My next project is to be a hackable, wearable LED toy. I’m designing it to be self-contained, with a lithium cell, charging circuit, and boost regulator all on the same board. To that end, I figured the easiest pathway to follow to make it easily hackable would be to use an ATMega32U4 MCU, and have it present over USB in the same way the Arduino Leonardo does.
Since I’d already measured the average power usage of the prototype at around 100mA, I figured I’d start with the power system.
I began my search looking for an all-in-one solution which could charge the battery, provide boost regulation to 5V for the LEDs, and provide an undervoltage lockout during discharge. While the lithium cell I’ve chosen in the interim has a protection PCB built-in (as will any future cell), said protection circuits are designed solely to save the battery from catastrophic failure modes — swelling, leaking, bursting into flames — but not from any mistreatment which will “only” shorten its cycle life by a large factor. And unless there’s something I’ve grossly misunderstood about protection circuits, I figure having a second UVLO can only add to the safety margin.