I will order the C1 - Parallel Port Interface Card as soon as I hear from you about the following relay board
I have a relay board that I bought with the RF Isolator. It has screw-terminal inputs & outputs. Any reason you think I should replace it with your C15 - Dual Relay Board?
If the relay is operating something now and the relay can be triggered with 5V, you should ne OK . . . . . unless it is RF isolated . . LOL! Be careful though that the relay doesn't draw more juice than the BOB can provide, or you can hurt the BOB. The chips are socketed, so it's easy to replace them (don't ask). Specs on the BOB are available on the site, you'd need to look up the specs on your relays.
You have some distance to go yet with this project and you are already getting plenty of opinions on this what-not and that doo-dad, so I am going to give you my best advice on the project menagement level. You stated that this is not a hobby project, so that changes the game. In my view, your decisions should boil down to how much your time is worth, and any losses associated with the machine not producing anything.These CNC parts are dirt cheap in comparison to what I might guess your wages are. You *might* be able to reuse an old piece and save $18, but if it takes you three hours and you need to buy or buld test equipment to figure that out, you have not saved anything for your company money AND, you still have an old part that nobody can give you advice on and now you also have a 'production' machine of unknown reliability. Would the relays shut down production if they fail?
As a matter of personal preference, I avoid 'multi function' stuff if possible. Problem is when one component goes bad, you need to replace the whole thing if you don't have room to add another board or if the failed feature can't be disabled, or if it took other stuff with it.