Design And Construction Of A Public Address System (Pa System) With A.C And Battery Power Source

ABSTRACT

This work is titled design and construction of a public address system with ac and battery power source. A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals.

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Intercom systems, installed in many buildings, have microphones in many rooms allowing the occupants to respond to announcements.

This system was built using some major electronics components such as transistor, resistor, capacitors, and an aluminum heatsink was used to protect the power transistors from overheating.

This Public Addressing Systems have a potential for audio feedback, which occurs when sound from the speakers is picked up by the microphone and is then re-amplified and sent through the speakers again. That makes it to sounds like a loud high-pitched squeal or screech, and can occur when the volume of the system is turned up too high.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM/OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• APPLICATION OF THE PROJECT
• PROJECT JUSTIFICATION
• SCOPE OF THE PROJECT
• LIMITATION OF THE PROJECT
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF PUBLIC ADDRESSING SYSTEM
• HISTORICAL BACKGROUND OF PUBLIC ADDRESSING SYSTEM
• DIFFERENT TYPES PUBIC ADDRESSING SYSTEM
• DIFFERENT TYPES PUBIC ADDRESSING SYSTEM
• CLASSIFICATION OF AMPLIFIERS
• CHARACTERISTICS OF ACTIVE COMPONENTS

CHAPTER THREE

METHODOLOGY

• INTRODUCTION
• FEATURES AND SPECIFICATIONS OF THE AUDIO AMPLIFIER SYSTEM
• BLOCK DIAGRAM
• DESIGN STAGES
• AMPLIFIER CIRCUIT DIAGRAM
• CIRCUIT DESCRIPTION
• AMPLIFIER CIRCUIT OPERATION
• POWER SUPPLY
• CALCULATION

CHAPTER FOUR

• PROJECT IMPLEMENTATION AND CONSTRUCTION
• CONSTRUCTION
• DESIGNING OF THE SCHEMATIC AND LAYOUT DIAGRAM
• TOOLS AND EQUIPMENT
• MOUNTING AND SOLDERING OF THE COMPONENTS ON THE PRINTED CIRCUIT BOARD
• CONSTRUCTION OF CASING
• PRECAUTION
• PROBLEMS ENCOUNTERED

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

• INTRODUCTION

In general, the purpose of an amplifier is to take an input signal and make it stronger. Amplifiers find application in all kinds of electronic devices designed to perform numbers of functions. There are many different types of amplifiers, each with a specific purpose. This project is specified on audio amplifier. Audio power amplifiers are those amplifiers which are designed to drive loudspeakers.

Scientifically, a public address system is an electronic device in which a small-signal vibration is amplified using pre-amplifier(s); this signal (audio frequency signal) is then amplified to a level required to drive a loudspeaker by a power amplifier.

1.1                          BACKGROUND OF THE PROJECT

A public address system comprises electrical equipment to greatly amplify a speaker’s voice so it will reach a much larger assemblage than he could speak to unaided. Beginning with the presidential conventions of the two major parties in 1920 and the inaugural address of President Harding in March 1921, when a special address system installed by the telephone engineers enabled him to address an audience estimated at 125,-000, there followed in rapid succession, many public events demonstrating the value of such systems. One of the most notable of these occurred on Armistice Day 1921, when the speeches, prayers and music at Arlington, Virginia, were heard, not only by 100,000 persons gathered there at the National Cemetery, but by some 35,000 in New York City and 20,000 in San Francisco. On this occasion the three public address systems, one for each of these cities, were joined by long distance telephone circuits.

The fundamental requirements of a satisfactory public address system are naturalness of reproduction and wide range of output volume. The meeting of these two requirements for music proves more difficult than for speech.

The public address system here described is most readily considered in three sections—“pick-up” apparatus which is placed in the neighborhood of the speaker and converts his words into undulatory electric currents; a vacuum tube amplifier for amplifying these currents; and a “receiver-projector” for reconverting the current into sound waves and distributing the sound over all of the audience. In the present system each of these three parts of the equipment has been designed with the intention of making it as nearly distortionless as possible, so that the various parts might be adaptable for audiences ranging in size from possibly one thousand to several hundred thousand, and might also be used in connection with the long distance telephone lines and with either radio broadcasting or receiving stations. One of the larger public address systems is easily capable of magnifying a speaker’s voice as many as 10,000 times.

