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AUTOMATIC IRRIGATION SYSTEM FOR FARMERS
ABSTRACT:
The continuous increasing demand of the food requires the
rapid improvement in food production technology. In a country
like India, where the economy is mainly based on agriculture and
the climatic conditions are isotropic, still we are not able to make
full use of agricultural resources. The main reason is the lack of
rains & scarcity of land reservoir water. The continuous extraction
of water from earth is reducing the water level due to which lot of
land is coming slowly in the zones of un-irrigated land. Another
very important reason of this is due to unplanned use of waterdue to which a significant amount of water goes waste.
In the field of agriculture, use of proper method of irrigation
is important and it is well known that irrigation by drip is very
economical and efficient. In the modern drip irrigation systems,
the most significant advantage is that water is supplied near the
root zone of the plants drip by drip due to which a large quantityof water is saved. At the present era, the farmers have been
using irrigation technique in India through the manual control in
which the farmers irrigate the land at the regular intervals. This
process sometimes consumes more water or sometimes the
water reaches late due to which the crops get dried. Water
deficiency can be detrimental to plants before visible wilting
occurs. Slowed growth rate, lighter weight fruit follows slight
water deficiency. This problem can be perfectly rectified if we use
automatic micro controller based drip irrigation system in which
the irrigation will take place only when there will be intense
requirement of water.
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The proposed Automatic Irrigation System for Farmers
project makes the irrigation automated. With the use of low cost
sensors and the simple circuitry, we can make this project as a
low cost product, which can be bought even by a poor farmer.
This project is best suited for places where water is scares and
has to be used in limited quantity.
The circuit comprises sensor parts built using an operational
amplifier. Two stiff copper wires are inserted in the soil to sense
whether the Soil is wet or dry. These sensors are buried in the
ground at required depth. Once the soil has reached desired
moisture level the sensors send a signal to the microcontroller to
turn on / off the relay. That is, the microcontroller is used to
control the whole system, which monitors the sensors and when
sensors sense the dry condition then the microcontroller will
switch on the motor and it will switch off the motor when sensors
sense the wet condition.
The system is built with Sensors, LM324 Comparator IC, and
a Relay. The software part of the system is designed using C
language. The Keil IDE is used as a development tool.
This project uses regulated 5V, 500mA power supply. The
AC mains supply is applied to a 12V step down transformer. The
transformer output is 12V AC which is rectified using a bridge
rectifier. The output of bridge rectifier is DC 12V which is filtered
by a capacitor, and then regulated using 7812 voltage regulator.
The output of 7812 is +12V DC which is the required voltage for
relay operation. The output of 7812 regulator is further filtered by
a capacitor, and then regulated using 7805 voltage regulator. The
output of 7805 is +5V DC which is the required voltage for
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microcontroller operation. Also an LED in series with 470 Ohms
resistor is used for power on indication.
INDEX
1. INTRODUCTION
OBJECTIVE OF THE PROJECT
BLOCK DIAGRAM
2. DESCRIPTION OF THE PROJECT
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BLOCK DIAGRAM DESCRIPTION
SCHEMATIC
3. HARDWARE DESCRIPTION
PRINTED CIRCUIT BOARD
AC MOTOR
COMPARATOR(LM358)
4. SOFTWARE DESCRIPTION
KEIL C
5. CONCLUSION
6. BIBLIOGRAPHY
INTRODUCTION
Objective:
The main aim of this embedded application is to save the
power as well as automatic starts the ac motor.
BLOCK DIAGRAM:
SENSORS
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Description:
This application is in the area of embedded systems.
An embedded system is some combination of computer
hardware and software, either fixed in capability or programmable,
that is specifically designed for a particular function
Since the embedded system is dedicated to specific tasks,
design engineers can optimize it reducing the size and cost of the
product and increasing the reliability and performance. Embedded
systems are controlled by one or more main processing cores that is
typically either a microcontroller or a digital signal
COMPARATOR DRIVER RELAY
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processor (DSP). Embedded systems control many devices in
common use today.
Irrigation is the key to a successful garden. Long gone are
the days of manual watering or relying on a friend to water when
you are on vacation or away on business. The Project presentedhere waters your plants regularly when you are out for vocation.
The circuit comprises sensor parts built using op-amp IC LM358.
