It floats in mid-air! Its magic!!

Not magic. Its a PID loop-controlled electromagnet.

Check out the videos. Short version:

Longer, with explanations:

Designed by Mr. Halverson at El Rancho High, built by Halverson and Miguel Limon, this magnetic levitator holds a small iron or steel object in mid-air, using an electromagnet. The electromagnet's strength is controlled by a circuit that constantly checks to see if the object is beginning to fall or go too high, and if it is, the power of the magnet is increased or decreased as needed.

Here is a circuit diagram of the levitator electronics.


For insights into how the op-amp circuit works, look in The Art of Electronics by Paul Horowitz and Winfield Hill. We used their derivative circuit.

Here's a picture of the levitator in action. No strings! Just the electromagnet holding up that steel eyelet screw. The black foam is for partially blocking the light of the photodetector.