Centrifugal/Acceleration LED switch

Discussion in 'The Projects Forum' started by noyil, Sep 24, 2015.

  1. noyil

    Thread Starter New Member

    Sep 2, 2015
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    Hi,

    I'm using CR2032 batteries to light 3mm LEDs, and I'm searching for the cheapest and smallest switch which would close the circuit only when a force is applied (this tiny system is mounted on a spinning surface, and should light up only when it's spinning).

    I tried using SW180-10P vibration switch, but I found out that the circuit is closed only when acceleration is changed. I just need a component like this vibration switch that would operate during the motion and not only when there is a change in motion.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Colleague uses mma8452 accelerometer for similar purpose, it has preettable thresholds to detect g force. However it needs a cpu to configure it after power up.
    What comes to mind would be a weight, a spring and a switch to detect centrifugal force.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Does it always spin in the same plane? If so, a ball bearing ball sitting on a conducting surface and surrounded by a circle of wire would be moved toward the wire when spinning, and settle back into the center (into a dimple or some other lower area) when stationary.

    ak
     
  4. MikeML

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  5. noyil

    Thread Starter New Member

    Sep 2, 2015
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    The system is mounted on a piece of fabric that spins most of the time in a horizontal plane, but it is not stationary so the spinning axis could change.
    The real problem is that when it does not spin we can't be sure the system would stay horizontal, someone could lay the fabric in a way that the system would be vertical and so affected by gravity.

    I thought there is a component just like the SW180-10P, which have a weight attached to a spring which allow the circuit to close only when a force bigger than G is applied. I just can't find the name/model of this component.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    What is the minimum acceleration that you want to consider as spinning?
     
  7. cmartinez

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    Jan 17, 2007
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    I'm with Mike on this one. The thing here would be to make sure that you get reliable contact all the time. Is your application an industrial one? or is it for some hobby or something that does not requires to be rugged and robust?
     
  8. noyil

    Thread Starter New Member

    Sep 2, 2015
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    It's not an industrial product but because it is mounted on a fabric, it needs to be small, lightweight and somehow resistant to small hits.
    That's why i'm trying to find a "closed" component which is probably in use in many toys.

    I think the minimum acceleration would be just above 1-2 G but this could change depending on the solution we find.
     
  9. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Just make sure that your "small hits" should be smaller than the centrifugal force being applied then... let me do a little research and then I'll get back to you
     
  10. noyil

    Thread Starter New Member

    Sep 2, 2015
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    well the purpose is to light up the LED when spinning, if it lights up for a few microseconds when someone put it on a table (and it gets a small hit), its good enough.

    thanks ahead
     
  11. dannyf

    Well-Known Member

    Sep 13, 2015
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    Use a mercury switch. Or salt water in a tube. Metal on a thin wire, .....
     
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  12. cmartinez

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    Jan 17, 2007
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    There are many "cheap" accelerometer sensors that you could use out there. And although they're relatively inexpensive, they're not easy to implement since they require to be interfaced to an MCU. That makes them very flexible and powerful too, as far as their ability to be configured goes.

    I'd suggest, however that you design and build a small mechanical contraption that could be described like this:
    • Place 2 metal rings in a small cereal bowl, just right below the brim
    • One ring should be above the other, but without making contact
    • The topmost ring should be a little smaller than the one below it
    • Connect one wire to each ring, using a brush-type contact
    • Place a small metallic ball in the bowl, whose diameter is somewhat larger than the distance between the rings.
    • Spin the bowl, and voilá! you have a centrifugal switch sensor.

    A second option, which would probably be simpler to implement is exactly what Mike said, to build a fly-ball governor
     
  13. blocco a spirale

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    Jun 18, 2008
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    Last edited: Sep 24, 2015
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  14. BR-549

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    Sep 22, 2013
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    What is the radius and speed of spin that you want light?
     
  15. noyil

    Thread Starter New Member

    Sep 2, 2015
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    The radius of the fabric surface is about 30 cm, so the minimum speed for getting 1.5G linear velocity would be above 467 RPM.
    The spin is not controlled by a computer so I can't really say what is the exact speed.

    The Jameco switch looks promising, I'll look into it.
     
  16. blocco a spirale

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    Jun 18, 2008
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    Using a couple of online calculators I got 67rpm for 1.5g at a 30cm radius, which sounds more likely to me.
     
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