This is a small blinky with 20 LEDs powered by one CR2032 coin cell
and with an ATTiny45 brain. The firmware is written in plain C and
compiled with the avr-gcc toolchain. The PCB is a two layer design made
Space efficient daisychained LED placing with shared anode/cathode soldering pads.
Firmware and gerbers are available on GitHub:
Jens has shared the board on OSH Park:
Here is a video of the LED in action: