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Monitor the Battery Voltages

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ONT

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I need a circuit with 3 LEDs to indicate the battery voltage level.

LED 1---LOW = 3 V
LED 2---Medium = 3.4 - 3.7 V
LED 3---High or Full = 4.0 V - 4.1 V (battery full or battery maximum voltage)

Supply voltages must be less than 4.2 V.
 

tusemo

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You can use lm311 voltage comparator, only thing you should do is obtain three voltages (3v, 3.5v, and 4v) you can use voltage divider (by 2-resistor) then connect the outputs of the comparator to the leds. comparator datasheet
 

ONT

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You can use lm311 voltage comparator, only thing you should do is obtain three voltages (3v, 3.5v, and 4v) you can use voltage divider (by 2-resistor) then connect the outputs of the comparator to the leds. comparator datasheet
I finally manage to design circuit that works for me

Low = 3 V
Med = 3.4 V
High = 4

I simulate this on Multisim with OP09 as there is not footprint of LM339. So can I use the same circuit with all these values with LM339? Kindly rectify if there is any fault in the circuit.



- - - Updated - - -

But I did this with hit and trial method....So anyone kindly explain me this with voltage divider formula. Actually I forget this.
 

tusemo

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Voltage divider can calculate shortly like in figure I added.
voltage divider.jpg
But your references are not your limit-voltages. You should calculate them correctly. For example U1:A-ref-voltage = 3.9*8500/8720=3.8V.
 

BradtheRad

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For simplicity it's hard to beat the diode drop method. It takes advantage of built-in volt thresholds.

Screenshot:



By choosing resistors properly, no led will be exposed to more than 20mA.

The led's turn on gradually, so you won't see a distinct change between levels. OTOH if you use the comparator method, the led's will turn on more abruptly.
 

ONT

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sorry I couldn't understand, so if you don't mind, kindly make above circuit and also mention the calculation of resistance values. Thanks in advance.
 

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