A 16 mm wide black track is located within the white field. The tracking car can follow the black track automatically, regardless of how the track is curved. Due to the difference in reflectivity between white and black surfaces under a light source, this system uses a red light source. Light reflects from the surface to a photoresistor, and by measuring the resistance of the photosensitive resistor, the system determines whether the car is on the white area. If the black track is detected, the car adjusts its direction, changes motor operation, or stops accordingly. A red LED on the front side of the PCB turns off when black is detected. The car drives in the opposite direction to remain aligned with the track. Model: D2-5 Name: D2-5 Intelligent Tracking Car DIY Kit PCB Size: 104x72x1.6mm Installation Dimension: 104x72x55mm Operating Voltage: 3V Color: Blue Material: Plastic + Metal Note: Soldering is required for assembly. Batteries not included. Package Contents: 1 x DIY Electronic Kit Note: Lighting conditions and display settings may cause slight variations in color between the product image and the actual item. Measurement tolerances are +/- 1-3 cm.