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ESP32 - Control Servo Motor via Web
This tutorial instructs you on how to use the ESP32 to control a servo motor via the web from a browser on your smartphone or PC. We'll use something called WebSocket to control the servo motor smoothly and dynamically through a graphical web user interface.
The video below is a demonstration:
Now, why use WebSocket? Here's the idea:
- Without WebSocket, every time you want to change the angle of the servo, you have to reload the page. Not great!
- But with WebSocket, we set up a special connection between the webpage and the ESP32. This means we can send the angle value to the ESP32 in the background, without reloading the page. That makes the servo move smoothly and in real-time. Pretty cool, huh?
Let's start!
Hardware Used In This Tutorial
Or you can buy the following sensor kits:
| 1 | × | DIYables Sensor Kit (30 sensors/displays) | |
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Disclosure: Some of the links in this section are Amazon affiliate links, meaning we may earn a commission at no additional cost to you if you make a purchase through them. Additionally, some links direct you to products from our own brand, DIYables.
Introduction to Servo Motor and WebSocket
We have specific tutorials about servo motor and WebSocket. Each tutorial contains detailed information and step-by-step instructions about hardware pinout, working principle, wiring connection to ESP32, ESP32 code... Learn more about them at the following links:
- ESP32 - Servo Motor tutorial
- ESP32 - WebSocket tutorial
How It Works
The ESP32 code creates both a web server and a WebSocket Server. Here's how it works:
- When you enter the ESP32's IP address in a web browser, it requests the webpage (User Interface) from the ESP32.
- The ESP32's web server responds by sending the webpage's content (HTML, CSS, JavaScript).
- Your web browser then displays the webpage.
- The JavaScript code within the webpage establishes a WebSocket connection to the WebSocket server on the ESP32.
- Once this WebSocket connection is established, if you turn the handle on the webpage, the JavaScript code quietly sends the angle value to the ESP32 through this WebSocket connection in the background.
- The WebSocket server on the ESP32, upon receiving the angle value, controls the servo motor accordingly.
In a nutshell, the WebSocket connection enables the smooth, real-time control of the servo motor angle.
Wiring Diagram between Servo Motor and ESP32
This image is created using Fritzing. Click to enlarge image
For the sake of simplicity, the above wiring diagram is used for the testing or learning purposes, and for small-torque servo motor. In practice, we highly recommend using the external power supply for the servo motor. The below wiring diagram shows how to connect servo motor to an external power source.
This image is created using Fritzing. Click to enlarge image
The below show a real wiring between servo motor and ESP32.
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
The webpage's content (HTML, CSS, JavaScript) are stored separately on an index.h file. So, we will have two code files on Arduino IDE:
- An .ino file that is ESP32 code, which creates a web sever and WebSocket Server, and control servo motor
- An .h file, which contains the webpage's content.
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.
- Open the Library Manager by clicking on the Library Manager icon on the left navigation bar of Arduino IDE.
- Search “ESPAsyncWebServer”, then find the ESPAsyncWebServer created by lacamera.
- Click Install button to install ESPAsyncWebServer library.
- You will be asked to install the dependency. Click Install All button.
- Search “WebSockets”, then find the WebSockets created by Markus Sattler.
- Click Install button to install WebSockets library.
- Type ServoESP32 on the search box, then look for the servo library by Jaroslav Paral. Please be aware that both version 1.1.1 and 1.1.0 are affected by bugs. Kindly choose a different version.
- Click Install button to install servo motor library for ESP32.
