VFD control voltage

[cncsnw]

This could also be an analog oscillation problem.

That theory would be supported if you get predictable spindle speed using a battery (e.g. 9V gives you 90% speed, 1.5V gives you 15% speed).

If that appears to be the case, you could try one of the "snubber" solutions.
See https://centroidcncforum.com/viewtopic. ... 98&p=46127

[offlanders]

Just wanted to close the loop on this. Per @tblough suggestion I ordered the signal isolator and installed it between the Acorn and VFD. I changed no settings from what we discussed, just installed it. Works like a champ. I can now scale from 0 to 10VDC and the VFD will operate from 500rpm to 24,000rpm.

Thank you all for your input.

P.S that is about the brightest LED i've ever seen for a power indicator.