Transcript A Secure, Multi-Channel Laser Communication System for

The Energy Directors
Jeremy Nash, Chris Lamb, Kelsey Whitesell, Josh Chircus
Milestone 1
 One way digital signal transmission through free
space
 Simple noise filtering
 Show functionality of ADC/DAC/SPI
 Basic motor movements
Milestone 2
 2 way signal transmission with
ADC/DAC/Encryption/TDM functionality over
short distance
 Full motor control
 Simple alignment functionality
Josh
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Josh
Full auto-alignment functionality
2 way optical communication of audio signal
with ADC/DAC/Encryption/TDM functionality
Package system in an aesthetic structure
Incorporate telephone handset for users to
communicate with
Laser setup:
• Successfully transmitted analog signal using laser diode and
photodiode setup at 1ft
Signal encoding:
• Several circuits, including the audio amplifier, summers, laser
diode driver, and transimpedance amplifier have been
implemented and debugged
Motor control:
• Pseudo code for motor alignment complete, awaiting motor
testing
PCB layout:
• Schematic complete. PCB design almost complete. PCBwill be
ordered within the week to implement a faster MCU for
encoding
Josh
Parts Bought
Part
Company
Price
10 Photodiodes
Thorlabs
$130
2 Laser Diodes
QPhotonics
$120
1 Optical Filter
Edmund Optics
$125
Inverters
DigiKey
$10
TOTAL
$385
Free Parts
Josh
Part
Company
2 Laser Diodes
Intense (Kevin Caughlin)
8 Low Noise Op Amps
Analog Devices
5 Multiplexers
DigiKey
Equipment
Purpose
Price
DEPS Funding
$2200
UROP Funding
$960
Laser Diodes
Transmits encoded information
-$120
Photodiodes
Detects laser signal
-$130
Lenses
Used in alignment system
-$125
Inverter
$10
Money Left
$2775
PCB parts (Original Design,
Redesign, Components, etc.)
Decodes voltage from photodiode and filters noise
$200
Motorized Track Actuators
Precision adjustment of photodiodes and lasers for automatic
alignment
$350
Tripods
Used for Mounting Transceivers
$100
Josh
Items Left to Purchase
650
Josh

Each transceiver will have an AC-DC power
adapter to supply power to the board
 Easy to implement
 All components run on 15V or less
 Allows for system portability

The motors will be powered by a separate
AC-DC power supply of 24-36V
 Decrease noise feedback from motors
Josh
Jeremy
Jeremy
Jeremy
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ADC
 12 bit samples
 200 ksps (1 sample per 5μs)
 Used to digitize audio signal
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DAC
 12 bit input
 Used to convert digital signal to audible signal
Jeremy
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1 ADC sample per packet
2 8 bit SPI transactions
12 bits for ADC sample STC
4 bits for checksum
UCLK
SIMO
Jeremy
Input
Signal
Offset
Summer
ADC
Data
Serialization
Speaker
Amplifi
er
DAC
Decoding
H/W
Input
Output
(No Load)
Jeremy
Input
Output
(Loaded)
AM H/W
Laser +
Optics
Transimpedence
Amplifier

