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LM3914 - question

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by caslor, Mar 22, 2010.

  1. Hero999

    Hero999 Banned

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    I didn't say otherwise.

    Surely there's a simpler solution than that though.
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    I know you didn't say otherwise, that was meant only as information for you.

    Read thru the posts and post your circuit option, after all it is an open Forum for all to contribute.:rolleyes:
     
  3. Hero999

    Hero999 Banned

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    I've already posted two rough ideas and wanted some feedback which I've yet to receive.

    What do you think of my previous suggestions?

    I'm not going to bother drawing up the circuits, if it won't work or can't be done for some reason, for example, there's no point in me suggesting replacing the thermistor with a linear temperature sensor IC if he can't replace the sensor.
     
  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi hero,
    I wrote a detailed reply to your last post..........but the site is screwed again.!
    So its gone down a black hole , somewhere.!!!
     
  6. caslor

    caslor Member

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    HI
    did you missed me? :) :D
    Here i am with 2 new questions :(

    i used the cool program about lm3914 in order to make it work from 5-14v input signal.. with 1volt step

    i want to use it as a car battery charging inspection...

    but i am a little confused about the pins 4,6 in lm3914 what values i will place there... how to connect them

    in pin 4 where should have 4,04v should i supply it with 4,04v? and in pin 6 where should be 14v have to supply it with 14v ??
     

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  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi again,:)
    If you want to monitor a 12V lead acid battery, for the best resolution measure from about 10.5V thru 15V thats 10 steps of half a volt.
    Do you want to monitor the same 12V battery as powering the LM3914 and LED's??

    If yes then make up a resistor divider, say two 10K's, connect the divider across the 12V battery so that the junction is 6V.
    As the battery discharges down to say 10.5V then the divider will read 5.25V and at 15V while charging the divider will read 7.5V
    EDIT: this divided voltage is connected to pin5

    So set the pins 6&7 to ~7.5v and pin4 to ~ 5.25V.
    Using 12V for the LED's supply you will require a series resistor

    Do you follow OK.?
     

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    Last edited: Jun 24, 2010
  8. caslor

    caslor Member

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    Hi again my friend and thanks one more time for the interesting about my problems :) :)

    Sorry for the delay to my answer but i was in a business trip .

    ok i think i understand what youo suggest me and here is the drawing.... (1st attachment )

    Can we make it work from 14v and under ? as 15 volt is not so necessary for the application i need it ...



    also i found and this drawing around the net about the last application i want to place in my car... an af meter... (2nd attachment )

    what is you opinion ? it will work?


    Thanks again very much helping me to this i am trying to build :)
     

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  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The 1st circuit will be ok on 10v to 14v.
    The 2nd circuit is for a 0 to 1V input, I am not sure what an 'af' meter is in this context.??
     
  10. caslor

    caslor Member

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    ouuups sorry not mention it ..
    Af = air fuel meter ... and is based in a Lambda sensor (oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed, In Automotive The sensor does not actually measure oxygen concentration, but rather the amount of oxygen needed to completely oxidize any remaining combustibles in the exhaust gas. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess.)

    and has range from 0-1 volt

    [​IMG]


    About the first - battery voltage metter
    if i want to measure from 9,5 volt until 14 volt ??
     
  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I will look at 0-1V Lm3914, I expect it will be OK.
    For the 9.5V adjust pin4 for approx 4.75V and pin6 for approx 7.0

    EDIT:
    Tested your 2nd circuit, it works fine..
     
    Last edited: Jun 28, 2010
  12. caslor

    caslor Member

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    Ok i will play with the values of the resistors in pin 4 and 6 to adjust them ...



    Thank you very much :) !!! now i think i have all the gauges - drawings i needed .... time to build it ;)
     
  13. caslor

    caslor Member

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    Hi my friend.... i need your help once again...

    i starting make the drawings to help me in building the board with all these cool staf :)

    But i stack in the head temp gauge #96


    i see that the best solution was to make it work with 20 led dot bar (2 lm3914)

    with 0.1v step and range from 1.15v - 3.25v

    so this is to complicate for my knowledges to make it.....



    Can you help me about the drawing i upload it? it is based in the previous 20led setup we had discus in previous post...

    the resistors are in previous setup values ...
     

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  14. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Where did you get that circuit and what LED display sequence are you expecting.??
     
  15. caslor

    caslor Member

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    Hi

    it is based in a previous post we had discus #80


    i want when the circuit at #96

    give me 1,25v output the first led goes on...
    then until the 10th led all the other light the first led... etc etc

    i want this in order to have always on the previous led until i had the next reading/voltage that interesting me to display
     
  16. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Look at this image, the two LM3914 are linked together.
    The 'exe' program for this dual LM3914 calculator is on my Blog, download it and make the settings exactly as shown in this image.
    Also download the latest version of the single LM3914.
     

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  17. caslor

    caslor Member

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    Wow.. my favorite program in dual :) :)
    i download both of them :)

    Thank you ericgibbs making our lifes easier :)

    but i need to bring an example to see if i have understand the Vext low and Vext Hi in this program

    in the picture as the pin 6 is in the ''ref inp '' the vext Hi is not something that will consider as if it is 0 or 12v .. right?

    Lets go to the Pin4 of the Lm3914 and the Vext Low

    the number there is the voltage we will connect to the pin4 before the resistance right ?

    and with a variable resistance we adjust the final voltage in the pin4 right?

    so if we want to have 1.5 volt there as the picture... we place a resistance to take 1,5volt from the 8volt input... right?

    v=8 R=20k so I = 8/20 = 0.4mA

    so if we place the 20k pot to have 3,75k we will get v= I*R = 0.4 * 3.75 = 1.5v

    ( i think i make a mistake in this as we have to place to resistors of 16.25k and 3.75 in serial in order to have the 1.5volt at the end of the second resistor 3.75k like the second picture)
     

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  18. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Look at this edited image, it may be easier to follow.
     

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    Last edited: Jun 30, 2010
  19. caslor

    caslor Member

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    Thanksssssss!!!!!! :) :)

    Online electronic lessons :)

    Thanks one more time (i have lost counting :p ) for the support to my project :)
     
  20. alex69

    alex69 New Member

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    Many thanks mr. ericgibbs for yours programs to calculate R for LM3914 in auto.
    I'm a newby and, for now, I'm not able to dowload the single calculator program. I wait with patient until I've more post to get it.
    Excuse me for my bad english.
    Alex.
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The datasheet for the LM3914 shows how simple arithmatic is used for its calculations. You don't need a calculator program.
     

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