Magnetic Suspension Device


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This is a simple device which suspends objects a cm below an electromagnet. If put in a proper casing it can make a wonderful display piece. Here is the circuit.

 

Circuit

The circuit basically turns the electromagnet off when an object gets to close, and turns it on again when no object is detected. This simple scheme lets it adjust for the weight of the object automatically. The signals from the sensors are compared, and an output is sent out. The output goes through a lead compensation network, which I don’t fully understand. ;-P From what I can tell it filters out low frequency changes, while letting high frequency signals pass. (For anyone who builds this later, try cutting out the lead compensation network, and just putting a 100nf capacitor between output and input. Let me know if it works!) Either way, it weakens the signal, so it is sent through an amplifier which drives the electromagnet.

 

Construction Details

The circuit says it all. The top detector is a reference detector and the bottom one senses when an object is in  position. Just build it and mount the IR photo detectors as shown, with an IR LED level with the object detector. The reference detector should “see” what the object detector sees, but never have it view of the IR LED blocked by an object.

The electromagnet should have maximum 15 ohms of resistance, any more and it will not be able to lift anything. Coil size should be about 3.5 x 3.5 cm, although fatter coils may work better. The coil can be wound around practically any iron or steel bolt. Round the end of the bolt with a file, as this will “balance” the magnet. I forgot to do so, and as a result objects tend to hang over near the edge of the bolt.

Often it is best to build the circuit in two parts, part 1 with the detectors and first op-amp, just to make sure the output swings when an object is put in the beam. And then part 2 with the rest, this way it will likely work the first time. 

Troubleshooting

If the device fails to suspend anything, but objects “flutter”, you will need to adjust the lead compensation network. Try changing resistor values and capacitor values. The lead compensation network is the 150K, 1K resistor and 100nf cap between op-amp 1 and 2.

If the coil doesn’t turn off even when an object is put in the beam, check the reference and object detectors.

Suspended Objects


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