As a follow on from my stuff on 16-to-2 multiplexing, here is a working standalone thingy. A 16-step sequencer.
This sequencer uses 16 to 2 multiplexing (via 2x 4021s), an SPI digitally controlled pot, an Arduino board and a square wave generator based on a 555.
The 16 pots to the left are the pitches. They are laid out like so (in terms of loop order):
02 04 06 08
10 12 14 16
01 03 05 07
09 11 13 15
The two pots on the right are tempo (lower one) and overal pitch (upper one).
I made a video of the whole affair. Check it out here: http://www.youtube.com/watch?v=pjxGPaUQrRg (length is 2:04).