Arduino UNO R4 - Control Car via Web

This tutorial instructs you how to control a 2WD RC robot car via the web using the Arduino Uno R4 WiFi. In this guide, we will walk you through the steps to set up and control your robot car remotely, utilizing the powerful capabilities of the Arduino Uno R4 with built-in WiFi. By the end of this tutorial, you will learn:

Arduino UNO R4 controls robot car via Web

This tutorial is perfect for hobbyists, students, and anyone interested in robotics and web-based control systems. Whether you are a beginner or have some experience with Arduino, our step-by-step instructions will help you achieve your goal of remotely controlling your 2WD RC robot car.

Let's get started on this exciting journey of combining robotics and web technology!

Hardware Preparation

1×Arduino UNO R4 WiFi
1×USB Cable Type-C
1×2WD RC Car
1×L298N Motor Driver Module
1×IR Remote Controller Kit
1×CR2025 Battery (for IR Remote controller)
1×1.5V AA Battery (for Arduino UNO R4 and Car)
1×Jumper Wires
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Optional) Transparent Acrylic Enclosure For Arduino Uno

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 provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.

Why needs WebSocket to control the RC car?

  • Without WebSocket, you would have to refresh the page every time you want to change the car's direction. This method is not very efficient.
  • With WebSocket, a dedicated connection is created between the webpage and the Arduino UNO R4. This setup allows you to send commands to the Arduino UNO R4 without needing to refresh the page. As a result, the robot car responds quickly and smoothly. Isn't that amazing?

To sum up, WebSocket allows you to control the robot smoothly and in real-time.

We provide detailed guides on using WebSocket with Arduino UNO R4. Find out more by visiting the links provided: Arduino UNO R4 - WebSocket tutorial

How It Works

The Arduino UNO R4 code creates a web server and a WebSocket server. Here's how it works:

  • When you enter the IP address of the Arduino UNO R4 into a web browser, it requests the User Interface webpage from the Arduino UNO R4. The web server on the Arduino UNO R4 responds by sending back the webpage's content made up of HTML, CSS, and JavaScript. Your web browser then shows this webpage. The JavaScript code on the webpage starts a WebSocket connection with the Arduino UNO R4's WebSocket server. When this WebSocket connection is working, any pressing or releasing of buttons on the webpage sends commands to the Arduino UNO R4 through this connection. The WebSocket server on the Arduino UNO R4 gets these commands and controls the robot car as directed.

Here is a table that displays the commands sent from the webpage to the Arduino UNO R4, based on what the user does:

User's Action Button Command Car Action

Wiring Diagram between 2WD RC Car and Arduino UNO R4

The wiring diagram between Arduino UNO R4 2WD RC Car

This image is created using Fritzing. Click to enlarge image

Usually, you would need two different sources of power:

  • One for the motor.
  • Another for the Arduino UNO R4 board and the L298N module, which is used as the motor driver.

You can simplify this setup by using one power source - four 1.5V batteries to make a total of 6V. Here is how to do it:

  • Attach the batteries to the L298N module as shown in the instructions.
  • Take off the two jumpers from the ENA and ENB pins
  • Put on a jumper marked 5VEN (shown with a yellow circle in the diagram).
  • Connect the 12V pin of the L298N module to the Vin pin on the Arduino UNO R4. This will power the Arduino UNO R4 using the batteries.

The 2WD RC car has an on/off switch. This lets you connect or disconnect the battery using the switch, turning the car's power on or off when needed. If you want something simpler, you can skip using the switch.

Arduino UNO R4 Code

The webpage's content (HTML, CSS, JavaScript) is saved in a separate file called index.h. Therefore, we will use two code files in the Arduino IDE.

  • An .ino file is a Arduino UNO R4 code that creates a web server and WebSocket Server to control the car.
  • An .h file stores the content of the webpage.

