Add function to average n readings

Examples currently use `refresh()` to fill the data into a `hackAIRData`
struct, extract the data into separate variables to calculate the mean
value and then put the data back into the struct to use the submit function.
This is kinda clunky and this change aims to provide a better API for something
commonly used.

Author: thgeorgiou

src/hackair.cpp

@@ -41,7 +41,7 @@ void hackAIR::begin() {
     }
 }
 
-void hackAIR::refresh(hackAirData &data) {
+void hackAIR::readData(hackAirData &data) {
     if (_sensorType == SENSOR_DFROBOT) {
         // DFRobot
         char index = 0;
@@ -134,6 +134,32 @@ void hackAIR::refresh(hackAirData &data) {
     data.error = 1;
 }
 
+void hackAIR::readAverageData(hackAirData &data, uint8_t n) {
+    float sum_pm25 = 0.0f;
+    float sum_pm10 = 0.0f;
+    uint8_t successes = 0;
+
+    for (uint8_t i = 0; i < n; i++) {
+        readData(data);
+
+        if (data.error == 0) {
+            sum_pm25 += data.pm25;
+            sum_pm10 += data.pm10;
+
+            successes += 1;
+        }
+    }
+
+    data.pm25 = sum_pm25 / successes;
+    data.pm10 = sum_pm10 / successes;
+
+    if (successes != n) {
+        data.error = 1;
+    } else {
+        data.error = 0;
+    }
+}
+
 void hackAIR::clearData(hackAirData &data) {
     data.pm25 = 0;
     data.pm10 = 0;

src/hackair.h

@@ -65,10 +65,14 @@ class hackAIR {
     void begin();
 
     /**
-     * Read data from the sensor and process packages. Mainly used for digital/serial
-     * sensors.
+     * Read data from the sensor.
      */
-    void refresh(hackAirData &data);
+    void readData(hackAirData &data);
+
+    /**
+     * Read data from the sensor n times and return the average reading.
+     */
+    void readAverageData(hackAirData &data, uint8_t n);
 
     /**
      * Empties a hackAir data structure