BeagleBone Black Linuxcnc with RAMPS 1.4 (part 1)

Recently I saw a news about using BBB connect to RAMPS-FD with LinuxCNC,  But problem is the RAMPS-FD is  still expensive compare to RAMPS 1.4.   I say to myself, why not just use RAMPS?

http://www.usinages.com/ressources/file/183401?sid=fc51dc402f87e25f3fa27fc31321e907

The first thing I do is to look for way to make RAMPS compatible with 3.3v (not sure why I did it, seem like BBB does have 5v tolerance).  There is a detail discussion on how to convert 5v version of RAMPS to 3.3v for Arduino DUE in the Deltabot forum, it very simple hack, basically remove 5v connection from the RAMPS board, and reconnect all of the to 3.3v, then replace the MOSFET that support 5V to 3V input.   Detail of modification could be found here.

I did some cost cutting by replacing PSMN1R1-30L with IRLB8743PBF, it $3.5 vs $1.20, else everything is the same as discuss in the forum. Here is the picture where I remove the MOSFET:

The problem is how to connect BBB to RAMPS, the original design is to RAMPS-FD, and try find a diagram that show the pinout of RAMPS connection to Mega, and I can't!!  It seem like there is no pinout information.  After a lot of googling.... I give up and create the diagram myself.

With that. all I have to do to connect the board with BBB, which I will update in my part 2 of my BBB to RAMPS 1.4 adventure.  Here is the finish board waiting to be connected.