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Digital Potentiometer or Variable Voltage Regulator?

Discussion in 'General Electronics Discussion' started by geekman92, Apr 3, 2013.

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  1. geekman92

    geekman92

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    Apr 3, 2013
    Hi guys! =)

    Okay I have a 3.3v output from an arduino and I want to programmatically control this voltage between 1.2v to 3v to control the speed a motor via a motor controller. I did some research and came across creating a variable voltage divider using a digital potentiometer. Whilst doing some more searching I came across variable voltage regulators. Are the regulators just a potentiometer inside a regulator?

    Which would be better to use in my situation and what sort of potentiometer or regulator should I use?

    Can anyone suggest a good product to use?

    Thanks in advance!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    To control the speed of a motor, you would be best using PWM. The arduino supports that and you'll be able to find many code samples and circuits.

    A voltage divider is a very poor option. A voltage regulator is almost as poor.

    No a regulator is not like potentiometer except in the most abstract sort of way.
     
  3. geekman92

    geekman92

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    Apr 3, 2013
    Sorry maybe I didn't make myself clear, I'm not controlling the motor directly, this is a big 72v motor I am controlling via the integrated motor controller that takes a voltage between 1.2V and 3V to vary the speed, I don't think PWM would work in this situation?!

    Thanks
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
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    Jan 21, 2010
    In that case, assuming the controller has a high input impedance, you could probably use one.

    Yes, you may also be able to use a PWM output. Pass the output via a resistor to a capacitor (a low pass filter) to convert the PWM to an analog voltage. Same caveat as before (high input impedance to controller) and note that there will be a limit on the speed that you can change the voltage.

    Arduino also has analog output (I'll confess I've never used it though)
     
  5. geekman92

    geekman92

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    Apr 3, 2013
    Correct me if I'm wrong but I thought that the analog output is the same as PWM as I read this from the analogWrite() page on the arduino site "Writes an analog value (PWM wave) to a pin."

    What is considered a high input impedance in this instance?!

    I haven't got the full specs of the motor controller from my mate yet but let's say it does have a high input impedance which would be the best solution to use?!

    Thanks
     
    Last edited: Apr 4, 2013
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Here is a (warning) thourough discussion on how to filter PWM.

    Here is a web based calculator tool for designing the filter. A Google search for >pwm filter calculator< will turn up quite a few more tools.

    Choose the R part of the filter such that Rfilter<<Rcontroller. E.g. if the controller's input impedance is 100kOhm, make R<=10kOhm. Otherwise the current flowing into the controller's input will discharge the capacitor too quickly and the filtered signal will contain noticeable amounts of ripple from the PWM.
     
  7. geekman92

    geekman92

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    Apr 3, 2013
    Okay thanks for that pdf it looks good! I will read through it and try and figure it out myself and comment again if I have any other questions!

    Thanks for your help so far guys! =)
     
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