Soil Moisture Indicator

7/31/2019 Soil Moisture Indicator

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Soil Moisture Indicator

In this project, the main concept exploited in designing of this equipment is the

variation of soil resistance or the soil voltage depending upon the variation of the soil

moisture. In other words the soil exhibits a variation in its resistance whenever the water

content in the soil increase or decreases. As the moisture in the soil increases the soil

resistance decreases that also amounts to saying that the soil voltage increases. Thus it

would be incorrect to state that the soil voltage is directly proportional to the soil moisture

content. Accordingly it follows that the soil voltage is maximum if the water content in the

soil is maximum i.e., the soil is totally wet and the soil voltage is minimum (approximately

equal to zero) in a dry soil

The high dry soil resistance may be owed to the fact that the absence of the water

content provides no conducting medium of the current flow. It may be then considered to

be similar to an insulator. When the soil is watered until it is fully wet it then begins to

conduct current like a metallic conductor. In the intermediate stages i.e., as the soil

moisture increases from 0% to 100% the soil voltage increases from minimum to

maximum.

The circuit basically consists of a step down center tap transformer that reduces the

230V supply from the mains to 12V peak-to-peak voltage. This is then fed to a bridgerectifier that converts this 12V peak-to-peak AC voltage to 12V DC voltage. The output of

the bridge rectifier for obvious reasons have very high ripple factor. Thus in order to

decrease the ripple the rectifier IC is used. This circuit now provides an output voltage of

12V DC. This is used as the Vcc or the biasing voltage for the next part of the circuit

comprising of the DARLINGTON CIRCUIT.

In some instances the need arises for an amplifier with high input impedance. To

achieve larger input, here the two transistors form a composite pair, the input resistance of

the second transistor constituting the emitter for the first. More specifically, the Darlington

circuit consists of two cascaded emitter followers with infinite emitter resistance in the first

stage.

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The output range of the Darlington circuit is proportional to the input range. In

order to use this voltage, it reduces to a more appropriate range by employing a signal

conditioning circuit. This circuit is designed to have a suitable gain to adjust the voltage

range. The output of this circuit is then passed through a voltage follower to nullify the

loading effects.

The voltage available at the end of the voltage follower is the value that is actually

proportional to the soil voltage. This is then fed to a buzzer of a predetermined

specifications stimulus to the input response. In other words the buzzer is set off when the

input voltage to it is high which happens in case of the dry soil.

This gives the birds eye view of the circuit for the indication of the wetness or

dryness of the soil.

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India is a land of farmers. With agriculture as the main occupation great deals of

research and developments have been taking place in the latest and the most upcoming

filed of AGRO-ELECTRONICS.

This field of science is completely devoted to the modernization of the agricultural

practices. It becomes all the more essential to keep the agricultural production in par with

the growing Indian population. A lot of attention should also be given to the quality of the

produce keeping in mind the quantity.

With the aid of ELECTRONICS AND INSTRUMENTATION TECHNOLOGY

this field of science Agro-Electronics is proving itself to be a boon to the farmers.

Some of its advance researches have now provided the farmers with latest equipments such

as the SOIL MOISTURE DETECTOR, ULTRA-SONIC PEST CONTROL and many

more.

The detection of the soil moisture is one of the most important pre-requisite for

many of the soil dependant activities. Reliable and accurate soil moisture monitoring and

control for:

Bioremediation

Wastewater Reclamation

Landfill Management

Agriculture

Considering agriculture, it helps the farmer to decide, depending upon the type of

plant or crop, the type soil and its water retention properties the amount of water it requires.

Especially since water nowadays is very precious resource and drought hit is not something

rare, it should be used more judiciously and cautiously. This equipment comes to the rescue

in such situation helping the farmer with the optimal usage of water. Precision irrigation

scheduling based on knowledge of soil moisture levels is very important for horticultural

crops, especially those of high value. Precision irrigation scheduling is closely related, not

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only to crop yield and quality, but also to conversation of irrigation water and reduction in

non-point source pollution from irrigated agriculture.

