PWM? phase width modulation

Discussion in 'General Electronics Chat' started by Rk17, May 4, 2011.

  1. Rk17

    Thread Starter Member

    Apr 23, 2011
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    what does phase width modulation mean? Im searching the net for info on how to program a pic to control a servo but i kinda see this a lot. Can someone please ellaborate it tnx!
     
  2. #12

    Expert

    Nov 30, 2010
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    I always thought that was "pulse width modulation".
    Hmmm...I learn something every day!
     
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  3. BillB3857

    Senior Member

    Feb 28, 2009
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    Don't know for a fact, but I would guess that Phase Width Modulation would be equated to having SCR controls operated at a line frequency. By controlling the phase relationship of the SCR triggers to the line, the output is controlled. Again, just a guess, but I think it sounds reasonable. How about other opinions.
     
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  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I have only used PWM with a 555 timer--basically, all it does is adjust the duty cycle of a square wave signal. In other words, it changes the length of on time vs off time during one cycle. Make sense?
     
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  5. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'd support you on that, but a guess as well.
     
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  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    A Google search on "phase width modulation" turns up bupkis.
     
  7. Rk17

    Thread Starter Member

    Apr 23, 2011
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    oh sori bout that.. yeah its pulse width modulation,, nwei,, how could you control a servo with it? can you please share me any source code relating to this? i wish to control a servo with it.. My idea is to rotate the servo to +90 then -90 with a given timespan,,for example +90 degrees to - 90degrees every 2 seconds. But how could i program that in c code? or .asm code? im using mplab compiler v 8.66 tnx
     
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    A good description of hobby servos is available at this link http://www.lynxmotion.com/images/html/servo01.htm

    On that page is a description of how to control a servo by varying a pulse signal. I have extracted it below:

    [​IMG]
     
  9. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    How in god's name can u modulate Phase width ? :confused::confused:
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I know phase angle...

    I just never realized it is same as width..

    Definitely angle is not width
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
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    It looks like the output gets wider and narrower to me;). I really think it is all in the semantics and the terms could almost be used interchangeably. Similar to the Lightfire's thread about "ground".
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Confusing ?????
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    So....tell me

    How is PPM done?
     
  15. BillB3857

    Senior Member

    Feb 28, 2009
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