When I have an Arduino hooked up to a 256 LED matrix that is separately powered by a power brick, I can hook up a power line from the matrix back to the Arduino's 5v to power the Arduino and the whole shebang works with just the one wall plug.
But I can also plug in a USB between Arduino and PC to change the patterns without unplugging any of the power stuff. What harm am I risking for doing this?
Um, I have read in a few places that you'd effectively be giving your arduino power from two sources at once and it would go up in smoke, but it could, as always, be false information. From what I've read, the arduino can automatically switch between the wall socket and usb port for power but it has no control over the 5V input. Anyway, I'm not qualified to vouch for the reputability of my sources.
In my uneducated head, it seems more like using a power supply with a high amperage rating at 5v. The Arduino only draws what it needs and the higher amperage rating isn't a danger.
So with 5v (let's say 8A) power brick going into the 5v pin, and the USB also getting 5v at some 500mA or whatever, would be no different than an 8.5A source going into the 5v pin.
Arduino isn't getting force fed power somehow just by having the two hookups.
But of course just because mine hasn't been engulfed in flames doesn't mean I'm not doing something wrong. I would like to know the truth.
Wawa:
The 7805 is the bigger inefficient brother of the inefficient 11117.
They are both lineair regulators, and convert "in-out voltage difference * current" into heat.
A "breadboard power supply" uses the same 1117 regulators.
800mA (total in for both) can only be achieved with ~6volt regulated in.
Expect ~300mA max with 9volt in.
All grounds are most likely already joined on a breadboard supply.
A Nano has a weak 3.3volt pin.
~50mA for an official one with FTDI chip, much less for a clone with a CH340 serial chip.
A 3.3volt breadboard supply solves that problem.
Maybe wise to supply the breadboard supply with a 5volt phone charger (if it has a USB socket).
That bypasses the 5volt regulator.
Leo..
This explains why i am getting such poor performance from the breadboard power supply using a 12v input, couldnt work out why it was overheating and a 500ma fuse was not even blown!
