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Thread: Fluctuating Input Values

  1. #1
    Newbie thwack's Avatar
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    Fluctuating Input Values

    Hi all,

    I am having trouble understanding where my issue is coming from.

    Basically I am measuring the voltage of my cars two batteries.
    I have setup a voltage divider for each with a 330ohm and 100ohm resistor.

    This gives an output of 2.91v when the battery is ~12.46
    for each the scaling factors are
    1. 0.2341920
    2. 0.2325581

    But the raw input values seem to fluctuate anywhere from 480 to 780 randomly even though the input voltage has not changed. I can stick the multimeter across the end and get a constant 2.67-2.68V stable, yet the display is showing anywhere from 1.76V to 3.8V

    I have tried multiple ports and this still seems to happen on every one. Even if I change the resistance to give a smaller value it is still happening.
    I am also running two temp sensors and these appear to be working well with stable values.

    What am I doing wrong or what can I try next??

    thanks
    Thwack
    Car PC -Jetway J7F2WE2G, 4Gb CF Boot, 32Gb CF Data, 1Gb Ram, M2-ATX PS, 8" 800x600 TS, SiLabs USB Radio, Garmin GPS15L, Ublox SBR-LS DR GPS, Fusion Brain, Multibay Card Reader, Panasonic Slotload DVD+-RW, Custom Fab Steel Case
    Car- 1988 Nissan Patrol 4WD

  2. #2
    Fusion Brain Creator
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    When did you buy it?

  3. #3
    Newbie thwack's Avatar
    Join Date
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    30th July This year
    Car PC -Jetway J7F2WE2G, 4Gb CF Boot, 32Gb CF Data, 1Gb Ram, M2-ATX PS, 8" 800x600 TS, SiLabs USB Radio, Garmin GPS15L, Ublox SBR-LS DR GPS, Fusion Brain, Multibay Card Reader, Panasonic Slotload DVD+-RW, Custom Fab Steel Case
    Car- 1988 Nissan Patrol 4WD

  4. #4
    Newbie thwack's Avatar
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    Would a capacitor from Vin to GND help filter out the fluctiations?
    Car PC -Jetway J7F2WE2G, 4Gb CF Boot, 32Gb CF Data, 1Gb Ram, M2-ATX PS, 8" 800x600 TS, SiLabs USB Radio, Garmin GPS15L, Ublox SBR-LS DR GPS, Fusion Brain, Multibay Card Reader, Panasonic Slotload DVD+-RW, Custom Fab Steel Case
    Car- 1988 Nissan Patrol 4WD

  5. #5
    Fusion Brain Creator
    Join Date
    Mar 2005
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    I didn't see that you're using temperature sensors with stable values. That means it's not the FB's fault.

    A capacitor or noise filter would help, yes.

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