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

Edesio Costa e Silva time-nuts at tardis.net.br
Tue Apr 22 07:26:29 EDT 2014


Hi!

If it is all the same for you, I prefer this thread continue "in the open"
as I am interested both in using an Arduino-like for my first GPSDO and
STM32 for event capture and timming.

Regards,

Edésio

On Mon, Apr 21, 2014 at 04:29:35PM -0400, paul swed 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
> WB8TSL
> 
> 
> 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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