Interfacing Relay module to demonstrate Bluetooth based home automation application. (using Bluetooth and relay).

Practical: Interfacing Relay module to demonstrate Bluetooth based home automation application. (using Bluetooth and relay).

Aim

To interface a relay module with Arduino and demonstrate a Bluetooth-based home automation application using an HC-05 Bluetooth module.

Components Required

1. Arduino UNO – 1
2. HC-05 Bluetooth Module – 1
3. 5V Single-Channel Relay Module – 1
4. Jumper wires
5. Breadboard
6. 5V power supply/USB cable
7. Mobile phone with Bluetooth Terminal application
8. LED + resistor or low-voltage DC lamp for classroom demonstration

Safety: For a classroom practical, use an LED or low-voltage DC load. Do not connect students directly to 220V AC mains. If an AC load is required, it should be wired by a qualified person using appropriate isolation and safety procedures.

Circuit Connections

HC-05 to Arduino

HC-05	Arduino UNO
VCC	5V
GND	GND
TXD	D10
RXD	D11

Relay Module to Arduino

Relay	Arduino UNO
VCC	5V
GND	GND
IN	D8

Arduino Program

#include <SoftwareSerial.h>

SoftwareSerial BT(10, 11);   // RX, TX
const int relayPin = 8;
void setup()
{
  Serial.begin(9600);
  BT.begin(9600);
  pinMode(relayPin, OUTPUT);
  // Relay OFF initially
  digitalWrite(relayPin, LOW);
  Serial.println("Bluetooth Home Automation Ready");
  Serial.println("Send 1 = ON, 0 = OFF");
}
void loop()
{
  if (BT.available())
  {
    char data = BT.read();
    if (data == '1')
    {
      digitalWrite(relayPin, HIGH);
      Serial.println("Relay ON");
    }
    else if (data == '0')
    {
      digitalWrite(relayPin, LOW);
      Serial.println("Relay OFF");
    }
  }
}

Procedure

Step 1: Connect the HC-05 Bluetooth module and relay module to Arduino according to the circuit diagram.

Step 2: Upload the Arduino program.

Step 3: Pair the mobile phone with HC-05.

Step 4: Open a Bluetooth Terminal application.

Step 5: Connect the application to HC-05.

Step 6: Send 1 from the mobile phone.

→ Arduino receives 1 → Relay turns ON → Connected load turns ON.

Step 7: Send 0 from the mobile phone.

→ Arduino receives 0 → Relay turns OFF → Connected load turns OFF.

Working Principle

Mobile Phone
     ↓
 Bluetooth
     ↓
   HC-05
     ↓
 Arduino UNO
     ↓
 Relay Module
     ↓
 Electrical Load

The mobile phone sends commands wirelessly through Bluetooth. The HC-05 transfers these commands to Arduino. Arduino processes the received command and controls the relay accordingly.

Expected Output

Mobile Command	Relay	Load
1	ON	ON
0	OFF	OFF

Result

The relay module was successfully interfaced with Arduino and controlled wirelessly through an HC-05 Bluetooth module, demonstrating a basic Bluetooth-based home automation system.