Simple battery level indicator circuit diagram

Photocoupler

Creating a battery level indicator circuit is quite straightforward. Typically, on mobile phones, the battery level is represented by points or bars, which makes it easy to identify the remaining charge at a glance. On this page, we present a circuit that allows you to monitor the battery level of your device numerically using LEDs. Each LED corresponds to 10% of the battery capacity. For instance, if three LEDs are lit, it signifies that the battery is at 30% capacity.

The functionality of this battery level indicator is integrated with the existing circuitry of the phone, differing only by the inclusion of a single comparator IC (LM3914). This IC divides the battery's voltage range into ten distinct segments, each representing a different battery level.

This circuit derives its power directly from the device’s own battery. The 10 LEDs are arranged in a linear fashion, and their colors vary to simplify identification. Red LEDs (LED1 through LED3) indicate that the battery is below 40% charged. Orange LEDs (LED4 through LED6) signal that the battery level is between 40% and 70%, while green LEDs (LED7 through LED10) show that the battery is between 70% and 100% full. The brightness of the LEDs can be adjusted by tweaking the variable resistor VR2 connected between pins 6 and 7.

To prevent damage from reverse polarity connections, diode D1 is placed in the circuit. Additionally, when the battery is fully charged, the tenth LED illuminates, and the relay triggers transistor T1, closing the normally open contact of relay RL1, thus halting the charging process.

For calibration purposes, connect the circuit to a 15V adjustable regulated power supply and set it initially to 3V. Adjust VR1 until LED1 lights up. Then incrementally raise the voltage to 15V in steps of 1.2V, ensuring that each subsequent LED (LED2 through LED10) lights up at the appropriate voltage.

Once calibrated, the circuit can display voltage values within its maximum range. Given that there are 10 LEDs, each representing 10% of the total capacity, determining the battery percentage becomes a simple task.

To test the circuit, connect the battery voltage to the input probes and observe how many LEDs are illuminated. For example, if five LEDs light up, the battery is at approximately 50-59% of its full capacity.

Finally, design a universal PCB for the battery level indicator circuit. After calibration, mount the components inside, including 10 LEDs, a variable resistor for adjusting the battery input, and two mounting holes for securing the PCB.