> I don't understand why he has the 1n4007 in there either. this seems 
> unnecessary. 

My understanding is that the standard 1N4007 is not a particularly
fast diode (for example it's not suitable for semi protection in noisy
applications). If a diode is at all necessary there I'd have thought even
a small fast signal diode (1N4148) might cope, given the current
limiting of the 2k2 and the opto's transistor. I have some UF4004
and SMT fast suppression diodes on stepper boards

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