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CHAPTER ONE

INTRODUCTION

The power supply is culmed produce power required by the component to function. It coverts line voltage which is AC to DC and to a level that can be used by the various components. This is achieved by the use of a step down transformer to step down rectify, filtrate and regulate the line voltage.

THE SHIFT REGISTER

The shift register is a serial-in, parallel out register, it is responsible for the display “WELCOME TO ELECT/ELECT DEPT.” WELCOME” comes up frist, after some time interval which will be determined by the 1MSO resistor or a variable resistor “TO” come up, followed by “ELECT/ELECT” and finally “DEPT”.

The process is repeated, The counter is a decade counter with a decorded outputs. It controls the boarder display pattern in the form of light laser pattern. The rate at which the lights display is determined by the frequency of the 55C1MOS timer chip which acts as a clock generator that generates square wave to the counter.

Hence, the timing of the whole circuit is controlled by the four 555CMOS I.C. in the circuit. Each timer controls the sequence of each lamp at the terminal with the help of the relay drive.

RELAY

A simple relay is made from a coil of wire wound around a soft iron core with the ends of this coil at erminals, when it is energized the soft iron core become a magnet and attracts the armature. The working principle of simple normally open relay found a wide application in this circuit for the switching “ON” and “OFF” of the lamps.

TRANSISTOR

This is another three terminal semi-conducting device. It is basically made of N-type material and P-type material.

A simple transistor is of two types namely:

NPN transistor and 

PNP transistor

A transistor always performs two or more functions in a circuit, it can either function as:

1. An amplifier 

2. A switch.

This functions depends on how it is connected in the circuit. In this work, we are going to dwell much on it’s function as a switch. The output squared wave signal from the timer is fed to the base of the PNP transistor this signal suffers several venations at the function of the transistor. Finally, passed through the emitter of the transistor to trigger the relay as required.