Checking sensor timer deviation

co2_sensor.cpp

@@ -2,17 +2,17 @@
 
 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 altitude_above_sea_level = ALTITUDE_ABOVE_SEA_LEVEL;  // [m]
-  uint16_t co2_calibration_level = ATMOSPHERIC_CO2_CONCENTRATION;  // [ppm]
+  uint16_t measurement_timestep = MEASUREMENT_TIMESTEP; // [s] Value between 2 and 1800 (range for SCD30 sensor)
+  const uint16_t altitude_above_sea_level = ALTITUDE_ABOVE_SEA_LEVEL; // [m]
+  uint16_t co2_calibration_level = ATMOSPHERIC_CO2_CONCENTRATION; // [ppm]
 #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.
-  const float temperature_offset = TEMPERATURE_OFFSET;  // [K]
+  const float temperature_offset = TEMPERATURE_OFFSET; // [K]
 #else
   const float temperature_offset = -3.0;  // [K] Temperature measured by sensor is usually at least 3K too high.
 #endif
-  const bool auto_calibrate_sensor = AUTO_CALIBRATE_SENSOR;  // [true / false]
+  const bool auto_calibrate_sensor = AUTO_CALIBRATE_SENSOR; // [true / false]
 }
 
 namespace sensor {
@@ -27,7 +27,7 @@ namespace sensor {
     Wire.begin(12, 14);  // ESP8266 - D6, D5;
 #endif
 #if defined(ESP32)
-    Wire.begin(21, 22);  // ESP32
+    Wire.begin(21, 22); // ESP32
     /**
      *  SCD30   ESP32
      *  VCC --- 3V3
@@ -46,11 +46,12 @@ namespace sensor {
     }
 
     // SCD30 has its own timer.
+    //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]
+    scd30.setMeasurementInterval(config::measurement_timestep); // [s]
 
     Serial.print(F("Setting temperature offset to -"));
     Serial.print(abs(config::temperature_offset));
@@ -66,10 +67,21 @@ namespace sensor {
     Serial.println(config::auto_calibrate_sensor ? "ON." : "OFF.");
   }
 
+  //NOTE: should time offset be used to reset measurement_timestep?
+  void checkTimerDeviation() {
+    static int32_t previous_measurement_at = 0; // Used to monitor sensor timer offset.
+    int32_t now = millis();
+    Serial.print("Measurement time offset : ");
+    Serial.print(now - previous_measurement_at - config::measurement_timestep * 1000);
+    Serial.println(" ms.");
+    previous_measurement_at = now;
+  }
+
   bool updateDataIfAvailable() {
     //TODO: Save count of stable measurements
-    //TODO: Compare time to previous measurements, check that it's not too far away from config::measurement_interval
+    static int16_t previous_co2 = 0;
     if (scd30.dataAvailable()) {
+      // checkTimerDeviation();
       co2 = scd30.getCO2();
       temperature = scd30.getTemperature();
       humidity = scd30.getHumidity();