ESP8266 NodeMCU Web Server (WebSocket) with Multiple Sliders: Control LEDs Brightness (PWM)

This tutorial shows how to build a web server with the ESP8266 NodeMCU board that displays a web page with multiple sliders. The sliders control the duty cycle of different PWM signals to control the brightness of multiple LEDs. Instead of LEDs, you can use this project to control DC motors or other actuators that require a PWM signal. The communication between the clients and the ESP8266 is done using the WebSocket protocol. Additionally, whenever there’s a change, all clients update their slider values simultaneously.

You can also modify the code presented in this tutorial to add sliders to your projects to set threshold values or any other values you need to use in your code.

For this project, the ESP8266 board will be programmed using the Arduino core. You can either use the Arduino IDE, VS Code with PlatformIO, or any other suitable IDE.

To better understand how this project works, we recommend taking a look at the following tutorials:

• ESP8266 NodeMCU PWM with Arduino IDE – Dim LED (Analog Output)
• ESP8266 NodeMCU WebSocket Server: Control Outputs (Arduino IDE)
• ESP8266 NodeMCU Web Server with Slider: Control LED Brightness (PWM)*

* This project shows how to build a web server with one slider, but it uses HTTP requests—in this tutorial, we’ll use WebSocket protocol.

We have a similar tutorial for the ESP32 board:

• ESP32 Web Server (WebSocket) with Multiple Sliders: Control LEDs Brightness (PWM)

Project Overview

The following image shows the web page we’ll build for this project:

• The web page contains three cards;
• Each card has a paragraph to display the card title (Fader 1, Fader 2, Fader 3);
• There’s a range slider in each card that you can move to set the brightness of the corresponding LED;
• In each card, another paragraph displays the current LED brightness (in percentage);
• When you set a new position for the slider, it updates all clients (if you have multiple web browser tabs opened (or multiple devices), they update almost simultaneously whenever there’s a change).

How it Works?

• The ESP hosts a web server that displays a web page with three sliders;

• When you set a new position for a slider, the client sends the slider number and slider value to the server via WebSocket protocol. For example, if you set slider number 3 to position number 40, it would send this message 3s40 to the server.

• The server (ESP) receives the slider number and corresponding value and adjusts the PWM duty cycle accordingly. Additionally, it also notifies all the other clients with the new current slider values—this allows us to have all clients updated almost instantaneously.

• The ESP8266 outputs the PWM signal with the corresponding duty cycle to control the LED brightness. A duty cycle of 0% means the LED is completely off, a duty cycle of 50% means the LED is half-lit, and a duty cycle of 100% means the LED is lit;

• Whenever you open a new web browser window (this is when a new client connects), it will send a message to the ESP8266 (also through WebSocket protocol) with the message getValues. When the ESP8266 gets this message, it sends the current slider values. This way, whenever you open a new tab, it always shows the current and updated values.

Prerequisites

Before proceeding with this tutorial, make sure you check all the following prerequisites.

1) Parts Required

To follow this project you need:

• ESP8266 NodeMCU Board – read Best ESP8266 Wi-Fi Development Board – Buying Guide
• 3x LEDs
• 3x 220Ohm resistors
• Breadboard
• Jumper wires

You don’t need three LEDs to test this project, you can simply see the results in the Serial Monitor or use other actuators that required a PWM signal to operate.

You can use the preceding links or go directly to MakerAdvisor.com/tools to find all the parts for your projects at the best price!

