Automatic Plant Irrigation System

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INDEX

Chapter-1

a. Abstract

b. Technical specifications

Chapter-2

a. introduction

Chapter-3

a. block diagram

b. working

Chapter-4

a. circuit components

b. components description

Chapter-5

a. advantages

b. applications

Chapter-6

a. conclusion

b. Bibliography

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CHAPTER-1

ABSTRACT

In the field of agriculture, use of proper method of irrigation is important because 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 water due to which a significant amount of water goes waste. For this purpose; we use this

automatic plant irrigation system.

In the conventional irrigation system, the farmer has to keep watch on irrigation

timetable, which is different for different crops. The project makes the irrigation automated.

With the use of low cost sensors and the simple circuitry makes this project 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 Project presented here

waters your plants regularly when you are out for vocation. The heart of the project is the IC

opamp lm324. This is safest and no manpower is required. Require smaller water sources, for

example, less than half of the water needed for a sprinkler system. This is very useful to all

climatic conditions any it is economic

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TECHNICAL SPECIFICATIONS

Title of the project : Automatic Plant Irrigation System with water pump

control based on soil moister condition

Domain : using IC OPAMP LM324

Power Supply : +5V, 500mA Regulated Power Supply

Sensors : Electro magnetic moister sensor

Load : 230 V ac motor

Applications : Roof Gardens, Lawns, Agriculture Lands,

Home Gardens

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CHAPTER-2

INTRODUCTION

Automatic plant watering systems have proved to be a boon for those, who lack time for

watering plants manually. Read on to know more about the various aspects of automatic plant

watering systems.

Nowadays, there are very few homes which do not have plants, both indoor and

outdoor ones. There are many plant enthusiasts, who keep on buying different varieties and

end up with no time to take care of those plants. One of the main aspects of plant care is

watering, which has to be done regularly for healthy growth of plants. While some people get

fed up with manual watering, others do not have enough time for this task. Automatic

watering systems can be of immense help to such people. You can either make some simple

homemade automatic plant watering systems or purchase the best suited one from the wide

range of systems available in the market. Scroll down for more information about automatic

plant watering system.

Automatic Plant Watering System

As you know that by installing an automatic watering system, you can do away with the task

of watering plants manually. There are various types of automatic plant watering systems,

which store water and supply the plants with the required amount of water. These types vary

from simple ones to most sophisticated systems and you have to choose the best suited one

for your plants. There are many types of watering systems, designed for both indoor and

outdoor potted plants as well as flower gardens. In short, such system takes care of the water

requirements of plants and totally eliminates manual watering. However, you have to fill

water in some systems, as and when it requires and set the timer, if the system has any.

Types of Automatic Plant Watering Systems

As mentioned above, these systems range from simple ones to sophisticated ones.

You can even make a watering system from materials used for household purposes. One of

the basic homemade automatic plant watering system can be made with plastic containers.

Clean the containers and make two to three small holes on their bottom. Now, fill the

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containers with water and set them in the dirt, next to the plant. If the soil is wet, very little

amount of water will be absorbed and as it get dry, more water will leak out of the container.

Now, you know, how to make automatic plant waterer. This is one of the basic methods, but,

you can make different types of automatic plant watering devices with various other

materials. Read more on gardening accessories.

Even commercial watering systems come in various types. There are stand-

alone systems, which come with pots, water reservoirs, etc. The water reservoirs too, are

available in different designs and patterns. Such systems may or may not have timers. These

systems take care of the water requirements of individual plants. There are multiple plant

watering systems, that can take care of a certain number of plants, simultaneously. These

systems constitute water tanks, pipes that supplies water from the tank to individual plants

and drips attached to the end of each pipe. For a garden, sprinkler and drip systems with

timers are available. In some sophisticated ones, even ground sensors are used, so that

watering will be done, whenever, the ground gets dry. While some of watering system work

on battery power, some others use power from the mains. There are simple ones too, that

work under gravity. Each type of plant watering system has its own features, which have to

be understood, before investing on it. Select the one, which is best suited for your

requirement.

