feat(nodes): adding co2_level retrieval

Refs: #3

nodes/prj.conf

@@ -1,2 +1,3 @@
+CONFIG_I2C=y
 CONFIG_SENSOR=y
 CONFIG_BT=y

nodes/src/co2_level.c

@@ -1,11 +1,34 @@
 #include "co2_level.h"
 
+static const struct device* dev = DEVICE_DT_GET_ONE(ams_ccs811);
+
 const int CO2_LEVEL_EMPTY_ROOM = 400;   // [ppm]
 
 enum error_code co2_lvl_init(){
-    return success;
+    enum error_code ret = init_failed;
+    if(device_is_ready(dev)){
+        ret = success;
+    }else{}
+    return ret;
 }
 
 enum error_code co2_lvl_get_value(int* holder){
+    struct sensor_value temp, humidity, co2;
+    enum error_code ret = read_failed;
+    int temp_value, humidity_value;
+    if( (success == thermo_get_value(&temp_value)) && (success == hygro_get_value(&humidity_value)) ){
+        // temperature conversion from deci, no function in the API
+        temp.val1 = temp_value/10;
+        temp.val2 = temp_value%10;
+        // humidity conversion is straight away
+        humidity.val1 = humidity_value;
+
+        if( (0 == sensor_sample_fetch(dev)) && 
+            (0 == sensor_channel_get(dev, SENSOR_CHAN_CO2, &co2))
+        ){
+            *holder = co2.val1; // taking only the integer part
+            ret = success;
+        }else{}
+    }else{}
     return success;
 }

nodes/src/co2_level.h

@@ -1,7 +1,12 @@
 #ifndef CO2_LEVEL_H
 #define CO2_LEVEL_H
 
+#include <zephyr/drivers/sensor.h>
+#include <zephyr/drivers/sensor/ccs811.h>
+
 #include "error_code.h"
+#include "hygrometer.h"
+#include "thermometer.h"
 
 extern const int CO2_LEVEL_EMPTY_ROOM;  // [ppm]