Single colour LEDs, I think, will be removed anyway

Gaugecontroller_no_VFD/Gaugecontroller_no_VFD.ino

@@ -7,9 +7,9 @@
 static const uint8_t GAUGE_COUNT = 5;
 
 // Backlight/status LEDs use an addressable strip. Indicator LEDs are
-// single-colour active-high outputs on per-gauge pins. The command protocol
+// single-colour active-high PWM outputs on per-gauge pins. The command protocol
 // still exposes one logical LED segment per gauge.
-static const uint8_t LED_DATA_PIN = 22;
+static const uint8_t LED_DATA_PIN = A8;
 static const uint8_t BREATHE_FRAME_MS = 16;
 static const uint8_t LED_SHOW_MIN_INTERVAL_MS = 16;
 static const uint8_t LED_SHOW_MOTION_INTERVAL_MS = 50;
@@ -161,6 +161,9 @@ uint8_t ledLocalIdx[TOTAL_LEDS];
 bool ledIsIndicator[TOTAL_LEDS];
 bool ledRgSwap[TOTAL_LEDS];
 BlinkState blinkState[TOTAL_LEDS];
+volatile uint8_t indicatorPwmLevel[TOTAL_INDICATOR_LEDS];
+volatile uint8_t* indicatorPwmPort[TOTAL_INDICATOR_LEDS];
+uint8_t indicatorPwmMask[TOTAL_INDICATOR_LEDS];
 bool mainLedsDirty = false;
 unsigned long lastLedShowMs = 0;
 
@@ -185,18 +188,16 @@ inline int8_t indicatorPinFor(uint8_t gaugeIdx, uint8_t localIdx) {
   return -1;
 }
 
-inline bool indicatorIsOn(uint8_t localIdx, CRGB color) {
+inline uint8_t indicatorLevel(uint8_t localIdx, CRGB color) {
-  if (localIdx == 3) return color.r >= 128;
+  if (localIdx == 3) return color.r;
-  if (localIdx == 4) return color.g >= 128;
+  if (localIdx == 4) return color.g;
-  return false;
+  return 0;
 }
 
 inline void writeIndicatorLed(uint8_t globalIdx, CRGB color) {
-  uint8_t gaugeIdx = ledGaugeIdx[globalIdx];
+  uint8_t pwmIdx = ledPhysicalIdx[globalIdx];
-  uint8_t localIdx = ledLocalIdx[globalIdx];
+  if (pwmIdx < TOTAL_INDICATOR_LEDS) {
-  int8_t pin = indicatorPinFor(gaugeIdx, localIdx);
+    indicatorPwmLevel[pwmIdx] = indicatorLevel(ledLocalIdx[globalIdx], color);
-  if (pin >= 0) {
-    digitalWrite(pin, indicatorIsOn(localIdx, color) ? HIGH : LOW);
   }
 }
 
@@ -480,7 +481,29 @@ void setupStepperTimer() {
   SREG = oldSreg;
 }
 
+inline void updateIndicatorPwmIsr() {
+  static uint8_t phase = 0;
+  phase++;
+
+  for (uint8_t i = 0; i < TOTAL_INDICATOR_LEDS; i++) {
+    volatile uint8_t* port = indicatorPwmPort[i];
+    if (port == nullptr) continue;
+
+    uint8_t mask = indicatorPwmMask[i];
+    uint8_t level = indicatorPwmLevel[i];
+    if (level == 0) {
+      *port &= ~mask;
+    } else if (level == 255 || phase < level) {
+      *port |= mask;
+    } else {
+      *port &= ~mask;
+    }
+  }
+}
+
 ISR(TIMER1_COMPA_vect) {
+  updateIndicatorPwmIsr();
+
   for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
     StepperRuntime& s = steppers[i];
     bool pulseJustEnded = false;
@@ -1219,6 +1242,7 @@ void setup() {
   // offsets for the addressable main strip.
   uint8_t ledOff = 0;
   uint8_t mainLedOff = 0;
+  uint8_t indicatorLedOff = 0;
   for (uint8_t i = 0; i < GAUGE_COUNT; i++) {
     gaugeLedCount[i] = cstrLen(gaugePins[i].ledOrder);
     gaugeLedOffset[i] = ledOff;
@@ -1232,9 +1256,17 @@ void setup() {
       ledIsIndicator[globalIdx] = indicator;
       ledRgSwap[globalIdx] = gaugePins[i].ledOrder[localIdx] == 'G' ||
                              gaugePins[i].ledOrder[localIdx] == 'g';
-      ledPhysicalIdx[globalIdx] = indicator
+      if (indicator) {
-          ? 0
+        ledPhysicalIdx[globalIdx] = indicatorLedOff;
-          : mainLedOff + localIdx - (localIdx > 4 ? 2 : 0);
+        int8_t pin = indicatorPinFor(i, localIdx);
+        if (pin >= 0) {
+          indicatorPwmPort[indicatorLedOff] = portOutputRegister(digitalPinToPort(pin));
+          indicatorPwmMask[indicatorLedOff] = digitalPinToBitMask(pin);
+        }
+        indicatorLedOff++;
+      } else {
+        ledPhysicalIdx[globalIdx] = mainLedOff + localIdx - (localIdx > 4 ? 2 : 0);
+      }
     }
 
     ledOff += gaugeLedCount[i];