Moisture determination of soil is required in agriculture also while using certain

machines, when applying fertilizer, during sowing and spraying. The determination of

moisture content of grain is a very important quality characteristic during the harvest,

purchase and sale but also during transportation and storage, and is defined by standards.

Moisture content and temperature are essential characteristics for biological decomposing

processes during composting and on waste disposals. The moisture content of snow is

important for predicting avalanches and introducing steps of prevention.

By continuously controlling soil moisture landslides and mud-streams can be

forecasted and/or prevented in high mountain regions. The determined moisture content of

soil can be used further as reference value for radiometric measurements made by aircrafts

or satellites.

Measuring the soil moisture, collecting the data, and interpreting the data are

essential in order to convert soil moisture information into practical irrigation decisions.

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AIM

TO RIG UP ANDTEST

SOIL

MOISTURE

INDICATOR

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Recent advances in remote sensing have shown that soil moisture can be measured

by a variety of techniques. This has proved very useful as it has demonstrated a quantitative

ability to measure soil moisture under a variety of topographic and vegetation cover

conditions so that it could be extended to routine measurements from a satellite system.

The major factor inhibiting wide spread use of remotely sensed soil moisture data in

hydrology is the lack of data-sets and optimal satellite systems.

Soil structure is the major factor in determining a soils ability to retain and

transmit fluids. Thus, it is very important that one knows a specific soils structure in order

to manage it efficiently. Soil structure has mostly been investigated in qualitative terms, for

example, concerning the characteristic shape and cohesiveness of soil aggregates, clods.

Because the unsaturated hydraulic properties are fundamentally quantitative, to

theoretically relate them to soil structure requires the development of concepts and

techniques that quantify soil structure.

The figure shows the required soil composition in the tropical countries such as

India for the optimum growth of the plants. As it can be seen that water content ins the soil

composes nearly 25%.

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The structure of the soil is relevant for agriculture and biodiversity as it determines

nutrient and water availability. Several processes determine soil structure, they are:

weathering processes (soil erosion), age of soil, parent material, and the vegetation (both

via the production of soil organic matter and the rooting systems). There are two types of

weathering processes: mechanical (glaciers, freeze/thaw cycles, waterways) and chemical

(oxidation, dissolving in water, hydrolysis, and carbonation) whereby the amount of water

or moisture determines the rate of weathering.

The water quantity in rivers and lakes can influence the groundwater level in

surrounding areas while in coastal areas, groundwater levels might experience changes

because of a rise in sea level. Climate induced changes in water consumption by society

(cities, industry and agriculture) will also change the groundwater level. Structure, the

arrangement of particles in a soil or other porous medium, is a major influence on the

hydraulic properties of the medium. Often it is the most important known factor, because

the arrangement of particles plays the biggest role in determining the size and shape of the

pores that conduct water. Analogous effects are important to the hydraulic properties of

fractured rocks. While nutrients are important to plant growth, more critical to their vitality,

plant requires moisture. Water is essential for the transport of nutrients to and from the

plant. This transport occurs laterally within the soil, and vertically within the plant. Water

therefore, is the lifeblood of the system. Without sufficient moisture, photosynthesis is

impossible. Perhaps more importantly is a proper balance of available water. Root system

of the plants also requires air in order to survive, with too much water, plants will literally

drown.

Before diving into soil water measurement, it will be helpful to explain some key

concepts about the soil moisture. In the soil, water adheres to soil particles and occupies the

spaces between soil particles, called pores. After a season of rainfall or a thorough

irrigation, all of the pores in the soil are completely filled with water. This leaves the soil

saturated. Gravity then begins to pull the water out of larger soil pores, leaving air in those

spaces. Once all of the water that gravity can pull away has been removed, the soil is at its

naturally full level of water content. This is called field capacity, abbreviated as FC.

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Since sandy soils have generally larger pores than clay soils, gravity will remove a larger

percentage of water from sandy soils. Thus, sandy soils have a lower field capacity than

clay soils.

After the soil has reached field capacity, its water content will remain stable unless

outside forces remove it. There are two such forces. The minor force is evaporation at the

soil surface. The major force by far is extraction by the roots of the trees and plants.

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A number of techniques or rather principles can be used to detect the soil moisture.