- On Arduino IDE, 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-controls-servo-motor-via-web
*/
#include <Servo.h>
#include <WiFi.h>
#include <ESPAsyncWebServer.h>
#include <WebSocketsServer.h>
#include "index.h"
#define SERVO_PIN 26 // ESP32 pin GPIO26 connected to servo motor
Servo servo;
const char* ssid = "YOUR_WIFI_SSID"; // CHANGE IT
const char* password = "YOUR_WIFI_PASSWORD"; // CHANGE IT
AsyncWebServer server(80);
WebSocketsServer webSocket = WebSocketsServer(81); // WebSocket server on port 81
void webSocketEvent(uint8_t num, WStype_t type, uint8_t* payload, size_t length) {
switch (type) {
case WStype_DISCONNECTED:
Serial.printf("[%u] Disconnected!\n", num);
break;
case WStype_CONNECTED:
{
IPAddress ip = webSocket.remoteIP(num);
Serial.printf("[%u] Connected from %d.%d.%d.%d\n", num, ip[0], ip[1], ip[2], ip[3]);
}
break;
case WStype_TEXT:
//Serial.printf("[%u] Received text: %s\n", num, payload);
String angle = String((char*)payload);
int angle_value = angle.toInt();
Serial.println(angle_value);
servo.write(angle_value);
break;
}
}
void setup() {
Serial.begin(9600);
servo.attach(SERVO_PIN); // attaches the servo on ESP32 pin
// 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");
// Initialize WebSocket server
webSocket.begin();
webSocket.onEvent(webSocketEvent);
// Serve a basic HTML page with JavaScript to create the WebSocket connection
server.on("/", HTTP_GET, [](AsyncWebServerRequest* request) {
Serial.println("Web Server: received a web page request");
String html = HTML_CONTENT; // Use the HTML content from the index.h file
request->send(200, "text/html", html);
});
server.begin();
Serial.print("ESP32 Web Server's IP address: ");
Serial.println(WiFi.localIP());
}
void loop() {
webSocket.loop();
}
- Modify the WiFi information (SSID and password) in the code to match your own network credentials.
- 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.
- Give the file's name index.h and click OK button
- Copy the below code and paste it to the index.h.
- 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
- Open the Serial Monitor
- Check out the result on Serial Monitor.
- Take note of the IP address displayed, and enter this address into the address bar of a web browser on your smartphone or PC.
- You will see the webpage it as below:
- The JavaScript code of the webpage automatically creates the WebSocket connection to ESP32.
- Now you can control the servo motor's angle via the web interface.
- 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....)
/*
* 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-controls-servo-motor-via-web
*/
const char *HTML_CONTENT = R"=====(
<!DOCTYPE html>
<html>
<head>
<title>ESP32 Controls Servo Motor via Web</title>
<meta name="viewport" content="width=device-width, initial-scale=0.7">
<style>
body { text-align: center; }
canvas { background-color: #ffffff; }
</style>
<script>
var canvas_width = 401, canvas_height = 466;
var pivot_x = 200, pivot_y = 200;
var bracket_radius = 160, bracket_angle = 0;
var bracket_img = new Image();
var click_state = 0;
var last_angle = 0;
var mouse_xyra = {x:0, y:0, r:0.0, a:0.0};
var ws;
bracket_img.src = "https://esp32io.com/images/tutorial/servo-bracket.png";
function init()
{
var servo = document.getElementById("servo");
servo.width = canvas_width;
servo.height = canvas_height;
servo.style.backgroundImage = "url('https://esp32io.com/images/tutorial/servo-body.png')";
servo.style.backgroundPosition = "center";
servo.style.backgroundSize = "contain";
servo.addEventListener("touchstart", mouse_down);
servo.addEventListener("touchend", mouse_up);
servo.addEventListener("touchmove", mouse_move);
servo.addEventListener("mousedown", mouse_down);
servo.addEventListener("mouseup", mouse_up);
