Grounding when using a power supply and USB - motor drivers to Arduino?

Hi all, just a quick question about grounding. I'm no electrician (Mechanical engineering student, really), so the topic of grounding has always been confusing to me.

I'm currently building a linear actuator and my electronics look a little bit like this: |500x473

Basically, I have a power supply connected to wall AC that powers two motor drivers. I know the motor driver ground needs to be connected to the power supply, but the drivers have another ground port. Does that need to be connected to the ground on the arduino? The arduino is powering two limit switches and two LED's with its 5V, so obviously those are grounded to the arduino.

I'm just unsure about all this grounding business. I know the power supply is grounded to the wall through the power cord, but the drivers confuse me. Anyone know what I should do with them?

PS. I'm using USB because I need to send serial information to and from the arduino.

Thanks!

All GNDs need to be connected to provide a common reference point for 3.3V and 5V signals. Preferably a common point (think a star spreading out) and not looped all over within the box.

In this case, would it be appropriate to have two "stars"? One at the Arduino for the 5V signals (LED, limit switch, motor driver Step/DIR) and one for the power supply?

Thanks.

No, connect all 3 devices (motor drivers and Arduino) back to the power supply Gnd. The switches and LEDs can connect to the Arduino Gnd,

Thank you for your help! I think I'm beginning to understand. I've attached an image of two ways I think would work. |500x473

1 - Connect the arduino directly to the power supply ground where the AC input connects

2- Because all the ground ports on the drivers are connected, connect the arduino to one or both of the drivers.

Would either of these ways work?

Thanks again for all the help.

2nd would be better. AC Gnd is not necessarily connected to the DC supply Gnd.

Awesome! Thanks. That was a big help - I feel much more confident now.