Transistor Affecting Timings?

[HenrikOlsson]

Those look like ceramic resonators. (?) The ceramic resonators aren't that accurate and I bet that the actual frequency differes ever so slightly between the two so your timing drifts. Capacitance in the breadboard may also have an effect on tha actual frequency.

If you really need to keep them in sync then I'd suggest driving both PICs from one oscillator or sync them thru one of the spare I/O's but I suspect that's not physically possible (?). Next suggestion is to use crystals instead of resonators, moving on from there there's almost no end to how much you want to spend to be accurate - temperature compensated?, oven controlled?, rubidium? - you name it.

/Henrik.

EDIT: I looked at a couple of resonators and they had a frequency tollerance of +/-0.5% typically. If you're unlucky and get one at +0.5 and the other at -0.5 (very unlikely but still) the difference between the two is 1%. Your 1000ms delay becomes 995ms on one and 1005ms on the other.

[Gusse]

I agree with Henrik, that syncing PIC's is the easiest way to proceed.
If you use internal 4MHz OSC in master PIC and set GP4 pin to provide Fosc/4 out, then your system will be in sync. Rest of the PIC's will use master PIC clock as reference.

Two totally independent systems are always out of sync, already from the beginning. Difference might be small at the beginning, but....