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Transcript of GSM Based Irrigation System
GSM BASED IRRIGATION SYSTEM
THE INSTITUTION OF ELECTRONICS
AND
TELECOMMUNICATION ENGINEERS
NEW DELHI
PROJECT REPORT
ON
“GSM Based Irrigation System”
Submitted to,
The Institution of Electronics & Telecommunication Engineers, New Delhi
at Rajkot center towards the partial fulfillment of the Degree of
The Institution of Electronics & Telecommunication Engineers in
“Electronics & Telecommunication Engineering”
Guided By.
Dr. H.N. Pandya (Ms.C., Ph. D)H.O.D. Electronics.(Saurashtra Univerity)Rajkot.
I.E.T.E. RAJKOT SUBCENTER 1
Submitted
LAKHANI ARCHITA M
(Mem. No.SG-172792)
GSM BASED IRRIGATION SYSTEM
THE INSTITUTION OF ELECTRONICS
AND
TELECOMMUNICATION ENGINEERS
NEW DELHI
C E R T I F I C AT E
This is to certify that this is a bonafide record of the project work done
satisfactorily by LAKHANI ARCHITA (Mem. No.SG- 172792) towards the partial
fulfillment of her AMIETE examination. This report has not been submitted for any
other examination and is not from a part of any other course undergone by the
candidate.
Guided By.
Dr. H.N. Pandya (Ms.C., Ph. D)H.O.D. Electronics.(Saurashtra Univerity)Rajkot.
I.E.T.E. RAJKOT SUBCENTER 2
GSM BASED IRRIGATION SYSTEM
THE INSTITUTION OF ELECTRONICS
AND
TELECOMMUNICATION ENGINEERS
NEW DELHI
DECLARATION
GSM Based Irrigation System
I hereby declare that the work presented in this project report entitled
“GSM Based irrigation System” is a partial fulfillment of my AMIETE in Electronics
institution of Electronics and Telecommunication and is an authenticated record of
my own work carried out under the valuable guidance of Dr. H. N. PANDYA The
matter embodied in the report has not been submitted for the award of any other
degree or diploma.
I.E.T.E. RAJKOT SUBCENTER 3
Submitted By:-
LAKHANI ARCHITA M
(Mem. No.SG-172792)
GSM BASED IRRIGATION SYSTEM
PREFACE
At present because of rapid globalization and industrialization there is a
big need of skilled and trained engineers. All industries need good and
trained engineers because of this reason “IETE” has adopted Degree in
Electronics and Telecommunication.
Degree in Electronics and Telecommunication is a unique course in
reputed IETE centers in India. This course provides both theoretical and
practical knowledge about Electronics. Student can get theoretical
knowledge by experienced and learned professors of IETE centers.
As a part of fulfillment of the degree I have selected a project Work on
“GSM BASED IRRIGATION SYSTEM” after the enough discussion
with my guide Mr. H. N. Pandya.
Describing the various methods of irrigation I have constructed on “GSM
BASED IRRIGATION SYSTEM”, I have used AT89 C2051 as Micro-
Controllers. Using different types of sensors the moisture is sensed and
thus water supply is control to soil.
I.E.T.E. RAJKOT SUBCENTER 4
GSM BASED IRRIGATION SYSTEM
ACKNOWLEDGEMENT
It is a great opportunity for a Degree student to prepare “Project Report”
to know about of practical aspects of the field.
First of all I am very much thankful to “IETE” to include this kind of
subjects in Degree syllabus in which students can get practical
knowledge. I humbly pay my respect to IETE authority and director for
giving me such opportunity to prepare my report.
I am thankful to Prof Dr. H. N. PANDYA for giving me his valuable time
and co-operation to develop the project on object counter by giving
guidance.
I.E.T.E. RAJKOT SUBCENTER 5
GSM BASED IRRIGATION SYSTEM
CONTENS
Sr No Name Page .No
1 PREFACE 4
2 ACKNOWLEDGEMENT 5
3 INTRODUCTION 7
4 GENERAL OVERVIEW 18
PROJECT MEANS 19
ABSTRACT 21
5 MAIN OVERVIEW 22
LIST OF COMPONENTS USED 23
CIRCUIT DESCRIPTION AND
OPERATION
24
6 MATERIALS OVERVIEW 29
MICROCONTROLLER 30
LED 46
DIODE 51
RESISTOR 67
CAPACITOR 73
TRANSSFORMER 79
7 DATASHEET OVERVIEW 90
MICROCONTROLLER
AT89C2O51
93
SINGLE TIMER 106
CIRCUIT SYMBOLE 116
8 REFERENCE BOOKS AND 120
I.E.T.E. RAJKOT SUBCENTER 6
GSM BASED IRRIGATION SYSTEM
WEBSITES
INTRODUCTION
Types of irrigation
Basin flood irrigation of wheat
Various types of irrigation techniques differ in how the water obtained from
the source is distributed within the field. In general, the goal is to supply the entire
field uniformly with water, so that each plant has the amount of water it needs,
neither too much nor too little.
Surface irrigation
Main article: Surface irrigation
In surface irrigation systems water moves over and across the land by simple
gravity flow in order to wet it and to infiltrate into the soil. Surface irrigation can be
subdivided into furrow, borderstrip or basin irrigation. It is often called flood
irrigation when the irrigation results in flooding or near flooding of the cultivated
land. Historically, this has been the most common method of irrigating
agricultural land.
I.E.T.E. RAJKOT SUBCENTER 7
GSM BASED IRRIGATION SYSTEM Where water levels from the irrigation source permit, the levels are controlled
by dikes, usually plugged by soil. This is often seen in terraced rice fields (rice
paddies), where the method is used to flood or control the level of water in each
distinct field. In some cases, the water is pumped, or lifted by human or animal
power to the level of the land.
Localized irrigation
Spray Head
Localized irrigation is a system where water is distributed under low
pressure through a piped network, in a pre-determined pattern, and applied as a
small discharge to each plant or adjacent to it. Drip irrigation, spray or micro-
sprinkler irrigation and bubbler irrigation belong to this category of irrigation
methods.
Drip Irrigation
Main article: Drip Irrigation
Drip Irrigation - A dripper in action
I.E.T.E. RAJKOT SUBCENTER 8
GSM BASED IRRIGATION SYSTEM Drip irrigation, also known as trickle irrigation, functions as its name
suggests. Water is delivered at or near the root zone of plants, drop by drop. This
method can be the most water-efficient method of irrigation, if managed properly,
since evaporation and runoff are minimized. In modern agriculture, drip irrigation is
often combined with plastic mulch, further reducing evaporation, and is also the
means of delivery of fertilizer. The process is known as fustigation.
Drip Irrigation Layout and its parts
Deep percolation, where water moves below the root zone, can occur if a
drip system is operated for too long of a duration or if the delivery rate is too high.
Drip irrigation methods range from very high-tech and computerized to low-tech and
relatively labor-intensive. Lower water pressures are usually needed than for most
other types of systems, with the exception of low energy center pivot systems and
surface irrigation systems, and the system can be designed for uniformity throughout
a field or for precise water delivery to individual plants in a landscape containing a
mix of plant species.
Although it is difficult to regulate pressure on steep slopes, pressure
compensating emitters are available, so the field does not have to be level. High-
tech solutions involve precisely calibrated emitters located along lines of tubing that
extend from a computerized set of valves. Both pressure regulation and filtration to
remove particles are important. The tubes are usually black (or buried under soil or
mulch) to prevent the growth of algae and to protect the polyethylene from
degradation due to ultraviolet light. But drip irrigation can also be as low-tech as a
I.E.T.E. RAJKOT SUBCENTER 9
GSM BASED IRRIGATION SYSTEMporous clay vessel sunk into the soil and occasionally filled from a hose or bucket.
Subsurface drip irrigation has been used successfully on lawns, but it is more
expensive than a more traditional sprinkler system.
Surface drip systems are not cost-effective (or aesthetically pleasing)
for lawns and golf courses. In the past one of the main disadvantages of the
subsurface drip irrigation (SDI) systems, when used for turf, was the fact of having to
install the plastic lines very close to each other in the ground, therefore disrupting
the turf grass area. Recent technology developments on drip installers like the drip
installer at New Mexico State University Arrow Head Center, places the line
underground and covers the slit leaving no soil exposed.
Sprinkler irrigation
Sprinkler irrigation of blueberries in Plainville, New York
A traveling sprinkler at Millets Farm Centre, Oxford shire, UK
I.E.T.E. RAJKOT SUBCENTER 10
GSM BASED IRRIGATION SYSTEM
In sprinkler or overhead irrigation, water is piped to one or more central
locations within the field and distributed by overhead high-pressure sprinklers or
guns.
A system utilizing sprinklers, sprays, or guns mounted overhead on
permanently installed risers is often referred to as a solid-set irrigation system.
Higher pressure sprinklers that rotate are called rotors and are driven by a ball drive,
gear drive, or impact mechanism. Rotors can be designed to rotate in a full or partial
circle. Guns are similar to rotors, except that they generally operate at very high
pressures of 40 to 130 lbf/in² (275 to 900 kPa) and flows of 50 to 1200 US gal/min (3
to 76 L/s), usually with nozzle diameters in the range of 0.5 to 1.9 inches (10 to 50
mm). Guns are used not only for irrigation, but also for industrial applications such
as dust suppression and logging.
Sprinklers may also be mounted on moving platforms connected to the
water source by a hose. Automatically moving wheeled systems known as traveling
sprinklers may irrigate areas such as small farms, sports fields, parks, pastures, and
cemeteries unattended. Most of these utilize a length of polyethylene tubing wound
on a steel drum. As the tubing is wound on the drum powered by the irrigation water
or a small gas engine, the sprinkler is pulled across the field. When the sprinkler
arrives back at the reel the system shuts off. This type of system is known to most
people as a "water reel" traveling irrigation sprinkler and they are used extensively
for dust suppression, irrigation, and land application of waste water. Other travelers
use a flat rubber hose that is dragged along behind while the sprinkler platform is
pulled by a cable. These cable-type travelers are definitely old technology and their
use is limited in today's modern irrigation projects.
I.E.T.E. RAJKOT SUBCENTER 11
GSM BASED IRRIGATION SYSTEM
Center pivot irrigation
The hub of a center-pivot irrigation system.
Center pivot irrigation is a form of sprinkler irrigation consisting of several
segments of pipe (usually galvanized steel or aluminum) joined together and
supported by trusses, mounted on wheeled towers with sprinklers positioned along
its length. The system moves in a circular pattern and is fed with water from the pivot
point at the center of the arc. These systems are common in parts of the United
States where terrain is flat.
Center pivot with drop sprinklers. Photo by Gene Alexander, USDA Natural
Resources Conservation Service.
I.E.T.E. RAJKOT SUBCENTER 12
GSM BASED IRRIGATION SYSTEM
Most center pivot systems now have drops hanging from a u-shaped pipe
called a gooseneck attached at the top of the pipe with sprinkler heads that are
positioned a few feet (at most) above the crop, thus limiting evaporative losses.
Drops can also be used with drag hoses or bubblers that deposit the water directly
on the ground between crops.
The crops are planted in a circle to conform to the center pivot. This type of
system is known as LEPA (Low Energy Precision Application). Originally, most
center pivots were water powered. These were replaced by hydraulic systems (T-L
Irrigation) and electric motor driven systems (Lindsay, Reinke, Valley, Zimmatic,
Pierce, Grupo Chamartin. Most systems today are driven by an electric motor
mounted low on each span. This drives a reduction gearbox and transverse
driveshafts transmit power to another reduction gearbox mounted behind each
wheel. Precision controls, some with GPS location and remote computer monitoring,
are now available.
