Ground Loop on Digital Output signal on sbRIO

[Nathan_B.]

We are trying to use PWM output to control a motor controller via the sbRIO-9626.  The motor controller references the system ground (this is a battery powered system) for it's PWM signal.  I've been trying to search around to find if connecting the motor controllers ground to the digital ground will cause a ground-loop but I've not been able to find anything definitively.  When I test for continuity between the negative power pin and the digital ground on the RMC, it does not indicate as being connected.  When I test the voltage while the sbRIO is powered, it shows 0 volts.

I'm quite sure that is what was done when we had a 9632 to do this but I wanted to make sure that I can connect the grounds like that.

[tannerite]

Nathan_B,

Digital ground is not the same ground as the negative input on the power supply. I do not recommend routing any ground that carries power through the sbRIO-9626 as the traces are not rated for this. Can you provide a simplified schematic of how you want to connect everything?

[Nathan_B.]

There will not be any major power through the RIO itself.  I simply need to make sure that the signal going to my servo's and motor controllers have the same reference (ground).  Also, I would like to be able to power my 5V devices from the external 5V to the daughter board (things like my encoders and my relays).  Here is a crude diagram of what I am doing.

In the Automated Home Brewing system here seems to have the grounds all connected (making everything reference the same ground).  I just want to make sure that I can connect the grounds.

[tannerite]

Hi,

From your diagram, everything appears to be wired properly. I was worried that your motor controller fed its power supply ground throug the sbRIO; this is not the case. This diagram looks good to me.

Best,