There is a 16 mm wide black track on a white surface. The tracking car can follow the black track automatically. Regardless of how the track is curved, the car follows it autonomously. A red light source is used, as white and black surfaces reflect light differently. The light reflects from the surface to a photoresistor. By detecting the resistance of the photoresistor, the system determines whether the car is over a white area. If the sensor detects the black track, the car adjusts its direction, the motor slows or stops, and the red LED on the front of the PCB turns off. The car then steers to stay aligned with the track. Model: D2-5 Name: D2-5 Intelligent Tracking Car DIY Kit PCB Size: 104 × 72 × 1.6 mm Installation Dimension: 104 × 72 × 55 mm Operating Voltage: 3 V Color: Blue Material: Plastic and metal Note: Soldering is required; batteries are not included. Package Contents: 1 × DIY Electronic Kit Note: Only the items listed above are included. Other accessories are not included. Note: Due to variations in lighting and display settings, the actual product color may differ slightly from images. Measurement tolerance: ±1–3 cm.