It’s been only a couple weeks since I discovered Arduino, an open source microcontroller platform. I was looking for a cheap interface between my laptop and electronic circuits. Arduino with its price $35 and easy to use development environment was the best choice. So after getting my Arduino Duemilanove board and ordering some cheap components from AllElectronics, I had everything to start working on my old dream, making a magnet fly. Well, float.
Update: detailed description here
It took only a few days to figure out all the problems and my magnet floating device was born:
As you can see by the blurred edges, the tiny magnet oscillates a bit. After a good calibration, the oscillations can be kept very small and the magnet can keep hovering for minutes. The big dart is much more stable and can float pretty much indefinitely. The device uses a small Hall effect sensor (SS19 from Honeywell, available for $0.50 from AllElectronics) to sense the field of the permanent magnet and uses that information to modulate the magnetic field of the electromagnet. Since the sensor is on the electromagnet,
the reading on it is the sum of the fields of the floating magnet as well as the electromagnet. The greatest challenge was separating these two and getting the floating magnet’s field only. After some theoretical research into inductors and the Amper’s law and experimentation, I achieved pretty good stability of a hovering magnet or a magnetic dart or whatever. The result is not completely perfect, some small oscillations are still noticeable. I think that I achieved the limitations given by the Arduino A/D converter. There is always some noise to be expected. I will post more details together with the source codes for both Arduino and my Mathematica 6 control center when I find just a little more time. I even created this blog because I wanted to share this beauty with the world 
Read more: Magnetic Levitation using the Arduino