Ultrasonic Distance Sensor

Requirements

• 1mm accuracy optimal, 3 mm is absolute max

Selection

• Maxbotics - 1 mm resolution options, not water protected - 12" minimum distance - $40 - [1]. Adafruit has it.

Comparisons

• http://www.robotshop.com/en/compare-infrared-ultrasonic-distance-sensors.html

Sourcing

• 4-30 cm - $99 - [2]
• 1-100 inch - $25 - [3]
• $4 Sparkfun - 6"-10' - [4]
• $6 - .5 cm accuracy - [5]