Toward the end of last year I decided to make a small antenna satellite tracking system that was based on the Raspberry Pi. It was to be entirely self-contained — no other computer devices required. Seven months later, I’ve finally gotten around to starting the project.
One of the most important components of the system is the GPS receiver, which is used to establish the antenna system lat/lon/altitude as well as the time and date (UTC). I’m happy to report that I have the Adafruit Ultimate GPS Breakout receiver up and running using the standard python GPS Daemon (gpsd).
The only trick was to modify the standard Rasberrian Wheezy distribution so that it no longer uses ttyAMA0 (the RPi’s RXD/TXD Serial Port) for the default Debug Terminal, which frees up those lines for use with the GPS. This is a two step process.
First, the /boot/cmdline.txt file has to be edited to remove the reference to “console=ttyAMA0,115200”. from the line that begins “dwc_otg.lpm_enable=0 console=ttyAMA0,115200 …”
Second, the /etc/inittab file has to be edited to comment out the final line (in my case) which spawns the getty process using ttyAMA0. Simply add a “#” in front of the line that begins “T0:23:respawn:/sbin/getty -L ttyAMA0 …”
After rebooting, to put the above two changes in place, add a gpsd process that uses the ttyAMA0 port to interface to the GPS: “sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock”
Finally “cgps -s” can be used to check things out. Do keep in mind that the receiver can take about a minute to lock onto satellites (you will see the red “FIX” LED blinking once every other second prior to the fix, then slow down to once every 15 seconds or so once a fix has been acquired).
Here’s the RPi Generation 2 hookup. Power the board with +5 and ground, then run RPi TXD to the GPS RX, and RPi RXD to the GPS TX. Note, the GPS has a built-in 5V to 3.3 converter, so all the I/O is RPi friendly 3.3 volts.
