Generally you only connect the Ground between two systems with different voltage requirements.
Quote from: johnwasser on Apr 08, 2013, 06:24 pmGenerally you only connect the Ground between two systems with different voltage requirements.John, actually I'm ok using two power supplies. Are you saying that connecting the ground and the vin from the 6V device to the UNO while powering the UNO with an additional 9V somehow prevents an over-voltage flow to the device?
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