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battery monitoring ckt using LM3914

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archana87

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hi
i am supposed to make a battery monitoring circuit using LM3914.i have gone through the datasheets and other ckts from many links.i am not able to decide the resistor values to be placed ..i am getting confused seeing so many ckts.

required specifications for my project:
lead acid battery monitoring ckt.
12V to 7V indicator (0.5V step)

please let me know the values of resistors to be placed at 6,7,8,4 and 5 pins.
 
please let me know the values of resistors to be placed at 6,7,8,4 and 5 pins.

The Ref Out formula on page 2 of
https://www.electro-tech-online.com/custompdfs/2008/09/LM3914.pdf
tells you the R2/R1 ratio to get your 12v; that's pins 6, 7, and 8 taken care of.
Once you know the pin 6 voltage, from the gizzards on page 7 you can pick the pin 4 resistor value.
Pin 5 is the signal in.
On this same page, note that the way the wiring is drawn going to pin 2 implies that they suggest a single point ground here.
 
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yeah ..now i got to some conclusion regarding the resistor values ..

the resistor connected at pin6 will decide the amount to reference voltage ..and the current the LED is going to be lit .

what i cudnt understand is the singal input at pin5 ..what shud i give there??how to calculate that value..
then what is the offset voltage at pin 8..datasheets say 10mv max..


as i need a 0.5v change in each led .....will the offset voltage decide the 0.5 change or something...
 
what i cudnt understand is the singal input at pin5 ..what shud i give there??
then what is the offset voltage at pin 8..datasheets say 10mv max..

You're almost there.

What could "signal" mean? There's not many choices left for what that could be. What other pages mention "signal"?

Looking at page 2, I think the voltage on pin 8 is more than 10 mV. Where do you think the 10 mV they talk about is coming from?
 
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i am not understanding that part...dat is wer i need help...

see pin2 is ground. pin3 we giv input voltage from battery.
pin 6 and 7 we decide the current at led and also the reference voltage..
fine i need a 0.5v change for each led that glows(dot mode).reference voltage that i ve to set is 1.2v which means for a 5v change in battery there is 1.2v change in lm3914.

1.2v appears at pin7 junction..then i am not gettin how to set this 0.5v change for each led ...does it anyway relate to the resistance connected at pin8...also what is it we have to giv at pin5....

plssss do help me to come out of this confusion........
 
What is the voltage of the supply that powers the LM3914 and the LED? I'm guessing it's 7-12V. After we know this, we can be more helpful.
 
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