[time-nuts] The STM32 GPSDO, a short presentation

[André Balsa]

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