In electrical engineering, a switch is an electrical component that can "make" or "break" an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated. It may be operated manually, for example, a light switch or a keyboard button, may be operated by a moving object such as a door, or may be operated by some sensing element for pressure, temperature or flow. A switch will have one or more sets of contacts, which may operate simultaneously, sequentially, or alternately. Switches in high-powered circuits must operate rapidly to prevent destructive arcing, and may include special features to assist in rapidly interrupting a heavy current. There are different types of switch with different applications, some switches are made for dc while some are made for ac for example, and toggle switch is used for ac while momentary switch is made for dc circuits. However, this work is focusing on using momentary switch to control the ON and OFF of ac appliances via a relay.

 

 CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                        PROJECT BACKGROUND

In the present modern world, switching circuits have become an indispensible part of our life. Right from your mobile phone to the various security systems, they can be seen everywhere. Even the horn of your motor car is a kind of switch used to warn people and vehicles in front of its presence. The sole purpose of a switch is to activate or deactivate a device. They may be in the form of a visual indicator, for example a flashing light, but switching circuit in the form of an audible tone or siren is more widely accepted as it is able to wake up even the unaware and the oblivious.
The word “switch” is a very common name found in almost all aspects electrical/electronic engineering. Switches can be found in information technology computers, telecommunications, power electronics, power systems, instrumentation etc.
They have been defined by various people or organizations in different ways. Some of the definitions of switches are listed below;

• As a device that is used to break or stop the flow of charges in a circuit.
• As a device used to connect two or more computers together
• A device used to interrupt the flow of electrons in a circuit.

 This work is on alternating ON-OFF switch.  Activation or deactivation is all about automating real life ac lamp or ac devices using momentary switch.
All the above definitions are correct, but for this project we are going to define this switch as a device which can be used to control the action of an electrical load, just by pressing momentary on-off switch.

1.2                 STATEMENT OF THE PROBLEM

• In the industries like the petroleum or chemical industries, some production processes have been started or stopped due to accidental switching of machinery leading to injury or death. This can cause financial strain on a company.
• Manual switching is an uphill task for the disabled and the aged due to movement constraints.
  
  1.3               PROJECT MOTIVATION

The motivation of this project is to fulfil the following;

• The device makes provision of safe guarding operators and equipment in that when power was restored is remains OFF until when the switch is been pressed.
• To ensure a reliable and safe method of switching domestic and industrial devices.

•                                      OBJECTIVE OF STUDY

The objective of this project is to construct a device which can be switched on and off ac appliances using momentary on-off switch. 
1.5                                                          SCOPE OF THE PROJECT
The scope of this work is defined by the following points
I.  The switching interface in this project is of the general purpose type as it is not restricted to only one type of load.
          II.      The first time the circuit is pressed activates the ac lamp and the second time deactivates the ac lamp.
       III.      It will not be limited to low voltage, low current AC/DC applications of 240V maximum operating voltage.
          V.      The type of control this project employs is the simple ON/OFF control of devices.

1.6                                        SIGNIFICANCE OF PROJECT
This project’s completion will be of great benefit to our ever demanding and developing society. Some of these benefits include;
    I.      Accidental switching of devices will be reduced to a minimum in our industries and homes.
II.      Sometimes, we are victims of electric shocks from our devices when we try to switch them ON/OFF due to leaking currents from the electric switches but this device stop this accident.
  III.      This project stops the wearing out the switch that usually happens to the normal ac switch.

1.7                                             APPLICATION OF THE PROJECT
This device can be found useful in the following places:

• information technology computers,
•  telecommunications,
•  power electronics,
• power systems,
• control of machinery, to reverse electric motors
• Instrumentation etc.

1.8                                        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 this study. In this chapter, the background, significance, application, objective limitation and problem of this work was discussed.
Chapter two is on literature review of a variable dc motor drive. 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.

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