Building a TCP/IP Socket Server for IoT Smart Lighting

Project Background

I participated in the 1st Woosong University National SW Club Competition and built an IoT smart lighting system that automatically adjusts brightness based on ambient light levels to save energy.

Components:

• NodeMCU (ESP8266): Measures ambient brightness via light sensor, controls the light
• Node.js Server: Acts as a relay for communication
• Android App: Real-time monitoring and manual control

---

Problem

I needed real-time communication between the NodeMCU and the Android app. I initially implemented this with HTTP, but ran into issues:

• The app had to continuously poll the server, which drained the battery
• State changes on the NodeMCU couldn’t be detected immediately by the app
• Overall responsiveness was poor

---

Solution: TCP/IP Socket Communication

I decided to use TCP sockets instead of HTTP.

Node.js Server (net module)

const net = require('net');

const clients = [];

const server = net.createServer((socket) => {
    clients.push(socket);
    
    socket.on('data', (data) => {
        // Broadcast received data to other clients
        clients.forEach(client => {
            if (client !== socket) {
                client.write(data);
            }
        });
    });
    
    socket.on('close', () => {
        const index = clients.indexOf(socket);
        clients.splice(index, 1);
    });
});

server.listen(3000);

Both the NodeMCU and the Android app connect to this server via TCP, and the server relays messages between them.

---

Results

• Light sensor changes were instantly reflected in the app
• Manual controls from the app reached the NodeMCU in real-time
• Battery consumption dropped significantly compared to HTTP polling

---

Lessons Learned

• I got to experience the difference between HTTP and TCP sockets firsthand
• Sockets are the way to go when you need real-time communication
• Choosing the right communication method for your use case matters

---

From developing the 2nd place award-winning project (President’s Award) at the 1st Woosong University National SW Club Competition.

• SmartIoTLightingController