper supply terminal to the right along the

red(positive) path to the output, and returns to the lower supply terminal via the blue

(negative) path.

32

Fig 4.12 Bridge rectifier

When the input connected to the left corner is negative, and the input connected to the right

corner is positive, current flows from the lower supply terminal to the right along the red path

to the output, and returns to the upper supply terminal via the blue path.

In each case, the upper right output remains positive and lower right output negative. Since

this is true whether the input is AC or DC, this circuit not only produces a DC output from an

AC input, it can also provide what is sometimes called "reverse polarity protection". That is,

it permits normal functioning of DC-powered equipment when batteries have been installed

backwards, or when the leads from a DC power source have been reversed, and protects the

equipment from potential damage caused by reverse polarity. Prior to availability of

integrated electronics, such a bridge rectifier was always constructed from discrete

components. Since about 1950, a single four terminal component containing the four diodes

connected in the bridge configuration became a standard commercial component and is now

available with various voltage and current ratings.

Output smoothing

For many applications, especially with single phase AC where the full-wave bridge serves to

convert an AC input into a DC output, the addition of a capacitor may be desired because the

bridge alone supplies an output of fixed polarity but continuously varying or pulsating

magnitude.

33

Fig 4.13 Bridge rectifier in parallel capacitor at the output

The function of this capacitor, known as a reservoir capacitor is to lessen the variation in the

rectified AC output voltage waveform from the bridge. One explanation of smoothing is that

the capacitor provides a low impedance path to the AC component of the output, reducing the

AC voltage across, and AC current through, the resistive load. In less technical terms, any

drop in the output voltage and current of the bridge tends to be cancelled by loss of charge in

the capacitor. This charge flows out as additional current through the load. Thus the change

of load current and voltage is reduced relative to what would occur without the capacitor.

Increases of voltage correspondingly store excess charge in the capacitor, thus moderating the

change in output voltage / current. The simplified circuit shown has a well-deserved

reputation for being dangerous, because, in some applications, the capacitor can retain a

lethal charge after the AC power source is removed. If supplying a dangerous voltage, a

practical circuit should include a reliable way to safely discharge the capacitor. If the normal

load cannot be guaranteed to perform this function, perhaps because it can be disconnected,

the circuit should include a bleeder resistor connected as close as practical across the

capacitor. This resistor should consume a current large enough to discharge the capacitor in a

reasonable time, but small enough to minimize unnecessary power waste. Because a bleeder

sets a minimum current drain, the regulation of the circuit, defined as percentage voltage

change from minimum to maximum load, is improved. However in many cases the

improvement is of in significant magnitude. capacitor and the load resistance have a typical

time constant τ = RC where C and R are the capacitance and load resistance respectively. As

long as the load resistor is large enough so that this time constant is much longer than the

time of one ripple cycle, the above configuration will produce a smoothed DC voltage across

the load.

34

In some designs, a series resistor at the load side of the capacitor is added. The smoothing can

then be improved by adding additional stages of capacitor–resistor pairs, often done only for

sub-supplies to critical high-gain circuits that tend to be sensitive to supply voltage noise. The

idealized waveforms shown above are seen for both voltage and current when the load on the

bridge is resistive. When the load includes a smoothing capacitor, both the voltage and the

current waveforms will be greatly changed. While the voltage is smoothed, as described

above, current will flow through the bridge only during the time when the input voltage is

greater than the capacitor voltage. For example, if the load draws an average current of n

Amps, and the diodes conduct for 10% of the time, the average diode current during

conduction must be 10n Amps.

This non-sinusoidal current leads to harmonic distortion and a poor power factor in the AC

supply. In a practical circuit, when a capacitor is directly connected to the output of abridge,

the bridge diodes must be sized to withstand the current surge that occurs when the power is

turned on at the peak of the AC voltage and the capacitor is fully discharged. Sometimes a

small series resistor is included before the capacitor to limit this current, though in most

applications the power supply transformer's resistance is already sufficient. Output can also

be smoothed using a choke and second capacitor. The choke tends to keep the current rather

than the voltage more constant. Due to the relatively high cost of an effective choke

compared to a resistor and capacitor this is not employed in modern equipment.

4.10 REGULATOR IC

It is a three pin IC used as a voltage regulator. It converts unregulated DC current into

regulated DC current. First pin is used for input, second for ground and third pin gives the

rectified and filtered output. It has an inbuilt filtering circuit which removes the ripples

present in the rectified DC obtained from full bridge rectifier circuit.

