I've actually used these IR ranging sensors before. They have circuitry built-in, so the interface is really simple (the drawbacks are that the output is non-li

I've actually used these IR ranging sensors before. They have circuitry built-in, so the interface is really simple (the drawbacks are that the output is non-linear with respect to distance, and the time between outputs is kind of slow ~50ms): http://www.acroname.com/robotics/info/articles/sharp/sharp.html http://www.acroname.com/robotics/info/articles/sharp/sharp.h... He uses a lot of LEDs. If I were to design something like this, I'd just use a speaker from a PC case and have it beep different tones depending on the distance to the object.