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();
}
}download all my books for free
- javascript handbook
- typescript handbook
- css handbook
- node.js handbook
- astro handbook
- html handbook
- next.js pages router handbook
- alpine.js handbook
- htmx handbook
- react handbook
- sql handbook
- git cheat sheet
- laravel handbook
- express handbook
- swift handbook
- go handbook
- php handbook
- python handbook
- cli handbook
- c handbook
subscribe to my newsletter to get them
Terms: by subscribing to the newsletter you agree the following terms and conditions and privacy policy. The aim of the newsletter is to keep you up to date about new tutorials, new book releases or courses organized by Flavio. If you wish to unsubscribe from the newsletter, you can click the unsubscribe link that's present at the bottom of each email, anytime. I will not communicate/spread/publish or otherwise give away your address. Your email address is the only personal information collected, and it's only collected for the primary purpose of keeping you informed through the newsletter. It's stored in a secure server based in the EU. You can contact Flavio by emailing [email protected]. These terms and conditions are governed by the laws in force in Italy and you unconditionally submit to the jurisdiction of the courts of Italy.