Wheel line irrigation system in Idaho. 2001. Photo by Joel McNee, USDA Natural
Resources Conservation Service.
Lateral move (side roll, wheel line) irrigation
A series of pipes, each with a wheel of about 1.5 m diameter permanently
affixed to its midpoint and sprinklers along its length, are coupled together at one
I.E.T.E. RAJKOT SUBCENTER 13
GSM BASED IRRIGATION SYSTEM
edge of a field. Water is supplied at one end using a large hose. After sufficient
water has been applied, the hose is removed and the remaining assembly rotated
either by hand or with a purpose-built mechanism, so that the sprinklers move 10 m
across the field. The hose is reconnected. The process is repeated until the opposite
edge of the field is reached. This system is less expensive to install than a center
pivot, but much more labor intensive to operate, and it is limited in the amount of
water it can carry. Most systems utilize 4 or 5-inch (130 mm) diameter aluminum
pipe. One feature of a lateral move system is that it consists of sections that can be
easily disconnected. They are most often used for small or oddly-shaped fields, such
as those found in hilly or mountainous regions, or in regions where labor is
inexpensive.
Sub-irrigation
Sub irrigation also sometimes called seepage irrigation has been used for
many years in field crops in areas with high water tables. It is a method of artificially
raising the water table to allow the soil to be moistened from below the plants' root \
zone. Often those systems are located on permanent grasslands in lowlands or river
valleys and combined with drainage infrastructure. A system of pumping stations,
canals, weirs and gates allows it to increase or decrease the water level in a network
of ditches and thereby control the water table.
Sub-irrigation is also used in commercial greenhouse production, usually for
potted plants. Water is delivered from below, absorbed upwards, and the excess
collected for recycling. Typically, a solution of water and nutrients floods a container
or flows through a trough for a short period of time, 10-20 minutes, and is then
pumped back into a holding tank for reuse. Sub-irrigation in greenhouses requires
fairly sophisticated, expensive equipment and management. Advantages are water
I.E.T.E. RAJKOT SUBCENTER 14
GSM BASED IRRIGATION SYSTEM
and nutrient conservation, and labor-saving through lowered system
maintenance and automation. It is similar in principle and action to subsurface drip
irrigation.
Manual irrigation using buckets or watering cans
These systems have low requirements for infrastructure and technical
equipment but need high labor inputs. Irrigation using watering cans is to be found
for example in peri-urban agriculture around large cities in some African countries.
Automatic, non-electric irrigation using buckets and ropes
Besides the common manual watering by bucket, an automated, natural
version of this also exist. Using plain polyester ropes combined with a prepared
ground mixture can be used to water plants from a vessel filled with water. The
ground mixture would need to be made depending on the plant itself, yet would
mostly consist of black potting soil, vermiculite and perlite. This system would (with
certain crops) allow you to save expenses as it does not consume any electricity and
only little water (unlike sprinklers, water timers, ...). However, it may only be used
with certain crops (probably mostly larger crops that do not need a humid
environment; perhaps e.g. paprika's).
Irrigation using stones to catch water from humid air
In countries where at night, humid air sweeps the countryside, stones are
used to catch water from the humid air by transpiration. This is for example practiced
in the vineyards at Lanzarote.
Dry terasses for irrigation and water distribution
In subtropical countries as Mali and Senegal, a special type of terrassing
(without flood irrigation or intent to flatten farming ground) is used. Here, a 'stairs' is
I.E.T.E. RAJKOT SUBCENTER 15
GSM BASED IRRIGATION SYSTEM
made trough the use of ground level differences which helps to decrease water
evaporation and also distributes the water to all patches (sort of irrigation).
Sources of irrigation water
Sources of irrigation water can be groundwater extracted from springs or by
using wells, surface water withdrawn from rivers, lakes or reservoirs or non-
conventional sources like treated wastewater, desalinated water or drainage water.
A special form of irrigation using surface water is spate irrigation, also called
floodwater harvesting. In case of a flood (spate) water is diverted to normally dry
river beds (wadi’s) using a network of dams, gates and channels and spread over
large areas. The moisture stored in the soil will be used thereafter to grow crops.
Spate irrigation areas are in particular located in semi-arid or arid, mountainous
regions. While floodwater harvesting belongs to the accepted irrigation methods,
rainwater harvesting is usually not considered as a form of irrigation. Rainwater
harvesting is the collection of runoff water from roofs or unused land and the
concentration of this water on cultivated land. Therefore this method is considered
as a water concentration method.
How an in-ground irrigation system works
Most commercial and residential irrigation systems are "in ground" systems,
which means that everything is buried in the ground. With the pipes, sprinklers, and
irrigation valves being hidden, it makes for a cleaner, more presentable landscape
without garden hoses or other items having to be moved around manually.
Water source and piping
The beginning of a sprinkler system is the water source. This is usually a
tap into an existing (city) water line or a pump that pulls water out of a well or a
pond.
I.E.T.E. RAJKOT SUBCENTER 16
GSM BASED IRRIGATION SYSTEM
The water travels through pipes from the water source through the valves to
the sprinklers. The pipes from the water source up to the irrigation valves are called
"mainlines", and the lines from the valves to the sprinklers are called "lateral lines".
Most piping used in irrigation systems today are HDPE and MDPE or PVC or PEX
plastic pressure pipes due to their ease of installation and resistance to corrosion.
I.E.T.E. RAJKOT SUBCENTER 17
GSM BASED IRRIGATION SYSTEM
I.E.T.E. RAJKOT SUBCENTER 18
GSM BASED IRRIGATION SYSTEM
PROJECT MEANS:-
Before tak ing p ro jec t work fo r execu t ion , i t i s
qu i te necessary to have an exac t i dea o f the word .
“PROJECT ”
“P ” s tands fo r P lann ing : P lann ing i s the word , wh ich
dea ls w i th the idea o f ac t p roposed to be done .
“R ” s tands fo r Resources : Resources a re the means ,
wh ich gu ide to p romote the func t ion o f the p lan . There
mus t be a l l necessary resources in o rder to ma in ta in
good p ro jec t work .
“O ” s tands fo r Opera t ion : Opera t ion i s ac tua l l y a l l t he
t ype o f work , wh ich i s to be per fo rmed by workers to
comple te the ob jec t .
“ J ” s tands fo r Jo in t e f fo r t : I t means the combined
e f fo r t s o f worker and o ther s ta f f to comple te the work .
“E ” s tands fo r Exp la in Eng ineer func t ion : Bo th the bod ies ’
i . e . p lann ing body and eng ineer ing body work toge ther
w i th eng ineers th rough the i r techn iques fo r good
p roduc t ion .
“C ” S ign i f ies Communica t ion : For the execu t ion o f the
p lan , the commun ica t ion i s ve ry necessary .
I.E.T.E. RAJKOT SUBCENTER 19
GSM BASED IRRIGATION SYSTEM
“T ” Symbo l i zes Task o f techn iques o f the work ing :
Task o f work ing w i th co - opera t ion o f the work ing
body and con t ro l work ing body .As a mat te r o f fac t the
word “PROJECT” i s used spec ia l l y fo r cons t ruc t iona l
and manufac tu r ing purpose .
I.E.T.E. RAJKOT SUBCENTER 20
GSM BASED IRRIGATION SYSTEM
ABSTRACT
This system is a remote controlled pump control system.
The remote control media used is the regular GSM cell phone.
The system installed at the farm has four moisture
sensors which analyse the moisture content of the soil.
When the sensors are dry, a buzzer is activated. When
the user call up the phone kept in the system, he hears the
buzzer which will let him know that the farm has dried up.
Then by pressing a particular switch on his phone he can
switch on the water pump. The pump can be switched off in the
same manner.
This system, if implemented, will save a lot of time,
energy and money of the farmers by automation of the job. A
simple modification can also make the system completely
automatic.
I.E.T.E. RAJKOT SUBCENTER 21
GSM BASED IRRIGATION SYSTEM
I.E.T.E. RAJKOT SUBCENTER 22
GSM BASED IRRIGATION SYSTEM
LIST OF COMPONENTS USED
FOR THE GSM BASED IRRIGATION SYSTEM
(1) DIODE
(2) TRANSISTOR
(i)PNP
(ii)NPN
(3) TRAMSFORMER 230V 12-0-12V/500 MA CAPACITOR
(i) 10
(ii) 100
(iii) 0.1
(iv) 22
(v)
(4) RESISTOR
(i) 100KΩ
(ii) 10K
(iii) 2k2
(iv) 220k
(v) 1k
(6) Cell phone interface
(7) DTMF decoder section
(8) Moisture sensors
(9) Main controller section
(10) Indicator section
(11) Relay driver and the pump control section
(12) Power supply section
I.E.T.E. RAJKOT SUBCENTER 23
GSM BASED IRRIGATION SYSTEM
CIRCUIT DESCRIPTION AND OPERATION
This system can be used in fields for providing them with water by switching
on and off the pumps at the field using a mobile phone. For this purpose a cell
phone with a sim card is to be attached to the system and placed at the farm itself.
The system has moisture sensors with variable sensitivity that can detect moisture
levels in the soil. Multiple sensors are used so that moisture in the soil can be
measured at more than one place. The system gives audible clues to the user about
the moisture content and the pump status to the user or the person who call up the
phone that is attached to the system and placed at the field.
For better understanding the system can be divided in to smaller parts.
Segregation according to small functional blocks can be done as below.
1. The cell phone interface
2. The DTMF decoder section
3. The moisture sensors
4. The main controller section
5. The indicator section
6. The relay driver and the pump control section
7. The power supply section
The cell phone interface: this section is the heart of the entire circuit. It is the
section with which the cell phone is attached to the system and through which it
communicates with the system. The cell phone that is attached to the system is kept
I.E.T.E. RAJKOT SUBCENTER 24
GSM BASED IRRIGATION SYSTEMin auto answer mode after connecting a hands free set to it. Whenever this phone is
called up, it picks up the phone after which the DTMF tones generated by the calling
cell phone will also be produced at the cell phone connected to the system. This fact
is the essence behind the working of the entire project. The DTMF tones from the
switches depressed at the calling cell phone are transmitted to the system cell
phone via the GSM network. Initially this system would seem rather costly as
whenever a pump is to be switched on or off or the status of the field is to be known,
a call has to be made. But since nowadays call costs are going so low that this is not
much of a problem. Moreover when the call cost is compared with the cost of
physical visit of the farmer to the field, it proves to be much cheaper. Also more and
more telecom service providers are giving CUG plans in which call rates are
negligible or even zero. The cell phone hands free is attached to a microphone is the
system. The mic picks up the DTMF tones from the hands free speaker. These
tones are very small in amplitude thus a single transistor collector feedback biased
amplifier stage has been employed for amplifying the signals to a specific level so
that they can be applied to the DTMF decoder for decoding.
The DTMF decoder section: this section is fed input from the single stage
transistor amplifier output. The output of the amplifier and thus the input to the
decoder are the DTMF tones from the system cell phone which are in turn the tones
which were send from the caller cell phone. The decoder is built around a very
popular ASIC the MT8870. This chip accepts DTMF tones and converts them into
BCD data corresponding to the switch that was depressed at the caller phone. Along
with this data, the decoder also generates one specific high signal called the StD
signal from its pin 15. This signal is generated whenever the chip receives any valid
DTMF tone and last for the instant for which the tone lasts. This signal is used to
convey the micro controller that a new data nibble has arrived. The decoder exactly
decodes the DTMF tones by the help of an in built oscillator that generates a very
stable frequency with the help of an externally connected crystal resonator of
3.5795MHz. the output of the DTMF decoder is fed to the controller for further
processing.
