[time-nuts] First success with very simple, very low cost GPSDO, under $8

paul swed paulswedb at gmail.com
Mon Apr 21 20:30:28 UTC 2014

Perhaps this thread should go off line not to distract from the originators

On Mon, Apr 21, 2014 at 4:29 PM, paul swed <paulswedb at gmail.com> wrote:

> Good afternoon very interested in the work you are doing with the STM
> board.
> As I mentioned far earlier in this thread I am attempting to use it to
> correct the BPSK WWVB signal here. Initial thoughts were using FORTH to
> program the STM board.
> Very curious what you are using as examples.
> My experience in FORTH is from many years ago and have done very poorly at
> C. But this may be the case to have something of interest to actually do.
> In either language.
> Regards
> Paul
> On Mon, Apr 14, 2014 at 12:27 PM, d0ct0r <time at patoka.org> wrote:
>> I was experimenting with the same setup for STM32 MCU. This
>> microprocessor has accept the sine wave from external OCXO or GPSDO. No
>> problem with this. The only thing: I was need to start MCU from slow
>> "watch" crystal first. And then switch it to work to external one. In
>> another case I got incorrect timing settings for MCU. Later, I decide to
>> implement LTC6957-3 chip to "share" REFCLOCK source, since that chip has
>> two equal CMOS-level outputs.
>> Unfortunately I have no tool to measure the phase noise and jitters on
>> each setup.
>>  It turns out all of this is built into the AVR chip.   There is a counter
>>> and logic to copy the current counter value to a register on a PPS pulse
>>> raising edge.    The counter keeps running and every second its value is
>>> trapped.
>>> I can connect the OCXO and the PPS directly to the AVR pin.  The AVR has
>>> hardware (a fast comparator) to "square" a low amplitude sine wave and
>>> trap
>>> the counter on a zero crossing.   So it looks like I can get rid of  ALL
>>> of
>>> the external chips.   The built in DAC is working well also but it needs
>>> some external resisters and caps.
>>> No need for '74 FFs or '373' or counter chips.    I do get precision
>>> timing
>>> with no time critical software, no 74xxx chips.
>> --
>> WBW,
>> V.P.
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