Making some headway, here is the current version of the schematic:


I have debugged it and all seems to be working in manual mode (I don't have the VFD yet, but the F/W and Run/Stop work, as well as a readout I put in for spindle speed, Z-bit, and an 84 ppm signal for the Mikini). Only hiccup so far is M3 and M4 don't seem to switch to RUN mode when in Mach control. May be a function of the VFD not being installed, though, so I am not too worried yet. I actually did all the programming of the Arduino myself after a bit of a training session with my work buddy. It's been fun! I added a small OLED screen to read out the modes and the spindle command and and actual speed so I have a bit of diagnostics feedback.

The PWM signals from the Mikini and Mach3 are so slow I am able to convert the PWM to spindle command speed directly in the Arduino instead of using a PWM to analog 0-10 v box. The box didn't work well since the signal was so slow. I think the Mikini is 8 hz, and Mach3 is set to 25 hz. The box wants 100 hz but would prefer 1 khz! It was a bugger to figure out how to parse the PWM signal in C, but I figured it out!!!