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Raspberry Pi as a break "alarm"

Former Member

Hi.

 

We have a customer at work that has a broken system for the announcing the breaks for it's employees.

It is as simple as making a ringing sound at certain times a day.

 

I would have no problem getting this to work with a Windows PC, but that seems a bit excessive image

 

I know this would be possible with a RPI, but i don't know where to even begin.

The sound will be played on a system that is being fed with a simple mini-jack cable.

 

I would say i'm an advanced beginner with the Pi's.
I have used them as airplay devices, Kodi and some retropie.

 

I hope that someone can help me image

Parents

  • 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 image

  • in reply to Former Member

    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.

  • in reply to rew

    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

  • in reply to clem57

    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.

Reply
  • in reply to clem57

    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.

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