For my project, I chose Adafruit's Ultimate GPS Breakout
. I searched some GPS modules on the web and Adafruit's one have detailed official guide and many reference article by users. Spec. seemed good, too:- External antenna
is easily attachable/removable with SMA to u.FL Adapter Cable
- Module itself works independently and stores data on itself
- Has LED to indicate FIX status
Freeing UART
2 ways of connection are introduced on the official guide:- using USB to TTL adapter cable
- using UART directly
The former seems easier and the guide recommends this way, but I chose the later one because I didn't want to use one of two USB ports. To do it some extra steps are required.
First you need to edit /boot/cmdline.txt
You need to remove those parts that include console=ttyAMA0 because we are going to use ttyAMA0 from now. I added rpitestmode=1 because other users' blog entries seem to include it.
Second you edit /etc/inittab
Then reboot and activate your change. This step is done.
Installing required packages
Before connecting GPS module, install required packages. It includes some interface that you can later use to interact with GPS data from python code.Connecting GPS module
This time we use the cobbler cable I introduced in my previous article about PiTFT. It looks like the capture below.
As shown in the second capture, you should connect GPS module's VIN to Pi's 5v, GND to GND, RX to TXD and TX to RXD. Note that TX and RX are cross wired since module's input is Pi's output and vise versa.
Check and debug
You execute `sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock` and now gpsd is running. Check if you can properly read the receiving data by `cgps -s`. If it's working, the output is something like below.In my case it didn't work at the first place and I had to go through debug process.
To add debug option to gpsd you add -D followed by a number that indicate debug level. e.g. `sudo gpsd /dev/ttyAMA0 -N -D3 -F /var/run/gpsd.sock`. I saw messages like below. It kept saying 'Satellite data no good (1 of 1).'
I couldn't really tell if the wiring connection has a problem or the GPS module is not receiving data. So I checked what's in /dev/ttyAMA0.
The GPS module was set by a window, soldering seemed O.K. and it looked like my GPS module was receiving some partial data. I couldn't really tell what to do so I posted to Adafruit's forum. As shown on the forum topic, they were kind and helped me well. Now my GPS module works perfect and I can receive consistent data.
Recommended
I didn't know GPS module is so sensitive until I faced the problem. Now I have my external antenna attached. You can set this antenna on the roof of your car to receive better data. To do this you'll need:Basically we installed all required packages and attached all modules we need. We are going to make a copy of OS before making any mistake and being forced to start all over again.
