laser torch
TRANSCRIPT
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 1 Dept. of ECE
1. INTRODUCTION
Laser as a communication medium can provide a good substitute for the present day
communication systems as the problem of interference faced in case of electromagnetic
waves is not there and high deal of secrecy is available. Laser communications offers a
viable alternative to RF communications for inter satellite links and other applications
where high performance links are a necessity.
High data rate, small antenna size, narrow beam divergence, and a narrow field of
view are characteristics of laser communications that offer a number of potential
advantages for system design.
The purpose of the project is to determine the feasibility of replacing microwave
communications with laser communications to remote locations. This link is unreliable and
can be disrupted in fog or rain. A basic communication system is made up of three main
parts being the transmitter, the medium over which the message is being sent, and the
receiver. A good example of this is two people communicating from one side of a room to
the other. If the person wants to communicate with the other person, he/she speaks words
towards the direction of the other individual who receives the voice information and
determines the message. This example is much like how any general communication
system works.
First, the message is determined that needs to be sent to the receiving end. The
message is then sent to the transmitter. The transmitter, much like the person’s mouth, is
sending the signal containing the message from one person to the other. This can be
compared to using an antenna to send out a signal.
Laser emission power and the nonlinear distortion depends on the bias current (IO),
so the laser light transmitter to set the bias circuit and pre-distortion compensation circuit
to ensure that the output of nonlinear index and emission stability. As the value of Laser
temperature increases, the threshold will increase, decrease saturated output intensity.
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 2 Dept. of ECE
The signal then must travel through some type of medium to reach the receiver. For
the two people talking, this medium would be air. But, sometimes this medium is some
type of cable or wire. The signal is then collected by the receiver, which is comparable to
the person on the receiving end hearing the sound of the person’s voice. Sometimes the
signal can be immediately understood, but other times the signal must first be decoded in
order to perfectly understand what actually the input signal that is fed to the transmitter-
section.
The transceiver basically comprises of a transmitter section and a receiver section
and the input is fed via a condenser mic that gives it to the transmitter and is carried by the
laser beam from the laser torch. The modulated input is received by the receiver at a
maximum possible distance of about 500m and is detected by the phototransistor and then
amplified by the amplifier circuit and is then given to the loud speaker which transforms it
to the original voice message input given initially to the mic . The basic principle
employed here is amplitude modulation where the laser beam is the carrier. A DC power
supply of 9V is used inorder to drive the laser torch and bias the entire transceiver circuit.
An approximate distance of about 500m is the considered range.
1.1 LITERATURE SURVEY
The idea that inspired laser communications is simple. In today’s world, data can
be packaged much more quickly and efficiently without wires and messy connectivity, a
stark contrast to only a few years ago, when wires were the necessity. We had the idea of
doing some communication related project as communication students.
The first thing that striked us was a sort of an FM station that would realize our
dream of a college station. But the problems regarding the outer noise, frequency band of
selection and the licencing and also the topography of our college, we were forced to drop
the idea. Then we adopted a new idea of using some carier for the purpose of modulation
which is highly coherent,directed,energized and reliable which finally took us to the idea
of constructing a laser based voice transceiver. With laser technology, data moves more
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 3 Dept. of ECE
quickly and with just as much integrity as it would have through a wire. Additionally, a
wire system imposes none of the messy assorted installation costs of a wired system: you
install the system, and then you can create wireless bridges without having to actually run
any more cord.
Laser line of sight communications have never been more practical. They offer
tremendous flexibility, allowing you to choose virtually any communication format you
prefer. They are also secure and more cost effective, even than wireless radio transmissions
over short range. They tend not to be such good choices if you intend to transmit frequent
long distance data bursts as the signal requires a specific line of sight, which can become
impaired over wider expanses.
Laser Communication systems are wireless communications through the
atmosphere. They work similarly to fiber optic links, except the beam is transmitted
through free space. While the transmitter and receiver must require line-of- sight
conditions, they have the benefit of eliminating the need for broadcast rights and buried
cables. Laser Communication systems can be easily deployed since they are inexpensive,
small, low power and do not require any radio interference studies. The carrier used for the
transmission signal is typically generated by a laser diode. Two parallel beams are needed,
one for the transmission and one for reception.
Using this circuit we decided to implement the idea of communicating with our
neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in
the circuit.
