4.3 MB PowerPoint - Department of Electrical, Computer, and

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The Energy Directors
Jeremy Nash, Chris Lamb, Kelsey Whitesell, Josh Chircus

Create a free-space laser communication
system capable of:
 Functioning in a high noise environment
 Encryption for secure transmission
 Transmitting multiple signals simultaneously
 Long-range, line-of-sight communication
JEREMY

Applications:
 Military communications
 Space communications
 High bandwidth applications

Advantages:
 Fast (high bandwidth)
 Lack of interference with other signals
 Secure (directed)
JEREMY

Low Priority
 Transmits digital audio and plays back audio successfully (one-way)
over 1 ft
 Performs well in high noise environment
 Encryption

Medium
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

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Time division multiplexing (TDM)
2 way communication
Alignment feedback system at beginning of/during transmission
Long distance transmission (>10 ft)
High
 Video transmission and raw data (digital)
 Continuous automatic alignment including beam splitter/Quad-
Detector feedback
JEREMY
Optics
* For tw0-way communication, this same
system will be mirrored and added
JEREMY
Packaged Transceiver Units
clamp
Bracket and
motorized stages
Two-way communication
Laser and photodiode on
optical mounts
Tripods
Alignment system
Inside the package
Transceiver Unit Detail
PCB
Side view
clamp
Back view
front
power
ground
JEREMY

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Need short processing time to avoid long
delays in transmission
Need line-of-sight
Mechanical stability
Laser beam attenuation constrained
Cost
Manpower
Need spacing between laser beams for twoway communication
JEREMY

Environmental impact
 Hard to dispose of parts
 Beam doesn’t interfere with the environment
because it’s directed energy at optical frequency
(no FCC regulation yet)

Safety
 Laser can damage eye
 Low power laser (Class IIIa)
CHRIS
●
Class IIIa (continuous wave, 1 to 5 mW)
●
●
●
●
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Visible Wavelengths (350 – 800 nm)
Low power/area (typically < 2 mW/cm2)
Corneal damage only (safe viewing time is 0.25
seconds)
Damage includes non-permanent retinal damage if
viewed for 1 or 2 seconds, permanent retinal
damage if viewed longer than a few seconds
Translated: Don't look into the laser (duh).
CHRIS

Manufacturability
 Photodiode needs to be accurate
 Motors need to be high resolution

Sustainability
 Low power consumption
 Resilient parts and reliable processors
 Easy to fix because its relatively straight-forward
to troubleshoot
CHRIS
CHRIS



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Signal Source(s): one or more current/voltage signal source(s), for
example the output from an iPod
Analog to Digital Converter: Allows for encryption of analog signal
Encryption: performed by encoding data from signal source with a
standard encryption algorithm, implemented on a MCU
Laser diode: output depends on current input, so the laser diode itself is
an AM modulator
Optics: Optical systems could include the following:



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Neutral density filters and mirrors to simulate longer distances in the lab
Spatial filters and collimating lenses to improve signal quality
Demodulator: at the receiver; this will consist of a photodiode to detect
the optical signal and turn it into an electrical signal
Decryption: also implemented on an MCU
Digital to Analog: Allows for playback of decrypted analog signal
Output: signal could be output to a speaker for playing a sound, to a
computer to display the received signal, etc.
CHRIS
Motor control
MCU –
Motor
Align
command
Mux
Hardware
Encoder
Laser
MCU –
Comm
Motors
Alignment Status
De-Mux
Transimpedance
Amplifier
Photodiode
CHRIS

Power Requirements
 Laser: 5 V DC/3 A = 15W
 MCU on PCB (x2 per transceiver = 4 total): 5 V DC /1.6 A=
8W
 Transimpedance amplifier: currently unknown, will
measure

