This is a simple magnetic levitation circuit which suspends objects a set distance below an electromagnet. The physics behind it is to simply provide a magnetic force which equal and opposite to the gravitational force on the object. The two forces cancel and the object remains suspended. Practically this is done by a circuit which reduces electromagnet force when an object gets to close, and increases it when the object is out of range.
This magnetic levitator circuit works by comparing the signals from the sensors with the first op-amp and sending out a voltage proportional to the difference or “error”. The error signal is then sent through a compensation network which acts a high-pass filter, allowing quick changes in error to pass easier than slow changes. This is required to stabilize the control loop, and without it objects would just flutter close to the electromagnet due to the system being unstable. The signal is then amplified to it’s original amplitude, since the compensation network attenuated it, and finally drives the TIP122 Darlington transistor, which controls the electromagnet current.
The extra diodes around the transistor are to prevent damage to the transistor. The signal diode on the base prevents reverse biasing the base, which is damaging, while the two 1N4001’s give a path for the magnetizing current to flow when the electromagnet turns off. The optical components used aren’t too critical, as long as their wavelengths match up ok, and the detection/emission angles aren’t too narrow. The IR LEDs are TIL38, which are 940nm peak, have 15 degree spread, 35mW and 100mA max. The detectors are PT204-6B, which are IR phototransistors.
Read more informations about this interesting project on the source page http://uzzors2k.4hv.org/index.php?page=magneticlevitation