Hi, Based on a request, I have put this together as a complete How-To on the ArduinoInfo.Info WIKI HERE: It looks like this, and is a handheld Ultrasonic distance sensor with audio output (So it's kind of like a handheld Bat):
The Project announcement is HERE:
Also available as an Instructable HERE:
This project is now linked to a section called Understanding the Science Behind the Ultrasonic Distance Sensor (click): That in turn links to Educational Lesson Plans and a SlideShow that can be used in the classroom (My wife is still updating that). If anyone uses this in a class or helps a teacher do this please let me know. I may make a low-cost parts kit available. UPDATE: Kit available HERE: DISCLAIMER: Mentioned stuff from my own shop...!!
Any feedback or suggestions appreciated!