SOLAR BASED GRASS CUTTER MACHINE

In today’s generation the major problems are
the pollutions, cut of power etc. Thus overcome to these
problems we have thought about device which can be
work efficiently without causing any types of problem. So
we work on the project of grass cutter machine which
performing fully automated and using renewable source
of energy that is solar power.

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“SOLAR BASED GRASS CUTTER MACHINE”
Project submitted to
NORTH MAHARASHTRA UNIVERSITY, JALGAON
in fulfillment of requirement for the award of degree of
BACHELOR OF ENGINEERING
Under the
Faculty of Engineering and Technology
In the discipline
Electrical Engineering

By ,
MR. RITESH PATIL
MR. SHUBHAM BHAD
MR. HEMANT AVASARMAL
B.E.Electrical
Guide
PROF. SACHIN R. MAHESHRI
(Asst. Prof. In Electrical Engg Dept.)

Department of Electrical Engineering
Godavari Foundation’s
Godavari College of Engineering, Jalgaon
( An affiliated to North Maharashtra University, Jalgaon)

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ACKNOWLEDGEMENT

We consider our self to be fortunate to get this opportunity to be part of a
Project Report on in “SOLAR BASED GRASS CUTTER MACHINE ” We are sincerely
grateful to PROF. SACHIN R. MAHESHRI(Guide) for his invaluable guidance, motivation
and support at all stages and creating a flexible and enjoyable environment to work in.
Special thanks to PROF. ATUL A. BARHATE (Head of Electrical
Engineering) for the support and help us in completing this seminar program successfully.
Last but not least; We are thankful to the God, my dearly beloved Parents, all Faculty
Members, my Friends and all who directly or indirectly supported for completion….



MR.RITESH PATIL
MR. SHUBHAM BHAD
MR. HEMANT AVASARMAL

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CONTENT
SR.
NO.
TOPICS NAME PAGE
NO.
LIST OF FIGURE I
ABSTRACT ii
1. CHAPTER-1 INTRODUCTION
1.1 Motivations
1.2 Objectives
1.3 Existing Technology
1.4 Design Method Considerations
01
2. CHAPTER-2 LITERATURE REVIEW 06
3. CHAPTER-3 SYSTEM DEVELOPMENT
3.1 Block Diagram
3.2 Electrical circuit of Wheat stone bridge
3.2.1 Function of wheat stone bridge circuit
3.2.2 Wheatstone Bridge Theory
3.3 Ultrasonic Sensor
3.3.1 Transmitted waves
3.3.2 Received waves
3.4 Circuit Diagram
3.5 Design of Individual Module
3.6 PCB Designing And Fabrication
3.6.2 PCB designing and fabrication
3.6.3 Pattern transfer onto the Screen
3.6.4 Functions of the Bit
3.6.5 Procedure of Soldering
3.6.6 PCB designing using computer aided
designing (CAD)
3.7 Development Board
07
4. CHAPTER-4 PERFORMANCE ANALYSIS
4.1 Flowchart
4.2 Program of microcontroller
4.3 Design with Analysis of the system
4.3.1 Design of Step down Transformer
4.3.2 Rectifier Design
4.3.3 Design of Filter Capacitor
4.3.4 Selection For Current Limiting
Resistance For Led
33
5. CHAPTER-5 CONCLUSION
5.1 Conclusion
5.2 Advantages
5.3 Application
5.4 Future Scope
44
REFERENCES 45

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LIST OF FIGURE



FIGURE NO.

FIGURE NAMES PAGE NO.
1.1 Robomow criss-cross cutting pattern 02
1.2 LawnBott random cutting pattern 04
3.1 Block diagram of system 07
3.2 Pin diagram of ATMEGA328 08
3.3 BC547 pin out 09
3.4 LED 09
3.5 Pin description of LM7805 10
3.6 LM7805 10
3.7 Voltage variation across capacitor 11
3.8 L298N module 12
3.9 L298N module pin out 12
3.10 Solar Panel 15
3.11 DC Motor 16
3.12 Wheat stone bridge electrical resistance
system
17
3.13 Circuit diagram of Wheastone Bridge 18
3.14 Ultrasonic Sensor 19
3.15 Working of Ultrasonic Sensor 20
3.16 Circuit diagram of system 21
3.17 Circuit diagram of inverter 22
3.18 Circuit diagram of power supply 23
3.19 Filter Circuit 24
3.20 3-Terminal Voltage Regulator 24
3.21 AT Mega328 Development Board Layout 32
3.22 Power supply layout 32
4.1 System flow chart 33
4.2 Current limiting resistance 42

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ABSTRACT
Due to the continuous increase in the cost of fuel and the effect of emission of
gases from the burnt fuel into the atmosphere, this necessitate d the use of the abundant solar
energy from the sun as a source of power to drive a lawn mower. A solar powered lawn
mower was designed and developed, based on the general principle of mowing. The designed
solar powered lawnmower comprises of direct current (D.C) motor, a rechargeable battery,
solar panel, a stainless steel blade and control switch . Mowing is achieved by the D.C
motor which provides the required torque needed to drive the stainless steel blade which is
directly coupled to the shaft of the D.C motor. The solar powered lawnmower is operated by
the switch on the board which closes the circuit and allows the flow of current to the motor
which in turn drive the blade used for mowing. The battery recharges through the solar
charging controller. Performance evaluation of the developed machine was carried out with
different types of grasses. The machine Was foun d to have an efficiency of 93% and a field
capacity of 1.11 × 10-4 ha/hr. No significant difference was observed with the height of
grasses at 5% confidence level.
The system will have some automation work for guidance and other obstacle
detection. The system will have a power source that is battery and a solar panel will be
attached on the top of the robot. Moving the grass cutters with a standard motor powered
grass cutters is an inconvenience, and no one takes pleasure in it. Cutting grass cannot be
easily accomplished by elderly, younger, grass cutter moving with engine create noise
pollution due to the loud engine, and local air pollution due to the combustion in the
engine. Also, a motor powered engine requires periodic maintenance such as changing the
engine oil. Even though electric solar grass are environmentally friendly, they too can be
an inconvenience. Along with motor powered grass cutter, electric grass cutters are also
hazardous and cannot be easily used by all. Also, if the electric grass cutter is corded,
mowing could prove to be problematic and dangerous. The prototype will also be will be
charged from sun by using solar panels.