Now, you have a basic idea about automatic plant watering systems, which can be very

useful for those, who don't have time to water their plants and also for those are going on a

vacation. Above all, automatic house plant watering systems can be of great help in water

conservation too.

Relevance:

1) Used in the field of agriculture as a new technology.

2) Used in conventional farming areas.

3) Used in the garden system.

Present theory:

The Project presented here waters your plants regularly when you are out for vocation.

The circuit comprises sensor parts built using op-amp IC LM324. Op-amp's are 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 Microcontroller was used to control the whole system it monitors the sensors and 6

when more than two sensors sense the dry condition then the microcontroller will switch on

the motor and it will switch off the motor when all the sensors are in wet. The microcontroller

does the above job it receives the signals from the sensors, and this signals operated under the

control of software which is stored in ROM.

Proposed Work:

A) Objective:

From this project we provide a new technology for automation of agriculture field.

Also avoid the waste of water which occurs in the older irrigation system. From this project

we can reduce the manpower. The Project presented here waters your plants automatically

and regularly when you are out for vocation.

B) Scope of Project:

In our India 70% people doing farming. This projects helps the farmer to overcome the

drawbacks of traditional irrigation system. From this project we provide the new technology

for farmer to improve the quality of their irrigation system. This project helps those farmers

which do not have sufficient water for their farming.

C). CURRENT SCENARIO

Greenhouses in India are being deployed in the high-altitude regions where the sub-

zero temperature up to -40° C makes any kind of plantation almost impossible and in arid

regions where conditions for plant growth are hostile. The existing set-ups primarily are:

D). MANUAL SET-UP:

This set-up involves visual inspection of the plant growth, manual irrigation of plants,

turning ON and OFF the temperature controllers, manual spraying of the fertilizers and

pesticides. It is time consuming, vulnerable to human error and hence less accurate and

unreliable.

E). PARTIALLY AUTOMATED SET-UP:

This set-up is a combination of manual supervision and partial automation and is similar

to manual set-up in most respects but it reduces the labor involved in terms of irrigating the set-up.

F). FULLY- AUTOMATED:

This is a sophisticated set-up which is well equipped to react to most of the climatic

changes occurring inside the greenhouse. It works on a feedback system which helps it to

respond to the external stimuli efficiently. Although this set-up overcomes the problems caused due to

human errors it is not completely automated and expensive.

G). PROPOSED MODEL FOR AUTOMATION OF GREENHOUSE

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The proposed system is an embedded system which will closely monitor and control

the microclimatic parameters of a greenhouse on a regular basis round the clock for

cultivation of crops or specific plant species which could maximize their production over the

whole crop growth season and to eliminate the difficulties involved in the system by reducing

human intervention to the best possible extent. The system comprises of sensors, Analog to

Digital Converter, microcontroller and actuators.

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CHAPTER-3

Block diagram

Soil dry – wet

Sensor LM324 Transistor led display Comparator driven circuit

Ref Voltage

water

Ac input RELAY pump

Step Bridge filter regulator power

Down t/f rectifier circuite supplies

To all Sectionns

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WORKING

The project presented here waters your plants regularly when you are out for

vocation .the circuit comprises sensor parts built using op-amp LM324. Op-amp is configured

here as a comparator. And electromagnetic moisture sensor is inserted into soil to measure

the moisture level in soil.

Comparator compares the voltage levels from sensor and reference values. If

moisture levels is low than reference value then it produces a dc signal and it passed to

transistor, this transistor send a signal to relay. Relay activates the motor to run and supply

water to the plant.

Now moisture level increases than the reference value then comparator gives another

signal to transistor. Then transistor stops the signal flow to the relay. Now relay stops the

electrical motor. This process is continuous to give healthy watering to the plant.

In this way we can control the water flow to a plant.

