This project is based on 555 timer and IC L293D.

1. INTELLIGENT AUTOMATIC PLANT IRRIGATION SYSTEM
A
Project Report
Submitted in Partial Fulfillment of the Requirements for the Degree of
BACHELOR OF TECHNOLOGY
In
ELECTRONICS & COMMUNICATION ENGINEERING
By
Deepesh Kumar Dubey
Susheel Kumar
Rambabu Gupta
Under the Supervision of
Mr. Sunny Kumar Paswan
Faculty, Electronics Engineering Department
DEPARTMENT OF ELECTRONICS ENGINEERING
INSTITUTE OF ENGINEERING & TECHNOLOGY
(APJAK TECHNICAL UNIVERSITY)
SITAPUR ROAD, LUCKNOW, U.P., 226021 (INDIA)
June, 2017

2. i
Candidate’s Declaration
I hereby declare that the work, which is being presented in the Major Project, entitled
“Intelligent Automatic Plant Irrigation System” in partial fulfilment for the award of Degree
of “Bachelor of Technology” in Electronics & Communication Engineering, and submitted to the
Department of Electronics Engineering, I.E.T Lucknow, A.P.J.Abdul Kalam Technical
University is a record of my own investigations carried under the Guidance of Mr Sunny Kumar
Paswan, Faculty in Department of Electronics Engineering, Institute of Enginering
&Technology, Sitapur road, Lucknow .
I have not submitted the matter presented in this report anywhere for the award of any other
Degree.
Signature
Name: Deepesh Kumar Dubey
Roll No. : 1305231020
Signature
Name : Susheel Kumar
Roll No. : 1305213045
Signature
Name : Rambabu Gupta
Roll No. : 1305231040

3. ii
CERTIFICATE
This is to certify that Mr Deepesh Kumar Dubey( Roll No. – 1305231020), Mr Susheel
Kumar (Roll No. – 1305213045), Mr Rambabu Gupta( Roll No. -1305231040) students of
B.Tech ( Electronics & Communication Engineering, Final year ) of Institute of Engineering
& Technology, Lucknow have worked under my supervision during the session 2016-2017
and have submitted their report titled ‘Automatic Plant Irrigation System’
Throughout the tenure of this project, their behaviour and performance has been found
excellent.
I wish them all success throughout the life.
(Mr. Sunny Kumar Paswan)
Faculty, Electronics Department
Institute of Engineering & Technology
Lucknow, Uttar Pradesh.

4. iii
ACKNOWLEDGEMENT
We take this opportunity to express our sincere thanks to all those people who extended their
whole hearted cooperation and helped us in completing this project. We are highly indepbted
to our project mentor Mr. Sunny Kumar Paswan ( Faculty of Electronics Engineering
Department, IET Lucknow) for guiding us in this project and steering us in proper direction
throughout the course of project to achieve our goal.
We also owe our gratitude to Dr. Subodh Wariya ( Head of the Electronics Engineering
Department, IET Lucknow), Dr. V.K. Singh ( Professor of the Electronics Engineering
Department, IET Lucknow), Dr. S.R.P. Sinha ( Professor Of the electronics Engineering
Department, IET Lucknow) and Mr. Amit Kumar ( Assistant Professor of the Electronics
Engineering Department, IET Lucknow) . His tremendous personal interest, inspiration,
encouraging support and sound advice went all the way in making this effort a success.
In all this we found a wonderful work environment and this completion of project will mark a
new beginning for us in coming future.
Deepesh Kumar Dubey
Susheel Kumar
Rambabu Gupta

5. iv
ABSTRACT
An automatic irrigation control system has been designed to facilitate the automatic supply of
adequate of water from a reservoir to field or domestic crops in all agricultural seasons. One
of the objectives of this work is to see how human control could be removed from irrigation
and also to optimize the use of water in the process. The method employed is to continuously
monitor the soil moisture level to decide whether irrigation is needed, and how much water is
needed in the soil. A pumping mechanism is used to deliver the needed amount of water to
the soil. The work can be grouped into four subsystems namely; power supply, sensing unit,
control unit and pumping subsystems which make up the automatic irrigation control system.
A moisture sensor was constructed to model the electrical resistance of the soil; a regulated
24 volts power supply unit was constructed to power the system; the control circuit was
implemented using operational amplifier ,555 timer, Motor diver IC and relay; and the
pumping subsystem consisting of a submersible water pump was constructed using a small
ac-operated motor. System response tests were carried out to determine the time taken for the
system to irrigate potted samples of different soil types having different levels of dryness.
The results obtained showed that sandy soils require less water than loamy soils and clay
soils require the most water for irrigation.

6. v
TABLE OF CONTENT
1 Introduction 1
2 Printed Circuit Board( PCB) 2
2.1 Procedure to design a layout 2
2.2 Designing of PCB layout 2
2.2.1 Proteus 3
2.2.2 Feature of Proteus 3
2.3 Layout of the project PCB 4
2.4 Artwork 5
2.5 Screen printing 5
2.6 Drill jig 6
2.6.1 Element of drill jig 7
2.7 Green masking 8
2.8 PCB designing 9
2.8.1 Processing 9
2.8.2 Cleaning 10
2.8.3 Etching 10
2.8.4 Drilling 12
2.8.5 Soldering 12
3 Component Used & Its Description 15
4 Block Diagram and Working 33
4.1 Block Diagram 33
4.2 Working Principal 34
4.3 Advantages 34
4.4 Applications 34
Conclusions 34
References 35

7. vi
LIST OF TABLES
S.no. Table Page
no.
2.1 PCB designing process 8
2.2 Cleaning process 10
2.3 Characteristics of different etchants 11

8. vii
LIST OF FIGURES
Fig.no. Figure Name Page
No.
2.1 Layout of PCB1 4
2.2 Layout of PCB2 4
3.1 Buck converter citcuit 11
3.2 Soil moisture sensor 15
3.3 Comparator 16
3.4 NE555 Timer 17
3.5 NE555 Timer based monostable multivibrator 18
3.6 L293D pin diagram 20
3.7 Solenoidal Valve 22
3.8 Relay Switch 23
3.9 Typical leaded carbon resistor 26
3.10 Typical SMD resistor on PCB 27
3.11 Paper capacitor 28
3.12 Air capacitor 29
3.13 Plastic film capacitor 29
3.14 Ceramic capacitor 30
3.15 LED 31

9. viii

10. ix

11. - 1 -
Chapter 1
INTRODUCTION
Irrigation is an artificial supplying of water to the root of plant. Irrigation has been used to
assist in the growing of agricultural crops, maintenance of landscapes, and re-vegetation of
disturbed soils in dry areas and during periods of inadequate rainfall. In crop production,
irrigation helps in protecting plants against frost, suppressing weed growth in grain fields and
preventing soil consolidation. Irrigation systems are also used for dust suppression, disposal
of sewage, and in mining. The old method used for irrigation was the use of watering cans,
water channels that have to be opened and closed manually or backpack sprinklers. In this
case, a lot of water is wasted in the process. There is need for improvement on the existing or
old forms of irrigation. An automated irrigation system needs to be developed to optimize
water use for agricultural crops. An intelligent automatic irrigation system has to have all the
components that autonomously monitor and control the level of water available to the plants
without any failure or human intervention. The intelligent system should perform the
following functions:
1. Continuously monitor the amount of soil water available to plants (this is usually achieved
using a sensing system).
2. Determine if watering is required for the plants based on the information obtained from
monitoring the soil water content.
3. Supply exact (or approximate) amount of water required for the plants.
4. Discontinue the water supply when the required amount has been delivered to the plants.
This feature is important as the amount of water available for the irrigation system is not
infinite, therefore water management is paramount.
The advantages of automatic irrigation to the plants include saving money, water,
conservation of labour and overall convenience. The water supply needed by the system to
perform its irrigation function can be from any source, i.e. well, river, stream, pond, lagoon,
etc. However, it is most desirable if a constant source of water is available to the system in
order to ensure continuity of operation. The most preferred arrangement will be a water
reservoir which is constantly maintained at full capacity or a large source of fresh water
which remains continually available irrespective of variations in weather or climatic
conditions.
There are about four categories of methods proposed for scheduling irrigation effectively:
• Entirely empirical method and without any kind of on-going measurement
• Method based on monitoring soil moisture
• Method based on estimates of water use from weather data, and
• Method based on tracking the condition of the crop usually referred to as crop water stress.
The method of monitoring the soil moisture is employed in this project work. By this method,
the amount of water applied to the agricultural products is minimized and it reduces crop
production cost. Irrigation methods, according to are based on the following; the experience
of the farmer, the soil properties and environmental conditions. A better way to monitor the
environmental conditions and effective use of water to avoid wastage is by the use of sensor
network

