Parallax QTI Sensor, Close-Proximity Infrared Sensor (555-27401)The QTI Sensor is a close proximity infrared emitter receiver that is able to differentiate between a dark surface) with low IR reflectivity) and a light surface (with high IR reflectivity). These little sensors can be very handy for line following, maze navigation, or sensing the outer rim of a SumoBot ring. Wiring options allow it to be used digitally for fast black white line following, or as an analog sensor to detect different shades of gray. A