The PCBs are ordered. I choose white this time, because I also found white battery holders, and the matrix has a white outside. Panelized two pieces on every PCB, to fill the whole 10x10cm area. There is a small square bit of the PCB added there to be glued under the USB plug, to make it thick enough (2.4mm) for the USB standard. Choose DittyPCBs, because they don't care how many designs you have on a panel.
RT @SmallCatgirl@twitter.com: i wanted to see what music was on voyager and like.... this is kind of sad.
we sent music to aliens in the 70s but we're not allowed to listen to it because "lol copyrights"
Of course each of those realizations was preceded by making a new design from scratch. Sigh. As a detour, I also experimented with putting the charlieplexed LEDs on the bottom, up-side-down, with square windows in the soldermask/copper, so that they would diffuse into nice pixels. It works, but soldering tiny LEDs up-side-down is a huge pain, and no fab house will do that for me.
Because of the thick matrix and even thicker batteries I had to ditch the business card idea. And added buttons instead of touch.
Today I worked on this design further to shave off dollars from the bill of materials. First realization: I don't actually need to have bi-color LEDs if I'm driving them in software, because I can do shades with PWM — great, now only 8x8 LEDs to charlieplex (9 pins) and single-color LEDs are *much* cheaper. Second realization: if I have single color, I can as well use a ready 8×8 matrix and drive it with 16 pins. Cheaper, less soldering and square pixels. Final realization: coin cell too weak, use 2×AA.
This took one sleepless night. In the end, I didn't charlieplex the whole 8×16 matrix (which would require making a 11×12 matrix and the rearranging it), but instead split it in two, into 9×8 and 8×7 matrices. That uses 17 pins instead of 12, but I have enough if I re-use the debugging/programming pins. It also gives me a better scanning time.
If this works, it's going to be great: apart from the bi-color LEDs and battery, I only have 3 components.
@MightyPork Yes, I know and love that family of chips — I have a whole series of projects using them at https://hackaday.io/project/20941 — and this is excellent practical advice, as it also frees the MCU to do other stuff. But this time I want to do it manually, because I want to minimize the number of parts and also because I want to learn to do this.
I need to charlieplex a 8×16 LED matrix, how hard can it be? Dear lazyweb, any hints on routing the traces for that in a reasonable way?