Minor Project-laser Torch-based Voice Transmitter and Receiver

ACKNOWLEDGEMENT I am thankful to Mr. Yogesh Bhomia (H.O.D) for providing me the opportunity to undertake project at Arya Institute of Engg. & Technology and especially for his invaluable guidance and frequent suggestions incorporated together with long hours of his precious time to help me during the course of this project and for helping me learn and gain knowledge and making everything worthwhile and fruitful throughout the project. I express my sincere gratitude to Mr.Aditya Agarwal (faculty) for their indispensable guidance and insightful criticism which helped me, surmount any of the hurdles encountered during the course of the project. I extend my thanks to all the staff members of the organization for their guidance. They have been a great source of inspiration for us.

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PREFACE

Because of the differences in our college level studies and industry level requirements ,we are allotted a project to get a knowledge about the on goings at industries . I did the minor 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.

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INDEX Sr. No.

Contents

Page No.

1.

Certificate of Completion

2.

Acknowledgement

1

3.

Preface

2

4.

Introduction; Laser based Voice Transmitter and Receiver

4-5

5.

Electronic Components

6-12

6.

Leads Identification

13-14

7.

BC 546

15-17

8.

BC 548

18-19

9.

UA 741

20-22

10.

SL 100

23-24

11.

LM 386

25-27

12.

L14F1

28-29

13.

Conclusion

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LASER TORCH-BASED VOICE TRANSMITTER AND RECEIVER

Using this circuit you can communicate with your neighbors 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 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 pomp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm potmeter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam.

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The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of The torch connected to the emitter ofBD139 and the spring-loaded lead protruding from inside the torch to circuit ground. 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.

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A BRIEF SUMMARY OF COMPONENTS USED When a beginner to electronics first looks at a circuit board full of components he/she is 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 schematical 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, Capactitors 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.

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.

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Condensers/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 a 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.

Inductors: You may remember from science class that adding electrical current to a coil of wire produces a magnetic field around itself. This is how the inductor works. It is charged with a magnetic field and when that field collapses it produces current in the opposite direction. Inductors are used in Alternating Current circuits to oppose changes in the existing current. Most inductors can be identified by the "coil" appearance. Others actually look like a resistor but are usually green in color.

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

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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.

LEDs (Light Emitting Diodes) 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.

Switch : This is a mechanical part which when pressed makes the current to flow through it. If the switch is released the current stops flowing through it. This helps to control a circuit.

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Transistors: The transistor performs two basic functions: 1) It acts as a switch turning current on and off. 2) It acts as a amplifier.This makes an output signal that is amagnified version of the input signal.Transistors come in several sizes dependingon their application. It can be a big power transistor such as is used in power applifiers 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 IntegratedCircuit.

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 withthe arrow).

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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 CED players, PNP transistors are used less frequently that the NPN type for amplification functions.

PCB’s: PCB stands for printed circuit board which are 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). Singlesided 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. In singlesided 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.

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Batteries: Symbol of batteries shows +ve terminal by a longer line than the –ve terminal. For low power circuit dry batteries are used.

Speakers: These convert electrical signals to accoustic viberations. It comprises a permanent magnet and a moving coil (through which electrical signal is passed). This moving coil is fixed to the diaphram which vibrates to produce sound.

ICs (Integrated Circuits): 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.

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Microprocessors (MPUs): Microprocessors and other large scale ICs are very complex ICs. At their core is the transistor which provides the logic for computers, cars, TVs and just about everything else electronic. Packages are becoming smaller and smaller as companies are learning new tricks to make the transistors ever tinier.

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General PurposeSingle Opeartional Amplifier

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SL 100 NPN Power Transistor

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CONCLUSION We got to have a practical overview of what we studied so far in our curriculum. We got a lot of knowledge .

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