So, Adafruit has those nice 8x8 LED matrix backpacks, which use I²C for communication and are generally very cool to play with. They even have shields (FeatherWings) for their boards with them. However, in my workshops I'm using D1 Mini boards (mostly because they are cheaper). I decided that it would be very nice to have such a shield for the D1 Mini, so I decided to try to make one.

I started by ordering a HT16K33 breakout board, some loose chips in the 20-pin packages, and a handful of those LED matrices. Once they arrived, I assembled a prototype on the breadboard, to make sure I got all the connections right:

Then I tested it with my HT16K33 MicroPython library. Turns out that the original backpacks are shifted by one column for some reason, so that they start at column 1 and end at column 0 (instead of starting at 0 and ending at 7). Oh well, a quick fix, and my shield is compatible.

Next, I need to design the actual PCB. To the Fritzing!

Maybe it's not the simplest thing to route, but it's not too horrible either. I kept all parts on the same side (the chip goes under the matrix), for ease of assembly. Unfortunately the board has to be duble-layer -- there are just too many crossing traces. I wonder why they didn't design those chips to match the matrix pinout better.

The board is exactly one inch by one inch, by the way -- would have been a nice candidate for the one square inch contest.

Next, to OSHPark to order the boards, and now I'm just waiting for them to arrive. Should be here before Christmas.