I can't hook the switch up until my Mega board shows up tomorrow... I'm already out of pins on this Uno board and I still have a lot more to hook up.
Again, I guess you don't want any of us to ask what else you have hooked up to the UNO or attempt to help you optimize the hookup and reduce pins used either. Just I/O pin sink current is asked so only answers to that is needed?!
The oscillation happens when you open the door and all the inside air comes out...The input temperature changes, the PID responds. The PID needs to know that the door is open and not to freak out. Enter the microswitch on the door. Door opens, microswitch tells arduino that the door is open and to freeze the integral until the switch is depressed again... Once the door closes then a 5min freeze on the integral starts.
Hope I'm not screwing you up on this but I find that as good as microswitches are, a latch-type Hall sensor and cheap magnet as used in security apps is far nicer and last for a larger chunk of forever. You don't need parts to make physical contact and wear out or dirt-up, the internals are solid state and the switching action is clean. However it's not good to mount the magnet directly on a steel door or frame, they do make mounting bits just to handle that.
Hall sensors are to microswitches like transistors are to tubes.
I know what you're talking about... You see them on doors/windows. That's a good idea and I'll definitely keep it in mind for my next prototype. I have micro-switches from work and I have other tiny dead-man switches laying around... But I want things to be as trouble free for my *hopefully* future customers and a latch-type Hall sensor would be good.