sorry that I didn't explain it clearly. Attached are the two circuits that I plan on using (sorry that I don't have software for this kind of drawing). Just not sure which grounding scheme is more appropriate. The first scheme treats the input to uno (reducing source power volt) and the output from uno as two circuits; the second one lumps them together. I worry that the 2nd one might accidentally feed undesired currently back to the power source (which will potentially blow the power source) if the relative voltage of uno ground is different from the ground of 7805. But I am not sure if scheme 1 is grounded sufficiently. Or maybe the basic design has some fundamental flaw?? Any suggestion will be greatly appreciated.
