HTTP requests from Arduino - Mini Project: Build & Apply

HTTP requests from Arduino

📖 Scenario: You want to make your Arduino send data to a web server. This is useful for projects like weather stations or smart home devices that share information online.

🎯 Goal: Build a simple Arduino program that connects to WiFi and sends an HTTP GET request to a web server.

📋 What You'll Learn

Create a const char* variable called ssid with the WiFi network name

Create a const char* variable called password with the WiFi password

Create a const char* variable called server with the server address

Use WiFi.begin(ssid, password) to connect to WiFi

Use WiFiClient client to create a client

Use client.connect(server, 80) to connect to the server

Send an HTTP GET request using client.print()

Print the server response using Serial.println()

💡 Why This Matters

🌍 Real World

Many IoT devices send data to web servers to share sensor readings or receive commands.

💼 Career

Understanding how to make HTTP requests from embedded devices is useful for IoT developers and embedded systems engineers.

1

Set up WiFi credentials

Create two const char* variables called ssid and password. Set ssid to "YourNetwork" and password to "YourPassword".

Arduino

# Create 'ssid' and 'password' variables with the exact values
// Your code here

Hint

Use const char* ssid = "YourNetwork"; and const char* password = "YourPassword";

2

Set up server address

Create a const char* variable called server and set it to "example.com".

Arduino

const char* ssid = "YourNetwork";
const char* password = "YourPassword";
// Create 'server' variable with value "example.com"
// Your code here

Hint

Use const char* server = "example.com";

3

Connect to WiFi and server

In setup(), start serial communication with Serial.begin(115200). Use WiFi.begin(ssid, password) to connect to WiFi. Then create a WiFiClient called client and connect to the server on port 80 using client.connect(server, 80).

Arduino

const char* ssid = "YourNetwork";
const char* password = "YourPassword";
const char* server = "example.com";

void setup() {
  Serial.begin(115200);
  // Connect to WiFi
  WiFi.begin(ssid, password);
  // Create WiFiClient and connect to server
  // Your code here
}

void loop() {
}

Hint

Use Serial.begin(115200);, WiFi.begin(ssid, password);, create WiFiClient client;, then client.connect(server, 80);

4

Send HTTP GET request and print response

After connecting to the server, send an HTTP GET request for the root path using client.print(). Then read the server response line by line using client.available() and client.readStringUntil('\n'). Print each line to serial using Serial.println().

Arduino

#include 

const char* ssid = "YourNetwork";
const char* password = "YourPassword";
const char* server = "example.com";

void setup() {
  Serial.begin(115200);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nWiFi connected");

  WiFiClient client;
  if (client.connect(server, 80)) {
    Serial.println("Connected to server");
    // Send HTTP GET request and print response
    // Your code here
  } else {
    Serial.println("Connection failed");
  }
}

void loop() {
}

Hint

Send the GET request with client.print(). Use a while loop with client.available() to read lines and print them with Serial.println().

Practice

1. What is the main purpose of using HTTPClient in Arduino sketches?

easy

A. To control digital pins

B. To connect to WiFi networks

C. To read analog sensor values

D. To send and receive HTTP requests easily

Solution

1. Step 1: Understand the role of HTTPClient

   The HTTPClient library is designed to simplify sending HTTP requests like GET and POST from Arduino.

2. Step 2: Differentiate from other libraries

   Connecting to WiFi is done by WiFiClient, not HTTPClient. Reading sensors or controlling pins is unrelated.

3. Final Answer:

   To send and receive HTTP requests easily -> Option D

4. Quick Check:

   HTTPClient = HTTP requests [OK]

Hint: HTTPClient handles web requests, not WiFi or sensors [OK]

Common Mistakes:

• Confusing HTTPClient with WiFi connection library
• Thinking HTTPClient reads sensors
• Assuming HTTPClient controls pins

2. Which of the following is the correct way to start a GET request using HTTPClient in Arduino?

easy

A. http.connect("http://example.com");

B. http.startGET("http://example.com");

C. http.begin("http://example.com");

D. http.open("http://example.com");

Solution

1. Step 1: Recall HTTPClient method for starting requests

   The correct method to initialize a request is begin() with the URL as argument.

