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

paul swed paulswedb at gmail.com
Mon Apr 21 20:29:35 UTC 2014

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.

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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