This small board displays the state of 16 of the GPIO pins of the Raspberry PI. It also features 4 push buttons to demonstrate 4 pins configured as inputs. It plugs directly on the 40-pin header of the Raspberry Pi.
Circuit diagram

Small low level demo program written in C. To use it :
- create a dedicated directory on the Raspberry Pi, for example rpitest
- copy to this directory the following files : rpitest.c, bcm2835.c, bcm2835.h, Makefile
- change to the new directory and enter the following commands :