Detailed Instructions

Follow these instructions step by step:

  • If this is your first time using the Arduino Uno R4 WiFi/Minima, refer to the tutorial on setting up the environment for Arduino Uno R4 WiFi/Minima in the Arduino IDE.
  • Connect the Arduino Uno R4 board to your computer using a USB cable.
  • Launch the Arduino IDE on your computer.
  • Select the appropriate Arduino Uno R4 board (e.g., Arduino Uno R4 WiFi) and COM port.
  • Open the Library Manager by clicking on the Library Manager icon on the left side of the Arduino IDE.
  • In the Library Manager, search for “mWebSockets” and locate the version by Dawid Kurek.
  • Click the Install button to install the mWebSockets library, .
Arduino UNO R4 mWebSockets library
  • In the Arduino IDE, start a new sketch and name it, for example,
  • Copy the following code and open it using the Arduino IDE
/* * This Arduino UNO R4 code was developed by * * This Arduino UNO R4 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ #include <WiFiS3.h> #include <WebSocketServer.h> #include "index.h" #define CMD_STOP 0 #define CMD_FORWARD 1 #define CMD_BACKWARD 2 #define CMD_LEFT 4 #define CMD_RIGHT 8 #define ENA_PIN 7 // The Arduino UNO R4 pin connected to the ENA pin L298N #define IN1_PIN 6 // The Arduino UNO R4 pin connected to the IN1 pin L298N #define IN2_PIN 5 // The Arduino UNO R4 pin connected to the IN2 pin L298N #define IN3_PIN 4 // The Arduino UNO R4 pin connected to the IN3 pin L298N #define IN4_PIN 3 // The Arduino UNO R4 pin connected to the IN4 pin L298N #define ENB_PIN 2 // The Arduino UNO R4 pin connected to the ENB pin L298N const char *ssid = "YOUR_WIFI_SSID"; // CHANGE IT const char *password = "YOUR_WIFI_PASSWORD"; // CHANGE IT using namespace net; WebSocketServer webSocket(81); WiFiServer server(80); int status = WL_IDLE_STATUS; void setup() { Serial.begin(9600); pinMode(ENA_PIN, OUTPUT); pinMode(IN1_PIN, OUTPUT); pinMode(IN2_PIN, OUTPUT); pinMode(IN3_PIN, OUTPUT); pinMode(IN4_PIN, OUTPUT); pinMode(ENB_PIN, OUTPUT); digitalWrite(ENA_PIN, HIGH); // set full speed digitalWrite(ENB_PIN, HIGH); // set full speed //Initialize serial and wait for port to open: Serial.begin(9600); String fv = WiFi.firmwareVersion(); if (fv < WIFI_FIRMWARE_LATEST_VERSION) Serial.println("Please upgrade the firmware"); // attempt to connect to WiFi network: while (status != WL_CONNECTED) { Serial.print("Attempting to connect to SSID: "); Serial.println(password); // Connect to WPA/WPA2 network. Change this line if using open or WEP network: status = WiFi.begin(ssid, password); // wait 4 seconds for connection: delay(4000); } // print your board's IP address: Serial.print("IP Address: "); Serial.println(WiFi.localIP()); server.begin(); webSocket.onConnection([](WebSocket &ws) { const auto protocol = ws.getProtocol(); if (protocol) { Serial.print(F("Client protocol: ")); Serial.println(protocol); } ws.onMessage([](WebSocket &ws, const WebSocket::DataType dataType, const char *message, uint16_t length) { String cmd_str = String((char *)message); int command = cmd_str.toInt(); Serial.print("command: "); Serial.println(command); switch (dataType) { case WebSocket::DataType::TEXT: switch (command) { case CMD_STOP: Serial.println("Stop"); CAR_stop(); break; case CMD_FORWARD: Serial.println("Move Forward"); CAR_moveForward(); break; case CMD_BACKWARD: Serial.println("Move Backward"); CAR_moveBackward(); break; case CMD_LEFT: Serial.println("Turn Left"); CAR_turnLeft(); break; case CMD_RIGHT: Serial.println("Turn Right"); CAR_turnRight(); break; default: Serial.println("Unknown command"); } break; case WebSocket::DataType::BINARY: Serial.println(F("Received binary data")); break; } }); ws.onClose([](WebSocket &, const WebSocket::CloseCode, const char *, uint16_t) { Serial.println(F("Disconnected")); }); Serial.print(F("New WebSocket Connnection from client: ")); Serial.println(ws.getRemoteIP()); }); webSocket.begin(); } void loop() { webSocket.listen(); // listen for incoming clients WiFiClient client = server.available(); if (client) { // read the HTTP request header line by line while (client.connected()) { if (client.available()) { String HTTP_header = client.readStringUntil('\n'); // read the header line of HTTP request if (HTTP_header.equals("\r")) // the end of HTTP request break; Serial.print("<< "); Serial.println(HTTP_header); // print HTTP request to Serial Monitor } } // send the HTTP response header 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(); // the separator between HTTP header and body String html = String(HTML_CONTENT); client.println(html); client.flush(); // give the web browser time to receive the data delay(100); // close the connection: client.stop(); } } void CAR_moveForward() { digitalWrite(IN1_PIN, HIGH); digitalWrite(IN2_PIN, LOW); digitalWrite(IN3_PIN, HIGH); digitalWrite(IN4_PIN, LOW); } void CAR_moveBackward() { digitalWrite(IN1_PIN, LOW); digitalWrite(IN2_PIN, HIGH); digitalWrite(IN3_PIN, LOW); digitalWrite(IN4_PIN, HIGH); } void CAR_turnLeft() { digitalWrite(IN1_PIN, HIGH); digitalWrite(IN2_PIN, LOW); digitalWrite(IN3_PIN, LOW); digitalWrite(IN4_PIN, LOW); } void CAR_turnRight() { digitalWrite(IN1_PIN, LOW); digitalWrite(IN2_PIN, LOW); digitalWrite(IN3_PIN, HIGH); digitalWrite(IN4_PIN, LOW); } void CAR_stop() { digitalWrite(IN1_PIN, LOW); digitalWrite(IN2_PIN, LOW); digitalWrite(IN3_PIN, LOW); digitalWrite(IN4_PIN, LOW); }
