Ground for mixed v+

Other Hardware General Electronics
1

If I have a sensor witch which powers at 5v from arduino with a 5v logic output, but also RGB led drive upto 12v, all with a common ground- what do I connect this ground to?

I assuming both the arduino and bench supply?

2

all with a common ground- what do I connect this ground to?

All the common grounds need to be wired together at some point. The Arduino has 3 ground pins avalible.

Lefty