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June 27, 2009
News - Enginursday: Levitating L…
about 7 months ago
Thanks for the reply Alex. My issues were primarily with the power supply. The DC resistance of the inductor and the on-resistance of the FET are really low. As a result, supplying 12V would result in some ridiculously high current. My supply was going down to 0.09V and 3.12A. The 12V was also powering the LM358, so when the voltage dropped it was no longer functioning properly. I isolated the problem by using separate power supplies for the FET/electromagnet and the rest of the circuit and that was able to fix the problem.
As a side note, I did notice that the resistance of the electromagnet significantly increases as it heats up. At that point the supply can push 12V 3A. The demand on the supply significantly reduces its slew rate so for anyone else with this problem I found it worked best adding a 4 Ohm power resistor in series with the electromagnet.
Awesome post. I’m a bit stuck on the levitation circuit though: What kind of power are you pulling running this?
I built this circuit part-for-part and I’m noticing that powering the FET drags the supply down considerably. The electromagnet has really low impedance at DC so this makes sense - I’m seeing my 12V supply drop to 0.09V at 3.12A when the FET is conducting. This also messes with the voltage on the rest of the circuit (since I’m driving an LM7805 to generate the 5V reference and it’s source is dropping out).
Next attempt is to use two isolated supplies for the decision making portion of the levitation circuit and electromagnet driving portion. Any tips would be much appreciated!
about 6 years ago
Could you please put a speaker next to the ruler so we can see how big the ruler is?
about 7 years ago
Long story short - its a two-way transducer.
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