MOUNT ZION COLLEGE OF ENGINEERING (Affiliated to M.G University&Approved by A.I.C.T.E) Kadammanitta, Pathanamthitta Kerala-689649 Email: mountzion01@ sify.com Website: www.mountzioncollege.org DEPARTMENT OF ELECTRONICS& COMMUNICATION CERTIFICATE Certified that this is a bonafide record of the mini project work done by SAM SUNNY (56601) of SIXTH semester, Electronics &Communication Engineering, under Mahatma Gandhi University during the year 2010. Project Guide HOD Internal Examiner External Examiner
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98978281 32618749 Sam Project Laser Torch Based Voice Transmitter Amp Receiver
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MOUNT ZION COLLEGE OF ENGINEERING(Affiliated to M.G University&Approved by A.I.C.T.E)
Certified that this is a bonafide record of the mini project
work done by SAM SUNNY (56601) of SIXTH semester, Electronics
&Communication Engineering, under Mahatma Gandhi University during the
year 2010.
Project Guide HOD
Internal Examiner External Examiner
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
ACKNOWLEDGEMENT
To bring something into existence is truly the work of
ALMIGHTY. We thank GOD ALMIGHTY for making this venture a success.
We express our wholehearted thanks to the Management
of the college, Mr. Abraham Kalammannil, Chairman, for providing us an
opportunity to do our studies in this esteemed institution. We thank our Principal,
Prof.P.C.Mohandas for providing the facilities for our studies and constant
encouragement in all achievements.
At the outset we wish to place on record our sincere
thanks to quite a few people without whose help, this venture would not have been a
success.
We would like to express profound gratitude to our Head
of the department, Mr. Rangit Varghese, for his encouragement and for providing all
facilities for carrying out this project. We express our highest regard and sincere thanks
to our project Co-ordinators, Mr. Sreeji Krishnan, who provided the necessary
guidance and serious advice to carry out this project. We also express my gratitude to
our Project Guide, Mr. Sudheesh S.R, for her apt suggestions and support. Our sincere
thanks to all the staff members of the department of Electronics and Communication
who guided as throughout the entire course
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
PREFACE
Because of the differences in our college level studies and
industry level requirements, we are allotted a project to get knowledge about the on
goings at industries. I did the mini project that covered up a practical knowledge of
what I have studied so far in books. I did experienced an exposure to various electronics
devices and equipments which I would not have able to get easily anywhere else. I
learnt a lot about processes of communication like sampling, quantization, detection,
error correction, broadcasting and reception of signals. All the topics which were dealt
with in the project duration are mentioned in an easy manner here in the report which I
am submitting to our college for reference purpose
I am highly thankful to the college faculty and the management for the insertion of
such a training period in our curriculum.
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
CONTENTS
1. INTRODUCTION
2. BLOCK DIAGRAM
3. BLOCK DIAGRAM EXPLANATION
3.1. CONDENSERMICROPHONE
3.2. TRANSMITTING SECTION
3.3. LASER TORCH
3.4. RECEIVING SECTION
3.5. LOUD SPEAKER
1. CIRCUIT DIAGRAM
4.1. TRANSMITTER
4.2. RECEIVER
2. COMPONENTSTUDY
5.1. OPERATIONAL AMPLIFIER
5.1.1. IC 741
5.1.1.1. NEGATIVE FEEDBACK CONTROL
5.2. VR (potentiometer/resistance variac/trimmer)
5.3. CAPACITOR
5.4. DIGITAL MULTIMETER (DMM)
5.5. BATTERY (9 VOLT)
5.6. LASER TORCH
5.7. MICROPHONE
5.7.1. CONDENSER MICROPHONE
5.8. INTEGRATED CIRCUIT (IC)
5.9. PHOTODIODES
5.9.1. PRINCIPLE OF OPERATION
5.9.2. APPLICATIONS
5.10. PHOTOTRANSISTORS
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
3. CIRCUIT DESCRIPTION
6.1. TRANSMITTER
6.2. RECEIVER
6.2.1. CONDENSER MICROPHONE
1. WORKING
2. PCB DESIGN AND FABRICATION
8.1. PCB DESIGN
8.2. PCB FABRICATION
3. COMPONENTS LAYOUT
9.1. TRANSMITTER
9.2. RECEIVER
4. PRINTED CIRCUIT BOARD (PCB) LAYOUT
9.1. TRANSMITTER
9.2. RECEIVER
5. LIST OF TOOLS AND INSTRUMENTS REQUIRED
6. COMPONENTS REQUIRED
12.1. TRANSMITTER
12.2. RECEIVER
7. CONSTRUCTION AND TESTING
13.1. CONSTRUCTION
13.2. TESTING
8. SETTING UP LINK AND PRECAUTIONS
14.1 SETTING UP A
14.2. PRECAUTIONS
14.2.1. LASER SAFETY
9. ADVANTAGES
10.DISADVANTAGES
11.PROBLEM FACED
12.APPLICATIONS
13.CONCLUSION
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
REFERENCES
APPENDIX
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
LIST OF FIGURES
1. TRANSMITTER……………………………………………..… xii2. RECEIVER…………………………………………………… xiii3. SYMBOL OF OP AMP…………………………………...…….xiv4. SYMBOL OF IC 741……………………………………...…… xv5. NEGATIVE FEED BACK CONTROL CIRCUIT………….….xvi6. CERAMIC CAPACITOR………………………………….… xvii7. 9V BATTERY………………………………………...……….xviii8. LASER TORCH………………………………………………...xix9. REVERSE BIASED CIRCUIT…………………………...…….xxi10.PHOTODIODE SYMBOL……………………………………..xxii11.PHOTODIODE CIRCUIT………………………………… …xxii12. PHOTOTRANSISTOR SYMBOL……………………….... …xxv13.PHOTOTRANSISTOR USED AS A PHOTODIODE………..xxvi14.COMPONENTS LAYOUT…………………………………..xxxiv15. PCB LAYOUT………………………………………………xxxiv
