YouTube channel posted a video on his work, a flexible PCB with a charging and voltmeter circuit. The idea behind this is to just flex the PCB around the battery and some magnets will keep it in place. On the flexible PCB there is a USB charging circuit and a small voltmeter taht will show you the voltage using some LEDs. Pretty nice right?
The design is quite simple. Around the charging circuit there is an STM8 microcontroller used to read the analog value and then turn on a few LEDs and by that show the voltage with a precision of 100mV.
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