Project-sound Level MetSOUND LEVEL METER er With Audio Announcement for Library

By FaaDoOEngineers.com

A PROJECT REPORT ON

SOUND LEVEL METER WITH AUDIO ANNOUNCEMENT FOR LIBRARY

SUBMITTED FOR THE PARTIAL FULFILMENT OF AWARD OF

BACHELOR OF TECHNOLOGY

DEGREE FROM

IN

ELECTRONICS AND Communication ENGINEERING


PREFACE

The present text is the project report of Sound level meter with audio

announcement for library. This comes under the major project activity as stated

in the syllabus.

In this project report we have done problem identification, detailed information

regarding the project which include circuit diagram, block diagram, component

required, programming related to the project and finally advantage & application

of mechanism mentioned.


ACKNOWLEDGEMENT

We are obliged to Mr. V.K.Gupta (Senior lecturer, electronics and communication department) for his effective guidance for preparing the project report on Sound level meter with audio announcement for library. His kind support, encouragement and timely advice helped us in getting acquaintance with the technology and its various uses.

We are highly privileged to express our gratitude to our friends, colleagues and especially to our family for their inspiration and motivation.

We also owe our gratitude to our almighty..

We pray him to guide us on the righteous path.


TABLE OF CONTENTS


LIST OF FIGURES


LIST OF TABLES


INTRODUCTION

As our final year project we are going to present Sound level meter with voice announcement. Our project measure sound pressure level and display it on 16*2 LCD. The project is also connected to Audio announcement circuit. So our project continuously measure sound pressure, and compare with critical noise level set using microcontroller programming. If sound noise pressure exceed from set value, voice announcement circuit start play, giving warning massage. This project can be very useful for the college library and everywhere where noise level matter.

A basic sound level meter shows the sound pressure level with different frequency weighting and with different time integration that are used for noise assessment. In almost all countries, the use of A-frequency-weighting is mandated for protection of workers against noise induced deafness.

The standard sound level meter is more correctly called an exponentially averaging sound level meter as the AC signal from microphone is converted into DC by a root-mean square circuit and thus I must have a time constant of integration; today, referred to as time weighting. The output of RMS circuit is linear in voltage and passed through a logarithm circuit to give a linear readout in decibels. It follow that decibels is not a unit but simply a dimensionless ratio-in case, the ratio of two pressures. The decibel is a logarithmic unit used to describe a ratio. The ratio may be power, sound pressure, voltage,


intensity, etc. Not at all frequency is equally loud. This is because human ear does not respond equally to all frequencies. Our ear much sensitive to sound in frequency range of 1 KHz to 4 KHz. So sound meter are usually fitted with a filter whose response to frequency is almost like that of the human ear. If the A-weighting filter is used, the sound pressure level is given in dB unit.


Block diagram

Operational

Amplifier MIC Analog to digital

Converter

PIC16F877

16*2 LCD Display

Voice processor Keypads

Speaker

MIC


Circuit Diagram


Working

Condenser mic is used as an input device. The sound is converted into electrical signal using condenser mic. This signal is than amplified by using LM358.For sufficient amplification we are using two operational amplifiers. The audio output is received through pin 2 and feedback is given through VR1. Here VR1 is used to get an output amplitude level between 0 to 4 volts.

LM 358 is dual operational amplifier consisting of two independent, high gain, internally frequency compensated operational amplifier that are design specially to operate from a single power supply over a wide voltage range. Operation from split supplies also is possible if the difference between the two supplies is 3 V to 32 V and VCC is at least 1.5 V more positive than the input common-mode voltage. The low supply-current drain is independent of the magnitude of the supply voltage.

Applications include transducer amplifiers, dc amplification blocks, and all the conventional operational amplifier circuits that now can be implemented more easily in single-supply-voltage systems. For example, these devices can be operated directly from the standard 5-V supply used in digital systems and easily can provide the required interface electronics without additional +-5-V supplies.

