[time-nuts] NTP Clock suggestions?

Graham / KE9H TIMENUT at austin.rr.com
Mon May 27 14:33:52 EDT 2013


If you are going to build your own, I would recommend you start with
something like the Microchip PIC32 Ethernet Starter Kit. Comes
with a free GCC C/C++ compiler and an Ethernet stack.

I happened to have one for another project, that already had a
four line serial LCD display hooked to it, as well as a serial port
command line interface running

Since I was already familiar with the Ethernet Stack that comes with
the Starter Kit, all it took was turning on the SNTP function in the
stack, and writing about ten lines of C code to get it running.

One update of NTP sourced UTC Hours-Minutes-Seconds time on the
display per command line request. (Anything more complicated is left as
an exercise for the student.)

That was after about an hour's research to find out the time
format that NTP uses (seconds since Jan 1, 1900) and the
(different) time format that UNIX uses (seconds since Jan 1, 1970).
And how they both deal with leap-seconds since their
epoch started.

Another hour of time figuring out how to convert that to
today's Hours, minutes, and seconds.  But that is easy,
once it (finally) sinks in how to work with an epoch.

Now, the real fun begins when you decide that you might
want to convert NTP or UNIX time to Day of Week, Month,
Calendar Year, Day of Year, Week of year, and
adjustments for local time zone, with daylight savings time.

That was worth about four hours research and going to bed with
a head-ache.  Learned all about "Julian Day" and "Modified
Julian Day", which it turns out has nothing to do with
the Julian Calendar.  (Did you know that time started at high noon
on January 1, 4713 BC. ?)  Finally discovered a code snippet
in Tom Van Baak's "C" code repository that will do the
conversion.  (Thanks, Tom.)

A pox upon leap years, un-leap centuries, re-leap 4th centuries,
Roman Numerals, modulus 7 weeks that do not align with the year boundary,
months with no regular modulus structure, and no year 0.

Who sold us this?

Makes you appreciate the decimal time "Star Date" system used on Startrek.

--- Graham


On 5/27/2013 9:56 AM, Miguel Barbosa Gonçalves wrote:
> Hi Bob!
> On 27 May 2013 14:56, Bob Camp <lists at rtty.us> wrote:
>> Hi
>> Correct answer:
>> I don't think there is such a beast. Once you get away from the radio
>> controlled (WWVB etc) clocks the cost goes up quickly.
> I don't understand why a microprocessor with an Ethernet controller and a 7
> segment display would cost so much to manufacture... I think I'll build my
> own.
>> Also correct, but a bit of a joke answer:
>> Raspberry PI driving your television set.  Alternatively make the Pi feed
>> control signals to a hacked normal clock.
> Good joke :-) I imagine the electricity bill at the end of the month.
> I would like to have a clock sync with my super precise stratum 1 servers
> :-) what's the point in having them if I can see the time anywhere? :-)
> Cheers,
> Miguel
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