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In lugnet.build, Christopher Snead writes:
> Hello, everyone!
>
> I've finally finished a project for my Physics class:
>
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=8857
>
> This device suspends small, ferromagnetic objects in midair using an
> electromagnet and a beam of light. The beam of light shines on a
> phototransistor, which translates via a control circuit into current to the
> electromagnet. An object in the path of the beam reduces the amount of light
> incident on the phototransistor. As the object falls, more light reaches the
> phototransistor, and the magnet gets stronger; as the object moves towards the
> magnet, less light reaches the detector, translating into a weaker magnetic
> field. The object reaches equilibruim, and hangs in midair!
Very cool! I was wondering, if you photographed the object using a
flash, wouldn't the object drop a fraction of a second after that ?
Also, I understand that the light shines from the right side,
and enters a photodiode on the left side (or the other way around).
So, if the object is exactly in the middle, there is no
relevant difference to measure, and neither if the object is getting
too low.
What are the highest frequencies you find on the output of the
phototransistor ? This would give an indication if it was possible
to do it all with an RCX, a lego lightsensor and lego lamp, with
either a slow language like BrickCC, java, or LegOS. Oh, and you
have to take into account the maximum sampling frequency of the
light sensor. Since I read that the rotation sensor cannot be sampled
with more than 300 Hz, there is probably a similar limitation for the
light sensor. Dunno if this is hardware, or a timer value in software
of the RCX firmware.
Mark-Jan
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Message has 1 Reply:
 | | Re: Magnetic Levitator
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| (...) The Phototransistor and diode are recessed deep inside the technic bricks, which make very effective lightshields. (...) The object is in the middle, but off of the axis formed by the phototransistor and the diode. the object only partially (...) (23 years ago, 8-Dec-01, to lugnet.robotics)
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Message is in Reply To:
| | Magnetic Levitator
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| Hello, everyone! I've finally finished a project for my Physics class: (URL) device suspends small, ferromagnetic objects in midair using an electromagnet and a beam of light. The beam of light shines on a phototransistor, which translates via a (...) (23 years ago, 6-Dec-01, to lugnet.build, lugnet.general)
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