I.E.T.E. RAJKOT SUBCENTER 25
GSM BASED IRRIGATION SYSTEMThe moisture sensors: there are three moisture sensors employed in the
system. The concept of multiple sensors is based on the fact that different parts of
the field may have different amount of moisture at the same time and that has to be
taken into consideration. As many no. of sensors can be used in the system
although here only four are employed. The sensors actually measure the soil
resistivity to gauge the amount of moisture present in it. Each sensor has been
made using a 555 timer employed as a schmitt trigger. The sensitivity of each
sensor is adjustable using a preset. Moreover each sensor has been fitted with fail
safe mechanism in the form of a 0.1uF capacitor to prevent false triggering. The
outputs of the sensors are active high which can be seen on an LED which has been
connected on the output pin of each sensor so that the status of the sensor can be
easily seen. These LEDs also help in setting the sensitivity of the sensors. The
sensors are fed from the probes that are to be inserted in the soil for measuring the
resistance between the two points at which the probes are entered. The probes can
be of any conductive material, but material which are not corrosive or prone to
rusting must be used. The best alternative is to use graphite rods as sensor probes.
These rods can be easily available by breaking exhausted dry batteries. The outputs
of the sensors are also fed to the microcontroller for further processing.
The main controller section: this section controls the entire system. It
actually integrates the individual components and then unifies their functions as one.
The controller that has been used here is the 89C2051 which belongs to the very
popular 8051 series of micro controllers from Intel. The 2051 has been utilized
because it is a 20 pin controller and thus far smaller in size than the usual 40 pin
version. The main purpose of the controller to be used in this project is that by its
usage further advancement and modification of the project becomes easy and
feasible. Moreover the component count of the entire system remains small in the
scenario when a micro controller is used. Less no of components mean less no of
failure points which increases the system reliability. The micro controller is clocked
by a 12MHz quartz crystal resonator. Other associated circuitry for the controller like
the power-on-reset network and the manual reset network are also connected to the
controller.
I.E.T.E. RAJKOT SUBCENTER 26
GSM BASED IRRIGATION SYSTEM The controller accepts input on its port 1 which has been configured as the
input port. The first nibble to the input port is the data from the sensors whereas the
second nibble is the data obtained from the DTMF decoder section. The StD output
of the DTMF decoder is applied as interrupt to the controller. As the entire 8051
family is built in such a way as to accept active low interrupts, the signal from the
DTMF decoder is first inverted with the help of a single npn transistor and then
applied to interrupt the controller.
The indicator section: contrary to other type of indicators, usually visual in the
form of leds, here audible indication is used. This is due to the fact that an audible
clue about the status is to be given to the user on the phone. To accomplish this two
different buzzers are implemented. One of the buzzers indicates that the pump has
been started and running. This buzzer plays a music to distinguish it from the other
continuous buzzer It stays on for the time the pump is on. The other buzzer is a
continuous one which rings when all the sensors are dry. Display LEDs are also
utilized for visual indication of the status.
The relay driver and the pump control section: this section is connected to
the output of the controller and is used to control the relay which in turn controls the
pump. There are two problems in driving the relay directly from the controller. The
first is that the outputof the controller is in the vicinity of +5V which will not be able to
drive the 12V /200ohm relay. The other thing is that the controller is also not able to
provided that high amount of current that is required by the magnetizing coils of the
relay.
The power supply section. The system requires two distinct dc voltages to
function- +5V dc for the entire circuit except the relay driver section and the relays
themselves as both are rated at 12V. The transformer used is the 12-0-12V/500mA
which is more than enough. The output ac voltage of the mains transformer is fed to
a rectifier for converting it into dc. This impure unregulated dc is applied to a large
value filter capacitor which smoothes the dc voltage. Finally the unregulated dc is
then applied to the 7805 voltage regulator chip so as to obtain the necessary +5
volts needed by the electronics circuit.
I.E.T.E. RAJKOT SUBCENTER 27
GSM BASED IRRIGATION SYSTEM
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GSM BASED IRRIGATION SYSTEM
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GSM BASED IRRIGATION SYSTEM
MICROCONTROLLER
Microcontroller is a computer on a single chip. Micro suggests that the device
is small and controller indicates that the device can be used to control the events,
processes or objects. Microcontroller is becoming a key component in many
electronics products like washing machine, un-interrupted power supply, color
television, CD player, remote control, robots, CNC machines, modems, printers,
keyboards, advertisement displays. Temperature indicator and controller, pressure
monitor, elevators, engine management system in automobiles, measurements
instruments, mobile phones, security system, fire alarm system and many others.
The use of microcontroller is so widespread that it is almost impossible to work in
electronics field without utilizing it.
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Overview Of Microcontroller
A microcontroller is an integrated chip that is often part of an embedded
system. The microcontroller includes a CPU, RAM, ROM, I/O ports and timers like a
standard computer but because they are designed to execute only a single specific
task to control a single system, they are much smaller and simplified so that they
can include all the functions required on a single chip.
Early controllers were built from discrete components and they were large in
size. Later microprocessors were build and microcontrollers were able to fit onto a
circuit board. Microcontroller now places all of the needed components onto a single
chip. With the advent of VLSI technology, microcontroller chip are becoming
essentially single chip microcomputers. Microcontrollers collect data from the input
devices, process the data and make decision based on the result of process. The
input may be for sensing and measurement of some aspects of the environment and
output may be generation of one or more control signals that effect the environment
in a desirable manner. Input may be simple binary valued signal from switch, group
of binary digits from ADC, serial data from computer, pulses from infrared receiver or
signals from sensors. Output may be solenoid, relay, LCD, LED, indicators,
Optodevices, motors etc. Assembly language is stored in either internal ROM or
external ROM. Internal RAM is used for processing and temporary storage.
Microcontrollers have become common in many areas, and can be found in
variety of applications like intercom, telephones, mobiles, security system, door
openers, curtain controller, answering machines, fax, television, CNC machines,
washing machines, VCR/VCD, DVD players, remote controls, musical instruments,
sewing machine, camera, Microwave ovens, laser printers computer equipments,
instrumentation and many other home appliances. They are widely used in
automobiles and have become a central part of industrial robotics. The
microcontrollers is most essential IC for continuous process- based industries like
chemical refinery, pharmaceuticals, steels, programmable logic control system(PLC)
and distributed control system(DCS).I.E.T.E. RAJKOT SUBCENTER 31
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Microcontrollers do not require significant processing power because they are
usually used to control a single process and execute simple instructions.
The automotive market has been a major driver of microcontrollers, many of
which have been developed for automotive applications. Because of automotive
microcontrollers have to withstand harsh environmental conditions, they may be
highly reliable and durable. Automotive microcontrollers, like their counterparts are
very inexpensive and are able to deliver powerful features that would otherwise be
impossible, or too costly to implement.
Brief History Of 8051 Microcontroller Family:-
Intel Corporation introduced an 8 bit 8051 microcontroller in 1981. This
microcontroller has 128 byte RAM, 4K bytes ROM, two timers one serial ports and
four I/O ports on single chip.8051 is a 8 bit processor because CPU can work 8 bit
data at a time. If data is larger then 8 bit, it has to be broken into pieces of 8 bit. Intel
allowed other manufacturers to make flavors of 8051 with the condition that it should
be code compatible with Intel 8051. There are 20 vendors like Philips, siemens;
Dallas, OKI, Fujitsu, Atmel, etc. are building their own versions of the 8051.
Comparison Of Some 8051 Family.
Chip ROM(bytes) RAM(bytes) Timers I/O pins
8031 -- 128 2 32
8032 -- 256 3 32
8051 4K 128 2 32
8052 8K 256 3 32
8751 4K(EPROM) 128 2 32
8752 8K(EPROM) 256 3 32
89C51 4K flash 128 2 32
89C52 8K flash 256 3 32
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89C1051
(20 pin)
1K flash 64 1 15
89C2051 2K flash 128 2 15
89S51 4K flash 128 2 40
Reasons For The Success Of Microcontroller:-
Microcontrollers have powerful, cleverly chosen electronics which is able to
control a variety of processes and devices( industrial automatics, voltage,
temperature, engines, etc) independently or by means of I/O instruments such
as switches, buttons, sensors, LCD screens, relays…. Etc.
Their low cost makes them suitable for installing in places, which attracted no
such interest in the past. This is the fast accountable for today’s market being
swamped with cheap automation and “intelligent” toys.
Writing and loading a program into microcontroller is very easy. All that is
required is; any PC (software is very friendly and intuitive) and one simple
device (programmer) for loading a written program in microcontroller.
Block Diagram Of Microcontroller:-
A microcontroller is an integrated chip that is often part of an embedded
system. The microcontroller includes a CPU, RAM, ROM, I/O ports and timers like a
standard computer, but because they are designed to execute only a single specific
task to control a single system, they are much smaller and simplified so that they
can include all the functions required on a single chip. Simplified block diagram of
the microcontroller is shown in figure1.
I.E.T.E. RAJKOT SUBCENTER 33
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Fig 1: simplified block diagram of the microcontroller
Microcontroller incorporates all features found in microprocessor Such as
ALU, General purpose registers, accumulators, program counters, stack pointer,
timing control unit, interrupts etc. In addition to these microcontrollers incorporates
ROM, RAM, I/O, serial I/O, timers etc.
Parallel Serial Input-Output Port:- Microcontroller contains parallel input
output ports to interface it with real world. For Example: 8051 contains 4 parallel
input-output ports to interface with I/O devices. The 8085 microprocessor requires
separate chips such as 8255 (programmable peripheral interface) to interface it with
I/O devices. Microcontroller also has in built serial port. Serial communication with
microcontroller is simpler.
Timers: Microcontroller has inbuilt timers. 8051 has 2 16 bit timers. Timers
provide real time interrupt to the processor for specific events. It can be used
as a counter to count number of events. Typical example is object counter.
Interrupt is generated when count value overflows.
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ROM : Microcontroller has inbuilt Read only memory (ROM) which is used to
store program code and data required during execution such as look up
tables. 8051 microcontrollers has 4K-ROM, 8751 has 4K EPROM (erasable
programmable read only memory), 89C51 has 4K flash memory. ROM is
programmed during manufacturing process. EPROM can be programmed using
EPROM programmer. It needs to erase using ultraviolet eraser. 89C51 is very
popular version of 8051 because it contains flash memory. It is ideal for fast
development since flash memory can be erased and programmed in seconds.
Erasing and programming can be done by microcontroller programmer unit itself.
RAM: Microcontroller has inbuilt Random Access Memory. It is used to store
information for temporary use. CPU can write RAM as well as read it. Any
information stored in the RAM is lost when power is switched off.
8031/8051has 128 bytes Ram while 8032/8052 has 256 byte of RAM.
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General Microcontroller based System:-
Fig 2: general microcontroller based system
Microcontroller are dedicated to one task and run one specific program. The
program is stored in ROM (read only memory) and generally does not change.
Microcontroller often uses flash, EEPROM or EPROM as their storage device to
allow field programmability so they are flexible to use.
Once program is tested and found correct i.e. prototype is developed then
OTP (one time programmable) microcontrollers can be used because they are chip.
These are multiple architecture used in microcontrollers, the predominant
architecture is CISC (complex instruction set computer), which allows the microcont-
I.E.T.E. RAJKOT SUBCENTER 36
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roller to contain multiple control instructions that can be executed with a single
macro instruction. Another is RISC (reduced instruction set computer ) architecture,
which implements fewer instructions, but delivers greater simplicity and lower power
consumption.