KEYWORDS:
Solar Power, Battery, Lawn, Mower, Dc Motor, Mowing, Emission

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CHAPTER NO.1
INTRODUCTION
Nowaday‟s pollution is a major issue for whole world. Pollution is manmade and can be seen
in own homes. In case Gas powered lawn mowers due to the emission of gases it is
responsible for pollution. Also the cost of fuel is increasing hence it is not efficient. So the
Solar powered grass cutters are introduced. Solar powered lawn mower can be described as
the application of solar energy to power an electric motor which in turn rotates a blade which
does the mowing of a lawn. But the cost of those grass cutters is high. But our automatic
grass cutter is consisting of rechargeable battery. This design is alternative for
environmentally hazardous gas powered grass cutter. Hydrogen powered lawn mower has
been operated without major interruption during the past fourteen years. The commercial
model was originally running on gasoline and was adapted to hydrogen by making small
adjustments to the carburettor and by installing a hydrogen reservoir containing solid-state
metal hydrides. During the evaluation period the only maintenance work was changing the
lubricating oil of the engine once a year, and reactivating the metal hydride powder by
external heating after an accidental inlet of air into the reservoir. And also it will be the
alternative for solar powered automatic grass cutter becauseits cost is more. So automatic
grass cutter using rechargeable battery is economically helpful for user. By using this
automatic grass cutter user can the cut the grass of the required area by giving input by using
keypad. Also the height of grass can be specified by adjusting the height of blades. The main
objective of this grass cutter is that the grass in the lawn must be mown with less effort. Also
to cut the grass of particular area as per user requirement.The sensors are the eyes of this
grass cutter.
The other objective is that the automatic grass cutter has to differentiate between grass
and concrete while monitoring its surroundings continuously. We wanted an ultrasonic sensor
to detect if the grass cutter was heading into an object. Safety is the main concern while
designing the grass cutter. As it has blades we wanted our grass cutter not to be in operating
mode if it was being held in the air by the user. Knowing that the user would be randomly
holding the grass cutter we needed a sensor to detect orientation. The accelerometer was
hence used in grass cutter so that it will not operate when user hold it. An automatic grass
cutter will relieve the consumer from mowing their own lawns and will reduce both
environmental and noise pollution.

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An automatic lawn cutter that will help the user to cut the grass in their lawn with less efforts.
The different sensors are used it will detect and avoid objects and humans while mowing. The
main objective of this automatic lawn cutter is that the user can specify the area that is to be
mown and also the height of grass as per there requirement by using the keypad. This design
contains a microcontroller like ATmega 328P, multiple sensors, Solar Panel, Battery,
Inverter, etc.
This project provides a design method of an automated lawn mower, whose task is to cut
grass whilst following a specified pattern with no need of user interaction. This task is
expected to be made possible by using sensors to provide a microcontroller with
measurement of distance. The device is expected to determine the path to follow, as shown in
Figure 23, calculate its position and stop upon completion of its tasks. The project aims to
produce a machine which would relieve people from a regular task of cutting grass in their
garden. Automated lawn mowers are presently available to the public, e.g. (Robomow, 1998),
but the low spread of these devices is mainly due to the cost which start at £918.13
(Mowermagic, 2011). The goal of this project is therefore to produce a similar device with
similar (if not better) performance, at a significantly lower cost. The present report will
provide an understanding the sensor selection process, an analysis of the microcontroller to
be used and the relevant functions it has to execute, a study of the relevant motors used and a
system overview. For this progress report some areas are incomplete.
1.1 Motivations-
Automated lawn mowers have been made available to the general public for over 30 years
(Georges 1999, p.195); its widespread or public use on the other hand has been limited
mainly due to the current costs of such devices. Existing technology sell at around £899 or
more (Lawn Mower Reviews, 2011) and considering the fact that the manual versions of
these devices, the standard lawn mowers, sell at around £86 (Lawn Mower Reviews, 2011)
although the cost of labour would need to be added to that of the equipment, the latter is still
a current viable and affordable option for most consumers. There are numerous real-world
benefits of having a machine that autonomously cuts grass, these include: Aid elderly users or
those with disabilities who are unable to fulfil this task themselves for users with a busy
schedule and rarely find time to mow, etc. It is a device that can fit into just about everyone's
lifestyle, therefore having a device that costs less, whilst accomplishing the same task as the

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higher end models is a great advantage in order to compete with the current market where the
end consumer will benefit from.
1.2 Objectives-
Existing automated lawn mowers each have a distinct working principle, for instance the
Robomow from Friendly Robotics (2011) requires the user to perform a onetime set up where
the garden perimeter is set. The perimeter is set using a battery powered wire that is laid
around the outer edges of the garden and any area where the robot is not to cover. Special
sensors inside Robomow enable the wires to be recognized and the robot is therefore kept
within the designated area. The robot travels on the garden in a systematic criss-cross pattern,
as shown in Figure 21, several times from side to side to ensure that the entire area is covered
and that the grass is cut from different angles (Friendly Robotics, 2011).

Fig. 1.1 - Robomow criss-cross cutting pattern
Other technologies work around a similar principal as the Robomow, in the sense that it
requires a perimeter wire to limit its cutting area. A difference between them may be added
features and the cutting pattern, for instance the Lawn Bott and the Husqvarna both have a
random operating principle (LawnBott 2011, p. 7 and 8), in the sense that they do not follow
any specific cutting pattern as illustrated in Figure2.

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Fig. 1.2 - LawnBott random cutting pattern
1.3 Existing Technology-
The operation method of the Robomow although effective, is to a certain degree inefficient
and contribute to a quite costly end product. The main advantages of their design include,
virtually any size or shape of garden can be specified, it is flexible and it can work without
requiring the user intervention at any stage, can operate at surface areas with slopes, these
points can also constitute a disadvantage. The system design has the following
disadvantageous aspects:
 The size and shape of the garden- as wires have to be placed in the garden area to be
covered by the robot; the cost of the entire system may be considerably higher
depending on the size. In the case of many plants being in the middle of the garden
area, the setup can become cumbersome.
 Damage or faults – the wires are set on the grass and although the company mentions
the fact that they would typically be covered by grass and become unnoticeable in a
matter of 2 to 3 weeks the wires are prone to damage. The damage can be from any
origin for example, pets can dig up and damage the wire, over time due to weather it
can wear off, amongst others.
 A fault on the wire can provide incorrect information to the device and as
consequence the device will not work as expected.Cutting pattern inefficiency – the
criss-cross pattern for Robomow and the random one used by LawnBott and
Husqvarna are all not very efficient due to the fact that it is required that the robot

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crosses the same location more than once, consequently more energy is dissipated and
the overall completion time is extended.
1.4 Design Method Considerations-
It is extrapolated from existing technology (section 2.1) that in order to achieve an end
product that is better than that currently available and at a lower cost, the overall design of the
system described in the present report would have to operate with the following
considerations: • The system would be required to be made such that it follows a certain path
and more efficient cutting pattern.
 A garden area limiting method that can be of long term, resistant life cycle and more
cost effective; that is a better solution than that of the guide wire.
 Good cutting methodology
 More cost effective sensor array arrangement that would enable for obstacle and
garden limit determination.
 Use of a two wheeled vehicle opposed to any other number would enable to the robot
to easily navigate around the track.
 Opposed of the robot relying on additional electronics set in the garden area; it should
be chosen that all electronics are on board and that the device is able to determine all
relevant parameters in this manner.

