Make a consistent line tracking sensor for your next robotic project! All you need is to shove a photoresistor and led into the holes they fit into and hook it up to an analog pin in your arduino or other favorite microcontroller. Original design... intended for my robotics class robot. Cadd files are included let me know if you need a different one! Was messing around with hole size, may need to drill out depending on how accurately your printer is calibrated. UPDATE: 12/15/14 Works great on final robot! Very consistent linear response. We used an op-amp wheatstone bridge type circuit to be fancy.....see images. Wiring diagram included. Thanks to Bradd Libby. Source: https://braddlibby.wordpress.com/2012/12/23/arduino-light-sensor/arduino-light-sensor-circuit-diagram/