Abstract
A digital soil moisture meter is used for indicating the water content of a given soil
sample. As crop production requires water at different stages and in different
amounts, it is important to measure soil moisture from time to time to know its
status. The digital soil moisture meter circuit presented here, for monitoring the
soil moisture content in irrigation farms, is an electronic device that measures soil
moisture content accurately and precisely. It measures the resistance of flow of the
electric current between two metallic probes. These probes act as sensor elements
that register moisture and change it into an electric value. This value is further
processed into information in the form of an electronic display. The probes used in
this project are made of nickel which is an anti-corrosive and robust material for
use in agricultural related applications. It helps in problems related to growing of
crops in which irrigation is required at irregular interval. It is also helpful in
monitoring of soil moisture in agricultural fields.
1
CHAPTER ONE: INTRODUCTION
1.1 General Introduction
Nigeria is a developing nation with a very large population. Due to increasing
population, the basic need such as food and water is increasing day by day. Thus
there is a need of saving these resources and utilize them in an efficient manner.
Since water is one of the most important elements in our daily life, thus we must
use efficient ways to utilize water and save it for future generations. One of method
is efficient irrigation management practices for fields. Irrigation water management
practices could greatly benefit by the knowledge of moisture in the soil. To
determine the soil moisture we have designed and developed a nickel probes based
soil moisture sensor and a response monitoring system. By knowing the moisture
value, we can estimate when to water and how much to water the fields so that
there is no over-watering or wilting of crops. These practices will increase crop
yield, improve quality of crops, conserve water resources, save energy, and
decrease fertilizer supplies. Here is a very simple circuit using IC LM3915 to
measure the moisture level in soil. The IC LM3915 is a dot/bar display driver
monolithic integrated circuit that sense analog voltage levels and drives ten light
emitting diodes (LEDs) and provides a logarithmic 3dB/step. This IC operates with
minimum 3V to maximum 25V DC bias. This project is really helpful for farmers.
Soil moisture level detector project can be used in the greenhouse to detect the
water contents for the moisture contents of the soil. The block diagram of the
circuit is as shown in figure 1.0 below.
POWER SUPPLY UNIT
SOIL MOISTURE SENSOR
UNIT
ANALOG TO DIGITAL
CONVERTER UNIT
Fig 1.0 digital soil moisture level indicator
2
LED INDICATOR UNIT
The basic function of each block above is as explained below;
 Power Supply Unit: this unit provides Low Dc power to the Dc circuitry
part of the system.
 Soil Moisture Sensor Unit: This unit consists of soil moisture sensing
probe; it consists of two probes which are used to measure the volumetric
content of water. The two probes allow the current to pass through the soil
and then it gets the resistance value to measure the moisture value.
 Analog to Digital Converter Unit: This unit consists of IC LM3915; The
IC LM3915 is a dot/bar display driver monolithic integrated circuit that
sense analog voltage levels and converts it to digital signal that is used to
drive ten LEDs.
 LED indicator Unit: ten LEDs are connected to the output terminals; the
led are of different color for different level of outputs.
1.2 Aim and Objectives
The aim of this project is to implement digital soil moisture level indicator circuit.
The objectives of this project are as follow:
i.
To implement moisture sensor that is convenient for farmers.
ii.
To reduce to rate of over irrigation/ under irrigation in manual watering
techniques.
iii.
To implement a circuit that will be useful in agricultural field.
3
1.3 Principle of Operation
The main supply to the circuit is 230VAC, mains supply is step down by the
transformer to 12V. The output from the transformer is fed to the rectifier. It
converts A.C. into pulsating D.C. filter capacitor filters the Ac ripples from the
rectifier, Lm7809 provides constant voltage output of 9V; the LM3915 connected
with 9V and ten LEDs are connected to the output terminals, different colored
LED for different level of outputs. The test probe is connected between divider
resistors R2 and R3 through VR1 and R1 resistors, the probe brings ground to the
reference voltage at pin6 and makes the variations to the reference voltage,
depends on the reference voltage LEDs are drive to glow. The circuit diagram is as
shown figure 1.1 below;
Fig 1.1 circuit diagram of digital soil moisture level indicator
4
1.3 Limitation of the Project
The following are limitations inherent in the course of the implementation of this
project.
