There is a 16 mm wide black runway in the white field.Our tracking car can drive along the black runway automatically. No matter how the runway is bent, the car can be driven automatically.We all know that the reflectivity is different when the light source to the white objects and black objects.Here we use red light source. 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 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. Model: D2-5 Name: D2-5 Intelligent Tracking Car DIY Kit PCB Size:104x72x1.6mm Installation dimension:104x72x55mm Work Voltage:3V Colour:blue Material:plastic+metal Note: Parts need to be welded; 2 AA batteries are not included Package Contents: 5 x DIY Electronic Kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.