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 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 Noise interference from Internal circuit Measuring equipment Smaller box and PCB board cause Shorts within the circuit Testing inconvenience Trade-off between high gain and stability Higher gains cause instability in the form of oscillations

Analog Circuit Design Co-ax cable HPF LPF CMOS R.2.R Op-Amp Digital Pot Amp Linux SBC Hydrophone The signals: μV in amplitude and between 20-30KHz in frequency HPF, LPF, N.I.Amps. : gain = 15dB Technical Specifications Amp

Solutions to the Analog Design Problems Break ground loops Supply multiple ground rails to prevent parasitic currents Use a bigger box Simplify testing procedures Improve isolation between channels and stages

Alternative Solutions to the Analog Design Problems Make a PCB Improve connectivity due to fixed path of conductor Reduce circuit size Use separate shielding boxes Improve noise interference Improve isolation between stages Use Low Noise Amplifier (LNA) 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 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 Integer Arithmetic 12 bit A/D converter Voltages scaled between 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 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 Left channel fixed Right channel delayed No circuit errors

Results of Algorithm Right channel fixed Left channel delayed No circuit errors

Results of Algorithm 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 Final test with hydrophones Final Demonstration Link the system with the Submarine’s controlling computer Pass No Yes No Test with higher amplitude input signals Yes No