2) Arduino IDE and ESP8266 Boards Add-on

We’ll program the ESP8266 using Arduino IDE. So, you must have the ESP8266 add-on installed. Follow the next tutorial if you haven’t already:

• Installing ESP8266 Board in Arduino IDE (Windows, Mac OS X, Linux)

If you want to use VS Code with the PlatformIO extension, follow the next tutorial instead to learn how to program the ESP8266:

• Getting Started with VS Code and PlatformIO IDE for ESP32 and ESP8266 (Windows, Mac OS X, Linux Ubuntu)

3) Filesystem Uploader Plugin

To upload the HTML, CSS, and JavaScript files needed to build this project to the ESP8266 flash memory (LittleFS), we’ll use a plugin for Arduino IDE: LittleFS Filesystem uploader. Follow the next tutorial to install the filesystem uploader plugin if you haven’t already:

• Install ESP8266 NodeMCU LittleFS Filesystem Uploader in Arduino IDE

If you’re using VS Code with the PlatformIO extension, read the following tutorial to learn how to upload files to the filesystem:

• ESP8266 NodeMCU with VS Code and PlatformIO: Upload Files to Filesystem (LittleFS)

4) Libraries

To build this project, you need to install the following libraries:

• Arduino_JSON library by Arduino version 0.1.0 (Arduino Library Manager)
• ESPAsyncWebServer (.zip folder);
• ESPAsyncTCP (.zip folder).

You can install the first library using the Arduino Library Manager. Go to Sketch > Include Library > Manage Libraries and search for the library name.

The ESPAsyncWebServer and ESPAsynTCP libraries aren’t available to install through the Arduino Library Manager, so you need to copy the library files to the Arduino Installation Libraries folder. Alternatively, in your Arduino IDE, you can go to Sketch> Include Library > Add .zip Library and select the libraries you’ve just downloaded.

Installing Libraries (VS Code + PlatformIO)

If you’re programming the ESP8266 using PlatformIO, you should add the following lines to the platformio.ini file to include the libraries (also change the Serial Monitor speed to 115200 and set the littleFS filesystem):

monitor_speed = 115200
board_build.filesystem = littlefs
lib_deps = ESP Async WebServer
  arduino-libraries/Arduino_JSON @ 0.1.0

Schematic Diagram

Wire three LEDs to the ESP8266. We’re using GPIOs 12 (D6), 13 (D7), and 14 (D5). You can use any other suitable GPIOs.

Recommended reading: ESP8266 Pinout Reference: Which GPIO pins should you use?

Organizing Your Files

To keep the project organized and make it easier to understand, we’ll create four files to build the web server:

• Arduino sketch that handles the web server;
• index.html: to define the content of the web page;
• sytle.css: to style the web page;
• script.js: to program the behavior of the web page—handle what happens when you move the slider, send, receive and interpret the messages received via WebSocket protocol.

You should save the HTML, CSS, and JavaScript files inside a folder called data inside the Arduino sketch folder, as shown in the previous diagram. We’ll upload these files to the ESP8266 filesystem (LittleFS).

You can download all project files:

• Download All the Arduino Project Files

HTML File

Copy the following to the index.html file.

<!-- Complete project details: https://randomnerdtutorials.com/esp8266-nodemcu-web-server-websocket-sliders/ -->

<!DOCTYPE html>
<html>
<head>
    <title>ESP IOT DASHBOARD</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="icon" type="image/png" href="favicon.png">
    <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
    <div class="topnav">
        <h1>Multiple Sliders</h1>
    </div>
    <div class="content">
        <div class="card-grid">
            <div class="card">
                <p class="card-title">Fader 1</p>
                <p class="switch">
                    <input type="range" onchange="updateSliderPWM(this)" id="slider1" min="0" max="100" step="1" value ="0" class="slider">
                </p>
                <p class="state">Brightness: <span id="sliderValue1"></span> &percnt;</p>
            </div>
            <div class="card">
                <p class="card-title"> Fader 2</p>
                <p class="switch">
                    <input type="range" onchange="updateSliderPWM(this)" id="slider2" min="0" max="100" step="1" value ="0" class="slider">
                </p>
                <p class="state">Brightness: <span id="sliderValue2"></span> &percnt;</p>
            </div>
            <div class="card">
                <p class="card-title"> Fader 3</p>
                <p class="switch">
                    <input type="range" onchange="updateSliderPWM(this)" id="slider3" min="0" max="100" step="1" value ="0" class="slider">
                </p>
                <p class="state">Brightness: <span id="sliderValue3"></span> &percnt;</p>
            </div>
        </div>
    </div>
    <script src="script.js"></script>
</body>
</html>

View raw code

Let’s take a quick look at the most relevant parts of the HTML file.

