Another, interesting arduino based step sequencer.
Very well documented.
People are just harvesting hardly!

as we want to connect 20 buttons, 2 potentiometers
and a 12 scale mode-selector, we need a total of 34 inputs. additionally, we want to control 20 led´s, so we need 20 digital outputs. the arduino has 6 analog inputs and 14 digital inputs/outputs, which is obviously not enough, so we are going to use five 4051 analog multiplexers to multiply our analog inputs and create a total of 40 inputs, and three 595 shift registers to multiply our digital outputs and create a total of 24 outputs.

Code Ready. Wow.
via [openskinnerbox]