uc300eth vfd connectios

[JAZZCNC]

I'd be looking at the RS485/ModBus controller (available for UCCNC and Mach3) - at least to see if it's viable for your VFD. It avoids some of the problems with analogue noise, linearity, etc.

There are a few ways to use the UC300ETH for VFD speed control - the usual PWM output on the more typical BoBs, the analogue output that Jazz covered, as well as the above suggestion to disregard it altogether.

I've fit 100's of Vfd's with analog speed control and never do I have any troubles with noise, even the linearity is acceptable for most machines. I think the only reason I'd fit Modbus is if I wanted long wire runs and slightly finer speed control.
But like you say if going to have to buy some board etc to get speed control then RS485 would be a sensible choice. It just seems to be waste money when the controller already provides Analog Output.!