GPS Logger Shield Hookup Guide

Contributors: jimblom

Example Sketch: GPS Serial Passthrough

Now that your hardware is all set up, we have three pieces of example code to give you a taste of the GPS Logger Shield's functionality. This first example isn't all that useful, but it will, at least, make sure everything's working. Plus it'll show you the raw ugliness of NMEA GPS strings and make you appreciate great libraries like TinyGPS even more.

This example doesn't require any additional libraries. Simply plug the shield into your Arduino and upload the example code. We've got a couple examples, depending on which Arduino and/or serial port you're using.

SoftwareSerial Port Example

If you're using an Arduino Uno, Redboard, any other ATmega328P-based Arduino, and have the UART-select switch in the SW-UART position, upload this piece of example code to your Arduino:

language:c
    /******************************************************************************
Basic_Passthrough_Software.ino
Basic Software Serial GPS Passthrough
By Jim Lindblom @ SparkFun Electronics
February 9, 2016
https://github.com/sparkfun/GPS_Shield

This example uses SoftwareSerial to communicate with the GPS module on
pins 8 and 9. SoftwareSerial should work on most Arduinos, but it's a
necessity on Arduino Uno's, RedBoard's and any other Arduino
based around an ATmega328P.

After uploading the code, open your serial monitor, set it to 9600 baud, and
watch the GPS module's NMEA strings begin to flow by. See if you can pick
out the latitude and longitude.

Resources:
SoftwareSerial Library (included with Arduino)

Development/hardware environment specifics:
Arduino IDE 1.6.7
GPS Logger Shield v2.0 - Make sure the UART switch is set to SW-UART
Arduino Uno, RedBoard, Pro, etc.
******************************************************************************/

#include <SoftwareSerial.h> // Include the SoftwareSerial library
#define ARDUINO_GPS_RX 9 // Arduino RX pin connected to GPS TX
#define ARDUINO_GPS_TX 8 // Arduino TX pin connected to GPS RX
#define GPS_BAUD_RATE 9600 // The GPS Shield module defaults to 9600 baud
// Create a SoftwareSerial object called gps:
SoftwareSerial gpsPort(ARDUINO_GPS_TX, ARDUINO_GPS_RX);

// We'll also define a more descriptive moniker for the Serial Monitor port.
// This is the hardware serial port on pins 0/1.
#define SerialMonitor Serial

void setup() 
{
  gpsPort.begin(GPS_BAUD_RATE);
  SerialMonitor.begin(9600);
}

void loop() 
{
  if (gpsPort.available()) // If GPS data is available
    SerialMonitor.write(gpsPort.read()); // Read it and print to SerialMonitor
  if (SerialMonitor.available()) // If SerialMonitor data is available
    gpsPort.write(SerialMonitor.read()); // Read it and send to GPS
}

Copy and paste the above code into your Arduino IDE. You can also download all of the example sketches from our GitHub repository.

This example uses the SoftwareSerial library to communicate with the GPS module, and leaves the hardware serial port for debugging with the serial monitor.

Hardware Serial Port Example

If you're using an Arduino Leonardo, Arduino Due, Arduino Zero, or any other Arduino with a free UART on pins 0/1, set the UART-select switch to HW-UART, and upload this example:

language:c
    /******************************************************************************
Basic_Passthrough_Hardware.ino
Basic Hardware Serial GPS Passthrough
By Jim Lindblom @ SparkFun Electronics
February 9, 2016
https://github.com/sparkfun/GPS_Shield

This example uses an Arduino's hardware serial port -- on pins 0 and 1 -- to
communicate with the GPS module. 

Hardware serial should work on any Arduino's with a free hardware serial 
UART on pins 0/1. That includes Arduino Leonardo, Zero, Due, and SparkFun's
SAMD21 Dev Board.

After uploading the code, open your serial monitor, set it to 9600 baud, and
watch the GPS module's NMEA strings begin to flow by. See if you can pick
out the latitude and longitude.

Development/hardware environment specifics:
Arduino IDE 1.6.7
GPS Logger Shield v2.0 - Make sure the UART switch is set to HW-UART
Arduino Leonardo, Arduino Zero, Arduino Due, SparkFun SAMD21 Dev Board, etc
******************************************************************************/

#define GPS_BAUD_RATE 9600 // The GPS Shield module defaults to 9600 baud

// Define the serial monitor port. On the Leonardo this is 'Serial'
//  but on other boards this may be 'SerialUSB'
#define SerialMonitor Serial // e.g. Arduino Leonardo
// Define the harware serial port on pins 0/1. On the Leonardo this is 'Serial1'
//  but on other boards this may be 'Serial'
#define gpsPort Serial1 // e.g. Arduino Leonardo
// See https://www.arduino.cc/en/Reference/Serial to find out which Serial ports
//  you should use in the defines above.

void setup() 
{
  SerialMonitor.begin(9600); // Initialize the serial monitor port at 9600 baud
  gpsPort.begin(GPS_BAUD_RATE); // The GPS module's default baud is 9600
}

void loop() 
{
  if (gpsPort.available()) // If GPS data is available
    SerialMonitor.write(gpsPort.read()); // Send it to the serial monitor
  if (SerialMonitor.available()) // If data is sent to the serial monitor
    gpsPort.write(SerialMonitor.read()); // send it to the GPS module
}

You may have to alter either or both of the serial port #defines at the top of the code. Refer to your development board's datasheet or product info page for more information on which serial port is which.

Using the Serial Passthrough Sketch

Once you've uploaded the sketch, open up your serial monitor and set the baud rate to 9600. You should immediately begin to see GPS NMEA data begin to flow by at a rate of 1Hz.

For example, one set of strings may look like:

$GPRMC,235316.000,A,4003.9040,N,10512.5792,W,0.09,144.75,141112,,*19
$GPGGA,235317.000,4003.9039,N,10512.5793,W,1,08,1.6,1577.9,M,-20.7,M,,0000*5F
$GPGSA,A,3,22,18,21,06,03,09,24,15,,,,,2.5,1.6,1.9*3E

If you don't see anything in the serial monitor, make sure the UART-select switch is in the correct position. Also double check that the blue "GPS Fix" LED is at least blinking. If it's not, the module may not be receiving power. Don't forget to supply VBAT!

If you're still not having any luck, get in touch with our technical support team.

NMEA strings are the standard message format produced by almost all GPS receivers. They can relay all sorts of information including the time, latitude, longitude, altitude, and number of satellites visible, but unless you're an incredibly fast parser, these sentences will mostly mean nothing. Fortunately, the Arduino can read those strings, parse them for you, and give you more human-readable pieces of data.