I think you can attach a keyboard to a phone over USB, and in theory it can provide both input and output (you can control the LEDs from the host computer). That would be a more convenient route, I suppose.
replyThat's true, although I don't know whether you can control the LEDs from within the app sandbox.
replyIf you can access it from within the sandbox, you don't need to be limited to keyboards - the HID framework allows for arbitrary I/O.