Kareem Nammari Edward Nicholson Kari Skupa Wes Stanway Cui Sun 1.

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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

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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

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Covert Surveillance Distance Measurements Vibration Monitoring

Applications

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Allows for long range surveillance Difficult to detect

Advantages

Disadvantages Needs stable environment Alignment

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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

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Working Laser Sound Detector Using Interferometry

Multiple Analog Filters DSP Serial I/O

◦ Terminal Control◦ Serial Communication to Matlab

Medium Goals

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Wireless Communication to Computer Data Storage LCD Display On Box Options

◦ Fourier◦ Filter Selection◦ Output on Display

High Goals

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Why use an interferometer?◦ Sensitive to small signals◦ Perpendicular setup

Complications◦ Phase difference between beams◦ Coherence Length

Interferometer Setup

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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

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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

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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

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Coherence

ΔL

Bandwidth small enough for ΔL

Laser Requirements

fn

cL

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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

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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

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Photodiodes◦ Respond quickly to photons. ◦ Provide a very small current.

Phototransistors◦ Respond slowly to photons.◦ Provide a moderate current.

Detector

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Wall Wart (~20 Vdc @ 1 A) Laser Driver ± 15 V + 5 V + 3.3 V

Power

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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

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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

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Resolution◦ 8 to 10 bits of resolution for audio

SPI interface◦ Two Way Communication◦ High Speed◦ Low Power

MCP3002 - ADS1115 -

ADCs

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Play back recorded audio. Matlab

◦ DSP◦ FFT

Terminal◦ I/O interface◦ Debugging

Software Interface

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Serial Communication DSP

◦ Filtering Specific Frequencies FFT

◦ Voice Identification

Matlab

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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

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Time Budget Physics Knowledge Base

Constraints

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Standard Components Precise Alignment RoHS Compliance Capable

Manufacturability

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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

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Schedule

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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

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Demonstration

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Do you have questions?