Josh Marchi, Jeff King, Paul Rosenberger, Dan Chambers – Software Design Considerations –

“Reverse Geocache” Box Locked box that will only open after one or more pre- determined GPS locations have been visited Directs user to next location by GPS coordinates, compass heading, or text description displayed on LCD. Route stored on microSD card located inside the box, able to be reprogrammed by PC RFID “master key” to allow access to box without finishing puzzle

An ability to obtain and decode global positioning data in order to verify if current location matches pre-determined desired location. An ability to utilize accelerometer and magnetometer data to determine a compass heading with tilt compensation. An ability to access and interpret files located on a microSD card. An ability to display information to the user via an LCD display. An ability to identify an RFID tag using an RFID reader.

GPS coordinate analysis at a rate of 1Hz Determine distance to next waypoint Compass heading / tilt compensation at a rate of approximately 5Hz Floating point values, trig functions required (lookup table) SD card interface uses MDD File System Library Large amount of Flash/SRAM

PIC24FJ256GA Bit Architecture Up to 16 MIPS CPU speed 256KB Flash 16KB RAM Memory Disk Drive File System Library Support 4 UART Modules 3 I 2 C Modules 3 SPI Modules 64 Total Pins Reasons for Selecting: Enough UART/SPI/I2C channels Adequate Flash/RAM for all code/libraries MDD File System Library Support

Interrupts Generated UART Rx character received (GPS, RFID) Flag set when entire message received Periodic Timers (compass, fuel gauge polling) Flag set, polling done in main loop Main Loop Analyze RFID message if flag is set If ID matches “master key”, unlock box, play buzzer, update LCD Analyze GPS message if flag is set If GPS matches desired waypoint, load next waypoint, update LCD If GPS doesn’t match waypoint, just update LCD with new position Obtain Compass data if flag is set Calculate heading with tilt compensation, update LCD Obtain Fuel Gauge data if flag is set Calculate and update LCD