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Thread: cheap pots over wire-wound for uC controls?

  1. #1
    Senior Member oddson's Avatar
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    cheap pots over wire-wound for uC controls?

    I bought an expensive wire-wound potentiometer (10KOhm) to see how much BETTER performance it would bring to a voltage-divider-as-controller.

    I thought there may be little or no difference but instead the expensive pot is much worse in terms of induced noise on a stationary control in the middle of its range.

    The 10mm PC-board-mounting cheap controls I normally use typically vary in the LSB only (10-bit readings) with occasional glitches to 2 bits but the wire wound has many 4 bit changes while stationary.

    I'm wondering if the wire coil is actually picking up noise itself (despite what looks like good shielding).

    Anyone else observe this?

  2. #2
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    Do you have a 10n capacitor in there somewhere?

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    The case always remains so in all models. Whatever the potentiometer it is and whoever the manufacturer is 95% of the times it is problematic and will continue to do so. For your specific circuit try different models somehow you'll get the perfect one for you. I do use potentiometers as last option (Since in my industry I get a lot of noise using them). Instead I prefer to use a simple resisitve based voltage divider, after doing calculations from some calc like this, I make my circuit. But in my case I always need constant voltage for example lets say I will be going with 5.6 V whole week. In case you opting for variable one you should use a pot and test a few models to find the best one. However for microcontrollers I'll recommend the voltage divider, also you can find some ready made voltage dividers providing a clean look to circuit as well as rid'ng you to get involved in design.

  4. #4
    Senior Member oddson's Avatar
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    Quote Originally Posted by Donziboy2 View Post
    Do you have a 10n capacitor in there somewhere?
    Not yet...

    I was just an experiment... but if the 50-cent pot doesn't need one but the $6 one does...

    Unless it's performance is actually better except for high frequency noise but it didn't appear that way from sampling at various rates.

    I was just curious about whether wire-wound pot induced noise is a known, common thing.
    Last edited by oddson; 10-01-2017 at 03:33 PM.

  5. #5
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    Does not really matter whether its a pot, a wire, or a trace on a PCB when measuring voltages you need some capacitance or your going to be subject to any RF noise in the area.

  6. #6
    Senior Member oddson's Avatar
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    It was the magnitude of the difference that surprised me... testing the effectiveness of passive filtering is next.

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    Hope you'll get better results next time

  8. #8
    Senior Member PaulStoffregen's Avatar
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    Maybe the wirewound pot has some inductance which is causing the ADC input to effectively be a higher impedance at the short duration where the ADC samples the signal?

  9. #9
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    Yeah, Paul, this can be furthermore more turns can lead to more noise.

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