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The LEDs are driven by a Trinket M0 microcontroller with a LiPo “backpack” to provide power, attachment points for the exposed power switch and recharging capability to the 110 mAh 3.7 V battery.

It turned out to be a very interesting project, with plenty of info on how to build an accurate voltage logger for really small projects. Adafruit’s TIMESQUARE watch is a small circuit board ...