12. - 2 -
Chapter 2
PCB (PRINTED CIRCUIT BOARD)
A printed circuit board, or PCB, is used to mechanically support and electrically connect
electronic components using conductive pathways, tracks or traces etched from copper sheets
laminated onto a non-conductive substrate. It is also referred to as printed wiring board
(PWB) or etched wiring board. A PCB populated with electronic components is a printed
circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).
PCBs are inexpensive, and can be highly reliable. They require much more layout effort and
higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are
much cheaper and faster for high-volume production. Much of the electronics industry's PCB
design, assembly, and quality control needs are set by standards that are published by the IPC
organization.
2.1 PROCEDURE TO DESIGN A LAYOUT
 Prepare each and every PCB layout as viewed from the component side, to avoid
confusion.
 Not to start the designing of a layout unless an absolutely clear circuit diagram is
available, if necessary, with a component list.
 Develop the layout in the direction of the signal flow as for as possible.
 Larger component are placed first and the space in between is filled with smaller
ones.
 Divide the circuit into functional subunits.
 Designer must verify that the layout realization conforms to the requirements of the
mother board or the external wiring.
2.2DESIGNING OF PCB LAYOUT
A PCB layout is required to place components on the PCB so that the component area can be
minimized and the components can be placed in an efficient manner. The components can be
placed in two ways, either manually or by software. The manual procedure is quiet
cumbersome and is very inefficient. The other method is by the use of computer software.

13. - 3 -
This method is advantageous as it saves time and valuable copper area. There are various
software’s available for this purpose like
1. Proteus
2. Express PCB
3. Circuit Wizard.
Many of them are loaded with auto routing and auto placement facility. The software that we
have used here is Proteus. This software has a good interface, easy editing options and a wide
range of components.
2.2.1 PROTEUS
Proteus is a simulation and design software tool developed by Labcenter
Electronics for Electrical and Electronic circuit design. It also possess 2D CAD drawing
feature. It deserves to bear the tagline “From concept to completion”.
It is a software suite containing schematic, simulation as well as PCB designing.
 ISIS is the software used to draw schematics and simulate the circuits in real time.
The simulation allows human access during run time, thus providing real time
simulation.
 ARES is used for PCB designing. It has the feature of viewing output in 3D view of
the designed PCB along with components.
 The designer can also develop 2D drawings for the product.
2.2.2Features
ISIS has wide range of components in its library. It has sources, signal generators,
measurement and analysis tools like oscilloscope, voltmeter, ammeter etc., probes for real
time monitoring of the parameters of the circuit, switches, displays, loads like motors and
lamps, discrete components like resistors, capacitors, inductors, transformers, digital and
analog Integrated circuits, semi-conductor switches, relays, microcontrollers, processors,
sensors etc.
ARES offers PCB designing up to 14 inner layers, with surface mount and through hole
packages. It is embedded with the foot prints of different category of components like ICs,
transistors, headers, connectors and other discrete components. It offers Auto routing and
manual routing options to the PCB Designer. The schematic drawn in the ISIS can be directly
transferred ARES.

14. - 4 -
2.3 LAYOUT OF THE PROJECT PCB
Fig.2.1:- Layout of PCB1
Fig.2.2:- Layout of PCB2

15. - 5 -
2.4 ARTWORK
The first step when producing a printed circuit board using an etch tank is to create an
artwork mask for the circuit. This mask is printed onto a clear laminate sheet and is used to
mark the areas that will eventually become copper on the printed circuit board.
Printout of the artwork is necessary to produce the PCB. The process used is to make a
contact print for each layer of the PCB . The top layer of a double sided PCB will need to be
mirrored in order to maintain the printed layer in contact with the photo - sensitive layer on
the PCB conductor. Each layer of artwork should be labelled with the relevant contact details,
substrate material & layer.
2.4.1 General Artwork Rule:
Conductor Orientation: In PCB artwork, conductors have to replace in other direction,
preference should be given to the 45 degree direction or to the 30/60 degree directions. This
rule helps in optimum utilization of the space available and gives a well-organized
appearance.
Conductor Routing Practice: Conductors forming sharp internal angles of less than 60
degree must be avoided. This is of particular importance for boards which have to be wave
soldered; excess solder would otherwise get deposited in such corners.
Component Polarity Identification: It is an essential requirement to index the orientation on
the artwork. This does not only help in assembling the PCB but it is also relied upon the
technician, engineer or customer who has to trouble-shoot and repair the board later. Overall,
without a screen –printed notation, the polarity identification must be given in the artwork
itself.
2.5 SCREEN PRINTING
Screen printing printed circuit boards (PCB) is typically performed in a clean, dust-free room
using semi-automatic or fully-automatic screen printing presses. The printed panel may
contain many PCB panels that are printed at once, and will eventually be separated. Screens
are stretched with precision, stable polyester meshes like SEFAR PME and SEFAR PMCE,
two meshes specifically engineered by SEFAR for competitive electronic printing. Solvent
and/or UV pastes are used for printing the etch resist patterns, plating resist patterns and
solder masks. Specially formulated solvent inks are used for legend printing.

16. - 6 -
Line art and text may be printed onto the outer surfaces of a PCB by screen printing. When
space permits, the screen print text can indicate component designators, switch setting
requirements, test points, and other features helpful in assembling, testing, and servicing the
circuit board.
Screen print is also known as the silk screen or in one sided PCBs, the red print. Lately some
digital printing solutions have been developed to substitute the traditional screen printing
process. This technology allows printing variable data onto the PCB, including serialization
and barcode information for traceability purposes. The actual screen-printing can be easily
carried out with a simple frame arrangement on a work bench.
Before ink is applied to the screen, the screen and frame must go through a process known as
pre-press. In this process, an emulsion is scooped across the mesh and the exposure unit
burns away the unnecessary emulsion leaving behind a clean area in the mesh with the
identical shape as the desired image. The surface (pallet) that the substrate will be printed
against is coated with a wide pallet tape. This serves to protect the pallet from any unwanted
ink leaking through the substrate and potentially staining the pallet or transferring unwanted
ink onto the next substrate. Next, the screen and frame are lined with a tap. These tapes are
generally used for UV and water-based inks due to the inks lower viscosities. The last process
in the pre-press is blocking out any unwanted pinholes in the emulsion. If these holes are left
in the emulsion, the ink will continue through and leave unwanted marks. To block out these
holes, materials such as tapes, emulsions are used.
2.6 DRILL JIG
A drill is a type of jig that expedites repetitive hole center location on multiple
interchangeable parts by acting as a template to guide the twist drill or other boring device
into the precise location of each intended hole center. In metalworking practice, typically a
hardened bushing lines each hole on the jig plate to keep the tool from damaging the jig. Drill
jigs started falling into disuse with the invention of the jig borer.
A jig is a special device that holds, supports, or is placed on a part to be machined. It is a
production tool made so that it not only locates and holds the work piece but also guides the
cutting tool as the operation is performed. Jigs are usually fitted with hardened steel bushings
for guiding drills or other cutting tools.