 Unavailability of IC LM3915 and 2.7V zener diode in Birnin-kebbi delayed
the realization of the construction in presumed time.
 As a beginner it was so tedious and hectic in prototyping the circuit on
breadboard and transferring it to vero board for permanent soldering.
5
CHAPTER TWO: LITERATURE REVIEW
Some similar studies and research work as related to this project will be reviewed
in this chapter and to ensure that other people work was not repeated without
acknowledging them.
Hisham J, (2004) implemented a simple soil moisture detector with alarm circuit,
in his project, he build a transistor based simple soil moisture detector circuit using
an NPN transistor to detect soil moisture. This Soil Moisture Detector Circuit is
very simple. Here we have used a soil moisture detector probe to sense the
moisture in the soil and an NPN transistor to trigger the Buzzer and LED. This soil
moisture detector probe is homemade and built using general purpose PCB (Perf
board). Buzzer and LED are used as an indication of soil moisture detection.
Antony E, (2005) described a simple soil moisture detector circuit; this simple soil
moisture detection circuit is based on commonly available IC 7404, relay and few
more components. CD7404 is an inverter IC which contain 6 individual NOT Gate
on a single IC. Its outputs go low when input is high. And its output becomes high
when input is low that’s why it is known as inverter IC. Moisture level is sensed by
probes which are embedded in the soil. Be careful while inserting the probes they
should inserted into a suitable depth and probes should be separated from each
other. When there is no moisture in soil Pin 1 of IC1 becomes low because of this
output pin 2 goes high.
Saddam, (2005) implements wet soil detector and alarm for irrigation system, in
his project, he builds a Transistor Based Simple Soil Moisture Detector Circuit. In
this circuit, he used an NPN transistor to detect soil moisture. He fabricates soil
moisture detector probe to sense the moisture in the soil and an NPN transistor to
trigger the Buzzer and LED. This soil moisture detector probe is homemade and
6
built using general purpose board (veroboard). Buzzer and LED are used as an
indication of soil moisture detection. His circuit work like this, when there is no
moisture in soil then probes does not allow voltage to the base of transistor so the
LED and Buzzer remain turned off. Now, whenever both probes will come in
contact with soil moisture or water then the probe gets shorted because and when
probes get shorted then the base of the transistor gets voltage, it gets turn on and
allow current to pass through the collector to emitter. And as soon as transistor
turns on it will trigger the Buzzer and LED.
Tarun, (2009) implements Automatic Plant Watering System using transistors; his
circuit uses two transistors that work as switches. If the probes do not sense the
moisture in the soil, then the resistance between the two probes will increase due to
which the transistor 1 will switch off, hence transistor switches off, it will provide
no voltage at the base terminal of transistor 2, as a result relay will become
activated i.e. it pumps water. But when the probe sense moisture it activate
transistor 1 thus transistor 2 will also be activated and relay switch off the water
pump motor.
Swagatam, (2012) an electronics hobbyist implements moisture detector circuit for
automated plant watering system, the design makes use of a single IC 741 opamp
comparator, the pin3 which is the non-inverting input of the opamp is used as the
main sensor probe with respect to the other probe connected with the ground. The
moisture level present in the soil develops a resistance across it which increases
with a decrease in the moisture level and decreases with an increase in the moisture
level, meaning a wet soil will have a much lower resistance compared to a dryer
soil. Therefore a relatively wet soil will keep the relay switched OFF, and a dry
soil will switch it ON.
7
Shedrack, (2014) designed a soil moisture level meter; this circuit utilizes four
LED’s to indicate the level of moisture in the soil. An increase in the number of
LED’s on indicates an increase in the amount of moister present. Current through
resistor to the moister in the soil and received at transistor when probes “P” and “I”
are inserted into the soil. Emitter and collector current of transistor display results
through a series of 4 LED’s. The greater the moisture at “I” the more voltage will
pass through transistor and more LED’s will be lit. If there is low moister little or
no current will pass through transistor and few or none of the LED’s will be on.
