Merry Christmas! PCB Christmas tree using WS2812C RGB LEDs and Attiny85.

[rohanwoods]

Decided to dive head first into some PCB design and make a Christmas tree that I could give out as gifts this festive season. Pictures and video of it in action below:
https://imgur.com/a/bX1Yeng
https://youtu.be/aDBNVOSA5uU
Only took me 3 revisions for a mostly finished version. Will most likely make a version that just runs off USB without a battery as this makes them quite a bit cheaper to make.
The design uses 3 interlocking boards in the shape of a Christmas tree and an Attiny85 to control 22x WS2812C RGB LEDS. These are lower power (5 ma per colour) versions of the WS2812B (also known as Neopixels). The B versions end up too bright, even with the C versions I ended up running at 20% brightness). These are covered with foam dots to defuse the light. A boost converter ups the battery voltage to 5v and a charge IC takes care of battery management. I have put in the circuitry for reprogramming the Attiny from the USB port, but I have not tested it yet.
Version 1 - Proof of concept, just ordered the main board. Turns out I should of listened when the datasheet for the boost controller said there is a DC path through the boost converter even when it is disabled. So it worked, it just wouldn't turn off. The whole circuit apparently runs on 3.7v without an issue.
Version 2 - All three boards. Put in a mosfet to switch power on and off. Routed the battery to a pin on the Attiny for voltage monitoring, turns out it will power the entire circuit from this pin. Missed a trace that connected VCC to the last LED. Ended up getting the base board from JLCPCB completely covered in soldermask despite following the Eagle export procedure exactly from their website for all three boards.

A cut trace, two mod wires (I think red mod wires look a little festive anyway) and much scraping gave a working prototype. Using the Seed Studio 2-layer export option to create gerbers from Eagle resulted in the next set of board turning out fine.

Version 3 - No real mistakes, but the battery is not removable.
I learnt that cheap batteries from eBay tell outrageous lies - the "2300 Mah" battery I used runs the tree for 4h20m at roughly 50ma consumption. I expected them to be a little off their quoted specs, but not by an order of magnitude!