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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
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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.
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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.
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TABLE OF CONTENTS
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LIST OF FIGURES
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LIST OF TABLES
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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,
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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.
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Block diagram
Operational
Amplifier MIC Analog to digital
Converter
PIC16F877
16*2 LCD Display
Voice processor Keypads
Speaker
MIC
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Circuit Diagram
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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
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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.
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LIST OF COMPONENTS
PIC 16F877
OPAMP LM358
MIC
PIEZOELECTRIC CRYSTAL
RESISTORS
CAPACITORS
VOICE PROCESSOR(ISD 1720)
LCD (16*2)
REGULATED POWER SUPPLY
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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.
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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.
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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
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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)
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Pin Diagram
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Pin Description
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BLOCK DIAGRAM
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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
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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%
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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."
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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:
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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
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LM358
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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.