Fig. 3. The ICTIOBOT on-board electronics.

On the subject of the target tracking sensors, the MBE sonar is a Tritech Seaking and converts it readings into RS232 streams according to a proprietary data format. The obstacle avoidance sonar is an Autohelm ST30 depth finder and sends its echoes using Seatalk protocol (NMEA) by RS422 electrical signals that can be easily converted into RS232 signals

Both the low level processor board and the high level board also communicate through RS232. Given the wide number of RS232 channels needed to interface all the modules and navigation sensors, it was decided to turn some of these signals into I2C communication interface format. This popular and versatile bus used for communications among devices nodes inside equipments, can communicate with the slaves using different addresses and is easily configurable.

The digital compass is a CMPS03 robotics board based on the Philips KMZ51 magnetic field sensor, and is used to obtain the AUV orientation with respect to the earth magnetic field. This device, directly interfaced with the PC, provides a pulse width modulation (PWM) signal with the positive width of the pulse representing the angle apart of the north point. As regards the actuators, two propellers provide the horizontal movement with no need of rudder, and its DC motors are driven by a MD22 Dual H-Bridge device made by Robot Electronics capable to provide 50V- 5A. The MD22 driver is based on a PIC microcontroller and accepts data communication over I2C bus. The vertical movement is provided by two propellants controlled by a MD03 50V - 5A driver from Devantech.

Finally, a link radio provides a safety mechanism to handle manually the AUV in the event of possible damages or flaws.

Any signal that comes from the transmitter at the frequency of 422MHz is considered as an interruption input to the microcontroller of the low level board, and consequently, stops attending the orders from the PC's communication serial port.

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