Mohankumar, (2016) designed soil moisture detector circuit using operational
circuit; this circuit indicates the level of moisture in a place due to rain or spilling
of water. Green LED lights when there is moisture and Red LED lights when there
is no moisture.IC1 (741) is used as a voltage comparator. Its non inverting input
(pin3) receives half supply voltage through the potential divider R2 and R3. Its
inverting input (pin2) gets a higher voltage only when the sensor connected to
points A and B are shorted with moisture. When the sensor is dry, the output of
IC1 will be high because its pin3 gets more current than pin2. This high output
makes the transistor T1 conducting and Red LED lights. At the same time T2
remains off because its base is not getting current since T1 takes all the current. So
Green LED remains off. When sensor gets moisture, current flows through the
sensor to the pin2 of IC1.As a result, pin2 of IC1 gets more current than pin3 and
its output becomes low. T1 then turns off allowing T2 to conduct. Red LED turns
off and Green LED turns on indicating the presence of moisture.
Presented here is a very simple circuit using IC LM3915 to measure the moisture
level in soil. The IC LM3915 is a dot/bar display driver monolithic integrated
circuit that sense analog voltage levels and drives ten LEDs and provides a
logarithmic 3dB/step. This IC operates with minimum 3V to maximum 25V DC
8
bias. In order to render the circuit cost effective, simple and more sensitive. This
will make the circuit more advantageous over the reviewed ones.
9
CHAPTER THREE: CONSTRUCTION
3.1 Introduction
Before the construction of this project several things were taken into consideration
among which were the theory and the practical aspect of the implementation of
each stage.
First and for most, the circuit was first of all built on a solder less bread board
which made it possible to make changes when the need arises and make easier to
locate bugs. It was later transferred on the Vero board where careful component
lead were kept at minimum to prevent accidental short circuit, the circuit was
carefully planned, minimum errors and make trouble shooting easier.
3.2 Construction Procedures
The circuit consists of four stages which are implemented on the bread board
temporarily and tested before being inter connected for the permanent soldering on
the Vero board.
3.2.1 Construction of Power Step-down Unit
The unit consists of a step down transformer rated 230VAC/15V-0-15V AC,
rectifiers diodes (IN4007), and a filter capacitor rated (2200uF, 25V). The
secondary windings of the transformer was connected across the rectifier diodes
arranged in full wave bridge form the output of the rectifier was connected to the
positive and negative pin of a capacitor respectively in accordance with the circuit
diagram below:
10
Fig 3.1
Circuit diagram of power step-down unit
3.2.2 Construction of Voltage Regulator Unit:
This unit consists of a voltage regulator I.C .LM 7812. The input terminal of the
regulator I.C (PIN 1) was connected for the positive output rail of the filter stage
which pin 2 (GND) terminals was connected to the GND rail of the circuit. This
arrangement was done as depicted by circuit diagram below.
Fig 3.2 Circuit diagram of voltage regulating unit
11
3.2.3 Construction of Moisture Sensing Unit
This soil moisture detector probe is homemade and built using general purpose
PCB (Veroboard). The veroboard was separated 2cm apart and two wires were
connected to the board. The figure 3.2 below depicts the circuit connections.
Fig 3.3 moisture sensing circuit
3.2.4 Construction of Alcohol Level indicating Unit
This unit consists of IC LM3914, resistor and LEDs, pin (3, 9) and pin (2,4) of the
IC were connected to Vcc and Gnd respectively. Pin 6was connected to the Vcc
through Zener diode (2.7v) while pin 7 was connected to Gnd through resistor. The
anodes
of
LED
(1,2,3,4,5,6,7,8,9
and
10)
were
connected
to
pin
(18,17,16,15,14,13,12,11, and 10) and their cathodes were connected to Gnd.
Figure 3.4 below depicts circuit connections.
