This looks like a pretty fun kit – “This simple electronic kit uses magnetic levitation to suspend small objects up to about 1/2 ounce (15 Grams) or so in mid air. The air gap is about 3/8″. The electromagnet dynamically controls the position of the suspended rare earth magnet(s) attached to the levitated object. Feedback is provided by a linear Hall Effect sensor mounted under the electromagnet. Suspended objects are absolutely stable after settling.” Link.