Differences

This shows you the differences between two versions of the page.

--- en:horloge_externe_gps_usb [2016/03/05 13:35]
+++ en:horloge_externe_gps_usb [2020/07/05 17:13] (current)
@@ Line 1: / Line 1: @@
+The Raspberry Pi, when isn't connected to the Internet can not synchronize its clock (date and time). So for a Raspberry Pi isolated synchronize the date and time can be achieved by **GPS satellite synchronization**. In this example we use a GPS receiver with a USB connection.
+====== GPS receiver ======
+Any GPS should head, insofar as it sending data to the **NMEA** standard. The time and date are provided in the frame ''GPRMC'', we use a model VK-162, available from [[http://www.banggood.com/fr/VK-162-Notebook-Usb-GPS-Navigation-Module-Support-Google-Earth-p-975418.html
+|Banggood]]
+{{ :fr:documents:gps_usb.png?direct&150 |}}
+====== Receive GPS data ======
+Then check if it sends back NMEA sentences, i.e. using cat: (CTRL-C to quit)
+<code bash>
+cat /dev/ttyACM0
+$GPRMC,191745.80,V,,,,,,,160314,,,N*7B
+$GPVTG,,,,,,,,,N*30
+...
+</code>
+For your information, the ''GPRMC'' frame is decoded by this way.
+<code>
+ $GPRMC,hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,ddmmyy,x.x,a*hh
+    = UTC of position fix
+    = Data status (V=navigation receiver warning)
+    = Latitude of fix
+    = N or S
+    = Longitude of fix
+    = E or W
+    = Speed over ground in knots
+    = Track made good in degrees True
+    = UT date
+   = Magnetic variation degrees (Easterly var. subtracts from true course)
+   = E or W
+   = Checksum
+</code>
+====== Install software to update time ======
+Download the ZIP archive or fetch source code using git:
+<code bash>
+git clone https://github.com/adamheinrich/gpsdate
+</code>
+To build the project, simply navigate to project's directory and call make:
+<code bash>
+cd gpsdate
+make all
+</code>
+Now you can use the gpsdate tool to change your local time. Simply call
+<code bash>
+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.
+</code>
+====== Autoupdate date and time ======
+==Auto update daily==
+For autoupdated daily you need addd line in CRON files [[https://en.wikipedia.org/wiki/Cron#crontab|CRON]]
+<code bash>
+sudo crontab -e
+</code>
+Clock updated every day at 11h30pm, add folowed lines:
+<code bash>
+23 * * * /home/pi/gpsdate/gpsdate /dev/ttyACM0
+</code>
+You can save and quit using CTRL-X, Y and ENTER.