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CHAPTER NO.2
LITERATURE REVIEW
For designing of Automatic Grass cutter we referred various literature, papers etc. The review
of previous method used given below: In this lawn mower uses an solar based energy source,
which is easier to use, more advantageous comparing to other energy source especially for
gas based source of power .But our grass cutter is not based on solar because of its cost and
may create some complexity during working. So we avoided solar powered lawn mower.
In this hydrogen based lawn mower, the advantage of powering a lawn mower by hydrogen
rather than by gasoline is mainly ecological. We not used this for our grass cutter because it is
very old method and many overcome produced from this type grass cutter.
The self- powered design objective is to come up with a mower that is portable, durable, easy
to operate and maintain. It also aims to design a self-powered mower of electrical source; a
cordless electric lawn mower.
The heart of the machine is a battery-powered dc electric motor. It is also useful method for
our lawn mower. It is similar to our grass cutter using display and keypad.The present
technology commonly used for trimming the grass is by using the manually handle device. In
this project we have automated the machine for trimming the grass.
The device consists of linear blade which is operated with the help of the motor the power
supply for the motor is by using battery. The battery can be charge by using power supply
and solar panel. In case of any obstacles in the path it is sensed by using an IR sensor.

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CHAPTER NO.3
SYSTEM DEVELOPMENT

3.1 System block diagram-


Fig.3.1 Block diagram of system
In this proposed system we have used the atmega328 AVR microcontroller, four DC
motor and driver circuits. In this project the system is been totally operated by solar energy.
The main aim of solar based grass cutter is to cut the grass in which farmer take too much
hard working so we can reduce all that. In above block diagram there is one ultrasonic sensor
which we have used for obstacle sensing when obstacle is detected the robot is stop and vice
versa. Microcontroller continuously check the output of ultrasonic sensor and gives signal to
the motor driver circuit which drives the motors.
1. AVR (ATMEGA 328)-
1) The high-performance Atmel 8-bit AVR RISC-based microcontroller combines 32KB
ISP flash memory with read-while-write capabilities, 1KB EEPROM, 2KB SRAM, 23
general purpose I/O lines, 32 general purpose working registers, three flexible

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timer/counters with compare modes, internal and external interrupts,serial programmable
USART, a byte-oriented 2-wire serial interface, SPI serial port, 6-channel 10-bit A/D
converter (8-channels in TQFP and QFN/MLF packages), programmable watchdog timer
with internal oscillator, and five software selectable power saving modes. The device
operates between 1.8-5.5 volts.
2) By executing powerful instructions in a single clock cycle, the device achieves
throughputs approaching 1 MIPS per MHz, balancing power consumption and processing
speed.


Fig.3.2 Pin diagram of ATMEGA328
Key Parameters-
Parameter Value
Flash (Kbytes): 32 Kbytes
Pin Count: 28
Max. Operating Freq. (MHz): 20 MHz
CPU: 8-bit AVR
No. of Touch Channels: 16
Max I/O Pins: 23
Ext Interrupts: 24

Table No.1 Parameters of ATMEGA328

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2. BC547-

Fig.3.3 BC547 pin out

 The BC547 transistor is an NPN Epitaxial Silicon Transistor.
 The BC547 transistor is a general-purpose transistor in small plastic packages.
 It is used in general-purpose switching and amplification BC847/BC547 series 45 V,
100 mA NPN general-purpose transistors.
 Whenever base is high, then current starts flowing through base and emitter and after
that only current will pass from collector to emitter

3. LED-

Fig.3.4 LED

LEDs are semiconductor devices are made out of silicon. When current passes through the
LED, it emits photons as a byproduct. Normal light bulbs produce light by heating a metal
filament until its white hot. LEDs present many advantages over traditional light sources
including lower energy consumption, longer lifetime, improved robustness, smaller size and
faster switching

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4 .LM7805 (3 TERMINAL VOLTAGE REGULATER) -


Fig.3.5 Pin description of LM7805


Fig.3.6 LM7805

This is used to make the stable voltage of +5V for circuits. The LM7805 is three terminal
positive regulators are available in the TO-220 - package and with several fixed output
voltages, making them useful in a wide range of applications. Each type employs internal
current limiting, thermal shut down and safe operating area protection, making it essentially
indestructible. If adequate heat sinking is provided, they can deliver over 1A output current.
Although designed primarily as fixed voltage regulators, More information please refer Data
sheet 0f LM7805
5. Filter-
The output of the rectifier is pulsating DC and it is passed through filter so as to smoothening
the output waveform to approximately pure DC. The task of filtering is performed by a set of
capacitor. The resulting waveform looks the same as shown below, the ripple present in
output waveform is due to non-ideal behavior of the capacitor as it takes time to charge as

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well as discharge decided by the time constant of the circuit in which it is connected. The
constant is decided by the numerical values of the resistor and the capacitor i.e. T=RC sec.
However the ripple waveform looks like triangular wave with Vp 2 as the peak to peak
voltage ripple.

Fig.3.7 Voltage variation across capacitor
In the Fig.3 the capacitor output voltage waveform is indicating presence of ripple. The ripple
present in waveform can be suitably removed by proper selection of R and C values since
time constant purely depends on their numerical values. It can be concluded that ripple factor
is the function of frequency, resistance, and capacitance. To reduce the effect of ripple the
capacitance value must be increased but there too is limitation.

6. L298N-
This allows you to control the speed and direction of two DC motors, or control one bipolar
stepper motor with ease. The L298N H-bridge module can be used with motors that have a
voltage of between 5 and 35V DC.
There is also an onboard 5V regulator, so if your supply voltage is up to 12V you can also
source 5V from the board.

