Re: parallel to usb? + can i "convert" open loop to closed loop steppers?
Good options all around. I'd just like to add that even with optical isolation, I would be wary of using my main PC to drive a mill. Better to use an old laptop, or a Rasberry Pi, or even just an Arduino with an SD card and LCD / switches user interface. I personally like using an old DOS PC with TurboCNC via the parallel port, but that's just me... when something works, I tend not to change it. And honestly, my test bed CNC machine isn't anything to look at. It's always torn up testing new drivers or whatever. I do also use a RAMPS/Marlin motion controller (Arduino based) but I feed the G-CODE from an old laptop. No optical isolation... so far so good... and if it does fry, that machine cost like $50. I should probably switch to my RasPi... since that cost $25.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)