Known connections
The board exposes expansion GPIO and a shared I²C connector. A physical button on verified GPIO14 is already used by the button diagnostic and LocalLink speech. Expansion I²C shares the bus used by touch and the ES8311 codec.
An addressable RGB LED and battery ADC pin are declared in the shared definitions, but current apps have no initialization/read path for them. Battery measurement calibration, power runtime, external electrical limits and attached expansion devices remain UNKNOWN. Do not present these as working firmware features.
Before attaching anything
Read the verified pin inventory. Occupied peripheral pins are not free merely because your current screen does not use them. Memory, USB and reset-strapping pins have restrictions. GPIO2 and GPIO21 are conditional candidates; connector orientation, voltage, current, loads and pulls must be checked before use. GPIO3 needs a reviewed strapping design.
A useful pattern
A physical push-to-talk button can complement touch. First run button-diag with the documented wiring, then combine it with a tested microphone path. Debounce and define press/hold/release behavior before integrating a more complex application.
Brief your coding agent
Read knowledge/pins.yaml before proposing an expansion connection. Identify occupied buses and unknown electrical details. Build a small diagnostic first. Keep pin assignments and hardware access in lib/fnk0104b.