Add build workflow to build code for each HW rev.

.github/workflows/build.yml

@@ -0,0 +1,48 @@
+name: Build
+
+on:
+  workflow_call:
+    inputs:
+      hwVersion:
+        description: "The version of the hardware to compile for (e.g. HW5, HW4, ...)"
+        required: true
+        type: string
+
+env:
+  ARDUINO_LIBRARY_ENABLE_UNSAFE_INSTALL: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Arduino CLI
+        uses: arduino/setup-arduino-cli@v1
+
+      - name: Install platform
+        run: |
+          arduino-cli core update-index
+          arduino-cli core install arduino:avr
+
+      - name: Install libraries
+        run: |
+          arduino-cli lib install \
+            "SdFat" \
+            "Adafruit SSD1306" \
+            "Adafruit GFX Library" \
+            "Adafruit BusIO" \
+            "U8g2" \
+            "Adafruit NeoPixel" \
+            "RotaryEncoder" \
+            "Etherkit Si5351" \
+            "RTClib" \
+            "FreqCount"
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Compile
+        run: |
+          cd Cart_Reader/
+          # Select hardware version by uncommenting it (using regular expression)
+          sed -i 's/^\/\/[\t ]*#define ${{ inputs.hwVersion }}/#define ${{ inputs.hwVersion }}/g' Cart_Reader.ino
+          arduino-cli compile --fqbn arduino:avr:mega

.github/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on: [push]
+
+jobs:
+  HW5:
+    uses: ./.github/workflows/build.yml
+    with:
+      hwVersion: "HW5"
+
+  HW4:
+    uses: ./.github/workflows/build.yml
+    with:
+      hwVersion: "HW4"
+
+  HW3:
+    uses: ./.github/workflows/build.yml
+    with:
+      hwVersion: "HW3"
+
+  HW2:
+    uses: ./.github/workflows/build.yml
+    with:
+      hwVersion: "HW2"
+
+  HW1:
+    uses: ./.github/workflows/build.yml
+    with:
+      hwVersion: "HW1"