Power Supply
 OTS power supply for each system
▪ AC/DC converter from wall to DC, probably 15V for rail power
CHRIS
WDM
TDM
Less coding – combination and
synchronization done through hardware
Can accommodate modulation at high data
rates
1 wavelength per channel
Sometimes requires optical 3R regeneration
(re-amplify, re-shaping, re-timing)
Requires more lasers/diodes
Combination of signal channels is done
within the software before it is even sent to
the laser to be transmitted
Works better for fiber optics system, since
the channels are combined into the fiber
upon transmission and demuxed from it
after being received
Often requires synchronization with
start/stop signals, as well as error channels
For non fiber system, requires lots of space
and optical combination equipment (i.e.
prism) to achieve combination and
transmission as well as demuxing
KELSEY
Four Quadrant Detector
Camera system
Neither
Small area (requires
approximate alignment by
eye)
Small area (requires
approximate alignment by
eye)
Guess and check
alignment, but with
limited accuracy
More expensive
More complex processing
No additional complexity
Beam Splitter
Laser Beam
Rx
Tx
Focusing lens
Four Quadrant
Detector
KELSEY

Photodiodes-Thorlabs FDS100
 350 - 1100 nm
 High Responsivity in red (635 nm) range
 Fast recovery time (35MHz)

Laser Diodes from Edmund Optics
 Built-in safety circuitry
▪ Maintains functionality
▪ Prevents back-current
▪ Provides some temperature control
 Max 5mW power (class 3a laser)
 635 nm (red) center wavelength
 Narrow bandwidth (± 10 nm)
 Low current draw
 Modulation bandwidth 6Hz-2MHz
KELSEY

Components to simulate additional distance
due to limited lab space
 Neutral Density (ND) filters for attenuation
 Mirrors



Beam Splitter
Focusing lens
If necessary: lenses for improving quality
and/or collimating
KELSEY





Filtering noise
ADC/DAC
Motor Control for alignment
Encryption/Decryption
Switching between modes of operation
 Audio, Raw Data Transfer, and Video options
KELSEY
Turn on laser
Alignment Procedure
ADC, Encryption, signal
modulated onto the laser
Optics
DAC
Noise filtering
Output
KELSEY
Digital Signal After ADC
Input Signal
Example Sample
Input Signal with DC Offset
Example Transmit-Ready Signal
KELSEY

MSP430 xxx series
 8-16MHz
 ADC/DAC options
 Up to 64 GPIO options
 Up to 120kB of RAM
 Ultra-low power usage
JOSH

Motorized track actuators for lateral translations

Stepper Motor for tilt adjustment
Plastic packaging for transceiver circuits and components
Stands (possibly tripod)
Clamps and Brackets for securing transceiver units
Various Mounts (can be machined, if need be)
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JOSH
Task
Primary
Secondary
Optoelectric Circuitry
Chris
Kelsey
Mechanical Structure/Alignment
Josh/Chris
Jeremy
Microcontroller (Communication)
Jeremy
Josh/Chris
Microcontroller (Motor Control)
Kelsey
Jeremy
Board Layout/Construction
Jeremy
Chris/Kelsey
Digital Signal Processing
Josh
Kelsey
Design Documentation
Kelsey
Chris/Josh/Jeremy
JOSH
JOSH
Equipment
Purpose
Estimated
Price
Laser Diodes
Transmits encoded information
$670
Photodiodes
Detects laser signal
$60
Microcontroller
Processes signal (see CPU tasks)
$50
PCB parts (board,
resistors, etc.)
Decodes voltage from photodiode and filters noise
$50
Motorized Track
Actuators
Precision adjustment of photodiodes and lasers for
automatic alignment
$340
4 Quadrant Sensor
Used in alignment system
$500
Lenses
Used in alignment system
$100
Beam Splitter
Used in alignment system
$90
Tripods
Used for Mounting Transceivers
$100
TOTAL
$2300
JOSH

DEPS Funding (Granted)
 $2200 all purpose funding
 Requires a report upon completion

UROP Funding (Pending)
 Up to $1000 funding
 Requires a report upon completion
▪ These grants should be enough to fund our project.
JOSH

Failure to implement automated alignment due to
cost of motors or unforeseen mechanical issues.
 Mitigate by finding low-cost motors and seeking advice
from mechanical engineer.

Failure to implement video transmission due to
insufficient time.
 Budget time effectively and seek advice for video
transmission requirements.

If a rock gets into the system:
 There is no possible mitigation – all members perform Hari
Kari.

Chris loses energy – not possible.
JOSH
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