Bela Gem Stereo schematics/drawings

tobias_s

Hello!
I just received my Bela Gem Stereo(s) and first of all Thanks so much for this amazing product!!

I had a custom pcb with buttons and stuff for my "old" bela and i would like to adapt it to the new one. Do you plan to release any schematics or ideally a KiCad footprint?

Thanks in advance for the response!

giuliomoro

great that they are being received already!

Here are the schematics and connector layouts: https://github.com/BelaPlatform/bela-hardware

You can also find the symbols and footprints and 3D models here: https://github.com/BelaPlatform/bela-hardware/tree/master/bela-kicad-library . Note that we made two symbols and footprints for each:

a "standard" one with only a subset of pins, the ones most likely to be used
an "advanced" one with all the pins:

tobias_s

great, thank you!

tobias_s

Hello! I’m currently working on a PCB using your library and noticed a potential problem.
In the schematic/footprint, I²C2 is mapped to P1.26 and P1.28, while the “main” I²C is shown on P1.33 and P1.36. However, as far as I understand, the I²C interface on P1.33 and P1.36 is no longer available, and P1.26/P1.28 are now the primary (or only) I²C pins.
It seems possible that this change comes from a hardware revision that hasn’t yet been included in the KiCad library.
Thanks a lot for the otherwise very helpful library!

giuliomoro

P1.26 and P1.28 are those used on the qwiic and labelled as SCL SDA on the cape itself (labelled GEM_I2C_Sxx in the symbol/footprint). Those are the recommended ones for connecting external devices, they are clocked at 400 kHz. P1.33 and P1.36 (labelled GEM_AUD_Sxx in the symbol/footprint) are used on board by the codecs and are clocked at 100 kHz.

Btw, I just pushed a update to the library, make sure you pull before continuing.

tobias_s

Aha, that makes sense, thanks for the information! that opened another question: i would like to connect a button matrix to bela - ideally with low latency and jitter. my idea was to connect an rp2040 over UART and send midi signals from it to bela. however after your last answer i suppose GEM_AUD_DOUT and GEM_AUD_IN are internally used. how would you advise to connect the rp2040 to the bela gem stereo?

giuliomoro

For UART you can use UART4 on P1.20 and P2.20. Simply update your board and add /overlays/PB2-UART4.dtbo to the correct line in extlinux.conf as explained here https://learn.bela.io/using-bela/technical-explainers/device-tree-overlays/#loading-a-device-tree-overlay.