The pick-up device whether of the carbon microphone variety or a condenser transmitter need not be placed close to the speaker’s lips but will operate satisfactorily when four or five feet away. The loud-speaking receiver mechanism is so designed that it will carry a power of several watts with small distortion. Under normal conditions, 40 watts distributed among a number of receiver-projectors arranged in a circle is ample to reach an audience of 700,000 persons.

1.2                                   PROBLEM STATEMENT

This project is to overcome communication problems that usually occur in areas where it is hard to find a device for making important announcements or speeches so that everyone can listen precisely to what the speaker is talking about. This simple project may also be used by lecturers in lecture halls to bridge communication gap between the lecturers and student in a lecture, as shouting during lectures may be very exhausting.

 

1.3                    AIM AND OBJECTIVE OF THE PROJECT

The objective of this work is to construct an electronic sound amplification and distribution device with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals, with ac and battery power source which prevents the device from power interruption. This project should not be bulky in size.

1. Acquaint with the use of basic Electronic Components and devices
2. Strengthen capacity for a better audience
3. Increase or magnify a low energy level signal (in this case sound).
4. Improve communication
5. Understand Basic Principles of Amplifiers.

 

1.4                             SIGNIFICANCE OF THE STUDY

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations.

1.5                               APPLICATION OF THE PROJECT

Public addressing system is often used in small venues such as school auditoriums, churches, and small bars. PA systems with many speakers are widely used to make announcements in public, institutional and commercial buildings and locations. Public addressing system is naturalness of reproduction and wide range of output volume. The meeting of these two requirements for music proves more difficult than for speech.

1.6                                 PROJECT JUSTIFICATION

Over the ages, science and technology has been developing with new inventions in various fields; including the increase in modifications on existing technology all gearing towards improving effectiveness and reliability of equipment and achieving to a great degree miniaturization and optimal cost.

This project is backed by my interest in the area of electronics and communication, and having been groomed to a great extent with introductions into the various fields of electrical and electronics engineering, with the knowledge in principles of telecommunications, telecommunication engineering.

1.7                                  SCOPE OF THE PROJECT

This system is for public address; it has an estimated power rating of 20watts. For power supplies, it uses a 220/12Vac transformer for the AC supply and a rechargeable 12v battery for the DC supply used in supplying power to the receiver, amplifier and loudspeaker units. It has a power On/Off button with volume control.

After designing all sub circuits, the PCB of each sub circuit is constructed. The project ends up with the combination of all sub circuits and troubleshooting should there be any problem.

1.8                                LIMITATION OF THE PROJECT

INTERFERENCE: Interference can be a problem. There are lots of devices that emit radio waves. If those radio waves are on the same frequency as with the transmitter and receiver, you could get some garbled signals as you listen to the output. Dropped signals can also be an issue — if a transmitter or receiver stops working or drops out, it will affect your listening experience.

BANDWIDTH: Another problem is bandwidth. Wired PA can carry a lot of information in the form of electrical signals. Audio may seem less full or rich. It’s a subjective element that can be difficult to put into words.

Another drawbacks of public addressing (PA) systems is the cabling that is required, which can be expensive, difficult and time-consuming to install. A wired PA system suffers from a number of drawbacks, that is to say: being “fixed” – it being difficult to relocate the speakers subsequent to installation; loss of operation and/or functionality in the event of one of more of the cables failing; and loss of operation and/or functionality in the event of a power outage.

Different power source, that is, a 12v battery and an ac power source. The battery power source is used to power the system during the electricity outage.

1.9                                PROJECT WORK ORGANISATION

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 public address system. In this chapter, the background, significance, objective limitation and problem of public address system with dual power supply were discussed.

Chapter two is on literature review of power restoration reminder. 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.