WEATHER STATION RECEIVER

Project report submitted in partial fulfillment of the requirements

for the award of the degree of

BACHELOR OF TECHNOLOGY

In

ELECTRICAL AND ELECTRONICS ENGINEERING

By

P. Jenyu Latha (09241A0215)

K. Navya (09241A0220)

C. Pratheeka (09241A0227)

Nibil Stephen (09241A0248)

Under the guidance of

G.SANDHYA RANI

(Asst. Professor)

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY

Hyderabad, Andhra Pradesh

2009-2013

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING &

TECHNOLOGY BACHUPALLY, HYDERABAD

DEPARTMENT OF ELECTRICAL ENGINEERING

CERTIFICATE

This is to certify that the Project entitled Weather Station Receiver, submitted by

P.Jenyu Latha, K.Navya, C.Pratheeka, Nibil Stephen in partial fulfillment of the

requirements for the award of Bachelor of Technology in Electrical and Electronics

Engineering during session 2013 at Gokaraju Rangaraju Institute of Engineering & Technology,

Hyderabad. A bonafide record of research work carried out by her under my supervision and

guidance. The candidate has fulfilled all the prescribed requirements. The Project which is based

on candidates own work, has not submitted elsewhere for a degree/diploma. In my opinion, the

Project is of standard required for the award of a Bachelor of technology degree in Electrical and

Electronics Engineering.

Internal Guide:

P.M.Sharma G.Sandhya Rani

HOD, EEE Assistant Professor

GRIET External Examiner GRIET, EEE

ACKNOWLEDGEMENTS

On the submission of my Project report of Weather Station Receiver, I would like

to extend my gratitude & my sincere thanks to my supervisor G.Sandhya Rani, Asst. Professor,

Department of Electrical Engineering for her constant motivation and support during the course

of my work in the last semester. I truly appreciate and value her esteemed guidance and

encouragement from the beginning to the end of this thesis. Her knowledge and company at the

time of crisis would be remembered lifelong.

I am very thankful to Prof. P.M.Sharma (H.O.D) for his valuable suggestions and

comments during this project period.

Special thanks to P.S.Raju (Director) for providing simulation laboratory to do

simulation work and his encouragement during my project work.

Last but not least I would like to thank my parents, who taught me the value of hard work

by their own example. I would like to share this moment of happiness with my father and

mother. They rendered me enormous support during the whole tenure of my stay in GRIET.

P.JENYU LATHA (09241A0215)

K.NAVYA (09241A0220)

C.PRATEEKA (09241A0227)

NIBIL STEPHEN (09241A0248)

ABSTRACT

The incredible popularity of home weather stations shows that its not just farmers who

are interested in the weather. Many people want to be able to track and record weather events

within their local environment rather than relying on a state or national weather service that may

not have adequate local details.

Our project is to sense and display the external weather conditions using arduino. The

external weather condition may be temperature, humidity, atmospheric pressure, rainfall, wind

speed. The sensed weather is transmitted to arduino kit. The program written in arduino software

is interfaced with arduino kit and the weather report is displayed on the display unit. Generally,

the external sensors are connected together with cables, with one sensor acting as a transmitter to

send updates wirelessly to the display unit.

Arduino is a fusion of three critical elements: hardware, software, and community.

Arduino contains a receiver module so we dont even need the display unit at all and gain far

more control over the data. Many weather station sensors are available individually, also gaining

the flexibility of managing the data through an Arduino.

