The "5V" pin is not by any means an output pin, if anything a "reference" pin but most certainly the preferred pin to which to supply a regulated 5 V.Ī practical power supply for the Nano (or UNO, Pro Mini, Leonardo etc.) is a "phone charger" with a USB output connector for 5 V, generally up to a couple of Amps though you can not feed more than 500 mA through the USB connection. Powering via the "barrel jack" or "Vin" connections is asking for trouble. The on-board regulator might be able to power a few other things if it had a heatsink, but on the (older) Arduinos, it does not. This is because the on-board regulator is essentially capable of powering only the microcontroller itself and no more than a couple of indicator LEDs. In which case, the answer is regulated 5 V. If you are asking this question, it is highly likely that you will wish to connect something else.
And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle. It is essentially only for demonstration use of the bare board back in the very beginning of the Arduino project when "9V" transformer-rectifier-capacitor power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes.
I was told this is the best way to power up the Arduino, because the VIN is regulated.Ī very real danger is that the obsolete tutorials on the Arduino site and others misleadingly imply that the largely ornamental "barrel jack" and "Vin" connections to the on-board regulator allow a usable source of 5 V power.
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