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 4 Dept. of ECE
2. LASER TORCH BASED VOICE TRANSCEIVER
BLOCK DIAGRAM
The basic circuit includes a transmitter and a receiver section. The above shown is
a schematic representation of LASER torch based voice transceiver. The input is fed to a
condenser mic which is modulated at the transmitter end and then detected by a photo
transistor at the receiver end and then it’s fed to a loud speaker where the voice is
regenerated.
Figure 2.1 Transceiver Block Diagram
2.1 TRANSMITTER
The transmitter circuit (Fig.2.2) comprises condenser microphone transistor
amplifier BC548 (T1) followed by an op-amp stage built around µA741 (IC1). The gain of
the op-amp can be controlled with the help of 1-mega-ohm potentiometer VR1.The AF
output from IC1 is coupled to the base of transistor BD139 (T2), which, inturn, modulates
the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch
(after removal of its battery) can be directly connected to the circuit. The torch connected
to the emitter ofBD139 and the spring-loaded lead protruding from inside the torch to
circuit ground.
CONDENSER
MIC
LOUD SPEAKER RECEIVER
TRANSMITTER LASER TORCH
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Figure 2.2.Transmitter circuit
2.2 RECEIVER
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 transmitter’s 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.
The receiver section comprises of a receiving phototransistor which will detect the
received laser beam containing the input information and then it is amplified by the two
stage amplifier section that is fed to the input terminals of the comparator circuit of the
receiver section as per the figure shown.
Laser Torch Based Voice Transceiver Miniproject “11
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The comparator is driven by the positive power supply and the terminal number
four of the audio power amplifier is then grounded and its output is the amplified version
of the input that is detected by the receiver. The actual input is then made ripple free by a
capacitor that is connected to the amplifier section and is fed to capacitor that is parallel to
the resistor at the load section as shown in the diagram below.
The above shown receiver receives signal which is carried by a laser beam that acts
as the carrier for this amplitude modulation technique employed. The received signal may
contain noises which will be filtered of using a pi filter.
Figure 2.3.Receiver circuit
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3. CIRCUIT COMPONENTS
When a beginner to the electronics first looks at a circuit board full of circuit
components he/ she often overwhelmed by the diversity of do-dads. In these next few
sections we will help you to identify some of the simple components and their schematic
symbol. Then you should be able to call them resistors and transistors instead of
“Whatchamacallits”.
Electronic component are classed into either being Passive devices Or Active devices.
A Passive Device is one that contributes no power gain (amplification) to a circuit or
system. It has not control action and does not require any input other than a signal to
perform its function. In other words, “A components with no brains!” Examples are
Resistors, Capacitors and Inductors
Active Devices are components that are capable of controlling voltages or currents and can
create a switching action in the circuit. In other words, “Devices with smarts!” Examples
are Diodes, Transistors and Integrated circuits. Most active components are
semiconductors.
3.1 RESISTORS
This is the most common component in electronics. It is used mainly to control
current and voltage within the circuit. You can identify a simple resistor by its simple cigar
shape with a wire lead coming out of each end. It uses a system of color coded bands to
identify the value of the component (measured in Ohms) .A surface mount resistor is in
fact mere millimeters in size but performs the same function as its bigger brother, the
simple resistor. A potentiometer is a variable resistor. It lets you vary the resistance with a
dial or sliding control in order to alter current or voltage on the fly. This is opposed to the
“fixed” simple resistors.
Laser Torch Based Voice Transceiver Miniproject “11
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Figure 3.1.1.Resistor bands
3.2 CAPACITORS
Capacitors, or "caps", vary in size and shape - from a small surface mount model
up to a huge electric motor cap the size of paint can. It storages electrical energy in the
form of electrostatic charge. The size of a capacitor generally determines how much charge
it can store. A small surface mount or ceramic cap will only hold a minuscule charge. A
cylindrical electrolytic cap will store a much larger charge. Some of the large electrolytic
caps can store enough charge to kill a person. Another type, called Tantalum Capacitors,
store a larger charge in a smaller package.
Figure 3.2.1.Capacitors
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3.3 DIODES
Diodes are basically a one-way valve for electrical current. They let it flow in one
direction (from positive to negative) and not in the other direction. This is used to perform
rectification or conversion of AC current to DC by clipping off the negative portion of a
AC waveform. The diode terminals are cathode and anode and the arrow inside the diode
symbol points towards the cathode, indicating current flow in that direction when the diode
is forward biased and conducting current. Most diodes are similar in appearance to a
resistor and will have a painted line on one end showing the direction or flow (white side is
negative). If the negative side is on the negative end of the circuit, current will flow. If the
negative is on the positive side of the circuit no current will flow.
