You for certain saw the soaring globes in shops of souvenirs. The device forcing the globe to soar, is called a magnetic levitator. In it there is a position sensor from which on a signal the electromagnet joins quickly and switched off, without allowing an object neither to fall, nor to stick to the core.
1. Take a ball from a computer mouse of old type (not optical).
2. Make the low-power electromagnet which is surely attracting to itself this ball at a voltage of 12 V and it is strong it holding.
3. Get or assemble two power supplies. One of them has to develop unipolar tension in 12 V at the current exceeding that which consumes an electromagnet. The second block has to develop bipolar tension in 15 V at current about 100 ma.
4. Pull out both phototransistors from the same mouse (strangely enough, in a ball mouse there are optical elements, just they others too). One of them will trace the provision of a ball, and - to be used by the second as the model light sensor. It is hardly possible to use in a magnetic levitator infrared light-emitting diodes from a ball mouse - they are too low-power. It is necessary to apply more powerful.
5. Collect an optomechanical part of the device. From above strengthen an electromagnet. At distance from which it still attracts a ball arrange to an optopar from an infrared light-emitting diode and the first phototransistor. The distance between them has to be more than diameter of a ball. Place the second phototransistor below that on it not only light of a light-emitting diode, but also surrounding light fell. At the bottom arrange a plastic cup with foam rubber that at power off the ball fell in it.
6. Collect an electronic part of the device according to the scheme provided according to the reference located at the end of article. The operational LM741 amplifier can be replaced with KR140UD708. Attach it to an infrared light-emitting diode, phototransistors and an electromagnet. It is not obligatory to establish three light-emitting diodes of visible radiation displaying existence of bipolar power supply of operational amplifiers and the included condition of an electromagnet. Do not forget to connect parallel to an electromagnet the diode in the return polarity at all (the cathode to plus, the anode to minus). Include food and bring a ball. Release it, and it has to begin to soar.