16-03-2012, 04:37 PM
WIRELESS LED TRANSMISSION
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Introduction
The superiority of light emitting diodes (LEDs) over incandescent lights, due to long life expectancy, high tolerance to humidity, low power consumption, and minimal heat generation, is well supported. LEDs are used in message display boards, signal devices, and many other means of illumination. One important characteristic of LEDs is that they are semiconductor devices capable of fast switching with the addition of appropriate electronics. That is, the visible light emitted by LEDs can be modulated and encoded with audio information for broadcasting. Therefore, in addition to their normal functions as indication and illumination devices, LEDs can be used as communication devices for transmitting and broadcasting audio and digital information. Hence, they can become part of wireless optical communication systems. This report describes an information system for the broadcasting of audio and digital signals using visible LEDs.
Wireless LED Transmission
Vehicle Information & Communication System (VICS) is starting to become practicable. The Infrared System of VICS detects vehicles on the road by using optical beacons to control traffic and to supply real time traffic information. But it is an enormous budget because the optical beacon must be located on every lane of the road throughout the country. Under this background, the utilization of LED traffic light to transmit information has been patented. This is because LED traffic light use low power, have better efficiency and have much longer lamp life. The proposed setup of this system is shown in fig1 in which traffic light is the transmitter and receiver is fixed in front of the vehicle.
System Description
The system description of the Traffic Light Information system consists of transmitter section and receiver section. Since the proposed system is under research, a block diagrammatic description of both sections only, has been revealed out by researchers.
1) TRANSMITTER SECTION:
A block diagram representation of the schematic diagram of the transmitter design is shown . The audio signal from the cassette tape or CD player has small amplitude; hence, amplification of this audio signal is necessary. The audio amplifier is used to amplify the weak audio signal and shift the average voltage level of the audio signal to an appropriate level so that the signal is within the capture range of a voltage-controlled oscillator (VCO). A VCO chip is used to modulate the incoming audio signal variations from the audio amplifier and generate the FM signal. The VCO has 2 output pins ( a square wave and a sine wave output). A square wave VCO is used instead of sine wave because there are only two states (on & off) for the LEDs. The carrier frequency is set at 100 kHz with a maximum frequency deviation of + or - 50 kHz. The switching of LEDs transmits the modulated signal. The frequency of switching is high enough that the perceivable light appears to be constantly illuminated to the human eye.