Figure 3.3.1. Diode
3.4 LED
LEDs are simply diodes that emit light of one form or another. They are used as
indicator devices. Example: LED lit equals machine on. The general purpose silicon diode
emits excess energy in the form of heat when conducting current.
If a different semiconductor material such as gallium, arsenide phosphide is used,
the excess energy can be released at a lower wavelength visible to human eye. This is the
composition of LED. They come in several sizes and colors. Some even emit Infrared
Light which cannot be seen by the human eye.
Laser Torch Based Voice Transceiver Miniproject “11
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Figure 3.4.1.LED
3.5 SWITCH
This is a mechanical part which when pressed makes the current to flow through
that. If the switch is released the current stops flowing through that. This helps to control a
circuit.
Figure 3.5.1.Switch
3.6 TRANSISTORS
The transistor performs two basic functions: It acts as a switch turning current on
and off and it acts as an amplifier. This makes an output signal that is a magnified version
of the input signal. Transistors come in several sizes depending on their application. It can
be a big power transistor such as is used in power amplifiers in your stereo, down to a
surface mount (SMT) and even down to .5 microns wide (I.E.: Mucho Small!) such as in a
microprocessor or Integrated Circuit.
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Figure 3.6.1.Transistors
3.6.1 NPN TRANSISTOR
Bipolar junction perform the function of amplifications where a small varying
voltage or current applied to the base (the lead on the left side of the symbol) is
proportionately replicated by a much larger voltage or current between the collector and
emitter leads. Bipolar junction refers to sandwich construction of the semiconductor, where
a wedge of "P" material is placed between two wedges of "N" material. In this NPN
construction a small base current controls the larger current flowing from collector to
emitter (the lead with the arrow).
Figure 3.6.2.NPN Transistor
3.6.2 PNP TRANSISTOR
Similar to NPN transistors, PNP's have a wedge of "N" material between two
wedges of "P" material. In this design, a base current regulates the larger current flowing
from emitter to collector, as indicated by the direction of the arrow on the emitter lead. In
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 12 Dept. of ECE
CED players, PNP transistors are used less frequently that the NPN type for amplification
functions.
Figure 3.6.3.PNP Transistor
3.7 PCB
PCB stands for printed circuit board which is used for wiring up of the components
of a circuit. PCBs are made of paper phenolic FR2 grade (low cost, for low frequency and
low power circuit assembly) and glass epoxy FR4 grade (for high frequency, high power
circuits) copper clad laminates (available in 1.6mm, 2.4mm and 3.6mm thickness).
Single sided PCBs have copper foil only on one side while double-sided PCBs
have copper foil on both side of the laminate. Thickness of copper foil is 35 micrometer
minimum on cheaper PCBs and 70 micrometer on slightly costlier PCBs. Tracks
(conductive paths) are made by masking (covering) the track part of copper with etch-resist
enamel paint (you can even use nail polish) and later dipping the laminate in ferric chloride
solutions to dissolve all copper except under the masked part. Holes in PCBs are drilled
after etching is over.
The tracks on two sides of a PCB are joined using printed through hole (PTH)
technique, which is equivalent to using slotted copper rivets for joining tracks on both
sides. On cheaper PCBs, PTH are not provided, only Pads (i.e. circular copper land with
centre hole) are provided and you have to join the tracks on both sides by soldering a
copper wire to the pads with a copper wire.
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In single sided PCB components are mounted on the side which has no track (called
component side). In a double-sided PCB the component side is defined (marked before
hand) or it will show component outline (also called silk screen).
Green masking is the process of applying a layer of green colour insulation varnish
on all parts of tracks except near the holes, to protect the tracks from exposure to
atmosphere and thus prolong its life and reliability.
Figure 3.7.1.PCB
3.8 SPEAKER
These convert electrical signals to acoustic vibrations. It comprises a permanent
magnet and a moving coil (through which electrical signal is passed). This moving coil is
fixed to the diaphragms which vibrate to produce sound.
Figure 3.8.1.Speaker
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3.9 ICs
Integrated Circuits, or ICs, are complex circuits inside one simple package. Silicon
and metals are used to simulate resistors, capacitors, transistors, etc. It is a space saving
miracle. These components come in a wide variety of packages and sizes.You can tell them
by their "monolithic shape" that has a ton of "pins" coming out of them. Their applications
are as varied as their packages. It can be a simple timer, to a complex logic circuit, or even
a microcontroller (microprocessor with a few added functions) with erasable memory built
inside.
