I've built several Arduino Nano/Si5351 VFO projects over the past year, but I'm consistently running into calibration problems. The EEPROM does not save the previous VFO frequency and reverts to default upon every restart, even though I've followed the standard calibration procedures from multiple sources. When I try to set correction factors over 32767 (like 93000), I get overflow warnings with 16-bit integers. Has anyone found a reliable workaround for persistent frequency storage and calibration value handling? Currently using the Etherkit Si5351 library v2.1.3 with Arduino IDE 1.8.19.

Check that you don't use any clone Arduino or ATMEGA – some don't have any EEPROM at all, some have flash installed which is obviously not compatible. I had the exact same issue with a cheap Nano clone last year.

Line 59 declares "corr" as int (16 bits) but the library uses 32 bit integer for "corr". Hence the compiler objects when you put 93000 in line 59 but it's ok to pass 93000 into the library call. Change your variable declaration to long instead of int.

I've been wrestling with this exact problem on my homebrew 40m transceiver. Because the newest version of Jason's Si5351 library is not compatible with older sketches, try using the 2015 version of the Si5351 library. Also try the calibration reset procedure - press the calibration button twice without tuning to reset, then recalibrate.