Infra Red Sensor
IR reflective sensors have one emitter (IR LED) and one receiver (Phototransistor or photo diode. If we have white surface it reflects the light and it will sensed by the receiver, similarly if we have black surface it absorbs the light and receiver can not sense light.
Photo
diode has property that if IR light fall on it its electrical resistance comes
down (i.e. it comes down from 150kΩ to 10kΩ if no noise present).
