I'm extremely conservative when it comes to hooking up devices. In my prior life, I designed, programmed and installed process control computers in the photo industry to run the Kodak-S series printers found in most professional photo labs (before the digital photo revolution made my services as valuable as a buggy whip manufacturer). I always use opto-isolators whenever interfacing anything into a control board. That means that the limit switches would have their own power supply and that the only connection between them and the controller board (breakout board) would be light pulses. The inexpensive Texas instruments TIL-111 series of opto-isolators can usually be purchased for a few cents each. My favorite is the Opto-22 G4 modules that run about $15 each for input modules, although they require a 'rack' for another $70 or so.
Connecting signal lines on a machine that has stepper/servo motors, VFDs and assorted other mechanical/electrical devices directly to a controller board is just asking for problems, either now, or sometime down the road. An extra $10 to $250 dollars up front to do things right will keep you safe and sane.
Some breakout boards are already opto-isolated. (I'm not familiar with the Campbell board - which might work perfectly right out of the box.) If that's the case, then you would only have to add a power supply that is independant of the controller's power supply to keep things isolated.  |