i

CONTENTS

Abstract

Contents i

CHAPTER 1

INTRODUCTION

1.1 Introduction 1

1.1.1 History 1

1.1.2 Present day monitoring techniques 2

1.2 Motivation of work 3

1.2.1 Applications for Weather Station 3

1.3 Literature overview 7

CHAPTER 2

WEATHER STATION RECEIVER AND ARDUINO

2.1Weather Station Receiver 8

2.1.1 Block Diagram 8

2.1.2 Explanation 9

2.2 Arduino 10

2.2.1 Hardware 10

2.2.2 Software 11

2.2.3 Pin Description 14

ii

CHAPTER 3

SENSORS

3.1 Humidity

3.1.1 Relative humidity 15

3.1.2 Humidity Measurement 15

3.1.3 Humidity sensing-Classification and principles 16

3.1.3(a) Sensing based on capacitive effect 16

3.1.3(b) Sensing based on resistive effect 17

3.1.4 Humidity Sensor-HTF3223 20

3.2 Temperature

3.2.1 Temperature Measurement 21

3.2.2 Temperature Sensor-LM35 24

3.3 Atmospheric Pressure 24

3.3.1 Pressure Measurement 25

3.3.2 Pressure Sensor-MP3V5050 25

3.4 Wind Speed

3.4.1 Anemometer 26

3.4.2 Wind Speed Measurement 27

CHAPTER 4

SIMULATION RESULTS

4.1 Simulation Results of Temperature

4.1(a) Program 28

4.1(b) Graph 29

iii

4.2 Simulation Results of Pressure

4.2(a) Program 30

4.2(b) Graph 31

4.3 Simulation Results of Wind speed

4.3(a) Program 32

4.3(b) Graph 33

4.4 Simulation Results of Humidity

4.4(a) Program 34

4.4(b) Graph 35

4.5 Simulation results of Weather Station Receiver

4.5(a) Program 36

4.5(b) Graph 37

CHAPTER 5

CONCLUSION AND FUTURE SCOPE

5.1 Conclusion 39

5.2 Future Scope 39

References 40

Appendix 41

CHAPTER 1

Introduction

1

1.1 INTRODUCTION

Weather forecasting is the application of science and technology to predict the state of the

atmosphere for a given location. Human beings have attempted to predict the weather informally

for millennia, and formally since the nineteenth century. Weather forecasts are made by

collecting quantitative data about the current state of the atmosphere on a given place and using

scientific understanding of atmospheric processes to project how the atmosphere will evolve on

that place.

Most internet based weather services get their information from publicly available sites

that are maintained by the government, or by private weather networks. Some apply forecasting

algorithms to adjust that data for regional variations but in most cases the data is only accurate at

the location of the measurement system.

Geological formations, large buildings, the proximity of a large body of water can

dramatically change the air temperature, humidity and wind patterns within a very short distance.

For real accuracy and reliable planning, Weather Station Receiver offers site specific weather

data, in real-time at a cost effective price.

Weather Station Receiver's ease of installation, low maintenance requirements, automatic

data storage, data management, and internet compatibility make it a cost effective choice for

industrial concerns, or municipalities,agriculture and ranching concerns that require real-time,

location specific weather information.

1.1.1 History

Sensing the winds and weather has been important to man over the centuries. Athenians

built the eight sided Tower of the Winds in the first century B.C. in honor of the eight gods of the

winds. The Tower of the Winds stands to this day in the ancient agora, or market, in Athens.

Many significant weather events have affected mankind over the years. Since much of

history is a recollection of a series of wars and battles, it is interesting to note that a well known

early reference to the importance of the weather is from the Chinese philosopher Sun Tsu, who

said, Know yourself and know your enemy, and victory is guaranteed. Know the terrain and

know the weather, and you will have total victory.

2

Much later in history, we know that Napoleons invasion of Russia in 1812 was stymied

when snow and cold weather came earlier in the season than he and his generals had planned.

This, combined with Russian militia attacks, helped defeat the French, who invaded with 50,000

troops, and left with only 20,000 survivors. One hundred thirty years later, this was repeated

when Hitlers invasion of the Soviet Union was again foiled in part by brutally cold winter

weather.

In the 20th century, large population migrations were brought about by adverse weather

conditions, including those of the Dust Bowl in the United States during the 1930s, multiple

Asian droughts throughout the century, and three significant periods of drought in the sahel

region of Africa. Individual events that killed and affected many people include the great smog

event in London in 1952, which killed 4,000 people in five days in December, hurricane impacts

on the coasts of the United States, from Galveston in 1900 to Katrina, Rita and Wilma last year,

and several notable blizzards.

Mans affect upon the environment has also been seen in the weather, in more recent

events, when the release of radioactive particles from the reactor accident at Chernobyl, Ukraine,

was detected by sensors outside of the Soviet Union, and traced back to Chernobyl using

sophisticated weather sensors and meteorological models. In a similar fashion, local weather

instruments were used to help estimate the impact of smoke and soot from oil well fires set

during the 1991 Gulf War.

1.1.2 Present day monitoring techniques

Today, the winds and other weather variables are of equal concern and can have an even

greater impact on our modern, high-tech life style. Weather affects a wide range of mans

activities, including agriculture, transportation and leisure time. Often the affects involve the

movement of gases and particulates through the atmosphere.

Modern weather monitoring systems and networks are designed to make the

measurements necessary to track these movements in a cost effective manner. This requires that

the total life-cycle cost of a monitoring system is minimized, and one way to do this is to

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minimize or eliminate the maintenance of the weather monitoring system. Using a solid-state

system to measure the weather, including the wind speed and direction, is paramount to

minimize equipment servicing and costs.

1.2 MOTIVATION OF WORK:

Weather reports are usually about major cities which covers a large area which is why it

may not provide the weather condition for a specific area. It is not possible to determine the

weather in a specified area. Home weather stations can be of great help in such situations. These

stations can provide you with the outdoor weather conditions that you need right at the comforts

of your homes. There are various types of weather stations available depending on what type of

design or information you would want to get from the station. They are used in many areas for

various purposes.

