Arduino Voltage Supply

Hi. In arduino mega 2560 overview page it says i can feed this board with dc adaptor between 7-12v . And i can feed with usb (5V). Thats very clear. But also in that page it says board probably cant operate good and cant give 5v output if i feed less than 7V with a dc supply. Yes i also get this. But i saw a project and guy feeds the board with 5V adator and this project drives 150 RGB leds!! But i no se any operation failure! My mind is stuck!!

Most people feed RGB strips from thier own power supply and just use the control lines to tell the RGB strips what to do.

You didnt include a link to the project so the best anyone can do is guess.

You can power the board with external 5v by hacking up a USB cable and connecting 5v and gnd to it (people often power arduinos and similar off a USB phone charger, which doesn't require slicing up the cable).

You can also apply 5v to the 5v pin, and power it that way, but you shouldn't do that, because you can damage the board if you plug it into USB while it's powered that way

In product overview it says dont feed board via 5V pin. Because its an Output! So i dont realy get why people feed board via 5V pin!! Realy… i cant start any project because of this problem.

This is the schematic down below. In this scheme they feed board with 5V pin! How?? Its and OUTPUT. Not and input for feed. There are 3 ways to feed this board : VIN pin, Usb input and DC jack ! But this guy feed via 5V pin and in overview they dont say this…i am lost!! Realy.

It is not an OUTPUT - calling it an output (particularly in caps) would imply that it's an I/O pin controlled by the microcontroller. It is not. It is connected directly to the +5v rail, so if there's no other power source connected, you can power it from the 5v pin just fine.

HOWEVER we all recommend against that, because you can easily damage the board if you power it that way and then connect a USB cable (connected to a computer or other thing that tries to supply power) - the two +5v supplies are connected directly together in this case, and they'll fight over which . It's better to chop a USB cable in half, and connect Gnd and 5v of supply to that, and plug it into the USB port to connect power to it.

As for the motivation for using the 5v pin to power it, instead of Vin or the barrel jack is so that a single +5v supply can be used (since Vin or the barrel jack go through a regulator with a couple volts of dropout - so you'd need 7v supply. But the regulator couldn't handle the current for all those leds, so you'd ALSO need a 5v supply for the LEDs.) But yeah, do the USB cable method instead of connecting it the way they did.

Sorry i cldnt understand ur usb method. Can u try to explain again? (Its about my english! Sorry)