2. Step 2: Check other options

   Methods like connect(), startGET(), or open() do not exist in HTTPClient library.

3. Final Answer:

   http.begin("http://example.com"); -> Option C

4. Quick Check:

   Use begin() to start HTTP request [OK]

Hint: Use begin() to start HTTP requests in Arduino [OK]

Common Mistakes:

• Using non-existent methods like connect() or open()
• Confusing begin() with WiFi connection functions
• Forgetting to pass the URL string

3. What will the following Arduino code print if the HTTP GET request to http://example.com/data returns status 200 and body "OK"?

HTTPClient http;
http.begin("http://example.com/data");
int httpCode = http.GET();
if (httpCode > 0) {
  String payload = http.getString();
  Serial.println(httpCode);
  Serial.println(payload);
} else {
  Serial.println("Error");
}
http.end();

medium

A. 200
OK

B. Error

C. 404
Not Found

D. 0

Solution

1. Step 1: Analyze the HTTP GET response code

   The code checks if httpCode > 0. Since the server returns 200, this condition is true.

2. Step 2: Print status code and response body

   The code prints the status code (200) and then the response body ("OK") on separate lines.

3. Final Answer:

   200 OK -> Option A

4. Quick Check:

   200 status means success, prints code and body [OK]

Hint: Status > 0 means success; print code and body [OK]

Common Mistakes:

• Assuming error when status is 200
• Confusing status code with response body
• Not calling http.end() to close connection

4. Identify the error in this Arduino code snippet for sending a POST request:

HTTPClient http;
http.begin("http://example.com/api");
http.addHeader("Content-Type", "application/json");
int httpCode = http.POST("{\"value\": 42}");
if (httpCode == 200) {
  Serial.println("Success");
}
http.end();

medium

A. Incorrect header name; should be "ContentType"

B. Missing WiFi connection before HTTPClient usage

C. POST method requires no argument

D. http.end() should be called before POST

Solution

1. Step 1: Check prerequisites for HTTP requests

   Before using HTTPClient, Arduino must be connected to WiFi. This code snippet does not show WiFi connection setup.

2. Step 2: Validate headers and method usage

   Header name "Content-Type" is correct, POST accepts a string argument, and http.end() is correctly called after POST.

3. Final Answer:

   Missing WiFi connection before HTTPClient usage -> Option B

4. Quick Check:

   WiFi must connect before HTTPClient [OK]

Hint: Always connect WiFi before HTTP requests [OK]

Common Mistakes:

• Skipping WiFi connection setup
• Using wrong header names
• Calling http.end() too early

5. You want to send sensor data as JSON to a server using Arduino's HTTPClient. Which sequence correctly sends a POST request with JSON data and handles the response?

hard

A. Connect WiFi -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> http.POST(jsonData) -> check httpCode -> http.end()

B. http.begin(url) -> http.POST(jsonData) -> http.addHeader("Content-Type", "application/json") -> check httpCode -> http.end()

C. Connect WiFi -> http.POST(jsonData) -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> check httpCode -> http.end()

D. Connect WiFi -> http.addHeader("Content-Type", "application/json") -> http.begin(url) -> http.POST(jsonData) -> check httpCode -> http.end()

Solution

1. Step 1: Establish WiFi connection first

   Arduino must connect to WiFi before making HTTP requests.

2. Step 2: Follow correct HTTPClient method order

   Start with http.begin(url), then set headers, then send POST with data, check response code, and finally call http.end().

3. Final Answer:

   Connect WiFi -> http.begin(url) -> http.addHeader("Content-Type", "application/json") -> http.POST(jsonData) -> check httpCode -> http.end() -> Option A

4. Quick Check:

   WiFi -> begin() -> headers -> POST -> end() [OK]

Hint: Connect WiFi first, then begin(), addHeader(), POST, end() [OK]

Common Mistakes:

• Calling POST before begin()
• Adding headers after POST
• Skipping WiFi connection