soil moisture indicator
TRANSCRIPT
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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.
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.
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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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. 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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