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Chapter-4

CIRCUIT COMPONENTS

1. TRANSFORMER

2. BRIDGE RECTIFIER

3. CERAMIC CAPACITOR (FILTER)

4. VOLTAGE REGULATOR

5. TRANSISTORS

6. RESISTOR

7. LED

8. MOISTURE SENSOR

9. RHEOSTAT(VARIABLE RESISTOR)

10. COMPARATOR( IC OP-AMP LM324)

11. DIODE

12. RELAY

13. ELECTICAL MOTOR

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COMPONENTS DISCRIPTION

1. TRANSFORMER

Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c

input available at the mains supply i.e., 230V is to be brought down to the required voltage

level. This is done by a transformer. Thus, a step down transformer is employed to decrease

the voltage to a required level.

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). Changing

the current in the primary coil changes the magnetic flux that is developed. The changing

magnetic flux induces a voltage in the secondary coil.

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An ideal transformer is shown in the adjacent figure. 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, so that most of the magnetic flux passes

through both the primary and secondary coils.

Induction law:

The voltage induced across the secondary coil may be calculated from Faraday's law of

induction, which states that:

Where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil

and Φ is the 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 flux density

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. Since the same magnetic flux passes through both the primary and

secondary coils in an ideal transformer, the instantaneous voltage across the primary winding

equals

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Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up or

stepping down the voltage

Np/Ns is known as the turns ratio, and is the primary functional characteristic of any

transformer. In the case of step-up transformers, this may sometimes be stated as the

reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for

example, a transformer with primary and secondary windings of, respectively, 100 and 150

turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150.

Ideal power equation

Fig. 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 into the secondary circuit. If this condition is met, the incoming electric

power must equal the outgoing power:

giving the ideal transformer equation

Transformers normally have high efficiency, so this formula is a reasonable approximation.

If the voltage is increased, then the current is decreased by the same factor. The impedance in

one circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is

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attached across the terminals of the secondary coil, it appears to the primary circuit to have an

impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the

primary circuit appears to the secondary to be (Ns/Np)2Zp.

2. BRIDGE RECTIFIER

The output from the transformer is fed to the rectifier. It converts A.C. into pulsating

D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier

is used because of its merits like good stability and full wave rectification.

The Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both

half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The

circuit has four diodes connected to form a bridge. The ac input voltage is applied to the

diagonally opposite ends of the bridge. The load resistance is connected between the other

two ends of the bridge.

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For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas

diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the

load resistance RL and hence the load current flows through RL.

For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1

and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load

resistance RL and hence the current flows through RL in the same direction as in the previous

half cycle. Thus a bi-directional wave is converted into a unidirectional wave.

3. CERAMIC CAPACITOR (FILTER)

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Capacitive filter is used in this project. It removes the ripples from the output of

rectifier and smoothens the D.C. Output received from this filter is constant until the mains

voltage and load is maintained constant. However, if either of the two is varied, D.C. voltage

received at this point changes. Therefore a regulator is applied at the output stage.

Capacitor blocks DC (constant) signals. Capacitors easily pass AC (changing) signals

Electronic filters are electronic circuits which perform signal processing functions,

specifically to remove unwanted frequency components from the signal, to enhance wanted

ones, or both.

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RECTIFIER OUTPUT

FILTER PURE DC

AC+DC DC

4. VOLTAGE REGULATOR

A voltage regulator is an electrical regulator designed to automatically maintain a constant

voltage level. It may use an electromechanical mechanism, or passive or active electronic

components. Depending on the design, it may be used to regulate one or more AC or DC

voltages.

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this

project, power supply of 5V and 12V are required. In order to obtain these voltage levels,

7805 and 7812 voltage regulators are to be used. The first number 78 represents positive

supply and the numbers 05, 12 represent the required output voltage levels. The L78xx series

of three-terminal positive regulators is available in TO-220, TO-220FP, TO-3, D2PAK and

DPAK packages and several fixed output voltages, making it useful in a wide range of

applications.

These regulators can provide local on-card regulation, eliminating the distribution

problems associated with single point regulation. Each type employs internal current limiting,

thermal shut-down and safe area protection, making it essentially indestructible. If adequate

heat sinking is provided, they can deliver over 1 A output current. Although designed

primarily as fixed voltage regulators, these devices can be used with external components to

obtain adjustable voltage and currents.