A highly integrated chip that contains all the components comprising a
controller. Typically this includes a CPU, RAM, some form of ROM, I/O ports, and
timers. Unlike a general-purpose computer, which also includes all of these
components, a microcontroller is designed for a very specific task -- to control a
particular system. As a result, the parts can be simplified and reduced, which cuts
down on production costs.
Microcontrollers are sometimes called embedded microcontrollers, which just
means that they are part of an embedded system -- that is, one part of a larger
device or system.
MicroMo Electronics: Microcontrollers :-
Specializes in the design, assembly and application of high precision,
miniature DC drive systems, components, and motion control systems.
Parallax Microcontrollers:-
Broad-line distributor web site features real-time stock status and
pricing, online ordering, RFQ, technical support, product datasheets and
photos.
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MICROCONTROLLER
I.E.T.E. RAJKOT SUBCENTER 38
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A Microcontroller (also MCU or µC) is a computer-on-a-chip. It is a type of
microprocessor emphasizing high integration, low power consumption, self-
sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor
(the kind used in a PC). In addition to the usual arithmetic and logic elements of a
general purpose
microprocessor, the microcontroller typically integrates additional elements
such as read-write memory for data storage, read-only memory, such as flash for
code storage, EEPROM for permanent data storage, peripheral devices, and
input/output interfaces. At clock speeds of as little as a few MHz or even lower,
microcontrollers often operate at very low speed compared to modern day
microprocessors, but this is adequate for typical applications. They consume
relatively little power (militates), and will generally have the ability to sleep while
waiting for an interesting peripheral event such as a button press to wake them up
again to do something. Power consumption while sleeping may be just nano watts,
making them ideal for low power and long lasting battery applications.
Microcontrollers are frequently used in automatically controlled products and
devices, such as automobile engine control systems, remote controls, office
machines, appliances, power tools, and toys. By reducing the size, cost, and power
consumption compared to a design using a separate microprocessor, memory, and
input/output devices, microcontrollers make it economical to electronically control
many more processes.
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EMBEDDED DESIGN:-
The majority of computer systems in use today are embedded in other
machinery, such as telephones, clocks, appliances, and vehicles. An embedded
system may have minimal requirements for memory and program length. Input and
output devices may be discrete switches, relays, or solenoids. An embedded
controller may lack any human-readable interface devices at all. For example,
embedded systems usually don't have keyboards, screens, disks, printers, or other
recognizable I/O devices of a personal computer. Microcontrollers may control
electric motors, relays or voltages, and may read switches, variable resistors or
other electronic devices.
HIGHER INTEGRATION:-
In contrast to general-purpose CPUs, microcontrollers may not implement an
external address or data bus as they integrate RAM and non-volatile memory on the
same chip as the CPU. Using fewer pins, the chip can be placed in a much smaller,
cheaper package.
Integrating the memory and other peripherals on a single chip and testing
them as a unit increases the cost of that chip, but often results in decreased net cost
of the embedded system as a whole. Even if the cost of a CPU that has integrated
peripherals is slightly more than the cost of a CPU + external peripherals, having
fewer chips typically allows a smaller and cheaper circuit board, and reduces the
labor required to assemble and test the circuit board.
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A microcontroller is a single integrated circuit, commonly with the
following features:-
central processing unit - ranging from small and simple 4-bit processors to
complex 32- or 64-bit processors
discrete input and output bits, allowing control or detection of the logic state of
an individual package pin
serial input/output such as serial ports (UARTs)
other serial communications interfaces like I²C, Serial Peripheral Interface
and Controller Area Network for system interconnect
peripherals such as timers, event counters, PWM generators, and watchdog
volatile memory (RAM) for data storage
ROM, EPROM, [EEPROM] or Flash memory for program and operating
parameter storage
clock generator - often an oscillator for a quartz timing crystal, resonator or
RC circuit
many include analog-to-digital converters
in-circuit programming and debugging support
This integration drastically reduces the number of chips and the amount of
wiring and PCB space that would be needed to produce equivalent systems using
separate chips. Furthermore, and on low pin count devices in particular, each pin
may interface to several internal peripherals, with the pin function selected by
software. This allows a part to be used in a wider variety of applications than if pins
had dedicated functions. Microcontrollers have proved to be highly popular in
embedded systems since their introduction in the 1970s.
Some microcontrollers use a Harvard architecture: separate memory buses
for instructions and data, allowing accesses to take place concurrently. Where a
Harvard architecture is used, instruction words for the processor may be a different
bit size than the length of internal memory and registers; for example: 12-bit
instructions used with 8-bit data registers.
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The decision of which peripheral to integrate is often difficult. The
microcontroller vendors often trade operating frequencies and system design
flexibility against time-to-market requirements from their customers and
overall lower system cost. Manufacturers have to balance the need to
minimize the chip size against additional functionality.
Microcontroller architectures vary widely. Some designs include general-
purpose microprocessor cores, with one or more ROM, RAM, or I/O functions
integrated onto the package. Other designs are purpose built for control applications.
A microcontroller instruction set usually has many instructions intended for bit-wise
operations to make control programs more compact. For example, a general
purpose processor might require several instructions to test a bit in a register and
branch if the bit is set, where a microcontroller could have a single instruction that
would provide that commonly-required function.
LARGE VOLUMES
Microcontrollers take the largest share of sales in the wider microprocessor
market. Over 50% are "simple" controllers, and another 20% are more specialized
digital signal processors (DSPs)[citation needed]. A typical home in a developed country is
likely to have only one or two general-purpose microprocessors but somewhere
between one and two dozen microcontrollers. A typical mid range automobile has as
many as 50 or more microcontrollers. They can also be found in almost any
electrical device: washing machines, microwave ovens, telephones etc.
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Manufacturers have often produced special versions of their microcontrollers
in order to help the hardware and software development of the target system. These
have included EPROM versions that have a "window" on the top of the device
through which program memory can be erased by ultra violet light, ready for
reprogramming after a programming ("burn") and test cycle.
An economical option for intermediate levels of production (usually a few
score to a few thousand parts) is a one-time programmable (OTP) microcontroller.
This uses the same die as the UV EPROM version of the part, and is programmed
on the same equipment, but the package does not include the expensive quartz
window required to admit UV light on to the chip.
Other versions may be available where the ROM is accessed as an external
device rather than as internal memory.
A simple EPROM programmer, rather than a more complex and expensive
microcontroller programmer, may then be used, however there is a potential loss of
functionality through pin outs being tied up with external memory addressing rather
than for general input/output.
These kind of devices usually carry a higher cost but if the target production
quantities are small, certainly in the case of a hobbyist, they can be the most
economical option compared with the set up charges involved in mask programmed
devices.
A more rarely encountered development microcontroller is the "piggy back"
version. This device has no internal ROM memory; instead pin outs on the top of the
microcontroller form a socket into which a standard EPROM program memory
device may be installed. The benefit of this approach is the release of
microcontroller pins for Input and output use rather than program memory. These
kinds of devices are normally expensive and are impractical for anything but the
development phase of a project or very small production quantities.
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The use of field-programmable devices on a microcontroller may allow field
update of the firmware or permit late factory revisions to products that have been
assembled but not yet shipped. Programmable memory also reduces the lead time
required for deployment of a new product.
Where a large number of systems will be made (say, several thousand), the
cost of a mask-programmed memory is amortized over all products sold. A simpler
integrated circuit process is used, and the contents of the read-only memory are set
In the last step of chip manufacture instead of after assembly and test. However,
mask-programmed parts cannot be updated in the field. If product firmware updates
are still contemplated, a socket may be used to hold the controller which can then be
replaced by a service technician, if required.
PROGRAMMING ENVIRONMENTS
Microcontrollers were originally programmed only in assembly language, but
various high-level programming languages are now also in common use to target
microcontrollers. These languages are either designed specially for the purpose, or
versions of general purpose languages such as the C programming language.
Compilers for general purpose languages will typically have some restrictions as well
as enhancements to better support the unique characteristics of microcontrollers.
Interpreter firmware is also available for some microcontrollers. The Intel
8052 and Zilog Z8 were available with BASIC very early on, and BASIC is more
recently used in the BASIC Stamp MCUs.
Some microcontrollers have environments to aid developing certain types of
applications, e.g. Analog Device's Blackfin processors with the LabVIEW
environment and its programming language "G".
I.E.T.E. RAJKOT SUBCENTER 44
GSM BASED IRRIGATION SYSTEMSimulators are available for some microcontrollers, such as in Microchip's
MPLAB environment. These allow a developer to analyse what the behaviour of the
microcontroller and their program should be if they were using the actual part. A
simulator will show the internal processor state and also that of the outputs, as well
as allowing input signals to be generated. While on the one hand most simulators
will be limited from being unable to simulate much other hardware in a system, they
can exercise conditions that may otherwise be hard to reproduce at will in the
physical implementation, and can be the quickest way to debug and analyse
problems. Recent microcontrollers integrated with on-chip debug circuitry accessed
by In-circuit emulator via JTAG enables a programmer to debug the software of an
embedded system with a debugger.
INTERRUPT LATENCY
In contrast to general-purpose computers, microcontrollers used in embedded
systems often seek to minimize interrupt latency over instruction throughput.
When an electronic device causes an interrupt, the intermediate results, the
registers, have to be saved before the software responsible for handling the interrupt
can run, and then must be put back after it is finished. If there are more registers,
this saving and restoring process takes more time, increasing the latency.
Low-latency MCUs generally have relatively few registers in their central
processing units, or they have "shadow registers", a duplicate register set that is
only used by the interrupt software.
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What is Inside an LED?
LED's are special diodes that emit light when connected in a circuit. They are
frequently used as "pilot" lights in electronic appliances to indicate whether the
circuit is closed or not. A a clear (or often colored) epoxy case enclosed the heart of
an LED, the semi-conductor chip.
The two wires extending below the LED epoxy enclosure, or the "bulb"
indicate how the LED should be connected into a circuit. The negative side of an
LED lead is indicated in two ways: 1) by the flat side of the bulb, and 2) by the
shorter of the two wires extending from the LED. The negative lead should be
connected to the negative terminal of a battery. LED's operate at relative low
voltages between about 1 and 4 volts, and draw currents between about 10 and 40
mill amperes. Voltages and currents substantially above these values can melt a
LEDchip.
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The most important part of a light emitting diode (LED) is the semi-
conductor chip located in the center of the bulb as shown at the right. The chip has
two regions separated by a junction. The p region is dominated by positive electric
charges,
The n region is dominated by negative electric charges. The junction acts as
a barrier to the flow of electrons between the p and the n regions. Only when
sufficient voltage is applied to the semi-conductor chip, can the current flow, and the
electrons cross the junction into the p region.
In the absence of a large enough electric potential difference (voltage) across
the LED leads, the junction presents an electric potential barrier to the flow of
electrons.
I.E.T.E. RAJKOT SUBCENTER
LED leads
<-- -->
side lead on flat
side of bulb = negative
47
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What Causes the LED to Emit Light and What Determines the
Color of the Light?
When sufficient voltage is applied to the chip across the leads of the LED,
electrons can move easily in only one direction across the junction between the p
and n regions. In the p region there are many more positive than negative charges.
In the n region the electrons are more numerous than the positive electric charges.
When a voltage is applied and the current starts to flow, electrons in the n region
have sufficient energy to move across the junction into the p region. Once in the p
region the electrons are immediately attracted to the positive charges due to the
mutual Coulomb forces of attraction between opposite electric charges. When an
electron moves sufficiently close to a positive charge in the p region, the two
charges"re-combine".