3.9.1 uA741
Of the different types of opamps produced, type 741 has achieved a very wide
popularity. It is available in 14- pin dual-in line, 8 – pin dual-in line or in TO- style
packages. Integrated circuit type 747 accommodates two type 741 operational amplifiers in
a single package.
The op-amp needs a dual symmetrical power supply. With its center tap grounded.
This enables the op-amp to amplify dc signals of both polarities, positive or negative, with
respect to ground. The circuit is so designed that if both inputs are connected to ground, the
dc output voltage is zero. However, because of small internal unbalances, a small dc
voltage may appear at the output. It is too small to be objectionable in normal applications.
For critical applications, the output voltage can be set precisely to zero by
connecting a 10K potentiometer between terminals marked “offset-null”. It is possible to
operate the 741 on a single rail supply also.
This is usually done by raising the standing dc input voltage to the non-inverting
input terminal to approximately half the supply voltage by a voltage divider network. The
output dc voltage in such cases stands at half the supply voltage. Bt this does not matter
because the dc can be easily blocked by a capacitor allowing only the ac signal to be
passed on to the next stage.
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Figure 3.9.1.1.uA741C Opamp
The operational amplifier type 741 has many features that have made it so popular.
It has an in-built circuitry that provides full protection against output overloads or even
shorts to ground for any length of time. The 741 does not need any external component for
phase compensation or adjusting its frequency response. This simplifies its circuit design
and minimizes the number of components used.
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4. CONDENSER MICROPHONE
The condenser microphone, invented at Bell Labs in 1916 by E. C. Wentes also
called a capacitor microphone or electrostatic microphone. Here, the diaphragm acts as
one plate of a capacitor, and the vibrations produce changes in the distance between the
plates. There are two types, depending on the method of extracting the audio signal from
the transducer: DC-biased and radio frequency (RF) or high frequency (HF) condenser
microphones. The voltage across the capacitor plates change according to the vibrations of
the plates in response to air variations. Voltage across the plates changes as (C= Q / V),
where Q = charge in coulombs, C = capacitance in farads and V = potential difference
in volts. The capacitance of the plates is inversely proportional to the distance between
them for a parallel-plate capacitor. (See capacitance for details.) The assembly of fixed and
movable plates is called an "element" or "capsule."
A nearly constant charge is maintained on the capacitor. As the capacitance
changes, the charge across the capacitor does change very slightly, but at audible
frequencies it is sensibly constant. The capacitance of the capsule (around 5 to 100 pF) and
the value of the bias resistor (100 mega ohms to tens of giga ohms) form a filter that is
high-pass for the audio signal, and low-pass for the bias voltage. Note that the time
constant of an RC circuit equals the product of the resistance and capacitance.
Within the time-frame of the capacitance change (as much as 50 ms at 20 Hz audio
signal), the charge is practically constant and the voltage across the capacitor changes
instantaneously to reflect the change in capacitance. The voltage across the capacitor varies
above and below the bias voltage. The voltage difference between the bias and the
capacitor is seen across the series resistor. The voltage across the resistor is amplified for
performance or recording. In most cases, the electronics in the microphone itself contribute
no voltage gain as the voltage differential is quite significant, up to several volts for high
sound levels. Since this is a very high impedance circuit, current gain only is usually
needed with the voltage remaining constant. The circuit is therefore often called an
"impedance converter" or "follower" because no voltage gain is provided]
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RF condenser microphones use a comparatively low RF voltage, generated by a
low-noise oscillator. The signal from the oscillator may either be amplitude modulated by
the capacitance changes produced by the sound waves moving the capsule diaphragm, or
the capsule may be part of a resonant circuit that modulates the frequency of the oscillator
signal. Demodulation yields a low-noise audio frequency signal with a very low source
impedance. The absence of a high bias voltage permits the use of a diaphragm with looser
tension, which may be used to achieve wider frequency response due to higher compliance.
The RF biasing process results in a lower electrical impedance capsule, a useful by-product
of which is that RF condenser microphones can be operated in damp weather conditions
that could create problems in DC-biased microphones with contaminated insulating
surfaces. The Sennheiser "MKH" series of microphones use the RF biasing technique.