Op-amp is configured here as a comparator. Two stiff copper
wires are inserted in the soil to sense the whether the Soil is wet
or dry. The comparator monitors the sensors and when sensors
sense the dry condition then the project will switch on the motor
and it will switch off the motor when the sensors are in wet. when
it receives the signals from the comparator.
SCHEMATIC:
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PRINTED CIRCUIT BOARD
Printed circuit boards may be covered in two topics namely
1) Technology
2) Design
Introduction to printed circuit boards:
It is called PCB in short, printed circuit consists of
conductive circuit pattern
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Applied to one or both sides of an insulating base, depending
upon that, it is called single sided PCB or double-sided PCB.
(SSB and DSB).
Conductor materials available are silver, brass, aluminium and
copper. Copper is most widely used. The thickness of conducting
material depends upon the current carrying capacity of circuit.
Thus a thicker copper layer will have more current carrying
capacity.
The printed circuit boards usually serves three distinct functions.
1) it provides mechanical support for the components
mounted on it.
2) It provides necessary electrical interconnections.
3) It acts as heat sink that is provides a conduction path
leading to removal of the heat generated in the circuit.
Advantages of PCB
1) When a number of identical assemblies are required. PCBs
provide cost saving because once a layout is approved there is
no need to check the circuit every time.
2) For large equipments such as computers, the saving on
checking connections or wires is substantial.
3) PCBs have controllable and predictable electrical and
mechanical properties.
4) A more uniform product is produced because wiring errors
are eliminated.
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5) The distributed capacitances are constant from one
production to another.
6) Soldering is done in one operation instead of connecting
discrete components by wires.
7) The PCB construction lands itself for automatic assembly.
8) Spiral type of inductors may be printed.
9) Weight is less.
10) It has miniaturization potential.
11) It has reproducible performance.
12) All the signals are accessible for testing at any point along
conductor track.
Classifications of laminates :
Laminates
Glass base lamination Paper
base
lamination
There materials are built from several layers of paper or
glass, which are bound together under heat and pressure to form
rigid sheets. The binder is usually a phenolic resin in the case of
glass base.
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The copper layer is formed on either side or two sides of the
laminate. Because of the different filters and binding resins the
characteristic properties of copper clad laminates change.
The rigid sheets of filters which form reinforcement use
paper in the form of alpha cellulose, craft or rags. These are
cheaper and have easy machinbillity. Glass filter uses glass fibers
which are woven to give cloth like appearance. This gives a high
mechanical strength, they are better moisture resistant than
above type.
Binding resins are either phenolic or epoxy as mentioned
before in addition to these; phenol formaldehyde and polyestersare also used. Of these, Epoxy resin has
Good electrical and mechanical properties.
Manufacture of cu clad laminate:
The base of laminate is either paper or glass fiber cloth, as
mentioned before.
The copper foil is produced by electroplating a thin layer of
copper on a large rotating drum of stainless steel. As the drum
runs the deposited copper layer is peeled off and forms a
continuous length, which is coiled into rolls for use. To ensure
good adhesion between copper foils and base material,
surface of copper on the laminate and both are kept under
hydraulic press for proper adhesion.
AC Motor
AC motors are configured in many types and sizes, including
brush less, servo, and gear motor types. A motor consists of a
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rotor and a permanent magnetic field stator. The magnetic field
is maintained using either permanent magnets or
electromagnetic windings. AC motors are most commonly used in
variable speed and torque.
Motion and controls cover a wide range of components that
in some way are used to generate and/or control motion. Areas
within this category include bearings and bushings, clutches and
brakes, controls and drives, drive components, encoders and
resolves, Integrated motion control, limit switches, linear
actuators, linear and rotary motion components, linear position
sensing, motors (both AC and AC motors), orientation positionsensing, pneumatics and pneumatic components, positioning
stages, slides and guides, power transmission (mechanical),
seals, slip rings, solenoids, springs.
In any electric motor, operation is based on simple
electromagnetism. A current-carrying conductor generates amagnetic field; when this is then placed in an external magnetic
field, it will experience a force proportional to the current in the
conductor, and to the strength of the external magnetic field. As
you are well aware of from playing with magnets as a kid,
opposite (North and South) polarities attract, while like polarities
(North and North, South and South) repel. The internal
configuration of a AC motor is designed to harness the magnetic
interaction between a current-carrying conductor and an external
magnetic field to generate rotational motion.
