I can't reverse the spindle rotation.

Hey everyone,

I'm stuck with a weird problem and could use some advice.

I've got a 3-axis mill with a 1.8kW AC servo on the spindle. It used to run perfectly from a parallel port and a Chinese BOB. I'm now upgrading to a Mesa 7i92, still using the same BOB.

To reverse the spindle I've always used a PC817 optocoupler module. When the REV signal is active, the module pulls the servo driver's DI4 pin to GND, and the spindle reverses. Simple.

Now with the 7i92, everything else works (motion, outputs, etc.), but the spindle reversal doesn't. The LED on the PC817 module lights up when REV is on, but the spindle doesn't reverse. If I take a piece of wire and manually jumper DI4 to GND, it reverses instantly. I've even tried a brand new PC817 module – same behavior.

Wiring of the PC817:

Input side: IN → pin 9 of the BOB, GND → BOB GND

Output side: V (collector/output) → DI4 on the servo driver, GND → servo driver GND

The BOB GND and the servo driver GND are common.

What puzzles me is that this exact setup worked fine with the parallel port. Why would the 7i92 cause a problem with the same BOB and wiring? Is there something different about the 7i92 outputs that could mess with the PC817?

 Is there a better or more reliable alternative to these PC817 modules for this kind of level shifting?

Thanks in advance

Is it a hal setup error?

For Mesa FPGA cards you need to know the GPIO pin number
for the pin and to set that GPIO pin into output mode.

Can you check the output of the module with an ohmmeter?

If the PC817 module needs 5V drive you would have to connect it in sinking
mode to the 7I92. ( +5V to PC817 module IN+ 7I92 output to
PC817 module IN-  and active low output )

Is there some other issue with reverse in the hal file
( like PWM connections if you have spindle speed control )