I have this nice Dynon EFIS in my airplane. It does just about everything all those old-fashioned airplane instruments do, all in one package, as well as some fancier things like an angle-of-attack readout (lower left colored bar)
While that AOA readout is great for making smooth landings, it's tough to see with a quick glance away from the runway that's approaching at freeway speeds.
So after getting Arduino to speak serial at 115.2Kbps by replacing the crystal and hand-compiling the binary images, I was able to connect my Dynon EFIS to a Protoduino board and set up a nice angle-of-attack and rotation-speed readout, right in my line of sight on top of the glareshield.
The 9 LEDs create a "bar graph" of the current angle-of-attack -- I have it set up so that any less than 3 LEDs is closer to stall than I want to be during the landing sequence. On takeoff, it will flash a few LEDs at rotation speed and Vy. The display dims with each press of the pushbutton in the middle.
The board is a Protoduino trimmed to remove the top half which wasn't needed for this project, and to keep the size small and inobtrusive. Since there's no need for outgoing serial communications, there's no need for a MAX232 or anything like that -- I just used a MC1489 quad-receiver which translates the incoming RS232 signal to TTL levels.
Here's a view in flight. You can just barely see the multi-color AOA display in the lower-left corner of the Dynon. The LEDs are quite a bit easier to see!