I have a project going on, to build a climate control system for a terrarium. I'm working right now on dimming the lights. They work just light a normal light and after research, I know they are dimmable, so that's not my problem. My issue is the board I'm looking at designing. I'm following a tutorial in order to make it. http://www.instructables.com/id/Arduino-controlled-light-dimmer-The-circuit/ It calls for a ZeroCrossing signal and sends it to pin 2. My question is, is that the only pin on the Arduino UNO R3 that takes a ZeroCross signal and if so, can I attach 3 of them to that pin? I want to dim three different lights with three of these boards. I've never heard of ZeroCrossing before, and am not quite sure how it works. Regardless, if anyone has any experience with this, any help would be much appreciated.