# Teacher's Notes: Solution for the Weighting Plate 3.0 Tasks ProPreview

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• #1104
• 08 Feb 2019

In order to use the weighing plate, we should first explain its working principle. The weighing plate is a rubber piece which goes down due to the weight of an object. The change in height decreases the distance between the plate and the color sensor. Therefore, the amount of reflected light is different, which changes the value measured by the sensor. In fact, we have some sort of a weighing machine.

Alarm

Let students have some fun with the alarm. It is important to use a tone and change its duration.

You should first show the port view option to students. Then, they should find the value measured by the sensor.

Program the plate to measure the brightness at the beginning of the program and to wait for a change in the value in order to trigger the alarm.

You can explain to students what calibration is. Use the wait compare block.

Program the weighing plate to wait for a 2% change in the value and to trigger the alarm.

Have some fun! Try to steal the phone without setting the alarm off or shutting the robot down:
When the color sensor cable is cut, the program will receive the value of 0. This is a huge change which is detected by the wait change block and the alarm is set off.