misoke:
i use the mp3 power supply connected to my usb printer then to arduino usb slot...
Can you draw a diagram? You have a MP3 power supply (whatever that is exactly) and you connected it to a USB printer and then (how?) into the Arduino.
Can you tell use more about this MP3 power supply? MP3 is a form of music file storage. In what way is there an MP3 power supply? And how did you connect it to your USB printer?