Hi,
I'm in the process of building my own Side Scan Sonar (SSS), or at least the electronics and software for it.
I have got a 'SSS fish' (watertight metal tube with ultrasonic transducers) identical to this one
http://www.abc.se/~pa/sture/project/tow2000.jpg.
My plan is to have almost all electronics located inside the 'SSS fish' to reduce the signal loss in the cable, interference, and the amount of data sent through the cables.
The data transfer and communication between the towed 'SSS fish' and the computer on the surface will be through standard 100 MBps Ethernet, and the power for the 'SSS fish' will come through the same Ethernet cable (POE, Power Over Ethernet).
The 'SSS fish' has two ultrasound transducers (left and right) that has a center frequency of approximately 220 KHz.
The electronics inside the 'SSS fish' will consist of five parts:
- Main controller board with a quite large FPGA that does digital signal processing of the received signals from the ultrasound transducers, the FPGA will also handle the Ethernet communication (I will include a micro controller of some sort (Altera NIOS or OpenRisc OR1200) that runs the TCP/IP protocol stack etc).
- Receiver board with analog to digital converters (16 bit ADC @ 2 MSPS), voltage gain amplifiers (VGA for time variation gain)
- Transmitter board with DC/AC step up converter (12V -> 500-1000V), digital to analog converters to be able to modulate the transmitted signal (sweep +/- 5% of center frequency, or something like that).
- Power supply board that conforms with POE+ (20-25W Power Over Ethernet), and produces the main voltages that the three other boards needs (+5V, +/-12V)
- Sensor board that has 3D accelerometers, 3D gyros, 3D compass, temperature sensors (both for internal temperature within the 'SSS fish' as well as external water temperature outside the 'SSS fish'), pressure sensor (to get the exact depth of 'SSS fish'). All sensors will be controlled by a small 8-bit microcontroller that process the raw data from the sensors, and sends it in human readable form to the microcontroller within the FPGA on the main controller board before it is sent to the PC software on the surface.
Since I will have a quite large FPGA (Altera Cyclon III (EP3C40)) controlling everything, I can do lots of computer intense digital signal processing in hardware, and I can experiment with different transmit modulations (CW, CHIRP etc).
The current status of the project is that I have finalized the design of the main controller board, and sent the Gerber files for the PCB to be manufactured (I'm using OSH Park, this is the first time using them to make a PCB for me, so it will be interesting to see the result). I have also ordered a solder paste stencil for the board. The board and stencil will hopefully arrive with 1-2 weeks.
I have also started on the receiver board design, but so far I'm mostly trying to figure out what components (ADC, VGA, LNA etc) to use, and the sensor board (here I know what components I will use).
This is a quite big project that I work on on my spare time, but I hope to have something working this year.
If you have any experience or suggestions on how I should implement stuff (electronic, FPGA RTL or PC Software), please let me know.
I will try to update this post when there are major progress in the project.
Regards
Max