Arduino Fans

Controlling 4 relays using a NodeMCU (ESP8266) via Wi-Fi and the Blynk app is a great way to build an IoT home automation project. Below is a step-by-step guide, including the circuit diagram, Blynk setup, and Arduino code.

🧰 Requirements

• NodeMCU (ESP8266)
• 4-channel Relay Module
• Blynk IoT App (on iOS/Android)
• Jumper Wires
• Power Supply (5V for relays, 3.3V logic for NodeMCU)

📲 Blynk App Setup

1. Install Blynk IoT app (new version, not legacy).
2. Create a New Project.
3. Add 4 buttons (set each to “Switch” mode).
4. Assign them to Virtual Pins V0, V1, V2, V3.
5. Note your Auth Token, or set up Blynk with template credentials.

NodeMCU        Relay Module
D1 (GPIO5)  -> IN1
D2 (GPIO4)  -> IN2
D3 (GPIO0)  -> IN3
D4 (GPIO2)  -> IN4
GND         -> GND
Vin (5V)    -> VCC (use external 5V if needed)

💻 Arduino Code

First, install the following libraries via Library Manager:

• Blynk (latest)
• ESP8266WiFi

Here’s a detailed explanation of how the NodeMCU (ESP8266), relay module, and Blynk app work together to control 4 relays:

🔁 Overall System Workflow

1. Blynk App (Mobile) → Sends virtual pin commands via Wi-Fi
2. Blynk Cloud Server → Transfers the virtual pin states to NodeMCU
3. NodeMCU (ESP8266) → Reads the states and controls the relays
4. Relay Module → Switches electrical devices ON/OFF

🔧 Component Breakdown

🧠 1. NodeMCU (ESP8266)

• A microcontroller with built-in Wi-Fi.
• Connects to your Wi-Fi network and communicates with Blynk Cloud.
• Uses GPIO pins to send signals to the relay module.
• Each relay is controlled using a digital output pin (D1 to D4).

📱 2. Blynk App

• Acts as a remote control interface.
• You add buttons in the app and link them to virtual pins (V0 to V3).
• When you tap a button, Blynk sends the signal via the internet to the NodeMCU.

Example:

• Tap “Relay 1 ON” → App sets V0 = 1 → Blynk Cloud → NodeMCU receives V0 = 1

☁️ 3. Blynk Cloud Server

• Middleware that handles communication between the app and your NodeMCU.
• Keeps your device and app synchronized, even when they’re on different networks.
• Your NodeMCU uses Blynk.run() in the loop() to constantly check for incoming messages.

⚡ 4. Relay Module

• A relay is an electromechanical switch.
• It has 3 pins: IN, VCC, and GND.
• IN pin is connected to a NodeMCU GPIO. When the GPIO goes LOW, the relay activates.
• It switches a higher-power circuit (like 220V light or fan) safely.

Most relay modules are active LOW, which means:

• LOW signal (0V) → Turns relay ON
• HIGH signal (3.3V) → Turns relay OFF

🔌 Power and Safety Notes

• NodeMCU operates at 3.3V logic.
• Relay module typically requires 5V VCC and uses optocouplers to isolate high-voltage devices.
• Use an external 5V power supply if you’re switching high-power loads.
• Always share GND between NodeMCU and the relay module.

🧪 How It All Comes Together

1. Power on the NodeMCU and relay module.
2. NodeMCU connects to your Wi-Fi and logs in to Blynk Cloud using your Auth Token.
3. The app initializes with buttons linked to virtual pins.
4. Pressing a button on the app:
   • Sends a 1 (ON) or 0 (OFF) to the virtual pin.
   • The BLYNK_WRITE(Vx) function in the code receives this signal.
   • The function uses digitalWrite() to toggle the respective GPIO pin.
   • The GPIO pin goes LOW or HIGH, activating or deactivating the relay.

📊 Example: What happens when you press “RELAY 2” button:

• Button linked to V1.
• Press ON → App sends 1 to V1.
• NodeMCU receives it and executes:
• BLYNK_WRITE(V1) { digitalWrite(RELAY2, param.asInt() ? LOW : HIGH); }
• LOW signal is sent to D2 (RELAY2).
• Relay2 switches ON.
• Light/Fan connected to that relay turns ON.

#define BLYNK_TEMPLATE_ID "YourTemplateID"
#define BLYNK_TEMPLATE_NAME "RelayControl"
#define BLYNK_AUTH_TOKEN "YourAuthToken"

#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>

// Replace with your network credentials
char ssid[] = "YourWiFiSSID";
char pass[] = "YourWiFiPassword";

// Define relay pins
#define RELAY1 D1  // GPIO5
#define RELAY2 D2  // GPIO4
#define RELAY3 D3  // GPIO0
#define RELAY4 D4  // GPIO2

void setup()
{
  // Debug console
  Serial.begin(9600);

  Blynk.begin(BLYNK_AUTH_TOKEN, ssid, pass);

  // Set relay pins as outputs
  pinMode(RELAY1, OUTPUT);
  pinMode(RELAY2, OUTPUT);
  pinMode(RELAY3, OUTPUT);
  pinMode(RELAY4, OUTPUT);

  // Initialize all relays off
  digitalWrite(RELAY1, HIGH); // Active LOW
  digitalWrite(RELAY2, HIGH);
  digitalWrite(RELAY3, HIGH);
  digitalWrite(RELAY4, HIGH);
}

// Blynk virtual pin handlers
BLYNK_WRITE(V0) {
  digitalWrite(RELAY1, param.asInt() ? LOW : HIGH);
}
BLYNK_WRITE(V1) {
  digitalWrite(RELAY2, param.asInt() ? LOW : HIGH);
}
BLYNK_WRITE(V2) {
  digitalWrite(RELAY3, param.asInt() ? LOW : HIGH);
}
BLYNK_WRITE(V3) {
  digitalWrite(RELAY4, param.asInt() ? LOW : HIGH);
}

void loop()
{
  Blynk.run();
}

🧪 Testing

1. Upload the code via Arduino IDE to the NodeMCU.
2. Open the Blynk app and press the buttons.
3. Each button should toggle one relay.

🛠️ Tips

• Relays are active LOW, meaning LOW turns them ON.
• Debounce logic is not needed as Blynk manages state.
• Secure your Wi-Fi and consider using Blynk cloud templates for better project management.

✅ Conclusion

Controlling 4 relays with a NodeMCU (ESP8266) and the Blynk app offers a flexible, wireless home automation solution. Here’s what we’ve achieved:

• ✅ Built a Wi-Fi-connected remote relay controller using NodeMCU
• ✅ Used the Blynk IoT app to toggle devices via virtual pins
• ✅ Interfaced with a 4-channel relay module to switch real-world appliances
• ✅ Ensured safe and effective control with simple code and circuit

This setup can be used to control:

• Lights
• Fans
• Garage doors
• Water pumps
• And more — all remotely from your phone

🔧 Want to expand further? You can:

• Add voice assistants (Alexa, Google Home)
• Use Blynk Automations (e.g., timer, geolocation)
• Integrate sensor feedback (temperature, motion, etc.)