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7/29/2019 Wireless Led Ppts
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WIRELESSLED
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OUTLOOK
INTRODUCTION
SYSTEM DESCRIPTION
TRANSMITTER
RECEIVER IMPLEMENTATION
EXPERIMENTAL RESULT
APPLICATION
ADVANTAGES DISADVANTAGES
CONCLUSION
REFERENCES
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INTRODUCTION
LED lights are more than an energy-efficient
lighting alternative— they’re also a potential Wi-Fi
replacement technology.
Researcher at Boston University are working on
Smart Lighting, a wireless technology based on
visible light instead of radio frequency.
Data is transferred through the Smart Lighting
system with LED light, so each light is essentially a
Wi-Fi hotspot as shown in figure.
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Initial speeds of the network will be about 1 to 10
megabits per second, and data transmission will
occur over existing electrical wiring.
LED wireless network are efficient—significantly
more so than a radio frequency-based network.
As light doesn’t travel through walls or other
opaque objects, chances of eavesdropping are
lowered.
BU`s technology is still in the prototype stage, but itcould potentially rival radio frequency networks for
wireless dominance
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SMART LED LIGHTING SYSTEM
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S YSTEM DESCRIPTION TRANSMITTER:
A block diagram representation of the schematicdiagram of the transmitter design is shown in figure.
Audio messages can be sent using the LED transmitter, andthe receiver located at a distance around 20 m away canplay back the messages with the speaker.
The audio amplifier is used to amplify the weak audio signal.
A VCO chip is used to modulate the incoming audio signalvariations from the audio amplifier and generate the FMsignal.
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AUDIO STAGE MODULATOR
FREQUENCY
OSCILLATOR
AMPLIFIER
The audio (or data) signal is modulated onto the
radio frequency carrier in this modulator stage.
The power amplification of the radio signal is carried out in
the final stage of the block diagram. It makes the signal
stronger so that it can be transmitted into the aerial.
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RECEIVER:
A block diagram schematic of the audio receiver is shown in
figure.
The photo-detector is used to detect a light signal from thetransmitter and convert it into an electrical signal.
The limiting pre-amplifier is used to amplify the electricalsignal from the photo-detector for the next stage.
The data-reproducing circuit is used to reconstruct thesquare wave.
The differentiator circuit is used to produce pulses accordingto the square wave.
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The pulse generator is used to convert the pulses
from the differentiator into sharp pulses for use by
the integrator and envelope detector in the nextstage for demodulation of the signal.
The band-pass filter is used to smooth out the
distortions from the integrator and envelopedetector to produce an appropriate waveform.
The power amplifier is used to amplify the weak
signal from the band-pass filter so that the audiosignal would be comfortable for hearing.
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BLOCK DIAGRAM REPRESENTATION OFRECEIVER:
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IMPLEMENTATION :
An LED traffic-signal head made up of 441 high
brightness LEDs has been implemented in the
Industrial Automation Research Laboratory at The
University of Hong Kong.
Each LED is a Hewlett Packard high intensity
AlInGaP type with a luminous intensity of 2000 mcd
at 20-mA rated driving current, and the viewing
angle is 30 .
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The specifications of the LED traffic signal head are
given in table below. Signal colour: Red
Construction: 441 red ultra-bright LEDs with a luminousintensity of 2000mcd @ 20mA.
Diameter: 8 in Nominal usage: 17V, 2A
Nominal power consumption: 8-34W
Luminous intensity: 300cd
Viewing angle 2q1/2 (half power): 30 deg.
A bit error rate (BER) experiment for the LED trafficlight has been performed (figure shown below).
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In the experiment, frames of data were transmitted
continuously from a computer to the serialcommunication interface circuit via the printer port of the
computer.
The modulated signal is transmitted by the LED traffic
light. The visible-light signal was transmitted to the
receiver, and the serial communication interface
performs demodulation of the data.
The computer at the receiver side would compare thereceived data with transmitted data. The number of error
bits would be recorded.
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The transmission speed of the visible-lightcommunication channel is 128 kbps.
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EXPERIMENTAL RESULT: Table shows the result of the BER test.
Power of visible-light signal at the receiver BER:
0.5μW: 2.1315*10^-3
0.6μW: 5.2177*10^-7
0.7μW: 2.4835*10^-7
0.8μW: 9.1982*10^-8
1.8μW: <2.2155*10^-10
It is observed that the BER decreases as the power
(or luminance) transmitted by the LED traffic light
increases. In other words, the brighter the traffic
light, the smaller is the BER.
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APPLICATIONS: High-brightness LEDs are increasingly being used in
traffic lights due to their low power consumption and
minimal required maintenance.
The next stage of development will involve the three-color LED signals. In Singapore, there has been a
complete change of traffic signals from the incandescent
to LED.
An LED traffic light can be used as an audio
broadcasting device, in addition to their normal function
of being an indication and signalling device.
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Applications can be found in a museum or exhibit-hall
environment. The information on an individual exhibit
can be broadcast via a plurality of LEDs, which is also
used for the purpose of illumination. With the guest
pointing the receiver to the relevant LEDs on atransmitter, with the head phone or ear jack attached to
a portable receiver, he can listen to the audio message
about the specific exhibit item he is interested.
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ADVANTAGES: LEDs and photo detectors capable of high speed
operation are available at low cost.
Like the IR, the visible spectral region is unregulatedworldwide and FCC licenses are not necessary, as thecommission does not regulate the visible lightfrequencies.
Like microwaves, visible-LED light beams follow astraight-line path and are well suited for the wirelessdelivery of large quantities of voice and data information.
For transmission to be possible there must be noobstructions standing in the way of the visible-LED lightbeam as it requires a clear LOS between the sendingside (LED) and the receiving side.
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DISADVANTAGES: They are suitable for short range only, as the photo-
detector current is proportional to the received power.
The relationship between the radiant intensity and the
distance from the receiver follows the inverse square
law. Hence, as a communication medium, it has limitedrange and is subjected to noise arising from sunlight,
incandescent lighting, and fluorescent lighting.
It is not suitable for broadcasting signals over a wide
coverage area or over long ranges.
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CONCLUSION
High brightness LEDs are getting more popular and are opening up anumber of new applications, especially with the improved efficiencyand new colours.
In this article, the novel idea is based on the fast switching of LEDsand the modulation of visible light is developed into a new kind of information system .
A visible-LED audio system that makes use of visual light rays totransmit audio messages to remotely located receiver is described.Such a system made up of high-brightness visible LEDs can providethe function of open space, wireless broadcasting of audio signals. Itcan be used as an information beacon for short-distance radiocommunication.
Any illumination device making using of high brightness visible LEDs
can be used as a kind of short-range information beacon.. Oneexample is an LED traffic light for the support of roadside-to-vehiclecommunications. There are many potential novel uses of visible lightfrom LEDs as a communication medium. This concurrent use of LEDs for simultaneous signaling and communications will open upmany new applications.
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REFERENCES:
“ LED WIRELESS” BY Grantham Pang, Thomas
Kwan, Hugh Liu& Chi-Ho Chan IEEE Industry
APPLICATIONS Jan/Feb 2002
“ INTELLIGENT TRANSPORTATION
SYSTEM”IEEE Transactions Dec 2001
www.bchydro.com/business/programs/led.html
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