OK so I'd like to just use the Mach PWM spindle output go thru a low pass R-C filter and run my VFD from 0 to 5 volts. Has or can this be done and what pulse freq. , resistor size and capacitor size should I try. I saw a post(72321) for a homemade H drive where AL sugested 10K and 0.005uf for the pwm going into it. And I found a simple R-C Filter cutoff calculator at http://www.muzique.com/schem/filter.htm but I'm not sure if I should shoot for the pulse freq or lower freq. I really would like to give the simple solution a try before buying a step or pwm to analog converter. Thanks Drew