Interrupt driven
 Receive Interrupt
 Transmit Interrupt
 Alignment Interrupt
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Interrupts are put into a FIFO buffer and
processed
Jeremy
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Transmitter
 Summer and bias circuits
for encoding data
 Filters
 Laser diode driver and laser diode
 MCU
 LED indicators, selection and
on/off buttons (switches)
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Josh
Jeremy
Chris
Receiver
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Kelsey
Photodiodes- receiving and alignment feedback array
Transimpedance amplifier
Audio amplifier with volume control
Bandpass filters
MCU
Kelsey
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12 bit DAC and ADC
Capable of data encryption
Easy to lay down (64 pins)
4 Synchronous SPI ports
116 KB Flash, 8KB RAM
16MHz clock suitable for audio and digital data
processing
Three-channel internal DMA for high-speed
memory access in video applications
Disadvantage: No available development
boards besides target boards
Kelsey
Kelsey
Transmitter
Kelsey
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Linear track actuators for X-Y plane control
 Motors: Firgelli Linear Track
Actuators
▪
▪
▪
▪
10’’ stroke length
24-36 VDC input
Bracket available separately
1-2.5 in/sec speeds depending on load
 Motor drivers: two relays for directional control from
the MSP 430; opto-isolators
 Pulse-width modulation input
Kelsey
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Stepper Motor for tilt control
 Use stepper motors from Lin Eng.
▪ High resolution: 0.45 degree step size
▪ High torque
▪ 4 Leads
 Pre-assembled motor driver from
Lin Engineering
▪ Max. step frequency 2.5 MHz
▪ Optically isolated I/O
▪ See schematic
Kelsey
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X-Y control
 If receiving photodiode has no current:
▪ check to see if any photodiodes on array have current
▪ If so, PWM linear actuator driver to move transceiver unit a precalibrated distance in the x-y plane (positions of diodes stored as 1x2
vectors)
▪ If not, scan up and down in a 5x5 ‘’ window until current is seen in one of
the diodes. If no current seen still, scan a 6x6’’ window… then adjust
transceiver position
 If receiving photodiode has current, no adjustment is
necessary
Kelsey
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Tilt control (sideways)
 Used when one photodiode is receiving and the other
is not, indicating a tilted transceiver
▪ Clamped transceivers should help reduce the chances of this
problem
▪ Optical encoders cannot be used alone since only one
transceiver has a motor and if misaligned, the other
transceiver cannot communicate its tilt to the other
▪ Use similar scanning technique as for x-y control
Forward-backward tilt control not possible in our
design
Kelsey
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Photodiodes – Thorlabs FDS100
 350 - 1100 nm
 High Responsivity in red (650 nm) range
 Fast recovery time (35MHz)
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Laser Diodes – QPhotonics QLD-658-20S
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 Single mode Fabry Perot laser
 1 mW to 14 mW operating range
 Pulsed operation with 0.5ns rise time easily allows 5
to 10 MHz modulation bandwidth
 Low threshold current (~60 mA) and high slope
efficiency
 657 nm, +/- 1nm
 Operating temperature range -40oC to +40oC
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Laser Diodes – Intense
 5mW - 10mW operating range
 650nm, +/- 10nm
 Low threshold current (~20 mA)
 Operating temperature range 20oC to 25oC
 Provided free of charge by Intense
Optical Filter – Edmund Optics NT67-023
 655 nm center wavelength, 40 nm bandwidth
 93% or better transmission
 1.25 mm (1 inch) diameter
 UV Grade Fused Silica (low reflectance)
Collimating Kit – Optima Precision Inc. LDM-3756
 Small, compact size (2 cm), focusable
 Low divergence
 High transmission of collimated beam, greater than
93%
 Simple built-In heat sink
Chris
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LIV Curves
 Non-ideal nature in power drift may be due to
temperature drift.
Power vs. Operating Voltage
14
14
12
12
Laser Diode Power (mW)
Laser Diode Power (mW)
Power vs. Current
10
8
6
4
2
10
8
6
4
2
0
0
12
Chris
32
52
72
Laser Diode Current (mA)
92
2
2.2
2.4
2.6
2.8
3
Laser Diode Operating Voltage (V)
3.2
3.4
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IV curve
 Linear nature of IV curve suggests that resistance of Laser
Diode remains constant throughout operating range.
Laser Operating Voltage Vs. Current
Laser Operating Voltage (V)
3.4
3.2
3
2.8
2.6
2.4
2.2
2
12
Chris
22
32
42
52
62
Laser Current (mA)
72
82
92
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Linearity Implies that resistance of photo diode is
essentially a constant at all power levels.
IV Curve for Photo Diode
20
Photo Diode Voltage (V)
19
18
17
16
15
14
13
12
0
Chris
1
2
3
Photo Diode Current (mA)
4
5
Profile agrees well with the laser diode LIV curves,
indicating that the photo diode is detecting the
laser diode correctly.
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Photo Diode Current vs. Laser Diode Bias Voltage
Photo Diode Current (mA)
5
4
3
2
1
0
0
Chris
2
4
6
8
10
12
Laser Diode Bias Voltage (V)
14
16
18
20
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The shift in responsivity suggests that the
wavelength of the laser diode is decreasing due to
power shift.
Responsivity
0.41
Responsivity (A/W)
0.405
0.4
0.395
0.39
0.385
0.38
6
Chris
7
8
9
10
Laser Diode Power (mW)
11
12
13
Chris
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Op-amp
 Must have > 112 V/μs slew rate for 16MHz Operation
(LF356N is 12 V/μs)
 Must be low noise to preserve digital signal integrity
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Speaker Driver
 Needed for drawing sufficient current
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Optical Issues
 Power loss and noise
 Difficulties with the beam divergence
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Chris
Mechanical awkwardness
Awkwardness