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Fig.3.7 L298N module

Module pin outs-
Consider the following image - match the numbers against the list below the image:

Fig.3.8 L298N module pin out

1. DC motor 1 "+" or stepper motor A+
2. DC motor 1 "-" or stepper motor A-
3. 12V jumper - remove this if using a supply voltage greater than 12V DC. This enables
power to the onboard 5V regulator
4. Connect your motor supply voltage here, maximum of 35V DC. Remove 12V jumper if
>12V DC
5. GND

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6. 5V output if 12V jumper in place, ideal for powering your Arduino (etc)
7. DC motor 1 enable jumper. Leave this in place when using a stepper motor. Connect to
PWM output for DC motor speed control.
8. IN1-Input
9. IN2-Input
10. IN3-Input
11. IN4-Input
12. DC motor 2 enable jumper. Leave this in place when using a stepper motor. Connect to
PWM output for DC motor speed control.
13. DC motor 2 "+" or stepper motor B+
14. DC motor 2 "-" or stepper motor B-
Controlling DC Motors-
To control one or two DC motors is quite easy. First connect each motor to the A and B
connections on the L298N module. If you're using two motors for a robot ensure that the
polarity of the motors is the same on both inputs. Otherwise you may need to swap them over
when you set both motors to forward and one goes backwards!
Next, connect your power supply - the positive to pin 4 on the module and negative/GND to
pin 5. If you supply is up to 12V you can leave in the 12V jumper (point 3 in the image
above) and 5V will be available from pin 6 on the module. This can be fed to your Arduino's
5V pin to power it from the motors' power supply. Don't forget to connect Arduino GND to
pin 5 on the module as well to complete the circuit.
Now you will need six digital output pins on your Arduino, two of which need to be PWM
(pulse-width modulation) pins. PWM pins are denoted by the tilde ("~") next to the pin
number, for example:

Finally, connect the Arduino digital output pins to the driver module. In our example we have
two DC motors, so digital pins D9, D8, D7 and D6 will be connected to pins IN1, IN2, IN3

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and IN4 respectively. Then connect D10 to module pin 7 (remove the jumper first) and D5 to
module pin 12 (again, remove the jumper).
The motor direction is controlled by sending a HIGH or LOW signal to the drive for each
motor (or channel). For example for motor one, a HIGH to IN1 and a LOW to IN2 will cause
it to turn in one direction, and a LOW and HIGH will cause it to turn in the other direction.
However the motors will not turn until a HIGH is set to the enable pin (7 for motor one, 12
for motor two). And they can be turned off with a LOW to the same pin(s). However if you
need to control the speed of the motors, the PWM signal from the digital pin connected to the
enable pin can take care of it.
Specifications
 Driver: L298N Dual H Bridge DC Motor Driver IC
 The terminal supply area of driven part Vs: +5 V ~ +35 V; such as the need to take power
within the board, the supply area Vs: 7V ~ 35V
 The peak current of driven part Io: 2A
 the terminal supply of area the logical part Vss: +5 V ~ +7 V (can take power within the
board +5 V)
 the operating current range of the logical part : 0 ~ 36mA
 control signal input voltage range:
 Low:-0.3V ≤ Vin ≤ 1.5V
 High: 2.3V ≤ Vin ≤ Vss
 enable signal input voltage range:
 Low: -0.3 ≤ Vin ≤ 1.5V (control signal is invalid)
 High: 2.3V ≤ Vin ≤ Vss (control signal active)
 Maximum power consumption: 20W (when the temperature T = 75 °C)
 Storage temperature: -25 °C ~ +130 °C
 Driver Board Size: 55mm * 49mm * 33mm (with fixed copper pillar and the heat sink
height)
 Driver Board Weight: 33g
 Other Extensions: control of direction indicators, the logic part of the plate to take power
interface.

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7. Solar panel:-

Fig.3.9 Solar Panel

Solar panel refers to a panel designed to absorb the sun's rays as a source of energy for
generating electricity or heating.
A photovoltaic (in short PV) module is a packaged, connected assembly of typically
6×10 solar cells. Solar PV panels constitute the solar array of a photovoltaic system that
generates and supplies solar electricity in commercial and residential applications. Each
module is rated by its DC output power under standard test conditions, and typically ranges
from 100 to 365 watts. The efficiency of a module determines the area of a module given the
same rated output – an 8% efficient 230 watt module will have twice the area of a 16%
efficient 230 watt module. There are a few solar panels available that are exceeding 19%
efficiency. A single solar module can produce only a limited amount of power; most
installations contain multiple modules. A photovoltaic system typically includes a panel or an
array of solar modules, a solar inverter, and sometimes a battery and/or solar tracker and
interconnection wiring.
8. DC Motor-
Almost every mechanical movement that we see around us is accomplished by an electric
motor. Electric machines are means of converting energy. Motors take electrical energy and
produce mechanical energy. Electric motor is used to power hundreds of devices we use in
everyday life. An example of small motor applications includes motors used in automobiles,
robot, hand power tools and food blenders. Micro-machines are electric machines with parts
the size of red blood cells and find many applications in medicine.

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Fig.3.10 DC Motor

Selecting the Right Motor
As part of the selection process for choosing the right DC motor, first learn about your exact
application and then consider several different characteristics and specifications ensure you
end up with the best product possible.
One characteristic of a 12v DC motor is the operating voltage. When a motor is powered by
batteries, low operating voltages are typically preferred since fewer cells are required to
obtain the specified voltage. However, at higher voltages, electronics to drive a motor are
typically more efficient. Although operation is possible with volts as low as 1.5 that goes up
to 100, the most common are the 6v DC motor, 12v DC motor, and 24v DC motor.
Other key specifications of a 12v DC motor can assist with include the operating current,
speed, torque, and power. Although a DC motor at this voltage is ideal for many applications,
the company will consider everything prior to making the final recommendation.
Specification:
Rat d To u : 60.00 mNm
To u Constant 26.0 mNm/A
Continuous Sta To u 78.0 mNm
Current at Rated Speed : 2.300 A
Length: 80mm
Torque: 1.5 kg.cm
Shaft Diameter: 6mm
Weight: 130.00g

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Features
 Dc motor has a big starting torque and excellent mobility and when comparing with
the same sized ac motor, the output is big and the efficiency is high.
 It is easy to control the speed and change the normal/ reverse rotation
 Comparing to AC motor , it is available to manufacture LV motor which can be
applied to portable machine which uses various spec., especially battery power (12V,
24V)
 Due to the wear of brush, there is a limit in the service life.
 Due to brush and commutator, noise generates when starting.

3.2 Electrical circuit of Wheat stone bridge
Project needed electrical circuit to charge the battery and to transmit power to motor, that all
done by capacitor, resistor diode etc. In this we have used Wheat stone bridge electrical
resistance system


Fig.3.11 Wheat stone bridge electrical resistance system
This is actual circuit diagram using in project
3.2.1 Function of wheat stone bridge circuit
For measuring accurately any electrical resistance Wheatstone bridge is widely used. There
are two known resistors, one variable resistor and one unknown resistor connected in bridge
form as shown below. By adjusting the variable resistor the current through the
Galvanometer is made zero. When the current through the galvanometer becomes zero, the
ratio of two known resistors is exactly equal to the ratio of adjusted value of variable

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resistance and the value of unknown resistance. In this way the value of unknown electrical
resistance can easily be measured by using a Wheatstone Bridge.

