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Using the Autoset mode to set sensor conditions for bright and dark looks deceivingly simple. However, students may have difficulties in both understanding the concept of a neutral reading and in actually obtaining one when first running the program.


What you can do: You can start by explaining manually set ranges. Tell students that there is some trial and error involved in determining the best ranges for a problem. Point out that getting light readings using the View button can reduce the guesswork involved.

You can model the steps you would take in solving a problem. For example, using a black marker, draw two dime-size circles on a piece of paper and color them in black. Attach a light sensor to a long connector wire and connect to the RCX. Moving the light sensor over the paper, tell students that you want the RCX to beep each time it detects a black circle.

Explain that before you write the program, you would get a light reading over a black circle, say 38. You will then use this number to help you determine the dark range where you will tell the RCX to beep. In this case you will probably set the range to 35-40.


Use the problem of having a vehicle moving on an area and stopping when it gets to a brighter area (e.g., move about on the floor and stop when it reaches a white sheet of paper.) to introduce the idea of an automatically set range.


Explain that what constitutes bright is defined by what the program considers as neutral. Point out that “bright” is used here as a relative term, where bright means a higher reading than neutral. In this case, the light sensor is pointing to the floor where it gets its first light reading, establishing this as neutral. As long as the white sheet of paper is brighter than the floor, the vehicle will stop when it gets there.


© The LEGO Group

As shown here in the StopBright program a robot will move forward in ambient light and to stop when the light is brighter.


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