Matthew Lurie & Kyle Spesard Team 18 TA: Lydia Majure

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

 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

Speaker Mic DSP Board Transmitter/Receiver Circuit Board

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

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

Chirp Reflected Signal + Noise Power Spectrum Cross-correlated Signal

 CMSIS function library caused hard faults  Floating point arrays would not function  Memory issue caused multiple boards to cease to be programmable

 Working Functions:  Input/ADC  Output/DAC  Cross-correlation  Non-Working Functions:  High-pass filter  Power spectrum  Output serial link

 Receiver pre-amp: ◦ Low-pass filter ◦ DC Bias & Gain ◦ Accomplished with Differential Op-amp  Transmitter amp: ◦ Amplifier ◦ Accomplished with Non-inverting amplifier

 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

 Receiver ◦ Input : 39.4mV Pk-Pk ◦ At ADC: 114 mV Pk-Pk ◦ Inverted, with Bias at 1.48V

 Transmitter ◦ Circuit gain is 2 before distortion ◦ Distortion added by speaker ◦ Outputs approx. 94 dB

 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

 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

 Ultrasonic sounds may cause discomfort to animals  Must be reliable if blind people end up using this system

 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

 Professor Doug Jones  James Norton  Erik Johnson  David Jun  Beckman Institute  Lydia Majure  Professor Andrew Singer