Fig.3.12 Circuit diagram of Wheastone Bridge
3.2.2 Wheatstone Bridge Theory
The general arrangement of Wheatstone bridge circuit is shown in the figure below. It is a
four arms bridge circuit where arm AB, BC, CD and AD are consisting of electrical
resistances P, Q, S and R respectively. Among these resistances P and Q are known fixed
electrical resistances and these two arms are referred as ratio arms. An accurate and sensitive
Galvanometer is connected between the terminals B and D through a switch S2. The voltage
source of this Wheatstone bridge is connected to the terminals A and C via a switch S1 as
shown. A variable resistor S is connected between point C and D. The potential at point D
can be varied by adjusting the value of variable resistor. Suppose current I1 and current I2
are flowing through the paths ABC and ADC respectively.
If we vary the electrical resistance value of arm CD the value of current I2 will also be
varied as the voltage across A and C is fixed. If we continue to adjust the variable resistance
one situation may come when voltage drop across the resistor S that is I2.S is becomes
exactly equal to voltage drop across resistor Q that is I1.Q.
Thus the potential at point B becomes equal to the potential at point D hence potential
difference between these two points is zero hence current through galvanometer is nil. Then
the deflection in the galvanometer is nil when the switch S2 is closed.

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3.3 Ultrasonic Sensor


Fig.3.13 Ultrasonic Sensor
This is a device which uses electrical energy to generate ultrasound waves, and which also
converts ultrasound vibrational energy into electrical signals. A barium titanate transducer
applying piezoelectric effect is normally used in ultrasound switches. The shape can be a disk
or a tube.
Ultrasonic sensors can detect movement of targets and measure the distance to them in
many automated factories and process plants. Sensors can have an on or off digital output for
detecting the movement of objects, or an analog output proportional to distance. They can
sense the edge of material as part of a web guiding system.
Ultrasonic sensors are widely used in cars as parking sensors to aid the driver in reversing
into parking spaces. They are being tested for a number of other automotive uses including
ultrasonic people detection and assisting in autonomous UAV navigation.
Because ultrasonic sensors use sound rather than light for detection, they work in applications
where photoelectric sensors may not. Ultrasonic are a great solution for clear object
detection, clear label detection and for liquid level measurement, applications that
photoelectric struggle with because of target translucence. As well, target color and/or
reflectivity do not affect ultrasonic sensors, which can operate reliably in high-glare
environments

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Passive ultrasonic sensors may be used to detect high-pressure gas or liquid leaks, or other
hazardous conditions that generate ultrasonic sound. In these devices, audio from the
transducer (microphone) is converted down to human hearing range.
High-power ultrasonic emitters are used in commercially available ultrasonic
cleaning devices. An ultrasonic transducer is affixed to a stainless steel pan which is filled
with a solvent (frequently water or isopropanol). An electrical square wave feeds the
transducer, creating sound in the solvent strong enough to cause cavitation.
Ultrasonic technology has been used for multiple cleaning purposes. One of which that is
gaining a decent amount of traction in the past decade is ultrasonic gun cleaning. Gun
cleaners based out of north NJ has been doing it for over 20 years with over two million guns
cleaned ultrasonically.

Fig.3.14 Working of Ultrasonic Sensor


3.3.1 Transmitted waves
Ultrasound waves that are emitted in the specified direction when the transducer is connected
to the oscillator. Normally expressed as a voltage applied to the transducer, or as a sound
pressure.

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3.3.2 Received waves
Transmitted ultrasound waves that are received at the transducer, and which are either direct
or reflected from an object. Normally expressed as a converted voltage, or as a sound
pressure

3.4 Circuit Diagram-


Fig.3.15 Circuit diagram of system

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Fig.3.16 Circuit diagram of inverter

The overall circuit with all the necessary equipment is laid down. This circuit is implemented
by making use of the transformer (220V/12V), Rectifier, Filter, Voltage regulator,
Comparator, Transistor and Relays.
The selection of equipment with proper rating is done by calculating their minimum and
maximum rating of voltage and current across them under normal as well as abnormal
operating conditions and proper care is taken in selection of the transformer as it is acting like
interface between the electrical and electronics circuit used. The protection of delicate ICs
must be ensured.

3.5 Design of Individual Module-
A] Power Supply-
Power is derived initially from standard 12V AC/DC adapter or 12V_500ma Transformer.
This is fed to bridge rectifier D1 ~ D4, the output of which is then filtered using 1000uf
electrolytic capacitor and fed to U2 (voltage regulator). U2 +5V output powers the PIC micro
controller. LED L10 and its associate 1K current limiting resistors provide power indication.
The unregulated voltage of approximately 12 V is required for relay driving circuit.

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Fig.3.17 Circuit diagram of power supply
Micro controller required 5V DC supply for operation, we used USB +5V Power from PC or
External +5V power supply via CN10. External Power and USB power cab be selectable via
J1. There is need 12V external Power supply for relay‟s and its driver circuits.
B] Power Supply Design
Filter Circuit-
Generally a rectifier is required to produce pure D.C. supply for using at various places in the
electronic circuit. However, the o/p of rectifier has pulsating character i.e. if such a D.C. is
applied to electronic circuit it will produce a hum i.e. it will contain A.C. and D.C.
components. The A.C. components are undesirable and must be kept away from the load. To
do so a filter circuit is used which removes (or filters out) the A.C. components reaching the
load. Obviously a filter circuit is installed between rectifier and voltage regulator. In our
project we use capacitor filter because of its low cost, small size and little weight and good
characteristic. Capacitors are connected in parallel to the rectifier o/p because it passes A.C.
but does not pass D.C. at all.

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Fig.3.18 Filter Circuit
Three terminal voltage regulators-
A voltage regulator is a circuit that supplies constant voltage regardless of change in load
current. IC voltage regulators are versatile and relatively cheaper. The 7800 series consists of
three terminal positive voltage regulators. These ICs are designed as fixed voltage regulator
and with adequate heat sink, can deliver o/p current in excess of 1A. These devices do not
require external component. This IC also has internal thermal overload protection and
internal short circuit and current limiting protection. For our project we use 7805 voltage
regulator IC.

