Wireless Introduction: HC-05 Bluetooth Basics

Bluetooth is the backbone of short-range telemetry. The Basic HC-05 Communication project is the absolute required first step before you can build a remote-control car or an automated curtain opener using your smartphone.

The Software Serial Bridge

An Arduino Uno has one hardware serial port (Pins 0 & 1).

• If you plug the Bluetooth module into 0 & 1, it will violently conflict with the USB cable when you try to upload your code!
• You must use the <SoftwareSerial.h> library to create a "fake" serial port on pins 10 and 11.
• You wire HC-05 TX -> Arduino Pin 10 (RX) and HC-05 RX -> Arduino Pin 11 (TX). (Note the crossover!).

Formatting Transmitted Characters

1. The Phone App: You download a free "Bluetooth Serial Terminal" app on Android. You connect to the HC-05 and type the letter "A".
2. The Code Listener:

if (bluetoothSerial.available()) {
  char command = bluetoothSerial.read();  
  if (command == 'A') { digitalWrite(13, HIGH); } // Light turns ON!
  if (command == 'B') { digitalWrite(13, LOW); }  // Light turns OFF!
}

3. A single tap on your glowing phone screen travels invisibly through the air and triggers massive relay drivers on the other side of the room.

Requirements

• Arduino Uno/Nano: The command logic.
• HC-05 or HC-06 Bluetooth Receiver: Ensure it is a 5V tolerant breakout board.
• A 5mm LED and Resistor.
• Android Smartphone/Tablet. (Note: iOS devices generally completely block communication with cheap SPP Bluetooth modules like the HC-05. An Android device or PC is highly recommended).