co2_sensor: Handle pre-calibration by states

* split state PREPARECALIBRATION into
PREPARECALIBRATION_INSTABLE (co2 measurements are changing
too much to start calibration) and

PREPARECALIBRATION_STABLE (co2 measurements are stable,
now waiting for 60 stable measurements)

* Handle all possible LED signal states in showState()
* drop now unused `waiting_color`

ampel-firmware/co2_sensor.cpp

@@ -24,7 +24,6 @@ namespace sensor {
   float humidity = 0;
   char timestamp[23];
   int16_t stable_measurements = 0;
-  uint32_t waiting_color = color::blue;
 
   /**
    * Define sensor states
@@ -36,13 +35,21 @@ namespace sensor {
    * PREPARECALIBRATION -> forced calibration was initiated, waiting for stable measurements
    * CALIBRATION -> the sensor does calibrate itself
    */
-  enum state {INITIAL, BOOTUP, READY, NEEDSCALIBRATION, PREPARECALIBRATION, CALIBRATION};
+  enum state {
+    INITIAL,
+    BOOTUP,
+    READY,
+    NEEDSCALIBRATION,
+    PREPARECALIBRATION_INSTABLE,
+    PREPARECALIBRATION_STABLE,
+    CALIBRATION};
   const char *state_names[] = {
     "INITIAL",
     "BOOTUP",
     "READY",
     "NEEDSCALIBRATION",
-    "PREPARECALIBRATION",
+    "PREPARECALIBRATION_INSTABLE",
+    "PREPARECALIBRATION_STABLE",
     "CALIBRATION"
   };
   state current_state = INITIAL;
@@ -114,19 +121,21 @@ namespace sensor {
     previous_measurement_at = now;
   }
 
-  void countStableMeasurements() {
+  bool countStableMeasurements() {
+    // Returns true, if a sufficient number of stable measurements has been observed.
     static int16_t previous_co2 = 0;
     if (co2 > (previous_co2 - config::max_deviation_during_calibration)
         && co2 < (previous_co2 + config::max_deviation_during_calibration)) {
       stable_measurements++;
       Serial.print(F("Number of stable measurements : "));
       Serial.println(stable_measurements);
-      waiting_color = color::green;
+      switchState(PREPARECALIBRATION_STABLE);
     } else {
       stable_measurements = 0;
-      waiting_color = color::red;
+      switchState(PREPARECALIBRATION_INSTABLE);
     }
     previous_co2 = co2;
+    return (stable_measurements == config::enough_stable_measurements);
   }
 
   void startCalibrationProcess() {
@@ -138,7 +147,7 @@ namespace sensor {
     scd30.setMeasurementInterval(2); // [s] The change will only take effect after next measurement.
     Serial.println(F("Waiting until the measurements are stable for at least 2 minutes."));
     Serial.println(F("It could take a very long time."));
-    switchState(PREPARECALIBRATION);
+    switchState(PREPARECALIBRATION_INSTABLE);
   }
 
   void calibrateAndRestart() {
@@ -191,7 +200,8 @@ namespace sensor {
       // No special signaling, we want to show the CO2 value
       case READY: break;
       case NEEDSCALIBRATION: led_effects::showWaitingLED(color::magenta); break;
-      case PREPARECALIBRATION: led_effects::showWaitingLED(waiting_color); break;
+      case PREPARECALIBRATION_INSTABLE: led_effects::showWaitingLED(color::red); break;
+      case PREPARECALIBRATION_STABLE: led_effects::showWaitingLED(color::green); break;
       // No special signaling here, too.
       case CALIBRATION: break;
       // This should not happen.
@@ -218,14 +228,17 @@ namespace sensor {
         // zero ppm but non-zero temperature and non-zero humidity.
         Serial.println(F("Invalid sensor data - CO2 concentration <= 0 ppm"));
         switchState(BOOTUP);
+      } else if ((current_state == PREPARECALIBRATION_INSTABLE) ||
+                 (current_state == PREPARECALIBRATION_STABLE)) {
+        // Check for pre-calibration states first, because we do not want to
+        // leave them before calibration is done.
+        bool ready_for_calibration = countStableMeasurements();
+        if (ready_for_calibration) {
+          calibrateAndRestart();
+        }
       } else if (co2 < 250) {
         // Sensor should be calibrated.
         switchState(NEEDSCALIBRATION);
-      } else if (current_state == PREPARECALIBRATION) {
-        countStableMeasurements();
-        if (stable_measurements == config::enough_stable_measurements) {
-          calibrateAndRestart();
-        }
       } else {
         switchState(READY);
       }