ESP32 HTTP POST with Arduino IDE (ThingSpeak and IFTTT.com)

In this guide, you’ll learn how to make HTTP POST requests using the ESP32 board with Arduino IDE. We’ll demonstrate how to post JSON data or URL encoded values to two web APIs (ThingSpeak and IFTTT.com).
Recommended:
ESP32 HTTP GET with Arduino IDE (OpenWeatherMap.org and ThingSpeak)
HTTP POST Request Method
The Hypertext Transfer Protocol (HTTP) works as a request-response protocol between a client and server. Here’s an example:
The ESP32 (client) submits an HTTP request to a Server (for example: ThingSpeak or IFTTT.com);
The server returns a response to the ESP32 (client);
Finally, the response contains status information about the request and may also contain the requested content.
HTTP POST
POST
is used to send data to a server to create/update a resource. For example, publish sensor readings to a server.
The data sent to the server with POST is stored in the request body of the HTTP request:
POST /update HTTP/1.1
Host: example.com
api_key=api&field1=value1
Content-Type: application/x-www-form-urlencoded
In the body request, you can also send a JSON object:
POST /update HTTP/1.1
Host: example.com
{api_key: "api", field1: value1}
Content-Type: application/json
(With HTTP POST, data is not visible in the URL request. However, if it’s not encrypted, it’s still visible in the request body.)
Prerequisites
Before proceeding with this tutorial, make sure you complete the following prerequisites.
Arduino IDE
We’ll program the
ESP32
using Arduino IDE, so make sure you have the ESP32 add-on installed.
Installing the ESP32 Board in Arduino IDE (Windows, Mac OS X, Linux)
Other Web Services or APIs
In this guide, you’ll learn how to setup your
ESP32 board
to perform HTTP requests to ThingSpeak and IFTTT.com. If you prefer to learn with a local solution you can use
HTTP with Node-RED
. All examples presented in this guide also work with other APIs.
In summary, to make this guide compatible with any service, you need to search for the service API documentation. Then, you need the server name (URL or IP address), and parameters to send in the request (URL path or request body). Finally, modify our examples to integrate with any API you want to use.
1. ESP32 HTTP POST Data (ThingSpeak)
In this example, the ESP32 makes an HTTP POST request to send a new value to ThingSpeak.
Using ThingSpeak API
ThingSpeak has a free API that allows you to store and retrieve data using HTTP. In this tutorial, you’ll use the ThingSpeak API to publish and visualize data in charts from anywhere. As an example, we’ll publish random values, but in a real application you would use
real sensor readings
To use ThingSpeak API, you need an API key. Follow the next steps:
Go to
ThingSpeak.com
and create a free account.
Then, open the
Channels
tab.
Create a
New Channel
Open your newly created channel and select the
API Keys
tab to copy your Write API Key.
Code ESP32 HTTP POST ThingSpeak
Copy the next sketch to your Arduino IDE:
/*

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files.

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
*/

#include <WiFi.h>
#include <HTTPClient.h>

const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";

// Domain Name with full URL Path for HTTP POST Request
const char* serverName = "http://api.thingspeak.com/update";
// Service API Key
String apiKey = "REPLACE_WITH_YOUR_API_KEY";

// THE DEFAULT TIMER IS SET TO 10 SECONDS FOR TESTING PURPOSES
// For a final application, check the API call limits per hour/minute to avoid getting blocked/banned
unsigned long lastTime = 0;
// Set timer to 10 minutes (600000)
//unsigned long timerDelay = 600000;
// Timer set to 10 seconds (10000)
unsigned long timerDelay = 10000;

void setup() {
Serial.begin(115200);

WiFi.begin(ssid, password);
Serial.println("Connecting");
while(WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.print("Connected to WiFi network with IP Address: ");
Serial.println(WiFi.localIP());

Serial.println("Timer set to 10 seconds (timerDelay variable), it will take 10 seconds before publishing the first reading.");

// Random seed is a number used to initialize a pseudorandom number generator
randomSeed(analogRead(33));
}

void loop() {
//Send an HTTP POST request every 10 seconds
if ((millis() - lastTime) > timerDelay) {
//Check WiFi connection status
if(WiFi.status()== WL_CONNECTED){
WiFiClient client;
HTTPClient http;

// Your Domain name with URL path or IP address with path
http.begin(client, serverName);

// Specify content-type header
http.addHeader("Content-Type", "application/x-www-form-urlencoded");
// Data to send with HTTP POST
String httpRequestData = "api_key=" + apiKey + "&field1=" + String(random(40));
// Send HTTP POST request
int httpResponseCode = http.POST(httpRequestData);

/*
// If you need an HTTP request with a content type: application/json, use the following:
http.addHeader("Content-Type", "application/json");
// JSON data to send with HTTP POST
String httpRequestData = "{\"api_key\":\"" + apiKey + "\",\"field1\":\"" + String(random(40)) + "\"}";
// Send HTTP POST request
int httpResponseCode = http.POST(httpRequestData);*/

Serial.print("HTTP Response code: ");
Serial.println(httpResponseCode);

// Free resources
http.end();
}
else {
Serial.println("WiFi Disconnected");
}
lastTime = millis();
}
}
Setting your network credentials
Modify the next lines with your network credentials: SSID and password. The code is well commented on where you should make the changes.
// Replace with your network credentials
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";
Setting your API Key
Modify the
apiKey
variable to include your ThingSpeak API key.
String apiKey = "REPLACE_WITH_YOUR_API_KEY";
Now, upload the code to your board and it should work straight away. Read the next section, if you want to learn how to make the HTTP POST request.
HTTP POST Request
In the
loop()
is where you make the HTTP POST request with URL encoded data every 10 seconds with random data:
// Specify content-type header
http.addHeader("Content-Type", "application/x-www-form-urlencoded");

// Data to send with HTTP POST
String httpRequestData = "api_key=" + apiKey + "&field1=" + String(random(40));

// Send HTTP POST request
int httpResponseCode = http.POST(httpRequestData);
For example, the ESP32 makes a URL encoded request to publish a new value (30) to
field1
POST /update HTTP/1.1
Host: api.thingspeak.com
api_key=api&field1=30
Content-Type: application/x-www-form-urlencoded
Or you can uncomment these next lines to make a request with JSON data (instead of URL-encoded request):
// If you need an HTTP request with a content type: application/json, use the following:
http.addHeader("Content-Type", "application/json");

// JSON data to send with HTTP POST
String httpRequestData = "{\"api_key\":\"" + apiKey + "\",\"field1\":\"" + String(random(40)) + "\"}";

// Send HTTP POST request
int httpResponseCode = http.POST(httpRequestData);
Here’s a sample HTTP POST request with JSON data:
POST /update HTTP/1.1
Host: api.thingspeak.com
{api_key: "api", field1: 30}
Content-Type: application/json
Then, the following lines print the server response code.
Serial.print("HTTP Response code: ")