Each time an electron recombines with a positive charge, electric potential energy is
converted into electromagnetic energy. For each recombination of a negative and a
positive charge, a quantum of electromagnetic energy is emitted in the form of a
photon of light with a frequency characteristic of the semi-conductor material (usually
a combination of the chemical elements gallium, arsenic and phosphorus). Only
photons in a very narrow frequency range can be emitted by any material. LED's
that emit different colors are made of different semi-conductor materials, and require
different energies to light them.
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DESCRIPTION
A miniaturized receiver for infrared remote control and IR data transmission.
PIN diode and preamplifier are assembled on lead frame.
The epoxy package is designed as IR filter.
The demodulated output signal can directly be decoded by a microprocessor.
The main benefit is the operation with high data rates and long distances.
FEATURES
o Photo detector and preamplifier in one package
o Internal band filter for PCM frequency
o Internal shielding against electrical field disturbance
o TTL and CMOS compatibility
o Output active low
o Small size package
SPECIAL FEATURES
o Supply voltage 5.5 V
o Short settling time after power on
o High envelope duty cycle can be received
o Enhanced immunity against disturbance from energy
o saving lamps
o B.P.F Center Frequency 38khz
o Peak Emission Wavelength 940nm
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APPLICATION
o AV instruments such as Audio, TV, VCR, CD, DVD,
o MD etc.
o Home appliances such as Air conditioner, Fan etc.
o The other equipments with wireless remote control.
o CATV set top boxes.
o Multi-media Equipment.
o Sensors and light barrier systems for long distances
IR RECEIVER CODES
o Best works with: Rc6 Code, Rcmm Code, Sony 15bit
o Code
o Also suitable for: Grundig Code, Nec Code, Rc5
o Code, R-2000 Code, Rca Code, Sharp Code, Sony
o 12bit Code, Zenith Code
o Not recommended for: Rcs-80 Code, High Data Rate
o Code
I.E.T.E. RAJKOT SUBCENTER 50
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Diode
Figure 1: Closeup of the image below, showing the square shaped semiconductor
crystal
Figure 2: Various semiconductor diodes. Bottom: A bridge rectifier
I.E.T.E. RAJKOT SUBCENTER 51
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Figure 3: Structure of a vacuum tube diode
In electronics, a diode is a two-terminal device (except that thermionic
diodes may also have one or two ancillary terminals for a heater). Diodes have two
active electrodes between which the signal of interest may flow, and most are used
for their unidirectional current property. The varicap diode is used as an electrically
adjustable capacitor.
The directionality of current flow most diodes exhibit is sometimes
generically called the rectifying property. The most common function of a diode is to
allow an electric current to pass in one direction (called the forward biased condition)
and to block it in the opposite direction (the reverse biased condition). Thus, the
diode can be thought of as an electronic version of a check valve. Real diodes do
not display such a perfect on-off directionality but have a more complex non-linear
electrical characteristic, which depends on the particular type of diode technology.
Diodes also have many other functions in which they are not designed to operate in
this on-off manner.Early diodes included “cat’s whisker” crystals and vacuum tube
devices (also called thermionic valves). Today the most common diodes are made
from semiconductor materials such as silicon or germanium.
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History
Although the crystal diode was popularized before the thermionic diode,
harmonic and solid state diodes were developed in parallel. The principle of
operation of harmonic diodes was discovered by Frederick Guthrie in 1873.[1] The
principle of operation of crystal diodes was discovered in 1874 by the German
scientist, Karl Ferdinand Braun.[2]
Thermion diode principles were rediscovered by Thomas Edison on
February 13, 1880 and he was awarded a patent in 1883 (U.S. Patent 307,031 ), but
developed the idea no further. Braun patented the crystal rectifier in 1899 [1].
Braun's discovery was further developed by Jag dish Chandra Bose into a useful
device for radio detection.
The first radio receiver using a crystal diode was built around 1900 by
Greenleaf Whittier Pickard. The first thermionic diode was patented in Britain by
John Ambrose Fleming (scientific adviser to the Marconi Company and former
Edison employee[2]) on November 16, 1904 (U.S. Patent 803,684 in November
1905). Pickard received a patent for a silicon crystal detector on November 20, 1906
[3] (U.S. Patent 836,531 ).
At the time of their invention, such devices were known as rectifiers. In 1919,
William Henry Eccles coined the term diode from Greek roots; di means "two", and
ode (from odos) means "path".
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Thermionic and gaseous state diodes
Figure 4: The symbol for an indirect heated vacuum tube diode. From top to bottom,
the components are the anode, the cathode, and the heater filament.
Thermionic diodes are thermionic valve devices (also known as vacuum
tubes), which are arrangements of electrodes surrounded by a vacuum within a
glass envelope. Early examples were fairly similar in appearance to incandescent
light bulbs.
In thermionic valve diodes, a current is passed through the heater filament.
This indirectly heats the cathode, another filament treated with a mixture of barium
and strontium oxides, which are oxides of alkaline earth metals; these substances
are chosen because they have a small work function. (Some valves use direct
heating, in which a tungsten filament acts as both cathode and emitter.) The heat
causes thermionic emission of electrons into the vacuum. In forward operation, a
surrounding metal electrode, called the anode, is positively charged, so that it
electrostatically attracts the emitted electrons. However, electrons are not easily
released from the unheated anode surface when the voltage polarity is reversed and
hence any reverse flow is a very tiny current.
For much of the 20th century, thermionic valve diodes were used in analog
signal applications, and as rectifiers in many power supplies. Today, valve diodes
I.E.T.E. RAJKOT SUBCENTER 54
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are only used in niche applications, such as rectifiers in guitar and hi-fi valve
amplifiers, and specialized high-voltage equipment.
Semiconductor diodes
Most modern diodes are based on semiconductor p-n junctions. In a p-n
diode, conventional current can flow from the p-type side (the anode) to the n-type
side (the cathode), but cannot flow in the opposite direction. Another type of
semiconductor diode, the Schottky diode, is formed from the contact between a
metal and a semiconductor rather than by a p-n junction.
Current–voltage characteristic
A semiconductor diode's current–voltage characteristic, or I–V curve, is
related to the transport of carriers through the so-called depletion layer or depletion
region that exists at the p-n junction between differing semiconductors. When a p-n
junction is first created, conduction band (mobile) electrons from the N-doped region
diffuse into the P-doped region where there is a large population of holes (places for
electrons in which no electron is present) with which the electrons "recombine".
When a mobile electron recombines with a hole, both hole and electron vanish,
leaving behind an immobile positively charged donor on the N-side and negatively
charged acceptor on the P-side. The region around the p-n junction becomes
depleted of charge carriers and thus behaves as an insulator.
However, the depletion width cannot grow without limit. For each electron-
hole pair that recombines, a positively-charged dopant ion is left behind in the N-
doped region, and a negatively charged dopant ion is left behind in the P-doped
region. As recombination proceeds and more ions are created, an increasing electric
I.E.T.E. RAJKOT SUBCENTER 55
GSM BASED IRRIGATION SYSTEMfield develops through the depletion zone which acts to slow and then finally stop
recombination. At this point, there is a "built-in" potential across the depletion zone.
If an external voltage is placed across the diode with the same
polarity as the built-in potential, the depletion zone continues to act as an insulator,
preventing any significant electric current flow. This is the reverse bias phenomenon.
However, if the polarity of the external voltage opposes the built-in potential,
recombination can once again proceed, resulting in substantial electric current
through the p-n junction. For silicon diodes, the built-in potential is approximately 0.6
V. Thus, if an external current is passed through the diode, about 0.6 V will be
developed across the diode such that the P-doped region is positive with respect to
the N-doped region and the diode is said to be "turned on" as it has a forward bias.
Figure 5: I–V characteristics of a P-N junction diode (not to scale).
A diode’s I–V characteristic can be approximated by four regions of operation
(see the figure at right).
At very large reverse bias, beyond the peak inverse voltage or PIV, a process
called reverse breakdown occurs which causes a large increase in current that
usually damages the device permanently. The avalanche diode is deliberately
designed for use in the avalanche region. In the zener diode, the concept of PIV is
not applicable.
I.E.T.E. RAJKOT SUBCENTER 56
GSM BASED IRRIGATION SYSTEM
A zener diode contains a heavily doped p-n junction allowing electrons to tunnel
from the valence band of the p-type material to the conduction band of the n-type
material, such that the reverse voltage is "clamped" to a known value (called the
zener voltage), and avalanche does not occur. Both devices, however, do have a
limit to the maximum current and power in the clamped reverse voltage region.
The second region, at reverse biases more positive than the PIV, has only a
very small reverse saturation current. In the reverse bias region for a normal P-N
rectifier diode, the current through the device is very low (in the µA range).
The third region is forward but small bias, where only a small forward current
is conducted.As the potential difference is increased above an arbitrarily defined
"cut-in voltage" or "on-voltage", the diode current becomes appreciable (the level of
current considered "appreciable" and the value of cut-in voltage depends on the
application), and the diode presents a very low resistance.
The current–voltage curve is exponential. In a normal silicon diode at rated
currents, the arbitrary "cut-in" voltage is defined as 0.6 to 0.7 volts. The value is
different for other diode types — Schottky diodes can be as low as 0.2 V and red
light-emitting diodes (LEDs) can be 1.4 V or more and blue LEDs can be up to 4.0
V.At higher currents the forward voltage drop of the diode increases. A drop of 1 V to
1.5 V is typical at full rated current for power diodes.
I.E.T.E. RAJKOT SUBCENTER 57
GSM BASED IRRIGATION SYSTEM
Schottky diode equation
The Shockley ideal diode equation or the diode law (named after transistor
co-inventor William Bradford Shockley, not to be confused with tetrode inventor
Walter H. Scotty) is the I–V characteristic of an ideal diode in either forward or
reverse
bias (or no bias). The equation is:
where
I is the diode current,
IS is a scale factor called the saturation current,
VD is the voltage across the diode,
VT is the thermal voltage,
and n is the emission coefficient, also known as the ideality factor. The
emission coefficient n varies from about 1 to 2 depending on the fabrication
process and semiconductor material and in many cases is assumed to be
approximately equal to 1 (thus the notation n is omitted).
The thermal voltage VT is approximately 25.85 mV at 300 K, a temperature close to
“room temperature” commonly used in device simulation software. At any
temperature it is a known constant defined by:
where
q is the magnitude of charge on an electron (the elementary charge),
I.E.T.E. RAJKOT SUBCENTER 58
GSM BASED IRRIGATION SYSTEMk is Boltzmann’s constant,
T is the absolute temperature of the p-n junction in kelvins
The Shockley ideal diode equation or the diode law is derived with the
assumption that the only processes giving rise to current in the diode are drift (due to
electrical field), diffusion, and thermal recombination-generation. It also assumes
that the recombination-generation (R-G) current in the depletion region is
insignificant. This means that the Shockley equation doesn’t account for the
processes involved in reverse breakdown and photon-assisted R-G. Additionally, it
doesn’t describe the “leveling off” of the I–V curve at high forward bias due to
internal resistance.
Under reverse bias voltages (see Figure 5) the exponential in the diode
equation is negligible, and the current is a constant (negative) reverse current value
of -IS. The reverse breakdown region is not modeled by the Shockley diode
equation.For even rather small forward bias voltages (see Figure 5) the exponential
is very large because the thermal voltage is very small, so the subtracted ‘1’ in the
diode equation is negligible and the forward diode current is often approximated as
The use of the diode equation in circuit problems is illustrated in the article on diode
modeling.
