There is a 16 mm wide black runway in the white field. tracking car can drive along the black runway automatically.No matter how the runway is bent, the car can be automatically.We all know that the reflectivity is different when the to the white objects and black objects.Here we use red .The light is reflected through the ground to the photoresistor.By detecting the resistance of the photosensitive resistor can determine whether the car is driving in the white area.If the detection is black runway, then the car to change the direction of driving and motor will or even stop and Red LED OFF on PCB front side.Drive the car in the opposite direction so that the car is always running along the runway.Instruction Download link:http://attach01.-us--1.aliyuncs./IC/DIY-Manual/10168.pdfModel: D2-5Name: D2-5 Intelligent Tracking Car DIY KitPCB Size:104x72x1.6mmInstallation dimension:104x72x55mmWork Voltage:3VColour:blueMaterial:plastic+metalNote: Parts need to be welded; 2 AA batteries are not includedPackage Contents:1 x DIY Electronic KitOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.