LIST OF TABLES
1. COMPONENTS REQUIRED FOR TRANSMITTER…xxxvii2. COMPONENTS REQUIRED FOR RECEIVER……….xxxviii
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
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 present paper involves the study of wireless, open channel
communication system using laser a carrier for voice signals. Using this
circuit we can communicate with your own neighbours wirelessly. Instead of
RF signals, light from a laser torch is used as the carrier in the circuit. The
laser torch can transmit light up to a distance of about 500 meters. The
phototransistor of the receiver must be accurately oriented towards the laser
beam from the torch. If there is any obstruction in the path of laser beam, no
sounds will be heard from the receiver.
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
2. BLOCK DIAGRAM
5DEPT.OF E & C MZC, KADAMMANITTA
CO
ND
EN
SE
R
MIC
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ITT
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SE
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LA
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MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
3. BLOCK DIAGRAM EXPLANATION
3.1 CONDENSER MICROPHONE
It is also called a capacitor or electrostatic microphone. Condenser means
capacitor, which stores energy in the form of an electric field. Condenser microphones
require power from a battery or external source. Condenser also tends to be more
sensitive and responsive than dynamic, making them well suited to capturing subtle
nuances in a sound.
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 and this current will
be used to trigger the transmitting section.
3.2 TRANSMITTING SECTION
The transmitter section comprises condenser microphone, transistor
amplifier BC548 followed by an op-amp stage built around 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, which in
turn, modulates the laser beam. The transmitter uses 9V power supply.
however, the 3-volt laser torch ( after the removal of its battery) can be
directly connected to the circuit--with the body of the torch connected to the
emitter of BD139 and the spring-loaded lead protruding from inside the
torch to circuit ground.
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
3.3 LASER TORCH
Here we use the light rays coming from laser torch as the medium for transmission.
Laser had potential for the transfer of data at extremely high rates, specific
advancements were needed in component performance and systems engineering,
particularly for space-qualified hardware. Free space laser communications systems are
wireless connections through the atmosphere. They work similar to fibre optic cable
systems except the beam is transmitted through open space. The laser systems operate in
the near infrared region of the spectrum. The laser light across the link is at a
wavelength of between 780 - 920 nm. Two parallel beams are used, one for
transmission and one for reception.
3.4 RECEIVING SECTION
The receiver circuit 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 doesn't 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.
3.5 LOUD SPEAKER
A loudspeaker (or "speaker") is an electro acoustic transducer that converts an
electrical signal into sound. The speaker moves in accordance with the variations of an
electrical signal and causes sound waves to propagate through a medium such as air or
water.
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
4. CIRCUIT DIAGRAM
4.1 TRANSMITTER
Fig 4.1. Transmitter
5DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
4.2 RECEIVER
Fig 4.2. Receiver
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
5. COMPONENT STUDY
5.1 OPERATIONAL AMPLIFIER
An op amp is a high-gain, direct-coupled differential linear amplifier whose response
characteristics are externally controlled by negative feedback from the output to the
input. OP amps, widely used in computers, can perform mathematical operations such
as summing, integration, and differentiation. OP amps are also used as video and audio
amplifiers, oscillators, etc. in the communication electronics. Because of their versatility
op amps are widely used in all branches of electronics both in digital and linear circuits.
OP amps lend themselves readily to IC manufacturing techniques. Improved IC
manufacturing techniques, the op amp's adaptability, and extensive use in the design of
new equipment have brought the price of IC ops amps from very high to very
reasonable levels. These facts ensure a very substantial role for the IC op amp in
electronics.
Fig shows the symbol for an op amp. Note that the operational amplifier has two inputs
marked (-) and (+). The minus input is the inverting input. A signal applied to the minus
terminal will be shifted in phase 180° at the output. The plus input is the non-inverting
input. A signal applied to the plus terminal will appear in the same phase at the output
as at the input. Because of the complexity of the internal circuitry of an op amp, the op
amp symbol is used exclusively in circuit diagrams.
