This video shows how the line follower works:

First of all, it's necessary to calibrate de IR sensors, which are readed as analog signals in order to get a smoth PD controller response.

The LEFT button enters calibration mode: In this mode, the first step  is to show the robot what is the color of the track, in order to get  the "floor" IR reflections...

The next step is to show the robot the line color and measurement what is the "lowest" white.

With track color and line color, then the robot can normalize each of the 16 IR sensors individually, tho achieve the low and high values and get a total range.

Once the calibration in done, the OLED screen show what the robot sees in each sensor and is ready to run...