In case your Raspberry Pi board is not connected to the internet, the date and time of your Raspberry Pi will not be updated and may drift over time. To enable automatic updating of a Raspberry Pi “isolated” in any place , without network, you can set up an external synchronization by GPS. This solution clearly brings great accuracy!
Once GPS is connected to your Raspberry Pi, the following command should allow you to verify that the data are available.
cat /dev/ttyACM0 $GPRMC,191745.80,V,,,,,,,160314,,,N*7B $GPVTG,,,,,,,,,N*30 ...
The GPRMC frame format is
1 = UTC of position fix
2 = Data status (V=navigation receiver warning)
3 = Latitude of fix
4 = N or S
5 = Longitude of fix
6 = E or W
7 = Speed over ground in knots
8 = Track made good in degrees True
9 = UT date
10 = Magnetic variation degrees (Easterly var. subtracts from true course)
11 = E or W
12 = Checksum
Download GPSDATE the program using git.
if you have not already git on your Raspberry Pi, install it with the command
sudo apt-get install git
git clone https://github.com/adamheinrich/gpsdate
Install the program from the doanload directory and typing the following commands:
cd gpsdate make all
Now you can use gpsdate to update your system time. Simply with the command:
sudo ./gpsdate /dev/ttyACM0 Local datetime was: 2014-03-16 20:19:06 (CET) GPS datetime is: 2014-03-16 19:19:07 (UTC) Succesfully updated local time.
For the system to be updated daily, we’ll add a command in the CRON file
sudo crontab -e
Updating the system clock every day at 1:10 am, add the following line:
10 01 * * * /home/pi/gpsdate/gpsdate /dev/ttyACM0
This article is an example of the many resources available for the Raspberry Pi and the repeater controlboard SvxLink Card (svxcard) on the site svxcard.f5uii.net