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Cool $5 Desk Toy — Parallax Forums

Cool $5 Desk Toy

ercoerco Posts: 20,256
edited 2017-03-30 21:49 in General Discussion
Mom, erco's spending my lunch money again!

Geeky tech educational fun. 9V battery powers an electromagnet in the base to keep the PM top spinning. The only component is a switching transistor, very simple. Electromagnetic coil is slightly off-center in the case. Coil is center-tapped, actually way off center. The electromagnet is ~67 ohms, the sense coil is ~15K IIRC, connected directly to the transistor base lead.

I added an LED & 1.5K resistor across the electromagnet coil to indicate when the power is on. LED polarity doesn't matter since the pulsing DC signal generates a reverse voltage across the coil as the field collapses.

http://www.ebay.com/itm/162112717652

Comments

  • MikeDYurMikeDYur Posts: 2,176
    Seen this on my eBay page the other day, the top could use a little Sharpie marker to add some contrast. Neat little gadget to demonstrate the principles of magnetic induction.
  • localrogerlocalroger Posts: 3,451
    How long does it run on a 9V battery?
  • ercoerco Posts: 20,256
    edited 2017-03-31 02:30
    localroger wrote: »
    How long does it run on a 9V battery?

    Gotta be a day or more, I've run mine for several hours and the carbon zinc battery still measures 9.3V. I stopped running it continuously because it gets into such a repeatable orbit that the tip of the spinning top polishes its path on the black plastic base. I didn't want to wear a groove in it. :)

    It's so regular and rhythmic that somehow there's a clock in there. For some reason the chrome top reminds me of the Foucault pendulum at the Smithsonian that knocks over markers every few minutes.



  • ercoerco Posts: 20,256
    Why buy one when you can have three for thrice the price? Will use these in a project.

  • ercoerco Posts: 20,256
    Today's affordable Ebay educational science project was building this Da Vinci clock kit. $14-20 on Ebay/Amazon. A very cool desk toy and a fun hour assembling with the twins. Easy assembly, although some of the press-fits were tight and it took Dad to squeeze the parts together. I'll defer to this guy's video since I can't do any better. "I was watching paint dry then I remembered this..." :)

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