Power Control

Goals

• Control a relay that supplies power to a computer
• Connect to a simple user interface consisting of:
  • a switch to suggest when to apply or cut power to the computer
  • a light to indicate the power status
• Communicate with computer using a simple protocol over RS-232 (standard stuff)
• Allow the computer time to shutdown
• Monitor the enviornment (temperature & power supply voltage) to determine when:
  • the computer can be turned on
  • the computer must be shutdown
• Provide the enviornmental data to the computer
• Be a bridge for the computer to talk to other embedded systems or input devices
  • Keypad interface
    • 74C922 or 74C923
  • CAN (Controller Area Network) bridge ???
    • This will allow the computer to talk to the rest of the embedded system I want to develop, but that system does not yet exist. This goal will not be met in the first working versions of the power control device.
    • I'm considering not making such a bridge because CAN is much faster than the chosen serial interface to the computer. I think it may be possible to easily connect a CAN interface IC, like Microchip's MCP2510, to the computer's parallel port.

Inputs

• Constant power
• Running power (for when the car's engine is running)
• External system power
  • optional; uses output from something like a stereo unit's anntenna / external amp power control output
• Temperature
  • DS1620 or DS1721
  • stubbed for now; comming in a later version
• Voltage of power supply
  • some ADC with an op amp setup to condition the voltage
  • stubbed for now; comming in a later version
• RS-232 from computer
• User button

Outputs

• Power control
  • to a relay or an on/off control on a DC-DC converter
• RS-232 to computer
• User indicator