[time-nuts] algorithms and hardware for comparing clock pulses

Magnus Danielson magnus at rubidium.dyndns.org
Tue Sep 22 16:31:54 EDT 2015


Jim,

I had the intent to try this, but never got around doing it. Thanks for 
reminding me. Please share any enhancements.

I did exchange some emails with Lars, but as that project never got off 
the ground, it faded out.

Cheers,
Magnus


On 09/21/2015 10:02 PM, Jim Harman wrote:
> Hi Can,
>
> For a simple analog solution, you might try a 74HC4046 phase detector
> followed by a diode and RC network as used in Lars Walenius' GPSDO,
> described here in the archives:
>
> https://www.febo.com/pipermail/time-nuts/2014-February/082820.html
>
> The phase detector produces a pulse whose width equals the time difference
> between the two pulses. The RC network converts this to a voltage
> proportional to the time difference, which you then measure with the MCU's
> A/D converter. Using the rising edge of the signal at pin 14 as the
> interrupt source triggers the A/D converter at the end of the pulse, which
> corresponds to the peak of the analog signal.. The 1 meg resistor
> discharges the capacitor between pulses.
>
> Lars' code also includes a filtering algorithm which does a nice job of
> controlling one of the oscillators to match the 1-PPS generated by the GPS.
> I have enhanced this if you are interested.
>
> On Mon, Sep 21, 2015 at 1:45 PM, Can Altineller <altineller at gmail.com>
> wrote:
>
>>
>>
>>     I probably need a hardware to measure the time pulses more precisely. I
>> thought of XOR'ing the clocks, and measuring both rising and falling edges
>> trough interrupts, but when the pulse is close enough, it will lead to same
>> condition.
>>
>>     Are there any solutions to this problem? Maybe an analog hack? And what
>> are the mostly used algorithms to tune an oscillator to another? Currently
>> my algorithm sign corrects the result difference, and adjusts aging
>> register simply by adding to it, then runs a conversion command each second
>> to add or substract the ppms.
>>
>>     This looks a lot of fun,
>>
>>     Best Regards,
>>     Can Altineller
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>
>
>


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