17. - 7 -
2.6.1 ELEMENTS OF DRILL JIG
There are many elements which make up the drill jig assembly:
 Jig plates
 Locating elements
 Clamping elements
 Drill bushes
Various types of pads for drill jig used in the circuit are:-
 2.28mm square pads with 1.09mm hole.
 2.28mm round pads with 1.09mm hole.
 4.06mm round pads with 3.2mm hole used as mounting holes of PCB.
 4.06mm round pads with 3.2mm hole used as mounting holes of DB9 connector.
2.7 GREEN MASKING
The bare copper PCB is silkscreened with a green solder mask which is designed to insulate
and protect the copper traces and keep them from shorting together during the soldering
process. The solder mask covers the whole board except solderable surfaces such as thru-hole
and surface mount pads. The green solder mask is dried or cured The PCB is tinned or plated
- solder, silver or gold is applied to exposed pads. The PCB is silkscreened with component
Identification lettering. The silkscreen legend is dried or cured . Any final drilling is done of
holes that are not to be plated through, any routing is done, and the laminate is cut into
individual printed circuit board.

18. - 8 -
2.8 PCB-DESIGNING FLOW CHART
PCB Designing includes the following steps:-
TABLE 2.1- PCB Designing process
PROCESSING
CLEANSING
ETCHING
PRINTING
DRILLING
SOLDERING
MASKING

19. - 9 -
2.8.1 PROCESSING
The layout of a PCB has to incorporate all the information on the board before one can go on
to the artwork preparation. This means that a concept that clearly defines all the details of the
circuit and partly also of the final equipment, is a prerequisite before the actual layout can
start. The detail circuit diagram is very important for the layout designer and he must also be
familiar with the design concept and with the philosophy behind the equipment. The General
Considerations are-
a-) Layout scale:-Depending on the accuracy required, artwork should be produced at a 1:1
or 2:1 or even 4:1 scale. The layout is best prepared on the same scale as the artwork. This
prevents all the problems which might be caused by redrawing of layout to the artwork scale.
b-) Grid system or Graph Paper: -It is commonly accepted practice to use these for
designing.
c-) Board types:-There are two side of a PCB board – Component side & Solder side.
Depending on these board are classified as-
 Single-sided Boards: - These are used where costs have to be kept at a minimum & a
particular Circuit can be accommodated on such board. To jump over conductor tracks,
components have to be utilized. If this is not feasible,
jumper wires are used. (Jumper wires should be less otherwise double-sided PCB
should be considered.
 Double-sided Boards: -These are made with or without plated through holes. Plated
through holes are fairly expensive.

20. - 10 -
2.8.2 CLEANING
The cleaning of the copper surface prior to resist application is an essential step for any type
of PCB process using etches or plating resist. After scrubbing with the abrasive, a water rinse
will remove most of the remaining slurry.
TABLE 2.2 - Cleaning process
2.8.3 ETCHING
It is of utmost importance to choose a suitable Etchant Systems. There are many factors to be
considered:-
 Etching speed
 Copper solving capacity
 Etchant price
 Pollution character
Factor
Etchant
Corrosiveness Neutralization
disposition
problem
Toxicity Required
ventilation
Operation
cost
Scrubbing
Water Rinse
Wet Brushing
Acid dip
Final Rinse
Drying
Pumice/ Acid Slurry
Tap Water
Tap Water
Hydrochloric Acid-HCl
De-ionized Water
Oven or Blowing of air.

21. - 11 -
FeCl3 High Medium Low Low Medium
CuCl2 High Low Medium Medium Low
Chromic
acid
High High High High High
Alkaline
ammonia
High Medium Medium High High
TABLE 2.3 - Characteristics of different etchants
Fig.2.3:- Etching Machine
Iron (III) chloride FeCl3
Iron(III) chloride, also called ferric chloride, is an industrial scale commodity chemical
compound, with the formula FeCl3. The colour of iron(III) chloride crystals depends on the
viewing angle: by reflected light the crystals appear dark green, but by transmitted light they

22. - 12 -
appear purple-red. Anhydrous iron(III) chloride is deliquescent, forming hydrated hydrogen
chloride mists in moist air. It is rarely observed in its natural form, mineral molysite, known
mainly from some fumaroles.
When dissolved in water, iron(III) chloride undergoes hydrolysis and gives off heat in an
exothermic reaction. The resulting brown, acidic, and corrosive solution is used as a
flocculent in sewage treatment and drinking water production, and as an etchant for copper-
based metals in printed circuit boards. Anhydrous iron(III) chloride is a fairly strong Lewis
acid, and it is used as a catalyst in organic synthesis.
Reactions Involved:-
FeCl3 + 3H 2O Fe(OH)3 + 3HCl (Free acid attack to copper)
FeCl3 + Cu FeCl2+ CuCl
FeCl3 + CuClFeCl2 + CuCl2
CuCl2 + Cu 2CuCl
2.8.4 DRILLING
The importance of hole drilling into PCB’s has further gone with electronic component
miniaturization and its need for smaller holes diameters (diameters less than half the board
thickness) and higher package density. The following hole diameter tolerances have been
generally accepted wherever no other specifications are mentioned.
Hole Diameter (D) <= 1mm + / - 0.05 mm
Hole Diameter (D) > 3 mm + / – 0.1 mm
Drill bits are made up of high-speed steel (HSS), Glass epoxy material, Tungsten Carbide.
2.8.5 SOLDERING
Electronic soldering connects electrical wiring and electronic components to printed circuit
boards (PCBs).Soldering is a process in which two or more metal items are joined together by
melting and flowing a filler metal (solder) into the joint, the filler metal having a lower

23. - 13 -
melting point than the work piece. Soldering differs from welding in that soldering does not
involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but
the work piece metal does not melt. Formerly nearly all solders contained lead, but
environmental concerns have increasingly dictated use of lead-free alloys for electronics and
plumbing purposes.
SOLDERS
Soldering filler materials are available in many different alloys for differing applications. In
electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost
identical in performance to the eutectic) has been the alloy of choice. Other alloys are used
for plumbing, mechanical assembly, and other applications. Some examples of soft-solder
types and their applications include tin-lead for general purposes, tin-zinc for joining
aluminium, lead-silver for strength at higher than room temperature, cadmium-silver for
strength at high temperatures, zinc-aluminum for aluminum and corrosion resistance, and tin-
silver and tin-bismuth for electronics.
A eutectic formulation has several advantages for soldering; chief among these is the
coincidence of the liquidus and solidus temperatures, i.e. the absence of a plastic phase. This
allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A
non-eutectic formulation must remain still as the temperature drops through the liquidus and
solidus temperatures. Any differential movement during the plastic phase may result in
cracks, giving an unreliable joint. Additionally, a eutectic formulation has the lowest possible
melting point, which minimizes heat stress on electronic components during soldering.
Common solder alloys are mixtures of tin and lead, respectively:
 63/37: melts at 183 °C (361 °F) (eutectic: the only mixture that melts at a point,
instead of over a range)
 60/40: melts between 183–190 °C (361–374 °F)
 50/50: melts between 185–215 °C (365–419 °F)
FLUX
The purpose of flux is to facilitate the soldering process. The obstacle to a successful solder
joint is an impurity at the site of the union, e.g. dirt, oils or oxidation. The impurities can be

