Short-Range Digital Laser Communication
System
Team Members
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Timothy Vitou, team leader (laser safety, Helmet
receiver circuit and diode array)
Cory Yambor (transmitter circuit)
Steven Young (receiver circuit cellphone, assisted with
transmitter circuit design)
Chase Novack (cell phone software demodulation and
playback)
Background
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RF communication is very common, but can have
limitations
Wireless signals can be intercepted and run into
interference
The laser communication system cannot be remotely
hacked and is very secure
Advantages
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No remote hacking or jamming
Versatile
Low Power (No more than 200 mW)
Varying wavelengths of light may be used based on
needs of user
Has potential in tactical applications
High speed
Disadvantages
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Not meant for long distances
Potential hazards of lasers
Aiming can be difficult at longer ranges
Prone to poor environmental conditions
Performance affected by weather
Line of sight requirement
How it works
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A microphone picks up a person’s voice
Analog signal is converted into a digital signal
Modulates a laser using Pulse Coded Modulation
Photodetectors send the signal to a DAC for the user to hear it
Our project does this using a helmet and a cell phone
Transmitter
Receiver
Cellphone
with
Android
Application
Transmitter Flow Diagram
Transmitter
Microphone
Pulse
Coded
Modulation
Amplifier
Digital Laser
Transmission
Buffer
A/D
Conversion
Transmitter components
LM386
OPA2134
Transmitter components
PCM4201
DIT4096
Receiver Flow Diagram
Receiver
Laser
Reception
Signal
Amplification
D/A
Conversion
Audio
Output
Receiver
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Array of phototransistors
Comparator circuit (Demodulation)
Cell phone software
Helmet’s TLV320DAC23 (DAC)
Serial to USB FT312 for cell phone
Receiver Components
TLV320DAC23
FT312
Software (Overall)
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The cell phone module is developed for the Android OS
platform
Targets version 2.3 and above
Makes use of the AudioRecord, AudioTrack, and
MediaPlayer Application Programming Interfaces
Saves and plays back voice data as MP3 files (utilizing
the free LAME encoder library)
Software (Transmitter Module)
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Built-in microphone takes in user’s voice
The signal is passed to AudioRecord, and
then AudioTrack which record and playback
the audio, respectively
The played back audio is sent via the
auxiliary jack to the transmitter circuitry
Is tested and verified working
Software (Receiver Module)
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Receives modulated digital voice signal from the
receiver circuitry via serial to USB cable
Converts the received signal back to analog, saves it
(via AudioRecord), then plays it back (with AudioTrack
and MediaPlayer APIs) via the phone’s speaker
Code is in development, and waiting on the completion
of the hardware and the arrival of the serial to USB
cable and accompanying IC
Remaining Work
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System integration testing
Cell phone integration testing
Timing for A/D and D/A (8 - 96kHz)
Laser Safety
The biggest concern for this project is the potential level
of danger
The laser is a class 3A
When used improperly, the system can cause eye injury
Proper training must be conducted to avoid misuse
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Calculations (at 50 feet)
Laser Wavelength
MPE (8KHz)
MPE(96KHz)
Visible Red (650nm)
1.111x10-4 W/m2
3.943x10-5 W/m2
Infrared (980nm)
0.00262 W/m2
2.1144x10-5 W/m2
Infrared (1550nm)
0.0125 W/m2
0.00104 W/m2
Potential Developments
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Open to modifications and other applications
Possible use for situations with poor radio reception
Air to ground communications
Conclusion
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Digital laser communication offers a strategic advantage
for law enforcement/military
Concept can be applied over a wide range of
applications
Over time, the system can be made to be more secure
and efficient
Questions?