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ABSTRACT
Using this circuit you can communicate with your neighbours wirelessly. Infrared
signals are used as the carrier in the circuit. The infrared signals can transmit up to a
distance of about 5 meters. The phototransistor of the receiver must be accurately oriented
towards the IR beam. If there is any obstruction in the path of the IR beam, no sound will
be heard from the receiver.
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INDEX
1. INTRODUCTION
1.1 Objective of the Project
1.2 Circuit Diagram
1.3 Principle of Operation
1.4 System Features
1.5 Equipments
2. DESCRIPTION OF THE PROJECT
2.1 Block Diagram Description
3. HARDWARE DESCRIPTION
3.1 Resistors
3.2 Capacitirs
3.3 Use of Infrared Detector Basics
3.4 Condenser Microphones
3.5 IC UA741
3.6 IC LM386
3.7 BD139 Heat Sink
3.8 Power Supply
4. CONCLUSION
5. BIBLIOGRAPHY
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CHAPTER 1
INTRODUCTION:
IR-BASED VOICE TRANSMITTER AND RECEIVER, the aim of the project is to
communicate wirelessly. In this project we are using various transistors, LED, op-amp etc.
and we made a detailed study on this so as to effectively use them in our project.
1.1 OBJECTIVE OF THE PROJECT: - The aim of the project is to communicate between any 2 distant places wirelessly
which are at a distance of 5meters apart. The distance can be improved to even 500meters
using Laser light devices. This communication is very much use full when you want to
communicate with some one which is very important.
This kind of technology is very much useful in Army and Defence, since their
communication is very much crucial.
1.2 CIRCUIT DIAGRAM :-
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Design and Fabrication of PCB
Project phase: -
Schematic design and drawing of PCB
Preparation of PCB
Assembling and Testing of Interfacing Circuits
Project Report
1.5 EQUIPMENTS: -
Printed Circuit Board
9volts Power Supply
IC UA741 and LM386
Transistors BC547 and BC548
Resistors and Capacitors
BD139 Heat Sink
Mike and Speaker
2N5777/L14F1 Photo Transistor
IR leds
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CHAPTER 2
2.1 BLOCK DIAGRAM DESCRIPTION:-
Using this circuit you can communicate with your neighbours wirelessly. The IR led
can transmit light up to a distance of about 5 meters. The phototransistor of the receiver
must be accurately oriented towards the IR beam. If there is any obstruction in the path of
the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1)
comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp
stage built around A741 (IC1). The gain of the op-amp can be controlled with the help of
1-mega-ohm pot.meter VR1.The AF output from IC1 is coupled to the base of transistor
BD139 (T2), which, in turn, modulates the laser beam.
The transmitter uses 9V power supply. The receiver circuit (Fig. 2) uses an npn
phototransistor as the light sensor that is followed by a two-stage transistor preamplifier
and LM386-based audio power amplifier. The receiver does not need any complicated
alignment. Just keep the phototransistor oriented towards the remote transmitters laser
point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the
speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected
sunlight, however, does not cause any problem. But the sensor should not directly face the
sun.
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Fixed and Variable Resistors
There are two kinds of resistors, FIXED and VARIABLE. The fixed resistor willhave one value and will never change (other than through temperature, age, etc.). The
resistors shown in A and B of figure 1-29are classed as fixed resistors. The tapped
resistor illustrated in B has several fixed taps and makes more than one resistance value
available. The sliding contact resistor shown in C has an adjustable collar that can be
moved to tap off any resistance within the ohmic value range of the resistor.
There are two types of variable resistors, one called a POTENTIOMETER and the
other a RHEOSTAT (see views D and E of fig. 1-29.)An example of the potentiometer
is the volume control on your radio, and an example of the rheostat is the dimmer
control for the dash lights in an automobile. There is a slight difference between them.
Rheostats usually have two connections, one fixed and the other moveable. Any variable
resistor can properly be called a rheostat. The potentiometer always has three
connections, two fixed and one moveable. Generally, the rheostat has a limited range of
values and a high current-handling capability. The potentiometer has a wide range of
values, but it usually has a limited current-handling capability. Potentiometers are
always connected as voltage dividers.
Presets
These are miniature
versions of the standard
variable resistor. They arePreset Symbol
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designed to be mounted directly onto the circuit board and adjusted only when the circuit is
built. For example to set the frequency of an alarm tone or the sensitivity of a light-
sensitive circuit. A small screwdriver or similar tool is required to adjust presets.