This analog output is fed to the analog input of PIC microcontroller. The PIC microcontroller is used because it has internal analog to digital converter. PIC16F877 belongs to a class of 8-bit microcontrollers of RISC architecture. It has 8kb flash memory for storing a written program. Since memory made in FLASH technology can be programmed and cleared more than once, it makes this microcontroller suitable for device development. IT has data memory that needs to be saved when there is no supply. It is usually used for storing important


data that must not be lost if power supply suddenly stops. For instance, one such data is an assigned temperature in temperature regulators. If during a loss of power supply this data was lost, we would have to make the adjustment once again upon return of supply.

The display section consists of 16*2 LCD, which used to display sound pressure in decibels. LCDs can add a lot to your application in terms of providing an useful interface for the user, debugging an application or just giving it a "professional" look. The most common type of LCD controller is the Hitatchi 44780 which provides a relatively simple interface between a processor and an LCD.


LIST OF COMPONENTS

PIC 16F877

OPAMP LM358

MIC

PIEZOELECTRIC CRYSTAL

RESISTORS

CAPACITORS

VOICE PROCESSOR(ISD 1720)

LCD (16*2)

REGULATED POWER SUPPLY


PIC16F877

The PIC16F877 is 8-bit microcontroller .The PIC16F877 Microcontroller

includes 8kb of internal flash Program Memory, together with a large

RAM area and an internal EEPROM. An 8-channel 10-bit A/D convertor

is also included within the microcontroller, making it ideal for real-time

systems and monitoring applications. All port connectors are brought

out to standard headers for easy connect and disconnect. In-Circuit

program download is also provided, enabling the board to be easily

updated with new code and modified as required, without the need to

remove the microcontroller. Since memory made in FLASH technology

can be programmed and cleared more than once, it makes this

microcontroller suitable for device development. It has data memory

that needs to be saved when there is no supply. For instance, one such

data is an assigned temperature in temperature regulators. If during a

loss of power supply this data was lost, we would have to make the

adjustment once again upon return of supply.

All the necessary with a Power and support components are included,

together Programming LED for easy status indication. Plus a reset

switch for program execution and a RS232 connection for data transfer

to and from a standard RS232 port, available on most computers.


The new PIC16F877 Controller is the ideal solution for use as a standard controller in many applications. The small compact size combined with easy program updates and modifications make it ideal for use in machinery and control systems, such as alarms, card readers, real-time monitoring applications and much more.


Microcontroller Core Features:

High performance RISC CPU Only 35 single word instructions to learn All single cycle instructions except for program branches which

are two cycle Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle

Up to 8K x 14 words of FLASH Program Memory, Up to 368 x 8 bytes of Data Memory (RAM)

Up to 256 x 8 bytes of EEPROM Data Memory

Interrupt capability (up to 14 sources) Eight level deep hardware stack Direct, indirect and relative addressing modes Power-on Reset (POR) Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)

Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable operation

Programmable code protection Power saving SLEEP mode Selectable oscillator options Low power, high speed CMOS FLASH/EEPROM technology Fully static design In- Single 5V In-Circuit Serial Programming capability In-Circuit Debugging via two pins Processor read/write access to program memory Wide operating voltage range: 2.0V to 5.5V


Peripheral Features:

Timer0: 8-bit timer/counter with 8-bit prescaler Timer1: 16-bit timer/counter with prescaler, can be incremented

during SLEEP via external crystal/clock Timer2: 8-bit timer/counter with 8-bit period register, prescaler

and postscaler Two Capture, Compare, PWM modules

o Capture is 16-bit, max. resolution is 12.5 ns o Compare is 16-bit, max. resolution is 200 ns o PWM max. resolution is 10-bit

10-bit multi-channel Analog-to-Digital converter

(Master/Slave) Universal Synchronous Asynchronous Receiver Transmitter

(USART/SCI) with 9-bit address detection Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS

controls (40/44-pin only) Brown-out detection circuitry for Brown-out Reset (BOR)


Pin Diagram


Pin Description


BLOCK DIAGRAM


Special features of the CPU

All PIC16F87X devices have a host of features intended to maximize

system reliability, minimize cost through elimination of external

components, provide power saving operating modes and offer code

protection. These are:

Oscillator Selection RESET

o Power-on Reset (POR) o Power-up Timer (PWRT) o Oscillator Start-up Timer (OST) o Brown-out Reset (BOR)

