Design And Construction Of A Digital Thermometer

ABSTRACT

The project is titled “The design and construction of a digital thermometer”. The device display temperature information numerically. Thus help to avoid the limitation due to parallax error in analogue device.

The whole system incorporates a microcontroller which is interfaced to other components. This component include temperature sensor, an analogue -to-digital converter, an 8051 microcontroller and a 16×2 LCD display unit. The temperature sensor used is thermistor. The sensor senses temperature and generates an analogue voltage which is proportional to the sensed temperature.

TABLE OF CONTENTS

 TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRCT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• OBJECTIVE OF THE STUDY
• PURPOSE OF THE PROJECT
• SIGNIFICANCE OF THE STUDY
• APPLICATION OF THE PROJECT
• SCOPE OF THE PROJECT
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

2.0      LITERATURE REVIEW
2.1      HISTORICAL BACKGROUND ANDDEVELOPMENT OF THE STUDY
2.2     PHYSICAL PRINCIPLES OF THERMOMETRY
2.3      THERMOMETRIC MATERIALS

2.4      PRIMARY AND SECONDARY THERMOMETERS

2.5      CALIBRATION OF THERMOMETERS

2.6     REVIEW OF TWO KINDS OF CONVENTIONAL THERMOMETERS

CHAPTER THREE

3.0      METHODOLOGY

3.1      SYSTEM BLOCK DIAGRAM
3.2      COMPONENTS OF THE SYSTEM

3.3      SYSTEM CIRCUIT DIAGRAM

3.4      SYSTEM WORKING PRINCIPLE

CHAPTER FOUR

4.0      CONSTRUCTION PROCEDURE AND TESTING

4.1      CASING AND PACKAGING

4.2      ASSEMBLING OF SECTIONS

4.3      TESTING OF SYSTEM OPERATION

CHAPTER FIVE

5.1      CONCLUSIONS

5.2      RECOMMENDATION

5.2      REFERENCES

 CHAPTER ONE

1.0                                                        INTRODUCTION

A thermometer is a device that measures temperature or a temperature gradient. A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer) in which some physical change occurs with temperature, and (2) some means of converting this physical change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer). Thermometers are widely used in industry to control and regulate processes, in the study of weather, in medicine, and in scientific research (Francesco, 2011).

There are various principles by which different thermometers operate. They include the thermal expansion of solids or liquids with temperature, and the change in pressure of a gas on heating or cooling. Radiation-type thermometers measure the infrared energy emitted by an object, allowing measurement of temperature without contact. Most metals are good conductors of heat and they are solids at room temperature. Mercury is the only one in liquid state at room temperature, and has high coefficient of expansion. Hence, the slightest change in temperature is notable when it’s used in a thermometer. This is the reason behind mercury and alcohol being used in thermometer (Francesc, 2011).

This work focuses on the a digital thermometer, In the field of healthcare, temperature monitoring has assumed a very vital role both in the management of patient’s condition and general hospital storage facilities.

Current advancements in the technology of temperature measurement have led to a huge variety of sensors and measuring instruments now being available for making accurate measurements. Most of the types available locally are the analogue type according to Benedict (2014).

In this work, a digital thermometer has been designed and constructed based on ATMega16 microcontroller using LM35 or thermistor as the temperature sensing device.

The design is in four modules; power supply, temperature sensor, LCD device and ATmega16 modules. While the ATmega16 forms the main control element, the temperature sensor senses the temperature to be measured and converts it to a corresponding analogue voltage.

The measured temperature is displayed on a 16 by 2 Character LCD incorporated in the system.

1.2                                   AIM AND OBJECTIVE OF THE PROJECT

The main aim of this work is to design a device used to measure the temperature of any particular device or living body and displays the reading. The objectives of the study are:

1. To digitally display the temperature of an object via LCD.
2. To control temperature of a room or object

• To solve the problem of taking a reading of an analogue thermometer

1.3                                              PURPOSE OF THE PROJECT

The main purpose of this work is to display temperature in Celsius. This project also uses 8051 microcontroller (AT89C51).

1.4                                         SIGNIFICANCE OF THE PROJECT

• Accuracy: The temperature reading does not depend on scale reading and instead shown directly on the display. Hence temperature can be read exactly and accurately.
• Speed: Digital thermometers can reach a final temperature in 5 to 10 seconds compared to conventional thermometers.
• Safety: Digital thermometers don’t use mercury, hence the hazards of the mercury is eliminated in case the thermometer breaks.
• Strong: The thermometer doesn’t needs to be shaken for the proper mercury level, hence the risk of the tube getting broken is eliminated.
• LCD display: this device has the ability of displaying the temperature value in Celsius and fahrenhelt

1.5                                         APPLICATIONS OF THE PROJECT

Medical Applications: The digital thermometers are used to measure human body temperature around 37⁰C. These thermometers are mostly probe type or ear type. It measures oral, rectal and arm pit body temperature (Lewis, 2011).

Marine Applications: Digital thermometers with high temperature exhaust gas sensor as the temperature sensor can be used in marine applications for measuring the local temperature (Lewis, 2011).

Industrial Applications: Digital thermometers are also used in power plants, nuclear power plants, blast furnaces, ship building industries etc. They can measure temperature from -220⁰C to +850⁰C (Lewis, 2011).

Other electrical appliances are as below:

1. Air conditioner
2. Refrigerator

• Fan,

1. furnace etc.
2. homes
3. industries

1.6                                                 SCOPE OF THE PROJECT

The above system consists of temperature sensor IC DS1620 which is an 8 pin IC and can measure temperature from -55 degree Celsius to +125 degree Celsius. It contains two pins which indicate if the measured temperature exceeds the user defined temperature. Thus this device can also be used to control the switching of loads incase of any temperature fluctuations according to Duncan (2013).

In the above system, the temperature IC first measures the ambient temperature and converts this temperature to digital data and feeds it to the microcontroller which displays the temperature reading on the display. Using the push button switches the user defined temperature can be set (Duncan, 2013). When the ambient temperature increases or decreases than the user defined temperature, the microcontroller display the value via LCD.

1.7                                        PROJECT WORK ORGANIZATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to the study. In this chapter, the background, significance, objective, purpose, application and scope of the study were discussed.

Chapter two is on literature review of this study. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.