ESP32 - Temperature via Web

In this guide, we'll explore the process of programming the ESP32 to function as a web server, allowing you to access temperature data via a web interface. Using an attached DS18B20 temperature sensor, you can easily check the current temperature by using your smartphone or PC to visit the web page served by the ESP32. Here's a brief overview of how it works:

ESP32 DS18B20 temperature sensor web server

We will go through two example codes:

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×USB Cable Type-C
1×Temperature Sensor DS18B20
1×Jumper Wires
1×(Recommended) ESP32 Screw Terminal Adapter

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
Disclosure: some of these links are affiliate links. We may earn a commission on your purchase at no extra cost to you. We appreciate it.

Buy Note: Numerous DS18B20 sensors available in the market are of poor quality. We strongly advise purchasing the sensor from the DIYables brand via the link above; we conducted tests, and it performed reliably.

Introduction to ESP32 Web Server and DS18B20 Temperature Sensor

If you do not know about ESP32 Web Server and DS18B20 temperature sensor (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

ESP32 Web Server DS18B20 Temperature Sensor Wiring Diagram

This image is created using Fritzing. Click to enlarge image

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

ESP32 Code - Simple Web Page

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-temperature-via-web */ #include <WiFi.h> #include <ESPAsyncWebServer.h> #include <OneWire.h> #include <DallasTemperature.h> #define SENSOR_PIN 17 // ESP32 pin GPIO17 connected to DS18B20 sensor's DATA pin const char* ssid = "YOUR_WIFI_SSID"; // CHANGE IT const char* password = "YOUR_WIFI_PASSWORD"; // CHANGE IT OneWire oneWire(SENSOR_PIN); // setup a oneWire instance DallasTemperature DS18B20(&oneWire); // pass oneWire to DallasTemperature library AsyncWebServer server(80); float getTemperature() { DS18B20.requestTemperatures(); // send the command to get temperatures float tempC = DS18B20.getTempCByIndex(0); // read temperature in °C return tempC; } void setup() { Serial.begin(9600); DS18B20.begin(); // initialize the DS18B20 sensor // Connect to Wi-Fi WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(1000); Serial.println("Connecting to WiFi..."); } Serial.println("Connected to WiFi"); // Print the ESP32's IP address Serial.print("ESP32 Web Server's IP address: "); Serial.println(WiFi.localIP()); // Define a route to serve the HTML page server.on("/", HTTP_GET, [](AsyncWebServerRequest* request) { Serial.println("ESP32 Web Server: New request received:"); // for debugging Serial.println("GET /"); // for debugging // get temperature from sensor float temperature = getTemperature(); // Format the temperature with two decimal places String temperatureStr = String(temperature, 2); String html = "<!DOCTYPE HTML>"; html += "<html>"; html += "<head>"; html += "<link rel=\"icon\" href=\"data:,\">"; html += "</head>"; html += "<p>"; html += "Temperature: <span style=\"color: red;\">"; html += temperature; html += "&deg;C</span>"; html += "</p>"; html += "</html>"; request->send(200, "text/html", html); }); // Start the server server.begin(); } void loop() { // Your code here }

Quick Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Do the wiring as above image.
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
  • On Arduino IDE, Navigate to Tools Manage Libraries
ESP32 add library
  • Type “OneWire” on the search box, then look for the OneWire library by Paul Stoffregen
  • Click Install button to install OneWire library.
ESP32 onewire library
  • Type “Dallas” on the search box, then look for the DallasTemperature library by Miles Burton.
  • Click Install button to install DallasTemperature library.
ESP32 Dallas Temperature library
  • Copy the above code and open with Arduino IDE
  • Change the wifi information (SSID and password) in the code to yours
  • Click Upload button on Arduino IDE to upload code to ESP32
  • Open the Serial Monitor
  • Check out the result on Serial Monitor.
COM6
Send
Connecting to WiFi... Connected to WiFi ESP32 Web Server's IP address: 192.168.0.2
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
  • You will find an IP address. Type this IP address into the address bar of a web browser on your smartphone or PC.
  • You will see the following output on the Serial Monitor.
COM6
Send
Connecting to WiFi... Connected to WiFi ESP32 Web Server's IP address: 192.168.0.2 ESP32 Web Server: New request received: GET /
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  
  • You will see a very simple web page of ESP32 board on the web browser as below:
ESP32 temperature web server

※ NOTE THAT:

With the code provided above, to get the termperature update, you have to reload the page on the web browser. In a next part, we will learn how to make web page update the temperature value on backround without reloading the webpage.

