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Topic: Accelerometer for sensing how fast a poi is spinning? (Read 2 times) previous topic - next topic

johnwasser

Maybe instead of detecting the acceleration shifts you could have an infrared beacon on the ground and an IR sensor in the poi to detect when it was passing near the beacon.  A pulse per revolution will tell you how fast they are spinning.  Something like a BlinkM (ATtiny plus RGB LED) can probably do the trick.  If you use an IR beacon you might even use it to send a pattern allowing you to switch light programs.
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Magician

The really "ingenious" solution I've seen in the book:
"tinyAVR Microcontroller Projects for the Evil Genius™".  :)
Author refers to Elektor magazine, December 2008("LED Top with Special Effects"), (magazine probably would be easier to find in the library)
Motion sensor include two coils and OPA's, that sense Earth magnetic field. It allows to get speed, direction of rotation, plus synchronize leds for POV effects. Last feature is impossible to obtain with accelerometers or force sensors.
I'm not sure why hall effect sensors were not used in design?

jfeldstein

Wow! So many ways to approach the same problem.

IR beacon is tough, because I won't always be in the same place, and may often move while playing.

I'm going to read up on how the magnetic option works. I think it'll wind up being too complicated for what I'm doing, but sounds really cool to know.

What do you guys think about measuring tension in the rope? Instead of measuring gravity at the end of the poi, measuring the poi's pull on the handle in your hand..?

MarkT


The really "ingenious" solution I've seen in the book:
"tinyAVR Microcontroller Projects for the Evil Genius™".  :)
Author refers to Elektor magazine, December 2008("LED Top with Special Effects"), (magazine probably would be easier to find in the library)
Motion sensor include two coils and OPA's, that sense Earth magnetic field. It allows to get speed, direction of rotation, plus synchronize leds for POV effects. Last feature is impossible to obtain with accelerometers or force sensors.
I'm not sure why hall effect sensors were not used in design?


Accelerometer wlll give synchronization, the centripetal force has a gravitational component that's a rough sinusoid(*) added onto a mean force - so long as its spinning in a vertical plane (if not it will be hard to see the PoV pattern anyway).  High speed spinning will possibly drown out the gravitational signal, but smooth low speed circles should show it up nicely.  Implementing a software PLL to pick out the phase will be an interesting problem too :)

(*) the maths isn't trivial because the angular velocity isn't constant due to gravity.
[ I won't respond to messages, use the forum please ]

johnwasser


Author refers to Elektor magazine, December 2008 ("LED Top with Special Effects").


Looks like you can get the parts list online and download the schematic for free if you register:
http://www.elektor.com/magazines/2008/december/led-top-with-special-effects.739805.lynkx?tab=2

To get the article in PDF form you have to spend "10 Elektor Credits", whatever that means.
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