Replacing pot with digital

Discussion in 'General Electronics Chat' started by Barry M, Aug 30, 2015.

  1. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    I would like to make a voltage controlled PWM fan controller.

    Essentially I would like to replace the pot in this diagram with a 100k pot that is controlled by 0-12v DC:

    [​IMG]

    Full article: http://www.overclockers.com/pwm-fan-controller/

    I have looked but I am getting conflicting information and the last time I built something everyone told me I was using outdated methods that were pointless (turned out I done three times the work I had to because a single chip replaced a lot if it) and that tutorial is 4 years old.

    Thanks in advance.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That circuit would require major surgery to provide a voltage-controlled PWM with a wide control range. As a simple alternative you could try one of my circuits in this article.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    That circuit looks more or less OK - but the resistor in series with the output pin should be moved to in series with the pot wiper, othererwise there will be a strong sawtooth component from the timing capacitor superimposed on the PWM fed to the power device.
     
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  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Oddly enough, pin 5 of the 555 is called the control pin. There are many variations on using a variable voltage on that pin to control the 555's output. Zero to 12V is not bad, so long as the power to the 555 is ≥ 12V. In other words, find the circuit you want to use for PWM and apply your variable voltage to pin 5. Not all will work, but most will.

    John
     
  5. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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    The circuit I posted only sends a signal to a PWM fan. In no way is it designed to supply anything else.

    I have a 0-12v control panel. All I want to do is remove the the pot in this diagram and replace it with one that is controlled by a voltage in the 0-12v range.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I have not seen a digital pot than handles 12V across its terminals. They may exist. Have you found one?

    What's your question?

    John
     
  7. Barry M

    Thread Starter Active Member

    Feb 11, 2009
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  8. crutschow

    Expert

    Mar 14, 2008
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    Why not use one of the circuits Alex referenced in Post #2?
    No difficult-to-acquire digital pot required.
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    MCP41HV1 allows to voltage across the pot to exceed VCC rails.
     
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