// The code includes reading the voltage from the temperature sensor (pin A0), 
//calculating the temperature and sending the data to ThingSpeak using the ESP8266 module.

#include <SoftwareSerial.h>

SoftwareSerial esp8266(2, 3);     // RX, TX   virtual
                                  
// Access Point Connection Data   
String AP   = "HPY413";        // Replaced with SSID: HPY413
String PASS = "HpyN0!@#";      // Replaced with WiFi password: HpyN0!@#

// ThingSpeak parameters for the first account
String API1 = "0BZ0QZFDWLLCZFVY";   // my Write API key 0BZ0QZFDWLLCZFVY
String field1 = "field1";
String field2 = "field2";

// ThingSpeak parameters for the second account
String API2 = "OI39DD1R52C0ZEHC";   // second Write API key OI39DD1R52C0ZEHC
String field4 = "field4";

String HOST = "api.thingspeak.com";
String PORT = "80";

// Global variables
int retransmissions_counter;
boolean response_found = false;
int sensorValue;

void setup() {

  Serial.begin(9600);       // Communication between PC and Arduino using the native serial port at 9600 baud
  esp8266.begin(115200);    // Communication between Arduino and ESP8266 using the virtual serial port at 115200 baud

  // Check the connection
  sendCommand("AT", 5, "OK");
  delay(2000);

  // Set the WiFi mode
  sendCommand("AT+CWMODE=1", 5, "OK");
  delay(2000);

  // Connect to the wireless Access Point (AP)
  sendCommand("AT+CWJAP=\"" + AP + "\",\"" + PASS + "\"", 20, "OK");
  delay(2000);
}

void loop() {
  
  int sensorValue = analogRead(A0);                          // Read the value of the sensor 0-1023
  float voltage   = sensorValue * (5.0 / 1023.0);            // Convert it to Voltage 0-5 V
  float temperatureC = (voltage * 100.0) - 273.2;            // Calculate Temperature
  Serial.println(temperatureC);                              // Print Temperature

  // Send data to the first ThingSpeak account
  sendDataToThingSpeak(API1, field1, voltage);
  delay(15000);
  sendDataToThingSpeak(API1, field2, temperatureC);
  delay(15000);
  
  // Send data to the second ThingSpeak account
  sendDataToThingSpeak(API2, field4, temperatureC);
  delay(15000);                                         // Delay between successive packet transmissions
}

void sendDataToThingSpeak(String API, String field, float value) {

  // The GET command is used to send data to the ThingSpeak channel
  String getData = "GET /update?api_key=" + API + "&" + field + "=" + String(value);
  //String getData = "GET /update?api_key=" + API + "&" + field1 + "=" + String(value1) + + "&" + field2 + "=" + String(value2);

  // Enable multiple connections
  sendCommand("AT+CIPMUX=1", 5, "OK");
  delay(2000);

  // Establish a TCP connection with the ThingSpeak platform
  sendCommand("AT+CIPSTART=0,\"TCP\",\"" + HOST + "\"," + PORT, 15, "OK");
  delay(2000);

  // Send the data
  sendCommand("AT+CIPSEND=0," + String(getData.length() + 4), 4, ">");
  esp8266.println(getData);
  delay(5000);

  // Close the TCP connection
  sendCommand("AT+CIPCLOSE=0", 5, "OK");
}

void sendCommand(String command, int maxRetransmissions, char expectedResponse[]) {

   Serial.print(command);
   Serial.print(" ");

  while (retransmissions_counter < maxRetransmissions) {
   
    esp8266.println(command);
    if (esp8266.find(expectedResponse)) {
      response_found = true;
      break;
    }
    retransmissions_counter++;
  }

  if (response_found == true) {
    Serial.println("Success!");
    retransmissions_counter = 0;
    
  } else if (response_found == false) {
     Serial.println("Fail!");
     retransmissions_counter = 0;
  }
  response_found = false;
}