24. - 14 -
removed by mechanical cleaning or by chemical means, but the elevated temperatures
required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-
oxidize. This effect is accelerated as the soldering temperatures increase and can completely
prevent the solder from joining to the work piece. One of the earliest forms of flux was
charcoal, which acts as a reducing agent and helps prevent oxidation during the soldering
process. Some fluxes go beyond the simple prevention of oxidation and also provide some
form of chemical cleaning (corrosion).
For many years, the most common type of flux used in electronics (soft soldering) was rosin-
based, using the rosin from selected pine trees. It was ideal in that it was non-corrosive and
non-conductive at normal temperatures but became mildly reactive (corrosive) at the elevated
soldering temperatures. Plumbing and automotive applications, among others, typically use
an acid-based (muriatic acid) flux which provides cleaning of the joint. These fluxes cannot
be used in electronics because they are conductive and because they will eventually dissolve
the small diameter wires. Many fluxes also act as a wetting agent in the soldering process,
reducing the surface tension of the molten solder and causing it to flow and wet the work
pieces more easily.
Flux should be removed after Soldering. It is done through washing by 0.5—1 % HCl
followed by Neutralization in dilute alkali to remove corrosive flux. Non-corrosive is
removed by Iso-Propanal.
TINNING
It is done for the protection of conductor track from Oxidation. Masking is the industrial
process and helps to protect the PCB. In order to save this circuit from oxidation a lab process
similar to masking is done, it is called tinning.
In tinning we use solder wire to cover up the track. It protects the track breakage as well as
protects the circuit from corrosion.

25. - 15 -
Chapter 3
COMPONENTS USED AND ITS DESCRIPTION
1. Buck Converter
2. Moisture Sensor
3. Comparator ( LM 358)
4. NE 555 Timer
5. Motor Driver IC ( L293D )
6. Solenoidal Valve
7. Relay
8. Water Motor
9. Resistors ( 10K, 1K, 1M)
10. Capacitors
11. Light Emitting Diode
The detail description of these components are as follows:-
1. Buck Converter:- The Buck Converter is used in SMPS circuits where the DC output
voltage needs to be lower than the DC input voltage. The DC input can be derived
from rectified AC or from any DC supply. It is useful where electrical isolation is not
needed between the switching circuit and the output, but where the input is from a
rectified AC source, isolation between the AC source and the rectifier could be
provided by a mains isolating transformer.
Fig.3.1:- Buck Converter Circuit.
The switching transistor between the input and output of the Buck Converter continually
switches on and off at high frequency. To maintain a continuous output, the circuit uses the

26. - 16 -
energy stored in the inductor L, during the on periods of the switching transistor, to continue
supplying the load during the off periods. The circuit operation depends on what is
sometimes also called a Flywheel Circuit. This is because the circuit acts rather like a
mechanical flywheel that, given regularly spaced pulses of energy keeps spinning smoothly
(outputting energy) at a steady rate.
2.Soil Moisture Sensor :- The Soil Moisture Sensor is a simple breakout for measuring the
moisture in soil and similar materials. The soil moisture sensor is pretty straight forward to
use. The two large exposed pads function as probes for the sensor, together acting as a
variable resistor. The more water that is in the soil means the better the conductivity between
the pads will be and will result in a lower resistance, and a higher SIG out.
To get the Soil Moisture Sensor functioning all you will need is to connect the VCC and
GND pins to your Arduino-based device (or compatible development board) and you will
receive a SIG out which will depend on the amount of water in the soil. One commonly
known issue with soil moisture senors is their short lifespan when exposed to a moist
environment. To combat this, we’ve had the PCB coated in Gold Finishing (ENIG or
Electroless Nickel Immersion Gold).
Fig.3.2:- Soil moisture sensor
3.Comparator :- IC LM358 is used here as comparator as well as adder. The Op-amp
comparator compares one analogue voltage level with another analogue voltage level, or
some preset reference voltage, VREF and produces an output signal based on this voltage
comparison. In other words, the op-amp voltage comparator compares the magnitudes of two
voltage inputs and determines which is the largest of the two. the operational amplifier can be
used with negative feedback to control the magnitude of its output signal in the linear region
performing a variety of different functions. the standard operational amplifier is characterised
by its open-loop gain AO and that its output voltage is given by the
expression: VOUT = AO(V+ – V-) where V+ and V- correspond to the voltages at the non-
inverting and the inverting terminals respectively.
Voltage comparators on the other hand, either use positive feedback or no feedback at all
(open-loop mode) to switch its output between two saturated states, because in the open-loop
mode the amplifiers voltage gain is basically equal to AVO. Then due to this high open loop

27. - 17 -
gain, the output from the comparator swings either fully to its positive supply rail, +Vcc or
fully to its negative supply rail, -Vcc on the application of varying input signal which passes
some preset threshold value.
The open-loop op-amp comparator is an analogue circuit that operates in its non-linear region
as changes in the two analogue inputs, V+ and V- causes it to behave like a
digital bistable device as triggering causes it to have two possible output states, +Vcc or -
Vcc. Then we can say that the voltage comparator is essentially a 1-bit analogue to digital
converter, as the input signal is analogue but the output behaves digitally. Consider the
basic op-amp voltage comparator circuit below.
Fig.3.3:- Comparator
With reference to the op-amp comparator circuit above, lets first assume that VIN is less than
the DC voltage level at VREF, ( VIN < VREF ). As the non-inverting (positive) input of the
comparator is less than the inverting (negative) input, the output will be LOW and at the
negative supply voltage, -Vcc resulting in a negative saturation of the output.
If we now increase the input voltage, VIN so that its value is greater than the reference
voltage VREF on the inverting input, the output voltage rapidly switches HIGH towards the
positive supply voltage, +Vcc resulting in a positive saturation of the output. If we reduce
again the input voltage VIN, so that it is slightly less than the reference voltage, the op-amp’s
output switches back to its negative saturation voltage acting as a threshold detector.
Then we can see that the op-amp voltage comparator is a device whose output is dependant
on the value of the input voltage, VIN with respect to some DC voltage level as the output is
HIGH when the voltage on the non-inverting input is greater than the voltage on the inverting
input, and LOW when the non-inverting input is less than the inverting input voltage. This
condition is true regardless of whether the input signal is connected to the inverting or the
non-inverting input of the comparator.
We can also see that the value of the output voltage is completely dependent on the op-amps
power supply voltage. In theory due to the op-amps high open-loop gain the magnitude of its
output voltage could be infinite in both directions, (±∞). However practically, and for
obvious reasons it is limited by the op-amps supply rails giving VOUT = +Vcc or VOUT = -Vcc.
We said before that the basic op-amp comparator produces a positive or negative voltage
output by comparing its input voltage against some preset DC reference voltage. Generally, a
resistive voltage divider is used to set the input reference voltage of a comparator, but a
battery source, zener diode or potentiometer for a variable reference voltage can all be used .

