Transcript presentation

Matthew Lurie
& Kyle Spesard
Team 18
TA: Lydia Majure
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Develop a way for a person to sense
their surroundings using sonar
Cheap, modular design
Interfaces with “Extended Reach”
Haptic Array
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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
Transmitter/Receiver
Circuit Board
Speaker
DSP
Board
Mic
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STM32F4 Discovery
Board
Three ADCs and
DACs
CMSIS Library
Cortex-M4 Processor
Keil uVision
Development
Software
1MB Flash Memory
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High-pass filter:
second order IIR with
-3dB at 22kHz
Cross-correlation
takes place in the
frequency domain
for efficiency
Chirp
Reflected Signal + Noise
Cross-correlated Signal
Power Spectrum
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CMSIS function library caused hard
faults
Floating point arrays would not
function
Memory issue caused multiple
boards to cease to be programmable
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Working Functions:
Input/ADC
Output/DAC
Cross-correlation
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Non-Working
Functions:
High-pass filter
Power spectrum
Output serial link
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Receiver pre-amp:
◦ Low-pass filter
◦ DC Bias & Gain
◦ Accomplished with
Differential Op-amp
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Transmitter amp:
◦ Amplifier
◦ Accomplished with
Non-inverting amplifier
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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)
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Transmitter Circuit
◦ Gain of 2.2 to obtain maximum speaker output
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Speaker
◦ Obtain a output of 100dB
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Receiver
◦ Input : 39.4mV Pk-Pk
◦ At ADC: 114 mV Pk-Pk
◦ Inverted, with Bias at 1.48V
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Transmitter
◦ Circuit gain is 2 before distortion
◦ Distortion added by speaker
◦ Outputs approx. 94 dB
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Receiver output was unexpectedly small
◦ Optimized gain
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Receiver was active
◦ Needed to bias correctly
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Receiver was a low pass filter
◦ Could only receive input lower than 30kHz
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Speaker added frequency dependent
distortion
◦ Voltage follower did not help
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Find range of speaker distortion
◦ Least distortion 18kHz – 24kH
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Optimize receiver gain
◦ Gain of 18dB was max for mic input
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Characterize mic
◦ The mic acted as a low pass filter with cutoff at
31kHz
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Ultrasonic sounds may cause discomfort to
animals
Must be reliable if blind people end up using
this system
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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
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Professor Doug Jones
James Norton
Erik Johnson
David Jun
Beckman Institute
Lydia Majure
Professor Andrew Singer