Creating a Slider

The following tags create the card for the first slider (Fader 1).

<div class="card">
  <p class="card-title">Fader 1</p>
  <p class="switch">
    <input type="range" onchange="updateSliderPWM(this)" id="slider1" min="0" max="100" step="1" value ="0" class="slider">
  </p>
  <p class="state">Brightness: <span id="sliderValue1"></span> &percnt;</p>
</div>

The first paragraph displays a title for the card (Fader 1). You can change the text to whatever you want.

<p class="card-title">Fader 1</p>

To create a slider in HTML you use the <input> tag. The <input> tag specifies a field where the user can enter data.

There are a wide variety of input types. To define a slider, use the type attribute with the range value. In a slider, you also need to define the minimum and the maximum range using the min and max attributes (in this case, 0 and 100, respectively).

You also need to define other attributes like:

• the step attribute specifies the interval between valid numbers. In our case, we set it to 1;
• the class to style the slider (class=”slider”);
• the id so that we can manipulate the slider value using JavaScript (id=”slider1″);
• the onchange attribute to call a function (updateSliderPWM(this)) when you set a new position for the slider. This function (defined in the JavaScript file) sends the current slider value via the WebSocket protocol to the client. The this keyword refers to the HTML slider element.

The slider is inside a paragraph with the switch class name. So, here are the tags that actually create the slider.

<p class="switch">
  <input type="range" onchange="updateSliderPWM(this)" id="slider1" min="0" max="100" step="1" value ="0" class="slider">
</p>

Finally, there’s a paragraph with a <span> tag, so that we can insert the current slider value in that paragraph by referring to its id (id=”sliderValue1″).

<p class="state">Brightness: <span id="sliderValue1"></span> &percnt;</p>

Creating More Sliders

To create more sliders, you need to copy all the HTML tags that create the complete card. First, however, you need to consider that you need a unique id for each slider and slider value. In our case, we have three sliders with the following ids: slider1, slider2, slider3, and three placeholders for the slider value with the following ids: sliderValue1, sliderValue2, sliderValue3.

For example, here’s the card for slider number 2.

<div class="card">
  <p class="card-title"> Fader 2</p>
  <p class="switch">
    <input type="range" onchange="updateSliderPWM(this)" id="slider2" min="0" max="100" step="1" value ="0" class="slider">
  </p>
  <p class="state">Brightness: <span id="sliderValue2"></span> &percnt;</p>
</div>

CSS File

Copy the following to the style.css file.

/*  Complete project details: https://randomnerdtutorials.com/esp8266-nodemcu-web-server-websocket-sliders/  */

html {
    font-family: Arial, Helvetica, sans-serif;
    display: inline-block;
    text-align: center;
  }
  h1 {
    font-size: 1.8rem;
    color: white;
  }
  p {
    font-size: 1.4rem;
  }
  .topnav {
    overflow: hidden;
    background-color: #0A1128;
  }
  body {
    margin: 0;
  }
  .content {
    padding: 30px;
  }
  .card-grid {
    max-width: 700px;
    margin: 0 auto;
    display: grid;
    grid-gap: 2rem;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  }
  .card {
    background-color: white;
    box-shadow: 2px 2px 12px 1px rgba(140,140,140,.5);
  }
  .card-title {
    font-size: 1.2rem;
    font-weight: bold;
    color: #034078
  }
  .state {
    font-size: 1.2rem;
    color:#1282A2;
  }
  .slider {
    -webkit-appearance: none;
    margin: 0 auto;
    width: 100%;
    height: 15px;
    border-radius: 10px;
    background: #FFD65C;
    outline: none;
  }
  .slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    background: #034078;
    cursor: pointer;
  }
  .slider::-moz-range-thumb {
    width: 30px;
    height: 30px;
    border-radius: 50% ;
    background: #034078;
    cursor: pointer;
  }
  .switch {
    padding-left: 5%;
    padding-right: 5%;
  }

View raw code

Let’s take a quick look at the relevant parts of the CSS file that style the slider. In this example, we need to use the vendor prefixes for the appearance attribute.

