invert voltage for motor spin direction

Discussion in 'The Projects Forum' started by jaskiewiczm, Nov 20, 2010.

  1. jaskiewiczm

    Thread Starter New Member

    Nov 1, 2010
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    Hello,

    I've got an old motor that I salvaged from a busted CD-ROM drive. If I hook up the battery one way, it spins forward. If I reverse the battery, it spins the other way.

    I figured that I could use 4 transistors to flip the direction of the current but I was wondering is there a simpler way?

    Thanks,

    mj
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    You could use a DPDT (double-pole, double-throw) switch, like this:

    [​IMG]

    You'd be best served to get a switch that has a center-off position. Suddenly reversing a motor by flipping it's polarity is very hard on it.
     
  3. jaskiewiczm

    Thread Starter New Member

    Nov 1, 2010
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    0
    I forgot one additional detail :)

    I plan on buying a gumstix computer on module that I want controlling this thing. Aren't DPDT switches flipped by hand?

    Thanks,

    mj
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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  5. debe

    Well-Known Member

    Sep 21, 2010
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    You could use these they are motor H drives from old VCRs very easy to use & cost nothing if you salvage them from old machines. Daryl
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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  7. jaskiewiczm

    Thread Starter New Member

    Nov 1, 2010
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    Thanks!

    Two questions though.

    Why are the resistors necessary as inputs into the transistors?

    Also, what are those symbols at the top that look like a stylized "S"?

    mj
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    You're referring to the schematic on this page: http://www.solarbotics.net/library/circuits/driver_4varHbridge.html
    Did you read the text?
    Current to the base of a transistor almost always has to be limited via some means when the transistor is used as a saturated switch.
    Without the resistors, it won't work at all.

    Those are symbols representing hysteresis, or a Schmitt trigger. A 74HC14 is a hex Schmitt-trigger inverter.
     
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