LM3914 resistor values for 3.7 V Li-Ion battery

Discussion in 'The Projects Forum' started by WonHungLo, Dec 18, 2013.

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  1. WonHungLo

    Thread Starter New Member

    May 9, 2011
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    i have the circuit built for a 12v dc monitor and i would like to adjust the values to read between 3.0V and 4.2V.
    i can not figure out for the life of me what the resistor values would be for the upper and lower limit. i know it's got to be simple.
    here is my original schematic and it works great. what would i modify to make it work on a li-ion battery.

    [​IMG]
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    datasheet remove the resistor R3 and connect pin 4 to pin 2, short out R1, this will give you a full scale of 1.25V.

    However the chip wont work below 3V, ideally it should have its own supply, and input the signal into pin 5, the led brightness is controlled by R4.
     
    Last edited: Dec 18, 2013
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  3. WonHungLo

    Thread Starter New Member

    May 9, 2011
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    does that mean the scale will be between 0V-1.25V.
    im trying to make the scale 3.0V-4.2V
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    No alter the preset resistor R2 to set the desired full scale when you connect it across the 3V battery.
     
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  5. WonHungLo

    Thread Starter New Member

    May 9, 2011
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    ok so far so good. i removed R3 and connected pin4 to pin2. when i adjust the 10k pot i can only get the lower half of the LED's to light (its a fully charged battery @ ~4.17V)
    what is the resistor i need to change to make all of them light up (i guess you would call it the upper limit)
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    short out R1, this will give you the full scale
     
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  7. WonHungLo

    Thread Starter New Member

    May 9, 2011
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    YOU ARE AWESOME. im going to post the revised schematic for anyone wanting to use this in the future.
     
  8. WonHungLo

    Thread Starter New Member

    May 9, 2011
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    [​IMG]
     
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  9. Seb1929

    New Member

    Feb 20, 2015
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    What does the arrow that points to the 10K resistor means?
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    R2 is a trimpot (three terminals: ends and wiper)
     
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  11. Seb1929

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    Feb 20, 2015
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    [​IMG]
    Like this? Is it possible to change it with something else because i need the board to be as low as possible and why does i need it?
     
  12. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Use the trimpot for initial setup then replace it with two resistors when you've measured the values?
     
  13. Seb1929

    New Member

    Feb 20, 2015
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    If so, will i only need to do it on one board? Because i don't want to do it on 1000 boards :p
     
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You should read this other thread...
     
  15. Seb1929

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    Feb 20, 2015
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    Why? I have found out how to do it.
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Care to share it with us?
     
  17. Seb1929

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    Feb 20, 2015
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    [​IMG]
    [​IMG]
     
  18. MikeML

    AAC Fanatic!

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    I was more interested in the underlying science of being able to determine the state of charge of batteries using a voltmeter.
     
  19. Seb1929

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    Feb 20, 2015
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    The LM3914 chip does it so..
     
  20. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Sorry to burst your bubble... The 3914 is nothing but a voltmeter, and not a very good one at that!
     
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