1.2.1 Applications of Weather Stations

Weather stations are used in a variety of commercial, industrial, governmental, and

military applications. They provide real-time, often critical, on-the-spot weather information for

users. The following weather station guide identifies a sampling of those applications:

Various areas where Weather Station Receivers are used

1. Agricultural sector

2. Industries

3. Educational institutions

4. Mining projects

5. Aviation

6. Construction

7. Firefighting

8. Transportation

9. Military

4

1.2.1 Agricultural Sector

Today's farms are efficient, high-tech businesses managed by educated professionals,

success depends largely on meeting the challenges of the weather. From the 200-acre family

dairy operation to the multi-section corporate farm modern agriculture demands precise real-time

weather data.

Most Internet-based weather services get their information from government or private

weather networks. Some attempt to adjust the data for regional variations, but the data is usually

accurate only where the measurements took place. Local terrain, soil, buildings, bodies of water

and other variables can dramatically influence air temperature, humidity and wind patterns. The

data you get on the Internet may be a poor representation of conditions in your locality.

A Weather Station Receiver on your farm gives site-specific weather data, in real time, at

a cost-effective pricedata you can count on when you're making critical management

decisions.

Examples of agricultural applications for the Weather Station Receiver include:

i. Spraying Operations

A portable Weather Station Receiver can be set up on site in minutes to better predict the

potential for over spray from wind drift.

ii. Crop Management

A Weather Station Receiver helps a farm manager know when conditions are appropriate

to seed, fertilize, apply herbicides, or harvest.

iii.Hay Production

A Weather Station Receiver can tell you when conditions are optimal for cutting and

properly curing hay prior to baling, and when rainfall threatens to cause mold.

iv.Forestry

Several Weather Station Receiver , with longitudinal recordation of weather data, can

assess the suitability of sites for planting particular species of trees and point to optimal planting

5

times.Track rainfall, heat, and humidity to help access forest fire danger. Monitor conditions for

and during a proscribed burn.

v.Livestock

Herd protection procedures can be instituted when temperatures reach pre-set values.

Young stock can be moved to protect them from weather stress. Rainfall sensors can tell farm

managers when range herds may not have access to adequate water.

vi.Vineyards and Orchards

When frost can mean the difference between a good year and a disaster, your Weather

Station Receiver's alarm feature can tell you when temperature and dew point are at critical

values.

For those applications that require sensors for soil moisture, leaf wetness, soil

temperature, etc., to supplement your weather data, a Weather Station Receiver system is

efficient.

1.2.2 Industries

Examples of industrial/municipal applications for a small, automatic weather station include:

i. External environment sensor set for large facilities' energy management systems.

ii. The Weather Hawk can be the first link in an early-warning system about facility status, when

conditions become extreme and physical plant staff must take action.

1.2.3 Educational Institutions

School weather stations are a wonderful tool that can enhance earth science and

geography classes, helping students improve their achievement in science and math, and in the

use of computer and network technology.

1.2.4 Mining Projects

In mining projects precise data for climate and hydrology is essential in EIA-process and

also extremely valuable for flight operation, construction and much more. The information is

6

necessary in the required environmental impact assessments, in tailing management, water

management and as basis for engineering design criterias.

1.2.5 Aviation

For many locations, weather at the nearest ASOS-equipped airport can be significantly

different than the weather at a smaller airport nearby. For the safety of pilots and passengers

using these smaller airfields it's important to have up-to-date weather data. Even at airports with

an automated weather station, air show coordinators often use weather stations to give their

participants instant information on winds, altimeter, temperature, and other vital data. They can

also be used as an emergency backup for the permanent weather station.

1.2.6 Construction

High winds and other adverse weather conditions are of major concern to the

construction industry. Workers on bridge and high rise building projects are especially

vulnerable to the adverse affects these weather conditions may cause. Under certain conditions,

the projects themselves could be affected. Keeping a close eye on the weather with an industrial

weather station is a must.

1.2.7 Firefighting

Fighting wildfires is a dangerous business and weather conditions (such as shifting

winds) has caused many accidents and deaths during operations. A meteorological weather

station (such as the Davis Vantage Pro2) can be deployed to help reduce those hazards, providing

immediate weather information to incident commanders and firefighters in the field. Besides

helping to keep them out of harm way when fire characteristics change, the information is critical

to decisions concerning public evacuations. Weather station data can also be used to support air

operations and in estimating coverage of the water and chemicals they release.

1.2.8 Transportation

For public transportation organizations, industrial weather stations can be used to

monitor conditions that may affect operations and traveler safety, such as freezing rain, heavy

rain, or high winds. They can also help to monitor severe weather events as they occur.

7

1.2.9 Military

Portable weather stations are an important resource used for battlefield operations,

nuclear-biological-chemical (NBC) threats, tactical air operations, artillery support, and more.

1.3 LITERATURE OVERVIEW:

The fully integrated Weather Station Receiver unit monitors weather conditions

including, indoor and outdoor temperature, humidity, barometric pressure and wind speed. This

model also interprets the localised data to give forecasts, graphs and more.

The different sensors used to measure the above parameters are given as input to the

arduino. Arduino is software where the outputs are obtained by writing program. This

programming in arduino is used to display the graphs in Megunolink software.