The

voltage

regulators are classified into two

types.

1. positive series(7805)

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2. Negative series(7905)

5. TRANSISTORS

A transistor is a semi conductor device commonly used to amplify or switch electronic

signals. A voltage or current applied to one pair of the transistor's terminals changes the

current flowing through another pair of terminals. Because the controlled (output) power can

be much more than the controlling (input) power, the transistor provides amplification of a

signal.

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7805

I/P GND O/P I/P

7905

O/PGND

7805SERIESOutput

voltage

The transistor is the key active component in practically all modern electronics. Many

consider it to be one of the greatest inventions of the 20th century. Its importance in today's

society rests on its ability to be mass produced using a highly automated process

(semiconductor device fabrication) that achieves astonishingly low per-transistor costs.

Although several companies each produce over a billion individually packaged (known as

discrete) transistors every year, the vast majority of transistors now are produced in integrated

circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors,

capacitors and other electronic components, to produce complete electronic circuits.

6. RESISTOR

A resistor is a device which opposes the flow of current. In a circuit offenly it is used to protect

the devices like LED etc,.

7. LED

LEDs emit light when an electric current passes through them.

A single LED is a low-voltage solid state device and cannot be directly operated on standard

AC current without some circuitry to control the voltage applied and the current flow through the

lamp. A series diode and resistor could be used to control the voltage polarity and to limit the current,

but this is inefficient since most of the applied voltage would be dropped as wasted heat in the

resistor. A single series string of LEDs would minimize dropped-voltage losses, but one LED failure

could extinguish the whole string. Paralleled strings increase reliability by providing redundancy. In

practice, three strings or more are usually used. To be useful for illumination for home or work

spaces, a number of LEDs must be placed close together in a lamp to combine their illuminating

effects. This is because individual LEDs emit only a fraction of the light of traditional light sources.

When using the color-mixing method, a uniform color distribution can be difficult to achieve, while

the arrangement of white LEDs is not critical for color balance. Further, degradation of different

LEDs at various times in a color-mixed lamp can lead to an uneven color output. LED lamps usually

consist of clusters of LEDs in a housing with both driver electronics, a heat sink and optics.

Circuit symbol:

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8. MOISTURE SENSOR

VH400 Soil Moisture Sensor Probes

Our high frequency VH400 series soil moisture sensor probes enable precise low cost

monitoring of soil water content. Because our probe measures the dielectric constant of the

soil using transmission line techniques, it is insensitive to water salinity, and will not corrode

over time as does conductivity based probes. Our probes are small, rugged, and low power.

Compared to other low cost sensor such as gypsum block

sensors, our probes offer a rapid response time. They can be

inserted and take an accurate reading in under 1 second.

The VH400 consumes more power than the VG400 series

sensors because it operates at a much higher frequency, however,

it is much more sensitive at higher VWC levels, and its curves are

more linear.

Probes come standard with a 2 meter cable.

Also see our extremely low power VG400 series soil moisture

sensors.

See our Soil Moisture Sensor Selector, to figure out which probe

is right for your application. VH400 - Soil Moisture

Sensor Probe

Soil Moisture Sensor Probe Applications

Irrigation and sprinkler systems.

Moisture monitoring of bulk foods.

Rain and weather monitoring.

Environmental monitoring.

Water conservation applications.

Fluid level measurements.

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Soil Moisture Sensor Probe Features

Extreme low cost with volume pricing.

Not conductivity based.

Insensitive to salinity.

Probe does not corrode over time.

Rugged design for long term use.

Small size.

Consumes less than 600uA for very low power operation.

Precise measurement.

Measures volumetric water content (VWC) or gravimetric water content (GWC).

Patent pending technology.

Output Voltage is proportional to moisture level.

Wide supply voltage range.

Can be buried and is water proof.

Probe is long and slender for wider use, including smaller potted plants.

