I'm among the group starting a tech media lab, open workshop, in rural, south central PA. We were given a Sieg KX1 benchtop mill that uses the same spindle control boards as one of your projects.
We've got the logic side working as it should but cannot get the spindle moving. There appear to be proper signals on the XMT SK board, a variable, analog signal on pin8, speed control & a logic signal, 4.2v or 0 on pin6. From the SK to the spindle driver & control boards all looks like gibberish, 60hz & something from 25-60v . . .
Appreciate any help! And all the encouragement in the world for you introducing Scratch & Scratch for Arduino to younger people, it's amazing what they can pick up uber fast! We've had a group of 20-30 young people playing with Arduino, Scratch & a variety of breadboarding, along with flying r/c's S107's & X1 Symas, you know, just 'cuz it's fun . . .