co2_sensor: Add new state INVALID (co2<=0)

This state is showed with red waiting LEDs.
Previously, the state 'BOOTUP' with blue
waiting LEDs was used to show invalid measurements.

Use blue waiting LEDs now only during sensor
acclimatization.

ampel-firmware/co2_sensor.cpp

@@ -33,6 +33,7 @@ namespace sensor {
    * INITIAL -> initial state
    * BOOTUP -> state after initializing the sensor, i.e. after scd.begin()
    * READY -> sensor does output valid information (> 0 ppm) and no other condition takes place
+   * INVALID -> sensor does output invalid CO2 measurements (== 0 ppm)
    * NEEDS_CALIBRATION -> sensor measurements are too low (< 250 ppm)
    * PREPARE_CALIBRATION -> forced calibration was initiated, waiting for stable measurements
    * CALIBRATION -> the sensor does calibrate itself
@@ -41,6 +42,7 @@ namespace sensor {
     INITIAL,
     BOOTUP,
     READY,
+    INVALID,
     NEEDS_CALIBRATION,
     PREPARE_CALIBRATION_UNSTABLE,
     PREPARE_CALIBRATION_STABLE,
@@ -50,6 +52,7 @@ namespace sensor {
       "INITIAL",
       "BOOTUP",
       "READY",
+      "INVALID",
       "NEEDS_CALIBRATION",
       "PREPARE_CALIBRATION_UNSTABLE",
       "PREPARE_CALIBRATION_STABLE",
@@ -210,7 +213,7 @@ namespace sensor {
       // NOTE: Data is available, but it's sometimes erroneous: the sensor outputs
       // zero ppm but non-zero temperature and non-zero humidity.
       Serial.println(F("Invalid sensor data - CO2 concentration supposedly 0 ppm"));
-      switchState(BOOTUP);
+      switchState(INVALID);
     } else if ((current_state == PREPARE_CALIBRATION_UNSTABLE) || (current_state == PREPARE_CALIBRATION_STABLE)) {
       // Check for pre-calibration states first, because we do not want to
       // leave them before calibration is done.
@@ -249,6 +252,9 @@ namespace sensor {
     case READY:
       displayCO2OnLedRing();
       break;
+    case INVALID:
+      led_effects::showWaitingLED(color::red);
+      break;
     case NEEDS_CALIBRATION:
       led_effects::showWaitingLED(color::magenta);
       break;