I told myself ,seeing his stuff, : OMG, I could use the *useless* vmu 2de port as a hub for custom controllers !
So i did. I cuted the vmu port pins and linked them to the corresponding buttons of my Dreamast controller (and its ground) then modded a Nes pad by removing the controller chip and putting wires in the corresponding holes of all the buttons (and ground) then connect it to the same pins as my controlelr's ones using a rumble pack shell.
It works perfectly... To play elevator action with a nes pad is better than with a DC pad, don't you think ? And the way I did it, no one would notice sketchy holes in your controller.
note: vmu 2de port can't be used anymore for anything else that nes controller, Snes controller would be feasible too, and a psone controlelr would be possible using the 2 vmu ports.
pics:
Modded Nes controller alone:

Modded Nes controller rear:

Modded Dreamcast controller alone:

Modded Dreamcast controller rear:

Everything plugged in:

[EDIT=Internals Pictures]
Nes controller top and Rumble Pack Shell

Nes controller other side and Rumble Pack Shell

Dreamcast controller top

Dreamcast controller other side

Done in 2.5 days
Thank you ! Any Comments are welcome !
-=FamilyGuy=-




