Read values from an Arduino via HTTP
In this tutorial I want to expand the Arduino Web Server tutorial to read the values measured by a sensor, so we can just open a page on our browser and see the data.
For example we’re going to measure the temperature using a DHT11 sensor, and we’re going to measure the distance from an object using a proximity sensor.
We light up the built-in LED on the Arduino by reaching out to the /on URL, and we turn it off by opening the /off URL. Anything else does nothing.
This is the code from the other tutorial:
#include <SPI.h>
#include <WiFiNINA.h>
WiFiServer server(80);
void setup() {
char ssid[] = SECRET_SSID;
char pass[] = SECRET_PASS;
Serial.begin(9600);
while (!Serial);
int status = WL_IDLE_STATUS;
while (status != WL_CONNECTED) {
Serial.print("Connecting to ");
Serial.println(ssid);
status = WiFi.begin(ssid, pass);
delay(5000);
}
Serial.print("IP address: ");
Serial.println(WiFi.localIP());
server.begin();
}
void loop() {
WiFiClient client = server.available();
if (client) {
String line = "";
while (client.connected()) {
if (client.available()) {
char c = client.read();
Serial.write(c);
if (c != '\n' && c != '\r') {
line += c;
}
if (c == '\n') {
if (line.length() == 0) {
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println("Connection: close"); // the connection will be closed after completion of the response
client.println();
client.println("<!DOCTYPE HTML>");
client.println("<html>");
client.println("test");
client.println("</html>");
break;
} else {
line = "";
}
}
}
}
client.stop();
}
}
In the last else you see, we have a full line, so we can check its content before clearing it. In this case we can check for GET /on and GET /off :
if (line.startsWith("GET /on ")){
digitalWrite(LED_BUILTIN, HIGH);
}
if (line.startsWith("GET /off ")) {
digitalWrite(LED_BUILTIN, LOW);
}
That’s it! Now load the code on the Arduino and call the /on URL, or the /off URL.
I reserved a static IP to the Arduino using my local network router, and I named it arduino.local in my /etc/hosts file, so reaching out to http://arduino.local/on turns the LED on, and to http://arduino.local/off turns the LED off.
Here’s the complete program:
#include <SPI.h>
#include <WiFiNINA.h>
WiFiServer server(80);
void setup() {
char ssid[] = SECRET_SSID;
char pass[] = SECRET_PASS;
Serial.begin(9600);
while (!Serial);
int status = WL_IDLE_STATUS;
while (status != WL_CONNECTED) {
Serial.print("Connecting to ");
Serial.println(ssid);
status = WiFi.begin(ssid, pass);
delay(5000);
}
Serial.print("IP address: ");
Serial.println(WiFi.localIP());
server.begin();
}
void loop() {
WiFiClient client = server.available();
if (client) {
String line = "";
while (client.connected()) {
if (client.available()) {
char c = client.read();
Serial.write(c);
if (c != '\n' && c != '\r') {
line += c;
}
if (c == '\n') {
if (line.length() == 0) {
client.println("HTTP/1.1 200 OK");
client.println("Content-Type: text/html");
client.println("Connection: close"); // the connection will be closed after completion of the response
client.println();
client.println("<!DOCTYPE HTML>");
client.println("<html>");
client.println("test");
client.println("</html>");
break;
} else {
if (line.startsWith("GET /on ")){
digitalWrite(LED_BUILTIN, HIGH);
}
if (line.startsWith("GET /off ")) {
digitalWrite(LED_BUILTIN, LOW);
}
line = "";
}
}
}
}
client.stop();
}
}
→ I wrote 17 books to help you become a better developer, download them all at $0 cost by joining my newsletter
→ JOIN MY CODING BOOTCAMP, an amazing cohort course that will be a huge step up in your coding career - covering React, Next.js - next edition February 2025