The ability to make custom electronics has seen something of a revolution in the last 10 years or so, with cheaply available microcontrollers, custom PCBs and accessible design software. One thing that is still a hassle for many, however, is figuring out how to appropriately power these devices. A DC power supply is one choice, as are disposable batteries, but you might also consider the common rechargeable 18650 cell that resembles a AA battery.
To charge these cells, YouTuber Androkavo has a novel solution made out of a flexible PCB. It bends into shape, then holds onto the battery contacts with magnets hidden in a novel “PCB pocket” or attached with wires. Because of its use of a flexible substrate, this charger is able to attach to many other types of rechargeable cells, such as the 26650 and 14500. For shorter cells, like the 10180, a secondary magnet is needed to complete the circuit without bending the PCB so far as to cause damage.
The charger is equipped with an STM8S003F3P6 microcontroller on its surface, as well as several other components including a micro USB breakout. This allows it to show the battery’s voltage level numerically via a series of LEDs that light up 4, 3, or blinking for 2 volts — along with a tenths place with LEDs indicating 0–9.