There is a 16mm wide black track in the white field. Our tracking car can drive along the black track automatically. No matter how the track is bent, the car can drive automatically. We all know that the reflectivity of white and black objects is different. Here we use red. The light is reflected through the ground to the photoresistor. By detecting the resistance of the photosensitive resistor, it can be determined whether the car is driving in the white area. If the detection is a black track, the car will change direction and the motor will stop and the red LED on the front of the circuit board will go out. Drive the car in the opposite direction so that the car always drives along the track. Instruction download link: http://attach01.-us-west-1.aliyuncs.com/IC/DIY-Manual/10168.pdf Model: D2-5 Name: D2-5 Intelligent Tracking Car DIY Kit PCB Size: 104x72x1.6mm Installation dimension: 104x72x55mm Working voltage: 3V Colour: blue Material: plastic + metal Note: Parts need to be welded; 2 AA batteries are not included Package Contents: 1 x DIY Electronics 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 +/- 1-3 cm.