Specifications

Sensors:

o SS model - Stainless Steel

o MS & HS models - Stainless Steel

o with Epoxy coating

All electronics are sealed in water-proof epoxy

Temperature range:

o Operating - 32° to 150° F

o Storage - 4° to 160° F

Output Format:

o Standard format - 0.5 - 5.0 mA

Power requirements:

o Standard 5.5 - 18 VDC, 10-20 mA (max)

Accuracy:

o 1% Volumetric Soil Moisture

Cable Length: 15 ft.

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Connection:

o 3 pin, IP66/IP68 rated environmental connector

Dimensions:

o 3.75" w x 1.5" d x 9.5" l

Weight:

o 1.5 lbs.

Product Advantages

Responds immediately and accurately to changes in soil moisture.

Designed to remain in the soil for the growing season or be installed permanently.

Unit is rugged, easy to use and maintenance-free.

Utilizes TDT technology (Time Domain Transmissometry) which is similar in

operating principle to TDR (Time Domain Reflectometry).

Sensor probes are factory calibrated and can operate in all soils and crops.

Optimizes water use and reduces excessive leaching, saving fertilizer and energy.

Install the Gro-Point sensor in the crop's root zone and read the percentage of soil

moisture on the Gro-Point Display Unit, record it on a Datalogger, or IrriWise

Wireless Radio Crop Monitoring System.

Typical measurement field is 2" in all directions from the outside element.

Sensor Selection Criteria

Gro-Point Sensor 37GP-SS

o Sands with up to 3.0 dS/L salinity

o Silt loam soils up to 1.0 dS/L salinity

Gro-Point Sensor 37GP-HS

o All clay soils (>40% clay particles) regardless of salinity

o Loam soils through clay soil with >2.0 dS/L salinity

Gro-Point Sensors 37GP-MS

o Sands >3.0 dS/L salinity

o Silt loam soils with 1.0 to 3.0 dS/L salinity

o Clay loam soils with up to 2.0 dS/L salinity

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9. RHEOSTAT

A rheostat is an electrical component that has an adjustable resistance. It is a type of

potentiometer that has two terminals instead of three. The two main types of rheostat are the

rotary and slider. The symbol for a rheostat is a resistor symbol with an arrow diagonally

across it. They are used in many different applications, from light dimmers to the motor

controllers in large industrial machines.

How they Work

The basic principle used by rheostats is Ohm's law, which states that current are inversely

proportional to resistance for a given voltage. This means the current decreases as the

resistance increases, or it increases as the resistance decreases. Current enters the rheostat

through one of its terminals, flows through the wire coil and contact, and exits through the

other terminal. Rheostats do not have polarity and operate the same when the terminals are

reversed. Three-terminal potentiometers can be used as rheostats by connecting the unused

third terminal to the contact terminal.

The rheostat is still a common and fundamental electronic component used to control the

flow of current in a circuit. However, it has largely been replaced by the triac, a solid-state

device also known as a silicon controlled rectifier (SCR). A triac do not waste as much power

as a rheostat and has better reliability due to the absence of mechanical parts. Rheostats

commonly fail because their contacts become dirty or the coil wire corrodes and breaks.

10. COMPARATOR(IC OP-AMP LM324)

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Low-Voltage, Rail-to-Rail Output Op Amps.The LMX321/LMX358/LMX324 are

single/dual/quad,low-cost, low-voltage, pin-to-pin compatible upgrades to the

LMV321/LMV358/LMV324 family of general purpose op amps. These devices offer Rail-to-

Rail® outputs and an input common-mode range that extends below ground. These op amps

draw only 105µA of quiescent current per amplifier, operate from a single +2.3V to +7V

supply, and drive resistive loads to within 40mV of either rail. The LMX321/ LMX358/2kΩ

LMX324 are unity-gain stable with a 1.3MHz gain-bandwidth product capable of driving

capacitive loads up to 400pF. The combination of low voltage, low cost, and small package

size makes these amplifiers ideal for portable/battery-powered equipment.