28. - 18 -
4. 555 Timer: - The 555 Timer is used here to work as monostable multivibrator. The 555
timer which gets its name from the three 5kΩ resistors it uses to generate the two
comparators reference voltage, is a very cheap, popular and useful precision timing device
that can act as either a simple timer to generate single pulses or long time delays, or as a
relaxation oscillator producing stabilized waveforms of varying duty cycles from 50 to 100%.
The 555 timer chip is extremely robust and stable 8-pin device that can be operated either as
a very accurate Monostable, Bistable or Astable Multivibrator to produce a variety of
applications such as one-shot or delay timers, pulse generation, LED and lamp flashers,
alarms and tone generation, logic clocks, frequency division, power supplies and converters
etc, in fact any circuit that requires some form of time control as the list is endless.
The single 555 Timer chip in its basic form is a Bipolar 8-pin mini Dual-in-line Package
(DIP) device consisting of some 25 transistors, 2 diodes and about 16 resistors arranged to
form two comparators, a flip-flop and a high current output stage as shown below. As well as
the 555 Timer there is also available the NE556 Timer Oscillator which combines TWO
individual 555’s within a single 14-pin DIP package and low power CMOS versions of the
single 555 timer such as the 7555 and LMC555 which use MOSFET transistors instead.
A simplified “block diagram” representing the internal circuitry of the 555 timer is given
below with a brief explanation of each of its connecting pins to help provide a clearer
understanding of how it works.
555 Timer Block Diagram
Fig.3.4:- NE555 Timer
• Pin 1. – Ground, The ground pin connects the 555 timer to the negative (0v) supply
rail.
• Pin 2. – Trigger, The negative input to comparator No 1. A negative pulse on this pin
“sets” the internal Flip-flop when the voltage drops below 1/3Vcc causing the output to
switch from a “LOW” to a “HIGH” state.

29. - 19 -
• Pin 3. – Output, The output pin can drive any TTL circuit and is capable of sourcing
or sinking up to 200mA of current at an output voltage equal to approximately Vcc –
1.5V so small speakers, LEDs or motors can be connected directly to the output.
• Pin 4. – Reset, This pin is used to “reset” the internal Flip-flop controlling the state of
the output, pin 3. This is an active-low input and is generally connected to a logic “1”
level when not used to prevent any unwanted resetting of the output.
• Pin 5. – Control Voltage, This pin controls the timing of the 555 by overriding the
2/3Vcc level of the voltage divider network. By applying a voltage to this pin the width
of the output signal can be varied independently of the RC timing network. When not
used it is connected to ground via a 10nF capacitor to eliminate any noise.
• Pin 6. – Threshold, The positive input to comparator No 2. This pin is used to reset
the Flip-flop when the voltage applied to it exceeds 2/3Vcc causing the output to
switch from “HIGH” to “LOW” state. This pin connects directly to the RC timing
circuit.
• Pin 7. – Discharge, The discharge pin is connected directly to the Collector of an
internal NPN transistor which is used to “discharge” the timing capacitor to ground
when the output at pin 3 switches “LOW”.
• Pin 8. – Supply +Vcc, This is the power supply pin and for general purpose TTL 555
timers is between 4.5V and 15V.
The 555 Timers name comes from the fact that there are three 5kΩ resistors connected
together internally producing a voltage divider network between the supply voltage at pin 8
and ground at pin 1. The voltage across this series resistive network holds the negative
inverting input of comparator two at 2/3Vcc and the positive non-inverting input to
comparator one at 1/3Vcc.
The two comparators produce an output voltage dependent upon the voltage difference at
their inputs which is determined by the charging and discharging action of the externally
connected RC network. The outputs from both comparators are connected to the two inputs
of the flip-flop which in turn produces either a “HIGH” or “LOW” level output at Q based on
the states of its inputs. The output from the flip-flop is used to control a high current output
switching stage to drive the connected load producing either a “HIGH” or “LOW” voltage
level at the output pin.
The most common use of the 555 timer oscillator is as a simple astable oscillator by
connecting two resistors and a capacitor across its terminals to generate a fixed pulse train
with a time period determined by the time constant of the RC network. But the 555 timer
oscillator chip can also be connected in a variety of different ways to produce Monostable or
Bistable multivibrators as well as the more common Astable Multivibrator.
The Monostable 555 Timer
Consider the 555 timer monostable circuit below.
Monostable 555 Timer

30. - 20 -
Fig.3.5:- NE555 Timer based Monostable multivibrator
When a negative ( 0V ) pulse is applied to the trigger input (pin 2) of the Monostable
configured 555 Timer oscillator, the internal comparator, (comparator No1) detects this input
and “sets” the state of the flip-flop, changing the output from a “LOW” state to a “HIGH”
state. This action in turn turns “OFF” the discharge transistor connected to pin 7, thereby
removing the short circuit across the external timing capacitor, C1.
This action allows the timing capacitor to start to charge up through resistor, R1 until the
voltage across the capacitor reaches the threshold (pin 6) voltage of 2/3Vcc set up by the
internal voltage divider network. At this point the comparators output goes “HIGH” and
“resets” the flip-flop back to its original state which in turn turns “ON” the transistor and
discharges the capacitor to ground through pin 7. This causes the output to change its state
back to the original stable “LOW” value awaiting another trigger pulse to start the timing
process over again. Then as before, the Monostable Multivibrator has only “ONE” stable
state.
The Monostable 555 Timer circuit triggers on a negative-going pulse applied to pin 2 and
this trigger pulse must be much shorter than the output pulse width allowing time for the
timing capacitor to charge and then discharge fully. Once triggered, the 555 Monostable will
remain in this “HIGH” unstable output state until the time period set up by the R1 x
C1 network has elapsed. The amount of time that the output voltage remains “HIGH” or at a
logic “1” level, is given by the following time constant equation.
Where, t is in seconds, R is in Ω’s and C in Farads.
5. Motor Driver IC :- The L293 and L293D are quadruple high-current half-H drivers. The
L293NE is designed to provide bidirectional drive currents of up to 1 A at voltages from 4.5
V to 36 V. This device is designed to drive inductive loads such as relays, solenoids, dc and
bipolar stepping motors, as well as other high-current/high-voltage loads in positive-supply
applications. All inputs are TTL compatible. Each output is a complete totem-pole drive
circuit, with a Darlington transistor sink and a pseudo- Darlington source. Drivers are enabled
in pairs, with drivers 1 and 2 enabled by 1,2EN and drivers 3 and 4 enabled by 3,4EN. When
an enable input is high, the associated drivers are enabled, and their outputs are active and in
phase with their inputs. When the enable input is low, those drivers are disabled, and their

31. - 21 -
outputs are off and in the high-impedance state. With the proper data inputs, each pair of
drivers forms a full-H (or bridge) reversible drive suitable for solenoid or motor applications.
Pin
No.
Pin Characteristics
1
Enable 1-2, when this is HIGH the left part of the IC will work and when it is low the
left part won’t work. So, this is the Master Control pin for the left part of IC
2 INPUT 1, when this pin is HIGH the current will flow though output 1
3 OUTPUT 1, this pin should be connected to one of the terminal of motor
4,5 GND, ground pins
6 OUTPUT 2, this pin should be connected to one of the terminal of motor
7 INPUT 2, when this pin is HIGH the current will flow though output 2
8
VC, this is the voltage which will be supplied to the motor. So, if you are driving 12 V
DC motors then make sure that this pin is supplied with 12 V
16 VSS, this is the power source to the IC. So, this pin should be supplied with 5 V
15 INPUT 4, when this pin is HIGH the current will flow though output 4
14 OUTPUT 4, this pin should be connected to one of the terminal of motor
13,12 GND, ground pins
11 OUTPUT 3, this pin should be connected to one of the terminal of motor
10 INPUT 3, when this pin is HIGH the current will flow though output 3
9
Enable 3-4, when this is HIGH the right part of the IC will work and when it is low the
right part won’t work. So, this is the Master Control pin for the right part of IC