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Let's start by looking at a simple 2-pole AC electric motor (here
red represents a magnet or winding with a "North" polarization,
while green represents a magnet or winding with a "South"
polarization).
Every AC motor has six basic parts -- axle, rotor (a.k.a.,
armature), stator, commutator, field magnet(s), and brushes. In
most common AC motors (and all that Beamers will see), the
external magnetic field is produced by high-strength permanent
magnets1
. The stator is the stationary part of the motor -- thisincludes the motor casing, as well as two or more permanent
magnet pole pieces. The rotor (together with the axle and
attached commutator) rotates with respect to the stator. The
rotor consists of windings (generally on a core), the windings
being electrically connected to the commutator. The above
diagram shows a common motor layout -- with the rotor inside
the stator (field) magnets.
The geometry of the brushes, commutator contacts, and
rotor windings are such that when power is applied, the polarities
of the energized winding and the stator magnet(s) are
misaligned, and the rotor will rotate until it is almost aligned with
the stator's field magnets. As the rotor reaches alignment, the
brushes move to the next commutator contacts, and energize the
next winding. Given our example two-pole motor, the rotation
reverses the direction of current through the rotor winding,
leading to a "flip" of the rotor's magnetic field, and driving it to
continue rotating.
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In real life, though, AC motors will always have more than
two poles (three is a very common number). In particular, this
avoids "dead spots" in the commutator. You can imagine how
with our example two-pole motor, if the rotor is exactly at the
middle of its rotation (perfectly aligned with the field magnets), it
will get "stuck" there. Meanwhile, with a two-pole motor, there is
a moment where the commutator shorts out the power supply
(i.e., both brushes touch both commutator contacts
simultaneously). This would be bad for the power supply, waste
energy, and damage motor components as well. Yet another
disadvantage of such a simple motor is that it would exhibit ahigh amount of torque ripple" (the amount of torque it could
produce is cyclic with the position of the rotor).
So since most small AC motors are of a three-pole design,
let's tinker with the workings of one via an interactive animation
(JavaScript required):
You'll notice a few things from this -- namely, one pole is
fully energized at a time (but two others are "partially"
energized). As each brush transitions from one commutator
contact to the next, one coil's field will rapidly collapse, as the
next coil's field will rapidly charge up (this occurs within a few
microsecond). We'll see more about the effects of this later, but
in the meantime you can see that this is a direct result of the coil
windings' series wiring:
There's probably no better way to see how an average AC
motor is put together, than by just opening one up. Unfortunately
this is tedious work, as well as requiring the destruction of a
perfectly good motor.
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This is a basic 3-pole ACmotor, with 2 brushes and three
commutator contacts.
Single-phase induction motors
A three phase motor may be run from a single phase power source.(Figure below) However, it will not self-start. It may be hand started in
either direction, coming up to speed in a few seconds. It will only
develop 2/3 of the 3- power rating because one winding is not used.
3-motor runs from 1- power, but does not start.
The single coil of a single phase induction motor does not produce a
rotating magnetic field, but a pulsating field reaching maximum
intensity at 0o and 180o electrical. (Figure below)
Single phase stator produces a nonrotating, pulsating magnetic field.
Another view is that the single coil excited by a single phase current
produces two counter rotating magnetic field phasors, coinciding twice
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per revolution at 0o (Figure above-a) and 180o (figure e). When the
phasors rotate to 90o and -90o they cancel in figure b. At 45o and -45o
(figure c) they are partially additive along the +x axis and cancel along
the y axis. An analogous situation exists in figure d. The sum of these
two phasors is a phasor stationary in space, but alternating polarity in
time. Thus, no starting torque is developed.
However, if the rotor is rotated forward at a bit less than the
synchronous speed, It will develop maximum torque at 10% slip with
respect to the forward rotating phasor. Less torque will be developed
above or below 10% slip. The rotor will see 200% - 10% slip with
respect to the counter rotating magnetic field phasor. Little torque (see
torque vs slip curve) other than a double freqency ripple is developed
from the counter rotating phasor. Thus, the single phase coil will
develop torque, once the rotor is started. If the rotor is started in the
reverse direction, it will develop a similar large torque as it nears the
speed of the backward
Rotating phasor.
Single phase induction motors have a copper or aluminum squirrel
cage embedded in a cylinder of steel laminations, typical of poly-phase
induction motors.
