The easiest way to get started is to use an inexpensive USB to TTL adapter cable with your GPS module.

You can of course use the HW UART directly on the Pi, but as you can see in this tutorial (Freeing UART on the Pi) it's a bit more complicated, and there are no secondary consequences with the USB adapter.

This tutorial will assume that we are using the USB to TTL cable mentioned above, and that we are running on Raspbian. Raspbian already has the drivers for PL2303-based cables pre-installed, so you just need to plug it in and it should show up as /dev/ttyUSB0).

Hooking The Breakout Up

The first thing you'll need to do is to hook your Ultimate GPS Breakout up to the Pi with the adapter cable. The following diagram shows you what you need to know, essentially just connecting the cables of the same color together.

• GPS Vin  to USB 5V or 3V (red wire on USB console cable)
• GPS Ground to USB Ground (black wire)
• GPS RX to USB TX (green wire)
• GPS TX to USB RX (white wire)

While the module on the Ultimate GPS Breakout has an exceptionally sensitive antenna and may work indoors as is, you may want to pick up an external GPS Antenna and an SMA to u.FL adapter cable if this is for indoor use. This will allow you to keep the Pi and GPS breakout indoors, but run the antenna out a window or at least near one for improved reliability and signal integrity.

Setting up the USB Adapter

Once you plug the USB cable into the Pi, the adapter should show up as /dev/ttyUSB0 (though the '0' may be different if you have other ttyUSB adapters present).

You can see a list of all ttyUSB devices by entering the following into the console (I'm using the 'terminal' feature in Adafruit's browser-based WebIDE here for convenience sake!):

ls /dev/ttyUSB*

ls /dev/ttyUSB*

If you have any problems, you can enter the following command to see the USB devices on your Pi:

sudo lsusb

sudo lsusb

Which should show you the USB adapter (Prolific PL2303), as follows:

If you just want to do a quick check to see what data is coming out of the GPS, you can enter the following command, followed by Ctrl-C to quit:

sudo cat /dev/ttyUSB0

sudo cat /dev/ttyUSB0

Installing a GPS Daemon (gpsd)

The next step is installing some software on your Raspberry Pi that understands the serial data that your GPS module is providing via /dev/ttyUSB0.

Thankfully other people have already done all the hard work for you of properly parsing the raw GPS data, and we can use (amongst other options) a nice little package named 'gpsd', which essentially acts as a layer between your applications and the actual GPS hardware, gracefully handling parsing errors, and providing a common, well-defined interfaces to any GPS module.

To install gpsd, simply run the following commands from the console:

sudo apt-get install gpsd gpsd-clients

sudo apt-get install gpsd gpsd-clients

... which will install the required packages (an internet connection will be required for this step!)

Raspbian Jessie systemd service fix

Note if you're using the Raspbian Jessie or later release you'll need to disable a systemd service that gpsd installs.  This service has systemd listen on a local socket and run gpsd when clients connect to it, however it will also interfere with other gpsd instances that are manually run (like in this guide).  You will need to disable the gpsd systemd service by running the following commands:

sudo systemctl stop gpsd.socket
sudo systemctl disable gpsd.socket

sudo systemctl stop gpsd.socket
sudo systemctl disable gpsd.socket

Should you ever want to enable the default gpsd systemd service you can run these commands to restore it (but remember the rest of the steps in this guide won't work!):

sudo systemctl enable gpsd.socket
sudo systemctl start gpsd.socket

sudo systemctl enable gpsd.socket
sudo systemctl start gpsd.socket

After disabling the gpsd systemd service above you're ready to try running gpsd manually.  Now run the following command to manually start gpsd and point it at the GPS breakout on the USB serial adapter port:

sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock

sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock

... which will point the gps daemon to our GPS device on the USB to TTY adapter cable (simply substitute '/dev/ttyUSB0' for another destination if required).

Testing it Out

After a few seconds, gpsd should open up the proper socket and if the GPS is locked we should be able to get some data from the GPS module.

To test this, we can use the following command:

cgps -s

cgps -s

If you have a fix, you'll see something like the following information in the terminal window:

sudo killall gpsd
sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock

sudo killall gpsd
sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock