A device that I'm working on is controlled by ATmega328P microcontroller.
This will be some sort of a watch, therefore I want it to be as precise as possible. For instance if left to run for a whole year I want the time deviation to be not more than absolute value of +/- 10 seconds by the end of the year. (I'm not saying the battery power will be enough for the whole year..)
Is crystal oscillator more precise than crystal with caps driven my micro? If so, are crystal oscillators more commonly used in time sensitive applications?
Or just a regular crystal will be sufficient and more suitable? (Especially when they will not consume power like oscillators) I don't need atomic precision of +/- 0.000001 sec/year.
Best Answer
10 seconds / year is 0.3 parts per million error (or as the time-nuts would usually put it, an error of 3 * 10^-7). A decent watch crystal is usually specified as +/- 20 ppm (2 * 10^-5), which is far worse than what you're asking for. The higher-frequency crystals used for clocking CPUs are usually worse than that.
Temperature-compensated oscillators (TCXOs) are better, in the 10^-6 range, but still worse than your spec.
Ovenized oscillators (OCXOs) can be better than 10^-7 but require watts of power, likely more than you can afford running on battery.