Hi,
Ive seen a topics asking similar questions with the VIN pin but none regarding the use of the 5v pin.
Basically, I am powering the Nano from the Adafruit Powerboost 500's 5v breakout to the Nano's 5v pin.
My concern is what will happen if I plug the Nano into USB to upload a sketch?
Im worried the Nano will have the current from the USB flow back into the Powerboost and brick it since ive heard the Nano auto-prefers USB power.
Should I cut the power and ground wires inside the USB cable so its always running on battery?
Im guessing they arent needed since they are directly tied to the Tx & Rx pins which dont need any other power source once the Nano is on?
I'm no expert, but since nobody else has yet replied...
I'd imagine that if you cut both vcc and gnd on the USB cable, your data pins wouldn't work as they'd have no reference to ground on your Nano. Cutting just VCC on the USB supply should work.
I've never ran vin and USB myself, but as a complete noob's guess, I'd imagine the two switch mode supplies would inevitably be out of phase and cause all sort of AC noise on vin. Apart from that I don't think it would be a problem, BUT, that's only my semi-educated guess and it's not worth risking your PC's motherboard on.
The 5V pin is connected directly to the USB power, AFAIK. On the Uno there is a polyfuse.
Just cut the 5V line on the USB cable, maybe cut an extender cable and mark it as such?
A Nano has a 500mA schottky backflow protection diode between USB supply and the 5volt pin (no polyfuse).
That means that you can safely connect 5volt to the 5volt pin when the USB lead is plugged in.
A Nano runs on 5volt if you supply 6-9volt to the V-in (raw) pin. Or 5volt to the 5volt pin.
But on USB supply the 5volt pin is about 4.6volt, because of the backflow diode drop.
Leo..
