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J_Hodgie writes –

This Instructable will show you how to make a device that can float almost any object with a magnet in it.

It is much like the floating globes you can buy, except it works by balancing the forces of permanent magnets with electromagnets, rather then simply using combinations of permanent magnets. This is done by using a microcontroller and an IR sensor to detect where an object is floating below. Then based on a set value, the microcontroller uses the electromagnets to to hold the floating object at a given height.

The place the object floats at depends on the weight of the object and the power of the magnets in the object. The height is set by holding the object under the magnets and sensor and pushing the button.
The object floats at the point where the force of gravity down equals the force of the magnets pulling up, which allows it to use non-industrial electromagnets and less power to float. The program also dynamically adjusts so the object is always at the perfect height.

I decided to make the electromagnetic floater because I have always been fascinated by the floating globes in the store, but I never wanted to pay their prices, and I never liked how they only floated objects that you had to buy or came with it. So, I decided to make my own that could float anything with a magnet. The results are what you see here.

instructables : Electromagnetic Floater – Link.