Figure 4.1.Condenser microphone
Condenser microphones span the range from telephone transmitters through
inexpensive karaoke microphones to high-fidelity recording microphones. They generally
produce a high-quality audio signal and are now the popular choice in laboratory and
studio recording applications. The inherent suitability of this technology is due to the very
small mass that must be moved by the incident sound wave, unlike other microphone types
that require the sound wave to do more work. They require a power source, provided either
via microphone inputs on equipment as phantom power or from a small battery. Power is
necessary for establishing the capacitor plate voltage, and is also needed to power the
microphone electronics (impedance conversion in the case of electret and DC-polarized
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microphones, demodulation or detection in the case of RF/HF microphones). Condenser
microphones are also available with two diaphragms that can be electrically connected to
provide a range of polar patterns (see below), such as cardioid, omnidirectional, and figure-
eight. It is also possible to vary the pattern continuously with some microphones, for
example the Røde NT2000 or CAD M179.
4.1 ELECTRET CONDENSER MICROPHONE
An electret microphone is a relatively new type of capacitor microphone invented
at Bell laboratories in 1962 by Gerhard Sessler and Jim West. The externally applied
charge described above under condenser microphones is replaced by a permanent charge in
an electret material. An electret is actually a ferroelectric material with the main feature of
having a permanently electrically charged or polarized state. This special characteristic
name comes from electrostatic and magnet; a static charge is embedded in an electret by
alignment of the static charges in the material, much the way a magnet is made by aligning
the magnetic domains in a piece of iron.
Due to their good performance and ease of manufacture, hence low cost, the vast
majority of microphones made today are electret microphones; a semiconductor
manufacturer estimates annual production at over one billion units. Nearly all cell-phone,
computer, PDA and headset microphones are electret types. They are used in many
applications, from high-quality recording and lavaliere use to built-in microphones in
small sound recording devices and telephones.
Though electret microphones were once considered low quality, the best ones can
now rival traditional condenser microphones in every respect and can even offer the long-
term stability and ultra-flat response needed for a measurement microphone. Unlike other
capacitor microphones, they require no polarizing voltage, but often contain an
integrated preamplifier that does require power (often incorrectly called polarizing power
or bias). This preamplifier is frequently phantom powered in sound reinforcement and
studio applications.
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Microphones designed for personal computer (PC) use, sometimes called
multimedia microphones, use a stereo 3.5 mm plug (though a mono source) with the ring
receiving power via a resistor from (normally) a 5 V supply in the computer; unfortunately,
a number of incompatible dynamic microphones are fitted with 3.5 mm plugs too. While
few electret microphones rival the best DC-polarized units in terms of noise level, this is
not due to any inherent limitation of the electret. Rather, mass production techniques
needed to produce microphones cheaply don't lend themselves to the precision needed to
produce the highest quality microphones, due to the tight tolerances required in internal
dimensions. These tolerances are the same for all condenser microphones, whether the DC,
RF or electret technology is used.
Figure 4.1.1.Small diaphragm mic
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5. CONSTRUCTION OF LASER TORCH
A laser is constructed from three principal parts:
� An energy source (usually referred to as the pump or pump source),
� A gain medium or laser medium, and
� Two or more mirrors that form an optical resonator.
5.1 PUMP SOURCE
The pump source is the part that provides energy to the laser system.
Examples of pump sources include electrical discharges, flash lamps, arc lamps, light
from another laser, chemical reactions and even explosive devices. The type of pump
source used principally depends on the gain medium, and this also determines how the
energy is transmitted to the medium. A helium-neon (HeNe) laser uses an electrical
discharge in the helium-neon gas mixture, a Nd:YAG laser uses either light focused
from a xenon flash lamp or diode lasers, and excimer lasers use a chemical reaction.
5.2 GAIN MEDIUM
The gain medium is the major determining factor of the wavelength of operation,
and other properties, of the laser. Gain media in different materials have linear spectra or
wide spectra. Gain media with wide spectra allow tune frequency of laser. First
wide tunable crystal laser with tunability more octave represent on photo
3 http://spie.org/x39922.xml . There are hundreds if not thousands of different gain media
in which laser operation has been achieved (see list of laser types for a list of the most
important ones). The gain medium is excited by the pump source to produce a population
inversion, and it is in the gain medium that spontaneous and stimulated emission of
photons takes place, leading to the phenomenon of optical gain, or amplification.
Examples of different gain media include:
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Liquids such as dye lasers. These are usually organic chemical solvents, such as
methanol, ethanol or ethylene glycol, to which are added chemical dyes such
as coumarin, rhodamine and fluorescein. The exact chemical configuration of the dye
molecules determines the operation wavelength of the dye laser.
Gases, such as carbon dioxide, argon, krypton and mixtures such as helium-neon.
