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Channel Update and Light Control with ESP32

This example shows how to update your channel and fetch commands from a ThingSpeak™ TalkBack queue. Use the commands to change the status of the onboard LED.

Use TalkBack when your application involves a machine that you want to run only when there is a command in the queue.

You can simultaneously update your channel and retrieve the latest command saved in a TalkBack queue. Add the parameter talkback_key to your POST request and ThingSpeak returns the latest TalkBack command in the response.

Supported Hardware

  • ESP32


You must have at least one channel set up to complete this example. Create a Channel, as shown in Collect Data in a New Channel and record the write API key. You also need to set up a TalkBack. Go to Apps > TalkBacks and choose New TalkBack.

Add Commands to TalkBack Queue

You can add commands to a TalkBack queue in one of two ways.

  • Use the ThingSpeak TalkBack web interface to add commands to the TalkBack queue. You can configure TalkBack to have up to 8000 commands.

  • Use the ThingSpeak API. You can use an HTTP POST request to add a command to the queue. In the following POST, replace TALKBACK_ID, YOUR_TALKBACK_API_KEY, TALKBACK_COMMAND, and POSITION_NUMBER with the appropriate values fro your channel.


Program Your ESP32

1) Download the latest Arduino® IDE.

2) Install the ESP32 core. For more information, see Install Arduino ESP32 Support.

3) In the Tools menu, select the appropriate port and board in the Arduino IDE. This example is tested using the Sparkfun ESP32 Thing option.

4) Paste the code into the Arduino IDE. Add your wireless network information, your TalkBack API key, and your TalkBack number.

5) Program the device and then watch the serial monitor and the LED to observe changes when commands are consumed. Each command that is executed is removed from the list. You need to add more commands to the list after they are consumed.


1) Begin by including the appropriate libraries and defining variables. Enter your network SSID and password. Enter your channel number and the TalkBack parameters: myTalkBackID and myTalkBackKey.


Description: Checks a TalkBack queue every 60 seconds and sets the state of the built in LED according
             to the latest command fetched. Turn the LED on and off by using the commands TURN_ON and TURN_OFF.
             The TalkBack documentation can be found at            

Hardware: ESP32-based boards

- Requires installation of EPS32 core. 
- Select the target hardware from the Tools -> Board menu

Copyright 2018, The MathWorks, Inc.

#include <WiFi.h>

char ssid[] = <enter your SSID>;   // your network SSID (name) 
char pass[] = <enter your password>;   // your network password

WiFiClient  client;

unsigned long myChannelNumber = <enter your channel ID>;
unsigned long myTalkBackID = <enter your talkback ID>;
const char * myTalkBackKey = <enter your TalkBack API Key>;

// Initialize values for ThingSpeak updates
int number1 = 0;
int number2 = random(0,100);
int number3 = random(0,100);
int number4 = random(0,100);

2) In the setup function, initialize the LED and start the serial monitor.

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);  // Set up LED
  Serial.begin(115200);  // Initialize serial

3) In the main loop, start by establishing a connection to the local Wi-Fi network. Create the POST message from the randomly generated numbers. Make the POST, verify the result, and check for a TalkBack command. Then generate new random numbers to post again in 20 seconds.

void loop() {

  // Connect or reconnect to Wi-Fi
  if(WiFi.status() != WL_CONNECTED){
    Serial.print("Attempting to connect to SSID: ");
    while(WiFi.status() != WL_CONNECTED){
      WiFi.begin(ssid, pass);  

  // Create the message body for the POST out of the values
  String postMessage =  String("field1=") + String(number1) +
                        String("&field2=") + String(number2) +
                        String("&field3=") + String(number3) +
                        String("&field4=") + String(number4) +
                        String("&api_key=") + String(myWriteAPIKey) +
                        String("&talkback_key=") + String(myTalkBackKey);                      

   // Make a String for any commands that might be in the queue
  String newCommand = String();

  // Make the POST to ThingSpeak
  int x = httpPOST(postMessage, newCommand);
  // Check the result
  if(x == 200){
    Serial.println("checking queue..."); 
    // Check for a command returned from TalkBack
    if(newCommand.length() != 0){

      Serial.print("  Latest command from queue: ");
      if(newCommand == "TURN_ON"){
        digitalWrite(LED_BUILTIN, HIGH);  

      if(newCommand == "TURN_OFF"){
        digitalWrite(LED_BUILTIN, LOW);
      Serial.println("  Nothing new.");  
    Serial.println("Problem checking queue. HTTP error code " + String(x));

  // Confirm code works by changing values
  if(number1 > 99){
    number1 = 0;
  number2 = random(0,100);
  number3 = random(0,100);
  number4 = random(0,100);
  delay(20000); // Wait 20 seconds to update the channel again

4) Use the httpPOST function to post data to ThingSpeak and read the next TalkBack command.

int httpPOST(String postMessage, String &response){

  bool connectSuccess = false;
  connectSuccess = client.connect("",80);

      return -301;   
  postMessage += "&headers=false";
  String Headers =  String("POST /update HTTP/1.1\r\n") +
                    String("Host:\r\n") +
                    String("Content-Type: application/x-www-form-urlencoded\r\n") +
                    String("Connection: close\r\n") +
                    String("Content-Length: ") + String(postMessage.length()) +


  long startWaitForResponseAt = millis();
  while(client.available() == 0 && millis() - startWaitForResponseAt < 5000){

  if(client.available() == 0){       
    return -304; // Didn't get server response in time

  if(!client.find(const_cast<char *>("HTTP/1.1"))){
      return -303; // Couldn't parse response (didn't find HTTP/1.1)
  int status = client.parseInt();
  if(status != 200){
    return status;

  if(!client.find(const_cast<char *>("\n\r\n"))){
    return -303;

  String tempString = String(client.readString());
  response = tempString;
  return status;