MIDI interface?

[>>>marjan<<<]

Hi,

I'm looking for midi interface for a small casio type keboard
like this one:
http://www.maxmidi.com/diy/sk1/index.html
but while sk1 one has 32 keys mine has 49 so I need something
expanded. I like sk1 interface, it's simple but it has just
hex code no source code. I'd like something with 8031/51 but pic
is alright too. My kbd configuration is 4 data lines with diodes
and 12 lines, one for each key forming the kbd matrix.
There is simple pic interface for korg polysix but that one uses
8/8 matrix which I guess wouldn't work here.
I ask this hoping someone here has played with this sk1 interface
or made something like that with more keys.