✨ LCD Backlight Timer (#23768)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/lcd/marlinui.cpp

@@ -180,6 +180,15 @@ constexpr uint8_t epps = ENCODER_PULSES_PER_STEP;
   volatile int8_t encoderDiff; // Updated in update_buttons, added to encoderPosition every LCD update
 #endif
 
+#if LCD_BACKLIGHT_TIMEOUT
+  uint16_t MarlinUI::lcd_backlight_timeout; // Initialized by settings.load()
+  millis_t MarlinUI::backlight_off_ms = 0;
+  void MarlinUI::refresh_backlight_timeout() {
+    backlight_off_ms = lcd_backlight_timeout ? millis() + lcd_backlight_timeout * 1000UL : 0;
+    WRITE(LCD_BACKLIGHT_PIN, HIGH);
+  }
+#endif
+
 void MarlinUI::init() {
 
   init_lcd();
@@ -1033,14 +1042,18 @@ void MarlinUI::init() {
 
           reset_status_timeout(ms);
 
+          #if LCD_BACKLIGHT_TIMEOUT
+            refresh_backlight_timeout();
+          #endif
+
           refresh(LCDVIEW_REDRAW_NOW);
 
           #if LED_POWEROFF_TIMEOUT > 0
             if (!powerManager.psu_on) leds.reset_timeout(ms);
           #endif
-        }
+        } // encoder activity
 
-      #endif
+      #endif // HAS_ENCODER_ACTION
 
       // This runs every ~100ms when idling often enough.
       // Instead of tracking changes just redraw the Status Screen once per second.
@@ -1137,6 +1150,13 @@ void MarlinUI::init() {
           return_to_status();
       #endif
 
+      #if LCD_BACKLIGHT_TIMEOUT
+        if (backlight_off_ms && ELAPSED(ms, backlight_off_ms)) {
+          WRITE(LCD_BACKLIGHT_PIN, LOW); // Backlight off
+          backlight_off_ms = 0;
+        }
+      #endif
+
       // Change state of drawing flag between screen updates
       if (!drawing_screen) switch (lcdDrawUpdate) {
         case LCDVIEW_CLEAR_CALL_REDRAW: