The multiplexer module (or tangle module) provides MIDI controlled routing. It can change patches with a program change message. The thought is that it can be used to recall patches during a performance, or between songs. The schematics and PCBs can (eventually) be viewed on CADLab.

This circuit consists of eight analog multiplexers, where each output is buffered and can select one of the inputs. This means that several outputs can select the same input, but an output can not give a mix of two inputs. There is a bi-color LED on each output indicating their voltage.

The buttons are connected in a 2x4 matrix to save pins on the MCU. Actually, the red LED is connected to the data pin of the programming interface because absolutely all the pins were used.

Laying out this PCB (left) has been my biggest routing challenge to date. I all the parallel traces pretty satisfying.

I had to do some botching (right PCB) because floating inputs would pick up signals from other inputs.