Cool $5 Desk Toy

ercoerco Posts: 17,674
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

"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

- Pablo Picasso

Comments

  • 4 Comments sorted by Date Added Votes
  • 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.
  • How long does it run on a 9V battery?
  • ercoerco Posts: 17,674
    edited March 31 Vote Up0Vote Down
    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.



    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • ercoerco Posts: 17,674
    Why buy one when you can have three for thrice the price? Will use these in a project.

    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
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