1. 1
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
2. 2
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
3. 3
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 SolarTracker
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
5. 5
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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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.
9. 9
Fig 3.3 Printed circuit board
Fig 3.4 Single sided PCB
Double-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 PCB
Multi-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 PCB
2) 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
13. 13
is about right. Etching time may vary between 10 to as long as 90 minutes, depending on the
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.
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4. COMPONENTS DESCRIPTION
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.
15. 15
4.3 Methods of Drive
1. Active Trackers
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
16. 16
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.
Fig 4.1 Light Dependent Resistor
2. 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
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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.
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
18. 18
Theory
Stepper motor
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
19. 19
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
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 4
1 1 0 1 0
2 1 0 0 1
3 0 1 0 1
4 0 1 1 0
1 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 transistors
Implementation
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
23. 23
Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
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
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Idle Mode: 0.35 mA
Power-down Mode: < 1 μA
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
25. 25
Overview-
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
26. 26
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
27. 27
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.
28. 28
• 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.
29. 29
• 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
30. 30
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.
31. 31
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
=
𝐕𝐬
𝐕𝐩
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.
32. 32
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.
33. 33
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.
34. 34
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.
35. 35
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.
36. 36
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
commonly used ones are 7805 and 7812. 7805 gives fixed 5V DC voltage if input voltage is
37. 37
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
without a filter is illustrated in figure 4.16 and figure 4.17. The output waveforms in figure
38. 38
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
capacitor is limited only by the resistance of the conducting diode, which is relatively low.
39. 39
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.
40. 40
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
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
41. 41
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 Er 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
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
42. 42
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.
The resistance of any material is dictated by four factors:
Material property-each material will oppose the flow of current differently.
43. 43
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.
Fig 4.22 from top to bottom:
1
4
W,
1
2
W, and 1-W resistors
44. 44
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
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.
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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.
