Pito wrote:@ahull - nice project!
I like the DS3231 module as it is precise - in 6months it did +6sec, so I added Aging reg writing to the lib and with +4 written into it may happen I will do a single second off per year
Oscillators with 32kHz fork resonator - you must tune them - a pF capacitance change does few seconds a day, moreover there is no temperature compensation. Of course, still ok for most apps.
Good points, you can of course tune the STM32F103 with its internal registers, but that still wont get you anywhere near the seconds per year mark.
For anything more precise, GPS or NTP (using an ESP8266 perhaps) or "mobile phone time" are probably the simplest options. If your device is designed to sit around in a remote location and know the time reasonably precisely, (sunset is a fairly long event, so a few seconds here or there 'aint going to be very important), then the STM32F10X is perfectly adequate.
I think I was getting of the order of a few seconds per week, comparable or better than most cheap wrist watches.