[time-nuts] iPhone keeping better time?

David J Taylor david-taylor at blueyonder.co.uk
Wed Nov 16 16:18:22 UTC 2011


>> 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!

> 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>

> 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.

> 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?

> I also have code that enables the user to telnet to the clock's IP 
> address
> and change its setting which are saved in the Arduino EEPROM.
>
> If you are interested in a parts list and even the code I can send it to
> you next week as soon as I add the RTC
>
> The most interesting part is that buying a clock from Inova (
> http://www.inovasolutions.com/network-clocks/products/digital-network-clock.htm)
> would cost be 5 times more and it would not be as accurate as this one.
>
> Cheers,
> Miguel

Yes, I would be interested, but others might as well, so perhaps put it up 
on the Web somewhere?

Cheers,
David
-- 
SatSignal software - quality software written to your requirements
Web:  http://www.satsignal.eu
Email:  david-taylor at blueyonder.co.uk 




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