Fig.3.19: 3-Terminal Voltage Regulator

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3.6 PCB Designing And Fabrication
3.6.1 PCB designing and fabrication
It is called PCB in short printed circuit pattern applied to one or both sides of an insulating
base, depending upon that, and it is called single sided PCB or double-sided PCB. Conductor
materials available are silver, brass, aluminum and copper; copper is most widely used which
is used here as well. The thickness of conducting material depends on the current carrying
capacity of the circuit.
The printed circuit board usually serves three functions:
1. It provides mechanical support to the components mounted on it.
2. It provides necessary electrical interconnection.
3. It acts as heat sink i.e., it provides a conduction path leading to removal of most of the
heat generated in the circuit.
 Cu clad
The base of laminate is either paper of glass fiber cloth. Cu foil, which is produced by the
method of electroplating, is placed on laminate and both are kept under hydraulic pressure for
proper adhesive pressure for proper adhesive. These Cu clad are easily available in the
market.
 Types of Laminates
National Electrical Manufactures Association (NEMA) has various grades of laminates that
are obtained by different resins and filters.
1. Phenol
Phenol and Formaldehyde produce phenolic paper base laminate it has phenolic resins with
proper filter. This is Brown in color and opaque. Disadvantage is poor moisture resistance.
2. Epoxy Laminates
Epoxy paper that is also paper based but impregnated with epoxy resin, yellowish white and
translucent.

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Epoxy Glass; this base material has high mechanical strength and good electrical properties
usually green in color and semitransparent.
There are a variety of laminates available. We have selected Fiber Glass epoxy laminate.
PCB fabrication includes following steps:
1) Layout of the circuit
2) Artwork designing
3) Printing
4) Etching
5) Drilling
6) Mounting of components and soldering
7) Finishing
 Layout
The layout of a PCB has to incorporate all the board before one can go onto the all work
preparation. Detailed circuit diagram, the design concept and the philosophy behind the
equipment are very important for the layout.
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 to prevent the entire
problem, which might be caused by redrawing of the layout to the artwork scale. The layout/
artwork scale commonly applied is 2:1 with a 1:1 scale, no demanding single sided boards
can be designed but sufficient care should be taken, particularly during the artwork
preparation.
 Procedure-The first rule is to replace each and every PCB layout as viewed from the
component side. This rule must be strictly followed to avoid confusion, which would
otherwise be caused.

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Another important rule is not to start the designing of a layout unless an absolutely clear
circuit diagram is available.
Among the components, the larger ones are placed first and the space in between is filled
with smaller ones. Components requiring input/output connecting come near the connector.
All components are placed in such a manner that de-soldering of other components is not
necessary if they have to be replaced.
 Layout sketch
The end product of the layout designing is the pencil sketched component and conductor
drawing which is caller „layout sketched‟. It contains all the information for the preparation
of the network.
 Component holes
In a given, PCB most all the holes required are one particular diameter. Holes of a different
are shown with a code in the actual layout sketch.
 Conductor Holes
A code can be used for the conductor with a special width. Minimum spacing should also be
provided.
A) Holes B) Conductor Widths
Standard holes Standard width, 0.5 mm
1.1 mm 1 mm
1.5 mm 2 mm
3.2 mm 4 mm
Table No.2- Standard holes and conductor width

 Artwork
The generation of PCB artwork should be considered as the first step of the PCB
manufacturing process. The importance of a prefect artwork should not be under estimated.

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Problems like inaccurate registered, broken annular rings or too critical spacing are often due
to bad artwork. And even with the most sophisticated PCB production facilities, PCB can be
made better than the quality of the artwork used.
 Basic Approaches
For ink drawing on white cardboard paper, good quality Indian ink and ink-pen set are
minimum requirements. Drawing practice-drawing procedure is very at-least by 0.1 – 0.2,
and solder pad locations. And conductors can be easily displaced by 0.3 – 0.5 mm
 Screen Printing
The process of screening – printing is well known to the printing industry because of its
inherent capabilities of printing a wide range of inks on almost any kind of surface including
glass, metal, plastic fabrics etc.
Found their way into an extremely broad field of applications.
Screen-printing offers the advantage of wide control on the ink deposition, thickness though
the selection of suitable mass density and composition. In the production of PCB‟s, it is
successfully employed in printing of
 Etch resists
 Plate resists
 Solder stop lacquers
 Notation printing
In its basic form, the screen-printing process is very simple. A screen fabric with uniform
meshes and opening is stretched and fixed on a solid frame of metal or wood. The circuit
pattern area open, while the meshes in the rest of the area is closed.
In the actual printing step, ink is forced by the moving squeeze thorough the open meshes
onto the surface of the material to be printed. The ink deposition, in a magnified cross
section, shows the shape of a trapezoid.

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3.7.2 Pattern transfer onto the Screen
There are two different methods in use, and each method has its own advantages and
disadvantages.
1) With the direct method, the screen is prepared by coating a photographic emulsion
directly onto the screen fabric and exposing it in the pattern area. The indirect method
makes use of a separate screen process film, supported on a backing sheet. The film on its
backing sheet that is there after pressed onto the screen fabric and sticks there. Finally,
the backing sheet is peeled off, opening all those screen meshes, which are not covered by
the film pattern.
2) The direct method provides very durable screen stencils with a higher dimensional
accuracy but the finest details are not reproduced. The indirect method is more suitable
for smaller series and where the finest details to be reproduced. The indirect method is
faster but dimensionally less accurate and the screen stencils are less durable, more
sensitive to mechanical damages and interruption in printing.
 Etching
In all subtractive PCB process, etching is one of the most important steps. The final copper
pattern is formed by selective removal of all the unwanted copper, which is not protected by
an etching unit.
Solutions, which are used in etching process, are known as enchants.
I) Ferric Chloride
II) Cupric Chloride
III) Chromic Acid
IV) Alkaline Ammonia.
Of these Ferric Chloride is widely used because it has short etching time and it can be stored
for a long time. Etching of PCBs as required in modern electronic equipment production, is
usually done in spray type etching machines.

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Tank or bubble etching, in which the boards kept in tank, were lowered and fully immersed
into the agitated, has almost disappeared.
 Component Mounting
Careful mounting of components on PCB increases the reliability of assembly.
1) The leads must be cleaned before they are inserted in PCB holes. Asymmetric lead
bending must be avoided; the ENT leads must fit into holes properly so that they can be
soldered.
2) When space is to be saved then vertical mounting is to be preferred. The vertical leads
must have an insulating sleeve.
3) Where jumper wire crosses over conductors, they must be insulated.
4) For mounting of PCBs, TO5, DIP packages special jigs must be used of easy insertion.
5) While mounting transistors, each lead must insulating sleeve. All the flat radial
components such as resistors, diodes and inductors are mounted and soldered. Then IC
bases are soldered. The vertical components such as transistors, gang condenser and FET
are mounted & soldered.
 Soldering
The next process after the component mounting is soldering; solder pint is achieved by
heating the solder and base metal about the melting point of the solders used.
The necessary heat depends upon
1) The nature and type of joints
2) Melting temperature of solder
3) Flux
Soldering techniques are of so many types but we are using iron soldering.
 Iron soldering
Soldering iron consists of an insulating handle connected through a metal shaft, os a bit
accurately makes contact with the component parts of the joint and solder and heats them
up. The electrical heating element is located in the hollow shank or handle to heat the bit.

