Cool $5 Desk Toy
erco
Posts: 20,261
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
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
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.