CHAPTER 2

Weather Station Receiver and

Arduino

8

2.1 Weather Station Receiver

In this chapter a detailed description of the circuit and information regarding arduino

is provided.

2.1 .1BLOCK DIAGRAM

Fig2.1

2.1.2 Explanation

The parameters we are going to measure are Temperature, Pressure, Wind Speed, Relative

Humidity. We are using sensors for each parameter:

1. LM35 Temperature

2. MP3V5050 -Pressure

3. HTF3223 Relative Humidity

4. Anemometer Wind Speed

9

Detailed information of each sensor is discussed in next chapter.

Sensors given above requires D.C. supply, for that purpose we designed a 5v power

circuit.LM35, HTF3223 requires 5v. Pressure sensor requires 3v supply, so we used a

potentiometer circuit to drop 5v to 3v.Wind sensor doesnt need any supply.

The important part of our project is arduino. Arduino is hardware-software equipment

which has an inbuilt micro-controller. It has 6 analog input pins and 14 digital I/O pins.

Output from LM35, MP3V5050 and speed sensor is analog, so we connect their voltage

outputs directly to 3 of 6 analog input pins of arduino. The output from humidity sensor is

frequency so we connect it to the digital input pin.

The output voltage from our wind sensor is in the range of 25 to 30mV, so we used

amplifying circuit in order to give it to arduino. Here we used 741 amplifier which requires +15v

and -15v.We designed a bridge rectifier circuit for +15v and -15v.

Program is written in arduino software and dumped to the arduino kit so that graphs can

be displayed in a software called megunolink. By using these graphs we can predict the weather.

Block Diagram showing connections and graphs using arduino:

Fig2.2

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2.2 ARDUINO:

Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use

hardware and software. It is an single board microcontroller, descendant of the open-

source wiring platform designed to make the process of using electronics in multidisciplinary

projects. Arduino Uno, a microcontroller board based on the ATmega328 is used in this project.

The hardware consists of a simple open hardware design for the Arduino board with an on-

board input/output support. The software consists of a standard programming language compiler

and the boot loader that runs on the board. Arduino hardware is programmed using a Wiring-

based language (syntax and libraries), similar to C++ with some slight simplifications and

modifications, and a Processing-based integrated development environment.

Arduino can sense the environment by receiving input from a variety of sensors and can

affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on

the board is programmed using the Arduino programming language (based on Wiring) and the

Arduino development environment (based on Processing). Arduino projects can be stand-alone

or they can communicate with software running on a computer (e.g. Flash,

Processing, MaxMSP,Meguno link). The hardware reference designs (CAD files) are

available under an open-source license, you are free to adapt them to your needs. The open-

source Arduino environment makes it easy to write code and upload it to the i/o board. It runs on

Windows, Mac OS X, and Linux. In addition to all the features of the previous board, the Uno

now uses an ATmega8U2 instead of the FTDI chip. This allows for faster transfer rates, no

drivers needed for Linux or Mac (inf file for Windows is needed), and the ability to have the Uno

show up as a keyboard, mouse, joystick, etc.

2.2.1 Hardware:

An Arduino board consists of an 8-bit Atmel AVR microcontroller with complementary

components to facilitate programming and incorporation into other circuits. An important aspect

of the Arduino is the standard way that connectors are exposed, allowing the CPU board to be

connected to a variety of interchangeable add-on modules known as shields. Some shields

communicate with the Arduino board directly over various pins, but many shields are

11

individually addressable via an IC serial bus, allowing many shields to be stacked and used in

parallel. Official Arduinos have used the megaAVR series of chips, specifically the ATmega8,

ATmega168, ATmega328, ATmega1280, and ATmega2560. A handful of other processors have

been used by Arduino compatibles. Most boards include a 5 volt linear regulator and a

16 MHz crystal oscillator (or ceramic resonator in some variants), although some designs such as

the LilyPad run at 8 MHz and dispense with the onboard voltage regulator due to specific form-

factor restrictions. An Arduino's microcontroller is also pre-programmed with a boot loader that

simplifies uploading of programs to the on-chip flash memory, compared with other devices that

typically need an external programmer.

At a conceptual level, when using the Arduino software stack, all boards are programmed

over an RS-232 serial connection, but the way this is implemented varies by hardware version.

Serial Arduino boards contain a simple inverter circuit to convert between RS-232-level

and TTL-level signals. Current Arduino boards are programmed via USB, implemented using

USB-to-serial adapter chips such as the FTDI FT232. Some variants, such as the Arduino Mini

and the unofficial Board uno, use a detachable USB-to-serial adapter board or

cable, Bluetooth or other methods. (When used with traditional microcontroller tools instead of

the Arduino IDE, standard AVR ISP programming is used.)

