I am designing a project where a nano will run a ring of WS2818 LED's
The control box will be on show so I want to to be as small as possible and preferably allow for reprogramming without taking it apart.
To this end I hope to be able to position the nano so the USB socket it accessible from the outside and will power the whole unit.
As I understand it the VIN pin is directly connected to the VIN of the USB socket so I don't have to worry about overloading any on-board voltage regulators.
So assuming a suitable PSU what current could be passed through the nano board?
Thanks.
Looking at the Nano schematic, it seems that Vin connects to the input of the 5V regulator, nothing else. So there is no current available at Vin when powered by USB.
The schematic I have for the Nano (R3 CH340 clone) says the USB 5V power line goes through an SD101CWS diode to 5V pin, which is the output of the voltage regulator. So that pin would be the only point where you could draw power for other devices. But that diode has an absolute maximum rating of 15mA or 30mA, depending on which manufacturer you're looking at. So based on that, there's no power to spare beyond what the 328P needs for itself. And actually, that diode rating doesn't make any sense. It think there must be many Nano projects where the Nano itself draws far in excess of 30mA, and which run fine from USB power. So I'm puzzled by that diode. The diode on my Nano clones is marked B2.
The official Arduino Nano schematic shows an SS1P3L diode connected between Vusb and 5V, which has a maximum forward continuous current rating of 1.0 A.
In that case, for current draw from the 5V pin, you are usually limited by the USB port, typically 500 mA or 1 A.