35

Fig 4.14 MCT7805CT voltage regulator

Normally we get fixed output by connecting the voltage regulator at the output of the filtered

DC see in above diagram. It can also be used in circuits to get a low DC voltage from a high

DC voltage for example we use 7805 to get 5V from 12V. There are two types of voltage

regulators 1. fixed voltage regulators 78xx, 79xx 2. Variable voltage regulators in fixed

voltage regulators there is another classification 1. + ve voltage regulators 2.–vevoltage

regulators positive voltage regulators this include 78xx voltage regulators. The most

36

commonly used ones are 7805 and 7812. 7805 gives fixed 5V DC voltage if input voltage is

in 7.5V, 20V. 7805 is a voltage regulator integrated circuit. It is a member of 78xx series of

fixed linear voltage regulator ICs. The voltage source in a circuit may have fluctuations and

would not give the fixed voltage output. The voltage regulator IC maintains the output

voltage at a constant value. The xx in 78xx indicates the fixed output voltage it is designed to

provide. 7805 provides +5V regulated power supply. Capacitors of suitable values can be

connected at input and output pins depending upon the respective voltage levels.

4.11 The Capacitor Filter

The simple capacitor filter is the most basic type of power supply filter. The application of

the simple capacitor filter is very limited. It is sometimes used on extremely high-voltage,

low current power supplies for cathode ray and similar electron tubes, which require very

little load current from the supply. The capacitor filter is also used where the power-supply

ripple frequency is not critical; this frequency can be relatively high. The capacitor C1 shown

in figure 4.15 is a simple filter connected across the output of the rectifier in parallel with the

load.

Fig 4.15 Full wave rectifier with a capacitor filter

When this filter is used, the RC charge time of the filter capacitor C1 must be short and the

RC discharge time must be long to eliminate ripple action. In other words, the capacitor must

charge up fast, preferably with no discharge a tall. Better filtering also results when the input

frequency is high; therefore, the full-wave rectifier output is easier to filter than that of the

half-wave rectifier because of its higher frequency. For you to have a better understanding of

the effect that filtering has on Eavg, a comparison of a rectifier circuit with a filter and one

37

without a filter is illustrated in figure 4.16 and figure 4.17. The output waveforms in figure

4.16 represent the unfiltered and figure 4.17 represents filtered outputs of the half-wave

rectifier circuit. Current pulses flow through the load resistance RL each time a diode

conducts. The dashed line indicates the average value of output voltage. For the half-wave

rectifier, Eavg is less than half of the peak output voltage. This value is still much less than that

of the applied voltage. With no capacitor connected across the output of the rectifier circuit,

the waveform in figure 4.16 has a large pulsating component compared with the average or

dc component. When a capacitor is connected across the output figure 4.17, the average value

of output voltage Eavg is increased due to the filtering action of capacitor C1

UNFILTERED

Fig 4.16 Half-wave rectifier without filtering

FILTERED

Fig 4.17 Half-wave rectifier with filtering

The value of the capacitor is fairly large, several microfarads, thus it presents a relatively low

reactance to the pulsating current and it stores a substantial charge. The rate of charge for the

38

capacitor is limited only by the resistance of the conducting diode, which is relatively low.

Therefore, the RC charge time of the circuit is relatively short. As a result, when the pulsating

voltage is first applied to the circuit, the capacitor charges rapidly and almost reaches the

peak value of the rectified voltage within the first few cycles. The capacitor attempts to

charge to the peak value of the rectified voltage anytime a diode is conducting, and tends to

retain its charge when the rectifier output falls to zero. The capacitor slowly discharges

through the load resistance RL during the time the rectifier is non-conducting.

The rate of discharge of the capacitor is determined by the value of capacitance and the value

of the load resistance. If the capacitance and load resistance values are large, the RC

discharge time for the circuit is relative Long. A comparison of the waveforms shown in

figure 4.16 and figure 4.17 illustrates that the addition of C1 to the circuit results in an

increase in the average of the output voltage Eavg and a reduction in the amplitude of the

ripple component Er, which is normally present across the load resistance. Now, let's consider

a complete cycle of operation using a half-wave rectifier, a capacitive filter C1, and a load

resistor RL. As shown in figure 4.16, the capacitive filter C1 is assumed to be large enough to

ensure a small reactance to the pulsating rectified current. The resistance of RL is assumed to

be much greater than the reactance of C1 at the input frequency. When the circuit is

energized, the diode conducts on the positive half cycle and current flows through the circuit,

allowing C1 to charge. C1 will charge to approximately the peak value of the input voltage.

The charge is less than the peak value because of the voltage drop across the diode D1. In the

figure 4.16 the heavy solid line on the waveform indicates the charge on C1. In the figure 4.17

the diode cannot conduct on the negative half cycle because the anode of D1 is negative with

respect to the cathode. During this interval C1 discharges through the load resistor RL. The

discharge of C1 produces the downward slope as indicated by the solid line on the wave form

in the figure 4.17. In contrast to the abrupt fall of the applied ac voltage from peak value to

zero, the voltage across C1 and thus across RL during the discharge period gradually

decreases until the time of the next half cycle of rectifier operation. Keep in mind that for

good filtering, the filter capacitor should charge up as fast as possible and discharge as little

as possible as shown in Figure 4.18 and figure 4.19.

