I installed the Modbus solution recommended by Danilo. I must say that it is a superior controller of the spindle than using the PWM method. No variances is speed and I have not had to use any special 'noise' suppression add-ons. It's a great plugin for the Huanyang VFD. I made sure that I used the RS485 converter that has the Prolific chip (PL2303). The other converter uses a CH341 chip. I ordered one of those also, to try out. It has not arrived yet.