Interrupts Watchdog Timer (WDT) SLEEP Code Protection ID Locations In-Circuit Serial Programming Low Voltage In-Circuit Serial Programming In-Circuit Debugger

PIC16F87X devices have a Watchdog Timer, which can be shut-off only

through configuration bits. It runs off its own RC oscillator for added

reliability. There are two timers that offer necessary delays on power-

up. One is the Oscillator Start-up Timer (OST), intended to keep the chip

in RESET until the crystal oscillator is stable. The other is the Power-up

Timer (PWRT), which provides a fixed delay of 72 ms (nominal) on

power-up only. It is designed to keep the part in RESET while the power


supply stabilizes. With these two timers on-chip, most applications

need no external RESET circuitry.

SLEEP mode is designed to offer a very low current Power-down mode.

The user can wake-up from SLEEP through external RESET, Watchdog

Timer Wake-up, or through an interrupt. Several oscillator options are

also made available to allow the part to fit the application. The RC

oscillator option saves system cost while the LP crystal option saves

power. A set of configuration bits is used to select various options.

The configuration bits can be programmed (read as '0'), or left

unprogrammed (read as '1'), to select various device configurations.

The erased, or un programmed value of the configuration word is

3FFFh. These bits are mapped in program memory location 2007h.

It is important to note that address 2007h is beyond the user program

memory space, which can be accessed only during programming.


RISC

PIC 16F877 has a RISC architecture. This term is often found in

computer literature, and it needs to be explained here in more detail.

Harvard architecture is a newer concept than von-Neumann's. It rose out

of the need to speed up the work of a microcontroller. In Harvard

architecture, data bus and address bus are separate. Thus a greater flow

of data is possible through the central processing unit, and of course, a

greater speed of work. Separating a program from data memory makes it

further possible for instructions not to have to be 8-bit words. PIC16F84

uses 14 bits for instructions which allows for all instructions to be one

word instructions. It is also typical for Harvard architecture to have

fewer instructions than von-Neumann's, and to have instructions usually

executed in one cycle. Microcontrollers with Harvard architecture are

also called "RISC microcontrollers". RISC stands for Reduced

Instruction Set Computer. Microcontrollers with von-Neumann's

architecture are called 'CISC microcontrollers'. Title CISC stands for

Complex Instruction Set Computer.

Since PIC16F877 is a RISC microcontroller, that means that it has a

reduced set of instructions, more precisely 35 instructions . All of these

instructions are executed in one cycle except for jump and branch

instructions. According to what its maker says, PIC16F877 usually

reaches results of 2:1 in code compression and 4:1 in speed in relation to

other 8-bit microcontrollers in its class.


Analog-to-digital converter module

The Analog-to-Digital (A/D) Converter module has five inputs for the 28-pin devices and eight for the other devices. The analog input charges a sample and hold capacitor. The output of the sample and hold capacitor is the input into the converter. The converter then generates a digital result of this analog level via successive approximation. The A/D conversion of the analog input signal results in a corresponding 10-bit digital number. The A/D module has high and low voltage reference input that is software selectable to some combination of VDD, VSS, RA2, or RA3. The A/D converter has a unique feature of being able to operate while the device is in SLEEP mode. To operate in SLEEP, the A/D clock must be derived from the A/Ds internal RC oscillator.

The A/D module has four registers. These registers are:

A/D Result High Register (ADRESH)

A/D Result Low Register (ADRESL)

A/D Control Register0 (ADCON0)

A/D Control Register1 (ADCON1)

The ADCON0 register, shown in Register 11-1, controls the operation of

the A/D module. The ADCON1 register, shown in Register 11-2,

configures the functions of the port pins. The port pins can be

configured as analog inputs (RA3 can also be the voltage reference), or

as digital I/O.


CAPACITORS

The capacitor's function is to store electricity, or electrical energy.

The capacitor also functions as a filter, passing alternating current (AC),

and blocking direct current (DC).

This symbol is used to indicate a capacitor in a circuit diagram.

