CHAPTER ONE

INTRODUCTION

1.1       BACKGROUND OF STUDY

Temperature is a numerical measure of hotness and coldness in a body that is in its             own state of internal thermal equilibrium. Its measurement is by detection of heat           radiation or particle velocity or kinetic energy, or by the bulk behavior of      thermometric material.

            Temperature is important in all fields of natural science, including physics, geology,           chemistry, atmospheric science and biology.

            Humidity is one of the important parameters in the atmospheric gases. The natural air        can contain humidity and varies from season to season. Humidity indicates the likelihood of precipitation, dew or fog. There are three main measurement of     humidity: absolute, relative, and specific. Absolute humidity is the water content in             the air. Relative humidity, expressed as a percentage, measures the current absolute           humidity relative to the maximum for the temperature. Specific humidity is a ratio of             the water vapor content of the mixture to the total air content on a mass basis.

            Microprocessor is a single-board microcontroller, intended to make the application of        interactive objects or environment more accessible. It’s an open-source physical            computing platform and a development environment for writing software for the       board. Microprocessor can be used to develop interactive objects, taking inputs from       variety of switches or sensors and controlling a variety of lights, motors and other physical outputs.

            This project is basically concerned with the design and construction of a     microprocessor-based Temperature and Humidity measuring system that measures             the ambient temperature and humidity of the environment, and display it on an LCD         screen. A combine temperature and humidity sensor DHT22 is used with micro       controller (Atmega328) to develop a Celsius scale Thermometer, and percentage scale       humidity measuring project.

1.2       AIM AND OBJECTIVES OF THE PROJECT

            The aim and objectives is to design and construct an electronics device that can be             used to measuring the temperature and humidity of an environment. The device is also            incorporated with LCD (liquid crystal display) that displays the numerical value of temperature and humidity.

1.3       SCOPE OF THE PROJECT

            The scope of this project include, the design and implementation of the eletronic    circuitry (hardware) and the code for the microcontroller PIC (software) neccessary to          measuring the temperature and humidity of the environment. The system should have            avariable temperature and humidity range. The design should be based on        microcontroller IDE, which includes writing the source codes, debugging any errors,         compiling it into a h Hex codes and burning itonto the  microcontroller             (ATMEGA328).The project has the following limitations:

            i.          The project measures a distance of just 20 meters.

            ii.         The temperature should not exceed 50°C.

            iii.        It only reads relative humidity from 20­-80%.

1.4       METHODOLOGY

The circuit that will be able to sense the temperature of the environment, do the     necessary conversion to its digital equivalents, process, display and switch the   relevant device (either the heater or the air conditioner) mainly consists of the DHT22            Centigrade temperature sensor, ATMEGA328P microcontroller, 16×2 LCD. The             output of the sensor is fed to the internal A/D of the microcontroller. The analogue            voltage output of the sensor is converted by the in-built analog –to-digital converter   into its equivalent digital value and then its equivalent degree Celsius value is      calculated by the software. The calculated temperature value in Degree Celsius scale    (oC) is displayed on the 16×2 LCD.

Fig.1.1 Block Diagram of Temperature and Humidity Measuring System

            The power supply been the one that energize the entire circuit, which supplies about          5volt DC to the whole circuit, the entire blocks get their supply from this 5volt,the   DHT22 sensor which is the next block, senses the environment of interest and pass it           to the MCU which do the necessary conversion of the output from the sensor, and the            last stage which is the LCD displays the result.

            1.4.1    Power Supply

These are the circuits that provide the main circuit with the required energy to drive           the load. The commonest types are the DC power source which could be a battery or       an AC-DC power supply. In the AC-DC power supply the high AC voltage is converted into the acceptable level which the electronics appliances can use. One of             such converters uses a step-down transformer, rectifier, filters and voltage regulators.

1.4.2    The Sensor (DHT22)

            This is an electrical transducer that converts heat energy into electrical energy         (voltage). This device has an output voltage of about 10 mV for every Degree rise in   temperature, it has a measurement ranges of 20-80% RH and 0-50ºC temperature.

            1.4.3    Micro-Processor (ATMEGA 328)

Microprocessor is a microcontroller board which depends on ATmega32. It consists           of 14 digital I/O pins, for analog inputs there are 6 analog pins which are very useful.            Microprocessor 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 C++   programming language.

            1.4.4    The LCD Display

Liquid crystal display which is commonly known as LCD is an alphanumerical       display. It means that it can display alphabets, numbers as well as special symbols     thus LCD is a user friendly display device which can be used for displaying various     messages unlike seven segment display which can display only numbers and some of             the alphabets. The only disadvantage over seven segment is robust display and be visualized from a longer distance as a compared to LCD. Here I have used 16x2       alphanumeric display which means on this display I can display two lines with             maximum of 16 characters in one line.

1.5       REPORT OUTLINE

This project is being categorized into five chapters which in all will shed light on the          construction. The following is a guide to what each chapter entails in it.

The report consists of five (5) chapters.Chapter one contains the general introduction of work carried out.Chapter two presents literature review.    Chapter three introduces the hardware and software design. This chapter describes the components and physical realization of the overall circuitry.Chapter four provides the general discussion hardware construction, testing and principle of operation of the system.Chapter five concludes the work carried out. It highlights the possible recommendations for further research.

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