ESP32 Code - Graphic Web Page

As a graphic web page contains a large amount of HTML content, embedding it into the ESP32 code as before becomes inconvenient. To address this, we need to separate the ESP32 code and the HTML code into different files:

  • The ESP32 code will be placed in a .ino file.
  • The HTML code (including HTML, CSS, and Javascript) will be placed in a .h file.

For detail of how to separate the HTML code from ESP32 code, please refer to ESP32 - Web Server tutorial.

Quick Instructions

  • Open Arduino IDE and create new sketch, Give it a name, for example, esp32io.com.ino
  • Copy the below code and open with Arduino IDE
/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-temperature-via-web */ #include <WiFi.h> #include <ESPAsyncWebServer.h> #include "index.h" // Include the index.h file #include <OneWire.h> #include <DallasTemperature.h> #define SENSOR_PIN 17 // ESP32 pin GPIO17 connected to DS18B20 sensor's DATA pin const char* ssid = "YOUR_WIFI_SSID"; // CHANGE IT const char* password = "YOUR_WIFI_PASSWORD"; // CHANGE IT OneWire oneWire(SENSOR_PIN); // setup a oneWire instance DallasTemperature DS18B20(&oneWire); // pass oneWire to DallasTemperature library AsyncWebServer server(80); float getTemperature() { DS18B20.requestTemperatures(); // send the command to get temperatures float tempC = DS18B20.getTempCByIndex(0); // read temperature in °C return tempC; } void setup() { Serial.begin(9600); DS18B20.begin(); // initialize the DS18B20 sensor // Connect to Wi-Fi WiFi.begin(ssid, password); while (WiFi.status() != WL_CONNECTED) { delay(1000); Serial.println("Connecting to WiFi..."); } Serial.println("Connected to WiFi"); // Print the ESP32's IP address Serial.print("ESP32 Web Server's IP address: "); Serial.println(WiFi.localIP()); // Serve the HTML page from the file server.on("/", HTTP_GET, [](AsyncWebServerRequest* request) { Serial.println("ESP32 Web Server: New request received:"); // for debugging Serial.println("GET /"); // for debugging request->send(200, "text/html", webpage); // webpage is from index.h file }); // Define a route to get the temperature data server.on("/temperature", HTTP_GET, [](AsyncWebServerRequest* request) { Serial.println("ESP32 Web Server: New request received:"); // for debugging Serial.println("GET /temperature"); // for debugging float temperature = getTemperature(); // Format the temperature with two decimal places String temperatureStr = String(temperature, 2); request->send(200, "text/plain", temperatureStr); }); // Start the server server.begin(); } void loop() { // Your code here }
  • Change the WiFi information (SSID and password) in the code to yours
  • Create the index.h file On Arduino IDE by:
    • Either click on the button just below the serial monitor icon and choose New Tab, or use Ctrl+Shift+N keys.
    Arduino IDE 2 adds file
    • Give the file's name index.h and click OK button
    Arduino IDE 2 adds file index.h
    • Copy the below code and paste it to the index.h.
