Hi,
some time ago I made an Arduino based custom control surface for DSI Tetra to control 95 or so parameters (via NRPN), inspired by the Waldorf Blofeld button-encoder matrix. I thought I’ll drop the info here too. Here’s a video of the basic operation:
I also posted DIY instructions & the code on the DSI forum, here’s the link in case anyone’s interested. Stupid though that you have to register in order to read the forum.
http://dsiforum.com/viewtopic.php?f=19&t=6778