32. - 22 -
Fig.3.6:- L293D Pin Diagram
6. Solenoidal Valve:- A solenoid valve is an electromechanical controlled valve. The valve
features a solenoid, which is an electric coil with a movable ferromagnetic core in its centre.
This core is called the plunger. In rest position, the plunger closes off a small orifice. An
electric current through the coil creates a magnetic field. The magnetic field exerts a force on
the plunger. As a result, the plunger is pulled toward the centre of the coil so that the orifice
opens. This is the basic principle that is used to open and close solenoid valves.
"A solenoid valve is an electromechanical actuated valve to control the flow of liquids and
gases."
Solenoid valves are amongst the most used components in gas and liquid circuits. The
number of applications is almost endless. Some examples of the use of solenoid valves
include heating systems, compressed air technology, industrial automation, swimming pools,
sprinkler systems, washing machines, dental equipment, car wash systems and irrigation
systems.
Circuit Functions Of Solenoid Valves
Solenoid valves are used to close, dose, distribute or mix the flow of gas or liquid in a pipe.
The specific purpose of a solenoid valve is expressed by its circuit function. A 2/2 way valve
has two ports (inlet and outlet) and two positions (open or closed). A 2/2 way valve can be
'normally closed' (closed in de-energized state) or 'normally open' (open in de-energized
state). A 3/2 way valve has three ports and two positions and can therefore switch between
two circuits. 3/2 way valves can have different functions such as normally closed, normally

33. - 23 -
open, diverting or universal. More ports or combinations of valves in a single construction are
possible. The circuit function can be expressed in a symbol. Below are some examples of the
most common circuit functions. The circuit function of a valve is symbolized in two
rectangular boxes for the de-energized state (right side, visualized by ) and energized state
(left). The arrows in the box show the flow direction between the valve ports. The examples
show a 2/2-way Normally Open (NO) valve, a 2/2-way Normally Closed (NC) valve and a
3/2-way Normally Closed valve. For more information about valve symbols and circuit
functions, please visit the page about valve symbols.
Fig.3.7:- Solenoidal Valve
7. Relay Switch :- A relay is an electrically operated switch. Current flowing through the coil
of the relay creates a magnetic field which attracts a lever and changes the switch contacts.
The coil current can be on or off so relays have two switch positions and they are double
throw (changeover) switches.
The relay’s switch connections are usually labeled COM(POLE), NC and NO
COM/POLE= Common, NC and NO always connect to this, it is the moving part of the
switch.
NC = Normally Closed, COM/POLE is connected to this when the relay coil is not
magnetized.
NO = Normally Open, COM/POLE is connected to this when the relay coil is
MAGNETIZED and vice versa.

34. - 24 -
Fig.3.8:- Relay Switch
There are 5 Pins in a relay. Two pins A and B are two ends of a coil that are kept inside the
relay. The coil is wound on a small rod that gets magnetized whenever current passes through
it.COM/POLE is always connected to NC(Normally connected) pin. As current is passed
through the coil A, B, the pole gets connected to NO(Normally Open) pin of the relay.
8. Water Motor :- Water motor is used to extract water from the source. We have used 220
volt AC water motor which has the capacity of 1300 Litres per hour.
9. Resistor :- The resistor is a passive electrical component to create resistance in the flow of
electric current. In almost all electrical networks and electronic circuits they can be found.
The resistance is measured in ohms. An ohm is the resistance that occurs when a current of
one ampere passes through a resistor with a one volt drop across its terminals. The current is
proportional to the voltage across the terminal ends. This ratio is represented by Ohm’s law:
Resistors are used for many purposes. A few examples include delimit electric current,
voltage division, heat generation, matching and loading circuits, control gain, and fix time
constants. They are commercially available with resistance values over a range of more than
nine orders of magnitude.
There are many different types of resistor available for use within electronic circuits. These
different resistor types have somewhat different properties dependent upon their construction
and manufacture. This makes the different types of resistor suitable for different applications.

35. - 25 -
Over the years the resistor types used in mass electronics production have changed. Years
ago, all the resistors used had leads and were relatively large, and by today's standards they
offered a low level of performance. Today, the resistor types used are much smaller and offer
much higher levels of performance.
Fixed & variable resistor types :
The first major categories into which the different types of resistor can be fitted is into
whether they are fixed or variable. These different resistor types are used for different
applications:
 Fixed resistors: Fixed resistors are by far the most widely used type of resistor.
They are used in electronics circuits to set the right conditions in a circuit. Their
values are determined during the design phase of the circuit, and they should never
need to be changed to "adjust" the circuit. There are many different types of resistor
which can be used in different circumstances and these different types of resistor are
described in further detail below.
 Variable resistors: These resistors consist of a fixed resistor element and a slider
which taps onto the main resistor element. This gives three connections to the
component: two connected to the fixed element, and the third is the slider. In this way
the component acts as a variable potential divider if all three connections are used. It
is possible to connect to the slider and one end to provide a resistor with variable
resistance.
Fixed resistor types:
There are a number of different types of fixed resistor:
 Carbon composition: These types were once very common, but are now seldom
used. They are formed by mixing carbon granules with a binder which was then made
into a small rod. This type of resistor was large by today's standards and suffered from
a large negative temperature coefficient. The resistors also suffered from a large and
erratic irreversible changes in resistance as a result of heat or age. In addition to this
the granular nature of the carbon and binder lead to high levels of noise being
generated when current flowed.
 Carbon film: This resistor type is formed by "cracking" a hydrocarbon onto a
ceramic former. The resulting deposited film had its resistance set by cutting a helix
into the film. This made these resistors highly inductive and of little use for many RF
applications. They exhibited a temperature coefficient of between -100 and -900 ppm
/ °Celcius. The carbon film is protected either by a conformal epoxy coating or a
ceramic tube.
 Metal oxide film: This type of resistor is now one of the most widely used form of
resistor along with the metal film type. Rather than using a carbon film, this resistor
type uses a metal oxide film deposited on a ceramic rod. Metals oxide such as tin
oxide areedeposited onto the ceramic rod. The resistance of the component is adjusted
in two ways. First the thickness of the deposited layer is controlled during the initial
manufacturing stages. Then it can be more accurately adjusted by cutting a helical
grove in the film. Again the film is protected using a conformal epoxy coating. This
type of resistor has a temperature coefficient of around ±15 parts per million / °K,

36. - 26 -
giving it a far superior performance to that of any carbon based resistor. Additionally
this type of resistor can be supplied to a much closer tolerance, ±5%, ±2% being
standard, and with ±1% versions available. They also exhibit a much lower noise
level than carbon types of resistor.
 Metal film: The metal film resistors is very similar to the metal oxide film resistor
in terms of visual appearance and performance. Instead of using a metal oxide film,
this type of resistor uses a metal film. Metals such as nickel alloy may be used.
 Wire wound: This resistor type is generally reserved for high power applications.
These resistors are made by winding wire with a higher than normal resistance
(resistance wire) on a former. The more expensive varieties are wound on a ceramic
former and they may be covered by a vitreous or silicone enamel. This resistor type is
suited to high powers and exhibits a high level of reliability at high powers along with
a comparatively low level of temperature coefficient, although this will depend on a
number of factors including the former, wire used, etc..
 Thin film: Thin film technology is used for most of the surface mount types of
resistor. As these are used in their billions these days, this makes this form of resistor
technology one of the most widely used
 Leaded and non-leaded resistor types
One of the key differentiators for resistors, and many other forms of component these days is
the way in which they are connected. As a result of the mass production techniques sued and
the widespread use of printed circuit boards, the form of connection used for components,
especially those to be incorporated into mass produced items changed.
The two main forms of resistor type according to their connection method are:
 Leaded resistors: This type of resistor has been used since the very first electronic
components have been in use. Typically components were connected to terminal posts
of one form or another and leads from the resistor element were needed. As time
progressed, printed circuit boards were used, and the leads were inserted through
holes in the boards and typically soldered on the reverse side where the tracks were to
be found.
Fig.3.9:-Typical leaded carbon resistor
 Surface mount resistors: These resistor types have been used increasingly since the
introduction of surface mount technology. Typically this type of resistor is
manufactured using thin film technology. A full range of values can be obtained.