Permanent-split capacitor motor
One way to solve the single phase problem is to build a 2-phase motor,
deriving 2-phase power from single phase. This requires a motor with
two windings spaced apart 90
o
electrical, fed with two phases ofcurrent displaced 90o in time. This is called a permanent-split capacitor
motor in Figure below.
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Permanent-split capacitor induction motor.
This type of motor suffers increased current magnitude and backward
time shift as the motor comes up to speed, with torque pulsations at
full speed. The solution is to keep the capacitor (impedance) small to
minimize losses. The losses are less than for a shaded pole motor. This
motor configuration works well up to 1/4 horsepower (200watt),
though, usually applied to smaller motors. The direction of the motor is
easily reversed by switching the capacitor in series with the other
winding. This type of motor can be adapted for use as a servo motor,
described elsewhere is this chapter.
Single phase induction motor with embedded stator coils.
Single phase induction motors may have coils embedded into the
stator as shown in Figure above for larger size motors. Though, the
smaller sizes use less complex to build concentrated windings with
salient poles.
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Capacitor-start induction motor
In Figure below a larger capacitor may be used to start a single phase
induction motor via the auxiliary winding if it is switched out by a
centrifugal switch once the motor is up to speed. Moreover, the
auxiliary winding may be many more turns of heavier wire than used ina resistance split-phase motor to mitigate excessive temperature rise.
The result is that more starting torque is available for heavy loads like
air conditioning compressors. This motor configuration works so well
that it is available in multi-horsepower (multi-kilowatt) sizes.
Capacitor-start induction motor.
Capacitor-run motor induction motor
A variation of the capacitor-start motor (Figure below) is to start the
motor with a relatively large capacitor for high starting torque, but
leave a smaller value capacitor in place after starting to improve
running characteristics while not drawing excessive current. The
additional complexity of the capacitor-run motor is justified for larger
size motors.
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Capacitor-run motor induction motor.
A motor starting capacitor may be a double-anode non-polar
electrolytic capacitor which could be two + to + (or - to -) series
connected polarized electrolytic capacitors. Such AC rated electrolytic
capacitors have such high losses that they can only be used forintermittent duty (1 second on, 60 seconds off) like motor starting. A
capacitor for motor running must not be of electrolytic construction,
but a lower loss polymer type.
Resistance split-phase motor induction motor
If an auxiliary winding of much fewer turns of smaller wire is placed at
90o
electrical to the main winding, it can start a single phase inductionmotor. (Figure below) With lower inductance and higher resistance, the
current will experience less phase shift than the main winding. About
30o of phase difference may be obtained. This coil produces a
moderate starting torque, which is disconnected by a centrifugal
switch at 3/4 of synchronous speed. This simple (no capacitor)
arrangement serves well for motors up to 1/3 horsepower (250 watts)
driving easily started loads.
Resistance split-phase motor induction motor.
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This motor has more starting torque than a shaded pole motor (next
section), but not as much as a two phase motor built from the same
parts. The current density in the auxiliary winding is so high during
starting that the consequent rapid temperature rise precludes frequent
restarting or slow starting loads.
Nola power factor corrrector
Frank Nola of NASA proposed a power factor corrector for improving
the efficiency of AC induction motors in the mid 1970's. It is based on
the premise that induction motors are inefficient at less than full load.
This inefficiency correlates with a low power factor. The less than unity
power factor is due to magnetizing current required by the stator. This
fixed current is a larger proportion of total motor current as motor load
is decreased. At light load, the full magnetizing current is not required.
It could be reduced by decreasing the applied voltage, improving the
power factor and efficiency. The power factor corrector senses power
factor, and decreases motor voltage, thus restoring a higher power
factor and decreasing losses.
Since single-phase motors are about 2 to 4 times as inefficient as
three-phase motors, there is potential energy savings for 1- motors.
