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Laser Microphone. Kareem Nammari Edward Nicholson Kari Skupa Wes Stanway Cui Sun. Abstract. This is a surveillance device that will use a laser to pick up vibrations on a surface and convert it to sound. . Objectives. Use a laser to measure the vibration on a surface.

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Laser Microphone


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

    2. Abstract This is a surveillance device that will use a laser to pick up vibrations on a surface and convert it to sound. Cole

    3. Objectives • 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. Cole

    4. Applications • Covert Surveillance • Distance Measurements • Vibration Monitoring Cole

    5. Advantages • Allows for long range surveillance • Difficult to detect Disadvantages • Needs stable environment • Alignment Cole

    6. Marketability • Relatively Cheap • Reliable Data • Hard to Detect • Established Market Cole

    7. Low Goals • Working laser based sound detector • 45º Bounce System • Basic filtering • Data output over Serial • Terminal Control Cole

    8. Medium Goals • Working Laser Sound Detector Using Interferometry • Multiple Analog Filters • DSP • Serial I/O • Terminal Control • Serial Communication to Matlab Cole

    9. High Goals • Wireless Communication to Computer • Data Storage • LCD Display • On Box Options • Fourier • Filter Selection • Output on Display Cole

    10. Interferometer Setup • Why use an interferometer? • Sensitive to small signals • Perpendicular setup • Complications • Phase difference between beams • Coherence Length Kareem

    11. Kareem

    12. Expected Signal • 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). Kareem

    13. Kareem

    14. Expected Signal • Small signal leads to low distortion • Large signals will produce a frequency that is a multiple of the original. • Differential measurement reduces distortions Kareem

    15. Kareem

    16. Kareem

    17. Kareem

    18. Kareem

    19. Interferometer Laser Detector Analog Filters A/D Converter SPI Microprocessor Optics Selector / Mux Memory Software Audio Amplifier Audio Source Audio Out I/O RS232 Hardware Post Processing POWER Terminal +5 V ±15 V Matlab +3.3V Wes

    20. Analog Hardware • Filters • Minimum filtering is an anti-aliasing filter right before the A/DC. • Audio Amplifier • Detector • A/D converter Wes

    21. Laser Requirements • Coherence • ΔL • Bandwidth small enough for ΔL Wes

    22. Laser Choices Wes

    23. Safety – DFB Laser • 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 Wes

    24. Detector • Photodiodes • Respond quickly to photons. • Provide a very small current. • Phototransistors • Respond slowly to photons. • Provide a moderate current. Wes

    25. Power • Wall Wart (~20 Vdc @ 1 A) • Laser Driver • ± 15 V • + 5 V • + 3.3 V Wes

    26. Digital Hardware • 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. Kari

    27. Microcontroller • 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 Kari

    28. ADCs • Resolution • 8 to 10 bits of resolution for audio • SPI interface • Two Way Communication • High Speed • Low Power MCP3002 - ADS1115 - Kari

    29. Software Interface • Play back recorded audio. • Matlab • DSP • FFT • Terminal • I/O interface • Debugging Kari

    30. Matlab • Serial Communication • DSP • Filtering Specific Frequencies • FFT • Voice Identification Kari

    31. Test Plans? • Conceptual • Simulate Optics • Proof of Concept in Optics Lab • Hardware • Software Kari

    32. Possible Problems • 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 Kari

    33. Constraints • Time • Budget • Physics • Knowledge Base Sun

    34. Manufacturability • Standard Components • Precise Alignment • RoHS Compliance Capable Sun

    35. Division of Labor Sun

    36. Schedule Sun

    37. Budget Sun

    38. Funding • UROP $1000.00 • Attempt DEPS funding • Personal donation $100 each • Donation/loans of equipment Sun

    39. Demonstration Sun

    40. Do you have questions?