I had been trying to think of ideas to use the various COB LEDs I had seen on AliExpress (eg https://www.aliexpress.us/item/2251832649051832.html) as personal illumination for Burning Man.
They're powered by an ATTINY85, a boost converter (to run 12V LEDs on a 5V USB pack), and because these share a common negative, a combo of P-channel FET + BJT to drive that.

Because they are very bright, usually they need to be very dim, so I needed better than 8-bit PWM, which needed some special handling to work on the ATTINY85 for 3 separate channels.

This is the first result. They work out very well attached to backpacks / hydration flasks. Easy to put on go out for the night with plenty of battery to last.