12
Fig 3.4 moisture level indicating circuit
3.2.5 Casing
This project circuit was enclosed in a suitable square shaped of dimension 6 x 6cm
plastic material, there were holes pierced on the casing that serves as ventilation
for the internal heat generated of some components.
Fig 3.5 Casing
13
3.2.6 Tools used
The following tools were used during the implementation of this project.
i.
Side cutter: This was sued for removing insulation and cutting off excess
component terminals
ii.
Soldering iron: A 60 watt heating element was used for soldering the
circuit.
iii.
Long nose plier: This tool was
used to bend the leads pin of the
component
iv.
Soldering hanger: This tool was used to position the soldering iron when
not in use.
v.
Lead sucker: This tool was used for sucking up melted solder
3.2.7 Materials used
The materials listed below were used during the implementation of his project.
i.
Electronic components: These components were used in realizing the
working circuit. These components include; transformer, diodes,
capacitor, integrated circuit (I.C), resistor and the wires
ii.
Bread board: This was used for marking temporary connection to
ascertain the circuit functionality before transferring it on the veroboard.
iii.
Jumper wire: This was used for connecting the circuit components
together.
iv.
Veroboard: It was used for the permanent soldering and interconnection
of the electronic components that form the circuit.
v.
Soldering lead: An alloy and containing 60% was sued for joining the
components terminals together
14
3.2.8 Instrument used
During the implementation of this project the following measuring instrument was
used as listed below:i.
Digital multimeter: The digital multimeter was used for measuring the
voltages across different stages, and the resistance on the circuit. It was
also used to measure the continuity in the circuit.
15
CHAPTER FOUR: TEST, RESULT AND DISCUSSION
4.1 Introduction
Testing is an important procedure employed in the field of engineering and
technology for the effective confirmation of genuine results of any circuit. Testing
will give the constructor the best opportunity to identify errors and find solution to
such errors, grant precautions were observed before the testing was done.
4.2
Testing Procedures
4.2.1 Power supply test procedure
The power supply unit was tested in accordance with the block diagram below.
The circuit was powered from the mains. Various results were read at the output of
each unit and recorded.
A.C
SOURCE
TRANSFORMER
DM
RECTIFIER
DM
VOLTAGE
REGULATOR
FILTER
DM
DM
Fig 4.1 Block diagram of power supply unit test.
16
DM
4.2.2 Soil Moisture Probe Test Procedure
The probe was tested using multimeter selected at continuity mode, the continuity
of the wire A to wire B was tested on two conditions i.e. when the probe is dip
inside dry soil and when it is dip inside wet soil. Figure 3.2 below depicts test
connections.
Fig 4.2 soil moisture sensor probe test
4.2.3 Overall circuit test Procedure
The overall circuit was tested by powering the circuit with 230VAC and was the
sensor was exposed to artificial alcohol; observations were made and recorded.
COMPLETE
220VAC
CIRCUIT
Fig. 4.3 block diagram of overall circuit test
17
4.3 Results
The result obtained from each unit tested is as follows:
4.3.1 Power Supply Test Result
Table 4.1Power supply circuit test result
Stage
Input voltage Output voltage
Transformer
232.58VAC
1.21VAC
Rectifier
12.21VAC
11.93VDC
Filtration
11.93VDC
11.93VDC
Voltage Regulator
11.93VDC
9.03VDC
4.3.2 Soil Moisture Probe Test Result
The results obtained from the test is as tabularized below
Table 4.2 Soil moisture test result
S/N
Condition
Meter Response
Remark
1
When Soil is wet
Beep
There is continuity
2
When Soil is Dry
Mute
There is no
continuity
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4.3.4 Overall circuit test result
When there is no presence of moisture in no LEDs were activated, but in the
presence of moisture the LEDs activated sequentially in respect to the amount of
water presence in soil.
4.6 Discussion
Digital soil moisture level indicator circuit has been implemented and tested
successfully. It has been developed by integrated features of all the hardware
components used. The system has been tested to function automatically. The
moisture sensors measure the moisture level (water content) of the soil. The circuit
indicators glows when it detects moisture, with the results obtained and the
functionality of the circuit ascertained the circuit by itself has confirmed that all
connections were well done.
