Hi Asish-The best I can tell, it works like this:The OP amp is being used as a comparator. Notice that R5, the feedback resistor, is going from the output to the NON-INVERTING input. Normally the feedback resistor would go to the inverting (-) input. The circuit starts out by turning on the lifting coil L1 hard. The sphere containing a magnet begins to lift toward L1. The magnetic field from L1 will cause the Hall effect sensor to produce a voltage that exceeds the threshold set by P1, so the Op amp (somparator) turns off L1. If the magnet in the sphere is close enough to the Hall effect sensor, L1 remains off, allowing the sphere to drop a little. If the sphere is already too far away, the comparator will turn L1 back on again, lifting the sphere. It's important to recognize that although the sphere will appear to be stable below the lifting coil, the circuit is actually oscillating (chasing it's tail), so the coil L1 is constantly switching on and off to maintain the sphere in the "suspended" position.I hope this makes sense.-Rick
