CONTROL & COMMUNICATION
The O-buoy is a sophisticated autonomous platform that needs to control several different instruments but also to carefully manage power. It does this through the use of a supervisory computer. The Supervisory Computer (SC) was based on a Technologic Systems TS-7260 single board computer (SBC) and additional peripheral components. The SBC has two 16C550 type serial communication ports, two USB 2.0 ports, a 10/100 MBps Ethernet port, an integral SPI interface, 64 MB of RAM memory, 128 MB of Flash memory, an SD card socket, a battery backed-up real time clock, a 16 bit PC-104 expansion interface, an on-board temperature sensor, a user selectable capability for RS-232 or RS485/422 compatibility on its COM 2 serial port, and an ARM9 processor to operate at a clock rate of 200 MHz. The software operating system was the Debian Linux distribution as adapted for the TS-7260 SBC. The SBC was fitted with a four-port 16C550 type serial expansion card and a second Ethernet port (connected via a PC-104 expansion interface). The SBC and its options were specified at the time of purchase for operation to -40oC. Typical power consumption on the buoy was observed to be approximately 1.5W while running a demanding computation benchmark load with all ports operating at high rates.
Upon start-up the computer performed an initial boot from its Flash memory in the YAFFS internal format followed by a “pivot boot” to the full operating system in EXT file format. The full Linux operating system was contained on a 512 MB solid state disk drive. A 16 MB solid-state USB memory was installed to provide an on-board archive of all data that was obtained from every instrument and sensor. In the event of a possible (but unlikely) failure in the satellite communications system, the data complete records from the buoy will be available when the buoy is recovered.
The SC was operated at all times in a watch-dog mode; therefore it represents the baseline power demand of the O-Buoy system. This device was the only subsystem on the buoy that was constantly operating.
Power distribution was managed by the SC via the power control circuit. Identical electronic switches supplied the unregulated +14.5 volt level to all scientific devices, meteorological instruments and a pre-packaged satellite transceiver system. The power control circuit provided regulated voltage at +3.3 volts for its own analog and digital circuits. This circuit utilized a set of voltage and current sensing amplifiers which were read via a multi-input multiplexer from the SPI port on the SBC. There were sufficient parameters available that the watch dog software could report the distributed voltage level and all significant current loads in the system.
Based on a predetermined scientific observation schedule (which was heavily dependent on the solar elevation angle), individual instruments were sequenced into operation as needed. The objective was to provide a maximum number of scientific observations consistent with the power available (maximum of 16W). The heaviest power consumer on the buoy was the satellite transceiver at 5.5W (up to 7W, for higher latitudes); with a typical data off-load requiring a two hour long satellite network window. Therefore, most scientific functions were scheduled for operation and data acquisition between satellite service intervals. Revised programs and schedules could be loaded to the buoy during an open satellite window. At present, the results of these revisions would have been seen at the next satellite service of the buoy which is 24 hours later.