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3.7.3 Functions of the Bit
It stored heat and convey it from the heat source to the work. It may be required to store
surplus solder from the joint. It may be required to store molten solder and flux to the work.
The surface must be lined and wetted; this encourages flow of solder into the joint. When the
surface of the work becomes tested by the solder, a continuous flow of liquid metal between
the bit and the work provides a path of high thermal conductivity through which heat can
flow into the work piece.
Solder bit are made up of copper; this metal has good wetting properly, heat capability and
thermal conductivity. Tin-lead solder affects copper during soldering operation. Production of
copper bit can be made with thick iron coating followed by Ni/Tin plating. The life of the bit
is increased by a factor of 10 to 15. Solder irons are specified in terms of wattage. Depending
on heat input intended for working and types of work (continuous or individual) the choice of
the solder iron can be made.
3.7.4 Procedure of Soldering
The points to be joined must be cleaned first and fluxed. The hard solder iron and solder wire
is applied to the work. The melted solder becomes bright and fluid. The iron must be
removed after sufficient time and joint is allowed to coal. At the end, finishing is done.
3.7.5 PCB designing using computer aided designing (CAD):
CAD has many advantages over manual designing, important among them is:
1) Changes can be easily made because we don‟t have to erase our pencil work on paper
repeatedly.
2) Time is saved.
3) Before taking printout we can have preview of the design etc.

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3.7 Development Board
A] AT Mega 328

Fig. 3.20 AT Mega328 Development Board Layout

B] Power Supply Layout-

Fig. 3.21 Power supply layout

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CHAPTER NO.4
PERFORMANCE ANALYSIS

4.1 FLOWCHART









No


Yes









Fig. 4.1 System flow chart
Program execution starts with initializing all the memory location and pointers. All the sensor
modules are initialized. Commands are checked for grass cutter or sprinkler. If sprinkler is
Start
Check
Obstacle
Rotate the motors forward and
start cutting
Stop the robot and stop cutting
wait to avoid the obstacle
Initialize the systems and sensors
End

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selected, sprinkler motor is started, if grass cutter action is selected grass cutter blade starts
functioning. Both grass cutter and water sprinkler can also be used at a time.
Under auto or manual selection condition selection, for auto made object detection signals are
monitored from the sensor units and commands are executed as per the program. For manual
mode commands are accepted from the external Bluetooth control module.

4.2 Program of microcontroller-

/* HC-SR04 Sensor
https://www.dealextreme.com/p/hc-sr04-ultrasonic-sensor-distance-measuring-module-
133696

This sketch reads a HC-SR04 ultrasonic rangefinder and returns the
distance to the closest object in range. To do this, it sends a pulse
to the sensor to initiate a reading, then listens for a pulse
to return. The length of the returning pulse is proportional to
the distance of the object from the sensor.

The circuit:
* VCC connection of the sensor attached to +5V
* GND connection of the sensor attached to ground
* TRIG connection of the sensor attached to digital pin 2
* ECHO connection of the sensor attached to digital pin 4
Original code for Ping))) example was created by David A. Mellis
Adapted for HC-SR04 by Tautvidas Sipavicius
This example code is in the public domain.
*/

const int trigPin = 2;
const int echoPin = 4;
const int motor1_1 = 5; // the number of the pushbutton pin
const int motor1_2 = 6;
const int motor2_1 = 7; // the number of the pushbutton pin

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const int motor2_2 = 8;
const int cuttm1 = 9; // the number of the pushbutton pin
const int cuttm2 = 10;

void setup() {
// initialize serial communication:
Serial.begin(9600);
pinMode(motor1_1, OUTPUT);
pinMode(motor1_2, OUTPUT);
pinMode(motor2_1, OUTPUT);
pinMode(motor2_2, OUTPUT);
pinMode(cuttm1, OUTPUT);
pinMode(cuttm2, OUTPUT);
}

void loop()
{

// establish variables for duration of the ping,
// and the distance result in inches and centimeters:
long duration, inches, cm;

// The sensor is triggered by a HIGH pulse of 10 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:

pinMode(trigPin, OUTPUT);
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);

// Read the signal from the sensor: a HIGH pulse whose
// duration is the time (in microseconds) from the sending

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// of the ping to the reception of its echo off of an object.
pinMode(echoPin, INPUT);
duration = pulseIn(echoPin, HIGH);

// convert the time into a distance
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);

Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
delay(100);
if(cm<60)
{
digitalWrite(motor1_1, LOW);
digitalWrite(motor1_2, LOW);
digitalWrite(motor2_1, LOW);
digitalWrite(motor2_2, LOW); /////stop
digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(1000);
digitalWrite(motor1_1, HIGH);
digitalWrite(motor1_2, LOW);
digitalWrite(motor2_1, HIGH);
digitalWrite(motor2_2, LOW); /////back
digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(3000);
digitalWrite(motor1_1, HIGH);
digitalWrite(motor1_2, LOW);
digitalWrite(motor2_1, LOW);
digitalWrite(motor2_2, HIGH); /////turn

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digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(7000);
digitalWrite(motor1_1, LOW);
digitalWrite(motor1_2, HIGH);
digitalWrite(motor2_1, LOW);
digitalWrite(motor2_2, HIGH); /////stright
digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(5000);
digitalWrite(motor1_1, LOW);
digitalWrite(motor1_2, HIGH);
digitalWrite(motor2_1, HIGH);
digitalWrite(motor2_2, LOW); /////turn
digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(7000);
digitalWrite(motor1_1, LOW);
digitalWrite(motor1_2, HIGH);
digitalWrite(motor2_1, LOW);
digitalWrite(motor2_2, HIGH); /////straight
digitalWrite(cuttm1, LOW);
digitalWrite(cuttm2, LOW);
delay(1000);

}
else
{
digitalWrite(motor1_1, LOW);
digitalWrite(motor1_2, HIGH);
digitalWrite(motor2_1, LOW);
digitalWrite(motor2_2, HIGH);
digitalWrite(cuttm1, HIGH);
digitalWrite(cuttm2, HIGH);

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delay(1000);
}
}

long microsecondsToInches(long microseconds)
{
// According to Parallax's datasheet for the PING))), there are
// 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
// second). This gives the distance travelled by the ping, outbound
// and return, so we divide by 2 to get the distance of the obstacle.
// See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
// The speed of sound is 340 m/s or 29 microseconds per centimeter.
// The ping travels out and back, so to find the distance of the
// object we take half of the distance travelled.
return microseconds / 29 / 2;
}

4.3 Design with Analysis of the system
4.3.1 Design of Step down Transformer
The following information must be available to the designer before he commences for the
design of transformer.
1) Power Output.
2) Operating Voltage.
3) Frequency Range.
4)Efficiency and Regulation.

