Transcript Final PDR

Developing a Sonar Sub-System for a
Submarine to Obtain Time Delays between
Received Signals
Gary Eades
Dy Eang
Diana Fuertes
12/04/2007
ECE4884
L03
Dr. Smith
Project Overview
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GT Marine Robotics Group (MRG)
needs a way to determine the
location of an underwater signal
source
GT MRG will compete in the
annual AUVSI and ONR
International Underwater Vehicle
Competition
The Sonar sub-system will be able
to calculate the delay times
between received signals. Once
these are known, the directions
and distances can be obtained.
Problems with Analog Circuit Design
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Noise interference from
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Smaller box and PCB board cause
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Internal circuit
Measuring equipment
Shorts within the circuit
Testing inconvenience
Trade-off between high gain and stability
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Higher gains cause instability in the form of
oscillations
Analog Circuit Design
Hydrophone
HPF
LPF
CMOS R.2.R Op-Amp
Amp
Amp
Co-ax cable
Digital Pot
Technical Specifications
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Linux SBC
The signals: μV in amplitude and between 20-30KHz
in frequency
HPF, LPF, N.I.Amps. : gain = 15dB
Solutions to the Analog Design Problems
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Break ground loops
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Supply multiple ground rails to prevent parasitic
currents
Use a bigger box
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Simplify testing procedures
Improve isolation between channels and stages
Alternative Solutions to the Analog Design
Problems
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Make a PCB
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Use separate shielding boxes
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Improve connectivity due to fixed path of conductor
Reduce circuit size
Improve noise interference
Improve isolation between stages
Use Low Noise Amplifier (LNA)
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Improve noise performance of the circuit
Provide initial gain > 15dB
The Algorithm
Loop (forever)
Perform automatic gain control
Perform cross-correlation
Calculate time delay
Transmit delays or error signals using three wire RS-232
End loop
Automatic Gain Control
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Initial resistance set
to minimum value
10 highest and
lowest values are
averaged
Averaged highs and
lows compared to
threshold
Resistance increased
until highs and lows
within upper and
lower bounds
Computational Efficiency
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Integer Arithmetic
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12 bit A/D converter
Voltages scaled between 0-4095
Not interested in actual voltage levels
Interest lies in the relative values from
each channel
Cross-Correlation Results (25kHz) 1000 Samples
.17 sec.
Results of Complete Algorithm
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Delay circuit used to test software
Interchanging the input and output caused a change
in time delay sign
Software troubleshoots electronic circuit
Errors or delays read by and displayed in a graphical
user interface
Results of Algorithm
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Left channel fixed
Right channel
delayed
No circuit errors
Results of Algorithm
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Right channel fixed
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Left channel delayed
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No circuit errors
Results of Algorithm
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Error in circuit
During AGC,
excessive dc level
shift occurred
Controlling computer
notified of error
Current Status and Future Plans
Test the mounted circuit
with the SBC
Determine a fixed Automatic
Gain Control algorithm
No
Pass
Yes
Final test with hydrophones
No
No
Pass
Test with higher amplitude
input signals
Yes
Yes
Link the system with the
Submarine’s controlling computer
No
Pass
Final Demonstration