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1
Laser MicrophoneKareem NammariEdward Nicholson
Kari SkupaWes Stanway
Cui Sun
Cole 2
This is a surveillance device that will use a laser to pick up vibrations on a surface and convert it to sound.
Abstract
Cole 3
Use a laser to measure the vibration on a surface.
Save and playback signal. Be able to post process the signal. Identify the audio source.
Objectives
Cole 4
Covert Surveillance Distance Measurements Vibration Monitoring
Applications
Cole 5
Allows for long range surveillance Difficult to detect
Advantages
Disadvantages Needs stable environment Alignment
Cole 6
Relatively Cheap Reliable Data Hard to Detect Established Market
Marketability
Cole 7
Working laser based sound detector◦ 45º Bounce System
Basic filtering Data output over Serial Terminal Control
Low Goals
Cole 8
Working Laser Sound Detector Using Interferometry
Multiple Analog Filters DSP Serial I/O
◦ Terminal Control◦ Serial Communication to Matlab
Medium Goals
Cole 9
Wireless Communication to Computer Data Storage LCD Display On Box Options
◦ Fourier◦ Filter Selection◦ Output on Display
High Goals
Kareem 10
Why use an interferometer?◦ Sensitive to small signals◦ Perpendicular setup
Complications◦ Phase difference between beams◦ Coherence Length
Interferometer Setup
Kareem 11
Kareem 12
To get a good signal at the sensor ΔL needs to impart a phase shift in the laser beam of φ radians.
φ must be such that the intensity of the combined wave falls in one of the linear regions of Cos(t)+Cos(t+φ).
Expected Signal
Kareem 13
Kareem 14
Small signal leads to low distortion Large signals will produce a frequency that
is a multiple of the original. Differential measurement reduces
distortions
Expected Signal
Kareem 15
Kareem 16
Kareem 17
Kareem 18
Wes 19
Post Processing
Interferometer
DetectorAnalog Filters
Audio Amplifier
A/D Converter
Microprocessor
Audio Out
Software
I/O
Matlab
Selector / Mux
Audio Source
POWER
Laser
Optics
SPI
Terminal
HardwareRS232
Memory
+5 V ±15 V
+3.3V
Wes 20
Filters◦ Minimum filtering is an anti-aliasing filter right
before the A/DC. Audio Amplifier Detector A/D converter
Analog Hardware
Wes 21
Coherence
ΔL
Bandwidth small enough for ΔL
Laser Requirements
fn
cL
Wes 22
Requirements Silicon Diode HeNe Gas Laser DFB
Coherence Length 1-10nm 30cm 0.07-100m
Wavelength 375-2680nm 632nm 808-2000nm
Power 5V 100mA 1250V 4mA 3.2V 100mA
Cost $3-30 $10-200 $50-1000
Size Small Packages Large Tubes Small Packages
Laser Choices
Wes 23
Range from Class 2 to Class 3B Class 2
◦ Safe because of Blink Reflex (0.25 sec viewing)◦ 400-800nm◦ Limited to 2mW
Class 3B◦ Hazardous if exposed directly to eye◦ Diffused reflections are not harmful◦ 315-2000nm◦ Limited to 0.5mW
Safety – DFB Laser
Wes 24
Photodiodes◦ Respond quickly to photons. ◦ Provide a very small current.
Phototransistors◦ Respond slowly to photons.◦ Provide a moderate current.
Detector
Wes 25
Wall Wart (~20 Vdc @ 1 A) Laser Driver ± 15 V + 5 V + 3.3 V
Power
Kari 26
A/D Converter◦ Low resolution◦ Separate chips
Serial I/O◦ Terminal control◦ Matlab communication
Memory ◦ Minimum capture rate of 44,100 samples per
second◦ Flash may be too slow.
Digital Hardware
Kari 27
MSP430 series◦ 16-bit CPU◦ 8-16 MHz CPU speed◦ Up to 256 kB of flash memory and 16 kB of RAM◦ Up to 80 I/O pins◦ Built-in ADC/DAC components◦ Low cost◦ Low power consumption
Microcontroller
Kari 28
Resolution◦ 8 to 10 bits of resolution for audio
SPI interface◦ Two Way Communication◦ High Speed◦ Low Power
MCP3002 - ADS1115 -
ADCs
Kari 29
Play back recorded audio. Matlab
◦ DSP◦ FFT
Terminal◦ I/O interface◦ Debugging
Software Interface
Kari 30
Serial Communication DSP
◦ Filtering Specific Frequencies FFT
◦ Voice Identification
Matlab
Kari 31
Conceptual◦ Simulate Optics◦ Proof of Concept in Optics Lab
Hardware Software
Test Plans?
Kari 32
Window vibration in comparison to the wavelength of the laser
Alignment and spacing of lasers and beam splitter
Noise Filtering Coherence length of lasers Integration between Hardware and Software
Possible Problems
Sun 33
Time Budget Physics Knowledge Base
Constraints
Sun 34
Standard Components Precise Alignment RoHS Compliance Capable
Manufacturability
Sun 35
Kari Sun Cole Wes Kareem
Software Analog Hardware
Software Layout Optics
Digital Hardware
Optics Digital Hardware
Full Schematic
AnalogHardware
Sound Box Power Sound Box Power Detector
Optics PopulateBoard
Populate Board
Populate Board
Budget
Division of Labor
Sun 36
Schedule
Sun 37
BudgetBlock Estimated
Cost
Laser $200
Optics $400
PCBs $100
Digital Components
$150
Analog Components
$200
Power $100
Demo Box $75
Expo Materials $75
Total $1300
Sun 38
UROP $1000.00 Attempt DEPS funding Personal donation $100 each Donation/loans of equipment
Funding
Sun 39
Demonstration
40
Do you have questions?