1.1 BACKGROUND OF THE STUDY
This research is on Design and construction of 20watts wireless public address system. A public address system allows you to broadcast information to a large group of people, whether you are giving a speech or playing live or recorded music. Public address systems typically consist of input sources, preamplifiers, control and monitoring equipment, and loudspeakers. Input sources refer to the microphones that provides a sound input for the system. These input sources are fed into the preamplifiers. The pre amplified signals are then passed into the audio power amplifiers.
These amplifiers will amplify the audio signals to an adequate speaker line level. In view of the above, one can now say that the public address system is an electronic amplification system used for communication in public areas.
Microphone is a device that converts sound waves into electrical waves. Some times colloquially called a micro mike is an acoustic to electric transducer or sensor that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, and for non-acoustic purposes such as ultrasonic checking. The sensitive transducer element of a microphone is called its element. Since a wireless microphone is used in this project; a wireless microphone is one in which communication is not limited by a cable.
Fig2:A transmitter circuit
The first transistor Q1 is the preamplifier for the microphone, and you can omit this circuit if you don’t want to transmit the sound picked up by the mic, for example you can connect your mp3 player directly to C1. The core of this FM transmitter circuit is Q2, a modified Culprits oscillator that the frequency is determined by L1, C4, C6, and the transistors internal base emitter capacitance. The antenna use 1/16 wave length to compromise between the efficiency and the size. If you want the microphone to be less sensitive, we can replace the R1 by a higher resistor, such as 10k or 22k, and this might overcome the feedback problem if you use this wireless microphone FM transmitter for a public address system
1.2 AIMS AND OBJECTIVES
Public speaking is the process of speaking to a group of people in a structured, deliberate manner intended to inform, influence, or entertain the audience. In public speaking, as in any form of communication, there are five basic elements, often expressed as who is saying what to whom using what medium with what effectsW.Kleitz;2005 pg134.
The major objective of this project is to design and construct a public address system with relatively unique operational characteristics that is capable of delivering 20 watts of electrical power into an 8 Ohms load loudspeaker. This will be achieved with adequate tone controls and mixer stages so as to enable communication or reproduction of speech and recorded music in buildings and institutions.
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,
1.4 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 receiver, amplifier and loudspeaker units. It has a power On/Off button with volume control.
1.5 SYSTEM BLOCK DIAGRAM
Fig 3: Block diagram of a public address system
The system is made up of the transmitter which is incorporated in the microphone; and the receiver unit, the tone control and mixer unit, the audio amplifier unit and the loudspeaker.
1.6 PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into six chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Table 1 : Project work organization