[time-nuts] NTP Clock suggestions?

[Bob Camp]

Hi

If you are doing this from scratch today, would you go IRIG or would you go RS-485 for a wall clock? Both will drive more cable than you are likely to have in a house. Both are reasonably noise immune. With RS-485 there's less to do. It's a serial stream like any other bunch of "stuff" into a UART. 

Some math:

YYMMDDHHMMSSCR  = 13 ASCII characters. With one check byte it would be 14. 
A baud rate of 115.4K isn't stretching things on RS-485 or on most UART's these days. 
Sent it at 7N1 you have 9 bits per character, 126 bits in the message.
Message takes a bit over 1 ms.

Time it to anywhere in the string and the clock should be within <+/- 2 ms. That's better than I can see on a clock. Better yet, time it to the first (or last) character in the string. More or less a 10X improvement. You could also drop the year / month / day if the clock isn't going to use them. 

Take any of the Arduino (or what ever) LED display boards and drive them with something cheap. I doubt the "clock" end plus the drivers would be over $30. I suspect IRIG would cost a bit more once you got it all worked out. 

Bob
 
On May 27, 2013, at 11:03 AM, Chris Albertson <albertson.chris at gmail.com> wrote:

> I've seen LLCD computer monitors used as clocks.  Seems this would be
> the perfect use for a Rasbury Pi. and a cheap monitor. $100 or maybe a
> low-end Android tablet.
> 
> The way it is more commonly done is you have you computer that is
> using NTP produce an IRIG time code.  Then there are any number of
> commercial clocks and large digital LED displays that will use IRIG.
> IRIG displays are not cheap but they sure are easy to find.
> 
> On Mon, May 27, 2013 at 6:29 AM, Miguel Barbosa Gonçalves <m at mbg.pt> wrote:
>> Hi!
>> 
>> I was wondering if anyone knows about a not so expensive wall digital clock
>> that gets its time from an NTP server...
>> 
>> TIA,
>> Miguel
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> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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