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bobc
One issue that I nearly mentioned but didn't was the question of opto-couplers. It seems on the skynet boards, they run off 5V which is provided externally. The optos would sink about 12mA each at 5V, or about 7.5ma at 3.3V which is a bit on the high side for the Due.
The optos also add a small extra delay of 1-2us, which may need to be accounted for.
So I think there is a definite need for a header module with level converter and pulse stretcher. I would like to use the standard pMinMo 10 pin connector, but it takes up a lot of space, so might be tricky. A possibility is to use the 4 pin motor connector for enable/step/dir/gnd, and hope that no one will try to plug an external driver into a Pololu motor output.
These (mine) opto-boards are already in use by several customers for 3D printers.
I have 2 printers running these drives on arduino with my own Ramps version without problems.
The firmware in use is Marlin and it's step output pulse is 2µsec, the optocouplers stretch this as they switch on fast but release slower.
I don't think there's a need for a pulse stretcher exept maybe for firmware wich really uses 1µsec step pulses.
A resistor change might be needed to reduce the current for Due, the drives still work on 5V with 1K series resistor for the optocoupler.
Level conversion isn't needed for these opto-drives, just a recalculation for the series resistor.
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bobc
Ok, that is useful info. I will order one of the boards for testing.
I will send you one for testing + one of those Pololu to PMinMO adapter PCB's, just need your address....