Logic Gates

Circuits which are used to process digital signals are called logic gates. In electronics, a logic gate is an idealized or physical device implementing a Boolean function; that is, it performs a logical operation on one or more logical inputs, and produces a single logical output. Logic gates are building blocks of digital electronics. They are used in digital

electronics to change one voltage level (input

voltage) into another (output voltage) according to some logical statement relating them. Thus logic gate is a digital circuit which works according to some logical relationship between input and output

voltages.

The earliest logic gates were made mechanically. Charles Babbage, around 1837, devised the

Analytical Engine. His logic gates relied on mechanical gearing to perform operations.

Electromagnetic relays were later used for logic gates. In 1891,Almon Strowger patented a device containing a logic gate switch circuit. Strowger's patent was not in widespread use until the1920s. Starting in 1898,Nikola Tesla filed for patents of devices containing logic gate circuits .Eventually, vacuum tubes replaced relays for logic operations. Lee De Forest's modification, in 1907, of the Fleming

valve, can be used as AND logic gate. Claude E. Shannon introduced the use of Boolean algebra in the analysis and design of switching circuits in 1937.WaltherBothe, inventor of the coincidence circuit, got part of the 1954Nobel Prize in physics, for the first modern electronic AND gate in 1924.

Generally, there are three types of logic gates:- 1.OR GATE

2.AND GATE 3.NOT GATE

The OR gate is a digital logic gate that

implements logical disjunction - it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are

HIGH (1). If neither input is high, a LOW output (0) results. In another sense, the function of OR

effectively finds the maximum between two binary digits.

Boolean expression - a + b = f

Symbol-

Truth table-

Circuit diagram-

OR GATE

The AND gate is a basic digital logic gate that implements logical conjunction - it behaves

according to the truth table to the right. A HIGH output (1) results only if both the inputs to the AND gate are HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output results. In

another sense, the function of AND effectively finds the minimum between two binary digits.

Boolean expression – a.b=f

Symbol-

Truth table-

Circuit diagram-

A NOT gate (also often called Inverter) is a logic gate. It takes one input signal. In logic, there are usually two states, 0 and 1. The gate therefore sends 1 as output, if it receives 0 as input.

Alternatively it received 1 as input, and sends 0 as output.

Boolean expression - a

Symbol-

Truth table-

Circuit

NOT GATE

The various possible combinations of the input and output of the

OR gate

can be easily understand with the help of the electrical circuit. In this electric circuit, a parallel combination of two switches A and B is connected to a battery and a lump L.

The following interference can be easily drawn from the working of electrical circuit:

a) If switch A & B are open lamp do not glow (A=0, B=0)

b) If Switch A open B closed then (A=0, B=1) Lamp glow.

c) If switch A closed B open then (A=1, B=0) Lamp glow.

d) If switch A & B are closed then (A=1, B=1) Lamp glow.

As we see truth table we found same as it is observation.

The various possible combination of the input and outputs of the AND gate can be easily found with the help of the electrical circuit. Here a series combination of the switch A and B is connected to a battery and a lump L.

The following conclusions can be easily drawn from the working of electrical circuit:

a) If both switches A&B are open (A=0, B=0) then lamp will not glow. (y=0)

b) If Switch A closed & B open (A=1, B=0) then Lamp will not glow. (y=0)

c) If switch A open & B closed (A=0, B=1) then Lamp will not glow. (y=0)

d) If switch A & B both closed (A=1, B=1) then Lamp will glow. (y=1)

As we see truth table we found same as it is observed experimentally.

The possible input and output combination of a

NOT

gate can be easily discussed with the help of electrical circuit. Here, the switch is connected in parallel to the lump of the battery. The following conclusion can be easily drawn from the working of the electrical circuit:

a) If switch A is open (i.e. A=0), the lump will glow (i.e. Y=1)

b) If Switch A is closed (i.e. A=1), the lump will not glow (Y=0).

It follows that in the given electrical circuit, the lump glows (or output is obtained), when the switch A is not closed. Far this reason, the electrical circuit is called not gate. The two possible input-output combinations can be written in the form of the table. It is called truth table of NOT gate.

To demonstrate the working of logic gates using torch, bulbs, battery and switches.

Torch, bulb, battery, switches, connecting wires, battery eliminator as source of EMF.

Q.

AIM

MATERIALS REQUIRED

1. INTRODUCTION

2. TYPES OF LOGIC GATES

3. USES

4. AIM

5. MATERIALS REQUIRED

6. PROCEDURE

7. RESULT

8. BIBLIOGRAPHY

CONTENTS

CERTIFICATE

This is to certify that this investigatory project titled to investigate about logic gates submitted by SHUBHAM TIWARI to physics department of OXFORD PUBLIC SCHOOL has been carried under the guidance and supervision during the academic year 2014-2015.

ACKNOWLEDGEMENT

This project shows my devotion of efforts. For

making this project more informative I would like to thanks principal ma’am REKHA SINGH for

providing me with all the required material for this project.

I would whole heartedly like to thanks SHELJA MA’AM for guiding me and my colleagues

throughout this project. She explained everything about the project. Moreover a great thanks to her as she gave us such a interesting project.

I would like to thank everyone who all supported me directly or indirectly, for helping me to complete this project effectively. I have tried to put my best efforts in this activity.

PREFACE

Action is the language of commitment, It speaks louder than words.

The theoretical knowledge and classroom discussion have its own limitation.

This project intends to study the basic logic gates. The data used in the project report are obtained mainly from physics department to suit the

requirements for project report.

Hence the purpose and interest of subject in maintained.

The external visits plays a dominant role to develop the practical.

OR GATE:

 DETECT TEMPERATURE  DETECT PRESSURE  COMMAND SIGNAL

AND GATE:

 TO MEASURE FREQUENCY

 AS AN INHIBIT AND EXIHIBIT GATE

NOT GATE

 LIGHT SENSOR  REGULATOR

 PRESSURE PLATE

BIBLIOGRAPHY

1. WWW.WIKIPEDIA.COM

2. WWW.CBSE.NIC.IN