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

d0ct0r time at patoka.org
Mon Apr 21 23:57:20 UTC 2014

Actually GCC supporting Cortex. So, I am using Raisonance IDE plus GCC 
Toolchain as a development environment. My current project functional 
diagram is following:

                   +--- STM32 -- (Pulse Counter, TTL Generator, DDS 
driver, GPSDO monitor)
GPSDO--LTC6957-3--|      |                        |
    |              +--- AD9852 -- VFO ->           |
    |                                              v
    +------------------------------------------- TADD3 -- (1PPS, TTL) -->

As I'll finish it more or less, I'd like to compare the 1PPS which comes 
directly from GPSDO with 1PPS which I could create on MCU (and probably 
on DDS).

As I mention before, each STM MCU comes with very useful Peripheral 
Library. That Library has tonnes of different examples.


On 2014-04-21 16:29, 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
> 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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