Assign correct board per sketch via sketch.yaml; gate in CI (#11)

.github/workflows/compile-sketches.yml

@@ -1,13 +1,18 @@
 # Compiles sketches on every push to master and every PR, so a change that breaks
 # a sketch is caught before it lands. Mirrors the CI in makelab-arduino-lib.
 #
-# START-GREEN POLICY: this gates only on folders verified to compile cleanly (via
+# START-GREEN POLICY: this gates only on sketches verified to compile cleanly (via
 # a full arduino-cli sweep). Coverage grows as issues close:
 #   - ESP32/ is mid core-v3.x migration .......... #12
-#   - Sensors/PlayingMusic/AddressableLEDs/Serial   have wrong-board sketches that
-#     need per-sketch sketch.yaml board targeting .. #11
-#   - CPX/ (samd), nRF52840/ (nrf52), UnoR4WiFi/ ... add once their heavier cores
-#     are wired in here.
+#   - The board-specific sketches in Sensors/AddressableLEDs/Serial are now gated
+#     on their real boards (SAMD / nRF52 / Leonardo) via the matrix jobs below; the
+#     per-sketch target lives in each sketch's sketch.yaml ........... #11
+#   - The remaining plain-Uno sketches in Sensors/PlayingMusic/AddressableLEDs/
+#     Serial all compile green and can be added to the Uno job in a follow-up.
+# NOTE: arduino/compile-sketches compiles every sketch in a job with that job's
+# single fqbn — it does NOT read sketch.yaml. So a folder path can only be gated
+# wholesale when every sketch under it targets the same board; mixed-board folders
+# must list individual sketches under the matching board's job.
 # Legacy sketches (docs/legacy-sketches.md) are never gated; add a skip step here
 # when a gated folder starts including any.
 name: Compile Sketches
@@ -27,28 +32,57 @@ jobs:
       matrix:
         include:
           - fqbn: arduino:avr:uno
-            platform: arduino:avr
+            platforms: |
+              - name: arduino:avr
             sketch-paths: |
               - Basics
               - OLED
               - Filters
               - Servo
           - fqbn: arduino:avr:leonardo
-            platform: arduino:avr
+            platforms: |
+              - name: arduino:avr
             sketch-paths: |
               - HumanInterfaceDevice
               - GameController
+              # Serial1 (a second hardware UART) doesn't exist on the Uno; these
+              # need a Leonardo-class board. See each sketch's sketch.yaml.
+              - Serial/SimpleSerial1Transmitter
+              - Serial/SimpleSerial1Receiver
+              - Serial/SimpleSerial1Bidirectional
+          # I2S MEMS-mic sketches: hardware I2S peripheral ⇒ SAMD (Feather M0).
+          # I2S.h ships with the Adafruit SAMD core (no separate library).
+          - fqbn: adafruit:samd:adafruit_feather_m0_express
+            platforms: |
+              - name: adafruit:samd
+                source-url: https://adafruit.github.io/arduino-board-index/package_adafruit_index.json
+            sketch-paths: |
+              - Sensors/i2s-Microphone
+          # Onboard-NeoPixel sketches (PIN_NEOPIXEL) ⇒ nRF52840 Feather.
+          - fqbn: adafruit:nrf52:feather52840
+            platforms: |
+              - name: adafruit:nrf52
+                source-url: https://adafruit.github.io/arduino-board-index/package_adafruit_index.json
+            sketch-paths: |
+              - AddressableLEDs/NeoPixel/BlinkOnboardNeoPixel
+              - Sensors/Microphone/SoundLevelOnboardNeopixel
 
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
+      # The Adafruit nRF52 core invokes adafruit-nrfutil (a pip tool) from its
+      # build recipe even for a plain compile, so it must be on PATH. It's
+      # bundled in a normal IDE install but not on the CI runner.
+      - name: Install adafruit-nrfutil (nRF52 build recipe needs it)
+        if: startsWith(matrix.fqbn, 'adafruit:nrf52')
+        run: pip install adafruit-nrfutil
+
       - name: Compile sketches
         uses: arduino/compile-sketches@v1
         with:
           fqbn: ${{ matrix.fqbn }}
-          platforms: |
-            - name: ${{ matrix.platform }}
+          platforms: ${{ matrix.platforms }}
           # Libraries used by the gated folders. The MakeabilityLab library is
           # installed straight from its repo (not yet in Library Manager). The
           # rest come from Library Manager; deps are listed explicitly so an
@@ -65,6 +99,9 @@ jobs:
             - name: Servo
             - name: Mouse
             - name: Keyboard
+            - name: Adafruit NeoPixel
+            - name: Adafruit Zero I2S Library
+            - name: Adafruit Zero DMA Library
           sketch-paths: ${{ matrix.sketch-paths }}
           enable-warnings-report: true
           verbose: false

AddressableLEDs/NeoPixel/BlinkOnboardNeoPixel/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather nRF52840 Express).
+default_fqbn: adafruit:nrf52:feather52840