There is no savings for a fully loaded motor since all the stator
magnetizing current is required. The voltage cannot be reduced. But
there is potential savings from a less than fully loaded motor. A
nominal 117 VAC motor is designed to work at as high as 127 VAC, as
low as 104 VAC. That means that it is not fully loaded when operated
at greater than 104 VAC, for example, a 117 VAC refrigerator. It is safe
for the power factor controller to lower the line voltage to 104-110
VAC. The higher the initial line voltage, the greater the potential
savings. Of course, if the power company delivers closer to 110 VAC,
the motor will operate more efficiently without any add-on device.Any
substantially idle, 25% FLC or less, single phase induction motor is a
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candidate for a PFC. Though, it needs to operate a large number of
hours per year. And the more time it idles, as in a lumber saw, punch
press, or conveyor, the greater the possibility of paying for the
controller in a few years operation. It should be easier to pay for it by a
factor of three as compared to the more efficient 3--motor. The cost
of a PFC cannot be recovered for a motor operating only a few hours
per day
Summary: Single-phase induction motors
Single-phase induction motors are not self-starting without an
auxiliary stator winding driven by an out of phase current of near
90o. Once started the auxiliary winding is optional.
The auxiliary winding of apermanent-split capacitor motorhas a
capacitor in series with it during starting and running.
A capacitor-start induction motor only has a capacitor in series
with the auxiliary winding during starting.
A capacitor-run motor typically has a large non-polarized
electrolytic capacitor in series with the auxiliary winding for
starting, then a smaller non-electrolytic capacitor during running.
The auxiliary winding of a resistance split-phase motordevelops
a phase difference versus the main winding during starting by
virtue of the difference in resistance.
Learn about "Capacitor Start - Induction Run" Motors
The starter winding has a capacitor incorporated which makes the
single-phase motor a self-starting one. Read here to know about the
different types of widely used capacitor-motors
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Introduction
We know that the single-phase induction motor can be made self-
starting in numerous ways. One such most used method was the Split
Phase motors which we discussed in my last article. In this article, we
will discuss about the Capacitor Start Induction Run Motors.
Capacitor-Start Induction-Run Motors
We know about the activity of a capacitor in a pure A.C. Circuit. When
a capacitor is so introduced, the voltage lags the current by some
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phase angle. In these motors, the necessary phase difference between
the Is and Im is obtained by introducing a capacitor in series with the
starter winding. The capacitor used in these motors are of electrolytic
type and usually visible as it is mounted outside the motor as a
separate unit.
During starting, as the capacitor is connected in series with the starter
winding, the current through the starter winding Is leads the voltage V,
which is applied across the circuit. But the current through the main
winding Im, still lags the applied voltage V across the circuit. Thus
more the difference between the Is and Im, better the resulting
rotating magnetic field.
When the motor reaches about 75% of the full load speed, the
centrifugal switch S opens and thus disconnecting the starter winding
and the capacitor from the main winding. It is important to point out
from the phasor diagram that the phase difference between Im and Is
is almost 80 degrees as against 30 degrees in a split-phase induction
motor. Thus a capacitor-start induction-run motor produces a better
rotating magnetic field than the split-phase motors. It is evident from
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the phasor diagram that the current through the starter winding Is
leads the voltage V by a small angle and the current through the main
winding Im lags the applied voltage. It is to be appreciated that the
resultant current I, is small and is almost in phase with the applied
voltage V.
As discussed earlier in my last article on split-phase motors, the torque
developed by a split-phase induction motor is directly proportional to
the sine of the angle between Is and Im. Also the angle is 30 degrees in
case of split-phase motors. But incase of capacitor-start induction-run
motors, the angle between Is and Im is 80 degrees. It is then obvious
that the increase in the angle (from 30 degrees to 80 degrees) alone
increases the starting torque to nearly twice the value developed by a
standard split-phase induction motor. The speed-torque characteristics
curve is exhibiting the starting and running torques of a capacitor-start
induction-run motor.
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Types of Motors
There are different types of Capacitor-start motors designed and used
in various fields. They are as follows:
1. Single-voltage, externally reversible type,
2. Single-voltage, non-reversible type,
3. Single-voltage reversible and with thermostat type,
4. Single-voltage, non-reversible with magnetic switch type,
5. Two-voltage, non-reversible type,
6. Two-voltage, reversible type,
7. Single-voltage, three-lead reversible type,
8. Single-voltage, instantly-reversible type,
9. Two speed type, and
10. Two-speed with two-capacitor type.
These motors can be used for various purposes depending upon the
need of the user. The starting, speed/torque characteristics of each of
the above motors can be analyzed before employing them in work.
