Grumpy_Mike, to conclude, what do you advice me?
I need the easiest way.
A guy (Brian: http://www.viddler.com/explore/dioioib/videos/9/) uses exactly the same stuff and uses only the usb power...!
without problem...
I don't understand..
I put the code from the atmega8 on the backpack
I should dive into it deeper... multiplexing is in it!