Hi all-I'm wondering if anyone may be able to help me out in both the "proof of concept" of a project, and possibly the coding portion of it as well.
I want to be able to turn on and off the 9V signal on an arduino board, and send it to a series of LED's using the outgoing midi(or possibly usb) signal from an external controller. I have an arduino kit, and am mildly acquainted with usage of the processor and breadboard. the board's 9v pin can definitely power the LED's, however, I don't know how to achieve control via the usb port to turn them on and off.
i'm very comfortable with a soldering iron, circuits, etc, but code is totally over my head. can this be done? is there possibly any pre-existing code for this usage? lastly, once the board is programmed to receive midi messages, will it reliably stay programmed for an indefinite period of time? thanks for any help. best, rj
You need drivers (like ULN200x) for the 9V voltage and possibly high current for each LED, switchable from the 5V logic level of the Arduino output pins.
It's not clear to me whether you want MIDI or USB input, but you'll find according libraries and tutorials in the Reference section.
And no, a program will not be retained indefinitely long. You should refresh it every 20 years of permanent use, or every 100 years when not used (storage temperature < 25°C). Have a backup of the binary code on some long life medium, like punched metal tape in a safe place 
thanks much, dr diettrich.
it's actually not clear to me just yet whether a usb OR midi output from the controller would be sufficient; that's why i'm not sure which input source to the arduino would be best.
i need to turn this around in about 10-15 days. would anyone here possibly be able to help me with this? i'm not sure if i have the time to get up to speed on the coding aspect. the wiring i can probably grasp easier than the coding. thanks for any possibly help!
MIDI input is easy to accomplish with a Serial connection (library exists), also using Serial via USB is standard (not requiring any additional libraries). In contrast an USB MIDI interface requires low level changes to the firmware, and then also disallows to program the controller further via USB - not recommendable unless absolutely required.