ampel-firmware/co2_sensor.cpp

@@ -3,10 +3,12 @@
 namespace config {
   // Values should be defined in config.h
   uint16_t measurement_timestep = MEASUREMENT_TIMESTEP; // [s] Value between 2 and 1800 (range for SCD30 sensor)
+  const uint16_t measurement_timestep_bootup = 2; // [s] Measurement timestep during acclimatization
   const uint16_t altitude_above_sea_level = ALTITUDE_ABOVE_SEA_LEVEL; // [m]
   uint16_t co2_calibration_level = ATMOSPHERIC_CO2_CONCENTRATION; // [ppm]
   int8_t max_deviation_during_calibration = 30; // [ppm]
   int8_t enough_stable_measurements = 60;
+  const uint8_t max_deviation_during_bootup = 20; // [%]
 #ifdef TEMPERATURE_OFFSET
   // Residual heat from CO2 sensor seems to be high enough to change the temperature reading. How much should it be offset?
   // NOTE: Sign isn't relevant. The returned temperature will always be shifted down.
@@ -31,27 +33,27 @@ 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
    */
   enum state {
     INITIAL,
     BOOTUP,
     READY,
+    INVALID,
     NEEDS_CALIBRATION,
     PREPARE_CALIBRATION_UNSTABLE,
-    PREPARE_CALIBRATION_STABLE,
-    CALIBRATION
+    PREPARE_CALIBRATION_STABLE
   };
   const char *state_names[] = {
       "INITIAL",
       "BOOTUP",
       "READY",
+      "INVALID",
       "NEEDS_CALIBRATION",
       "PREPARE_CALIBRATION_UNSTABLE",
-      "PREPARE_CALIBRATION_STABLE",
-      "CALIBRATION" };
+      "PREPARE_CALIBRATION_STABLE" };
   state current_state = INITIAL;
   void switchState(state);
 
@@ -78,6 +80,10 @@ namespace sensor {
       ESP.restart();
     }
 
+    // Sometimes after a hard reset of the ESP the SCD30 needs
+    // a long time until returning the first measurement. Resetting it
+    // after startup seems to fix this behaviour.
+    scd30.reset();
     switchState(BOOTUP);
 
     Serial.print(F("Setting temperature offset to -"));
@@ -97,9 +103,9 @@ namespace sensor {
     //NOTE: The timer seems to be inaccurate, though, possibly depending on voltage. Should it be offset?
     Serial.println();
     Serial.print(F("Setting SCD30 timestep to "));
-    Serial.print(config::measurement_timestep);
-    Serial.println(" s.");
-    scd30.setMeasurementInterval(config::measurement_timestep); // [s]
+    Serial.print(config::measurement_timestep_bootup);
+    Serial.println(" s during acclimatization.");
+    scd30.setMeasurementInterval(config::measurement_timestep_bootup); // [s]
 
     sensor_console::defineIntCommand("co2", setCO2forDebugging, F(" 1500 (Sets co2 level, for debugging purposes)"));
     sensor_console::defineIntCommand("timer", setTimer, F(" 30 (Sets measurement interval, in s)"));
@@ -122,6 +128,16 @@ namespace sensor {
     previous_measurement_at = now;
   }
 
+  bool hasSensorSettled() {
+    static uint16_t last_co2 = 0;
+    uint16_t delta;
+    delta = abs(co2 - last_co2);
+    last_co2 = co2;
+    // We assume the sensor has acclimated to the environment if measurements
+    // change less than a specified percentage of the current value.
+    return (co2 > 0 && delta < ((uint32_t)co2 * config::max_deviation_during_bootup / 100));
+  }
+
   bool countStableMeasurements() {
     // Returns true, if a sufficient number of stable measurements has been observed.
     static int16_t previous_co2 = 0;
@@ -152,7 +168,6 @@ namespace sensor {
   }
 
   void calibrateAndRestart() {
-    switchState(CALIBRATION);
     Serial.print(F("Calibrating SCD30 now..."));
     scd30.setAltitudeCompensation(config::altitude_above_sea_level);
     scd30.setForcedRecalibrationFactor(config::co2_calibration_level);
@@ -185,11 +200,20 @@ namespace sensor {
   }
 
   void switchStateForCurrentPPM() {
+    if (current_state == BOOTUP) {
+      if (!hasSensorSettled()) return;
+      switchState(READY);
+      Serial.println(F("Sensor acclimatization finished."));
+      Serial.print(F("Setting SCD30 timestep to "));
+      Serial.print(config::measurement_timestep);
+      Serial.println(" s.");
+      scd30.setMeasurementInterval(config::measurement_timestep); // [s]
+    }
     if (co2 == 0) {
       // 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.
@@ -228,6 +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;
@@ -237,8 +264,6 @@ namespace sensor {
     case PREPARE_CALIBRATION_STABLE:
       led_effects::showWaitingLED(color::green);
       break;
-    case CALIBRATION: // Nothing to do, will restart soon.
-      break;
     default:
       Serial.println(F("Encountered unknown sensor state")); // This should not happen.
     }
@@ -264,8 +289,10 @@ namespace sensor {
     }
 
     showState();
-
-    return freshData;
+    
+    // Report data for further processing only if the data is reliable 
+    // (state 'READY') or manual calibration is necessary (state 'NEEDS_CALIBRATION').
+    return freshData && (current_state == READY || current_state == NEEDS_CALIBRATION);
   }
 
   /*****************************************************************