Using Pic as a digital clock/timer. How accurate?

[Acetronics2]

Hi, Rocky

I just built Thermo-baro-clock with a MS5534 sensor.( 16F876 ) the clock is driven by a 32.7... khz "clock crystal" connected to RC0,RC1 pins and using TMR1 ovf interrupt.

The only way to adjust reading is to trim the TMR1 preset ( 32768 ...in theory ). an adjustable capacitor parallelled to one of the xtal load caps could also help a bit.

Possible also to use two pushbuttons to inc/dec the TMR preset value, you then store in the EEPROM ... but do not forget to limit the trim range !!!

But as always ... no simple automatic trimming.

Absolute references will always be our main headaches ... cause there's none naturally existing !!!

best regards
Alain