Line Following Glossary

Quick definitions for the core terms used in this session.

ColorSensor: The Pybricks tool for the SPIKE Prime color sensor. It can read colors and, today, how much light bounces back off the floor. You create it with the port it’s plugged into: line_sensor = ColorSensor(Port.D).

reflection: How much light bounces back to the sensor, as a number from 0 to 100. Black tape reflects little (a low number); a white floor reflects a lot (a high number). You read it with line_sensor.reflection().

threshold: The dividing line between “I’m over the line” and “I’m over the floor.” We set it to the midpoint between the BLACK and WHITE readings — that’s the value you’d read right at the edge of the line.

BLACK: The reflection reading you measure on the tape. It’s a calibration value, not a fixed number — measure it on your own tape.

WHITE: The reflection reading you measure on the floor. Also a calibration value you measure yourself.

deviation: How far the current reading is from the threshold (reflection() - threshold). Zero means you’re right on the edge; a big number (plus or minus) means you’ve drifted off.

proportional control: Steering in proportion to how far off you are — a little off means steer a little, way off means steer hard. It makes the robot follow the line smoothly instead of jerking side to side.

GAIN: The number that decides how hard the robot steers for each unit of deviation. You tune it: too low = sloppy (drifts off the line), too high = wobbly (swings back and forth). Finding “just right” is the whole game.

edge (of the line): The robot follows the edge of the line — half on the black tape, half on the white floor — not the dead center. That’s why a small, steady wobble is normal.

calibration: Measuring what the sensor actually reads on your tape and floor and setting the numbers to match. (“Black read 12, white read 78 — so the threshold is about 45.”)

while loop: while True: repeats the steps inside it forever. The line-follower keeps reading and steering until you press the editor’s Stop button.

bug: When the robot does something you didn’t want. It’s not a mystery — it’s sensor data: the robot did exactly what the code said. Read the code (and your numbers) to find what you actually told it to do.