for my project I need “precise” timing so I started to play with crystals. I have GPS module and consider the 1PPS signal as a “gold standard”. Problem is I can catch the signal only outside. So I checked the DS3231 board 32kHz output and confirmed it has <3ppm deviation from the 1PPS with minimal jitter and I am using this as precise time for testing other sources.
I have 20 watch crystals from eBay and a few PCF8563 RTC chips. On solderless breadboard I connected the watch crystal to the RTC chip and measured its 32kHz output - it was a lot faster, about 200ppm compared with DS3231. But compared to other crystals in the batch they have the same “offset”. Now I see two possible explanations:
- The crystals are poorly cut and are off
- My “layout” is poor and parasitic capacitance of the breadboard pulls the crystal off
What do you think about it?