Re: First time with STM32
Posted: Sun Jun 14, 2020 12:03 am
back on the topic about the cheap 20 for a dollar crystals, i very much doubt they are quartz crystals.
the technologies to process quartz is far more elaborate and difficult.
more than likely the cheap 32k crystals may be made up of a grain of PZT, and who knows if they simply put a grain of rochelle salt
i'd guess that may be part of the reason for the large drifts if you happen to be using one.
i researched some of the specs, for genuine quartz crystals, the frequency variation due to temperature changes are in the order of 5 ppm if the temperature swings away from room temp of 25 deg C (e.g. like 0 deg C or lower to get that 5ppm deviation).
the kind of errors i noted for a cheap crystal i used is more like 1 / a few thousand, this is way higher than those ppm standards specified for real quartz crystals (e.g. from Epson). japanese quartz watch makers (e.g. Citizen, Seiko (Epson) ) are quite well known to make very accurate quartz watches. those are real accurately calibrated cuts crystals and and certainly not these 20 for a dollar ones.
the technologies to process quartz is far more elaborate and difficult.
more than likely the cheap 32k crystals may be made up of a grain of PZT, and who knows if they simply put a grain of rochelle salt
i'd guess that may be part of the reason for the large drifts if you happen to be using one.
i researched some of the specs, for genuine quartz crystals, the frequency variation due to temperature changes are in the order of 5 ppm if the temperature swings away from room temp of 25 deg C (e.g. like 0 deg C or lower to get that 5ppm deviation).
the kind of errors i noted for a cheap crystal i used is more like 1 / a few thousand, this is way higher than those ppm standards specified for real quartz crystals (e.g. from Epson). japanese quartz watch makers (e.g. Citizen, Seiko (Epson) ) are quite well known to make very accurate quartz watches. those are real accurately calibrated cuts crystals and and certainly not these 20 for a dollar ones.