Wait until measurements are stable. Code mostly from Mario Lukas. GPL

co2_sensor.cpp

@@ -46,33 +46,61 @@ namespace sensor {
     }
 
     // SCD30 has its own timer.
-    Serial.println("\nSetting SCD30 timestep to " + String(config::measurement_timestep) + " s.");
+    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("Setting temperature offset to -");
+    Serial.print(F("Setting temperature offset to -"));
     Serial.print(abs(config::temperature_offset));
     Serial.println(" K.");
     scd30.setTemperatureOffset(abs(config::temperature_offset)); // setTemperatureOffset only accepts positive numbers, but shifts the temperature down.
 
-    Serial.print("Temperature offset is : -");
+    Serial.print(F("Temperature offset is : -"));
     Serial.print(scd30.getTemperatureOffset());
     Serial.println(" K");
 
-    Serial.print("Auto-calibration is ");
+    Serial.print(F("Auto-calibration is "));
     Serial.println(config::auto_calibrate_sensor ? "ON." : "OFF.");
   }
 
-// Force SCD30 calibration with countdown.
-  void startCalibrationProcess() {
+  void waitUntilMeasurementsAreStable() {
+    //TODO: Refactor completely, in order to avoid very long loop?
     /** From the sensor documentation:
      * For best results, the sensor has to be run in a stable environment in continuous mode at
      * a measurement rate of 2s for at least two minutes before applying the FRC command and sending the reference value.
      */
-    Serial.println("Setting SCD30 timestep to 2s, prior to calibration.");
-    scd30.setMeasurementInterval(2);  // [s] The change will only take effect after next measurement.
-    LedEffects::showKITTWheel(color::blue, config::measurement_timestep);
-    Serial.println("Waiting 2 minutes.");
-    LedEffects::showKITTWheel(color::blue, 120);
+    Serial.println(F("Setting SCD30 timestep to 2s, prior to calibration."));
+    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."));
+
+    //########################################################################################################
+    // (c) Mario Lukas
+    // https://github.com/mariolukas/Watterott-CO2-Ampel-Plus-Firmware/blob/main/CO2-Ampel_Plus/Sensor.cpp#L57
+    uint32_t last_color = color::blue;
+    int stable_measurements = 0, last_co2 = 0;
+    for (stable_measurements = 0; stable_measurements < 60;) {
+      if (scd30.dataAvailable()) {
+        co2 = scd30.getCO2();
+        //No more than +/-30ppm variation compared to previous measurement.
+        if ((co2 > (last_co2 - 30)) && (co2 < (last_co2 + 30))) {
+          last_color = color::green;
+          stable_measurements++;
+        } else {
+          last_color = color::red;
+          stable_measurements = 0;
+        }
+        last_co2 = co2;
+      }
+      LedEffects::showKITTWheel(last_color, 1);
+    }
+    //########################################################################################################
+  }
+
+  void startCalibrationProcess() {
+    waitUntilMeasurementsAreStable();
     Serial.print("Starting SCD30 calibration...");
     scd30.setAltitudeCompensation(config::altitude_above_sea_level);
     scd30.setForcedRecalibrationFactor(config::co2_calibration_level);