How to Use the ESP32 to Listen for TCP Packets on a Specific Port

The ESP32 is a powerful microcontroller with Wi-Fi and Bluetooth capabilities, making it perfect for network-based applications. In this tutorial, you’ll learn how to use your ESP32 to act as a TCP server, listening for incoming TCP packets on a specific port.

Requirements

Set Up the Arduino IDE for ESP32

If you haven’t already:

1. Open Arduino IDE.

2. Go to File > Preferences, and in the “Additional Board Manager URLs”, add: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

3. Go to Tools > Board > Boards Manager, search for esp32, and install the package.

4. Select your ESP32 board under Tools > Board.

The TCP Server Code

Here’s a simple sketch that creates a TCP server on port 8080:

#include <WiFi.h>

const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";

WiFiServer tcpServer(8080); // Listen on port 8080

void setup() {
    Serial.begin(115200);
    delay(1000);

    // Connect to Wi-Fi
    WiFi.begin(ssid, password);
    Serial.print("Connecting to WiFi...");
    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }
    Serial.println(" connected!");
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());

    // Start the server
    tcpServer.begin();
    Serial.println("TCP server started on port 8080");
}

void loop() {
    WiFiClient client = tcpServer.available(); // Check for incoming clients

    if (client) {
        Serial.println("Client connected!");
        while (client.connected()) {
            if (client.available()) {
                String data = client.readStringUntil('\n');
                Serial.print("Received: ");
                Serial.println(data);
                client.println("Data received."); // Echo back
           }
       }
       client.stop();
       Serial.println("Client disconnected.");
    }
}

Testing the TCP Server

1. Upload the code to your ESP32.

2. Open the Serial Monitor (baud 115200) and wait for the ESP32 to connect to Wi-Fi.

3. Note the IP address shown.

From a PC:

If you’re on Windows/Linux/macOS, use telnet or netcat:

telnet 192.168.X.X 8080
# or
nc 192.168.X.X 8080

Then type a message and press Enter. You should see it printed in the Serial Monitor and echoed back.

Notes & Troubleshooting

• Ensure your PC and ESP32 are on the same Wi-Fi network.

• Some networks (like guest networks) may block TCP connections.

• You can change the listening port by modifying the WiFiServer tcpServer(8080); line.

• You can add custom logic to parse and respond to commands from the client.

Use Cases

• Remote monitoring/control of sensors or relays

• Data logging from a mobile app or PC

• Creating a simple REST-like TCP interface

What’s Next?

• Try handling multiple clients using a WiFiClient array.

• Add encryption using SSL (with WiFiServerSecure).

• Combine with sensors and actuators to build interactive IoT projects.

If you found this guide helpful, feel free to bookmark it or share it with fellow tinkerers! 😊 Let me know if you want a follow-up article with enhancements like handling multiple clients or sending sensor data.