Same as the Arduino one here, but this is cheaper. PAY ATTENTION, put 10K resistors between the BT5/BT6 out and the actual buttons or it freeze

the USB stuck, i don't know why but it seems to be a current sink problem, maybe because all the PULL-UPs enabled, but the strange thing

is that these inputs only have the problem. 

Sourcecode here

GERBER here

PDF scheme here

20160423 170810

 

layout