davedarkoBy now I've realised that I forgot to add all the 20 diodes to make the charlie-plexed keyboard function. In the current arrangement there will be no way of telling if I have pressed the button connected to the 1-2 pins, or the 2-1 pins.
This basically made me choose between upscaling the SAML22 to the version that Joey Castillo is using for his amazing casio F91W replacement boards. I could also try to place twenty diodes all over the board. Or ten and do some crazy "check if both combinations are working or just one" firmware. In the end I used an IO expander that is dedicated to read keyboard matrices, got some TCA8418RTWR on aliexpress, as they're out of stock everywhere else.
Soon I will try to get the UF2 bootloader running on the watch and then start programming it via the USB socket. First I need to cut out room for the plug though :)
https://github.com/joeycastillo/uf2-samdx1
Little side note: Joey will soon start a crowdfunding campaign with his awesome project, find it here:
https://www.crowdsupply.com/oddly-specific-objects/sensor-watch
More on the project on the blog:
https://hackaday.com/2021/08/08/wristwatch-pcb-swaps-must-be-in-the-air/
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74922/3 FTW
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Aww...
Those kinds of mistakes always suck - they're just past the "I can easily fix this" portion, but still kinda in the "I want to try and get it working" range.
In any case, a dedicated button matrix IC sounds like a decent option. I think I used one once that had a lovely combination of button scanning + seven-segment driving, all in one chip.
Most button ICs should also have an interrupt line, so you could use that to save some power by sleeping the MCU!
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sounds like one of those fancy IS51 chips, I think I used one too :) I still have to find out if everything else checks out and only then I will work in the revisions and reorder.
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I wouldn't really call it "fancy"
For some reason, the default I2C address was... 0
The general-call address. And you have to use that 0 address plus a hardware pin to set it to a different address <.<
I also think it didn't have a power-on reset, so sometimes I had to leave it unplugged for a bit longer before it was back to zero...?
It was an odd fella.
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