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Developing a Sonar Sub-System for a Submarine to Obtain Time Delays between Received Signals

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

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Developing a Sonar Sub-System for a Submarine to Obtain Time Delays between Received Signals

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  1. 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

  2. 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.

  3. 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

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

  5. 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

  6. 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

  7. 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

  8. 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

  9. Computational Efficiency • Integer Arithmetic • 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

  10. Cross-Correlation Results (25kHz) 1000 Samples .17 sec.

  11. 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

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

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

  14. Error in circuit During AGC, excessive dc level shift occurred Controlling computer notified of error Results of Algorithm

  15. Current Status and Future Plans Test the mounted circuit with the SBC Determine a fixed Automatic Gain Control algorithm Yes Pass Final test with hydrophones No Pass Yes Link the system with the Submarine’s controlling computer No Pass Test with higher amplitude input signals Final Demonstration No Yes No

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