Nice, I'm trying to do something similar. But without the PICdiv or the
TIC measurement. Only the GPS PPS into the STM32 and the stabilized PPS
is generated by a timer in the STM32
First step was to measure against the running average of the GPS PPS.
As can be seen in attached Timeplot measurement the phase error is (when
temperatures stabilized) in the order of 10ns.
Erik.
On 31-3-2022 12:52, André Balsa wrote:
Hello fellow time-nuts,
My second post to the list. I just wanted to mention that the STM32 GPSDO
is a 100% Open Source project, fully documented in the GitHub repository
https://github.com/AndrewBCN/STM32-GPSDO and the EEVblog thread
https://www.eevblog.com/forum/projects/yet-another-diy-gpsdo-yes-another-one/
. Also some details are available about the firmware in the stm32duino
forum thread https://www.stm32duino.com/viewtopic.php?f=10&t=1031
The project has some unique features compared to any other commercial or
hobby GPSDO and it is still very much in full swing and actively developed
not only by myself but also by a few collaborators.
One of the unique features of the STM32 GPSDO is that it uses both a PLL
and an FLL. I developed the 100% software FLL around May 2021 and for the
PLL I have borrowed Lars Walenius genius TIC design with Erik Kaashoek's
modifications (using a 74HC74 instead of a 74HC4046) (WIP). I am also using
a picDIV by Tom Van Baak to generate a UTC synchronized PPS (again, WIP).
The project can be assembled on a breadboard in one afternoon provided one
has all the parts and it works "out of the box". The BOM total cost stands
at around 45€ for the basic version and 70€ with all the bells and whistles.
The firmware leverages the Arduino programming environment and the hundreds
of available libraries, and it is written with the express purpose of being
easy to understand, maintain and further develop. It now stands at around
1700 lines of C/C++ code with extensive comments.
The main communications channel for this project is the EEVblog thread
mentioned above.
Greetings from France,
Andrew
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