Ultrasonic range finder

Maxsonar
檢測距離範圍：6~254inches (15.24cm~6.45m)
啟動時保持36公分的淨空較佳(至少18)
Datasheet - maxbotix
FAQ

電路與arduino sketch教學(analog&PWM singal)
http://craft.mos-com.net/articles/arduino-maxsonar-ez1/

Reading analog values with an Arduino
An example using an ultrasonic distance sensor
http://sheepdogguides.com/arduino/aht1a.htm

用平均值之方式穩定數值(arduino sketch)
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1226321702

Simple fix for when electrical noise interferes with the MaxSonar sensors.