Just recommissioned my i3 clone after it sat unused for months, now I remember why it was unused 
it’s a totaly pain in the but to deal with compared to a Delta with a 32 bit board with a web interface.
I had to spin this stupid little dial back and forth over and over.
If you want 100 of something with a stupid little dial you have to turn it precisely the right amount 100 freaking times!!! It’s like a phone from 1975!
I really dont like plugging the half burned out Melzi with the positive to the heatbed a burned out area on the PCB (even a capacitor that is brown from fire on one side) into anything USB. 12v down a USB cable into my PC, this clone of an old design is so not worth that risk for slow and fairly crappy prints.
Not wanting to spin that stupid freaking dial anymore, I am tearing this thing down and using whatever I can on a new control board in a better frame design. But until then, and possibly to try and salvage the Melzi in it, is there a way to make a current cutoff USB link? Some function of a better USB hub maybe? Some easy to make electronics possibly? Something so that if the control board just eats itself and there is 12v 150w of angry pixies looking for a new land to conquer, the device or setup of cheap hardware will stop the flow to the PC at the other end. This so I can use pronterface or something to not spin that stupid dial.
My thumb still hurts when I think about calibrating E steps.