The Arduino board exposes most of the microcontroller's I/O pins for use by other circuits. The

Diecimila, Duemilanove, and current Uno provide 14 digital I/O pins, six of which can

produce pulse-width modulated signals, and six analog inputs. These pins are on the top of the

board, via female 0.1 inch headers. Several plug-in application shields are also commercially

available.

2.2.2 Software:

The Arduino IDE is a cross-platform application written in Java, and is derived from the

IDE for the Processing programming language and theWiring project. It is designed to introduce

programming to artists and other newcomers unfamiliar with software development. It includes a

code editor with features such as syntax highlighting, brace matching, and automatic indentation,

and is also capable of compiling and uploading programs to the board with a single click. There

12

is typically no need to edit makefiles or run programs on a command-line interface. Although

building on command-line is possible if required with some third-party tools such as Ino.

The Arduino IDE comes with a C/C++ library called "Wiring" (from the project of the same

name), which makes many common input/output operations much easier. Arduino programs are

written in C/C++, although users only need define two functions to make a runnable program:

setup() a function run once at the start of a program that can initialize settings

loop() a function called repeatedly until the board powers off

It is a feature of most Arduino boards that they have an LED and load resistor connected

between pin 13 and ground, a convenient feature for many simple tests.[29]

The above code

would not be seen by a standard C++ compiler as a valid program, so when the user clicks the

"Upload to I/O board" button in the IDE, a copy of the code is written to a temporary file with an

extra include header at the top and a very simple main() function at the bottom, to make it a valid

C++ program. The Arduino IDE uses the GNU tool chain and AVR Libc to compile programs,

and uses avrdude to upload programs to the board.

As the Arduino platform uses Atmel microcontrollers Atmels development environment,

AVR Studio or the newer Atmel Studio, may also be used to develop software for the Arduino.

The Arduino hardware reference designs are distributed under a Creative Commons Attribution

Share-Alike 2.5 license and are available on the Arduino Web site. Layout and production files

for some versions of the Arduino hardware are also available. The source code for the IDE and

the on-board library are available and released under the GPLv2 license.

Arduino and Arduino-compatible boards uses of shields, which are printed circuit boards

that sit atop an Arduino, and plug into the normally supplied pin-headers. These are expansions

to the base Arduino. There are many functions of shields, from motor controls, to breadboarding

(prototyping).

Features:

ATmega328 microcontroller

Input voltage - 7-12V

14 Digital I/O Pins (6 PWM outputs)

13

6 Analog Inputs

32k Flash Memory

16Mhz Clock Speed

The maximum values that Arduino can handle:

Max frequency: 16MHz

Max Voltage:5V

Max Current: 50mA

Fig2.3: Arduino

14

2.2.3 Pin description:

Arduino can be powered using power jack, USB port. Apart from this it can also be

powered by using a external battery or AC to DC adaptor through pin Vin.

5V, 3.3V: there is a inbuilt regulator on the board. Through this regulator a constant DC

supply of 5V, 3.3V is provided.

Reset: This pin enables to reset the micro controller.

IOREF: This pin acts as reference to the inputs given to the arduino board.

There are 6 pins A0 A5 through which analog input can be given to the arduino board.

There are 14 digital pins 0-13. Among these (3,5,6,9,10,11) are PWM pins(pulse width

modulation) from which analog output can be taken from the arduino board.

There is a inbuilt LED on pin 13.

AREF- This pin acts as reference to the analog inputs.

Rx,Tx are used for receiving and transmitting serial data.

ICSP- (In circuit serial programming)- These pins enable the user to programme the chips

on the circuit.

CHAPTER 3

Sensors

15

Sensors

3.1 Humidity

Humidity is the amount of water vapor in the air. Humidity indicates the likelihood of

precipitation, dew, or fog. There are three main measurements of humidity: absolute, relative and

specific. Absolute humidity is the water content of air. Relative humidity, expressed as a percent,

measures the current absolute humidity relative to the maximum for that temperature. Specific

humidity is a ratio of the water vapor content of the mixture to the total air content on a mass

basis.

3.1.1 Relative humidity

Relative humidity is the ratio of the partial pressure of water vapor in the air-water

mixture to the saturated vapor pressure of water at those conditions. The relative humidity of air

is a function of both its water content and temperature.

Relative humidity is normally expressed as a percentage and is calculated by using the following

equation. It is defined as the ratio of the partial pressure of water vapor (H2O) ( we ) in the

mixture to the saturated vapor pressure of water ( *we ) at a prescribed temperature.

%100*

w

w

e

e

Relative humidity is an important metric used in weather forecasts and reports, as it is an

indicator of the likelihood of precipitation, dew, or fog

3.1.2 Measurement

There are various devices used to measure and regulate humidity. Humidity is measured

on a global scale using remotely placed satellites. These satellites are able to detect the

concentration of water in the troposphere at altitudes between 4 and 12 kilometers

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3.1.3 HUMIDITY SENSING CLASSIFICATION & PRINCIPLES

According to the measurement units, humidity sensors are divided into two types:

Relative humidity (RH) sensors and absolute humidity (moisture) sensors. Most humidity

sensors are relative humidity sensors and use different sensing principles.

