Hi David! On 16 November 2011 16:18, David J Taylor <david-tay...@blueyonder.co.uk>wrote:
> Yes, Miguel, someone did mention an NTP synched clock some time back, and >>> I thought it might be a fun project. Based on an Arduino board IIRC? >>> Although I don't think it had Wi-Fi by default.... >>> >> >> >> I have it running at the moment. Have to build a case tough. See attached >> picture. >> > > It looks very smart! I have a small plate of frosted plexiglass in front of the display to diffuse the strong light of the LED. I am about 4 meters away from it and it looks great. The digits are 29 mm tall while with 5 mm LED they would be 50 mm tall. Too big for my office but perhaps some might want larger digits. > > It syncs at the 9th, 19th, 29th, ... second mark from a local GPS based >> NTP >> server. >> >> On every sync, the timestamp returned from the NTP server is on the 6 ms >> mark this means that the local clock of the Arduino drifts a lot. >> > > 6 ms per 10 s. Outside the 500 ppm allowed for NTP! <G> A bit too much... The RTC will help a lot. Actually, the RTC performance is great. 2 ppm means 0.02 ms every 10 seconds (0.12 ms every minute). Not bad! With 3 local GPS stratum 1 servers peered together I can pool them every 10 seconds and maintain sub ms accuracy. Inova clocks talk about 200 ms accuracy. Even with Internet NTP servers and pooling every 5 minutes the accuracy of this RTC would be 0.6 ms. 200 times better than the commercial product. I don't understand why a company like Meinberg sells these clocks! > > I am >> installing a realtime clock (Chronodot) this weekend that has an accuracy >> of +/- 3.5 ppm from -40C to 85C (I read somewhere that between 0 and 40C >> it >> is 2 ppm). This RTC can output a square wave signal at 1 Hz and Arduino >> can >> read that and use it to update the display at the exact second mark. >> >> With the RTC and synching every 10 minutes (9th, 19th, 29th, 39th, 49th >> and >> 59th of every hour) I expect a maximum error of 1.2 ms (based on 2 ppm). >> My >> eyes can't read that :-) >> > > Nor mine! On my PC, the radio pips, and the hands on the analogue clock I > wrote, appear to be precisely in sync, but I expect that means within a few > tens of milliseconds. :-) Perhaps we both need to wear glasses :-) > > > A neat feature I added is that when the clock can't synch it won't show a >> time. It will show -- : --. >> > > Shouldn't that be the classic video recorder display? A flashing 00:00 or > whatever? 00:00 flashing... done! I'll post a video for you to see soon. You'll tell me if you like it or not. You'll be my beta tester :-) Yes, I would be interested, but others might as well, so perhaps put it up > on the Web somewhere? I'll do that as soon as possible. Cheers, Miguel _______________________________________________ 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.