Wi-Fi Controlled Relay using NodeMCU – Control Appliances with Your Phone!

Controlling electrical devices with your smartphone has never been easier, thanks to Wi-Fi-enabled microcontrollers like the NodeMCU. In this DIY project, you’ll learn how to build a Wi-Fi Controlled Relay that lets you switch any appliance on/off from your phone — without any remote or switch.

This beginner-friendly project is perfect for smart home enthusiasts, students, and DIYers. Let’s dive into the full guide!

---

📌 Table of Contents

1. What is a Wi-Fi Controlled Relay?
2. Features
3. Applications
4. Required Components
5. Circuit Diagram
6. How It Works
7. How to Make It (Step-by-Step Guide)
8. Arduino Code
9. FAQs
10. Final Thoughts

---

🔍 What is a Wi-Fi Controlled Relay?

A Wi-Fi Controlled Relay is an IoT-based switch that connects to your home Wi-Fi network and allows you to control appliances using a smartphone or browser. It uses a Wi-Fi microcontroller (like NodeMCU/ESP8266) and a relay module to switch high-voltage loads safely.

---

✨ Features

• 📱 Control using your smartphone via browser
• 🌐 Wi-Fi connectivity using NodeMCU (ESP8266)
• 🔌 Can switch AC devices (like fan, light, charger)
• 🛡️ Fully isolated relay control
• 🧠 Easy to modify and expand (add more relays or sensors)
• 🔧 DIY-friendly and low cost

---

💡 Applications

• Smart home automation
• Remote-controlled light or fan
• Automatic plant watering system
• Wireless switch for power outlets
• Voice control (via Google Assistant + IFTTT integration)

---

✅ Required Components

Component	Quantity	Notes
NodeMCU (ESP8266)	1	Microcontroller with built-in Wi-Fi
5V Relay Module (1-Channel)	1	Opto-isolated preferred for AC safety
AC Appliance (e.g., Bulb, Fan)	1	Use with caution, must be plugged through a relay
Female Plug + Socket	1	For AC appliance connection (optional but recommended)
Jumper Wires (Male-to-Female)	5+	For relay-to-NodeMCU connections
Breadboard or PCB	1	Optional, but helps keep circuit stable
Micro USB Cable	1	For programming and powering NodeMCU
USB Charger or 5V Adapter	1	To power NodeMCU after uploading the code
Screwdriver + Wire Cutter	1 set	For wiring relay to AC terminals
2-pin Wire or Power Cord	1	For relay COM/NO connection to appliance

---

🔐 Safety Tip:

If you’re working with AC 220V, always use a plug board for testing. Never handle live wires directly — use a proper relay module with screw terminals and opto-isolation.

⚠️ Safety Note: Relays handle AC voltage. Take proper precautions or use an AC bulb connected through a plug board during testing.

---

🧠 How It Works

The NodeMCU connects to your Wi-Fi and hosts a simple web server. When you access the NodeMCU IP in a browser, you’ll see ON/OFF buttons. Clicking these buttons sends signals to the relay module which, in turn, turns the connected appliance ON or OFF.

---

📊 Circuit Diagram

Here’s the correct circuit diagram showing how to connect the NodeMCU to a 5V Relay Module:

1. NodeMCU ↔ Relay Module (3 Wires)

These are low-voltage connections:

From NodeMCU	To Relay Module	Purpose
D1 (GPIO5)	IN	Control signal to turn relay ON/OFF
G (GND)	GND	Common ground
VIN	VCC	Powers relay module (5V input)

📌 You can also use 3.3V from NodeMCU in some relay modules, but 5V (VIN) is safer and more reliable.

2. Relay Module ↔ AC Appliance (3 Wires)

These are high-voltage (230V) wires, handled carefully:

Relay Terminal	Connected To	Description
COM	Live wire (from AC plug)	Entry point for power
NO (Normally Open)	Live input of appliance	Only connected when relay is ON
Neutral	Direct to appliance	Goes from wall socket to appliance

⚠️ Make sure to insulate all AC connections properly or use a plug-and-socket setup.

---

🛠️ How to Make a Wi-Fi Controlled Relay – Step-by-Step

🔌 Step 1: Hardware Setup

• Connect IN of Relay Module to D1 (GPIO5) on NodeMCU.
• Relay VCC → NodeMCU 3V, GND → GND.
• Plug in your relay’s NO/NC and COM terminals as per device.
• Optional: Add a plug socket and connect the appliance through it for safe testing.

🔁 Step 2: Upload Arduino Code

• Install ESP8266 board from Arduino IDE board manager.
• Connect NodeMCU via USB.
• Upload the following code.

---

🧾 Arduino Code for Wi-Fi Relay

cppCopyEdit#include <ESP8266WiFi.h>

// Replace with your network credentials
const char* ssid = "Your_SSID";
const char* password = "Your_PASSWORD";

WiFiServer server(80);

const int relayPin = D1;

void setup() {
  Serial.begin(115200);
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Relay OFF initially

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  server.begin();
}

void loop() {
  WiFiClient client = server.available();
  if (!client) return;

  while(!client.available()) delay(1);

  String request = client.readStringUntil('\r');
  client.flush();

  if (request.indexOf("/ON") != -1) {
    digitalWrite(relayPin, LOW); // Relay ON
  }
  if (request.indexOf("/OFF") != -1) {
    digitalWrite(relayPin, HIGH); // Relay OFF
  }

  // HTML Response
  client.println("HTTP/1.1 200 OK");
  client.println("Content-Type: text/html");
  client.println("");
  client.println("<!DOCTYPE HTML>");
  client.println("<html>");
  client.println("<h1>Wi-Fi Relay Control</h1>");
  client.println("<a href=\"/ON\"><button>ON</button></a>");
  client.println("<a href=\"/OFF\"><button>OFF</button></a>");
  client.println("</html>");
}

🔐 Note: Replace "Your_SSID" and "Your_PASSWORD" with your Wi-Fi credentials.

---

🔍 How to Use

1. Power NodeMCU via USB or 5V.
2. Open Serial Monitor at 115200 baud. Note the IP address.
3. Type that IP in your phone or PC browser (on the same Wi-Fi).
4. Tap ON/OFF — your relay should click, and your device will respond.

---

❓ FAQs – Wi-Fi Controlled Relay

Q1. Can I control multiple relays with this code?
Yes! Just add more relays to unused GPIOs and duplicate the HTML & code logic.

Q2. Is it safe to control 230V appliances?
Yes, as long as your relay module is properly rated and isolated. Avoid touching any AC lines.

Q3. Can I control it from outside my home Wi-Fi?
Yes, using port forwarding or services like Blynk or Telegram Bot for remote control.

Q4. Can I use ESP32 instead of NodeMCU?
Absolutely! Just update pin numbers accordingly.

---

🧠 Final Thoughts

Building a Wi-Fi Controlled Relay is an excellent way to get started with home automation and IoT. It’s cost-effective, simple, and can be expanded into full smart home systems.

If you’re interested in turning this into a full Alexa or Google Assistant-controlled switch, stay tuned — we’ll cover that in upcoming posts!

---

💬 Need Help?

If you face any problems while making this project, feel free to ask your question in the comments below. I’d love to help you troubleshoot!