Maybe you're troubleshooting your Kyria, or maybe you're looking to add modifications to it. Here's an overview of the microcontroller connections on the Kyria. The pins used will be the same regardless of whether you're using a Pro Micro or an Elite C, with the main difference being that the Elite C will have four more unused pins available.
If you're not using a pin, such as if you're not using a rotary encoder or if you've chosen to break off the sixth column, you can reuse the pin for modifications. All used pins on the Kyria are broken out along the top edge of the board, but you can also choose to connect them to the microcontroller directly.
The Kyria makes use of serial by default. Both halves also make use of their local individual I2C bus. This means that when adding devices on I2C, they will be local to just the half you add them on.
Making use of I2C across halves instead of serial is not recommended: the OLED displays share an address and the ATmega32u4 isn't powerful enough to drive two OLED displays at once, so when using a single I2C bus you are restricted to using only a single OLED display.
For the key matrix, COL7 can be broken off and can be reused for modding. A 2u key can be used on MXa21 (the outer thumb key), freeing up MX13 on the matrix (ROW2, COL0). A 2u key can be used on MXa22 (the inner thumb key), freeing up MX14 (ROW2, COL1).
If you're using a rotary encoder, the button functionality of the encoder uses the following pins depending on the spot you placed the encoder:
- ENC1: ROW0, COL7
- ENC2: ROW2, COL7
- ENC3: ROW3, COL4
If your encoder does not have a button, you can reuse the spot on the matrix. For the encoder functionality itself, pin A and pin B of the encoder are shared among all encoder positions, so they can only be reused if you use no encoder at all.
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If you made a cool modification to your Kyria, I'd love to know about it! Send me a photo, link or other info to firstname.lastname@example.org and maybe I'll be able to add your mod in a future revision or feature it in a blog post for others to apply as well.