Hi One word of caution:
You really can’t compute things like ADEV by observing the device against itself. You need an external / stable reference that is (hopefully) much more accurate than the GPSDO to compare it to. Bob > On Mar 31, 2022, at 2:18 PM, André Balsa <andreba...@gmail.com> wrote: > > Hello time-nuts, > This is a quick follow-up to my short presentation of the STM32 GPSDO > project, because as some of you noticed, the EEVblog thread is > unfortunately 27 pages long and growing... :( > A few pointers: > 1. If you are interested in the technical details or further understanding > of the project, I suggest reading **only the first post** in the EEVblog > thread and then jumping straight to the schematics in post #378, page 16 in > the thread, and then reading the generously commented source code on GitHub > (download the zip file for the latest release and check the GPSDO.ino > sketch). > 2. The core of this project is made of just three components: > a. The STM32F411CEU6 "Black Pill" > b. The 10 MHz OCXO > c. The ublox M8N GPS receiver module > These three components plus a few resistors, capacitors and an LED and > voila!, you have a working GPSDO. Everything else is optional. But of > course the optional parts are where the fun is, really. > 3. Likewise the core of the firmware is just 15 lines of C code, which are > used to setup the 64-bit counter (10 lines) and the interrupt service > routine that reads the counter (5 lines). Everything else in the firmware > is built around these 15 lines of C code. Also to be honest, while these 15 > lines of C code are well written, the rest... not so much. ;) > 4. So how does it work? Essentially we measure the frequency of the OCXO > every second (the 64-bit counter), average it over the last 10/100/1000 > seconds (data stored in circular buffers), and adjust the OCXO control > voltage Vctl accordingly: if the frequency is too high, we decrease Vctl, > and if the frequency is too low, we increase Vctl. In other words, it's a > simple frequency locked loop, which all of you are familiar with. > 5. The performance? Hmmm... honestly I started working on this project with > the modest aim of 1ppb stability and that was achieved almost immediately, > also from the anecdotal data I and others have collected, the STM32 GPSDO > achieves 0.1ppb stability after a couple of hours and 0.01ppb is also > achievable, without any correction being applied from the various > environmental sensors. I think ultimately 0.001ppb should be achievable but > that will take some work on the firmware. > 6. Those nice ADEV plots? Ouch: I don't have any. In the coming days I will > push to GitHub a new version of the firmware with reporting with proper > tab-delimited fields that will allow people to plot various charts and > study the correlation between supply voltages, OCXO power consumption, OCXO > frequency, atmospheric pressure, humidity, etc... A true smorgasboard for > statisticians! > > Greetings from France, > Andre' (Andrew) > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.