This project uses a standard NMEA-base GPS modules to track the current position, and determine the current position's distance from a pre-defined destination position (defined in degrees latitude and longitude).
The design can be used as a simple treasure-hunt demo where you have a limited number of tokens to read the distance from the target, with the goal of finding the hidden object before the tokens are used up.
More generally, it demonstrates how you can parse GPS data, though, which provides data not just on position, but an accurate timestamp, speed, altitude, and other useful datapoints.
This project is based on the free MCUXpresso IDE from NXP. This IDE includes the required toolchain, and is available for Windows, OS X and Linux.
The GPS should be connected to the LPC845-BRK (etc.) as follows:
o TXD to P0_26 (USART1 TXD)
o RXD to P0_27 (USART1 RXD)
o FIX to P0_28 (GPIO Input)
o PIEZO to P0_29 (SCT_OUT2 PWM)
This project is configured to output PRINTF to USART0, which will be redirected through the USB CDC available on the debugger. This is more reliable than using SEMIHOSTING, although it does require an extra step to open a connection from the console (etc.).
To see debug messages, simply open a terminal emulator at 9600 bps.
On Linux or OS X, you can use minicom as follows:
$ minicom -D /dev/tty.usbmodem1201F2 -b 9600
The RGB LED on the LPC845-BRK is used as a status indicator with the following meaning:
- GREEN LED: Waiting for a GPS fix.
- BLUE LED: Parsing a GPS packet.
- RED LED: Error (invalid GPS packet, etc).
By default, the firmware will be built using the release mode GPS
parser, which has minimal PRINTF output.
If you wish to do something different with the GPS data, or see more
GPS data over USB Serial, you can change the following macro at the
top of main.c:
/* Set this to the `_debug` or `_release` variant depending on your needs. */
#define NMEA_PARSER parse_nmea_sentence_release
Change the target function to parse_nmea_sentence_debug.