[time-nuts] iPhone keeping better time?

[Miguel Gonçalves]

Hi David!

On 16 November 2011 15:03, David J Taylor <david-taylor at blueyonder.co.uk>wrote:

>  I own a Mac Mini and a MacBook. Their NTP implementation is simply a joke.
>> Even with a local stratum 1 I can't get decent accuracy. :-(
>>
>> David, weren't you interested in a LED clock I was going to build?
>>
>> Cheers,
>> Miguel
>>
>
> A pity that there isn't a port of the reference NTP for the Mac, such as
> we have on Windows.
>
> 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 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. 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 :-)

A neat feature I added is that when the clock can't synch it won't show a
time. It will show -- : --.

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
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