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CONSTRUCTION AND DESIGN OF POLICE SIREN

CHAPTER ONE

INTRODUCTION 

1.1 BACKGROUND OF THE STUDY

A siren is a loud noise making device. Civil defense sirens are mounted in fixed locations and used to warn of natural disasters or attacks. Sirens are used on emergency service vehicles such as ambulance, police cars and fire trucks. There are two general types of siren:

1-Pneumatic Siren 

2-Electronic Siren 

Many fire sirens (used for calling the volunteer fire fighters) serve double duty astornado or civil defense sirens, alerting an entire community of impending danger. Most fire sirens are either mounted on the roof of a fire station, or on a pole next to the fire station. Fire sirens can also be mounted on or near government buildings, on tall structures such as water towers as well as in systems, where several sirens are distributed around a town for better sound coverage. Most fire sirens are single tone and mechanically driven by electric motors with a rotor attached to the shaft. Some newer sirens are electronically driven by speakers. Though, these are not as common. 
Fire sirens are often called “fire whistles”, “fire alarms”, or “fire horns.” Although there is no standard signaling of fire sirens, some utilize codes to inform fire fighters of the location of the fire. Civil defence sirens pulling double duty as a fire siren often can produce an alternating “hi-b” signal (similar to a British police car) as the fire signal, or a slow wail (typically 3x) as to not confuse the public with the standard civil defense signals of alert (steady tone) and attack (fast wavering tone). Fire sirens are often blasted once a day at noon and are also called “noon sirens” or ‘noon whistles”. 
Pneumatic Siren consists of a rotating disk with holes in it such that the material between the holes interrupts a flow of air from fixed holes on the outside of the unit. As the holes in the rotating disk alternately prevent and allow air to flow it results on alternating compressed and rarefied air pressure i.e. sound. It consumes large amount of energy. 
Electronic Siren incorporate circuits such as oscillators, modulators and amplifiers it synthesize a selected tone which is played through external speakers. It is not unusual especially in the case of modern engines, to see an emergency vehicle equipped with both types of siren. 
1.2 OBJECTIVES OF THE STUDY
The main objective of this project is to implement Electronic Siren in both the software and hardware version. We are going to learn the PCB designing, Proteus software handling in an effective manner. At the end of this project student will be able to learn all these things. Electronic Siren is basically high-performance sound signal electronic amplifiers. These siren works with substantially higher outputs and specific demand are placed on them in terms of desired extreme reliability and different methods of control on them. Moreover control infrastructure must also be reliable and usually two independent control channels are required. 
The loudspeakers for these amplifiers are placed in specially- designed sound battles and they play the signals stored in the siren’s digital memory or signals fed to the siren from external sources. 
1.3 SCOPE OF THE STUDY
It is possible to add an external signal source with these devices. Moreover it provides enhanced automatic testing. It is employed at user friendly level easily. In industry it will be a great advantage to the people.