co2_sensor.cpp

#include "co2_sensor.h"

namespace config {
  // UPPERCASE 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]
  const uint16_t measurement_timestep_bootup = 5; // [s] Measurement timestep during acclimatization.
  const uint8_t max_deviation_during_bootup = 20; // [%]
  const int8_t max_deviation_during_calibration = 30; // [ppm]
  const int16_t timestep_during_calibration = 10; // [s] WARNING: Measurements can be unreliable for timesteps shorter than 10s.
  const int8_t stable_measurements_before_calibration = 120 / timestep_during_calibration; // [-] Stable measurements during at least 2 minutes.

#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]
#else
  const float temperature_offset = -3.0;  // [K] Temperature measured by sensor is usually at least 3K too high.
#endif
  bool auto_calibrate_sensor = AUTO_CALIBRATE_SENSOR; // [true / false]
  const bool debug_sensor_states = false; // If true, log state transitions over serial console
}

namespace sensor {
  SCD30 scd30;
  uint16_t co2 = 0;
  float temperature = 0;
  float humidity = 0;
  char timestamp[23];
  int16_t stable_measurements = 0;

  /**
   * Define sensor states
   * BOOTUP -> initial state, until first >0 ppm values are returned
   * READY -> sensor does output valid information (> 0 ppm) and no other condition takes place
   * NEEDS_CALIBRATION -> sensor measurements are too low (< 250 ppm)
   * PREPARE_CALIBRATION_UNSTABLE -> forced calibration was initiated, last measurements were too far apart
   * PREPARE_CALIBRATION_STABLE -> forced calibration was initiated, last measurements were close to each others
   */
  enum state {
    BOOTUP,
    READY,
    NEEDS_CALIBRATION,
    PREPARE_CALIBRATION_UNSTABLE,
    PREPARE_CALIBRATION_STABLE
  };
  const char *state_names[] = {
      "BOOTUP",
      "READY",
      "NEEDS_CALIBRATION",
      "PREPARE_CALIBRATION_UNSTABLE",
      "PREPARE_CALIBRATION_STABLE" };

  state current_state = BOOTUP;
  void switchState(state);

  void initialize() {
#if defined(ESP8266)
    Wire.begin(12, 14); // ESP8266 - D6, D5;
#endif
#if defined(ESP32)
    Wire.begin(21, 22); // ESP32
    /**
     *  SCD30   ESP32
     *  VCC --- 3V3
     *  GND --- GND
     *  SCL --- SCL (GPIO22) //NOTE: GPIO3 Would be more convenient (right next to GND)
     *  SDA --- SDA (GPIO21) //NOTE: GPIO1 would be more convenient (right next to GPO3)
     */