Sensing Principle

Humidity measurement can be done using dry and wet bulb hygrometers, dew point

hygrometers, and electronic hygrometers. There has been a surge in the demand of electronic

hygrometers, often called humidity sensors. Electronic type hygrometers or humidity sensors can

be broadly divided into two categories: one employs capacitive sensing principle, while other use

resistive effects

Fig 3.1

3.1.3(a) Sensors based on capacitive effect

Humidity sensors relying on this principle consists of a hygroscopic dielectric material

sandwiched between a pair of electrodes forming a small capacitor. Most capacitive sensors use

a plastic or polymer as the dielectric material, with a typical dielectric constant ranging from 2 to

15. In absence of moisture, the dielectric constant of the hygroscopic dielectric material and the

sensor geometry determine the value of capacitance. At normal room temperature, the dielectric

constant of water vapor has a value of about 80, a value much larger than the constant of the

sensor dielectric material. Therefore, absorption of water vapor by the sensor results in an

increase in sensor capacitance. At equilibrium conditions, the amount of moisture present in a

17

hygroscopic material depends on both the ambient temperature and the ambient water vapor

pressure.

Basic structure of capacitive type humidity sensor is shown below:

Fig 3.2

On Alumina substrate, lower electrode is formed using gold, platinum or other material. A

polymer layer such as PVA is deposited on the electrode. This layers senses humidity. On top of

this polymer film, gold layer is deposited which acts as top electrode. The top electrode also

allows water vapour to pass through it, into the sensing layer . The vapors enter or leave the

hygroscopic sensing layer until the vapour content is in equilibrium with the ambient air or

gas.Thus capacitive type sensor is basically a capacitor with humidity sensitive polymer film as

the dielectric.

3.1.3(b) Sensors based on Resistive effect

Resistive type humidity sensors pick up changes in the resistance value of the sensor

element in response to the change in the humidity. Basic structure of resistive type humidity

sensor from TDK is shown below

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Fig 3.3

Thick film conductor of precious metals like gold, ruthenium oxide is printed and calcinated in

the shape of the comb to form an electrode. Then a polymeric film is applied on the electrode;

the film acts as a humidity sensing film due to the existence of movable ions. Change in

impedance occurs due to the change in the number of movable ions.

Fig3.4

Selecting a humidity Sensor:

As there is no real physical standard for relative humidity calibration, humidity

instruments are not specified properly. And it makes it really difficult for a user to compare the

sensors from different manufacturers. This makes it mandatory for a user to go deeper into the

specifications and attempt to verify the claims of the instrument manufacturer. Various sensor

characteristics, viz., accuracy, linearity, hysteresis, calibration errors, long term stability of

sensor and electronics, need to be examined.

Rapid advancements in semiconductor technology, such as thin film deposition, ion

sputtering, and ceramic/silicon coatings, have made possible highly accurate humidity sensors at

economical prices. No single sensor, however, can satisfy every application. Resistive and

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capacitive sensing technologies each offer distinct advantages. Resistive sensors are

interchangeable, usable for remote locations, and cost effective. Capacitive sensors provide wide

RH range and condensation tolerance, and, if laser trimmed, are also interchangeable. For most

applications, therefore, the environmental conditions dictate the sensor choice.

Capacitive types humidity sensors

1)HCH-1000-001

2) HS 1101

3) HIH 4000- 001

4) NM522-H

5) DHT 11

6)HTF3223

Fig 3.5

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Resistive type humidity sensors

1) RHG-23HBNL

2) HY-233HB

3) HM 1500

Fig3.6

3.1.4 Humidity Sensor-HTF3223:

In our project we are using a capacitive humidity sensor HTF3223.It is an IC which gives

a linear frequency output. It can measure humidity from 10 to 95% of RH. It can be interfaced

directly with a micro-controller.

21

Fig 3.7

This sensor consists of 4 pins.

T-NC

G-Ground

F-Output Frequency

V-Input Voltage (5v)

Data Sheet of HTF3223 is given in appendix

3.2 TEMPERATURE

Temperature is a physical quantity that is a measure of hotness and coldness on a

numerical scale. It is a measure of the local thermal energy of matter or radiation. It is measured

by a thermometer, which may be calibrated in any of various temperature scales, Celsius,

Fahrenheit, Kelvin, etc.

3.2.1 Measurement of temperature

The most commonly used type of sensors are those which detect Temperature or heat.

These types of temperature sensors vary from simple ON/OFF thermostatic devices which

22

control a domestic hot water system to highly sensitive semiconductor types that can control

complex process control plants.

