Light Fidelity (Li-Fi)

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INTRODUCTION
For years, infrared LED has been merely a system for piping light around corners and into the inaccessible places to allow the hidden to be lighted. But now, infrared LED has evolved into a system of significantly greater importance and use. Throughout the world, it is now being used to transmit voice, television and data signals as light waves. Its advantages as compared with conventional coaxial cable or twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave communication systems into operation. One of the most interesting developments in recent years in the field of telecommunication is the use of laser light to carry information over large distances. It has been proved in the past decade that light wave transmission through laser light is superior than that achieved through wires and microwave links. Typically, infrared LED has a much lower transmission loss per unit length (0.15-5db/km) and is not susceptible to electromagnetic interference. Economically also, it serves our purpose. The ever increasing cost and the lack of space available in the congested metropolitan cities asks for advent of a less costly system. The conventional telephonic systems use copper wires, which easily get oxidized and as such require high maintenance cost. The laser light being made of glass are non-reactive and hence economical. Also, the noise pick up by the copper wire or in electrical signals is quite substantial whereas in laser light, the noise pick up is negligible. Basic elements of a infrared LED system

Applications
(i) Applications for video transmission include high quality video Trunked from studio Transfeter, Broadcast CATV video, Video Trunking within city or between cities, Baasedand Video for closed. CONSTRUCTION AND WORKING

MIKE: Its converts sound signals into electrical signals.
AMPLIFIER (A): Signals from mike are amplified so that it can drive to infrared-LED. INFRARED-LED: It carries signals.
PHOTO TRANSISTOR: The electrical signals are regained from the optical signals. AMPLIFIER (B): Energy of signals is amplified to drive the speaker. SPEAKER: Electrical signals which are amplified are reconverted into sound signals at the speaker. DTMF CODER: It is generates the DTMF signal corresponding to the number entered from the keyboard. DTMF DECODER : It is fed to DTMF decoder which gives the binary output corresponding to the signal received from the transmitter. DECODER DRIVER : To drive the 7 segment display.

The circuit
The main part of Circuit is an amplifier. This sound signals (even at a distance of 2 meters from the mic) are picked up by the condenser microphone and converted into electrical variation, which are amplified by the op-amp. (Operational amplifier) IC- 741 is use in the inverting mode with a single supply using divider network of resistor the gain of IC can be set be varying the feed back through R5/6 resistance (can place a 1M variable) here the output of IC is further amplified buy the push-pull amplifier using transistor BC.548/558 pair, in this circuit are R2 is feed back resistance with R1/8 and C1/3 to connected IC-741. The IC’s pin 2 is connect VR1 (variable resistance) through connect to O/P of T1 (transistor) also use 6volt DC. The microphone should be placed near the circuit with the shield wire to suppress tune. The output of the amplifier is taken from emitter of two transistors, with a filter C5 from speaker. Same process continues in the second amplifier. CIRCUIT DESCRIPTION OF SWITCH SECTION

This project was based on photo diodes and photo transistor. Photo diodes had been used as a transmitter and photo transistor as a receiver. This project had been divided in two part, First part transmitter section and second part receiver section. Slide switch selected to voice communication and data. TRANSMISSIONSECTION :When switch key is pressed, circuit is energised. The output of The transmit IR beams modulated at same...
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