Presets are much cheaper than standard variable resistors so they are sometimes used
in projects where a standard variable resistor would normally be used.
Multiturn presets are used where very precise adjustments must be made. The screw
must be turned many times (10+) to move the slider from one end of the track to the
other, giving very fine control.
Preset(open style)
Presets(closed style)
Multiturn preset
3.2 CAPACITORS:
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Function
Capacitors store electric charge. They are used with resistors in timing circuitsbecause
it takes time for a capacitor to fill with charge. They are used to smooth varying DC
supplies by acting as a reservoir of charge. They are also used in filter circuits because
capacitors easily pass AC (changing) signals but they block DC (constant) signals.
Capacitance
This is a measure of a capacitor's ability to store charge. A large capacitance means that
more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is
very large, so prefixes are used to show the smaller values.
Three prefixes (multipliers) are used, (micro), n (nano) and p (pico):
means 10-6 (millionth), so 1000000F = 1F
n means 10-9 (thousand-millionth), so 1000nF = 1F
p means 10-12 (million-millionth), so 1000pF = 1nF
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Capacitor values can be very difficult to find because there are many types of
capacitor with different labeling systems!
There are many types of capacitor but they can be split into two groups, polarised
and unpolarised. Each group has its own circuit symbol.
Polarised capacitors (large values, 1F +)
Electrolytic Capacitors
Electrolytic capacitors are polarised and they must be connected the correct way
round, at least one of their leads will be marked + or -. They are not damaged by heat
when soldering.
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There are two designs of electrolytic capacitors; axial where the leads are attached to
each end (220F in picture) and radial where both leads are at the same end (10F in
picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit
board.
It is easy to find the value of electrolytic capacitors because they are clearly printed
with their capacitance and voltage rating. The voltage rating can be quite low (6V for
example) and it should always be checked when selecting an electrolytic capacitor. If the
project parts list does not specify a voltage, choose a capacitor with a rating which is
greater than the project's power supply voltage. 25V is a sensible minimum most battery
circuits.
3.3 Use of Infrared Detectors Basics
IR emitter and IR phototransistor
An infrared emitter is an LED made from gallium arsenide, which emits near-infrared
energy at about 880nm.
The infrared phototransistor acts as a transistor with the base voltage determined by the
amount of light hitting the transistor.
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Hence it acts as a variable current source. Greater amount of IR light cause greater
currents to flow through the collector-emitter leads.
As shown in the diagram below, the phototransistor is wired in a similar configuration
to the voltage divider.
The variable current traveling through the resistor causes a voltage drop in the pull-up
resistor.
This voltage is measured as the output of the device
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IR reflectance sensors contain a matched infrared transmitter and infrared receiver pair.
These devices work by measuring the amount of light that is reflected into the receiver.
Because the receiver also responds to ambient light, the device works best when well
shielded from abient light, and when the distance between the sensor and the reflective
surface is small(less than 5mm).
IR reflectance sensors are often used to detect white and black surfaces. White surfaces
generally reflect well, while black surfaces reflect poorly. One of such applications is the
line follower of a robot.
Schematic Diagram for a Single Pair of Infrared Transmitter and Receiver
3.4 Condenser Microphones
Condenser means capacitor, an electronic component which stores energy in the form of
an electrostatic field. The term condenser is actually obsolete but has stuck as the name for
this type of microphone, which uses a capacitor to convert acoustical energy into electrical
energy.
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Condenser microphones require power from a battery or external source. The resulting
audio signal is stronger signal than that from a dynamic. Condensers also tend to be more
sensitive and responsive than dynamics, making them well-suited to capturing subtle
nuances in a sound. They are not ideal for high-volume work, as their sensitivity makes
them prone to distort.
How Condenser Microphones Work:
A capacitor has two plates with a voltage between them. In the condenser mic, one of
these plates is made of very light material and acts as the diaphragm. The diaphragm
vibrates when struck by sound waves, changing the distance between the two plates and
therefore changing the capacitance. Specifically, when the plates are closer together,
capacitance increases and a charge current occurs. When the plates are further apart,
capacitance decreases and a discharge current occurs.
A voltage is required across the capacitor for this to work. This voltage is supplied
either by a battery in the mic or by external phantom power.
