[time-nuts] 10 MHz to 32.768 kHz converter

Chris Albertson albertson.chris at gmail.com
Sun Mar 20 20:33:53 EDT 2016


In theory what is the best you can do using division of a 10MHz signal.
It's really not very good the period of the 32768 hz output will always be
"off".

I think the best way is to divide the 10MHz signal by some power of five
(like 78125) then use that to phase lock your 32768 oscillator.  In other
words use the 10MHz signal to discipline the 32K crystal.

On Sun, Mar 20, 2016 at 3:23 PM, Vlad <time at patoka.org> wrote:

>
>
> How about Bresenham's Algorithm to alternate imperfect periods to produce
> an average that matches any "perfect" period.
>
> Refer to Bob Ammerman work to use Bresenham-type system for PIC MCU. He
> was using the counter works in the background, either by polling or
> Interrupt-Driven. So, the "SuperCycle" continues to run. The timer count
> the value is stored in a 3-byte register that is decremented by the
> software.
>
> Regards,
> Vlad
>
> On 2016-03-20 14:26, Martyn Smith wrote:
>
>> Hello,
>>
>>
>>
>> First of all quick apologies for sending an email last week without
>> deleting all the old information from previous postings.
>>
>>
>>
>> I have been playing around with producing 32.768 kHz from 10 MHz using
>> a PIC chip.
>>
>>
>>
>> I  have a real time clock calendar chip that requires a 32.768 kHz
>> crystal.  I want to feed it with 10 MHz signal instead, so it is
>> synchronised to my main 10 MHz in a frequency standard I am designing.
>>
>>
>>
>> The method I’m using has been documented before where we have two
>> loops running 9632 times through a 39 instruction loop and
>> 55904 times through a 38 instruction loop, each time toggling the output
>> pin.
>>
>>
>>
>> I have done this and am getting approximately 32.768 kHz with the FM
>> modulation as described by previous authors.
>>
>>
>>
>> My question is should I expect exactly 32.768000000 kHz (obviously
>> assuming we use the same 10 MHz to drive the divider and all test
>> equipment)?
>>
>>
>>
>> The closest I can get the 32.768 kHz is within about 0.1 Hz.
>>
>>
>>
>> Does the actual model of PIC chip influence the accuracy?
>>
>>
>>
>> Regards
>>
>>
>>
>> Martyn
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> --
> WBW,
>
> V.P.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 

Chris Albertson
Redondo Beach, California


More information about the time-nuts mailing list