The water content of the soil affects a number of other parameters of the soil for example:

resistance, soil voltage, temperature, roughness and dielectric constant. Thus the moisture

content can be determined by many physical parameters such as bulk density,

concentration of sugar solutions, consistency of pulp and conductivity of soil. Accordingly

there are different kinds of soil moisture detectors available with some of them being the

radiometer which sense changes in the temperature of the soil depending on the moisture

content. Microwave soil moisture detectors are also available. But these equipments

sometimes though are accurate, may prove complicated in operation and construction. Here

is another simple procedure to rig up a circuit that not only detects the water content of the

soil, but also displays it as a value proportional to a fixed parameter.

In this project the main concept exploited in designing of this equipment in the

variation of the soil resistance or the soil voltage depending upon the variation of the soil

moisture. In other words the soil exhibits a variation in its resistance whenever the water

content in the soil increase or decreases. As the moisture in the soil increases the soil

resistance decreases that also amounts to saying that the soil voltage increases. Thus it

would be incorrect to state that the soil voltage is directly proportional to the soil moisture

content. Accordingly it follows that the soil voltage is maximum if the water content in the

soil is maximum i.e., the soil is totally wet and the soil voltage is minimum (approximately

equal to zero) in a dry soil.

The high dry soil resistance may be owed to the fact that the absence of the water

content provides no conducting medium of the current flow. It may be then considered to

be similar to an insulator. When the soil is watered until it is fully wet it then begins to

conduct current like a metallic conductor. In the intermediate stages i.e., as the soil

moisture increases from 0% to 100% the soil voltage increases from minimum to

maximum.

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The circuit basically consists of a step down center tap transformer that reduces the

230V supply from the mains to 12V peak-to-peak voltage. This is then fed to a bridge

rectifier that converts this 12V peak-to-peak AC voltage to 12V DC voltage. The output of

the bridge rectifier for obvious reasons have very high ripple factor. Thus in order to

decrease the ripple the rectifier IC is used. This circuit now provides an output voltage of

12V DC. This is used as the Vcc or the biasing voltage for the next part of the circuit

comprising of the DARLINGTON CIRCUIT.



the second transistor constituting the emitter for the first. More specifically, the Darlington

circuit consists of two cascaded emitter followers with infinite emitter resistance in the first

stage.

The output range of the Darlington circuit is proportional to the input range. In

order to use this voltage, it reduces to a more appropriate range by employing a signal

conditioning circuit. This circuit is designed to have a suitable gain to adjust the voltage

range. The output of this circuit is then passed through a voltage follower to nullify the

loading effects.

The voltage available at the end of the voltage follower is the value that is actually

proportional to the soil voltage. This is then fed to a buzzer of a predetermined

specifications stimulus to the input response. In other words the buzzer is set off when the

input voltage to it is high which happens in case of the dry soil.

This gives the birds eye view of the circuit for the indication of the wetness or

dryness of the soil.

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Some of the major components that are used in this project are listed below:

o Step down transformer- 12-0-12 V

o Diodes - IN4001

o Capacitance - 1000F

o Regulators - IC LM7812, LM7912

o Transistors - BC 148

o Resistors - 1K, 2K, Potentiometer

o OP-AMP - A 741

o Buzzer

o Metallic Probes

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As it was explained earlier this circuit begins with a step down transformer. Since

the operating voltage of this device is just 12V DC as compared to the 230V AC from the

mains, there arises a need for stepping down this supply voltage to the operating voltage.

Thus a 12-0-12 step down transformer is used.

Also the operating voltage is a constant voltage unlike the alternating voltage of the

mains. For this purpose the bridge rectifier is employed that converts the alternating

voltage from the mains to the DC voltage. This DC voltage is unstable as against the

requirements of the experiment. This is accomplished by the capacitor that effectively

removes the ripple in the DC and the regulator ICs. All these constitute the power supply

block.

The next block is of the sensing element that is the unit that measures the soil

voltage. This block contains a DARLINGTON CIRCUIT which is shown in the figure.

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the second transistor constituting the emitter for the first. Most specifically, the

DARLINGTON circuit consists of two cascaded emitter followers with infinite emitter

resistance in the first stage as shown in the figure below.