COMPARATOR(LM358):
Features
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Internally Frequency Compensated for Unity Gain
Large DC Voltage Gain: 100dB
Wide Power Supply Range:
LM258/LM258A, LM358/LM358A: 3V~32V (or 1.5V
~ 16V)
LM2904: 3V~26V (or 1.5V ~ 13V)
Input Common Mode Voltage Range Includes Ground
Large Output Voltage Swing: 0V DC to Vcc -1.5V DC
Power Drain Suitable for Battery Operation.
Description
The LM2904, LM358/LM358A, LM258/LM258A consist of two
independent, high gain, Internally frequency compensated
operational amplifiers which were designed specifically to
operate from a single power supply over a wide range of voltage.
Operation from split power supplies is also possible and the low
power supply current drain is independent of the magnitude of
the power supply voltage. Application areas include transducer
amplifier, DC gain blocks and all the conventional OP-AMP circuits
which now can be easily implemented in single power supply
systems.
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Power Supply:
BR1
100 uf1000 uf
LM7812 LM7805
Red led
100 ohm470 ufI/P power
O/P power
Power supply
The power supply consists of ac voltage transformer, diode
rectifier, ripple filter, and voltage regulators. The transformer is an AC
device, which increases or decreases the input supply voltage withoutchange in frequency. There are 2 types of transformers. One of Step-
up and the other is Step-down. Here we are using a Step-down
transformer, which decreases the 230 supply volts to 12 volts. The
rectifier is a device which converts an AC voltage to the pulsating DC
voltage. Here IN4007 diodes are used as rectifiers. A bridge type full
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wave rectifier is constructed using these diodes, as its efficiency is
81.2% and ripple factor is 0.482.
After the rectification, the output voltage signal contains both an
average dc component and a time varying ac component called the
ripple. To reduce or eliminate the ac component, one needs low pass
filter(s). The low pass filter allows the dc component to pass through it
but attenuate the ac at 60 Hz or its harmonics, i.e., 120 Hz. Here we
use 1000Mf, 470Mf & 100Mf capacitors at the o/p and i/p of regulators.
The 12v DC output of the filter is passed through voltage regulators of
7812 & 7805. 78 indicates that it is a regulator for positive voltage.
There is a corresponding 79 model for negative voltage. 12
indicates that it has an output of 12 V. similarly we are connecting a7805 to the 7812 regulator o/p, to generate 5volts. An LED in series to
a 100ohms resistor is connected in parallel to the output voltage to
indicate the supply. And also a switch is connected in series to the o/p
voltage terminal to ON/OFF the supply.
Transformer:
Definition: -
The transformer is a static electro-magnetic device that
transforms one alternating voltage (current) into another voltage
(current). However, power remains the some during the
transformation. Transformers play a major role in the transmission and
distribution of ac power.
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Principle: -
Transformer works on the principle of mutual induction. A
transformer consists of laminated magnetic core forming the magnetic
frame. Primary and secondary coils are wound upon the two cores of
the magnetic frame, linked by the common magnetic flux. When an
alternating voltage is applied across the primary coil, a current flows in
the primary coil producing magnetic flux in the transformer core. This
flux induces voltage in secondary coil.
Transformers are classified as: -
(a) Based on position of the windings with respect to core i.e.
(1) Core type transformer
(2) Shell type transformer
(b) Transformation ratio:
(1) Step up transformer
(2) Step down transformer
(a) Core & shell types: Transformer is simplest electrical machine,
which consists of windings on the laminated magnetic core.
There are two possibilities of putting up the windings on the core.
(1) Winding encircle the core in the case of core type transformer
(2) Cores encircle the windings on shell type transformer.(b) Step up and Step down: In these Voltage transformation takes
place according to whether the
Primary is high voltage coil or a low voltage coil.
(1) Lower to higher-> Step up
(2) Higher to lower-> Step down
DIODES
It is a two terminal device consisting of a P-N junction formed
either of Ge or Si crystal. The P and N type regions are referred to as
anode and cathode respectively. Commercially available diodes usually
have some means to indicate which lead is P and which lead is N.
