18F2525 ADC Accuracy


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  1. #1
    Join Date
    Sep 2005
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    5

    Default 18F2525 ADC Accuracy

    I am seeing a number jump of 144 to 155 on my analog conversions of 5VDC with a 740 millivolt input. I don't see the input changing but the conversion seems to be not as accurate as I would like it to be. I am using a 10 bit result and a 4mhz crystal.
    Is this normal or do I have some settings hosed up?
    Last edited by mungam753; - 28th December 2005 at 11:36.

  2. #2
    Join Date
    Jul 2003
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    2,405


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    Default

    It's very normal to see AD values jump if you're not using a filter circuit on the input.

    Try a filter something like this;

    AD input
    o-----/\/\/\/\---1K--- external analog input
    |---| |---0.1uF---gnd

    There are other simple tricks like using sleep mode, and filters on Vref for noisy power rails.
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

  3. #3
    Join Date
    Sep 2005
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    5


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    Default Thank you

    I am testing right now and it seems to have cut the jumping around in half. I thank you for your help as this has been driving my nuts for the last week.

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