.
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CHAPTER FIVE: CONCLUSION & RECOMMENDATIONS
5.1 Conclusion
Based on the findings of this project the following conclusion is reached:
i.
The implemented circuit is very simple to understand and handle.
ii.
It can be operated by all age-groups of farmer.
iii.
The moisture is measured up to the root zone of the crop.
iv.
Sensor can be placed vertically in the soil to check the depth of irrigated
water and also it can be placed horizontally at different heights in the soil
according to the crop.
v.
It is user friendly and can also be used by uneducated farmers.
5.2 Recommendations
Based on findings of this study, the following recommendations have been made:
i.
Soil moisture sensor should be designed according to the various types
of soil and it should be able to determine the types of acids, alkalis or salts
present in the soil.
ii.
Entire system should be incorporated with auxiliary power supply source
e.g. solar power system, thus, this guarantees constant supply of power to
the main circuit, in order in increase the reliability of the entire system.
iii.
Salinity of soil can also be calculated by correlating it with the output
voltage. Wireless transmission of the output data directly to the user can
be done using Zigbee or Bluetooth.
iv.
The system can be integrated with temperature and humidity sensors to
monitor the weather conditions in the farm.
20
REFERENCES
1. Saddam.
F, (2005).
system”Electric
“Wet soil detector and alarm for irrigation
Information
and
Control
Engineering
(ICEICE),
International Conference, vol.4, no.1, pp. 15-17.
2. Tarun. Y (2009) “Implementation of Automatic Plant Watering System”
International Journal of Advanced Information Technology, Vol. 2, No.1,
pp.11
3. Swagatam. H (2012) “An Automated Drip Irrigation System Based on Soil
ElectricalConductivity”, The Philippine Agricultural Scientist, Vol. 94, No.
4, p.343
4. Mathurkarand D. (2013) “Prototype model based on moisture, temperature
and humidity sensor” published in International Journal Of plant, Animal
and Environmental Science-Volume 3, pp.45
5. https://theorycircuit.com/simple-soil-dryness-detector-circuit/
6. https://www.researchgate.net/publication/276417195_DESIGN_AND_DEV
ELOPMENT_OF_SOIL_MOISTURE_SENSOR_AND_RESPONSE_MON
ITORING_SYSTEM
7. www.electronicsforu.com/electronics-projects/hardware-diy/automaticplant-watering-system
21
Appendix A: Cost Analysis
S/N
QTY
DESCRIPTION
OF COMPONENT
1
1
Transformer
UNIT/PRICE AMOUNT
₦
₦
1500
1500
(230v/12v/500mA)
2
4
Diodes (1N4007)
50
200
3
3
Resistor
50
150
4
1
I.C 3915
600
600
5
11
Light Emitting
50
550
Diode
6
1
Voltage regulator
200
200
7
1
Electrolyte
150
150
Capacitor
8
1
I.C socket
100
100
9
1
Power inlet cord
150
150
10
1
Plastic casing
1000
1000
11
1
Vero board
300
300
12
1
Soil moisture sensor
250
250
13
1
Variable resistor
150
150
14
1
Gum
300
300
₦ 5 600
TOTAL
22
LABOUR COST
The estimated labour cost (direct and indirect) is 20% of the material cost ₦ 1 120
MISCELLANEOUS
The miscellaneous of this project reached up to 5% of the material cost ₦ 28
TOTAL COST
Material Cost + Labour Cost + Miscellaneous
5600 + 1120 + 280 = ₦7000
23
Appendix B: Symbols and Notations
S/N
SYMBOLS
NOTATIONS
Transformer
1
2
Diode Rectifier
3
Resistor
4
Polarized capacitor
Moisture Sensor
5
6
Light emitting diode
7
IC LM3915
8
Voltage regulator I.C
9
Diode
10
Ground
24
Appendix C: Complete Circuit Diagram
25
PLATE 1: Photograph of Construction on Its Veroboard
26
PLATE 2: Photograph of Construction in Its Plastic Casing.
27