LED fan pattern

Discussion in 'General Electronics Chat' started by denno, Feb 2, 2009.

  1. denno

    Thread Starter Active Member

    Jul 1, 2008
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    Hey all, I was just wondering how those LED pattern fans are made? Those are the one's with LED's in one blade, and some sort of circuit which makes each LED flicker at a certain rate so that when the blades are rotating, different patterns are created. I am just wondering how the LED flickering is created and whether it's as involved as having to work out the timing of the motor that is driving the fan blades?
    If you need a photo of what I'm talking about just say so and I find one..

    Cheers
    Denno
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    You'd need to know the position of the fan at least once every revolution.
    From that position, time delay(s) could be calculated as to when to fire the LEDs to display a pattern or message.

    I've seen some "time/date" sticks; you just wave them back and fourth in front of you, and your persistence of vision enables you to read the time and date. They're really quite clever. I haven't dissassembled one, but I can imagine that they have a G-force sensor IC inside to detect movement and compute when to flash the LEDs. Such ICs are available for sensing G-forces in single and multiple axis.
     
  3. denno

    Thread Starter Active Member

    Jul 1, 2008
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    well I have bought one of these fans, and haven't taken it apart, but the part that controls the LED's is covered in a whole heap of glue or something, and I can't actually see it. But it's only very very small, so it looks like just a single IC which is connected to the LED's. So I don't imagine that there is any sensing of the motor going on, which leads me to believe that the programmer originally hard coded for a certain motor, and if this motor runs slow, or fast then the LED's won't make the same patterns, it will just be random...
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    There must be some kind of synchronization going on, whether you can discern it or not.

    Otherwise, it would be random garbage, just like you suggested.

    It may be as simple as counting makes/breaks of the brush/commutator connections on the motor; relying on gravity to return the fan to a predictable starting position.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    What you are referring to is a technique often referred to as POV or Persistence Of Vision. Youtube contains many examples of these projects. As sgtwookie has indicated, there must be a means of establishing a reference point for the rotational position of the fan motor for this to work with any consistency. I suspect that there is a shaft encoder involved in the most successful of these projects.

    hgmrj
     
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