inspired by TWIT.TV KnowHow Episode 178 about Arduino Collision Avoidance https://twit.tv/shows/know-how/episodes/178
Arduino code rewritten extensively
Enclosure pretty much designed from scratch using OpenSCAD
Used VERY handy OpenSCAD routine from WarrantyVoider, published May 26, 2011 http://www.thingiverse.com/thing:8812 see README_attributions