37. - 27 -
Fig.3.10:-Typical SMD resistors on a PCB
10. Capacitor :- Capacitor is a passive element that stores electric charge statistically and
temporarily as an static electric field. It is composed of two parallel conducting plates
separated by non-conducting region that is called dielectric, such as vacuum, ceramic, air,
aluminum, etc.
The capacitance formula of the capacitor is represented by, C is the capacitance
that is proportional to the area of the two conducting plates (A) and proportional with the
permittivity ε of the dielectric medium. The capacitance decreases with the distance between
plates (d). We get the greatest capacitance with a large area of plates separated by a small
distance and located in a high permittivity material. The standard unit of capacitance is Farad,
most commonly it can be found in micro-farads, pico-farads and nano-farads.
General uses of Capacitors
1. Smoothing, especially in power supply applications which required converting the signal
from AC to DC.
2. Storing Energy.
3. Signal decoupling and coupling as a capacitor coupling that blocks DC current and allow
AC current to pass in circuits.
4. Tuning, as in radio systems by connecting them to LC oscillator and for tuning to the
desired frequency.
5. Timing, due to the fixed charging and discharging time of capacitors.
6. For electrical power factor correction and many more applications.
Charging a Capacitor
Capacitors are mainly categorized on the basis of dielectric used in them. During choosing a
specific type of capacitors for a specific application, there are numbers of factors that get
considered. The value of capacitance is one of the vital factors to be considered. Not only
this, many other factors like, operating voltage, allowable tolerance stability,
leakage resistance, size and prices are also very important factors to be considered during
choosing specific type of capacitors.
We know that capacitance of a capacitor is given by , Hence, it is cleared that, by
varying ε, A or d we can easily change the value of C. If we require higher value of

38. - 28 -
capacitance (C) we have to increase the cross-sectional area of dielectric or we have to reduce
the distance of separation or we have to use dielectric material with stronger permittivity.
If we go only for the increasing area of cross-section, the rise of the capacitor may become
quite large; which may not be practically acceptable. Again if we reduce only the distance of
separation, the thickness of dielectric becomes very thin. But the dielectric cannot be made
too thin in case its dielectric strength in exceeded.
Types of Capacitors
The various types of capacitors have been developed to overcome these problems in a
number of ways.
Paper Capacitor
It is one of the simple forms of capacitors. Here, a waxed paper is sandwiched between two
aluminium foils.
Process of making this capacitor is quite simple. Take place of aluminium foil. Cover this foil
with a waxed paper. Now, cover this waxed paper with another aluminium foil. Then roll up
this whole thing as a cylinder. Put two metal caps at both ends of roll. This whole assembly is
then encapsulated in a case. By rolling up, we make quite a large cross-sectional area of
capacitor assembled in a reasonably smaller space.
Fig.3.11:- Paper Capacitor
Air Capacitor
There are two sets of parallel plates. One set of plates is fixed and another set of plates is
movable. When the knob connected with the capacitor is rotated, the movable set of plates
rotates and overlapping area as between fixed and movable plates vary. This causes variation
in effective cross-sectional areas of the capacitor. Consequently, the capacitance varies when
one rotates the knob attached to the air capacitor. This type of capacitor is generally used to
tune the bandwidth of a radio receiver.

39. - 29 -
.
Fig.3.12:- Air capacitor
Plastic Capacitor
When various plastic materials are used as dielectric material, the capacitors are said to be
plastic capacitors. The plastic material may be of polyester, polystyrene, polycarbonate or
poly propylene. Each of these materials has slightly different electrical characteristics, which
can be used to advantage, depending upon the proposed application.
This type of capacitors is constructional, more or less same as paper capacitor. That means, a
thin sheet one of the earlier mentioned plastic dielectrics, is kept between two aluminium
foils. That means, here the flexible thin plastic sheet is used as dielectric instead of waxed
paper. Here, the plastic sheet covered by aluminium foil from two sides, is first rolled up,
then fitted with metal end caps, and then the whole assembly is encapsulated in a case.
Plastic Film Capacitor
Plastic capacitor can be made also in form of film capacitor. Here, thin strips or films of
plastic are kept inside metallic strips. Each metallic strip is connected to side metallic contact
layer alternatively; as shown in the figure below. That means, if one metallic strip is
connected to left side contact layer, then the very next is connected to right side contact layer.
And there are plastic films in between these metallic strips. The terminals of this type of
capacitors are also connected to side contact layer and whole assembly is covered with
insulated non metallic cover as shown.
Fig.3.13:- Plastic film capacitor

40. - 30 -
Silvered Mica Capacitor
A silvered mica capacitor is very accurate and reliable capacitor. This type of capacitors has
very low tolerance. But on the other hand, cost of this capacitor is quite higher compared to
other available capacitors in the market. But this high cost capacitor can easily be
compensated by its high quality and performance. A small ceramic disc or cylinder is coated
by silver compound. Here, electrical terminal is affixed on the silver coating and the whole
assembly is encapsulated in a casing.
Ceramic Capacitor
Construction of ceramic capacitor is quite simple. Here, one thin ceramic disc is placed
between two metal discs and terminals are soldered to the metal discs. Whole assembly is
coated with insulated protection coating as shown in the figure below.
Fig.3.14 Ceramic Capacitor
Mixed Dielectric Capacitor
The way of constructing this capacitor is same as paper capacitor. Here, instead of moving
waxed paper as dielectric, paper impregnated with polyester is used as dielectric between two
conductive aluminium foils.
Electrolyte Capacitor
Very large value of capacitance can be achieved by this type of capacitor. But working
voltage level of this electrolyte capacitor is low and it also suffers from high leakage current.
The main disadvantage of this capacitor is that, due to the use of electrolyte, the capacitor is
polarized. The polarities are marked against the terminals with + and – sign and the capacitor
must be connected to the circuit in proper polarity.
A few micro meter thick aluminium oxide or tantalum oxide film is used as dielectric of
electrolyte capacitor. As this dielectric is so thin, the capacitance of this type of capacitor is
very high. This is because; the capacitance is inversely proportional to thickness of the
dielectric. Thin dielectric obviously increases the capacitance value but at the same time, it
reduces working voltage of the device. Tantalum type capacitors are usually much smaller in
size than the aluminium type capacitors of same capacitance value. That is why, for very high
value of capacitance, aluminium type electrolyte capacitors do not get used generally. In that

