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Digital Potentiometer or Variable Voltage Regulator?

geekman92

Apr 3, 2013
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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!
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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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.
 

geekman92

Apr 3, 2013
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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
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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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)
 

geekman92

Apr 3, 2013
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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:

Harald Kapp

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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.
 

geekman92

Apr 3, 2013
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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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