Raspberry Pi as a break "alarm"

That could be as simple as creating a cron job to play a bell MP3 at certain times of the day.

Mike

As the Pi does not contain a real time clock (RTC), you may need to synch the time with NTP. This can also be done using the crontab that Mike suggested.

Or buy the cheap rtc board that works very well. In the case the Internet access is difficult.

Enrico

Hi all.

I created a thread on another forum as well and i got basically the same answer

I think I got it made now.

I've installed raspian.

Chosen correct timezone in raspi-config, and disabled the gui.

Used crontab to play a sound at the times it's needed.

Which command do i use to get the Pi to sync with the NTP server with crontab? i could that an daily event to make sure the time is right.

Look at How to force a clock update using ntp? - Ask Ubuntu They do the following:

$ date ; sudo service ntp stop ; sudo ntpdate -s time.nist.gov ; sudo service ntp start ; date
Thu Jan 1 00:00:58 UTC 1970
* Stopping NTP server ntpd [ OK ]
* Starting NTP server [ OK ]
Thu Feb 14 18:52:21 UTC 2013

You can see the default time change to the correct time. You will need internet for above or local network if you have your own private NTP server.

Clem

If it there is no NTP server available, does the Pi get lost, or just reuse what time it had before?

I'm guessing the last one

The PI does not have any RTC hardware. So when it is off, it has no notion of time. When it comes on the best it can do is to guess that it has been off for less than 30 seconds, and use the last time recorded while it was on. So if you turn it off before the weekend, and on Monday the pi doesn't have internet, then the pi will still think it is Friday.

That said... If you install "ntp" you should get "ntpd" running, NTP will then keep your clock in sync with "the internet". In practise, it does this MUCH MUCH better than you can do with an occasional sync with a time server.

On my raspberry I get:

raspberrypi:~> ntpdc -p localhost

     remote           local      st poll reach  delay   offset    disp

=======================================================================

=sip.dicode.nl   192.168.234.48   2 1024  377 0.00229  0.003280 0.12398

=16-164-ftth.ons 192.168.234.48   2 1024  377 0.00705 -0.000572 0.13979

=87.233.197.123  192.168.234.48   3 1024  327 0.00256 -0.000103 0.13345

*ntp1.mediamatic 192.168.234.48   2 1024  377 0.00258  0.000114 0.12468

raspberrypi:~>

This means that it has deemed ntp1.media.... the most reliable server, it is now checking the time with that server every 20 minutes (1024 seconds), it has been able to reach it 8/8 the last 8 times it tried (377 is octal for 8-bit-set). The delay was about 2.6 miliseconds round trip, and the current offset is estimated to be about 0.1 milisecond.

Let that sink in... My raspberry pi KNOWS that it is about 114 microseconds fast (or slow: I don't know which way is positive) compared to THE TIME. (that's the global time kept with 5 (or now more?) atomic clocks around the world....)

Due to the measurement errors, that's about as good as it will get in the long run. Now, that raspberry is on a very low-latency link to the internet (it is more important that the delays are consistent).

On my home network, my internet connection is a lot worse. ping times about 10 times longer. This results in a 10x  bigger offset measured. Still less than a milisecond though!

So.... just check that ntpd is running, and let it do its job.

I see you tuned yours, since mine is:

pi@raspberrypi:~ $ ntpdc -p localhost
     remote           local      st poll reach  delay   offset    disp
=======================================================================
=jikan.ae7.st    192.168.1.235    2 1024   13 0.07292 -0.008775 0.46675
=linode227395.st 2602:30a:c01d:2  2 1024  127 0.13684 -0.031865 0.22397
*vimo.dorui.net  192.168.1.235    2 1024  357 0.07854 -0.001950 0.14117
=four10.gac.edu  192.168.1.235    2 1024  177 0.06204  0.000857 0.19566

Clem

Nope. No tuning.

Apparently they automatically chose a set of NTP servers at "post-install" or something like that. My other raspberry pi that I checked had a totally different set of NTP servers...

seniorservix:~> ntpdc -p localhost

     remote           local      st poll reach  delay   offset    disp

=======================================================================

*debmirror.tuxis 192.168.234.66   2 1024  377 0.00290  0.000368 0.12466

=ntp0.technl.net 192.168.234.66   2 1024  377 0.00337 -0.001179 0.12375

=services.freshd 192.168.234.66   2 1024  337 0.00322  0.000753 0.13942

=arethusa.tweake 192.168.234.66   2 1024  377 0.00301  0.000731 0.13864

seniorservix:~>

This, is ANOTHER pi, not the same one I checked this morning as being different from the one I posted.

I changed to a NTP pool in the US and rebooted. Now I see:

pi@raspberrypi:~ $ ntpdc -s
     remote           local      st poll reach  delay   offset    disp
=======================================================================
.biisoni.miuku.n 2602:30a:c01d:2  3  512  377 0.07732 -0.001032 0.10809
.mirror          192.168.1.235    3  512  367 0.05081  0.007038 0.10269
*palpatine.steve 192.168.1.235    2  512  377 0.06754  0.003799 0.12860
 propjet.latt.ne 192.168.1.235    3  512  377 0.07921 -0.008028 0.14401

Seems better to me. The old pool was Debian default.

Clem