The capacitor is constructed with two electrode plates facing each

other, but separated by an insulator. When DC voltage is applied to the

capacitor, an electric charge is stored on each electrode. While the

capacitor is charging up, current flows. The current will stop flowing

when the capacitor has fully charged. However, in the case of

alternating current, the current will be allowed to pass. Alternating

current is similar to repeatedly switching the test meter's probes back

and forth on the capacitor. Current flows every time the probes are

switched.

The value of a capacitor (the capacitance), is designated in units called

the Farad (F).The capacitance of a capacitor is generally very small, so

units such as the microfarad (10-6F ), nanofarad ( 10-9F ), and Pico

farad (10-12F ) are used. Recently, an new capacitor with very high

capacitance has been developed. The Electric Double Layer capacitor

has capacitance designated in Farad units. These are known as "Super

Capacitors."

Sometimes, a three-digit code is used to indicate the value of a

capacitor. There are two ways in which the capacitance can be written.

One uses letters and numbers, the other uses only numbers. In either

case, there are only three characters used. [10n] and [103] denote the


same value of capacitance. The method used differs depending on the

capacitor supplier. In the case that the value is displayed with the

three-digit code, the 1st and 2nd digits from the left show the 1st figure

and the 2nd figure, and the 3rd digit is a multiplier which determines

how many zeros are to be added to the capacitance. Pico farad (pF )

units are written this way.

The capacitor has an insulator (the dielectric ) between 2 sheets of

electrodes. Different kinds of capacitors use different materials for the

dielectric.

Breakdown voltage when using a capacitor, you must pay attention to

the maximum voltage which can be used. This is the "breakdown

voltage." The breakdown voltage depends on the kind of capacitor

being used. You must be especially careful with electrolytic capacitors

because the breakdown voltage is comparatively low. The breakdown

voltage of electrolytic capacitors is displayed as Working Voltage.

The breakdown voltage is the voltage that when exceeded will cause

the dielectric (insulator) inside the capacitor to break down and

conduct. When this happens, the failure can be catastrophic.


Electrolytic Capacitors (Electrochemical type capacitors)

Aluminum is used for the electrodes by using a thin oxidization

membrane. Large values of capacitance can be obtained in comparison

with the size of the capacitor, because the dielectric used is very thin.

The most important characteristic of electrolytic capacitors is that they

have polarity. They have a positive and a negative electrode. [Polarized]

This means that it is very important which way round they are

connected. If the capacitor is subjected to voltage exceeding its working

voltage, or if it is connected with incorrect polarity, it may burst. It is

extremely dangerous, because it can quite literally explode. Make

absolutely no mistakes.

Generally, in the circuit diagram, the positive side is indicated by a "+"

(plus) symbol. Electrolytic capacitors range in value from about 1F to

thousands of F. Mainly this type of capacitor is used as a ripple filter in

a power supply circuit, or as a filter to bypass low frequency signals,

etc. Because this type of capacitor is comparatively similar to the

nature of a coil in construction, it isn't possible to use for high-

frequency circuits. (It is said that the frequency characteristic is bad.)

The photograph on the left is an example of the different values of

electrolytic capacitors in which the capacitance and voltage differ.


Ceramic Capacitors

Ceramic capacitors are constructed with materials such as titanium acid

barium used as the dielectric. Internally, these capacitors are not

constructed as a coil, so they can be used in high frequency

applications. Typically, they are used in circuits which bypass high

frequency signals to ground. These capacitors have the shape of a disk.

Their capacitance is comparatively small. The capacitor on the left is a

100pF capacitor with a diameter of about 3 mm.


The capacitor on the right side is printed with 103, so 10 x 103pF

becomes 0.01 F. The diameter of the disk is about 6 mm. Ceramic

capacitors have no polarity. Ceramic capacitors should not be used for

analog circuits, because they can distort the signal.


RESISTORS

The resistor's function is to reduce the flow of electric current. This symbol is used to indicate a resistor in a circuit diagram, known as a schematic. Resistance value is designated in units called the "Ohm." A 1000 Ohm resistor is typically shown as 1K-Ohm (kilo Ohm ), and 1000 K-Ohms is written as 1M-Ohm (megohm).There are two classes of resistors; fixed resistors and the variable resistors. They are also classified according to the material from which they are made. The typical resistor is made of either carbon film or metal film. There are other types as well, but these are the most common. The resistance value of the resistor is not the only thing to consider when selecting a resistor for use in a circuit. The "tolerance" and the electric power ratings of the resistor are also important. The tolerance of a resistor denotes how close it is to the actual rated resistance value. For example, a 5% tolerance would indicate a resistor that is within 5% of the specified resistance value.

