Robotwizard wrote: Yes, between the VFD and par port. The FM-50's I was looking at don't have Modbus/RS-485 so thanks for the advice. I haven't been able to find any manuals or specs for the Huanyang products yet tho.
Try this link:
www.jinlantrade.com/ebay/invertermanual.pdf
But you don't need to know most of that if using the
LinuxCNC HAL component
If you prefer to use parport control then you ideally need to convert 3 of your output pins to FWD/REV or ENA/DIR and a PWM output for the speed control. You can potentially configure the VFD for 0 to 5V operation and use a simple RC filter to make the parport PWM into a variable voltage, but it is likely to be non-linear and isn't well isolated.
Better than using a simple RC filter would be to use an opto-isolator and then use the 10V supply from the VFD into your RC filter. This gives you the full 0 to 10V range, protects the parport and should be more linear if (and ony if) you select an opto-isolator with both current-sourcing and current-sinking outputs.
One of these will work well
www.farnell.com/datasheets/611920.pdf
Basically you connect the parport to the left-hand side and the VFD 10V and GND to Vcc and GND. Then a resistor from Vo to one side of a capacitor, the other side of the cap to GND and then connect the VFD 0-10V input to the top of the cap too. Choose R and C to suit the time-constant you need. (say 1/20 the PDM rate. (Use PDM rather than PWM for this)). The reason to use this device is that it will actively charge and discharge the cap through the filter resistor, whereas using a conventional 4-pin opto you need a bleed resistor to discharge the cap, and that makes it non-linear.
Or get a
Mesa SPINX1
which is meant for exactly this job