    /* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-temperature-via-web */ #ifndef WEBPAGE_H #define WEBPAGE_H const char* webpage = R"=====( <!DOCTYPE html> <html> <head> <title>ESP32 - Web Temperature</title> <meta name="viewport" content="width=device-width, initial-scale=0.7, maximum-scale=0.7"> <meta charset="utf-8"> <link rel="icon" href="https://diyables.io/images/page/diyables.svg"> <style> body { font-family: "Georgia"; text-align: center; font-size: width/2pt;} h1 { font-weight: bold; font-size: width/2pt;} h2 { font-weight: bold; font-size: width/2pt;} button { font-weight: bold; font-size: width/2pt;} </style> <script> var cvs_width = 200, cvs_height = 450; function init() { var canvas = document.getElementById("cvs"); canvas.width = cvs_width; canvas.height = cvs_height + 50; var ctx = canvas.getContext("2d"); ctx.translate(cvs_width/2, cvs_height - 80); fetchTemperature(); setInterval(fetchTemperature, 4000); // Update temperature every 4 seconds } function fetchTemperature() { fetch("/temperature") .then(response => response.text()) .then(data => {update_view(data);}); } function update_view(temp) { var canvas = document.getElementById("cvs"); var ctx = canvas.getContext("2d"); var radius = 70; var offset = 5; var width = 45; var height = 330; ctx.clearRect(-cvs_width/2, -cvs_height + 80, cvs_width, cvs_height + 50); ctx.strokeStyle="blue"; ctx.fillStyle="blue"; //5-step Degree var x = -width/2; ctx.lineWidth=2; for (var i = 0; i <= 100; i+=5) { var y = -(height - radius)*i/100 - radius - 5; ctx.beginPath(); ctx.lineTo(x, y); ctx.lineTo(x - 20, y); ctx.stroke(); } //20-step Degree ctx.lineWidth=5; for (var i = 0; i <= 100; i+=20) { var y = -(height - radius)*i/100 - radius - 5; ctx.beginPath(); ctx.lineTo(x, y); ctx.lineTo(x - 25, y); ctx.stroke(); ctx.font="20px Georgia"; ctx.textBaseline="middle"; ctx.textAlign="right"; ctx.fillText(i.toString(), x - 35, y); } // shape ctx.lineWidth=16; ctx.beginPath(); ctx.arc(0, 0, radius, 0, 2 * Math.PI); ctx.stroke(); ctx.beginPath(); ctx.rect(-width/2, -height, width, height); ctx.stroke(); ctx.beginPath(); ctx.arc(0, -height, width/2, 0, 2 * Math.PI); ctx.stroke(); ctx.fillStyle="#e6e6ff"; ctx.beginPath(); ctx.arc(0, 0, radius, 0, 2 * Math.PI); ctx.fill(); ctx.beginPath(); ctx.rect(-width/2, -height, width, height); ctx.fill(); ctx.beginPath(); ctx.arc(0, -height, width/2, 0, 2 * Math.PI); ctx.fill(); ctx.fillStyle="#ff1a1a"; ctx.beginPath(); ctx.arc(0, 0, radius - offset, 0, 2 * Math.PI); ctx.fill(); temp = Math.round(temp * 100) / 100; var y = (height - radius)*temp/100.0 + radius + 5; ctx.beginPath(); ctx.rect(-width/2 + offset, -y, width - 2*offset, y); ctx.fill(); ctx.fillStyle="red"; ctx.font="bold 34px Georgia"; ctx.textBaseline="middle"; ctx.textAlign="center"; ctx.fillText(temp.toString() + "°C", 0, 100); } window.onload = init; </script> </head> <body> <h1>ESP32 - Web Temperature</h1> <canvas id="cvs"></canvas> </body> </html> )====="; #endif
    • Now you have the code in two files: esp32io.com.ino and index.h
    • Click Upload button on Arduino IDE to upload code to ESP32
    • Access the web page of ESP32 board via web browser on your PC or smartphone as before. You will see it as below:
    ESP32 temperature web browser server

    ※ NOTE THAT:

    • If you modify the HTML content in the index.h and does not touch anything in esp32io.com.ino file, when you compile and upload code to ESP32, Arduino IDE will not update the HTML content.
    • To make Arduino IDE update the HTML content in this case, make a change in the esp32io.com.ino file (e.g. adding empty line, add a comment....)

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