Guys, sometimes I see a charging animation on my device that appears as a brief green/flickering light along the edge of the screen. What exactly is this signaling? Is it testing the battery, managing the battery, or is it a software thing? How can I replicate something similar or what’s its relation to circuit design?
How does the instant charging animation work?
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A few days ago, I encountered this issue while flashing firmware on an old Android flagship device. Here's the scenario: the device was connected to its original charger on a desk, the screen was locked (not in sleep mode, but the display was off with the lock screen interface still visible), when suddenly a thin 2-3mm high green horizontal strip appeared in the top-left corner, flashing briefly before disappearing. It happened three or four times within a minute. At first, I thought it was a notification icon from a desktop app, but after pulling logs via ADB, I realized it was a system-level indicator light behavior.
Upon opening the device, I checked the back panel battery connector and found that the voltage sampling resistor's resistance was 15% higher than the official bill of materials. This was clearly due to a previous user modification where they "thickened the resistor to increase voltage when it was too low," causing the BMS (Battery Management System) to misjudge. To verify sampling accuracy, the BMS triggers a "quick battery estimation adjustment" under specific conditions (screen locked + constant voltage charging + sudden current change), briefly illuminating the LED to prompt hardware self-checking. That green light is merely a debug signal for engineers and isn't something regular users would typically encounter. If you've modified your battery circuitry, it might be worth checking the precision of the sampling voltage divider network. If the error exceeds ±5%, the system will enter this "flash light for help" mode.
And in my opinion, that's the LED charging indicator which blinks when the device is in sleep mode and connected to a charger – manufacturers use this to show that power is being supplied while the battery is being tested by the system. In most smartphones, this is configured at the firmware level, but to do it yourself, you’d need to solder a separate circuit using a controller like an ATtiny or Arduino with an RGB LED. The datasheets for these microcontrollers include examples of "blink" circuits, and if you're interested, you can even check out the sketch there.
That low battery light is probably just your battery screaming, "Hey, I'm still here!" 😂 Or maybe your system's just messing with you? Keep experimenting and learning! 🔌🌱