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“Extended Reach” Echolocation Sensor

“Extended Reach” Echolocation Sensor. Matthew Lurie & Kyle Spesard Team 18 TA: Lydia Majure. Introduction. D evelop a way for a person to sense their surroundings using sonar Cheap, modular design Interfaces with “Extended Reach” Haptic Array. Objectives.

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“Extended Reach” Echolocation Sensor

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  1. “Extended Reach” Echolocation Sensor Matthew Lurie & Kyle Spesard Team 18 TA: Lydia Majure

  2. Introduction • Develop a way for a person to sense their surroundings using sonar • Cheap, modular design • Interfaces with “Extended Reach” Haptic Array

  3. Objectives • Ability to sense distance to an object 20 ft • Ability to determine characteristics of object based on reflected signal • Ultrasonic frequency transmission from 22kHz – 40kHz • Fast processing speed allowing continuous updates of sensing feedback

  4. Design Transmitter/Receiver Circuit Board Speaker DSP Board Mic

  5. Design

  6. DSP Board • STM32F4 Discovery Board • Three ADCs and DACs • CMSIS Library • Cortex-M4 Processor • Keil uVision Development Software • 1MB Flash Memory

  7. SoftwareFlowchart • High-pass filter: second order IIR with -3dB at 22kHz • Cross-correlation takes place in the frequency domain for efficiency

  8. MATLAB Simulations Reflected Signal + Noise Chirp Cross-correlated Signal Power Spectrum

  9. Software Problems • CMSIS function library caused hard faults • Floating point arrays would not function • Memory issue caused multiple boards to cease to be programmable

  10. Summary of Results • Working Functions: • Input/ADC • Output/DAC • Cross-correlation • Non-Working Functions: • High-pass filter • Power spectrum • Output serial link

  11. Circuit Design • Receiver pre-amp: • Low-pass filter • DC Bias & Gain • Accomplished with Differential Op-amp • Transmitter amp: • Amplifier • Accomplished with Non-inverting amplifier

  12. Requirements • Receiver Circuit • Gain of .6 to map input to ADC (0 to 3V) • Bias to center input to ADC (1.5V) • Low-pass filter to prevent aliasing (cutoff at 60kHz) • Transmitter Circuit • Gain of 2.2 to obtain maximum speaker output • Speaker • Obtain a output of 100dB

  13. Verifications • Receiver • Input : 39.4mV Pk-Pk • At ADC: 114 mV Pk-Pk • Inverted, with Bias at 1.48V

  14. Transmitter Verification • Transmitter • Circuit gain is 2 before distortion • Distortion added by speaker • Outputs approx. 94 dB

  15. Challenges • Receiver output was unexpectedly small • Optimized gain • Receiver was active • Needed to bias correctly • Receiver was a low pass filter • Could only receive input lower than 30kHz • Speaker added frequency dependent distortion • Voltage follower did not help

  16. Additional tests • Find range of speaker distortion • Least distortion 18kHz – 24kH • Optimize receiver gain • Gain of 18dB was max for mic input • Characterize mic • The mic acted as a low pass filter with cutoff at 31kHz

  17. Ethical Considerations • Ultrasonic sounds may cause discomfort to animals • Must be reliable if blind people end up using this system

  18. Future Work • Coding High pass filter without CMSIS library • Coding FFT without use of CMSIS library • Test on other DSP boards • Build housing for circuit • Mitigate distortion of speaker • Power system off of batteries

  19. Thank You • Professor Doug Jones • James Norton • Erik Johnson • David Jun • Beckman Institute • Lydia Majure • Professor Andrew Singer

  20. Questions?

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