Introduction

How easy is it to get your Raspberry Pi eavesdropping on satellites 20,000 km up in the sky? Wonderfully easy thanks to Linux, and affordable thanks to Adafruit's Ultimate GPS Breakout!

This quick learning guide will show you everything you need to do to add position tracking to your Pi project using the open source GPS daemon 'gpsd' and an inexpensive USB to TTL adapter cable or via direct-wiring to the built-in Pi UART pins

What you'll need:

Don't forget to also read our Ultimate GPS tutorial which has a lot of information about this GPS module and datasheets/example code that you will find handy!

    Setting Everything Up

    The easiest way to get start 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 mentionned above, and that we are running on Occidentalis or Rasbian using the wonderfully painless WebIDE. Occidentalis & Rasbian 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.
    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 ans 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*
    If you have any problems, you can enter the following command to see the USB devices on your Pi:
    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, following by CTRL+C to quit:
    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 python-gps
    ... 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

    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

    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
    ... 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
    If you have a fix, you'll see something like the following information in the terminal window:
    If you have any problems and cgps always displays 'NO FIX' under status and then aborts after a few seconds, you may need to restart the gpsd service. You can do that via the following commands:
    sudo killall gpsd
    sudo gpsd /dev/ttyUSB0 -F /var/run/gpsd.sock

    Using your GPS

    Now that you're GPS is up and running, and gpsd is playing nice with it, it's time to do something with the data!

    The easiest way to get started is using the WebIDE and a bit of python code to access gpsd.

    Create a new file in the WebIDE, and then add and run the following code:
    import gps
    
    # Listen on port 2947 (gpsd) of localhost
    session = gps.gps("localhost", "2947")
    session.stream(gps.WATCH_ENABLE | gps.WATCH_NEWSTYLE)
    
    while True:
        try:
        	report = session.next()
    		# Wait for a 'TPV' report and display the current time
    		# To see all report data, uncomment the line below
    		# print report
            if report['class'] == 'TPV':
                if hasattr(report, 'time'):
                    print report.time
        except KeyError:
    		pass
        except KeyboardInterrupt:
    		quit()
        except StopIteration:
    		session = None
    		print "GPSD has terminated"
    
    This should give you something similar to the following (with an update every second or so):
    Looking for position data rather than just the timestamp? Essentially, all you have to do is parse the 'report' data following the example above.

    To see what data is available, you can uncomment the 'print report' line, and then just look at the different values and class names and pick and choose whatever you want.

    For example, you could use the following code to get the current speed using the TPV class:
    		if report['class'] == 'TPV':
    			if hasattr(report, 'speed'):
    				print report.speed * gps.MPS_TO_KPH
    That's it! It's pretty painless, and now it's up to you to figure out what you want to do with you latitude, longitude, date and time, speed, altitude, etc.!

    Using UART instead of USB

    If you wish to use HW UART instead of the USB cable, it's perfectly possible ... you just need to do a bit more work to free the UART up on your Pi.

    To get started, hook the GPS module up to your Pi as follows, cross-connecting the TX and RX pins (TX on one device goes to RX on the other and vice versa), and supply 5V from the Pi to the VIN pin on the GPS module:
    We designed the Ultimate GPS with a built-in regulator, so even if it's powered with 5V, the signal levels are still 3.3V - safe for your Pi!

    Step One: Edit /boot/cmdline.txt

    Next, enter the following command from the command line:
    $ sudo nano /boot/cmdline.txt

    And change:

    dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait

    to:

    dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait

    (eg, remove console=ttyAMA0,115200 and if there, kgdboc=ttyAMA0,115200)

    Note you might see console=serial0,115200 or console=ttyS0,115200 and should remove those parts of the line if present.

    Raspbian Wheezy only

    Step Two: Edit /etc/inittab

    From the command prompt enter the following command:

    $ sudo nano /etc/inittab

    And change:

    #Spawn a getty on Raspberry Pi serial line
    T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

    to:

    #Spawn a getty on Raspberry Pi serial line
    #T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

    That is, add a # to the beginning of the line!

     

    Raspbian Jessie

    Step Two:

    For the Raspberry Pi 1 or 2 (but NOT the 3!) Run the following two commands to stop and disable the tty service:

    sudo systemctl stop [email protected]
    sudo systemctl disable [email protected] 

    However for the Raspberry Pi 3 you need to use the /dev/ttyS0 port since that is what is normally connected to the GPIO serial port pins.  Use these two commands instead:

    sudo systemctl stop [email protected]
    sudo systemctl disable [email protected]

    Step Three: Raspberry Pi 3 Only

    For the Raspberry Pi 3 you need to explicitly enable the serial port on the GPIO pins.  The reason for this is a change with the Pi 3 to use the hardware serial port for Bluetooth and instead use a slightly different software serial port for the GPIO pins.  A side effect of this change is that the serial port will actually change speed as the Pi CPU clock throttles up and down--this will unfortunately cause problems for most serial devices like GPS receivers!  

    Luckily there's an easy fix detailed in this excellet blog post to force the Pi CPU into a fixed frequency which prevents speed changes on the serial port.  The Pi might not perform as well but it will have a stable serial port speed.

    To make this change edit the /boot/config.txt file by running:

    sudo nano /boot/config.txt

    At the very bottom of the file add this on a new line:

    enable_uart=1

    Save the file (press Ctrl-O, then enter) and exit (press Ctrl-X).  You're all set!

    Step Four: Reboot your Pi

    After rebooting the Pi for the above changes to take effect, you can proceed with running gpsd ...

    Step Five: Restart GPSD with HW UART

    Restart gpsd and redirect it to use HW UART instead of the USB port we pointed it to earlier. Simply entering the following two commands.

    For the Raspberry Pi 1 or 2 (but NOT the 3!) run these commands:

    $ sudo killall gpsd
    $ sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock

    And for the Raspberry Pi 3 run these commands to use the different serial port:

    sudo killall gpsd
    sudo gpsd /dev/ttyS0 -F /var/run/gpsd.sock
    As with the USB example, you can test the output with:
    $ cgps -s

    Further Resources

    Doing something fun with GPS and tracking data? Be sure to post about it in the Adafruit forums so everyone else can get inspired by it!