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Size of core
Size of core is one of the first considerations in regard of weight and volume of transformer.
This depends on type of core and winding configuration used. Generally following formula is
used to find area or size of core.
Ai =
P1/0.87

Ai = Area of cross - section in Sq. cm. and

P1= Primary voltage.
In transformer P
1
= P
2
The project requires +5V regulated output. So transformer secondary rating is 12V, 500mA.
So secondary power wattage is,
P2 = 12 x 500 x 10
-3
w.
= 6w

So Ai = 6/0.87
= 2.62
Generally 10% of area should be added to core to accommodate all turns for low Iron losses
and compact size.
So, Ai = 2.88.
Turns per volt
Turns per volt of transformer are given by relation
Turns / Volt = 10000/4.44 f Bm Ai
Here, F is the frequency in Hz

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Bm is flux density in Wb/m
2

Ai is net area of cross section.
Following table gives the value of turns per volt for 50 Hz frequency.
Flux density Wb/m
2

1.14 1.01 0.91 0.83 0.76
Turns per volt 40/Ai 45/Ai 50/Ai 55/Ai 60/Ai
Table No. 1- Value of turns per volt for 50 Hz frequency

Generally lower the flux density better be quality of transformer. For project for 50 H
z
the
turns per Volt for 0.91 Wb/m
2
from above table.
Turns per Volt = 50 / Ai
=50/2.88
 17
Thus for Primary winding = 220 x 17 = 3800.
& for Secondary winding = 12 x 17= 204.
Wire size
As stated above size depends upon the current to be carried out by the winding, which
depends upon current density of 3.1 A/mm
2
. For less copper losses 1.6 A/mm
2
or 2.4 A/mm
2

may be used. Generally even size gauge of wire are used.
4.3.2 Rectifier Design
R.M.S. Secondary voltage at secondary of transformer is 12V.
So maximum voltage Vm across Secondary is
= Rms. Voltage x 2
= 12 x 2
= 16.97

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D.C. O/p Voltage at rectifier O/p is 2 Vm
Vdc = 2Vm/ 
= 2 x 16.97/ 
= 10.80 V
PIV rating of each diode is,
PIV = 2 Vm.
= 2 x 16.97
= 34 V
Maximum forward current which flow from each diode is 500mA. So from above parameter
we select diode IN 4007 from diode selection manual.
4.3.3 Design of Filter Capacitor
Formula for calculating filter capacitor is,
C= 1/43 r f RL.
r = ripple present at o/p of rectifier. (This is maximum 0.1 for full wave rectifier.)
F = frequency of mains A.C.
RL = I/p impedance of voltage regulator IC.
C=1/43 x 0.1 x 50 x 28
= 1030 f
 1000 f

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Voltage rating of filter capacitor is double of Vdc i.e. rectifier o/p which is 20V. So we
choose 1000 f / 25V filter capacitor.
IC7805 (Voltage Regulator IC)
Specifications:
Available o/p D.C. Voltage = + 5V.
Line Regulation = 0.03
Load Regulation = 0.5
Vin maximum = 35 V
Ripple Rejection= 66-80 (dB)
4.3.4 Selection For Current Limiting Resistance For Led-

Fig.4.2 - Current limiting resistance
The output of microcontroller is equal to supply voltage i.e. +5V DC. If directly connected
LED to micro controller then very high current flowing through it because internal resistance
of LED is very small about 5 to 8 ohm so it is possibility to damage LED so we place current
limiting resistance R in series with diode the value of this resistance is calculated.
From ohms low

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V = R I
Where , I= If safe forward current flowing through LED which normal intensity glow and
this value near about 8 to 10 mA
5 = Rx 8mA
R = 625 
So we select near about value 680.
Limiting current into an LED is very important. An LED behaves very differently to a
resistor in circuit. Resistors behave linearly according to Ohm's law: V = IR. For example,
increase the voltage across a resistor, the current will increase proportionally, as long as the
resistor's value stays the same. Simple enough. LEDs do not behave in this way. They behave
as a diode with a characteristic I-V curve that is different than a resistor.
he voltage versus current characteristics of an LED are similar to any diode. Current is
approximately an exponential function of voltage according to the Shockley diode equation,
and a small voltage change may result in a large change in current. If the voltage is below or
equal to the threshold no current flows and the result is an unlit LED. If the voltage is too
high the current exceeds the maximum rating, overheating and potentially destroying the
LED.
As an LED heats up, its voltage drop decreases (band gap decrease). This can encourage the
current to increase.
It is therefore important that the power source provides an appropriate current. LEDs should
only be connected to constant-current sources. Series resistors are a simple way to passively
stabilize the LED current. An active constant current regulator is commonly used for high
power LEDs, stabilizing light output over a wide range of input voltages which might
increase the useful life of batteries. Low drop-out (LDO) constant current regulators also
allow the total LED voltage to be a higher fraction of the power supply voltage. Switched-
mode power supplies are used in some LED flashlights and household LED lamps.

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CHAPTER NO. 5
CONCLUSION
5.1 Conclusion
This project provides a design method of an automated grass cutter operated on solar power,
whose task is to cut grass with no need of user interaction. This task is expected to be made
possible by using sensors to provide an Arduino with controlling.
The obstacle is automatically avoided, here for obstacle avoidance the ultrasonic sensor is
used. The system also provides power backup by using inverter. The proposed system will be
cost efficient with higher reliability.

5.2 Advantages-
1. The use of solar power saves the non-renewable energy
2. No need of human interface
3. Obstacle is automatically avoided 4. Non skilled person can also operate.
5. It is pollution free.
6. No required any external supply.
7. It is economical.
8. Compact in size and portable.
9. No any fuel cost.
10. Easy to move from one place to another place.
11. Freedom from long extension wires.
5.3 Application
1. In agriculture
2. In gardens
3. Big lawns 4. For a garden.
5. For hospital.
6. For collages.

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7. For small farms.
8. For nurseries.
9. Playground like, cricket ground, football ground etc.

5.4 FUTURE SCOPE

We completed our project successfully with the available sources. But the results
and modifications are not up to the expectations. This can be further improved by
incorporating the following modifications to obtain better results. The mechanism
which we used i.e. scotch yoke mechanism does not given excepted efficiency. This
efficiency can be increased by using some other mechanism. and speed of motor is
reduce because we have used heavy material and this material can be replaced by
using light weight material .and design of blades should be done based on types of
grass is used to cut. The project which we have done surly reaches the average
families because the grass can be trimmed with minimum cost and with minimum
time Finally this project may give an inspiration to the people who can modify and
can obtain better results

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