Features:

1. Upgrade to LMV321/LMV358/LMV324 Family

2. Single +2.3V to +7V Supply Voltage Range

3. Available in Space-Saving Packages14-Pin TSSOP (LMX324)

4.1.3 MHz Gain-Bandwidth Products

5.105µA Quiescent Current per Amplifier (VCC = +2.7V)

6.No Phase Reversal for Overdriven Inputs

7. No Crossover Distortion

8. Rail-to-Rail Output Swing

9.Input Common-Mode Voltage Range: VEE – 0.2V to VCC – 0.8V

10.Resistive LoadsDrives 2kΩ

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Applications:

1. Cellular Phones.

2. Laptops.

3. Low-Power, Low-Voltage Applications.

4. Portable/Battery-Powered Equipment.

5. Cordless Phones.

6. Active Filters.

The OP-AMP is a basic component in the circuits of data acquisition and control. All

8051 based data acquisition board must have used the opAmps in any form, the purpose of

use of OPAMPs in data acquisition system is to interface the sensors and the ADC, the ADC

then give digital data to microcontrollers. Thus Opamp are used in the analog section of the

data acquisition board. Like in this project a furnace is of main concern whose temperature is

read, if the temp is low then set point then heater is switched ON and heater is switched off

when required set point is achieved. Thus we can say that is one of the data acquisition and

control project related to temperature monitoring and control projects based on

microcontrollers or microprocessors.

An operational amplifier IC is a solid-state integrated circuit that uses external feedback

to control its functions. It is one of the most versatile devices in all of electronics. The term

‘op-amp’ was originally used to describe a chain of high performance dc amplifiers that was

used as a basis for the analog type computers of long ago. The very high gain op-amp IC’s

our days uses external feedback networks to control responses. The op-amp without any

external devices is called ‘open-loop’ mode, referring actually to the so-called ‘ideal’

operational amplifier with infinite open-loop gain, input resistance, bandwidth and a zero

output resistance. However, in practice no op-amp can meet these ideal characteristics.

The operational amplifier is used in the applications in filter, in wave generation,

mathematical operations, and analog to digital and digital to analog conversions

Offset voltage at the input of an operational amplifier is comprised of two components; these

components are identified in specifying the amplifier as input offset voltage and input bias

current. The input offset voltage is fixed for a particular amplifier, however the contribution

due to input bias current is dependent on the circuit configuration used. For minimum offset

voltage at the amplifier input without circuit adjustment the source resistance for both inputs

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should be equal.

The gain-frequency characteristic of the amplifier and its feedback network must be

such that oscillation does not occur. To meet this condition, the phase shift through amplifier

and feedback network must never exceed 180 degree for any frequency where the gain of the

amplifier and its feedback network is greater than unity. In practical applications, the phase

shift should not approach 180 degree since this is the situation of conditional stability.

Obviously the most critical case occurs when the attenuation of the feedback network is zero.

11. DIODE

A Diode is a two terminal electronic component that conducts electric current only in one

direction. The most common function of a diode is to allow an electric current in one

direction (called the forward direction) while blocking current in the opposite direction (the

reverse direction).

However, diodes can have more complicated behavior than this simple on-off action.

Semiconductor diodes do not begin conducting electricity until a certain threshold voltage is

present in the forward direction (a state in which the diode is said to be forward biased). The

voltage drop across a forward biased diode varies only a little with the current, and is a

function of temperature; this effect can be used as a temperature sensor or voltage reference.

Semiconductor diodes have non-linear electrical characteristics, which can be tailored

by varying the construction of their P-N junction. These are exploited in special purpose

diodes that perform many different functions. For example, diodes are used to regulate

voltage (Zenor diodes), to protect circuits from high voltage surges (Avalanche diodes), to

electronically tune radio and TV receivers (varactor diodes), to generate radio frequency

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oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light

emitting diodes). Tunnel diodes exhibit negative resistance, which makes them useful in

some types of circuits.

