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#8 Arduino Mega: Display Realtime Temperature graph on cloud (using LM35 and ESP01)

IoT Tutorial #8 [ Arduino Mega Tutorials #8 ]
In this program,
Analog Temperature sensor (LM35) is connected to the Arduino Mega board and Its output will be sent to server (Cloud) where we can see the visual graph of Temperature vs Time.

ESP01 WiFi Module is used to connect to the Internet and send data to server

The output is shown using GRAPH (Temperature vs Time)on thinkspeak server.

Internal 10 bit ADC (A0) is used to read the Analog output of the Temperature Sensor.

Physical Connections: 
Arduino Mega  ->  LM35 (Analog Tempt Sensor)
5v            ->  Vcc (Left Pin - Flat side facing towards you)
A0            ->  Analog Out (Middle Pin)  (10mV / degree Celcious) 
Gnd           ->  Gnd (Right Pin - Flat side facing towards you)

Pin 13 -> LED+ 
Gnd    -> LED-

PIN DIAGRAM OF ESP01: (This module works on 3.3v) (NOT 5v)
| |=| |=| |=|============== |
| | | | | | |    ANTENA     |
| | |=| |=| | Facing ur side|
| ========================= |
|                           |
| GND   GPIO0   GPIO2   RxD |
|  o      o      o       o  |
|                           |
|  o      o      o       o  |
| TxD   CH_PD    RST    Vcc |

ESP01   ->  Arduino
Vcc     ->  3.3V
GND     ->  GND
TxD     ->  Rx1 (Pin 19)
RxD     ->  Tx1 (Pin 18)
CH_PD   ->  3.3V

Serial Communication with PC through USB cable (Tx0 and Rx0)

  1. Sign up at
  2. Channels > New Channel > Update "Name" and "Field 1" field names > Save Channel
  3. Click On API keys > Copy "Write API key"
  4. Make all the Connections to Arduino Mega board mentioned Above.
  5. Change Following 3 fields in below written program.
    a. apiKey by above copied "Write API key" (in step 3)
    b. ssid_name (Name of you WiFi)
    c. password (Passord of your WiFi)
  6. Upload Program to Arduino Mega Board
  7. Open Arduino Serial Monitor on PC (Set Baud Rate to 9600 and set "Both NL & CR"
  8. Go to and login
    Channels > My Channels > Click on Channel Name (created in step 2) > Private View
    Here you can observe the Graph of Temperature Vs Day.
For Better understanding you can watch demonstration video given below:

Download link is given in the Description of the YouTube video shown below.



int ledPin = 13;      // LED+
//float j=0;          
int temp_sensor = A0; // LM35 Output

String apiKey = "W4BW8JXBYH3NBUMS";  //Change this key to your "Write API key"

void setup() {
  // put your setup code here, to run once: 
  pinMode(ledPin, OUTPUT); // Set ledPin as Output
  Serial.begin(9600);      // PC Arduino Serial Monitor
  Serial1.begin(115200);   // Arduino to ESP01 Communication
  connectWiFi();           // To connect to Wifi

void loop() { 
  // put your main code here, to run repeatedly:
  float analog_val = analogRead(temp_sensor);     // Read Analog Temperature
  float digital_vout = (analog_val*5000.0)/1023;  // Convert Analog Tempt. to Digital Value (10 bit ADC) // mV
  float tempc = digital_vout/10;                  // Storing value in Degree Celsius

  digitalWrite(ledPin, HIGH); // LED ON
  delay(500);                 // wait for 500 mSec
  digitalWrite(ledPin, LOW);  // LED OFF

  Serial1.println("AT+CIPMUX=0\r\n");      // To Set MUX = 0
  delay(2000);                             // Wait for 2 sec

  // TCP connection 
  String cmd = "AT+CIPSTART=\"TCP\",\"";   // TCP connection with server
  cmd += "";                // IP addr of
  cmd += "\",80\r\n\r\n";                  // Port No. = 80

  Serial1.println(cmd);                    // Display above Command on PC
  Serial.println(cmd);                     // Send above command to Rx1, Tx1

  delay(20000);                            // Wait for 20 Sec

  if(Serial1.find("ERROR"))                // If returns error in TCP connection
    Serial.println("AT+CIPSTART error");   // Display error msg to PC

  // prepare GET string 
  String getStr = "GET /update?api_key=";   
  getStr += apiKey;
  getStr +="&field1=";
  getStr += tempc; 
  getStr += "\r\n\r\n"; 