Cross-Section of a Typical Condenser Microphone
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The loudspeakers are almost always the limiting element on the fidelity of a reproduced
sound in either home or theater. The other stages in sound reproduction are mostly
electronic, and the electronic components are highly developed. The loudspeaker involves
electromechanical processes where the amplified audio signal must move a cone or other
mechanical device to produce sound like the original sound wave. This process involves
many difficulties, and usually is the most imperfect of the steps in sound reproduction.
Choose your speakers carefully. Some basic ideas about speaker enclosures might help
with perspective. Once you have chosen a good loudspeaker from a reputable manufacturer
and paid a good price for it, you might presume that you would get good sound
reproduction from it. But you won't --- not without a good enclosure. The enclosure is an
essential part of sound production because of the following problems with a direct
radiating loudspeaker:
Loudspeaker Details
An enormous amount of engineering work has
gone into the design of today's dynamic
loudspeaker. A light voice coil is mounted so that
it can move freely inside the magnetic field of a
strong permanent magnet. The speaker cone is
attached to the voice coil and attached with a
flexible mounting to the outer ring of the speaker
support. Because there is a definite "home" or
equilibrium position for the speaker cone and there
is elasticity of the mounting structure, there is inevitably a free cone resonant frequency
like that of a mass on a spring. The frequency can be determined by adjusting the mass and
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stiffness of the cone and voice coil, and it can be damped and broadened by the nature of
the construction, but that natural mechanical frequency of vibration is always there and
enhances the frequencies in the frequency range near resonance. Part of the role of a good
enclosure is to minimize the impact of this resonant frequency.
3.5 IC UA741:
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3.6 IC LM386:-
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Its a low voltage Audio power amplifier. The gain is internally set to 20 to keep
external part count low, but the addition of an external capacitor and resistor between pins
1 and 8 will increase the gain to any value from 20 to 200.
The inputs are ground referred while the output automatically biases to one-half the
supply voltage. The quiscent power drain is only 24milliwatts when operating froma a
6volts supply, making the LM386 ideal for battery operation.
FEATURES:
Wide supply voltage range: 4v-12v or 5v-18v
Low quiscent current drain: 4mA
Voltage drains from 20 to 200
Ground referred input
Self-centering output quiscent voltage
Low distortion: 0.2%
Available in 8 pin MSOP package
APPLICATIONS:-
AM-FM radio amplifiers
Portable tape player amplifiers
TV sound systems
Line drivers
Ultra sonic drivers
Small servo drivers
Power converters
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3.7 BD139 Heat Sink:-
Description:
TRANSISTOR, NPN, SOT-32
Transistor Polarity: NPN
Collector-to-Emitter Breakdown Voltage:80V
Power Dissipation Pd:1.25W
DC Collector Current:1.5A
DC Current Gain hFE:40
Transistor Case Style:SOT-32
No. of Pins:3
Case Style:SOT-32
Current Ic hFE:0.5A
Full Power Rating Temperature:25C
Max Current Ic:3A
Max Current Ic Continuous a:1.5A
Max Power Dissipation Ptot:12.5W
Max Voltage Vce Sat:0.5V
Min Hfe:25
Power Dissipation:1.25W
Termination Type: SMD
Transistor Type: Bipolar
Voltage Vcbo:80V
3.8 POWER SUPPLY:-
Here we use a 9volts DC external battery to avoid complexity of the circuit.
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CHAPTER 4
CONCLUSION:-
Hence we conclude that by using our equipment there is easy transmission and
receiving of information for a short range of distance. The distance can be increased by
using lasers instead of IR devices. More over we got to have a practical overview of what
we studied so far in our curriculum.
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CHAPTER 5BIBILOGRAPHY:
5.1 Books Referred:
Jacob Millman Christos C. Halkias.: Electronic Devices And Circuits, Tata
McGraw-Hill Publishing Company Ltd. Sep, 2003.
Electronic Devices and Circuits by SALIVAHANA, Tata McGraw-Hill
Publishing Company.
5.2 Sites visited:
1. www.howthisstuffworks.com
2. www.wikepedia.com3. www.alldatasheets.com
4. www.hobbyprojects.com
5. www.guidecircuit.com
5.3 Data Sheets:
IC UA741 and LM386
Transistors BC547 and BC548
BD139 Heat Sink
2N5777/L14F1 Photo Transistor
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