Security Plate, a pressure plate detecting the weight changes with light sensor built with LEGO Mindstorms EV3

Weighing plate, using weight change block

The sensor of the robot from the previous lesson was binary. This means there was only one state possible – either there is an object or there is no object. Therefore, it was very easy to press the plate, take the exhibit and put a stone instead. And the system could not detect us anyway. That is why now we have to think of something better in order to protect the valuable exhibits.

A clever solution is to have a robot which “senses” each change in weight. If the weight is greater, this will mean there is someone pressing the plate and the system should trigger the alarm. If the weight becomes lower, this will mean someone has stolen the exhibit and the alarm should also go off.

A phone holder that rings an alarm when the phone is picked up. It is a plate, lying on a rubber wheel, that changes its height, based on the weight of the object placed on top. The color sensor detects these changes and rings the alarm. With some fine tuning, this robot can even act as a weighing machine.