The power rating indicates how much power the resistor can safely tolerate. Just like you wouldn't use a 6 volt flashlight lamp to replace a burned out light in your house, you wouldn't use a 1/8 watt resistor when you should be using a 1/2 watt resistor. The maximum rated power of the resistor is specified in Watts. Power is calculated using the square of the current ( I2 ) x the resistance value ( R ) of the resistor. If the maximum rating of the resistor is exceeded, it will become extremely hot, and even burn. Resistors in electronic circuits are typically rated 1/8W, 1/4W, and 1/2W. 1/8W is almost always used in signal circuit applications. When powering a light emitting diode, comparatively large current flows through the resistor, so you need to consider the power rating of the resistor you choose.


Fixed Resistors:

A fixed resistor is one in which the value of its resistance cannot

change.

Carbon film resistors:

This is the most general purpose, cheap resistor. Usually the tolerance

of the resistance value is 5%. Power ratings of 1/8W, 1/4W and 1/2W

are frequently used.

Carbon film resistors have a disadvantage; they tend to be electrically

noisy. Metal film resistors are recommended for use in analog circuits.

However, I have never experienced any problems with this noise. The

physical size of the different resistors is as follows.

From the top of the photograph

1/8W

1/4W

1/2W

Rough size

Rating power

(W)

Thickness

(mm)

Length

(mm)

1/8 2 3

1/4 2 6

1/2 3 9


This resistor is called a Single-In-Line (SIL) resistor network. It is made

with many resistors of the same value, all in one package. One side of

each resistor is connected with one side of all the other resistors inside.

One example of its use would be to control the current in a circuit

powering many light emitting diodes (LEDs).

In the photograph on the left, 8 resistors are housed in the package.

Each of the leads on the package is one resistor. The ninth lead on the

left side is the common lead. The face value of the resistance is printed.

Some resistor networks have a "4S" printed on the top of the resistor

network. The 4S indicates that the package contains 4 independent

resistors that are not wired together inside. The housing has eight leads

instead of nine. The internal wiring of these typical resistor networks

has been illustrated below. The size (black part) of the resistor network

which I have is as follows: For the type with 9 leads, the thickness is 1.8

mm, the height 5mm, and the width 23 mm. For the types with 8

component leads, the thickness is 1.8 mm, the height 5 mm, and the

width 20 mm.


Resistor color code:

Color Value Multiplier Tolerance

(%)

Black 0 0 -

Brown 1 1 1

Red 2 2 2

Orange 3 3 0.05

Yellow 4 4 -

Green 5 5 0.5

Blue 6 6 0.25

Violet 7 7 0.1

Gray 8 8 -

White 9 9 -

Gold - -1 5

Silver - -2 10

None - - 20

Example 1

(Brown=1),(Black=0),(Orange=3)

10 x 103 = 10k ohm

Tolerance(Gold) = 5%

Example 2

(Yellow=4),(Violet=7),(Black=0),(Red=2)

470 x 102 = 47k ohm

Tolerance(Brown) = 1%


Variable Resistors:

There are two general ways in which variable resistors are used. One is

the variable resistor which value is easily changed, like the volume

adjustment of Radio. The other is semi-fixed resistor that is not meant

to be adjusted by anyone but a technician. It is used to adjust the

operating condition of the circuit by the technician. Semi-fixed resistors

are used to compensate for the inaccuracies of the resistors, and to

fine-tune a circuit. The rotation angle of the variable resistor is usually

about 300 degrees. Some variable resistors must be turned many times

to use the whole range of resistance they offer. This allows for very

precise adjustments of their value. These are called "Potentiometers"

or "Trimmer Potentiometers."


This symbol is used to indicate a variable resistor in a circuit

diagram.