.slider {
  -webkit-appearance: none;
  margin: 0 auto;
  width: 100%;
  height: 15px;
  border-radius: 10px;
  background: #FFD65C;
  outline: none;
}
.slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background: #034078;
  cursor: pointer;
}
.slider::-moz-range-thumb {
  width: 30px;
  height: 30px;
  border-radius: 50% ;
  background: #034078;
  cursor: pointer;
}
.switch {
  padding-left: 5%;
  padding-right: 5%;
}

Vendor Prefixes

Vendor prefixes allow a browser to support new CSS features before they become fully supported. The most commonly used browsers use the following prefixes:

• -webkit- Chrome, Safari, newer versions of Opera, almost all iOS browsers,
• -moz- Firefox,
• -o- Old versions of Opera,
• -ms- Microsoft Edge and Internet Explorer.

Vendor prefixes are temporary. Once the properties are fully supported by the browser you use, you don’t need them. You can use the following reference to check if the property you’re using needs prefixes: http://shouldiprefix.com/

Let’s take a look at the .slider selector (styles the slider itself):

.slider {
  -webkit-appearance: none;
  margin: 0 auto;
  width: 100%;
  height: 15px;
  border-radius: 10px;
  background: #FFD65C;outline: none;
}

Setting -webkit-appearance to none overrides the default CSS styles applied to the slider in Google Chrome, Safari, and Android browsers.

-webkit-appearance: none;

Setting the margin to 0 auto aligns the slider inside its parent container.

margin: 0 auto;

The width of the slider is set to 100% and the height to 15px. The border-radius is set to 10px.

margin: 0 auto;
width: 100%;
height: 15px;
border-radius: 10px;

Set the background color for the slider and set the outline to none.

background: #FFD65C;
outline: none;

Then, format the slider handle. Use -webkit- for Chrome, Opera, Safari and Edge web browsers and -moz- for Firefox.

.slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background: #034078;
  cursor: pointer;
}
.slider::-moz-range-thumb {
  width: 30px;
  height: 30px;
  border-radius: 50% ;
  background: #034078;
  cursor: pointer;
}

Set the -webkit-appearance and appearance properties to none to override default properties.

-webkit-appearance: none;
appearance: none;

Set a specific width, height and border-radius for the handler. Setting the same width and height with a border-radius of 50% creates a circle.

width: 30px;
height: 30px;
border-radius: 50%;

Then, set a color for the background and set the cursor to a pointer.

background: #034078;
cursor: pointer;

Feel free to play with the slider properties to give it a different look.

JavaScript File

Copy the following to the script.js file.

// Complete project details: https://randomnerdtutorials.com/esp8266-nodemcu-web-server-websocket-sliders/

var gateway = `ws://${window.location.hostname}/ws`;
var websocket;
window.addEventListener('load', onload);

function onload(event) {
    initWebSocket();
}

function getValues(){
    websocket.send("getValues");
}

function initWebSocket() {
    console.log('Trying to open a WebSocket connection…');
    websocket = new WebSocket(gateway);
    websocket.onopen = onOpen;
    websocket.onclose = onClose;
    websocket.onmessage = onMessage;
}

function onOpen(event) {
    console.log('Connection opened');
    getValues();
}

function onClose(event) {
    console.log('Connection closed');
    setTimeout(initWebSocket, 2000);
}