.There are different types of Temperature Sensors available and all have different

characteristics depending upon their actual application. Temperature sensors consist of two basic

physical types:

Contact Temperature Sensor Types - These types of temperature sensor are required to be

in physical contact with the object being sensed and use conduction to monitor changes in

temperature. They can be used to detect solids, liquids or gases over a wide range of

temperatures.

Non-contact Temperature Sensor Types - These types of temperature sensor use

convection and radiation to monitor changes in temperature. They can be used to detect

liquids and gases that emit radiant energy as heat rises and cold settles to the bottom in

convection currents or detect the radiant energy being transmitted from an object in the

form of infra-red radiation (the sun).

The two basic types of contact or even non-contact temperature sensors can also be sub-

divided into the following three groups of sensors, Electro-mechanical, Resistive and

Electronic and all three types are discussed below.

The Thermostat

The Thermostat is a contact type electro-mechanical temperature sensor or switch, that

basically consists of two different metals such as nickel, copper, tungsten or aluminium etc, that

are bonded together to form a Bi-metallic strip. The different linear expansion rates of the two

dissimilar metals produce a mechanical bending movement when the strip is subjected to heat.

The bi-metallic strip is used as a switch in the thermostat and is used extensively to control hot

water heating elements in boilers, furnaces, hot water storage tanks as well as in vehicle radiator

cooling systems.

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The Thermistor

The Thermistor is another type of temperature sensor, whose name is a combination of

the words THERM-ally sensitive res-ISTOR. A thermistor is a type of resistor which changes its

physical resistance with changes in temperature.

Thermistor

Thermistors are generally made from ceramic materials such as oxides of nickel,

manganese or cobalt coated in glass which makes them easily damaged. Their main advantage

over snap-action types is their speed of response to any changes in temperature, accuracy and

repeatability.

Most types of thermistors have a Negative Temperature Coefficient of resistance or

(NTC), that is their resistance value goes DOWN with an increase in the temperature but some

with a Positive Temperature Coefficient, (PTC), their resistance value goes UP with an increase

in temperature are also available.

Thermistors are rated by their resistive value at room temperature (usually at 25oC), their

time constant (the time to react to the temperature change) and their power rating with respect to

the current flowing through them. Like resistors, thermistors are available with resistance values

at room temperature from 10's of M down to just a few Ohms, but for sensing purposes those

types with values in the kilo-ohms are generally used.

Resistive Temperature Detectors (RTD).

RTD's are precision temperature sensors made from high-purity conducting metals such

as platinum, copper or nickel wound into a coil and whose electrical resistance changes as a

function of temperature, similar to that of the thermistor.

RTD have positive temperature coefficients but unlike the thermistor their output is

extremely linear producing very accurate measurements of temperature. However, they have

poor sensitivity, that is a change in temperature only produces a very small output change for

example, 1/oC. One of the main disadvantages of this type of device is its cost.

The Thermocouple

The Thermocouple is by far the most commonly used type of all the temperature sensing devices

due to its simplicity, ease of use and their speed of response to changes in temperature, due

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mainly to their small size. Thermocouples also have the widest temperature range of all the

temperature sensors from below -200oC to well over 2000

oC.

Thermocouples are thermoelectric sensors that basically consist of two junctions of dissimilar

metals, such as copper and constantan that are welded or crimped together. One junction is kept

at a constant temperature called the reference (Cold) junction, while the other the measuring

(Hot) junction. When the two junctions are at different temperatures, a voltage is developed

across the junction which is used to measure the temperature.

3.2.2 The LM35

LM35 is an integrated circuit sensor that can be used to measure temperature with an

electrical output proportional to the temperature (in oC). You can measure temperature more

accurately than a using a thermistor. The sensor circuitry is sealed and not subject to oxidation,

etc. The LM35 generates a higher output voltage than thermocouples and may not require that

the output voltage be amplified.

Fig 3.8

It gives an output voltage proportional to the Celsius temperature. The LM35 does not

require any external calibration or trimming and maintains an accuracy of +/-0.4 oC at room

temperature and +/- 0.8 oC over a range of 0

oC to +100

oC. The scale factor is 01V/

oC.

The general equation used to convert output voltage to temperature is:

Temperature ( oC) = Vout * (100

oC/V)

So if Vout is 1V , then, Temperature = 100 oC

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The output voltage varies linearly with temperature.

3.3 Atmospheric pressure

Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above

that surface in the atmosphere of Earth (or that of another planet). In most circumstances

atmospheric pressure is closely approximated by the hydrostatic pressure caused by the mass of

air above the measurement point. Low-pressure areas have less atmospheric mass above their

location, whereas high-pressure areas have more atmospheric mass above their location.

Likewise, as elevation increases, there is less overlying atmospheric mass, so that atmospheric

pressure decreases with increasing elevation. The standard atmosphere (symbol: atm) is a unit of

pressure equal to 101.325 kPa ("kiloPascals")[2]

or 1013.25 millibars or hectopascals. It is

equivalent to 760 mmHg (torr), 29.92inHg and 14.696 psi.