servo.addEventListener("mousemove", mouse_move);
var ctx = servo.getContext("2d");
ctx.translate(pivot_x, pivot_y);
rotate_bracket(0);
ws = new WebSocket("ws://" + window.location.host + ":81");
document.getElementById("ws_state").innerHTML = "CONNECTING";
ws.onopen = function(){ document.getElementById("ws_state").innerHTML = "CONNECTED" };
ws.onclose = function(){ document.getElementById("ws_state").innerHTML = "CLOSED"};
ws.onerror = function(){ alert("websocket error " + this.url) };
ws.onmessage = ws_onmessage;
}
function ws_onmessage(e_msg)
{
e_msg = e_msg || window.event; // MessageEvent
alert("msg : " + e_msg.data);
}
function rotate_bracket(angle)
{
var servo = document.getElementById("servo");
var ctx = servo.getContext("2d");
ctx.clearRect(-pivot_x, -pivot_y, canvas_width, canvas_height);
ctx.rotate(angle / 180 * Math.PI);
ctx.drawImage(bracket_img, -pivot_x, -pivot_y);
ctx.rotate(-angle / 180 * Math.PI);
}
function check_range_xyra(event, mouse_xyra)
{
var x, y, r, a, rc_x, rc_y, radian;
var min_r, max_r, width;
if(event.touches)
{
var touches = event.touches;
x = (touches[0].pageX - touches[0].target.offsetLeft) - pivot_x;
y = pivot_y - (touches[0].pageY - touches[0].target.offsetTop);
min_r = 60;
max_r = pivot_x;
width = 40;
}
else
{
x = event.offsetX - pivot_x;
y = pivot_y - event.offsetY;
min_r = 60;
max_r = bracket_radius;
width = 20;
}
/* cartesian to polar coordinate conversion */
r = Math.sqrt(x * x + y * y);
a = Math.atan2(y, x);
mouse_xyra.x = x;
mouse_xyra.y = y;
mouse_xyra.r = r;
mouse_xyra.a = a;
radian = bracket_angle / 180 * Math.PI;
/* rotate coordinate */
rc_x = x * Math.cos(radian) - y * Math.sin(radian);
rc_y = x * Math.sin(radian) + y * Math.cos(radian);
if((r < min_r) || (r > max_r))
return false;
if((rc_y < -width) || (rc_y > width))
return false;
return true;
}
function mouse_down()
{
if(event.touches && (event.touches.length > 1))
click_state = event.touches.length;
if(click_state > 1)
return;
if(check_range_xyra(event, mouse_xyra))
{
click_state = 1;
last_angle = mouse_xyra.a / Math.PI * 180.0;
}
}
function mouse_up()
{
click_state = 0;
}
function mouse_move()
{
var angle;
if(event.touches && (event.touches.length > 1))
click_state = event.touches.length;
if(click_state > 1)
return;
if(!click_state)
return;
if(!check_range_xyra(event, mouse_xyra))
{
click_state = 0;
return;
}
angle = mouse_xyra.a / Math.PI * 180.0;
if((Math.abs(angle) > 90) && (angle * last_angle < 0))
{
if(last_angle > 0)
last_angle = -180;
else
last_angle = 180;
}
bracket_angle += (last_angle - angle);
last_angle = angle;
if(bracket_angle > 90)
bracket_angle = 90;
if(bracket_angle < -90)
bracket_angle = -90;
rotate_bracket(bracket_angle);
if(ws.readyState == 1)
ws.send(Math.floor(90 - bracket_angle) + "\r\n");
debug = document.getElementById("debug");
debug.innerHTML = Math.floor(90 - bracket_angle);
event.preventDefault();
}
window.onload = init;
</script>
</head>
<body>
<h2>
ESP32 - Servo Motor via Web<br>
<canvas id="servo"></canvas>
<p>
WebSocket : <span id="ws_state" style="color:blue">null</span><br>
Angle : <span id="debug" style="color:blue">90</span>
</p>
</h2>
<div class="sponsor">Sponsored by <a href="https://amazon.com/diyables">DIYables</a></div>
</body>
</html>
)=====";
COM6
Connecting to WiFi...
Connected to WiFi
ESP32 Web Server's IP address IP address: 192.168.0.2
Autoscroll
Clear output
9600 baud
Newline
To save the memory of ESP32, the images of servo motor are NOT stored on ESP32. Instead, they are stored on the internet, so, your phone or PC need to have internet connection to load images for the web control page.
※ NOTE THAT:
Line-by-line Code Explanation
The above ESP32 code contains line-by-line explanation. Please read the comments in the code!