Small-signal behavior
For circuit design, a small-signal model of the diode behavior often proves useful. A
specific example of diode modeling is discussed in the article on small-signal
circuits.
I.E.T.E. RAJKOT SUBCENTER 59
GSM BASED IRRIGATION SYSTEM
Types of semiconductor diode:-
DiodeZener
diode
Schottky
diode
Tunnel
diode
Light-emitting
diodePhotodiode Varicap Silicon controlled rectifier
Figure 7: Some diode symbols
There are several types of junction diodes, which either emphasize a
different physical aspect of a diode often by geometric scaling, doping level,
choosing the right electrodes, are just an application of a diode in a special circuit, or
are really different devices like the Gunn and laser diode and the MOSFET:
Normal (p-n) diodes which operate as described above. Usually made of
doped silicon or, more rarely, germanium. Before the development of modern silicon
power rectifier diodes, cuprous oxide and later selenium was used; its low efficiency
gave it a much higher forward voltage drop (typically 1.4–1.7 V per “cell”, with
multiple cells stacked to increase the peak inverse voltage rating in high voltage
rectifiers), and required a large heat sink (often an extension of the diode’s metal
substrate), much larger than a silicon diode of the same current ratings would
require. The vast majority of all diodes are the p-n diodes found in CMOS integrated
circuits, which include two diodes per pin and many other internal diodes.
I.E.T.E. RAJKOT SUBCENTER 60
GSM BASED IRRIGATION SYSTEM
Avalanche Diodes:-
Diodes that conduct in the reverse direction when the reverse bias voltage
exceeds the breakdown voltage. These are electrically very similar to Zener
diodes, and are often mistakenly called Zener diodes, but break down by a
different mechanism, the avalanche effect. This occurs when the reverse
electric field across the p-n junction causes a wave of ionization, reminiscent
of an avalanche, leading to a large current. Avalanche diodes are designed to
break down at a well-defined reverse voltage without being destroyed. The
difference between the avalanche diode (which has a reverse breakdown
above about 6.2 V) and the Zener is that the channel length of the former
exceeds the “mean free path” of the electrons, so there are collisions between
them on the way out. The only practical difference is that the two types have
temperature coefficients of opposite polarities.
Cat’s whisker or crystal diodes:-
These are a type of point contact diode. The cat’s whisker diode consists of a
thin or sharpened metal wire pressed against a semiconducting crystal,
typically galena or a piece of coal.[4] The wire forms the anode and the
crystal forms the cathode. Cat’s whisker diodes were also called crystal
diodes and found application in crystal radio receivers. Cat’s whisker diodes
are obsolete.
Constant current diodes:-
These are actually a JFET with the gate shorted to the source, and function
like a two-terminal current-limiting analog to the Zener diode; they allow a
current through them to rise to a certain value, and then level off at a specific
I.E.T.E. RAJKOT SUBCENTER 61
GSM BASED IRRIGATION SYSTEM
value. Also called CLDs, constant-current diodes, diode-connected
transistors, or current-regulating diodes.
Esaki or tunnel diodes
these have a region of operation showing negative resistance caused by
quantum tunneling, thus allowing amplification of signals and very simple
bistable circuits. These diodes are also the type most resistant to nuclear
radiation.
Gunn diodes :-
These are similar to tunnel diodes in that they are made of materials such as
GaAs or InP that exhibit a region of negative differential resistance. With
appropriate biasing, dipole domains form and travel across the diode,
allowing high frequency microwave oscillators to be built.
Light-emitting diodes ( LEDs ):-
In a diode formed from a direct band-gap semiconductor, such as gallium
arsenide, carriers that cross the junction emit photons when they recombine
with the majority carrier on the other side. Depending on the material,
wavelengths (or colors) from the infrared to the near ultraviolet may be
produced. The forward potential of these diodes depends on the wavelength
of the emitted photons: 1.2 V corresponds to red, 2.4 to violet. The first LEDs
were red and yellow, and higher-frequency diodes have been developed over
time. All LEDs produce incoherent, narrow-spectrum light; “white” LEDs are
actually combinations of three LEDs of a different color, or a blue LED with a
yellow scintillator coating. LEDs can also be used as low-efficiency
photodiodes in signal applications. An LED may be paired with a photodiode
or phototransistor in the same package, to form an opto-isolator.
I.E.T.E. RAJKOT SUBCENTER 62
GSM BASED IRRIGATION SYSTEM
Laser diodes:-
When an LED-like structure is contained in a resonant cavity formed by
polishing the parallel end faces, a laser can be formed. Laser diodes are
commonly used in optical storage devices and for high speed optical
communication.
Peltier diodes :-
Are used as sensors, heat engines for thermoelectric cooling. Charge carriers
absorb and emit their band gap energies as heat.
Photodiodes :-
All semiconductors are subject to optical charge carrier generation. This is
typically an undesired effect, so most semiconductors are packaged in light
blocking material. Photodiodes are intended to sense light(photodetector), so
they are packaged in materials that allow light to pass, and are usually PIN
(the kind of diode most sensitive to light). A photodiode can be used in solar
cells, in photometry, or in optical communications. Multiple photodiodes may
be packaged in a single device, either as a linear array or as a two-
dimensional array. These arrays should not be confused with charge-coupled
devices.
Point-contact diodes:-
These work the same as the junction semiconductor diodes described above,
but their construction is simpler. A block of n-type semiconductor is built, and
a conducting sharp-point contact made with some group-3 metal is placed in
contact with the semiconductor. Some metal migrates into the semiconductor
to make a small region of p-type semiconductor near the contact. The long-
I.E.T.E. RAJKOT SUBCENTER 63
GSM BASED IRRIGATION SYSTEM
popular 1N34 germanium version is still used in radio receivers as a detector
and occasionally in specialized analog electronics.
PIN diodes:-
A PIN diode has a central un-doped, or intrinsic, layer, forming a
p-type/intrinsic/n-type structure. They are used as radio frequency switches
and attenuators. They are also used as large volume ionizing radiation
detectors and as photodetectors. PIN diodes are also used in power
electronics, as their central layer can withstand high voltages. Furthermore,
the PIN structure can be found in many power semiconductor devices, such
as IGBTs, power MOSFETs, and thyristors.
Switching diodes :-
Switching diodes, sometimes also called small signal diodes, are a single p-n
diode in a discrete package. A switching diode provides essentially the same
function as a switch. Below the specified applied voltage it has high
resistance similar to an open switch, while above that voltage it suddenly
changes to the low resistance of a closed switch. They are used in devices
such as ring modulation.
Schottky diodes :-
Schottky diodes are constructed from a metal to semiconductor contact. They
have a lower forward voltage drop than p-n junction diodes. Their forward
voltage drop at forward currents of about 1 mA is in the range 0.15 V to 0.45
V, which makes them useful in voltage clamping applications and prevention
of transistor saturation. They can also be used as low loss rectifiers although
their reverse leakage current is generally higher than that of other diodes.
I.E.T.E. RAJKOT SUBCENTER 64
GSM BASED IRRIGATION SYSTEMSchottky diodes are majority carrier devices and so do not suffer from
minority carrier storage problems that slow down many other diodes — so
they have a faster “reverse recovery” than p-n junction diodes. They also tend
to have much lower junction capacitance than p-n diodes which provides for
high switching speeds and their use in high-speed circuitry and RF devices
such as switched-mode power supply, mixers and detectors.
Super Barrier Diodes : -
Super barrier diodes are rectifier diodes that incorporate the low forward
voltage drop of the Schottky diode with the surge-handling capability and low
reverse leakage current of a normal p-n junction diode.
Gold -doped” diodes:-
As a dopant, gold (or platinum) acts as recombination centers, which help a
fast recombination of minority carriers. This allows the diode to operate at
signal frequencies, at the expense of a higher forward voltage drop. Gold
doped diodes are faster than other p-n diodes (but not as fast as Schottky
diodes). They also have less reverse-current leakage than Schottky diodes
(but not as good as other p-n diodes).[7].[3] A typical example is the 1N914.
Snap-off or Step recovery diodes :-
The term ‘step recovery’ relates to the form of the reverse recovery
characteristic of these devices. After a forward current has been passing in an
SRD and the current is interrupted or reversed, the reverse conduction will
cease very abruptly (as in a step waveform). SRDs can therefore provide very
fast voltage transitions by the very sudden disappearance of the charge
carriers.
I.E.T.E. RAJKOT SUBCENTER 65
GSM BASED IRRIGATION SYSTEM
Transient voltage suppression diode (TVS):-
These are avalanche diodes designed specifically to protect other
semiconductor devices from high-voltage transients. Their p-n junctions have
a much larger cross-sectional area than those of a normal diode, allowing
them to conduct large currents to ground without sustaining damage.
Varicap or varactor diodes :-
These are used as voltage-controlled capacitors. These are important in PLL
(phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning
circuits, such as those in television receivers, to lock quickly, replacing older
designs that took a long time to warm up and lock. A PLL is faster than an
FLL, but prone to integer harmonic locking (if one attempts to lock to a
broadband signal). They also enabled tunable oscillators in early discrete
tuning of radios, where a cheap and stable, but fixed-frequency, crystal
oscillator provided the reference frequency for a voltage-controlled oscillator.
Zener diodes :-
Diodes that can be made to conduct backwards. This effect, called Zener
breakdown, occurs at a precisely defined voltage, allowing the diode to be
used as a precision voltage reference. In practical voltage reference circuits
Zener and switching diodes are connected in series and opposite directions to
balance the temperature coefficient to near zero. Some devices labeled as
high-voltage Zener diodes are actually avalanche diodes (see below). Two
(equivalent) Zeners in series and in reverse order, in the same package,
constitute a transient absorber (or Transorb, a registered trademark). The
Zener diode is named for Dr. Clarence Melvin Zener of Southern Illinois
University, inventor of the device.
I.E.T.E. RAJKOT SUBCENTER 66
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RESISTOR
A Resistor is a two-terminal electrical or electronic component that opposes
an electric current by producing a voltage drop between its terminals in accordance
with Ohm's law: The electrical resistance is equal to the voltage drop across the
resistor divided by the current through the resistor. Resistors are used as part of
electrical networks and electronic circuits.
IDENTIFYING RESISTORS
Most axial resistors use a pattern of colored stripes to indicate resistance.
Surface-mount ones are marked numerically. Cases are usually brown, blue, or
green, though other colors are occasionally found such as dark red or dark grey.
One can also use a multimeter or ohmmeter to test the values of a resistor.
FOUR-BAND AXIAL RESISTORS
I.E.T.E. RAJKOT SUBCENTER 67
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Color 1st band 2nd band 3rd band (multiplier) 4th band (tolerance) Temp. Coefficient
Black 0 0 ×100
Brown 1 1 ×101 ±1% (F) 100 ppm
Red 2 2 ×102 ±2% (G) 50 ppm
Orange 3 3 ×103 15 ppm
Yellow 4 4 ×104 25 ppm
Green 5 5 ×105 ±0.5% (D)
Blue 6 6 ×106 ±0.25% (C)
Violet 7 7 ×107 ±0.1% (B)
Gray 8 8 ×108 ±0.05% (A)
White 9 9 ×109
Gold ×10-1 ±5% (J)
Silver ×10-2 ±10% (K)
None ±20% (M)
Electronic Color Code
I.E.T.E. RAJKOT SUBCENTER 68
GSM BASED IRRIGATION SYSTEM Four-band identification is the most commonly used color coding scheme
on all resistors. It consists of four colored bands that are painted around the body of
the resistor. The scheme is simple: The first two numbers are the first two significant
digits of the resistance value, the third is a multiplier, and the fourth is the tolerance
of the value. Each color corresponds to a certain number, shown in the chart below.
