Hi Again, the math is pretty simple.
A 16 bit capture running at a 1/4 clock is not going to get you very near a Shera. It's even further from the more modern "enhanced Shera" designs. Bob On Dec 6, 2012, at 6:59 PM, David <[email protected]> wrote: > You can use the ATmega328 16 bit timer/counter in input capture mode > to count the number of 10 MHz OCXO cycles per pulse per second period > to a resolution of 100ns but there are some problems: > > The ATmega328 16 bit timer/counter external clock is limited to 1/4 of > the CPU frequency with an asynchronous source so the 10 MHz OCXO would > need to be divided down which would further limit performance and > require an external divider. Modifying the Aruino board to use the 10 > MHz OCXO in place of the CPU clock solves that problem. > > Then operating the counter/timer in input capture mode with the GPS > pulse per second signal connected to the input capture pin would allow > almost Shera like performance. The timing resolution would be 2.4 > times lower (and not asynchronous) limiting performance over short > time spans. > > On Thu, 6 Dec 2012 14:57:19 -0800, Chris Albertson > <[email protected]> wrote: > >> You'd have to seriously divide down the output from the 10MHz OCXO if you >> were going to use it as an interrupt. Maybe to divide by 10,000? and even >> at the higher clock rate you'd still have poor resolution. >> >> I image each interrupt handler would sample some internal counter and the >> background task would look at the delta between the two and adjust the DAC >> to drive the OCXO to close the difference. The resolution would be >> (maybe?) a "handful" of clock cycles. Given enough time, say a 1000 >> second period it might wrk well enough. I can't know without doing a more >> detailed design >> >> >> On Thu, Dec 6, 2012 at 1:59 AM, Don Latham <[email protected]> wrote: >> >>> Chris: >>> >>>> The question I have again is about a simple phase detector. >>> >>> I did ask if the arduino interrupt ports could be used as a phase >>> detector; one on the GPS and one on the OXCO. Too much jitter? If the 12 >>> MHz clock is too slow, would an 80 MHz clock ARM arduino style processor >>> work? I'm simply too new at this to decide. >>> >>> Don > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
