Air cutting with the baseplate!

Slight issue with the Acorn and the CNCdrive servo drivers. The Acorn step and direction signals are generated by open collector (low side) outputs, while the CNCdrive servo drives have opto inputs that require a high (>5V, up to 24V) signal. In other words, a low side driver and a low side load. Hmm. That doesn't usually work too well.

The servo drive manual is a bit sketchy on the input circuit but recommends a 2k2 resistor when driving from 24V. So a 2k2 pullup to the 24V should do the trick. I was worried about the rise and fall times but my wiring is short and it all looks pretty good.

Tried it out with a flying lead on the X axis step input. I left the direction input as-is, which meant that the X axis could only travel in one direction but this at least showed I was onto something. Ran one of the demo programs and it seems to have life in it, at least on the X axis.

Emboldened by this, I removed the Acorn board and fitted 2k2 pullups to the step and direction inputs on all 4 axis outputs. Found a convenient 24V track nearby and tacked through hole resistors onto the back of the relevant connector pins. Checked it all worked again with the scope. It's not pretty if you look closely but there again, I've hidden it under the board....

These are the Toshiba low side / open collector drivers that create the drive signals.

So we seem to have working servo drivers. And I checked the spindle control voltage appears to be modulating as the set speed is changed by the demo program.

So now, let's drill some holes in the cabinet for the various cables....