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FEATURE
Low forward voltage
High current capabilityLow leakage current
High surge capability
Low cost
MECHANICAL DATA
Case:Molded plastic use UL 94V-0 recognized
Flame retardant epoxy
Terminals:Axial leads, solderable per
MIL-STD-202, method 208
Polarity:Color band denotes cathode
Mounting Position:Any
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RESISTORS: -
A Resistor is a heat-dissipating element and in the electronic
circuits it is mostly used for either controlling the current in the circuit
or developing a voltage drop across it, which could be utilized for many
applications. There are various types of resistors, which can be
classified according to a number of factors depending upon:
Material used for fabrication
Wattage and physical size
Intended application
Ambient temperature rating
Cost
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Basically the resistor can be split in to the following four parts from the
construction view point.
(1) Base
(2) Resistance element
(3) Terminals
(4) Protective means.
The following characteristics are inherent in all resistors and may
be controlled by design considerations and choice of material i.e.
Temperature coefficient of resistance, Voltage coefficient of
resistance, high frequency characteristics, power rating, tolerance &
voltage rating of resistors. Resistors may be classified as
(1)Fixed
(2)Semi variable
(3)Variable resistor.
CAPACITORS
The fundamental relation for the capacitance between two flat
plates separated by a dielectric material is given by:-
C=0.08854KA/D
Where: -
C= capacitance in pf.
K= dielectric constant
A=Area per plate in square cm.
D=Distance between two plates in cm
Design of capacitor depends on the proper dielectric material
with particular type of application. The dielectric material used for
capacitors may be grouped in various classes like Mica, Glass, air,
ceramic, paper, Aluminum, electrolyte etc. The value of capacitance
never remains constant. It changes with temperature, frequency and
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aging. The capacitance value marked on the capacitor strictly applies
only at specified temperature and at low frequencies.
LED (Light Emitting Diodes):
As its name implies it is a diode, which emits light when forward
biased. Charge carrier recombination takes place when electrons from
the N-side cross the junction and recombine with the holes on the P
side. Electrons are in the higher conduction band on the N side
whereas holes are in the lower valence band on the P side. During
recombination, some of the energy is given up in the form of heat and
light. In the case of semiconductor materials like Gallium arsenide
(GaAs), Gallium phoshide (Gap) and Gallium arsenide phoshide
(GaAsP) a greater percentage of energy is released duringrecombination and is given out in the form of light. LED emits no light
when junction is reverse biased.
LM7812 AND LM7805:
Features Output Current of 1.5A
Output Voltage Tolerance of 5%
Internal thermal overload protection
Internal Short-Circuit Limited
No External Component
Output Voltage 5.0V, 6V, 8V, 9V, 10V,
12V, 15V, 18V, 24V
Offer in plastic TO-252, TO-220 & TO-263
Direct Replacement for LM78XX
Description:
The Bay Linear LM78XX is integrated linear positive regulator
with three terminals. The LM78XX offer several fixed output voltages
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making them useful in wide range of applications. When used as a
zener diode/resistor combination
replacement, the LM78XX usually results in an effective output
impedance improvement of two orders of magnitude, lower quiescent
current.
The LM78XX is available in the TO-252, TO-220 & TO-263 Packages
Applications:
Post regulator for switching DC/DC converter
Bias supply for analog circuits
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CONCLUSION:
The project AUTOMATIC IRRIGATION SYSTEM FOR
FARMERS has been successfully designed and tested. It has
been developed by integrating features of all the hardware
components used. Presence of every module has been reasonedout and placed carefully thus contributing to the best working of
the unit.
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Secondly, using highly advanced ICs and with the help of
growing technology the project has been successfully
implemented.
Finally we conclude that EMBEDDED SYSTEM system is an
emerging field and there is a huge scope for research and
development.
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BIBLIOGRAPHY
The 8051 Micro controller and Embedded
Systems
-Muhammad Ali Mazidi
Janice Gillispie Mazidi
The 8051 Micro controller Architecture,
Programming & Applications
-Kenneth J.Ayala
Fundamentals Of Micro processors and
Micro computers
-B.Ram
Micro processor Architecture, Programming
& Applications
-Ramesh S.Gaonkar
Electronic Components
-D.V.Prasad
Wireless Communications
- Theodore S. Rappaport
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Mobile Tele Communications
- William C.Y. Lee
References on the Web:
www.national.com
www.atmel.com
www.microsoftsearch.com
www.geocities.com
http://www.national.com/http://www.atmel.com/http://www.microsoftsearch.com/http://www.geocities.com/http://www.national.com/http://www.atmel.com/http://www.microsoftsearch.com/http://www.geocities.com/