I have a mega and i am a bit confused.
it came with a 9 volt wall adapter. so contrary to what i previously thought...the barrel jack on the board must run through the on board voltage regulator to get the 5 volts needed ??????
is there some reason I cant get a 5 volt wall adapter and wire it to the 5 volt pin?
is the wall adapter "regulated" enough?
seems silly why arduino doesnt just require 5 volt adapters and bypass the regulator
I have other 5 volt stuff in my project so i was hoping to not be limited to what the regulator can handle.
Check out the following page. You can find the schematic and power description for the board.
The power pins are as follows: Vin. The input voltage to the board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V).
Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
Additionally, the regulator is not the only thing limiting the amount of current the board can handle. You did not design the board, so you do not know exactly how much current every trace can carry.
To get nice smooth 5V you need a higher voltage to "waste" some. The components used cannot just "waste" 0.1V. There is a minimum voltage drop accross the regulator. Thats why the recommendation is 7-12V input voltage.
And no, cheap 5V power supplies are not regulated enough. The voltage comming out of your wall socket is AC. So a nice sin wave. Getting this smooth under changing load is hard. And most devices have internal regulators anyways. Why would the power adapter guys spend any more money than necessary?