# Read values from an Arduino via HTTP > Learn how to read sensor values from an Arduino over HTTP, expanding a WiFiNINA web server so you can open a page in your browser and see the measured data. Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2021-08-25 | Updated: 2026-08-07 | Topics: [Arduino](https://flaviocopes.com/tags/electronics/) | Canonical: https://flaviocopes.com/arduino-read-values-http/ You can read the values measured by an Arduino by making the board serve them over HTTP. The Arduino runs a tiny web server on your WiFi network, and you open its address in the browser to see the latest sensor data. In this tutorial I want to expand the [Arduino Web Server tutorial](https://flaviocopes.com/arduino-webserver/) to do exactly that. We're going to measure the temperature using a DHT11 sensor, and print it in the page. ## The starting point This is the code from the other tutorial. It connects to WiFi using the WiFiNINA library, starts a server on port 80, and answers every request with a small HTML page: ```c #include #include 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"); client.println(); client.println(""); client.println(""); client.println("test"); client.println(""); break; } else { line = ""; } } } } client.stop(); } } ``` The interesting part is where we print `test` inside the HTML. That's where we'll put the sensor value instead. ## Adding the DHT11 sensor Connect the DHT11 data pin to digital pin 2 on the Arduino, plus power and ground. In the Arduino IDE, install the **DHT sensor library** by Adafruit from the Library Manager. Then set it up at the top of the sketch: ```cpp #include #define DHTPIN 2 #define DHTTYPE DHT11 DHT dht(DHTPIN, DHTTYPE); ``` In `setup()`, initialize it: ```cpp dht.begin(); ``` ## Serving the temperature Now, in the part of `loop()` that builds the response, read the temperature and print it instead of `test`: ```cpp float temperature = dht.readTemperature(); client.println(""); client.println(""); if (isnan(temperature)) { client.println("Failed to read from the sensor, reload the page"); } else { client.print("Temperature: "); client.print(temperature); client.println(" C"); } client.println(""); ``` Notice the `isnan()` check. That's the realistic failure you'll hit with this sensor: `dht.readTemperature()` occasionally fails and returns `nan`, for example when you request readings too close together. Without the check, the page would show `Temperature: nan C`. With it, you tell the visitor to reload, and the next read usually works. We read the sensor only when a request comes in. The value in the page is always the value measured at the moment you loaded it, so reloading the page gives you a new measurement. ## Trying it out Load the code on the Arduino, check the serial monitor for the IP address, and open it in the browser. 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 I just open `http://arduino.local/` and I see something like: ``` Temperature: 24.00 C ``` ## The complete program Here's the full sketch with the sensor integrated: ```cpp #include #include #include #define DHTPIN 2 #define DHTTYPE DHT11 DHT dht(DHTPIN, DHTTYPE); 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()); dht.begin(); 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) { float temperature = dht.readTemperature(); client.println("HTTP/1.1 200 OK"); client.println("Content-Type: text/html"); client.println("Connection: close"); client.println(); client.println(""); client.println(""); if (isnan(temperature)) { client.println("Failed to read from the sensor, reload the page"); } else { client.print("Temperature: "); client.print(temperature); client.println(" C"); } client.println(""); break; } else { line = ""; } } } } client.stop(); } } ``` From here you can extend the idea to any sensor. Read the value, print it in the HTML, and anything on your network, a browser, a script, a dashboard, can fetch it over HTTP.