41. - 31 -
case, tantalum type electrolyte capacitors get used. Aluminium electrolyte capacitor is formed
by a paper impregnated with an electrolyte and two sheets of aluminium. These two sheets of
aluminium are separated by the paper impregnated with electrolyte. The whole assembly is
XXXIthen rolled up in a cylindrical form, just like a simple paper capacitor. This roll is then
placed inside a hermetically sealed aluminium canister. The oxide layer is formed by passing
a charging current through the device, and it is the polarity of this charging process that
determines the resulting terminal polarity that must be subsequently observed. If the opposite
polarity is applied to the capacitor, the oxide layer is destroyed.
11. Light Emitting Diode (LED) :- The “Light Emitting Diode” or LED as it is more
commonly called, is basically just a specialised type of diode as they have very similar
electrical characteristics to a PN junction diode. This means that an LED will pass current in
its forward direction but block the flow of current in the reverse direction.
Light emitting diodes are made from a very thin layer of fairly heavily doped semiconductor
material and depending on the semiconductor material used and the amount of doping, when
forward biased an LED will emit a coloured light at a particular spectral wavelength.
When the diode is forward biased, electrons from the semiconductors conduction band
recombine with holes from the valence band releasing sufficient energy to produce photons
which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable
number of these photons can leave the junction and radiate away producing a coloured light
output.
Fig.3.15:- LED
Then we can say that when operated in a forward biased direction Light Emitting Diodes are
semiconductor devices that convert electrical energy into light energy.
The construction of a Light Emitting Diode is very different from that of a normal signal
diode. The PN junction of an LED is surrounded by a transparent, hard plastic epoxy resin
hemispherical shaped shell or body which protects the LED from both vibration and shock.
Surprisingly, an LED junction does not actually emit that much light so the epoxy resin body
is constructed in such a way that the photons of light emitted by the junction are reflected
away from the surrounding substrate base to which the diode is attached and are focused
upwards through the domed top of the LED, which itself acts like a lens concentrating the
amount of light. This is why the emitted light appears to be brightest at the top of the LED.
Types of Light Emitting Diode
 Gallium Arsenide (GaAs) – infra-red

42. - 32 -
 Gallium Arsenide Phosphide (GaAsP) – red to infra-red, orange
 Aluminium Gallium Arsenide Phosphide (AlGaAsP) – high-brightness red, orange-red,
orange, and yellow
 Gallium Phosphide (GaP) – red, yellow and green
 Aluminium Gallium Phosphide (AlGaP) – green
 Gallium Nitride (GaN) – green, emerald green
 Gallium Indium Nitride (GaInN) – near ultraviolet, bluish-green and blue
 Silicon Carbide (SiC) – blue as a substrate
 Zinc Selenide (ZnSe) – blue
 Aluminium Gallium Nitride (AlGaN) – ultraviolet

43. - 33 -

44. - 34 -
4.2 Working Principal
The soil moisture sensor is inserted in the soil . When the soil is dry the resistivity of the soil
increases and current flowing between probes of moisture sensor decreases. This leads to less
voltage sensed at non-inverting terminal than inverting terminal of comparator, as inverting
terminal is already set at a reference voltage by potentiometer. As a result output voltage of
opamp is negative voltage . The output pin of the op-amp is connected to the pin no.2 of
NE555 timer . The pin no.2 is the trigger pin of 555 timer which get triggered by negative
triggering voltage. A positive pulse of time duration 1.1RC is generated at the output of 555
timer. The output of 555 timer is connected to the motor driver input pin as well as to the
relay circuit which switch on the water motor as well as solenoidal valve. As soon as the
water level in the soil become enough to allow sufficient current flow between probes of
sensor so that voltage at the non inverting terminal becomes larger than the reference voltage
at the inverting terminal of comparator. This will give positive comparator output voltage
which will disable 555 timer which leads to switch off the water pump as well as solenoidal
valve.
4.3 Advantages:-
(i) Highly sensitive
(ii) Works according to the soil condition
(iii) Fit and Forget system
(iv) Low cost and reliable circuit
(v ) Complete elimination of manpower
(vi) System can be switched into manual mode whenever required.
Applications :-
1.Roof Gardens
2. Lawns
3. Agriculture Lands
4.Home Gardens
Conclusion
Automatic irrigation control system has been designed and constructed. The prototype of the
system worked according to specification and quite satisfactorily. The system components are
readily available, relatively affordable and they operate quite reliably. The system helps to
eliminate the stress of manual irrigation and irrigation control while at the same time
conserving the available water supply. Improving Irrigation efficiency can contribute greatly
to reducing production costs of agricultural products, thereby making the industry to be more
competitive and sustainable. The system was tested on three types of soil and from the result
analysis sandy soils require less water than loamy soils and clay soils require the most water
for irrigation. For future work on this project, we recommend that for a large scale
implementation a more powerful water pump can be used. Also a microcontroller should be
used to accommodate more than one sensor input and also control different irrigation regimes
independently. A wireless sensor and GPRS (General Packet Radio Service) based automated
irrigation system can also be employed, which according to [13, 14],
will help monitor the soil moisture and to control the application of water to the agricultural
products thereby saving water .

45. - 35 -
References
1.Pavithra D.S, Srinath M.S “GSM based automatic irrigation control system for efficient use
of resources and crop planning by using an Android mobile” IOSR Journal of Mechanical
and Civil Engineering Volume 11, Issue 4 Ver.1 July-August 2014 p. 49-55.
2. Abhinav Rajpal, Sumit Jain, Nistha Khare and Anil Kumar Shukla “Microcontroller-based
Automatic Irrigation System with Moisture Sensor” Proceedings of the International
Conference on Science and Engineerin (ICSE 2011).
3. Gutierrez J, Villa-medina, J,F, Nieto- Garibay, A. and Porta-Gandara, M.A Journal of
Instrumentation and Measurement, IEEE Transactions Volume 63 Issue 1, p. 166-176
4. Qiuming K.; Yandong Z.; Chenxiang B.: “Automatic monitor and control system of water
saving irrigation”, Transactions of the Chinese Society of Agricultural Engineering, Vol.
2007 no.6, Society of Agricultural Engineering.
5. Venkata Naga Rohit Gunturi “Microcontroller based automatic plant irrigation System”
International Journal of Advancement in Research and Technology, Vol.2, issue 4, April
2013 p. 194-198
6. Automatic Irrigation Systems available on www.irrigation.org accessed on 2nd
October,
2015
7. S.K Luthra, M.J Kaledhaikar, O.P Singh, N.K Tyagi “design and development of an auto
irrigation System” Elsevier journal of Agricultural water Management 33(1997) p.169-1819
Journal of Electrical Engineering
www.jee.ro
8. Rafael Munoz-Carpena and Michael D.Dukes “Automatic Irrigation Based on Soil
moisture for vegetable crops” available online at
http://edis.ifas.ufl.edu accessed on 2nd
October, 2015
9 Cornelius H.M Van Bavel, Michael G.Van Bavel and Robert J. Lascano “Automatic
Irrigation Based on monitoring plant transpiration” p. 1088-1092
10. Rahim Khan, Ihsan Ali, M.Asif Suryani, Mushtag Ahmad and Muhammad Zakarya “
Wireless sensor Network based Irrigation Management System for Container Grown Crops in
Pakistan” World Applied Science Journal 24(8),2013 p.1111- 1118.
11. Purnima, SRN, Reddy “Design of a remote monitoring and control System with
Automatic Irrigation System using GSM blue-tooth” International Journal of Computer
Applications Vol. 47 No 12, June 2012.
12. www.owue.water.ca.gov/landscape/pubs/pubs.cfm .
13. Karthikeswari M, Mithraderi P “Automated Irrigation System in Agriculture using
wireless Sensor Technology” International journal of Advanced research in Electrical,
Electronics and Instrumentation Engineering Vol.3, issue 12, December 2014 p. 13622-
13627.

46. - 36 -
14. Liai Gao, Meng Zhang, Geng Chen “An Intelligent Irrigation System based on wireless
Sensor Network and Fuzzy control” Journal of Networks, Vol. 8, No 5, 2013 p. 1080-1087
15. Suraj S. Avatade, Dhanure S.P “Irrigation System Using wireless Sensor network and
GPRS” International Journal of Advance Research in Computer and Communication
Engineering. Vol.4, issue 4, May 2015 p.521-524