These lasers are often pumped by electrical discharge. Solid host materials include
YAG (yttrium aluminium garnet).
5.3 OPTICAL RESONATOR
The optical resonator, or optical cavity, in its simplest form is two parallel mirrors
placed around the gain medium which provide feedback of the light. The mirrors are
given optical coatings which determine their reflective properties. Typically one will be
a high reflector, and the other will be a partial reflector. The latter is called the output
coupler, because it allows some of the light to leave the cavity to produce the laser's output
beam.
Light from the medium, produced by spontaneous emission, is reflected by the
mirrors back into the medium, where it may be amplified by stimulation. The light may
reflect from the mirrors and thus pass through the gain medium many hundreds of times
before exiting th In more complex lasers, configurations with four or more mirrors forming
the cavity are used. The design and alignment of the mirrors with respect to the medium is
crucial to determining the exact operating wavelength and other attributes of the laser
system.
Other optical devices, such as spinning mirrors, modulators, filters, and absorbers,
may be placed within the optical resonator to produce a variety of effects on the laser
output, such as altering the wavelength of operation or the production of pulses of laser
light.
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Some lasers do not use an optical cavity, but instead rely on very high optical gain
to produce significant amplified spontaneous emission (ASE) without needing feedback of
the light back into the gain medium. Such lasers are said to be super luminescent, and emit
light with low coherence but high bandwidth. Since they do not use optical feedback, these
devices are often not categorized as lasers.
Figure 5.1.Nd:YAG solid-state laser
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6. RESULTS AND DISCUSSIONS
LASER TORCH BASED VOICE TRANSCEIVER is well built and the output is
verified. Basically the circuit comprises of a transmitter and a receiver section. The input
voice signal is fed through a condenser mic and the same is modulated via Am at the
transmitter section. The input only if uninterrupted will be heard properly at the receiver
end.
There is a coupling capacitance at the input end that couples the ac and removes the
dc components. That means the input if given only, are there the transistor will be forward
biased. Else the transistor will be reversed biased and there will be high voltage at the
collector terminal. This high voltage will be coupled by the capacitance and is given to the
comparator which is an op-amp here. The noise from the power supply is filtered out by
the pi filter. The output of the comparator is given to the transistor which act as the heat
sink and the emitter voltage drives the LASER that acts as the carrier for the amplitude
modulation.
The input that is given to the mic at the transmitter section will be carried to the
receiver photo transistor by the laser beam and is detected by the photo transistor and then
given to the two stage amplifier. Then this is fed to the audio power amplifier that
amplifies the output that is intended at the receiver section. This amplified voice signal is
then detected by the RC circuit and is fed to the loudspeaker. During the experiment it has
been identified that the terminals between which the phototransistor when shorted yields a
drip sound. This is one of the methods to determine whether the circuit is right or wrong.
If the above mentioned method is employed, then the circuit can be checked almost
accurately.
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7. CONCLUSION
The “LASER TORCH BASED VOICE TRANSCEIVER” is successfully
completed with proper output. Even though similar projects are available, it is arguable for
us that our project is most convenient circuit with comparatively high throughput at
minimum cost. We have done our maximum to update appropriate changes in the hardware
to make our project a standard one. We are happy to put our entire effort open source and
are interested to promote among people who make use of highly accurate signal analysis in
the lab experiments. While pursuing our mini project, we have learned a lot new things
both in circuit designing and debugging. Even a beginner looks at this circuit, it is easier
for him to recognize what the circuit actually comprises of. The voltage drops are such that
the total voltage of 9V is obtained across the biasing resistors. The potential of 0.6V is
obtained across the base to emitter junction. There is a volume control which is a pot and
that is fed to the input of the op-amp which is an audio power amplifier and then fed to the
speaker. It is evident that the project has helped us lot to understand the basic concept of
amplitude modulation. The laser which acts as the carrier for the modulation process is
well modulated during the transmission process.
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 25 Dept. of ECE
BIBLIOGRAPHY
1. www.seminarprojects.com
2. www.electronicsforu.com/efylinux/circuit/jan2002/circuit
3. www.elxproject.com
4. www.fullinterview.com
5. epfy.blogspot.com/2009/02
6. sourceforge.net/projects
7. qt.nokia.com
8. en.wikipedia.org
9. www.matni.com
10. www.howstuffworks.com
Laser Torch Based Voice Transceiver Miniproject “11
Jyothi Engineering College 26 Dept. of ECE