  Serial.println(getStr);                 // Display GET String on PC

  cmd = "AT+CIPSEND=";                    // send data length 
  cmd += String(getStr.length());

  Serial.println(cmd);                   // Display Data length on PC
  Serial1.println(cmd);                  // Send Data length command to Tx1, Rx1
  delay(20000);                          // wait for 20sec

  if(Serial1.find(">"))                    // If prompt opens //verify connection with cloud
    Serial.println("connected to Cloud");  // Display confirmation msg to PC
    Serial1.print(getStr);                 // Send GET String to Rx1, Tx1
    Serial1.println("AT+CIPCLOSE\r\n");    // Send Close Connection command to Rx1, Tx1
    Serial.println("AT+CIPCLOSE");         // Display Connection closed command on PC
  // thingspeak free version needs 16 sec delay between updates 
  delay(16000);                            // wait for 16sec


boolean connectWiFi() {               // Connect to Wifi Function
  Serial1.println("AT+CWMODE=1\r\n"); // Setting Mode = 1 
  delay(100);                         // wait for 100 mSec

  String cmd = "AT+CWJAP=\"";         // Connect to WiFi
  cmd += "SuiteUp";                   // ssid_name
  cmd += "\",\"";
  cmd += "welcome@10";                // password
  cmd += "\"\r\n";              
  Serial.println(cmd);                // Display Connect Wifi Command on PC
  Serial1.println(cmd);               // send Connect WiFi command to Rx1, Tx1 
  delay(10000);                       // wait for 10 sec

  Serial1.println("AT+CWJAP?");       // Verify Connected WiFi

    Serial.println("OK, Connected to WiFi.");         // Display Confirmation msg on PC
    return true;
    Serial.println("Can not connect to the WiFi.");   // Display Error msg on PC
    return false;

Click here to see more codes for Arduino Mega (ATMega 2560) and similar Family.

Feel free to ask doubts in the comment section. I will try my best to solve it.
If you find this helpful by any mean like, comment and share the post.
This is the simplest way to encourage me to keep doing such work.

Thanks and Regards,
-Akshay P. Daga


  1. Showing warnings like:

    C:\Users\Divyanshu\Desktop\Temperature_Graph_WiFi-APDaga\Temperature_Graph_WiFi-APDaga.ino: In function 'void loop()':

    C:\Users\Divyanshu\Desktop\Temperature_Graph_WiFi-APDaga\Temperature_Graph_WiFi-APDaga.ino:41:26: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]

    if(Serial1.find("ERROR")) // If returns error in TCP connection


    C:\Users\Divyanshu\Desktop\Temperature_Graph_WiFi-APDaga\Temperature_Graph_WiFi-APDaga.ino:65:22: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]

    if(Serial1.find(">")) // If prompt opens //verify connection with cloud


    C:\Users\Divyanshu\Desktop\Temperature_Graph_WiFi-APDaga\Temperature_Graph_WiFi-APDaga.ino: In function 'boolean connectWiFi()':

    C:\Users\Divyanshu\Desktop\Temperature_Graph_WiFi-APDaga\Temperature_Graph_WiFi-APDaga.ino:98:27: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]



  2. I need some help....
    I would like to send sensor data to my LocalHost. so i changed the

    String cmd = "AT+CIPSTART=\"TCP\",\""; // TCP connection with server
    cmd += "my local host ip address"; // IP addr of
    cmd += "\",80\r\n\r\n"; // Port No. = 80

    // prepare GET string
    String getStr = "sensordata.php?api_key=";

    But no success....I would appreciate your efforts

  3. Hi sir, i need a help sir
    I am getting a connected to cloud statement in serial monitor but i am not getting my result on thingspeak graph,
    Plzz help me sir

  4. i am getting this error while varifying program - Serial1 was not declare in this scope
    please help

    1. Are you sure, you are using Arduino Mega 2560 board ?
      If you are using Arduino Uno or similar small board, there is no Serial1 in Arduino Uno. (Uno has only one serial module : Serial)

  5. i'm having a problem, the sketch doesn't upload to the board, every time it shows me this message:avrdude: stk500v2_getsync(): timeout communicating with programmer, what i'm i doing wrong? i have the same arduino, the same esp-01, i configured it with no problem (using the previous video), but now it won't upload

    1. I won't be able to debug your problem with this much information.
      Please try again by following each and every step I mentioned.