Very neat, you do understand "THOSE connections are for the polarity" of the signal you are supplying? probably opto isolated LED-transistor inside it, so you can use a positive signal and a negative on the other side, or a positive pwr and a negative (sinking) Signal on the other side. Think of a opto-diode as a one way switch, power flows through in one direction only, and "if you have a negative (sinking) signal, or a Positive (sourcing signal) it will work with either by routing the proper "other pwr" to the other terminal.
I want one too.. my problems.. well.. the arduino "reprap" code I downloaded has a 1ms signal length, a "geckodrive" from
www.geckodrive.com has a desire for a 6ms signal.. so.. I was going to go in and alter the wavelength in the arduino code.. but the new "look ahead software" is so complicated I need a school sized chalkboard to keep track of what goes where,when and how.
I want to see this project work, as I am hard on your heels with one of my own.
I ran the 3d printer drives (geckos from my cnc mill) with the 2amp motors in Mach3 just the other day (pc based).. I have had more trouble with the WINDOWS on the cnc than the cnc.. even with the dog pulling cables out the side.. (+300 wires going to shop automation)
THIS arduino has been a new interesting journey for me. It kicks the basic stamps butt that turned me off on micro-controllers for sure.
I do not mind sharing anything I have figured out.