function updateSliderPWM(element) {
    var sliderNumber = element.id.charAt(element.id.length-1);
    var sliderValue = document.getElementById(element.id).value;
    document.getElementById("sliderValue"+sliderNumber).innerHTML = sliderValue;
    console.log(sliderValue);
    websocket.send(sliderNumber+"s"+sliderValue.toString());
}

function onMessage(event) {
    console.log(event.data);
    var myObj = JSON.parse(event.data);
    var keys = Object.keys(myObj);

    for (var i = 0; i < keys.length; i++){
        var key = keys[i];
        document.getElementById(key).innerHTML = myObj[key];
        document.getElementById("slider"+ (i+1).toString()).value = myObj[key];
    }
}

View raw code

Here’s a list of what this code does:

• initializes a WebSocket connection with the server;
• sends a message to the server to get the current slider values;
• uses the response to update the slider values on the web page;
• handles data exchange through the WebSocket protocol.

Let’s take a look at this JavaScript code to see how it works.

The gateway is the entry point to the WebSocket interface. window.location.hostname gets the current page address (the web server IP address).

var gateway = ws://${window.location.hostname}/ws;

Create a new global variable called websocket.

var websocket;

Add an event listener that will call the onload function when the web page loads.

window.addEventListener('load', onload);

The onload() function calls the initWebSocket() function to initialize a WebSocket connection with the server.

function onload(event) {
  initWebSocket();
}

The initWebSocket() function initializes a WebSocket connection on the gateway defined earlier. We also assign several callback functions for when the WebSocket connection is opened, closed, or when a message is received.

function initWebSocket() {
  console.log('Trying to open a WebSocket connection…');
  websocket = new WebSocket(gateway);
  websocket.onopen = onOpen;
  websocket.onclose = onClose;
  websocket.onmessage = onMessage;
}

Note that when the websocket connection in open, we’ll call the getValues function.

function onOpen(event) {
  console.log('Connection opened');
  getValues();
}

The getValues() function sends a message to the server getValues to get the current value of all sliders. Then, we must handle what happens when we receive that message on the server side (ESP8266).

function getStates(){
  websocket.send("getValues");
}

We handle the messages received via websocket protocol on the onMessage() function.

function onMessage(event) {
  console.log(event.data);
  var myObj = JSON.parse(event.data);
  var keys = Object.keys(myObj);

  for (var i = 0; i < keys.length; i++){
    var key = keys[i];
    document.getElementById(key).innerHTML = myObj[key];
    document.getElementById("slider"+ (i+1).toString()).value = myObj[key];
  }
}

The server sends the states in JSON format, for example:

{
  sliderValue1: 20;
  sliderValue2: 50;
  sliderValue3: 0;
}

The onMessage() function simply goes through all the values and places them on the corresponding places on the HTML page.

The updateSliderPWM() function runs when you move the sliders.

function updateSliderPWM(element) {
  var sliderNumber = element.id.charAt(element.id.length-1);
  var sliderValue = document.getElementById(element.id).value;
  document.getElementById("sliderValue"+sliderNumber).innerHTML = sliderValue;
  console.log(sliderValue);
  websocket.send(sliderNumber+"s"+sliderValue.toString());
}

This function gets the value from the slider and updates the corresponding paragraph with the right value. This function also sends a message to the server so that the ESP8266 updates the LED brightness.

websocket.send(sliderNumber+"s"+sliderValue.toString());

The message is sent in the following format:

• slidernumbersslidervalue

For example, if you move slider number 3 to position 40, it will send the following message:

3s40

Arduino Sketch

Copy the following code to your Arduino IDE or to the main.cpp file if you’re using PlatformIO.

/* 
  Rui Santos
  Complete project details at https://RandomNerdTutorials.com/esp8266-nodemcu-web-server-websocket-sliders/
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files.
  