The tolerance for a 4-band resistor will be 1%, 5%, or 10%.
PREFERRED VALUES:-
Preferred Number
Resistors are manufactured in values from a few milliohms to about a
gigaohm; only a limited range of values from the IEC 60063 preferred number series
are commonly available. These series are called E6, E12, E24, E96 and E192. The
number tells how many standardized values exist in each decade (e.g. between 10
and 100, or between 100 and 1000). So resistors conforming to the E12 series, can
have 12 distinct values between 10 and 100, whereas those confirming to the E24
series would have 24 distinct values. In practice, the discrete component sold as a
"resistor" is not a perfect resistance, as defined above. Resistors are often marked
with their tolerance (maximum expected variation from the marked resistance).
NOISE
I.E.T.E. RAJKOT SUBCENTER 69
GSM BASED IRRIGATION SYSTEMIn precision circuits, electronic noise becomes of utmost concern. As
dissipative elements, resistors will naturally produce a fluctuating "noise" voltage
across their terminals. This Johnson–Nyquist noise is predicted by the Fluctuation-
Dissipation theorem and is a fundamental noise source present in all resistors which
must beconsidered in constructing low-noise electronics. For example, the gain in a
simple (non-)inverting amplifier is set using a voltage divider. Noise considerations
dictate that the smallest practical resistance should be used, since the noise voltage
scales with resistance, and any resistor noise in the voltage divider will be impressed
upon the amplifier's output.
Although Johnson-Nyquist noise is a fundamental noise source, resistors
frequently exhibit other, "non-fundamental" sources of noise. Noise due to these
sources is called "excess noise." Thick-film and carbon composition resistors are
notorious for excess noise at low frequencies. Wire-wound and thin-film resistors,
though much more expensive, are often utilized for their better noise characteristics.
FAILURE MODES AND PITFALLS
I.E.T.E. RAJKOT SUBCENTER 70
GSM BASED IRRIGATION SYSTEMLike every part, resistors can fail; the usual way depends on their
construction. Carbon composition resistors and metal film resistors typically fail as
open circuits. Carbon-film resistors typically fail as short circuits.
Various effects become important in high-precision applications. Small
voltage differentials may appear on the resistors due to thermoelectric effect if their
ends are not kept at the same temperature. The voltages appear in the junctions of
the resistor leads with the circuit board and with the resistor body. Common metal
film resistors show such effect at magnitude of about 20 µV/°C. Some carbon
composition resistors can go as high as 400 µV/°C, and specially constructed
resistors can go as low as 0.05 µV/°C. In applications where thermoelectric effects
may become important, care has to be taken to e.g. mount the resistors horizontally
to avoid temperature gradients and to mind the air flow over the board.
CAPACITOR
I.E.T.E. RAJKOT SUBCENTER 71
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Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-
hole tantalum at top right; through-hole electrolytic at bottom right. Major scale
divisions are cm.
A capacitor is an electrical/electronic device that can store energy in the
electric field between a pair of conductors (called "plates"). The process of storing
energy in the capacitor is known as "charging", and involves electric charges of
equal magnitude, but opposite polarity, building up on each plate.
Capacitors are often used in electrical circuit and electronic circuits as
energy-storage devices. They can also be used to differentiate between high-
frequency and low-frequency signals. This property makes them useful in electronic
filters.
Capacitors are occasionally referred to as condensers. This is considered an
antiquated term in English, but most other languages use an equivalent, like
"Kondensator" in German.
I.E.T.E. RAJKOT SUBCENTER 72
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CAPACITANCE
The capacitor's capacitance (C) is a measure of the amount of charge (Q)
stored on each plate for a given potential difference or voltage (V) which appears
between the plates:
C=
In SI units, a capacitor has a capacitance of one farad when one coulomb of
charge is stored due to one volt applied potential difference across the plates. Since
the farad is a very large unit, values of capacitors are usually expressed in
microfarads (µF), nanofarads (nF), or picofarads (pF).
When there is a difference in electric charge between the plates, an electric
field is created in the region between the plates that is proportional to the amount of
charge that has been moved from one plate to the other. This electric field creates a
I.E.T.E. RAJKOT SUBCENTER 73
GSM BASED IRRIGATION SYSTEMpotential difference V = E·d between the plates of this simple parallel-plate
capacitor.
The capacitance is proportional to the surface area of the conducting plate
and inversely proportional to the distance between the plates. It is also proportional
to the permittivity of the dielectric (that is, non-conducting) substance that separates
the plates.
The capacitance of a parallel-plate capacitor is given by:
C=
where ε is the permittivity of the dielectric (see Dielectric constant), A is the
area of the plates and d is the spacing between them.
In the diagram, the rotated molecules create an opposing electric field that partially
cancels the field created by the plates, a process called dielectric polarization.
STORED ENERGY
As opposite charges accumulate on the plates of a capacitor due to the
separation of charge, a voltage develops across the capacitor due to the
electric field of these charges. Ever-increasing work must be done against
this ever-increasing electric field as more charge is separated.
I.E.T.E. RAJKOT SUBCENTER 74
GSM BASED IRRIGATION SYSTEMThe energy (measured in joules, in SI) stored in a capacitor is equal to the
amount of work required to establish the voltage across the capacitor, and therefore
the electric field. The energy stored is given by:
Where V is the voltage across the capacitor.The maximum energy that can be
(safely) stored in a particular capacitor is limited by the maximum electric field that
the dielectric can withstand before it breaks down. Therefore, all capacitors made
with the same dielectric have about the same maximum energy density (joules of
energy per cubic meter).
Estored=
DC SOURCES:-
The dielectric between the plates is an insulator and blocks the flow of
electrons. A steady current through a capacitor deposits electrons on one plate and
removes the same quantity of electrons from the other plate. This process is
commonly called 'charging' the capacitor. The current through the capacitor results
in the separation of electric charge within the capacitor, which develops an electric
field between the plates of the capacitor, equivalently, developing a voltage
difference between the plates. This voltage V is directly proportional to the amount
of charge separated Q. Since the current I through the capacitor is the rate at which
charge Q is forced through the capacitor (dQ/dt), this can be expressed
mathematically as:
I=
I.E.T.E. RAJKOT SUBCENTER 75
GSM BASED IRRIGATION SYSTEM
Where I is the current flowing in the conventional direction, measured in
amperes, dV/dt is the time derivative of voltage, measured in volts per second, and
C is the capacitance in farads.
For circuits with a constant (DC) voltage source and consisting of only
resistors and capacitors, the voltage across the capacitor cannot exceed the voltage
of the source. Thus, an equilibrium is reached where the voltage across the
capacitor is constant and the current through the capacitor zero. For this reason, it is
commonly s dV/dt is the time derivative of voltage, measured in volts per second,
and C is the capacitance aid that capacitors block DC.
AC SOURCES:-
The current through a capacitor due to an AC source reverses direction
periodically. That is, the alternating current alternately charges the plates: first in one
direction and then the other. With the exception of the instant that the current
changes direction, the capacitor current is non-zero at all times during a cycle. For
this reason, it is commonly said that capacitors "pass" AC. However, at no time do
electrons actually cross between the plates, unless the dielectric breaks down. Such
a situation would involve physical damage to the capacitor and likely to the circuit
involved as well.
Since the voltage across a capacitor is proportional to the integral of the
current, as shown above, with sine waves in AC or signal circuits this results in a
phase difference of 90 degrees, the current leading the voltage phase angle. It can
be shown that the AC voltage across the capacitor is in quadrature with the
I.E.T.E. RAJKOT SUBCENTER 76
GSM BASED IRRIGATION SYSTEMalternating current through the capacitor. That is, the voltage and current are 'out-of-
phase' by a quarter cycle. The amplitude of the voltage depends on the amplitude of
the current divided by the product of the frequency of the current with the
capacitance, C.
APPLICATIONS
(1) ENERGY STORAGE:-
A capacitor can store electric energy when disconnected from its charging
circuit, so it can be used like a temporary battery. Capacitors are commonly used in
I.E.T.E. RAJKOT SUBCENTER 77
GSM BASED IRRIGATION SYSTEMelectronic devices to maintain power supply while batteries are being changed. (This
prevents loss of information in volatile memory.)
(2) POWER CONDITIONING:-
Capacitors are used in power supplies where they smooth the output of a full
or half wave rectifier. They can also be used in charge pump circuits as the energy
storage element in the generation of higher voltages than the input voltage.
Capacitors are connected in parallel with the power circuits of most electronic
devices and larger systems (such as factories) to shunt away and conceal current
fluctuations from the primary power source to provide a "clean" power supply for
signal or control circuits. Audio equipment, for example, uses several capacitors in
this way, to shunt away power line hum before it gets into the signal circuitry. The
capacitors act as a local reserve for the DC power source, and bypass AC currents
from the power supply. This is used in car audio applications, when a stiffening
capacitor compensates for the inductance and resistance of the leads to the lead-
acid car battery.
TRANSFORMER
Transformer is a device that transfers electrical energy from one circuit to
another through inductively coupled wires. A changing current in the first circuit (the
primary) creates a changing magnetic field; in turn, this magnetic field induces a
changing voltage in the second circuit (the secondary). By adding a load to the
I.E.T.E. RAJKOT SUBCENTER 78
GSM BASED IRRIGATION SYSTEMsecondary circuit, one can make current flow in the transformer, thus transferring
energy from one circuit to the other.
The secondary induced voltage VS is scaled from the primary VP by a factor
ideally equal to the ratio of the number of turns of wire in their respective windings:
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 less.
A key application of transformers is to reduce the current before transmitting
electrical energy over long distances through wires. Most wires have resistance and
so dissipate electrical energy at a rate proportional to the square of the current
through the wire. By transforming electrical power to a high-voltage, and therefore
low-current form for transmission and back again afterwards, transformers enable
the economic transmission of power over long distances. Consequently,
transformers have shaped the electricity supply industry, permitting generation to be
located remotely from points of demand. All but a fraction of the world's electrical
power has passed through a series of transformers by the time it reaches the
consumer.
Transformers are some of the most efficient electrical 'machines', with some
large units able to transfer 99.75% of their input power to their output. Transformers
come in a range of sizes from a thumbnail-sized coupling transformer hidden inside
a stage microphone to huge units weighing hundreds of tonnes used to interconnect
I.E.T.E. RAJKOT SUBCENTER 79
GSM BASED IRRIGATION SYSTEMportions of national power grids. All operate with the same basic principles, though a
variety of designs exist to perform specialized roles throughout home and industry.
BASIC PRINCIPLES:-
The transformer is based on two principles: first, that an electric current can
produce a magnetic field (electromagnetism) and, second, that a changing magnetic
field within a coil of wire induces a voltage across the ends of the coil
(electromagnetic induction). By changing the current in the primary coil, one
changes the strength of its magnetic field; since the secondary coil is wrapped
around the same magnetic field, a voltage is induced across the secondary.An ideal
step-down transformer showing magnetic flux in the core
A simplified transformer design is shown to the right. A current passing
through the primary coil creates a magnetic field. The primary and secondary coils
are wrapped around a core of very high magnetic permeability, such as iron; this
ensures that most of the magnetic field lines produced by the primary current are
within the iron and pass through the secondary coil as well as the primary coil.
