Actually, you can power the Nano with regulated 5VDC on pin 27 or from 6-20 VDC unregulated on pin 30.
Pin 30 power is rated at 6-20 VDC unregulated, but I tend to keep it close to the minimum as the on-board regulator will overheat at higher voltages. A diode there will work as long as you allow for the diode drop in the 6V minimum.
Of course, if you're building a circuit board anyway, a diode (or bridge), a TO-220 regulator and a decent filter cap will give you ultimate power flexibility, either AC or DC. The selection of half-wave or full-wave power rectification will be based on the need (or lack of need) of a common ground with the input power source.
BTW MJCAT, there's no need to quote a fist full of graphics when they're right above, just makes the thread much bulkier.
