I understand how you extend the number of digital ins and outs on an arduino using de/multiplexer chips, but how do you extend the number of analogue ports?
I'm looking into making a simple hardware controller for a synthesiser. It would have many pots, nearly 50! Although the design would be quite simple. When a pot value changes the arduino converts it into a MIDI control message and spits it out a MIDI port, simple as that.
Actually the multiplexor Ic's ARE used for expanding the number of analog pins.
The number of digital in/out pins is expanded with shiftregisters.
Check the playground for an example for using the 4051 mux, it will give you 8 extra analog ins, and they can easily be hooked up so you can have many more.