I have built this really neat dataloggerhttp://www.youtube.com/watch?v=RwoIPodGIQI
on an ATMEGA2560 over the last year and I use it a lot. I have expanded it a few times and now I am running out of pins, or will pretty soon.
I need to add 4 more thermocouple amplifiers, (2 Max6675's that I already have, and two Max31855's) read an O2 sensor and then add some servo drivers.
Can I add all that additional stuff on another 2560 and then link that one to my current "main" 2560? I'd write appropriate code for both microprocessors, but, using one as a master, it would ask the other one for data from time to time. Is this a practical approach?