Lesson 8 Worksheet 8.1 – Line tracking sensor

The Edison robot is equipped with a line tracking sensor. The sensor is made up of two main electronic components:

  1. Red Light Emitting Diode (LED)
  2. Phototransistor (light sensor)

The LED shines light on the surface that the robot is driving on. If you press the round button on Edison twice the LED will come on. By lifting up the robot slightly have a close look at the round spot of light that the LED produces on the surface. Compare how bright the spot of light is when placed on either a black or white surface.

Is the spot brighter (reflects more light) when placed on black or white? ____________

The phototransistor component is a light sensor and measures the amount of light that is reflected from the surface.


As you saw from the exercise above, there is more light reflected from a white surface than from a black surface. Therefore the phototransistor gives a higher light reading when on a white surface than on a black surface. This allows the robot to be programmed to behave and respond to the surface that it is driving on. A black surface is considered to be ‘non-reflective‘ and a white surface is considered to be ‘reflective‘.


How do you think the line tracker would respond to the following surface colours, reflective or non-reflective? (Hint: the light is red)

red surface ____________, green surface____________, blue surface____________

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