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
*/

#include <Arduino.h>
#include <ESP8266WiFi.h>
#include <ESPAsyncTCP.h>
#include <ESPAsyncWebServer.h>
#include "LittleFS.h"
#include <Arduino_JSON.h>

// Replace with your network credentials
const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";

// Create AsyncWebServer object on port 80
AsyncWebServer server(80);
// Create a WebSocket object

AsyncWebSocket ws("/ws");
// Set LED GPIO
const int ledPin1 = 14;
const int ledPin2 = 12;
const int ledPin3 = 13;

String message = "";
String sliderValue1 = "0";
String sliderValue2 = "0";
String sliderValue3 = "0";

int dutyCycle1;
int dutyCycle2;
int dutyCycle3;

//Json Variable to Hold Slider Values
JSONVar sliderValues;

//Get Slider Values
String getSliderValues(){
  sliderValues["sliderValue1"] = String(sliderValue1);
  sliderValues["sliderValue2"] = String(sliderValue2);
  sliderValues["sliderValue3"] = String(sliderValue3);

  String jsonString = JSON.stringify(sliderValues);
  return jsonString;
}

// Initialize LittleFS
void initFS() {
  if (!LittleFS.begin()) {
    Serial.println("An error has occurred while mounting LittleFS");
  }
  else{
   Serial.println("LittleFS mounted successfully");
  }
}

// Initialize WiFi
void initWiFi() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi ..");
  while (WiFi.status() != WL_CONNECTED) {
    Serial.print('.');
    delay(1000);
  }
  Serial.println(WiFi.localIP());
}

void notifyClients(String sliderValues) {
  ws.textAll(sliderValues);
}

void handleWebSocketMessage(void *arg, uint8_t *data, size_t len) {
  AwsFrameInfo *info = (AwsFrameInfo*)arg;
  if (info->final && info->index == 0 && info->len == len && info->opcode == WS_TEXT) {
    data[len] = 0;
    message = (char*)data;
    if (message.indexOf("1s") >= 0) {
      sliderValue1 = message.substring(2);
      dutyCycle1 = map(sliderValue1.toInt(), 0, 100, 0, 1023);
      Serial.println(dutyCycle1);
      Serial.print(getSliderValues());
      notifyClients(getSliderValues());
    }
    if (message.indexOf("2s") >= 0) {
      sliderValue2 = message.substring(2);
      dutyCycle2 = map(sliderValue2.toInt(), 0, 100, 0, 1023);
      Serial.println(dutyCycle2);
      Serial.print(getSliderValues());
      notifyClients(getSliderValues());
    }    
    if (message.indexOf("3s") >= 0) {
      sliderValue3 = message.substring(2);
      dutyCycle3 = map(sliderValue3.toInt(), 0, 100, 0, 1023);
      Serial.println(dutyCycle3);
      Serial.print(getSliderValues());
      notifyClients(getSliderValues());
    }
    if (strcmp((char*)data, "getValues") == 0) {
      notifyClients(getSliderValues());
    }
  }
}
void onEvent(AsyncWebSocket *server, AsyncWebSocketClient *client, AwsEventType type, void *arg, uint8_t *data, size_t len) {
  switch (type) {
    case WS_EVT_CONNECT:
      Serial.printf("WebSocket client #%u connected from %s\n", client->id(), client->remoteIP().toString().c_str());
      break;
    case WS_EVT_DISCONNECT:
      Serial.printf("WebSocket client #%u disconnected\n", client->id());
      break;
    case WS_EVT_DATA:
      handleWebSocketMessage(arg, data, len);
      break;
    case WS_EVT_PONG:
    case WS_EVT_ERROR:
      break;
  }
}

void initWebSocket() {
  ws.onEvent(onEvent);
  server.addHandler(&ws);
}

void setup() {
  Serial.begin(115200);
  pinMode(ledPin1, OUTPUT);
  pinMode(ledPin2, OUTPUT);
  pinMode(ledPin3, OUTPUT);
  initFS();
  initWiFi();

  initWebSocket();
  
  // Web Server Root URL
  server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send(LittleFS, "/index.html", "text/html");
  });
  
  server.serveStatic("/", LittleFS, "/");

  // Start server
  server.begin();
}

void loop() {
  analogWrite(ledPin1, dutyCycle1);
  analogWrite(ledPin2, dutyCycle2);
  analogWrite(ledPin3, dutyCycle3);

  ws.cleanupClients();
}

View raw code

How the Code Works

Let’s take a quick look at the relevant parts for this project. To better understand how the code works, we recommend following this tutorial about WebSocket protocol with the ESP8266 and this tutorial about PWM with the ESP8266.

