Date post: | 28-Dec-2015 |
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“Reverse Geocache” BoxLocked box that will only open after one or
more pre-determined GPS locations have been visited
Directs user to next location by GPS coordinates or text displayed on LCD, or by an LED compass
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
Overview
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.
PSSCs
ComputationGPS Coordinate analysis, tilt compensation
calculationsCommunication
Interact with GPS, RFID, Compass, LCD in a timely fashion
Battery Powered DeviceLow power usage / rechargeable battery
PackagingCompact, “personal-sized” box
Major Design Constraints
Compass heading / tilt compensation (polled) Floating point values, trig functions required
(lookup table)GPS coordinate analysis (1Hz)
Distance from targetSD card file system, interface library
Large amount of Flash/SRAM
Computational Requirements
Receive data from a variety of sensors/modulesGPS, RFID, Accelerometer/Magnetometer
Read data from MicroSD cardOutput audio to speakerControl servo locking mechanismLCD Display
Parallel GPIO / shift register (6 - 12 GPIO pins)LED compass ring
Shift registers (2 GPIO pins)1-2 Pushbuttons (GPIO)
Interface Requirements
3 UART ModulesGPS, RFID, Debug
1 SPI ModuleMicroSD interface
1 I2C ModuleAccelerometer / Magnetometer
2 PWM ChannelsSpeaker, Servo Control
2+ Output Compare Timer ChannelsCompass polling, LCD strobe
On-Chip Peripheral Requirements
PIC24FJ256GA10616 Bit Architecture16 MIPS CPU speed256KB Flash16KB RAMMemory Disk Drive File
System Library Support4 UART Modules3 I2C Modules3 SPI Modules64 Total Pins
Component SelectionMicrocontroller
GPS ModuleRFID ReceiverDigital Compass
Accelerometer/MagnetometerSerial to USB Bridge
Debug
Off-Chip Peripheral Requirements
Trimble Copernicus IITime to first lock: 38
secDual serial portsReconfigurable UART
ratesPosition Accuracy: <2.5 m 50%, <5 m 90%
Component SelectionGPS Receiver
LSM303DLH+- 2/4/8 g
Accelerometer+-1.3 to +- 8.1 gauss
MagnetometerI2C Serial OutExcellent application
notes for tilt compensation
Component SelectionDigital Compass
Battery powered deviceLithium-Ion Polymer single cell battery (3.7 VDC)3300 mAh
Multiple operating voltagesMicro, GPS, MicroSD, Compass (3.3V)LCD, RFID (5V)Two converters be used to regulate both voltage
levels.Must be rechargable
MAX1555 USB battery charger IC will be usedAllows charging through USB or additional DC
source
Power Constraints
Highly durableEasy to carryRelatively small in sizeShould be able to receive GPS signal from within
the box through an antenna
Packaging Constraints
• Pelican 1150 Case– Inside dimensions 8-3/8" x 5-7/8" x 3-11/16" – Outside dimensions 9-1/4" x 7-9/16" x 4-3/8"
– Lid Depth 3/4"
Most expensive: GPS receiver - $80RFID kit - $50 Digital Compass - $30GPS, RFID, and Compass initially include
breakout boards, which increase their costBox should not exceed $300Box made without breakout boards would
cost less than $225
Cost Constraints