[time-nuts] Features of a Precision Clock?

Brooke Clarke brooke at pacific.net
Thu Oct 5 15:26:36 EDT 2006


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:

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

w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml

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