Fig 5.1 symbol of op-amp
5.1.1 IC-741
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
An operational amplifier often referred to as op Amp, is a very high gain high
performance amplifier designed to amplify ac and dc signal voltages. Modern integrated
circuit technology and large-scale production techniques have brought down the prices
of such amplifiers within reach of all amateurs, experimenters and hobbyists. The Op
Amp is now used as a basic gain element, like an elegant transistor, in electronic
circuits.
The availability of two input terminals simplifies feedback circuitry and makes the
operational amplifier a highly versatile device. If a feedback is applied from the output
to the inverting input terminal, the result is a negative feedback, which gives a stable
amplifier with precisely controlled gain characteristics. On the other hand, if the
feedback is applied to the non-inverting input, the result is positive feedback, which
gives oscillators and multivibrator. Special effects are obtained by combination of both
types of feedback.
Fig 5.1.1 symbol of IC741
5.1.1.1 NEGATIVE FEEDBACK CONTROL
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
Fig 5.1.1.1. Negative feedback control circuit
The above figure shows the basic circuit, including the negative feedback loop of an op
amp. The output is fed back to the inverting input terminal in order to provide negative
feedback for the amplifier. The input signal is applied to the inverting input. As a result,
the output will be inverted. It is possible to operate the op amp as a non-inverting
amplifier by applying the signal to the plus input. In this circuit the feedback network is
still connected to the inverting input.
5.2 VR (potentiometer/resistance variac/trimmer):
1DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
fig 6.2 symbol
The potentiometer is a resistor of variable resistance. It has three terminals; a fixed
resistance is found between two of the terminals and the third terminal slides along the
fixed resistor. Often, it is used to control the volume in an audio amplifier.
5.3 CAPACITOR:
The capacitor plays a crucial role in electronics -- it stores electrons for when they're
needed most. Capacitors consist of two conducting plates placed near each other. Inside
the capacitor, the terminals connect to two metal plates separated by a dielectric. The
dielectric can be air, paper, plastic or anything else that does not conduct electricity and
keeps the plates from touching each other..
fig 5.3. Ceramic capacitor
They can store electric charge for later discharge. Direct current through a capacitor
will charge the capacitor for a short time, and then stop flowing. Alternating current,
because of the changing electric fields it generates, can “flow” across a capacitor.
5.4 DIGITAL MULTIMETER (DMM)
3DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
The DMM is an instrument that is able to measure voltage, current, and resistance in a
circuit, or across circuit components and displays its measurements on a digital display.
5.5 BATTERY (9 VOLT)
If you look at any battery, you'll notice that it has two terminals. One terminal is marked
(+), or positive, while the other is marked (-), or negative. In an normal flashlight
batteries, the ends of the battery are the terminals. In a large car battery, there are two
heavy lead posts that act as the terminals.
Electrons collect on the negative terminal of the battery. If you connect a wire between
the negative and positive terminals, the electrons will flow from the negative to the
positive terminal as fast as they can (and wear out the battery very quickly -- this also
tends to be dangerous, especially with large batteries, so it is not something you want to
be doing). Normally, you
connect some type of load
to the battery using the
wire.
Fig 5.5: 9V Battery
Inside the battery itself, a chemical reaction produces the electrons. The speed of
electron production by this chemical reaction (the battery's internal resistance) controls
how many electrons can flow between the terminals. Electrons flow from the battery
into a wire, and must travel from the negative to the positive terminal for the chemical
reaction to take place. That is why a battery can sit on a shelf for a year and still have
plenty of power unless electrons are flowing from the negative to the positive terminal,
the chemical reaction does not take place. Once you connect a wire, the reaction starts.
5.6 LASER TORCH
5DEPT.OF E & C MZC, KADAMMANITTA
MINI PROJECT 2010 LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
For this project we have removed the laser assembly from a small laser pointer. The
power supply circuit is the green board attached to the brass laser head. We carry
similar laser pointers in our catalog that are easily disassembled for this project. The
power supply circuit came conveniently marked with a plus and a minus next to two
holes in the board. We solder the black negative lead from the battery clip to the hole
marked minus. We solder one of the coil leads to the hole marked plus. We solder the
red positive lead of the battery clip to the other lead from the coil.
Fig 3.7. Laser torch
5.7 MICROPHONE
Sound is an amazing thing. All of the different sounds that we hear are caused by
minute pressure differences in the air around us. What's amazing about it is that the air
transmits those pressure changes so well, and so accurately, over relatively long
distances. It was a metal diaphragm attached to a needle, and this needle scratched a
pattern onto a piece of metal foil. The pressure differences in the air that occurred when
you spoke toward the diaphragm moved the diaphragm, which moved the needle, which
was recorded on the foil. When you later ran the needle back over the foil, the vibrations
scratched on the foil would then move the diaphragm and recreate the sound. The fact
that this purely mechanical system works shows how much energy the vibrations in the
air can have! All modern microphones are trying to accomplish the same thing as the
original, but do it electronically rather than mechanically. A microphone wants to take
varying pressure waves in the air and convert them into varying electrical signals. There