  • Change the WiFi details (SSID and password) in the program to use your network information.
  • Create the file named index.h in Arduino IDE by doing one of the following:
    • Click the button located below the serial monitor icon and select New Tab, or press Ctrl+Shift+N on your keyboard.
    Arduino IDE 2 adds file
    • Name the file index.h and press the OK button.
    Arduino IDE 2 adds file index.h
    • Copy the following code and paste it into the index.h file.
    /* * This Arduino UNO R4 code was developed by * * This Arduino UNO R4 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ const char *HTML_CONTENT = R"=====( <!DOCTYPE html> <html> <head> <title>Arduino Uno R4 Control Car via Web</title> <meta name="viewport" content="width=device-width, initial-scale=0.7, maximum-scale=1, user-scalable=no"> <style type="text/css"> body { text-align: center; font-size: 24px;} button { text-align: center; font-size: 24px;} #container { margin-right: auto; margin-left: auto; width: 400px; height: 400px; position: relative; margin-bottom: 10px; } div[class^='button'] { position: absolute; } .button_up, .button_down { width:214px; height:104px;} .button_left, .button_right { width:104px; height:214px;} .button_stop { width:178px; height:178px;} .button_up { background: url('') no-repeat; background-size: contain; left: 200px; top: 0px; transform: translateX(-50%); } .button_down { background: url('') no-repeat; background-size: contain; left:200px; bottom: 0px; transform: translateX(-50%); } .button_right { background: url('') no-repeat; background-size: contain; right: 0px; top: 200px; transform: translateY(-50%); } .button_left { background: url('') no-repeat; background-size: contain; left:0px; top: 200px; transform: translateY(-50%); } .button_stop { background: url('') no-repeat; background-size: contain; left:200px; top: 200px; transform: translate(-50%, -50%); } </style> <script> var CMD_STOP = 0; var CMD_FORWARD = 1; var CMD_BACKWARD = 2; var CMD_LEFT = 4; var CMD_RIGHT = 8; var img_name_lookup = { [CMD_STOP]: "stop", [CMD_FORWARD]: "up", [CMD_BACKWARD]: "down", [CMD_LEFT]: "left", [CMD_RIGHT]: "right" } var ws = null; function init() { var container = document.querySelector("#container"); container.addEventListener("touchstart", mouse_down); container.addEventListener("touchend", mouse_up); container.addEventListener("touchcancel", mouse_up); container.addEventListener("mousedown", mouse_down); container.addEventListener("mouseup", mouse_up); container.addEventListener("mouseout", mouse_up); } function ws_onmessage(e_msg) { e_msg = e_msg || window.event; // MessageEvent //alert("msg : " +; } function ws_onopen() { document.getElementById("ws_state").innerHTML = "OPEN"; document.getElementById("wc_conn").innerHTML = "Disconnect"; } function ws_onclose() { document.getElementById("ws_state").innerHTML = "CLOSED"; document.getElementById("wc_conn").innerHTML = "Connect"; console.log("socket was closed"); ws.onopen = null; ws.onclose = null; ws.onmessage = null; ws = null; } function wc_onclick() { if(ws == null) { ws = new WebSocket("ws://" + + ":81"); document.getElementById("ws_state").innerHTML = "CONNECTING"; ws.onopen = ws_onopen; ws.onclose = ws_onclose; ws.onmessage = ws_onmessage; } else ws.close(); } function mouse_down(event) { if ( !== event.currentTarget) { var id =; send_command(id); = "url('" + img_name_lookup[id] + "_active.png')"; } event.stopPropagation(); event.preventDefault(); } function mouse_up(event) { if ( !== event.currentTarget) { var id =; send_command(CMD_STOP); = "url('" + img_name_lookup[id] + "_inactive.png')"; } event.stopPropagation(); event.preventDefault(); } function send_command(cmd) { if(ws != null) if(ws.readyState == 1) ws.send(cmd + "\r\n"); } window.onload = init; </script> </head> <body> <h2>Arduino Uno R4 - RC Car via Web</h2> <div id="container"> <div id="0" class="button_stop"></div> <div id="1" class="button_up"></div> <div id="2" class="button_down"></div> <div id="8" class="button_right"></div> <div id="4" class="button_left"></div> </div> <p> WebSocket : <span id="ws_state" style="color:blue">closed</span><br> </p> <button id="wc_conn" type="button" onclick="wc_onclick();">Connect</button> <br> <br> <div class="sponsor">Sponsored by <a href="">DIYables</a></div> </body> </html> )=====";
    • You now have the code in two files named and index.h. To upload the code to Arduino UNO R4, click the Upload button in the Arduino IDE.

