I am trying to make a Battery Monitor Circuit using a LM3914 to drive 10 LEDs. I have found this circuit design but don't know how to calculate the values of the resistors..as in what formulas to use etc. I want one LED to be on at 11.5V and all 10 to be on at 12.8V.

 

You need to set the upper and lower limits to 12.8v and 11.5v, there is an internal lm317 regulator that needs to be set to 12.8v, using a 1.2K R1, and 11.6K R2 resistor. The lower limit resistor R3 is 86.9K. You can put your input on pin 5 direct to the supply on pin 3.

 

You need to set the upper and lower limits to 12.8v and 11.5v, there is an internal lm317 regulator that needs to be set to 12.8v, using a 1.2K R1, and 11.6K R2 resistor. The lower limit resistor R3 is 86.9K.

Can the vr1 and vr2 be any value ? And r4?

 

You can omit the other resistors on pin 5.. you can use variable resistors to get the required voltage upper limit, and lower resistance.

 

The 3914 datasheet and app notes have complete design methods and examples.

ak

 

12V battery monitor, alter the Vres to give your upper/ lower limit

http://www.electroniq.net/other-projects/car-battery-monitor-using-lm3914.html