Insert your network credentials in the following variables to connect the ESP8266 to your local network:

const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";

The getSliderValues() function creates a JSON string with the current slider values.

String getSliderValues(){
  sliderValues["sliderValue1"] = String(sliderValue1);
  sliderValues["sliderValue2"] = String(sliderValue2);
  sliderValues["sliderValue3"] = String(sliderValue3);

  String jsonString = JSON.stringify(sliderValues);
  return jsonString;
}

The notifyClients() function notifies all clients with the current slider values. Calling this function is what allows us to notify changes in all clients whenever you set a new position for a slider.

void notifyClients(String sliderValues) {
  ws.textAll(sliderValues);
}

The handleWebSocketMessage(), as the name suggests, handles what happens when the server receives a message from the client via WebSocket protocol. We’ve seen in the JavaScript file, that the server can receive the getValues message or a message with the slider number and the slider value.

When it receives the getValues message, it sends the current slider values.

if (strcmp((char*)data, "getValues") == 0) {
  notifyClients(getSliderValues());
}

If it receives another message, we check to which slider corresponds the message and update the corresponding duty cycle value. Finally, we notify all clients that a change occurred. Here’s an example for slider 1:

if (message.indexOf("1s") >= 0) {
  sliderValue1 = message.substring(2);
  dutyCycle1 = map(sliderValue1.toInt(), 0, 100, 0, 1023);
  Serial.println(dutyCycle1);
  Serial.print(getSliderValues());
  notifyClients(getSliderValues());
}

In the loop(), we update the duty cycle of the PWM channels to adjust the brightness of the LEDs.

void loop() {
  analogWrite(ledPin1, dutyCycle1);
  analogWrite(ledPin2, dutyCycle2);
  analogWrite(ledPin3, dutyCycle3);

  ws.cleanupClients();
}

Upload Code and Files

After inserting your network credentials, save the code. Go to Sketch > Show Sketch Folder, and create a folder called data.

Inside that folder you should save the HTML, CSS and JavaScript files.

Then, upload the code to your ESP8266 board. Make sure you have the right board and COM port selected. Also, make sure you’ve added your network credentials.

After uploading the code, you need to upload the files. Go to Tools > ES8266 LittleFS Data Sketch Upload and wait for the files to be uploaded.

When everything is successfully uploaded, open the Serial Monitor at a baud rate of 115200. Press the ESP8266 EN/RST button, and it should print the ESP8266 IP address.

Demonstration

Open a browser on your local network and paste the ESP8266 IP address. You should get access to the web server page to control the brightness of the LEDs.

Move the sliders to control the brightness of the LEDs.

Open several tabs or connect to the web server using another device, and notice that the slider values update almost instantaneously whenever there’s a change.

You can watch the video demonstration (the following video shows a demonstration for the ESP32, but it works similarly with the ESP8266):

Wrapping Up

In this tutorial, you’ve learned how to build a web server with the ESP8266 that serves a web page with multiple sliders. The sliders allow you to control the brightness of LEDs connected to the ESP8266. In addition, we’ve used the WebSocket protocol to communicate between the ESP8266 and the clients.

To learn more about building web servers with the ESP8266 boards, we really recommend taking a look at our eBook:

• Build Web Servers with ESP32 and ESP8266 eBook

Learn more about the ESP8266 with our resources:

• Home Automation using ESP8266
• More ESP8266 Projects and Tutorials…

Thank you for reading.