This level battery indicator circuit that lets you know the battery level of a device from the number of LEDs that are glowing, it uses ten LEDs in all. So if three LEDs glow, it indicates battery capacity of 30 percent. Unlike in mobile phones where the battery-level indicator function is integrated with other functions, here only one comparator IC (LM3914) does it all.

The battery indicator circuit derives the power supply for its operation from the battery of the device itself. It uses ten LEDs wired in a 10-dot mode. Red LEDs (LED1 through LED3) indicate battery capacity of less than 40 percent. Orange LEDs (LED4 through LED6) indicate battery capacity of 40 to less than 70 percent and green LEDs (LED7 through LED10) indicate battery capacity of 70 to under 100 percent. The tenth LED glows only when the battery capacity is full, i.e., the battery is fully charged. When the battery is fully charged, relay-driver transistor T1 conducts to energise relay RL1. This stops the charging through normally-open (N/O) contacts of relay RL1.

The brightness of the LEDs can be adjusted by varying the value of preset VR2 between pins 6 and 7. For calibration, connect 15V variable, regulated power supply and initially set it at 3V. Slowly adjust VR1 until LED1 glows. Now, increase the input voltage to 15V in steps of 1.2V until the corresponding LED (LED2 through LED10) lights up.

Level battery indicator circuit diagram

battery indicator