Moin,
On Fri, 17 May 2013 14:45:09 +1000 "Grant Waldram" <gr...@remobs.com.au> wrote: > > I've not had much need for time synchronisation over the years, but in > recent years NTP has been able to get me by. Unfortunately I'm now faced > with a network that needs a moderately correct clock (I'm scared of using > the word 'acurate' around you folks!) to the order of a few seconds or so, > but with no possibility of an external internet connection (for a number of > reasons). At present I'm using one PC running Windows Server as an SNTP > server to synchronise all of the devices, as it is the only device in a > physically secure location. How "secure" is the location? Is it a secure server room (bank/insurance style) or is it a military facility with 10m thick concrete walls, 100m below a mountain (swiss bunker style)? Ie. can you get radio signals in and if so, how strong and which frequency range? GSM would be a possibility as you said, but GSM networks itself tend to have a very weakly synchronized clock. I've seen GSM networks with the network provided clock being off by minutes. If your requried accuracy is just a couple of seconds, and you can get GSM (probably even EDGE) in your location, then i would run an internet connection trough GSM and use NTP over that. That should give you something better than 1s at least, probably in the range of 10-100ms. If this is not good enough, and you can get 70cm signals into the facility, then one way would be to build your own time signal. Use a cheap GPS receiver outside, that drives a CC1100 (or a CC430) to create a time signal, that you receive inside the facility with another CC1100 which then creates a time pulse. That should get you below 1ms. As for the device, i would not use an Raspberry Pi. Get a Beaglebone Black instead. The advantage is that you have most of the peripherials directly connected to the CPU instead of funneling everything trough a single USB peripherial with a hub inbetween. (The RPI is really just a GPU with a small CPU glued to it, and not really ment for that kind of job) Oh.. and switch your central NTP server to Linux. Windows isn't really a good choice for that stuff. Not at all. HTH Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.