I'm working on a project that uses a Atmega329 with a 2 digit lcd 7 segment display. It needs to keep track of days, using a small coin cell battery.
I originally planned on using the on board clock, as the accuracy doesn't have to be great, I'm fine with a couple hours each month off.
Doing some testing, I noticed that it is off by up to a few seconds every minute (this is used in varying temperatures). So I need an external clock source.
Should I use a higher frequency crystal and clock it down internally? Example: 16Mhz crystal, using a clock speed of 8 or 4 mhz to save battery life. Or should I use a 8Mhz crystal and keep it at that speed?
Would a ceramic oscillator have enough accuracy and temperature stability to use? I'll be going from 0c to 25c