    You will see an error as shown below:

    In file included from c:\Users\YOU_ACCOUNT\Documents\Arduino\libraries\mWebSockets\src/utility.h:3:0, from c:\Users\YOU_ACCOUNT\Documents\Arduino\libraries\mWebSockets\src/WebSocket.h:5, from c:\Users\YOU_ACCOUNT\Documents\Arduino\libraries\mWebSockets\src/WebSocketServer.h:5, from C:\Users\YOU_ACCOUNT\Documents\Arduino\\ C:\Users\YOU_ACCOUNT\Documents\Arduino\libraries\mWebSockets\src/platform.h:54:12: fatal error: Ethernet.h: No such file or directory # include <Ethernet.h> ^~~~~~~~~~~~ compilation terminated. exit status 1

    To fix this error:

    • Navigate to the folder: C:\Users\YOUR_ACCOUNT\Documents\Arduino\libraries\mWebSockets\src/
    • Look for the file named config.h and open it using a text editor.
    • Go to line 26, and it will appear as follows:
    • Change the line to the following and save it:
    • Click the Upload button in the Arduino IDE to load your code onto the Arduino UNO R4.
    • Open the Serial Monitor.
    • Look at the results displayed on the Serial Monitor.
    Connecting to WiFi... Connected to WiFi Arduino UNO R4 Web Server's IP address IP address:
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    • Write down the IP address shown and type it into the address bar in a web browser on your smartphone or computer.
    • The webpage will appear as follows:
    Arduino UNO R4 controls car via web browser
    • Press the CONNECT button to link the webpage with Arduino UNO R4 through WebSocket.
    • You can now direct the car to turn left or right, and move forward or backward using the web interface.

    The control button images are not saved on the Arduino UNO R4 to save its memory. Instead, they are stored online. Therefore, your phone or computer must be connected to the internet to load these images on the web control page.

    ※ NOTE THAT:

    If you change the HTML in the file named index.h but do not change anything in the file named, then when you compile and upload the code to the Arduino UNO R4, the Arduino IDE will not update the HTML content. To make the Arduino IDE to update the HTML content, you must make a small change in the file, like adding an empty line or a comment.

    Line-by-line Code Explanation

    The Arduino UNO R4 code provided includes explanations for each line. Be sure to read the comments within the code!

Troubleshooting For Arduino Uno R4

If the above code does work, please update the latest version for the WiFi module of Arduino UNO R4

  • Connect your Arduino Uno R4 WiFi to your PC
  • Open Arduino IDE 2
  • Go to Tools Firmware Updater
Arduino Uno R4 WiFi Update Firmware
  • Select the Arduino Uno R4 WiFi board and port
  • Click CHECK UPDATES button
  • A list of available firmware versions will appear
  • Select the latest version of firmware
  • Click INSTALL button
  • Wait until it done
  • Reboot your Arduino Uno R4 WiFi
  • Re-compile and upload your code to Arduino Uno R4 WiFi
  • Check the result


  • As freelancers, We are AVAILABLE for HIRE. See how to outsource your project to us
  • Please feel free to share the link of this tutorial. However, Please do not use our content on any other websites. We invested a lot of effort and time to create the content, please respect our work!