The first circuit is the simplest battery indicator circuit. It can apply to an input voltage of 3V to 15V. The LED will begin to light up. we can adjust VR1 to set a level of checking voltage. When the battery voltage reduces down to a set point. The LED will bright immediately. Look: in the circuit.
The battery level indicator circuit works by comparing the battery voltage to fixed voltage levels. The operation of the battery level indicator (D1) is the voltage reference zener. Tied to this is a string of divider resistors (R2-6) that set the various fixed voltage levels. R7 & 8 form a voltage divider to reduce the battery voltage by a factor of 3. U1 is an LM339 quad comparator that compares the various voltages from the two dividers.
For use the battery level indicator in an advance electronics project, we have to design another circuit for more accurate data. Problem in the LM3914 circuit was that it was showing the linear decrease of battery voltage and it was occurring due to its internal 1kΩ resistor ladder.
This circuit is most suitable for indicating 12V battery level. In this circuit each led indicates 10 percent battery level. We can extend this circuit to 100 steps by cascading lm3914 IC’s. How To Operate Battery Level Indicator Circuit?
The 12V battery level indicator and the one with R2 are both inexpensive and BRIGHT. The 12v battery level indicator unit in the photo does not have a reverse polarity diode, and R2 is the calibration potentiometer.
Connect battery to be tested to the input of the circuit. Now adjust the pot RV1 so that LED D1 just starts glowing. First led will glow for 1.2V and second LED is for 2.4 V and so on. Below table shows the status of LED’s with input voltage level. We can use this circuit to measure car battery level.