add co2, eco2

Adafruit_Sensor.cpp

@@ -70,6 +70,12 @@ void Adafruit_Sensor::printSensorDetails(void) {
   case SENSOR_TYPE_NOX_INDEX:
     Serial.print(F("Nitrogen Oxides (Index)"));
     break;
+  case SENSOR_TYPE_CO2:
+    Serial.print(F("Carbon Dioxide (ppm)"));
+    break;
+  case SENSOR_TYPE_eCO2:
+    Serial.print(F("Equivalent/estimated CO2 (ppm)"));
+    break;
   }
 
   Serial.println();

Adafruit_Sensor.h

@@ -69,7 +69,9 @@ typedef enum {
   SENSOR_TYPE_COLOR = (17),
   SENSOR_TYPE_TVOC = (18),
   SENSOR_TYPE_VOC_INDEX = (19),
-  SENSOR_TYPE_NOX_INDEX = (20)
+  SENSOR_TYPE_NOX_INDEX = (20),
+  SENSOR_TYPE_CO2 = (21),
+  SENSOR_TYPE_eCO2 = (22),
 } sensors_type_t;
 
 /** struct sensors_vec_s is used to return a vector in a common format. */
@@ -142,6 +144,9 @@ typedef struct {
                           normal (unitless) */
     float nox_index; /**< NOx (Nitrogen Oxides) index where 100 is normal
                           (unitless) */
+    float CO2;       /**< Measured CO2 in parts per million (ppm) */
+    float eCO2;      /**< equivalent/estimated CO2 in parts per million (ppm
+                        estimated from some other measurement) */
     sensors_color_t color; /**< color in RGB component values */
   };                       ///< Union for the wide ranges of data we can carry
 } sensors_event_t;

README.md

@@ -77,7 +77,9 @@ typedef enum
   SENSOR_TYPE_COLOR                 = (17),
   SENSOR_TYPE_TVOC                  = (18),
   SENSOR_TYPE_VOC_INDEX             = (19),
-  SENSOR_TYPE_NOX_INDEX             = (20)
+  SENSOR_TYPE_NOX_INDEX             = (20),
+  SENSOR_TYPE_CO2                   = (21),
+  SENSOR_TYPE_eCO2                  = (22),
 } sensors_type_t;
 ```
 
@@ -143,6 +145,8 @@ typedef struct
         float           tvoc;
         float           voc_index;
         float           nox_index;
+        float           CO2,
+        float           eCO2,
         sensors_color_t color;
     };
 } sensors_event_t;
@@ -188,6 +192,8 @@ A key part of the abstraction layer is the standardisation of values on SI units
 - **tvoc**: values are in **parts per billion** (ppb)
 - **voc_index**: values are an **index** from 1-500 with 100 being normal
 - **nox_index**: values are an **index** from 1-500 with 100 being normal
+- **CO2**: values are in **parts per million*** (ppm)
+- **eCO2**: values are in **parts per million*** (ppm)
 
 
 ## The Unified Driver Abstraction Layer in Practice ##