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//Air Quality Monitoring #include "MQ135.h" #include <ESP8266WiFi.h>   String apiKey = " ";     //  Enter your Write API key from ThingSpeak  const char *ssid =" ";     // replace with your wifi ssid and wpa2 key const char *pass =" "; const char* server = "api.thingspeak.com"; const int sensorPin= 0; int air_quality; WiFiClient client;  void setup()  {        Serial.begin(115200);        delay(10);        Serial.println("Connecting to ");        Serial.println(ssid);         WiFi.begin(ssid, pass);        while (WiFi.status() != WL_CONNECTED)       {             delay(500);             Serial.print(".");      }       Serial.println("");       Serial.println("WiFi connected");   }   void loop()  {               MQ135 gasSensor = MQ135(A0);       air_quality = gasSensor.getPPM(); 

 if (client.connect(server,80))   //   "184.106.153.149" or api.thingspeak.com                       {                                                             String postStr = apiKey;                                                            postStr +="&field1=";                              postStr += String(air_quality);                              postStr += "\r\n\r\n";                                client.print("POST /update HTTP/1.1\n");                              client.print("Host: api.thingspeak.com\n");                              client.print("Connection: close\n");                              client.print("X-THINGSPEAKAPIKEY: "+apiKey+"\n");                              client.print("Content-Type: application/x-www-form-urlencoded\n");                              client.print("Content-Length: ");                              client.print(postStr.length());                              client.print("\n\n");                              client.print(postStr);                                                              //Serial.print("%, Gas Value: ");                              //Serial.print(h);                              Serial.print("%, Air Quality: ");                              Serial.print(air_quality);                              Serial.println("PPM. Send to Thingspeak.");                         }           client.stop();            Serial.println("Waiting...");      // thingspeak needs minimum 15 sec delay between updates   delay(1000); }