I have to disagree here...........
Opto Isolation is THE way to go. I was getting my 5 axis Shoptask ready for the Mach3 Convention SE. The computer motor board was old (BTW opto isolation works both ways). Any way I was using some first Generation C-10's from CNC4PC (the new stuff is isolated, the old was not). At any rate I was testing my machine, and something went BANG in my computer, and it promply died.......... I opened the case and some capacitors had Blown up (this machine had run for about 5 years), these caps took out my mother board and PP ports......
But that is not the worst, it also took out BOTH of my BOBs (I held these up and showed the participants of the show why ISO is good), and further when the BOBs went they in turn took out 3 or my 5 Geckos.......... Total cost: One computer, 2 BOBs, 2 PP's, 3 Geckos and lots and lots of Klenex tisssues for all the crying that I did.
The lesson is, sometimes it is NOT you, sometimes Electronics just go bad with age and Fail ALWAYS at an inopertune time, like 2 Days before a planned Demo.....
Scott