Usb audio device

Hardware

KiCad 10 project for the board the firmware in ../firmware/ runs on.

USB_Audio_Device.kicad_pro     project
USB_Audio_Device.kicad_sch     schematic
USB_Audio_Device.kicad_pcb     layout
USB_Audio_Device-BOM.csv       bill of materials
schematic_export.pdf           schematic, no KiCad needed
fp-lib-table / sym-lib-table   library tables
_USB_Audio_Device.pretty/      project-local footprints

Design summary

Full net-to-GPIO mapping is in ../firmware/main/board.h, annotated against this schematic.

Three things missing from this snapshot

These came from the working copy of the project and are worth knowing about before you open it on a different machine.

1. The symbol library isn't here. sym-lib-table points at an absolute Windows path:

(lib (name "_USB_Audio_Device") (type "KiCad")
     (uri "D:/USB_Audio_Device_PCB/Components/_USB_Audio_Device.kicad_sym") ...)

The schematic still opens and renders correctly — KiCad caches every symbol definition inside the .kicad_sch itself — but the library shows as missing, and "Update Symbols from Library" won't work. To fix it, copy _USB_Audio_Device.kicad_sym into this folder and change that uri to:

${KIPRJMOD}/_USB_Audio_Device.kicad_sym

fp-lib-table already uses ${KIPRJMOD}, so footprints resolve fine as-is.

2. One footprint is absent. USB_A_Molex_48037-2200_Horizontal is referenced by J2 in the BOM but its .kicad_mod file wasn't in the set I was given. The PCB will open — the layout stores its own copy of every placed footprint — but the library entry is missing. Drop the file into _USB_Audio_Device.pretty/ when you find it.

3. 3D models point at D:/. Every footprint references a .step/.iges under D:/USB_Audio_Device_PCB/Components/. The 3D viewer will show those parts as blank. Harmless for fabrication; only matters if you want a rendering.

Note on footprint filenames

KiCad resolves a footprint by filename, so each .kicad_mod here is named after the footprint it declares — e.g. the file declaring (footprint "SOT95P280X145-6N_(USB_ESD)") is saved as SOT95P280X145-6N_(USB_ESD).kicad_mod. If you re-export from your working copy, keep that convention or the library won't resolve.

If there's a rev B

One suggestion from writing the firmware: add a dedicated user button on a spare GPIO. SW1 is hardwired to the module's EN pin so it can only reset, which leaves SW2 (on IO0, a strapping pin) as the only button software can read. That works, but it means holding the button while the board powers up drops it into flashing mode instead of playing. GPIO21, 34, 35, 36 and 37 are all unused and unstrapped.