[time-nuts] Features of a Precision Clock?

James Maynard james.h.maynard at usa.net
Thu Oct 5 16:13:47 EDT 2006


On receipt of Bulletin C, can you arm this clock to display the upcoming 
leap second? That's a feature that I would desire.

Brooke Clarke wrote:
> Hi:
> 
> I've got the Precision Clock to work and have some questions about the 
> priority of the features.  As it is now the clock allows user selection 
> of the input frequency at power up that determines the instruction clock 
> for the PIC micro controller.  The choices are 2.5, 5, 10 or 20 Mhz.  
> The clock displays on line one HH:MM:SS and on line two Day of Week, 
> YYYY, Mon, Day of Month.  The leap year testing uses the 4, 100 and 400 
> year rules and so you can determine the day of the week for any Georgian 
> calendar (1583 onwards) date.
> 
> Setting is by means of 4 buttons, Right, Left, Increment, Decrement.  
> This is very intuitive and quick.  During setting the clock continues to 
> keep time.  Also a new data field to the right of the seconds appears as 
> 4 hex digits to allow moving the LED/1 PPS output pulse in 1 ms steps. 
> 
> If the input frequency fails then all the fields that can blink do blink 
> and the clock stops.  Pressing and holding Right or Left for a few 
> seconds clears the blinking and restarts the clock using the input 
> frequency that was selected at power up.
> 
> For more see:
> http://www.pacificsites.com/~brooke/PRC68COM.shtml#PC3
> 
> Now for the possible next features to be added.  It would be nice to get 
> some feel for how important they are:
> 
> (1) Synchronize the 1 PPS output rising edge to be near a 1 PPS input 
> pulse on a one time basis (the 1 PPS edge will have an error of a few 
> instruction cycles which are each 4/Fin long).  If this was done the 
> manual setting would be removed.
> 
> (2) Add another mode of operation where the clock runs on it's internal 
> RC oscillator and the timing is determined by an external 1 PPS that 
> needs to always be connected.
> 
> (3) Add a backup Real Time Clock with it's own coin cell battery to 
> allow using the clock in a portable application and allow the clock to 
> be shipped while running.  The chip has a 0.1 ppm aging trim capability 
> and there could be a provision to automatically trim it when one of the 
> above precision input frequencies is applied for maybe a day.  Then when 
> the input frequency is disconnected the clock would continue to tell the 
> time.  There are also many options for alarms.
> 
> (4) Other displays such as fractional Julian Day number, fractional 
> Modified Julian Day number. sidereal time, or ??? 
> 
> I don't think there's enough memory for all of the above, probably only 
> one or two of them so I'm hoping to get some input on the priorities.
> 
> Have Fun,
> 
> Brooke Clarke
> 


-- 
James Maynard
Salem, Oregon, USA




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