====Adding a DS3231 Real Time Clock To The Raspberry Pi, module DS3231 or DS1307====
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===Activation I2C et installation of Real Time Clock===

In order to ensure you ha€™ve got the latest updates you should run the following commands :
<code bash>
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install i2c-tools
</code>
I2C activation on Raspberry Pi
<code bash>
sudo raspi-config
</code>
Choose **8-Advanced Options** -> **A7 I2C** answer **Yes** and press enter -> **Ok** -> **Yes** -> **Ok**

Now we need to modify a system file using :
<code bash>
sudo nano /etc/modules
</code>

If it isn't already there add rtc-ds1307€ to the bottom so it looks something like :
<code python | modules>
snd-bcm2835
i2c-bcm2835
i2c-dev
rtc-ds1307
</code>
You can save and quit using CTRL-X, Y and ENTER.

restart the system 
<code bash>
sudo reboot
</code>

Test of I2C interface

Power up the Pi and run the following command :
<code bash>
sudo i2cdetect -y 1
</code>
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If you are using a Rev 1 you will need to use œsudo i2cdetect -y 0€.</WRAP>

===Commands:===
You can read the Pi system time using :
<code bash>
date
</code>

If you need to set the system time for any reason you can use the following command :
<code bash>
sudo date -s "29 AUG 2015 13:00:00"
</code>
Once correct you can write the system date and time to the RTC module using :
<code bash>
sudo hwclock -w
</code>
 Should be able to read the date and time back from the RTC using :
<code bash>
sudo hwclock -r
</code>

===Setup auto update of system date and time :===

==Update with reboot==

Synchronize DS1307 ou DS3231 ;you need add 2 lines in system file:
<code bash>
sudo nano /etc/rc.local
</code>

Add the following two lines before the exit 0 line :
use the line that corresponds to your version

(Raspberry Pi V1)
<code bash>
echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device 
hwclock -s
</code>
(Raspberry Pi V2)
<code bash>
echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
hwclock -s 
</code>
like this:
{{ :fr:documents:ds1308_rtc_module_06.png?nolink&500 |}}

reboot system 
<code bash>
sudo reboot
</code>

==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>
30 23 * * * hwclock -s
</code>
You can save and quit using CTRL-X, Y and ENTER.
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Force clock update using ntp
<code bash>
sudo service ntp stop
sudo ntpd -gq
sudo service ntp start
</code>
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