Design And Construction Of An Astable Multivibrator Using Transistors

ABSTRACT

The aim of this work is to design and fabricate an astable multivibrator. An Astable Multivibrator is an oscillator circuit that continuously produces rectangular wave without the aid of external triggering. Astable Multivibrator is also known as Free Running Multivibrator. The astable multivibrator is not stable and it repeatedly switches from one state to the other. Astable Multivibrator using transistor is very simple, easy to design, very stable and low cost. It can be used for timing from microseconds to hours.

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE PROJECT
• AIM OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• APPLICATION OF THE PROJECT
• ADVANTAGES OF THE PROJECT
• LIMITATION OF THE PROJECT
• SCOPE OF THE PROJECT
• METHODOLOGY
• PROJECT ORGANISATION

CHAPTER TWO

2.0     LITERATURE REVIEW

2.1     OVERVIEW OF THE STUDY

2.2     HISTORICAL BACKGROUND OF THE STUDY

2.3     OPERATIONAL REVIEW OF ASTABLE

CHAPTER THREE

3.0     CONSTRUCTION METHODOLOGY

3.1     BASICS OF THE SYSTEM

3.2      SYSTEM DIAGRAM

3.3     CIRCUIT DESCRIPTION

3.4     LIST OF COMPONENTS

3.5      OUTPUT WAVEFORM

3.5      DESIGN OF TRANSISTORISED ASTABLE MULTIVIBRATOR

3.6      THEORY OF COMPONENTS USED

CHAPTER FOUR

RESULT ANALYSIS

4.0      CONSTRUCTION PROCEDURE

4.1      CASING AND PACKAGING

4.2      ASSEMBLING OF SECTIONS

4.3      TESTING OF SYSTEM OPERATION

4.4     PACKAGING

4.5     MOUNTING PROCEDURE

4.6     RESULT

4.7     COST ANALYSIS

CHAPTER FIVE

5.1      CONCLUSION AND RECOMMENDATION

5.2      REFERENCES

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                           BACKGROUND OF THE STUDY

A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers and flip-flops. It consists of two amplifying devices (transistors, vacuum tubes or other devices) cross-coupled by resistors or capacitors. The first multivibrator circuit, the astable multivibrator oscillator, was invented by Henri Abraham and Eugene Bloch during World War I. They called their circuit a “multivibrator” because its output waveform was rich in harmonics.

Multivibrators find applications in a variety of systems where square waves or timed intervals are required. For example, before the advent of low-cost integrated circuits, chains of multivibrators found use as frequency dividers. A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency would accurately lock to the reference frequency. This technique was used in early electronic organs, to keep notes of different octaves accurately in tune. Other applications included early television systems, where the various line and frame frequencies were kept synchronized by pulses included in the video signal.

Multivibrators are classified into three types based on the circuit operation, namely Astable multivibrators, Bistable multivibrators and Monostable multivibrators. The astable multivibrator is not stable and it repeatedly switches from one state to the other. In monostable multivibrator, one state is stable and remaining state is unstable. A trigger pulse is the root to the circuit to enter the unstable state. When the circuit enters into the unstable state, then it will return to the normal state after a fixed time. A bistable mutivibrator circuit is stable that can be changed from one stable to other stable by an external trigger pulse. This multivibrator circuit is also called as flip-flop which can be used to store one bit of data.

However, for the course of this work we are dealing with an astable type of multivibrator. This type of multivibrator includes two amplifying stages that are connected with a two capacitive-resistive coupling networks in a positive feedback.

The aim of this work is to design an astable multivibrator using transistors.

1.2                                                   AIM OF THE PROJECT

There are three different types of multivibrator, but the main aim of this work is to design an astable multivibrator using transistor.

1.3                                             OBJECTIVE OF THE PROJECT

After completing this work, student involved would able to learn:

1. What is an astable Multivibrator.
2. How transistors are wired to works as an astable multivibrator.
3. How it produces square wave.
4. What is the role of capacitor in an astable multivibrator circuit.

1.4                                         SIGNIFICANCE OF THE PROJECT

The oscillation frequency can be measured manually by small modification. Transistors used are relatively cheap, stable and user-friendly circuit.

1.5                                         APPLICATIONS OF THE PROJECT

The applications of Astable multivibrators involve in radio gears to transmit and receive radio signals and also in time, morse code generators and some systems which require a square wave like analog integrated circuits and TV broadcasts.

1.6                                          ADVANTAGES OF THE PROJECT

These multivibrators are changes between one stable state to another continuously. This permits multivibrators to power themselves and achieve work at a constant rate without impact from any external forces or actions. Also, these multivibrators are low cost to produce, and simple to design.

• LIMITATION OF THE PROJECT

These multivibrators do not transfer the whole o/p signal to the i/p. This is due to resistance in the circuit, nonexistence of a totally closed loop at the o/p terminals, and the leaning of one transistor/capacitor to absorb energy at a somewhat different rate than the other. Although the amplifier restores the lost energy when it amplifies the signal, the signal will finally be too small to be of any use.

1.8                                                 SCOPE OF THE PROJECT

This work is on transistor based astable multivibrator which is a type of cross-coupled transistor switching circuit that has NO stable output states as it changes from one state to the other all the time. The astable circuit consists of two switching transistors, a cross-coupled feedback network, and two time delay capacitors which allows oscillation between the two states with no external triggering to produce the change in state.

1.9                                                        METHODOLOGY

To achieve the aim and objectives of this work, the following are the steps involved:

1. Study of the previous work on the project so as to improve it efficiency.
2. Draw a block diagram.

• Test for continuity of components and devices,

1. Design and calculation for the device was carried out.
2. Studying of various component used in circuit.
3. Construction of the circuit was carried out.

• Finally, the whole device was cased and final test was carried out.

1.10                                             PROJECT ORGANISATION

This work is divided into five sections including this introduction. Section 2 is on the literature review and method of data collection are in Section 3. Results of findings are discussed in Section 4. The way forward is and conclusion in Section 5.