I am building a distance sensor..I have the ucontroller portion done. I was going to use IR to reflect a beam and get a proportional analog voltage to estimate distance but...it has no range
You want an IR distance sensor like this http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=164
(I am sure there are lots of sources).
Just hook it up to an analog pin of your UC and you will get your proportional voltage.
I think a key to this kind of thing is to modulate the IR. Then in the detector have a lot of gain in the band you used to modulate the signal. This lets you extend the range without picking up a lot of other light noise. Reflection can depend a lot on the surface you are reflecting from so distance is still uncertain. Using time of flight is a different method, but to measure 30 cm involves measureing down to 1 nano second with light, easier to apply to sound. There is also triangulation using light, do not know any simple, reliable systems using this. Unless you are really into buiding your own I would consider buying one, perhaps as the earlier suggestion.