CLAUDE.md

@@ -18,7 +18,7 @@ There is **no build system, package manifest, or automated test suite.** Each pr
   ```
   arduino-cli compile --fqbn <board-fqbn> <SketchFolder>
   ```
-  Each sketch lives in its own folder whose name matches the `.ino` file (Arduino requirement). There is no committed board config; choose the FQBN per sketch by hardware folder:
+  Each sketch lives in its own folder whose name matches the `.ino` file (Arduino requirement). Most sketches have no committed board config — choose the FQBN per sketch by hardware folder (table below). The exceptions are board-specific sketches that carry a `sketch.yaml` pinning their exact target (see note after the table):
   | Folder | Board | FQBN |
   |---|---|---|
   | `Basics/`, `OLED/`, `Filters/`, `Sensors/`, `Servo/`, etc. | Arduino Uno (AVR) | `arduino:avr:uno` |
@@ -29,6 +29,8 @@ There is **no build system, package manifest, or automated test suite.** Each pr
   | `nRF52840/` | nRF52840 board (verify exact board) | `adafruit:nrf52:feather52840` |
 
   Installed cores: `arduino:avr`, `arduino:renesas_uno`, `esp32:esp32`, `adafruit:samd`, `adafruit:nrf52`. The AVR/HID split is inferred from each sketch's APIs (`Mouse.h`/`Keyboard.h` ⇒ Leonardo-class); the `nRF52840/` board defaults to Feather Express but confirm the exact board from the sketch header. Legacy `RedBearDuo/` and Processing have no installable core — skip compile-checking them.
+
+  **Per-sketch `sketch.yaml` (board pinning):** a handful of sketches whose required board differs from their folder default (e.g. the i2s-mic sketches under `Sensors/` need SAMD, the `Serial1` sketches need a Leonardo) carry a one-key `sketch.yaml` with `default_fqbn:`. `arduino-cli` reads it so a bare `arduino-cli compile <Folder>` targets the right board; students using the Arduino IDE still select the board manually via `Tools → Board` (the file just shows as a tab). Each `sketch.yaml` is commented to explain this so it isn't a mystery to readers. Note: `arduino/compile-sketches` (the CI action) does **not** read `sketch.yaml` — it compiles a folder with one FQBN per matrix job — so the CI matrix in `.github/workflows/compile-sketches.yml` must independently list mixed-board sketches under the matching board's job.
 - **Python helpers** (`Python/`): require Python 3 and `pip install pyserial`. Run directly, e.g. `python Python/SerialReader/serial_reader.py --list`. Note the common pitfall: install `pyserial`, **not** `serial`.
 - **Processing sketches** (`.pde`, `Processing/`): legacy/historical only — the project has shifted to p5.js. Don't invest in modernizing these unless asked.
 

PlayingMusic/SimpleMp3PlayerWithi2sMic/SimpleMp3PlayerWithi2sMic.ino

@@ -1,3 +1,10 @@
+// ============================================================================
+// LEGACY EXAMPLE (does not compile).
+// An abandoned experiment: it #includes the SAMD-only <I2S.h> on an nRF52840
+// Feather, and—per the original note below—the i2s-mic and VS1053 mp3 libraries
+// are mutually incompatible, so it never worked. Kept for reference only.
+// Excluded from compile CI. See docs/legacy-sketches.md.
+// ============================================================================
 /**
  * WARNING: this sketch doesn't work due to incompatibilities between the i2s mic library
  * and the mp3 player library.

Sensors/Microphone/SoundLevelOnboardNeopixel/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather nRF52840 Express).
+default_fqbn: adafruit:nrf52:feather52840

Sensors/i2s-Microphone/MicInputPlotter/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/MicInputPlotterInterrupt/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/MicPlotterAdafruitZeroI2s/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/VUMeter/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/VUMeterInterrupt/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/VUMeterInterruptLED/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/VUMeterInterruptLEDWithFade/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Sensors/i2s-Microphone/VUMeterInterruptOnboardNeopixel/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Adafruit Feather M0 Express).
+default_fqbn: adafruit:samd:adafruit_feather_m0_express

Serial/SimpleSerial1Bidirectional/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Arduino Leonardo).
+default_fqbn: arduino:avr:leonardo

Serial/SimpleSerial1Receiver/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Arduino Leonardo).
+default_fqbn: arduino:avr:leonardo

Serial/SimpleSerial1Transmitter/sketch.yaml

@@ -0,0 +1,4 @@
+# Records the board this sketch is written for, so the Arduino CLI and our
+# compile-check CI build it for the right target. In the IDE you still pick the
+# board yourself via Tools -> Board (here: Arduino Leonardo).
+default_fqbn: arduino:avr:leonardo

docs/legacy-sketches.md

@@ -27,3 +27,12 @@ ESP32/Tone/AnalogInputToneWithOLED
 ESP32/Tone/BallBounceTone32WithOLED
 ESP32/Tone/PlayScale
 ESP32/Tone/PlayScaleWithOLED
+
+## PlayingMusic — abandoned i2s-mic + mp3 experiment (never worked)
+
+`SimpleMp3PlayerWithi2sMic` #includes the SAMD-only `<I2S.h>` on an nRF52840
+Feather and combines the i2s-mic and Adafruit VS1053 mp3 libraries, which are
+mutually incompatible — the sketch's own header documents that it never worked.
+Kept for reference; it compiles on no board.
+
+PlayingMusic/SimpleMp3PlayerWithi2sMic