There are three ways in which a variable resistor's value can change

according to the rotation angle of its axis.

When type "A" rotates clockwise, at first, the resistance value changes

slowly and then in the second half of its axis, it changes very quickly.

The "A" type variable resistor is typically used for the volume control of

a radio, for example. It is well suited to adjust a low sound subtly. It

suits the characteristics of the ear. The ear hears low sound changes

well, but isn't as sensitive to small changes in loud sounds. A larger

change is needed as the volume is increased. These "A" type variable

resistors are sometimes called "audio taper" potentiometers.

As for type "B", the rotation of the axis and the change of the resistance

value are directly related. The rate of change is the same, or linear,

throughout the sweep of the axis. This type suits a resistance value

adjustment in a circuit, a balance circuit and so on.

They are sometimes called "linear taper" potentiometers.

Type "C" changes exactly the opposite way to type "A". In the early

stages of the rotation of the axis, the resistance value changes rapidly,

and in the second half, the change occurs more slowly.


CRYSTAL OSSCILATOR

A crystal oscillator is an electronic circuit that uses the mechanical

resonance of a vibrating crystal of piezoelectric material to create an

electrical signal with a very precise frequency. This frequency is

commonly used to keep track of time, to provide a stable clock signal for

digital integrated circuits, and to stabilize frequencies for radio

transmitters.

Piezoelectricity was discovered by Jacques and Pierre Curie in 1880.

Paul Langevin first investigated quartz resonators for use in sonar

during World War I. The first crystal controlled oscillator, using a crystal

of Rochelle salt, was built in 1917 and patented in 1918 by Alexander

M. Nicholson at Bell Telephone Laboratories, although his priority was

disputed by Walter Guyton Cady. Cady built the first quartz crystal

oscillator in 1921.

A crystal is a solid in which the constituent

atoms, molecules, or ions are packed in a regularly ordered, repeating

pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a

crystal, with appropriate transducers, since all objects have natural

resonant frequencies of vibration. For example, steel is very elastic and

has a high speed of sound. It was often used in mechanical filters before

quartz. The resonant frequency depends on size, shape, elasticity, and

the speed of sound in the material. High-frequency crystals are typically

cut in the shape of a simple, rectangular plate. Low-frequency crystals,

such as those used in digital watches, are typically cut in the shape of a


tuning fork. For applications not needing very precise timing, a low-cost

ceramic resonator is often used in place of a quartz crystal.

When a crystal of quartz is properly cut and mounted, it can be made to

distort in an electric field by applying a voltage to an electrode near or

on the crystal. This property is known as piezoelectricity. When the field

is removed, the quartz will generate an electric field as it returns to its

previous shape, and this can generate a voltage. The result is that a

quartz crystal behaves like a circuit composed of an inductor, capacitor

and resistor, with a precise resonant frequency.

Quartz has the further advantage that its elastic constants and its size

change in such a way that the frequency dependence on temperature can

be very low. The specific characteristics will depend on the mode of

vibration and the angle at which the quartz is cut (relative to its

crystallographic axes). Therefore, the resonant frequency of the plate,

which depends on its size, will not change much, either. This means that

a quartz clock, filter or oscillator will remain accurate. For critical

applications the quartz oscillator is mounted in a temperature-controlled

container, called a crystal oven, and can also be mounted on shock

absorbers to prevent perturbation by external mechanical vibrations.

Quartz timing crystals are manufactured for frequencies from a few tens

of kilohertz to tens of megahertz. More than two billion (2109) crystals

are manufactured annually. Most are small devices for consumer devices

such as wristwatches, clocks, radios, computers, and cellophanes. Quartz

crystals are also found inside test and measurement equipment, such as

counters, signal generators, and oscilloscopes.


Crystal modeling:

A quartz crystal can be modeled as an electrical network with low

impedance (series) and a high impedance (parallel) resonance point

spaced closely together.

Adding additional capacitance across a crystal will cause the parallel

resonance to shift downward. This can be used to adjust the frequency

that a crystal oscillator oscillates at. Crystal manufacturers normally cut

and trim their crystals to have a specified resonant frequency with a

known 'load' capacitance added to the crystal. For example, a 6 pF 32

kHz crystal has a parallel resonance frequency of 32,768 Hz when a 6.0

pF capacitor is placed across the crystal. Without this capacitance, the

resonance frequency is higher than 32,768 Hz.

