I would love to read about that!
Basically it was just a big ass 8x8 switch matrix made with multiplexers and shift registers and cobbled together with some diode logic. This gives 64 "buttons", some of which are wired to rotary encoders and the rest are buttons and switches.
It's got enough knobs and buttons to deal with all the navigation and communication instruments in a small civilian aircraft. Alternatively, I've thought of using it as a MIDI or similar controller for my software synth projects.
The coolest feature was that there is a row of backlit buttons that have two colored, two wire LEDs. Current goes one way -> LED is red, current goes opposite, LED is green. Alternate the current direction quickly and you get yellow. This is used for autopilot status indicator, e.g. when running in heading hold (HDG) mode and going to intercept a VOR or ILS beam, the HDG led is green and VOR led is yellow. When you intercept and autopilot changes mode, the HDG goes off and VOR goes green.
Right now it's gathering dust, which is a shame but I haven't had time for flight simming in ages. Building this thing cost me a lot of money since I bought all the hardware new, and big beefy switches are damn expensive.
I learned a lot when doing it. Like that electrical current flows both ways in a copper wire. I felt really stupid when I realized that I must use some diodes to get my switches working.
They're the best part about projects like this, though :) Right now I'm working on the most overbuilt egg-timer known to man with big chunky rotary switches to input the time.
The only issues I had were getting the LUFA firmware built to make the device work as a USB HID game controller.