RFID and the Crystal Ball
Many objects these days are tagged electronically. When leaving a store, it’s possible that an alarm will go off if you leave with an item that still has a tag on it. A purchase can be made by waving a tag over a credit card machine. These technologies use radio-frequency identification (RFID) to tag and track items based on a chip placed on an item and a device that can read it. You can use this technology to trigger reactions in your LEGO creations, like the crystal ball you are going to build in this chapter.
The RFID chip contains a radio-frequency electromagnetic field coil that modulates a magnetic field ...