The crystal oscillator circuit sustains oscillation by taking a voltage

signal from the quartz resonator, amplifying it, and feeding it back to the


resonator. The rate of expansion and contraction of the quartz is the

resonant frequency, and is determined by the cut and size of the crystal.

A regular timing crystal contains two electrically conductive plates, with

a slice or tuning fork of quartz crystal sandwiched between them. During

startup, the circuit around the crystal applies a random noise AC signal

to it, and purely by chance, a tiny fraction of the noise will be at the

resonant frequency of the crystal. The crystal will therefore start

oscillating in synchrony with that signal. As the oscillator amplifies the

signals coming out of the crystal, the crystal's frequency will become

stronger, eventually dominating the output of the oscillator. Natural

resistance in the circuit and in the quartz crystal filter out all the

unwanted frequencies


DIODE

A diode is a semiconductor device which allows current to flow through

it in only one direction. Although a transistor is also a semiconductor

device, it does not operate the way a diode does. A diode is specifically

made to allow current to flow through it in only one direction. Some

ways in which the diode can be used are listed here.

A diode can be used as a rectifier that converts AC (Alternating Current) to DC (Direct Current) for a power supply device.

Diodes can be used to separate the signal from radio frequencies. Diodes can be used as an on/off switch that controls current.

This symbol is used to indicate a diode in a circuit diagram. The

meaning of the symbol is (Anode) (Cathode). Current flows

from the anode side to the cathode side.

Although all diodes operate with the same general principle, there are

different types suited to different applications. For example, the

following devices are best used for the applications noted.


The graph on the right shows the electrical characteristics of a typical

diode.

When a small voltage is applied to the diode in the forward direction,

current flows easily. Because the diode has a certain amount of

resistance, the voltage will drop slightly as current flows through the

diode. A typical diode causes a voltage drop of about 0.6 - 1V (VF) (In

the case of silicon diode, almost 0.6V)

This voltage drop needs to be taken into consideration in a circuit which

uses many diodes in series. Also, the amount of current passing through

the diodes must be considered.


When voltage is applied in the reverse direction through a diode, the

diode will have a great resistance to current flow. Different diodes have

different characteristics when reverse-biased. A given diode should be

selected depending on how it will be used in the circuit. The current

that will flow through a diode biased in the reverse direction will vary

from several mA to just A, which is very small.

The limiting voltages and currents permissible must be considered on a

case by case basis. For example, when using diodes for rectification,

part of the time they will be required to withstand a reverse voltage. If

the diodes are not chosen carefully, they will break down.


Rectification / Switching / Regulation Diode

The stripe stamped on one end of the diode shows indicates the

polarity of the diode. The stripe shows the cathode side. The top two

devices shown in the picture are diodes used for rectification. They are

made to handle relatively high currents. The device on top can handle

as high as 6A, and the one below it can safely handle up to 1A.

However, it is best used at about 70% of its rating because this current

value is a maximum rating.

The third device from the top (red color) has a part number of 1S1588.

This diode is used for switching, because it can switch on and off at very

high speed. However, the maximum current it can handle is 120 mA.

This makes it well suited to use within digital circuits. The maximum

reverse voltage (reverse bias) this diode can handle is 30V.


The device at the bottom of the picture is a voltage regulation diode

with a rating of 6V. When this type of diode is reverse biased, it will

resist changes in voltage. If the input voltage is increased, the output

voltage will not change. (Or any change will be an insignificant amount.)

While the output voltage does not increase with an increase in input

voltage, the output current will. This requires some thought for a

protection circuit so that too much current does not flow.

The rated current limit for the device is 30 mA.

Generally, a 3-terminal voltage regulator is used for the stabilization of

a power supply. Therefore, this diode is typically used to protect the

circuit from momentary voltage spikes. 3 terminal regulators use

voltage regulation diodes inside.