INDUCTION LAW:-
The voltage induced across the secondary coil may be calculated from
Faraday's law of induction, which states thatWhere VS is the instantaneous voltage,
NS is the number of turns in the secondary coil and Φ equals the total magnetic flux
through one turn of the coil. If the turns of the coil are oriented perpendicular to the
magnetic field lines, the flux is the product of the magnetic field strength B and the
area A through which it cuts. The area is constant, being equal to the cross-sectional
area of the transformer core, whereas the magnetic field varies with time according
to the excitation of the primary.I.E.T.E. RAJKOT SUBCENTER 80
GSM BASED IRRIGATION SYSTEMSince the same magnetic flux passes through both the primary and
secondary coils in an ideal transformer, the instantaneous voltage across the
primary winding equals
Taking the ratio of the two equations for VS and VP gives the basic equationfor
stepping up or stepping down the voltage
IDEAL POWER EQUATION
I.E.T.E. RAJKOT SUBCENTER 81
GSM BASED IRRIGATION SYSTEM
The ideal transformer as a circuit element
If the secondary coil is attached to a load that allows current to flow, electrical
power is transmitted from the primary circuit to the secondary circuit. Ideally, the
transformer is perfectly efficient; all the incoming energy is transformed from the
primary circuit to the magnetic field and thence to the secondary circuit. If this
condition is met, the incoming electric power must equal the outgoing power
Pincoming = IPVP = Poutgoing = ISVS
giving the ideal transformer equation
Thus, if the voltage is stepped up (VS > VP), then the current is stepped down
(IS < IP) by the same factor. In practice, most transformers are very efficient (see
below), so that this formula is a good approximation.
The impedance in one circuit is transformed by the square of the turns ratio.
For example, if an impedance ZS is attached across the terminals of the secondary
coil, it ppears to the primary circuit to have an impedance of . This relationship is
reciprocal, so that the impedance ZP of the primary circuit appears to the secondary
to be .
TECHNICAL DISCUSSION:-
The simplified description above avoids several complicating factors, in
particular the primary current required to establish a magnetic field in the core, and
the contribution to the field due to current in the secondary circuit.
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GSM BASED IRRIGATION SYSTEMModels of an ideal transformer typically assume a core of negligible
reluctance with two windings of zero resistance.[7] When a voltage is applied to the
primary winding, a small current flows, driving flux around the magnetic circuit of the
core. The current required to create the flux is termed the magnetising current; since
the ideal core has been assumed to have near-zero reluctance, the magnetising
current is negligible, although a presence is still required to create the magnetic field.
The changing magnetic field induces an electromotive force (EMF) across
each winding. Since the ideal windings have no impedance, they have no associated
voltage drop, and so the voltages VP and VS measured at the terminals of the
transformer, are equal to the corresponding EMFs. The primary EMF, acting as it
does in opposition to the primary voltage, is sometimes termed the "back EMF".This
is due to Lenz's law which states that the induction of EMF would always be such
that it will oppose development of any such change in magnetic field.
PRACTICAL CONSIDERATIONS:-
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Flux leakage in a two-winding transformer
FLUX LEAKAGE:
Leakage Inductance
The ideal transformer model assumes that all flux generated by the primary
winding links all the turns of every winding, including itself. In practice, some flux
traverses paths that take it outside the windings. Such flux is termed leakage flux,
and manifests itself as self-inductance in series with the mutually coupled
transformer windings. Leakage results in energy being alternately stored in and
discharged from the magnetic fields with each cycle of the power supply.
It is not itself directly a source of power loss, but results in poorer voltage
regulation, causing the secondary voltage to fail to be directly proportional to the
primary, particularly under heavy load. Distribution transformers are therefore
normally designed to have very low leakage inductance
However, in some applications, leakage can be a desirable property, and long
magnetic paths, air gaps, or magnetic bypass shunts may be deliberately introduced
to a transformer's design to limit the short-circuit current it will supply. Leaky
transformers may be used to supply loads that exhibit negative resistance, such as
electric arcs, mercury vapor lamps, and neon signs; or for safely handling loads that
become periodically short-circuited such as electric arc welders. Air gaps are also
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GSM BASED IRRIGATION SYSTEMused to keep a transformer from saturating, especially audio-frequency transformers
that have a DC component added.
EFFECT OF FREQUENCY
The time-derivative term in Faraday's Law shows that the flux in the core is
the integral of the applied voltage. An ideal transformer would, at least
hypothetically, work under direct-current excitation, with the core flux increasing
linearly with time. In practice, the flux would rise very rapidly to the point where
magnetic saturation of the core occurred, causing a huge increase in the
magnetising current and overheating the transformer. All practical transformers must
therefore operate under alternating (or pulsed) current conditions.
Transformer universal EMF equation
If the flux in the core is sinusoidal, the relationship for either winding between
its rms EMF E, and the supply frequency f, number of turns N, core cross-sectional
area a and peak magnetic flux density B is given by the universal EMF equation:
.
The EMF of a transformer at a given flux density increases with frequency, an
effect predicted by the universal transformer EMF equation. By operating at higher
frequencies, transformers can be physically more compact because a given core is
able to transfer more power without reaching saturation, and fewer turns are needed
to achieve the same impedance. However properties such as core loss and
conductor skin effect also increase with frequency.
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GSM BASED IRRIGATION SYSTEMAircraft and military equipment traditionally employ 400 Hz power supplies
which are less efficient but this is more than offset by the reduction in core and
winding weight. In general, operation of a transformer at its designed voltage but at a
higher frequency than intended will lead to reduced magnetising current. At a
frequency lower than the design value, with the rated voltage applied, the
magnetising current may increase to an excessive level. Operation of a transformer
at other than its design frequency may require assessment of voltages, losses, and
cooling to establish if safe operation is practical. For example, transformers may
need to be equipped with "volts per hertz" over-excitation relays to protect the
transformer from overvoltage at higher than rated frequency.
Knowledge of natural frequencies of transformer windings is of importance for
the determination of the transient response of the windings to impulse and switching
surge voltages.
ENERGY LOSSES:-
An ideal transformer would have no energy losses, and would therefore be
100% efficient. Despite the transformer being amongst the most efficient of electrical
machines, with experimental models using superconducting windings achieving
efficiencies of 99.85%,energy is dissipated in the windings, core, and surrounding
structures. Larger transformers are generally more efficient, and those rated for
electricity distribution usually perform better than 95%. A small transformer, such as
a plug-in "power brick" used for low-power consumer electronics, may be no more
than 85% efficient; although individual power loss is small, the aggregate losses
from the very large number of such devices is coming under increased scrutiny.
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GSM BASED IRRIGATION SYSTEM Transformer losses are attributable to several causes and may be
differentiated between those originating in the windings, sometimes termed copper
loss, and those arising from the magnetic circuit, sometimes termed iron loss. The
losses vary with load current, and may furthermore be expressed as "no-load" or
"full-load" loss, respectively. Winding resistance dominates load losses, whereas
hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The
no-load loss can be significant, meaning that even an idle transformer constitutes a
drain on an electrical supply, and lending impetus to development of low-loss
transformers (also see energy efficient transformer).
Losses in the transformer arise from:
Winding Resistance :-
Current flowing through the windings causes resistive heating of the
conductors. At higher frequencies, skin effect and proximity effect create
additional winding resistance and losses.
Hysteresis losses :-
Each time the magnetic field is reversed, a small amount of energy is
lost due to hysteresis within the core. For a given core material, the loss is
proportional to the frequency, and is a function of the peak flux density to
which it is subjected.
Eddy Currents :-
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Ferromagnetic materials are also good conductors, and a solid core
made from such a material also constitutes a single short-circuited turn
throughout its entire length. Eddy currents therefore circulate within the core
in a plane normal to the flux, and are responsible for resistive heating of the
core material. The eddy current loss is a complex function of the square of
supply frequency and inverse square of the material thickness.
Magnetostriction:-
Magnetic flux in a ferromagnetic material, such as the core, causes it to
physically expand and contract slightly with each cycle of the magnetic field, an
effect known as magnetostriction. This produces the buzzing sound commonly
associated with transformers,[6] and in turn causes losses due to frictional heating in
susceptible cores.
Mechanical losses :-
In addition to magnetostriction, the alternating magnetic field causes fluctuating
electromagnetic forces between the primary and secondary windings. These incite
vibrations within nearby metalwork, adding to the buzzing noise, and consuming a
small amount of power.[19]
Stray losses :-
Leakage inductance is by itself lossless, since energy supplied to its magnetic
fields is returned to the supply with the next half-cycle. However, any leakage flux
that intercepts nearby conductive materials such as the transformer's support
structure will give rise to eddy currents and be converted to heat.
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v
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Circuit Symbols
Circuit symbols are used in circuit diagrams which
show how a circuit is connected together. The actual layout of the
components is usually quite different from the circuit diagram. To build a
circuit you need a different diagram showing the layout of the parts on
strip board or printed circuit board .
Resistors
Component Circuit Symbol Function of Component
Resistor
A resistor restricts the flow of
current, for example to limit the
current passing through an LED. A
resistor is used with a capacitor in a
timing circuit.
Variable Resisto
r
(Rheostat)
This type of variable resistor with 2
contacts (a rheostat) is usually used
to control current. Examples include:
adjusting lamp brightness, adjusting
motor speed, and adjusting the rate
of flow of charge into a capacitor in a
timing circuit.
Variable Resisto
r
(Potentiometer)
This type of variable resistor with 3
contacts (a potentiometer) is usually
used to control voltage. It can be
used like this as a transducer
converting position (angle of the
control spindle) to an electrical
signal.
Variable Resisto
r
(Preset)
This type of variable resistor (a
preset) is operated with a small
screwdriver or similar tool. It is
designed to be set when the circuit is
made and then left without further
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adjustment. Presets are cheaper than
normal variable resistors so they are
often used in projects to reduce the
cost.
Capacitors
Component Circuit Symbol Function of Component
Capacitor
A capacitor stores electric charge. A
capacitor is used with a resistor in a
timing circuit. It can also be used as
a filter, to block DC signals but pass
AC signals.
Capacitor,
polarized
A capacitor stores electric charge.
This type must be connected the
correct way round. A capacitor is
used with a resistor in a timing
circuit. It can also be used as a
filter, to block DC signals but pass
AC signals.
Variable Capacito
r
A variable capacitor is used in a
radio tuner.
Trimmer
Capacitor
This type of variable capacitor (a
trimmer) is operated with a small
screwdriver or similar tool. It is
designed to be set when the circuit
is made and then left without
further adjustment.
Diodes
Component Circuit Symbol Function of Component
DiodeA device which only allows
current to flow in one direction.
LED
Light Emitting Diod
A transducer which converts
electrical energy to light.
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e
Zener Diode
A special diode which is used to
maintain a fixed voltage across its
terminals.
Photodiode A light-sensitive diode.
Transistors
Component Circuit Symbol Function of Component
Transistor NP
N
A transistor amplifies current. It can be used
with other components to make an amplifier or
switching circuit.
Transistor PNP
A transistor amplifies current. It can be used
with other components to make an amplifier or
switching circuit.
Pezos Transducer A transducer which converts electrical
energy to sound.
Amplifier
(general symbol)
An amplifier circuit with one input.
Really it is a block diagram symbol
because it represents a circuit rather
than just one component.
EarphoneA transducer which converts electrical
energy to sound.
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Books
1. Electronics projects
September 2004 edition
2. Principal of electronics
By. V.K. Mehta,
3. Electronics devices and circuits
By. J.B. Gupta,
4. Computer fundamental
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By. B. Ram
Web site
1. www.google.com
2. www.efy.com
3. www.electronicslab.com
4. www.electronicsproject.com
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