A two-sensor line follower has one light sensor on each side of the line. Its program is a set of rules: if the left sensor sees black, the line has moved left, so turn left; else if the right sensor sees black, turn right; else (both white) the line is between the sensors, so go forward. The robot checks many times a second and wiggles gently along the line. When both sensors see black, the first true rule decides.
Turn towards the line — “the sensor that sees black shows which way the line went”
Left sees black → turn left; right sees black → turn right; both white → go forward.
In an if / else if chain the first true rule wins (both black → the rule written first).
With numbers: a reading below the threshold (for example below 40) means black.
Use it for: Programming a line follower robot, robotics competitions and if / else practice in coding.
Worked example: ⬛ A line follower runs:
if (left sees black) { turn left } else if (right sees black) { turn right } else { go forward }
The left sensor sees black and the right sensor sees white. What does it do? → turn left
The first rule asks: does the left sensor see black? Yes.
Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.
Right: 0 · Tried: 0
🏁 Lesson 24 test
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
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