Battery Level Monitor Using LM3914

Components:

LM3914 (Dot/bar display driver)
resisters: R1 = 1K2
R2 = 3K9
R3 = 10K
R4 = 33K
Variable resistor: VR1 = 20K
VR2 = 50K
Capacitor C1 = 10F
Diode D1 = 1N4001
LED1-3 = red LED
LED4-7 = yellow LED
LED8-10 = green LED

Monitoring of your expensive battery level or voltage is important to extend its life span, this simple circuit will help you do that. The major component of the circuit is LM3914 (dot/bar display driver). I came across this IC a few years ago and it caught my attention. I quickly browsed for its data sheet for better understanding of its connections and specifications. It is widely used for this type of application; original circuit on which a slight modification was done was from the data sheet. It is a great IC as I am concerned as it gives me nothing but the expected result. Of course, the IC can do more than monitoring battery level or voltage as it is used and described in this write up. See my 'lead-acid battery charger circuit' for how it is used to do a good job.

You need a digital voltmeter and a variable power supply like the one on this site for final setting of your circuit. To set the upper limit, connect the power supply to the circuit and adjust it to give 13.8V (check manufacturer sheet of your battery). Now, adjust VR1 till all the ten LEDs light up, this is the upper limit. For the lower limit, adjust the supply voltage to give 10V (also check manufacturer sheet of your battery) and adjust VR2 till just LED1 lights.

The circuit is in bar configuration mode. To connect it in dot mode, pin9 will not be connected. You need to be mindful of the polarity as LM3914 is very sensitive to polarity and get damage immediately you connect to wrong polarity. To protect it against wrong polarity, diode D1 is used as you can see in the circuit.