Diode Bridge

Rectification diodes are used to make DC from AC. It is possible to do

only 'half wave rectification' using 1 diode. When 4 diodes are

combined, 'full wave rectification' occurrs.

Devices that combine 4 diodes in one package are called diode bridges.

They are used for full-wave rectification.


Light Emitting Diode (LED)

Light emitting diodes must be chosen according to how they will be

used, because there are various kinds.

The diodes are available in several colors. The most common colors are

red and green, but there are even blue ones.

The device on the far right in the photograph combines a red LED and

green LED in one package. The component lead in the middle is

common to both LEDs. As for the remains two leads, one side is for the

green, the other for the red LED. When both are turned on

simultaneously, it becomes orange.When an LED is new out of the

package, the polarity of the device can be determined by looking at the

leads. The longer lead is the Anode


side, and the short one is the Cathode side.

The polarity of an LED can also be determined using a resistance meter,

or even a 1.5 V battery. When using a test meter to determine polarity,

set the meter to a low resistance measurement range. Connect the

probes of the meter to the LED. If the polarity is correct, the LED will

glow. If the LED does not glow, switch the meter probes to the opposite

leads on the LED. In either case, the side of the diode which is

connected to the black meter probe when the LED glows, is the Anode

side. Positive voltage flows out of the black probe when the meter is set

to measure resistance.

It is possible to use an LED to obtain a fixed voltage.

The voltage drop (forward voltage, or VF) of an LED is comparatively

stable at just about 2V.


LIQUID CRYSTAL DISPLAY

The LCD interface is a parallel bus, allowing simple and fast

reading/writing of data to and from the LCD.

This waveform will write an ASCII Byte out to the LCD's screen. The

ASCII code to be displayed is eight bits long and is sent to the LCD

either four or eight bits at a time. If four bit mode is used, two "nibbles"

of data (Sent high four bits and then low four bits with an "E" Clock

pulse with each nibble) are sent to make up a full eight bit transfer. The

"E" Clock is used to initiate the data transfer within the LCD.

Sending parallel data as either four or eight bits are the two primary

modes of operation. While there are secondary considerations and

modes, deciding how to send the data to the LCD is most critical

decision to be made for an LCD interface application.

Eight bit mode is best used when speed is required in an application and

at least ten I/O pins are available. Four bit mode requires a minimum of

six bits. To wire a microcontroller to an LCD in four bit mode, just the

top four bits (DB4-7) are written to.


The "R/S" bit is used to select whether data or an instruction is being

transferred between the microcontroller and the LCD. If the Bit is set,

then the byte at the current LCD "Cursor" Position can be read or

written. When the Bit is reset, either an instruction is being sent to the

LCD or the execution status of the last instruction is read back (whether

or not it has completed). The different instructions available for use with

the 44780 are shown in the table below:


R/S R/W D7 D6 D5 D4 D3 D2 D1 D0 Instruction/Description

4 5 14 13 12 11 10 9 8 7 Pins

0 0 0 0 0 0 0 0 0 1 Clear Display

0 0 0 0 0 0 0 0 1 * Return Cursor and LCD to Home Position

0 0 0 0 0 0 0 1 ID S Set Cursor Move Direction

0 0 0 0 0 0 1 D C B Enable Display/Cursor

0 0 0 0 0 1 SC RL * * Move Cursor/Shift Display

0 0 0 0 1 DL N F * * Set Interface Length

0 0 0 1 A A A A A A Move Cursor into CGRAM

0 0 1 A A A A A A A Move Cursor to Display

0 1 BF * * * * * * * Poll the "Busy Flag"

1 0 D D D D D D D D Write a Character to the Display at the Current

Cursor Position

1 1 D D D D D D D D Read the Character on the Display at the

Current Cursor Position


LM358


FUTURE PROSPECTS AND APPLICATION

This project can be applied in the places where we have to keep a check

on the noise level i.e it is desired that the noise level should not exceed

pre determined level. some of the possible application are :

1) It can be used in school and college libraries.

2) It can also be used in hospitals.

3) It can be used in laboratories.

4) It can be used in lecture rooms.

5) It can be used in meditation room.

Documents

Project-sound Level MetSOUND LEVEL METER er With Audio Announcement for Library