Youmile Infrared IR Line Track Follower Sensor Module Obstacle Avoidance PCB Sensor Module 4-Channel with DuPont cable for Smart Car

Used this with a Raspberry Pi 4. The four sensors can be separated and adjusted with each potentiometer. There's an LED for each sensor - when the light is red the IR beam hasn't been broken. When the light is out the beam is being broken on the range set by the pot. There's a lot of fine adjustment that can be made. Additional cables are provided too - real value for money.