In case the soil is dry as explained earlier as quiet as enormous resistance. Thus,

this acts as the high input impedance to the DARLINGTON circuit. Then the output of this

circuit also known as the common emitter amplifier is given by the equation

Vo = Av X Vi

Where Vi is the input voltage, i.e., the soil voltage.

Vo is the output voltage of the circuit.

Av is the gain of the circuit.

As it can be seen from the circuit diagram, this DARLINGTON circuit also has a

variable resistance potentiometer. This is varied in order to obtain the proper value of the

current that is flowing.

This output, which is the proportional value of the soil voltage, is in a form that

cannot be used directly for the display purposes. Thus it is then fed to a signal conditioning

circuit that basically consists of an operational amplifier that has been rigged up as an

inverting amplifier with a specified gain.

The gain is so chosen that the output range of the OP-AMP inverting amplifier is

compatible with display devices that are going to be used for example 0-5V or 0-10V etc.

In this experiment the inverting amplifier has been designed that provide an output

in the range of 0-5V DC, the 0V corresponding to the wet soil voltage and 5V

corresponding to the dry soil voltage. This circuit has been designed by suitably choosing

the values of R and RF in order to adjust the gain.

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The gain of a inverting amplifier is given by

Gain = ( R / RF )

In this case considering the voltage range of the buzzer the gain has been chosen to

be half () i.e.,

R = 1K R F = 2 K

The figure shows the inverting amplifier. This is followed by a voltage follower

which is nothing but a simple approach to avoid the loading of the previous stage. The

circuit of a voltage follower is very similar to that of the inverting amplifier except that the

voltage gain in the voltage follower is unity (1). Thus here though the voltage remains the

same the current gets amplified. This is important in order to drive the buzzer. Finally the

voltage follower feeds its output to the buzzer.

When the soil is wet its resistance being very less offers a very low voltage drop. In

ideal conditions this voltage drop may be completely neglected. Thus the emitter of the two

transistors in the DARLINGTON circuit get short giving a zero (0) output. Thus the current

flowing into the buzzer is very less, thus the buzzer remains OFF. Whereas under practical

considerations, due to the impurities present in the water in the soil its a finite but a very

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less resistance. This may lead to as small amount of current flowing into the buzzer giving

a feeble sound. This is though a limitation gets masked by the other major advantages of

the device.

When the soil is kept dry as discussed earlier the soil voltage is high owing to the

high soil resistance. When this high resistance is introduced across the probes of the device

it brings into the picture the high input impedance or the biasing impedance to the

DARLINTON pair of transistors.

Here one of the major factors that need to be considered is the range of the soil

voltage from the dry soil to the wet soil. This range has to be converted to another range so

that it can be further used for buzzer or any other indicating devices such as L.E.D etc. The

signal conditioning circuit is used mainly for this purpose.

Also the DARLINGTON circuit is a high gain circuit. Thus the loading problems

may be frequently encountered. In order to overcome this short coming too, the signal

conditioning circuit consisting of the voltage follower circuit is used.

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TRANSFORMER:

A transformer is a static electrical device, which transfers electrical power from one

electrical circuit to another, which is magnetically coupled together with or without change

of voltage and without any change in power and frequency. The basic use of a transformer

is to increase or decrease voltage. If it is used to decrease the voltage then its called a step

down transformer, if it is used to increase the voltage then it is called a step up transformer,

if the voltage is not changed then it is called 1 to 1 transformer. The efficiency of a

transformer is very high of the order 95% to 98%. A transformer consists of mainly two

parts windings and the core. There are two windings that are wound on the two limbs of

the core, which are insulated from each other and the limbs.

A single phase transformer works on the principle of mutual inductance between

two magnetic coupled coils. When the primary winding is connected to an alternating

voltage of RMS value V1 volts, an alternating current flows though through the primary

winding and sets up an alternating flux, in the material of the core. This alternating flux

links not only the primary windings but also the secondary windings. Therefore an EMF E1

is induced in the primary winding and an EMF E2 is induced in the secondary winding.