12. RELAY

A relay is an electrically operated switch. Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are

used where it is necessary to control a circuit by a low-power signal (with complete electrical

isolation between control and controlled circuits), or where several circuits must be

controlled by one signal. The first relays were used in long distance telegraph circuits,

repeating the signal coming in from one circuit and re-transmitting it to another. Relays were

used extensively in telephone exchanges and early computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric

motor is called a contactor. Solid-state relays control power circuits with no moving parts,

instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits

from overload or faults; in modern electric power systems these functions are performed by

digital instruments still called "protective relays".

BASIC DIAGRAM OF INDUCTION RELAY

A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core,

an iron yoke which provides a low reluctance path for magnetic flux, a movable iron 29

inductor

armature, and one or more sets of contacts (there are two in the relay pictured). The armature

is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is

held in place by a spring so that when the relay is de-energized there is an air gap in the

magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is

closed, and the other set is open. Other relays may have more or fewer sets of contacts

depending on their function. The relay in the picture also has a wire connecting the armature

to the yoke. This ensures continuity of the circuit between the moving contacts on the

armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is

soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that

attracts the armature and the consequent movement of the movable contact either makes or

breaks (depending upon construction) a connection with a fixed contact. If the set of contacts

was closed when the relay was de-energized, then the movement opens the contacts and

breaks the connection, and vice versa if the contacts were open. When the current to the coil

is switched off, the armature is returned by a force, approximately half as strong as the

magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity

is also used commonly in industrial motor starters. Most relays are manufactured to operate

quickly. In a low-voltage application this reduces noise; in a high voltage or current

application it reduces arcing.

13. ELECTICAL MOTOR

It is used to supply water to plants.

An electric motor converts electrical energy into mechanical energy.

Most electric motors operate through the interaction of magnetic fields and current-

carrying conductors to generate force. The reverse process, producing electrical energy from

mechanical energy, is done by generators such as an alternator or a dynamo; some electric

motors can also be used as generators, for example, a traction motor on a vehicle may perfom

both tasks. . Electric motors and generators are commonly referred to as electric machines.

Electric motors are found in applications as diverse as industrial fans, blowers and

pumps, machine tools, household appliances, power tools, and disk drives. They may be

powered by direct current (e.g., a battery powered portable device or motor vehicle), or by

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alternating current from a central electrical distribution grid or inverter. The smallest motors

may be found in electric wristwatches. Medium-size motors of highly standardized

dimensions and characteristics provide convenient mechanical power for industrial uses. The

very largest electric motors are used for propulsion of ships, pipeline compressors, and water

pumps with ratings in the millions of watts. Electric motors may be classified by the source

of electric power, by their internal construction, by their application, or by the type of motion

they give.

The physical principle of production of mechanical force by the interactions of an

electric current and a magnetic field was known as early as 1821. Electric motors of

increasing efficiency were constructed throughout the 19th century, but commercial

exploitation of electric motors on a large scale required efficient electrical generators and

electrical distribution networks.

Motor rating is 230V AC, 2KW

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CHAPTER-5

ADVANTAGES

_ Highly sensitive

_ Works according to the soil condition

_ Fit and Forget system

_ Low cost and reliable circuit

_ Complete elimination of manpower

_ Can handle heavy loads up to 7A

_ System can be switched into manual mode whenever required

APPLICATIONS

_ Roof Gardens_ Lawns_ Agriculture Lands_ Home Gardens

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CHAPTER-6CONCLUSION

Even commercial watering systems come in various types. There are stand-alone

systems, which come with pots, water reservoirs, etc. The water reservoirs too, are available

in different designs and patterns. Such systems may or may not have timers. These systems

take care of the water requirements of individual plants. There are multiple plant watering

systems that can take care of a certain number of plants, simultaneously. These systems

constitute water tanks, pipes that supplies water from the tank to individual plants and drips

attached to the end of each pipe. For a garden, sprinkler and drip systems with timers are

available. In some sophisticated ones, even ground sensors are used, so that watering will be

done, whenever, the ground gets dry. While some of watering system works on battery

power, some others use power from the mains. There are simple ones too, that work under

gravity. Each type of plant watering system has its own features, which have to be

understood, before investing on it. Select the one, which is best, suited for your requirement.

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