39

POSITIVE HALF-CYCLE

Fig 4.18 Capacitor filter circuit

NEGATIVE HALF-CYCLE

Fig 4.19 Capacitor filter circuit

Since practical values of C1 and RL ensure a more or less gradual decrease of the discharge

voltage, a substantial charge remains on the capacitor at the time of the next half cycle of

operation. As a result, no current can flow through the diode until the rising ac input voltage

at the anode of the diode exceeds the voltage on the charge remaining on C1. The charge on

C1 is the cathode potential of the diode. When the potential on the anode exceeds the

potential on the cathode the charge on C1, the diode again conducts and C1 begins to charge

to approximately the peak value of the applied voltage. After the capacitor has charged to its

peak value, the diode will cut off and the capacitor will start to discharge. Since the fall of the

ac input voltage on the anode is considerably more rapid than the decrease on the capacitor

voltage, the cathode quickly become more positive than the anode and the diode ceases to

40

conduct. Operation of the simple capacitor filter using a full-wave rectifier is basically the

same as that discussed for the half-wave rectifier. Referring to figure, you should notice that

because one of the diodes is always conducting on alternation, the filter capacitor charges and

discharges during each half cycle. Note that each diode conducts only for that portion of time

when the peak secondary voltage is greater than the charge across the capacitor.

Fig 4.20 Full-wave rectifier with capacitor filter

Another thing to keep in mind is that the ripple component E r of the output voltage is an ac

voltage and the average output voltage Eavg is the dc component of the output. Since the filter

capacitor offers relatively low impedance to ac, the majority of the ac component flows

through the filter capacitor. The ac component is therefore bypassed around the load

resistance and the entire dc component Eavg flows through the load resistance. This statement

can be clarified by using the formula for XC in a half wave and full-wave rectifier. First, you

must establish some values for the circuit. As you can see from the calculations by doubling

the frequency of the rectifier, you reduce the impedance of the capacitor by one-half. This

allows the ac component to pass through the capacitor more easily. As a result, a full wave

rectifier output is much easier to filter than that of a half-wave rectifier. Remember the

smaller the XC of the filter capacitor with respect to the load resistance the better the filtering

action.

Xc = 1

2 π fC

Since the largest possible capacitor will provide the best filtering. Remember, also, that the

load resistance is an important consideration. If load resistance is made small, the load

current increases, and the average value of output voltage Eavg decreases. The RC discharge

41

time constant is a direct function of the value of the load resistance therefore the rate of

capacitor voltage discharge is a direct function of the current through the load. The greater

load current the more rapid the discharge of the capacitor and the lower the average value of

output voltage. For this reason, the simple capacitive filter is seldom used with rectifier

circuits that must supply a relatively large load current. Using the simple capacitive filter in

conjunction with a full-wave or bridge rectifier provides improved filtering because the

increased ripple frequency decreases the capacitive reactance of the filter capacitor.

4.12 Light Emitting Diode

An LED is a very simple electronics component which lights up when electricity flows

through it. Since it is a diode, electricity can only flow one way. There is usually a flat

section on the side of the LED to mark its polarity: this side should be connected to ground.

This side usually also has a shorter leg. In order to prevent too much current flowing through

an LED and damaging it, it should be connected in series with a resistor.

Fig 4.21 Light Emitting Diode 4.13 Resistor

A resistor is a component of a circuit that resists the flow of electrical current. It has two

terminals across which electricity must pass, and it is designed to drop the voltage of the

current as it flows from one terminal to the other. Resistors are primarily used to create and

maintain known safe currents within electrical components. Resistance is measured in ohms,

after Ohm's law. This law states that electrical resistance is equal to the drop in voltage across

the terminals of the resistor divided by the current being applied. A high ohm rating indicates

a high resistance to current. This rating can be written in a number of different ways - for

example, 81R represents 81 ohms, while 81K represents 81,000 ohms. Materials in general

have a characteristic behavior of opposing the flow of electric charge. This opposition is due

to the collisions between electrons that make up the materials. This physical property, or

ability to resist current, is known as resistance and is represented by the symbol R. Resistance

is expressed in ohms which is symbolized by the capital Greek letter omega.

42

The resistance of any material is dictated by four factors:

Material property-each material will oppose the flow of current differently.

Length-the longer the length, the more is the probability of collisions and, hence, the

larger the resistance.

Cross-sectional area-the larger the area A, the easier it becomes for electrons to flow

and, hence, the lower the resistance.

Temperature-typically, for metals, as temperature increases, the resistance increases.