3.3.1 Pressure Measurement

Electronic measuring sensor serves for transformation of air pressure value to electric

signal. It is designed for operation in meteorology and environmental observation, e.g. automatic

weather stations, at airports, on research vessels, at industrial sites, for mobile measuring systems

etc. With a piezoresistive pressure sensor and signal conditioning electronic the actual air

pressure will be transformed into a proportional standardized electrical output.

Pressure sensors

BMP 085

SS110

MP3V5050

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MPXH6101A

Fig3.9

3.3.2 MP3V5050:

The MP3V5050 series piezoresistive transducer is a state-of-the-art monolithic silicon

pressure sensor designed for a wide range of applications, but particularly those employing a

microcontroller or microprocessor with A/D inputs. This patented, single element transducer

combines advanced micromachining techniques, thin-film metallization, and bipolar processing

to provide an accurate, high level analog output signal that is proportional to the applied

pressure.

Data Sheet of MP3V5050 is given in appendix

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Speed:

Wind speed, or wind velocity, is a fundamental atmospheric rate. Wind speed

affects weather forecasting, aircraft and maritime operations, construction projects, growth and

metabolism rate of many plant species, and countless other implications. Wind speed is

commonly measured with an anemometer.

3.4.1 Anemometer

An anemometer is a device for measuring wind speed, and is a common weather

station instrument. The term is derived from the Greek word anemos, meaning wind, and is used

to describe any airspeed measurement instrument used in meteorology or aerodynamics.

Model of an anemometer is shown below:

Fig 3.10

Fig 3.11

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3.4.2 Measurement

In our project we designed our own anemometer. Our anemometer contains 3 cups

symmetrically attached to the shaft of the motor. The force impinged on the cups make them to

rotate which in turn rotates the motor shaft. Depending on the wind speed the generated voltage

varies. Therefore generated voltage is proportional to the wind speed.

Fig 3.12

From emf equation,

KNE

A

PZNE

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Here , K is the proportionality constant.

We determined K by the following process,

We attached a proximity sensor to our wind sensor and 9v is supply is given to our wind sensor.

The no. of pulses per second is counted using a program in arduino.

Now

N = rps /60.

By using, E=KN/60 we found K= (9*60)/N.

We got K=0.6466.

In order to convert speed into m/s we measured the circumference of the sensor and multiplied it

with the rps value of speed. The output voltage from the speed sensor is too low so we used

amplifying circuit in order to amplify it.

CHAPTER 4

Simulation results

29

SIMULATION RESULTS 4.1 Simulation results of temperature sensor

5v is given to LM35 and output pin is connected to analog pin of arduino.

4.1(a) The programming in arduino is as follows:

Fig 4.1

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4.1(b) Display of graph in Megunolink:

Fig 4.2

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4.2 Simulation results of pressure sensor

Pressure sensor MP3V5050 requires 2.7 to 3.3v.We are giving 3v supply. The output pin

is given to analog pin of arduino.

4.2(a) Program

Fig 4.3

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4.2(b) Graph

Fig 4.4

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4.3 Simulation results of wind speed sensor

The output voltage of speed sensor is amplified and given to analog input pin of arduino.

4.3(a) Program

Fig 4.5

34

4.3(b) Graph in Megunolink

Fig 4.6

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4.4 Simulation results of humidity sensor

4.4(a) Program

36

Fig 4.7

4.4(b) Graph

Fig 4.8

37

Simulation results of Weather Station Receiver

4.5(a) Program

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Fig 4.9

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4.6(b) Graph

Fig 4.10

CHAPTER 5

Conclusion and future work

40

5.1 CONCLUSION

Weather Station model discussed in this document can be installed anywhere outdoors

and weather can be monitored through PCs. This model is simple and economical. Continuous

recording of data can be done in this method. The recorded data can be used to predict the

weather. The four different parameters that are measured by using this Weather Station Receiver

can also be measured by using various measuring instruments but with the help of few sensors, a

PC and Arduino, we can do the same job in simpler and efficient manner.

5.2 FUTURE SCOPE

Modern forecasts are made with ultra-powerful computer modelseffectively reams of

equations that computers chew through to make an accurate prediction up to 15 days ahead. The

equations describe Earth's atmosphere using a 3D grid of points, with temperature, pressure,

humidity, wind speed, and other factors measured for each one. A modern forecast, involving

billions of calculations, needs a supercomputer to crack it.

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REFERENCES

"Automated Weather Observing System (AWOS)".

"All Weather".

"Mesotech".

"Vaisala".

Automated Lightning Detection and Ranging System - National Weather Service.

Arduino.cc

Wikipedia

Datasheetsforum.com

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APPENDIX

DATA SHEET OF HTF 3223:

43

44

45

Data Sheet of LM35

46

47

48

49

50

51

52

53

54

55

56

57

DATA SHEET OF MP3V5050

58

59

60

61

62

63

64

65

66