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|The Brain Behind The 'Bot|
The brains behind Groundhog are easily contained with in a 4"x4"x6" box. The PC104 form factor computer, running at 300 Mhz, provides all of the control, data logging, and communication that Groundhog requires.
In addition to the motherboard, this particular stack has a number of powerful card. The power distribution card supplies a constant 5 volts from an input voltage anywhere in the range of 8 to 30 volts. This card is used to not only power the computer but also some external devices. The 1394 (Firewire) card provides support for the digital cameras used to capture and record images of the mine interior. The DAC (Data Acquistion) card provides support for the analog and digital sensors as well as providing the output control bits which are feed into the solid state relays. Finally, and RS422 card complements the inbuilt RS232 serial ports and connects directly to the laser scanners used to map the mine.Computer Packaging
The PC104 stack, while very powerful, is rather fragile compared to the rest of the robot. Therefore, it was placed in a NEMA 4 enclosure with routing of the wires through a face plate.
One other critical function of the PC104 stack is to make sure that the robot is always under control. Achieving this require a little custom circuitry combined with the in-built watchdog timer of the DAC board. If the CPU doesn't send a keep-alive message to the DAC within a given amount of time, the DAC triggers the custom flip-flop based circuit, which kills power to all of the solid state relays. The watchdog signal also initiates a reboot of the computer. In this way, a simple software error will not cause Groundhog to become inoperable.