The amount of resistance offered by a resistor is determined by its physical construction. A

carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a

carbon film resistor consists of a similar ceramic tube, but has conductive carbon film

wrapped around the outside. Metal film or metal oxide resistors are made much the same

way, but with metal instead of carbon. A wire wound resistor, made with metal wire wrapped

around clay, plastic, or fibre glass tubing, offers resistance at higher power levels. Those used

for applications that must withstand high temperatures are typically made of materials such as

cermets, a ceramic-metal composite, or tantalum, a rare metal, so that they can endure the

heat. Resistors are coated with paint or enamel, or covered in moulded plastic to protect them.

Because they are often too small to be written on, a standardized color-coding system is used

to identify them. The first three colors represent ohm value, and a fourth indicates the

tolerance, or how close by percentage the resistor is to its ohm value. This is important for

two reasons: the nature of its construction is imprecise, and if used above its maximum

current, the value can change or the unit itself can burn up. The circuit element used to model

the current-resisting behavior of a material is the resistor. For the purpose of constructing

circuits, resistors shown in Figure 4.22 are usually made from metallic alloys and carbon

compounds. The resistor is the simplest passive element.

43

Fig 4.22 from top to bottom: 14 W,

12 W, and 1-W resistors

TYPES OF RESISTER

Different types of resistors have been created to meet different requirements. Some resistors

are shown in Figure 4.23. The primary functions of resistors are to limit current, divide

voltage and dissipate heat. A resistor is either fixed or variable. Most resistors are of the fixed

type that is their resistance remains constant. The two common types of fixed resistors wire

wound and composition are shown in Figure 4.24. Wire wound resistors are used when there

is a need to dissipate a large amount of heat while the composition resistors are used when

large resistance is needed.

Fig 4.23 Different types of resistors

(a) (b)

Fig 4.24 Fixed resistors: (a) wire wound type (b) Carbon film type

RESISTOR COLOUR CODE

Some resistors are physically large enough to have their values printed on them. Other

resistors are too small to have their values printed on them. For such small resistors color

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coding provides a way of determining the value of resistance. As shown in Figure 4.25 the

color coding consists of three, four, or five bands of color around the resistor.

Fig 4.25 Color coding

The first three bands specify the value of the resistance. Bands A and B represent the first and

second digits of the resistance value and C is usually given as a power of 10 as shown in

figure 4.25. If present the fourth band D indicates the tolerance percentage. For example a 5

percent tolerance indicates that the actual value of the resistance is within ± 5 of the color-

coded value. When the fourth band is absent, the tolerance is taken by default to be ± 20

percent. The fifth band E, if present is used to indicate a reliability factor which is a

Statistical indication of the expected number of components that will fail to have the

indicated resistance after working for 1,000 hours. As shown in Figure 4.25 the statement

“Big Boys Race Our Young Girls, But Violet Generally Wins” can serve as a memory aid in

remembering the color code.

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5. CONCLUSION

From the design of experimental set up with Micro Controller Based Solar Tracking System

Using Stepper Motor If we compare Tracking by the use of LDR with Fixed Solar Panel

System we found that the efficiency of Micro Controller Based Solar Tracking System is

improved by 30-45% and it was found that all the parts of the experimental setup are giving

good results. The required Power is used to run the motor by using Step-Down T/F by using

220V AC. Moreover, this tracking system does track the sun in a continuous manner. And

this system is more efficient and cost effective in long run. From the results it is found that,

by automatic tracking system, there is 30 % gain in increase of efficiency when compared

with non-tracking system. The solar tracker can be still enhanced additional features like rain

protection and wind protection which can be done as future work.

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6. REFERENCES

[1] Rizk J. and Chaiko Y. “Solar Tracking System: More Efficient Use of Solar Panels”,

World Academy of Science, Engineering and Technology 41 2008.

[2] Filfil Ahmed Nasir, Mohussen Deia Halboot, Dr. Zidan Khamis A. “Microcontroller-

Based Sun Path Tracking System”, Eng. & Tech. Journal, Vol. 29, No.7, 2011.

[3] Alimazidi Mohammad, Gillispie J, Mazidi, Rolin D. McKinlay, “The 8051

Microcontroller and Embedded Systems”, An imprint of Pearson Education.

[4] Mehta V K, Mehta Rohit, “Principles of Electronics”, S. Chand & Company Ltd.

[5] Balagurusamy E, “Programming in ANSI C”, Tata McGraw-Hill Publishing Company

Limited.

[6] Damm, J. Issue #17, June/July 1990. An active solar tracking system, Home Brew

Magazine.

[7] Koyuncu B and Balasubramanian K, “A microprocessor controlled automatic sun

tracker,” IEEE Trans. Consumer Electron., vol. 37, no. 4,pp. 913-917, 1991.

[8] Konar A and Mandal A K, “Microprocessor based automatic sun tracker,” IEE Proc. Sci.,

Meas. Technol., vol. 138, no. 4, pp. 237-241,1991.

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