SPECIFICATIONS:

o 12-0-12 step down transformer

o Center tap

DIODE:

It is a P-N junction two lead component with non-ohmic characteristics. It is used

in forward and reverse bias conditions. There are different kinds of diodes depending upon

the manufacturing company, P-N characteristics, doping properties, semiconductor

material, doping material and many other factors. Thus depending on the circumstance the

particular diode is used. A diode always offers low resistance when it is forward biased and

offers very high resistance when it is reverse biased.

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When diodes are used in a circuit, the voltages and currents flowing through them

should be such that, the devices remain safe.

The diode used in the bridge rectifier circuit in this experiment is IN4001

SPECIFICATIONS:

o Forward voltage

o Power dissipation

o Forward current

o Peak inverse voltage

TRANSISTORS:

Transistor is a two junction three lead component. These leads are emitter, base and

collector. A transistor is a semiconductor device in which current flows through

semiconductor materials. In a bipolar junction transistor the term bipolar is used as two

type of charge carriers, holes and electrons are involved in current flow. When a thin layer

of P-type or N-type semiconductor is sandwiched between a pair of opposite types, the

result is a transistor.

There are two types of transistors

o PNP transistor

o NPN transistor

In a PNP transistor a thin layer of N type semiconductor is placed between two Ptype semiconductors. In a NPN transistor a thin layer of P type semiconductor is placed

between two N type semiconductors. The transistor BC 148 is used in the experiment is

NPN type transistors.

REGULATORS:

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Ideally the purpose of the power supply regulator is to provide a predetermined

output DC voltage Vo which is independent of the load current I L drawn from Vo, of the

temperature and of any variations in the AC line voltage.

The regulator that is used in the experiment is of 3 terminals type and it is available

in several output voltages. The voltages available allow these regulators to be used in wide

range of applications such as logic systems, instrumentation, and other solid state electronic

equipments.

The regulators used in the experiment are LM7812 and LM7912.

OPERATIONAL AMPLIFIER:

The operational amplifier (abbreviated as OP-AMP) is a direct coupled high gain

amplifier to which a feed back is added to control its overall response characteristics. It is

used to perform a number of linear as well as non-linear operations.

Many of the analog systems constructed with help of the Op-Amp constitute the

basic building blocks. These ICs augmented by a few external discrete components, either

singly or in combination, are used in a number of systems such as: amplifiers of different

types, voltage followers, active filters, analog multipliers, sample-and-hold circuits,

comparators, square and triangular wave form generators.

The Op-Amp used is this experiment is A 741. the pin details and other

specifications are given at the end.

This is one of the simplest ways of detecting the soil moisture. This instrument can

be made automatic which then becomes a self-sufficient soil moisture controller. In other

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words when a motor is attached via a relay to the output of the circuit, then the motor is

turned ON whenever the soil is detected as dry.

The enhancement of this equipment is that, instead of connecting the output to a

buzzer, it is connected to an Analog-to-Digital Converter (ADC) which converts the

corresponding voltage into digital signals which is then connected to a microcontroller and

the voltages or the moisture content level is indicated through an LCD.

As compared to the other currently available soil moisture indicators such as the

microwave soil moisture detectors, the remote sensing soil moisture indicators. This circuit

is one of the simplest one. Also the working of the circuit is easily understandable.

The major applications of soil moisture indicator is

Used in detecting the moisture content in the soil in agriculture.

Used in the field of Bioremediation for accurate soil moisture monitoring.

Used in waste water reclamation.

Used for forecasting landslides in high mountain regions.

It can thus be concluded as, this is one of the most versatile device with some of the

important properties, which is also the advantages of the device is

Simple circuitry

No handling complications

Portable

Can be easily made automatic

Easily perceivable output such as beeper or L.E.D

The only disadvantage is that of the feeble sound produced by the buzzer.

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1. EARTH SCIENCE BY ORDWAY.

2. FUNDAMENTALS OF SOIL SCIENCE BY FOTH AND TURK

3. INTEGRATED ELECTRONICS BY MILMAN AND HALKIAS.

4. ELECTRONICS FOR YOU.

5. WEBSITES: www.google.com andwww.alldatasheets.com
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Soil Moisture Indicator