I refuse to believe that a power supply can 'know' how to develop a 'virtual ground' regardless of which way around the mains are connected. There must be some physical connection between mains ground and circuit common for this to happen as you describe.
I would suggest that you measure the resistance between the two 'grounds' with a fully isolated meter, and disconnect each other peripheral one by one. At some point the 'ground' connection must disappear.
-- Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
te:
regardless of whether I plug it into ungrounded 120V or 240V, the ground on the processor is at 0V (or very close) to power line ground. I'd love to l earn why.
supply does an excellent job of building a virtual ground that is spaced f rom 5V in the same relation that the spacing of ac ground is relative to th e ac power. You must not run a BBB without a grounded power supply, yet the Beagleboard site recommends power supplies similar to the one I'm using (2 prongs, no ground prong.)
sounds most unlikely
NT
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