Bluetooth with HC-05/HC-06 module in Arduino - Mini Project: Build & Apply

Bluetooth with HC-05/HC-06 module

📖 Scenario: You want to control an LED on your Arduino board using a Bluetooth module like HC-05 or HC-06. This project will help you set up the Bluetooth communication and turn the LED on or off by sending simple commands from your phone or computer.

🎯 Goal: Build a simple Arduino program that reads data from the HC-05/HC-06 Bluetooth module and turns an LED on or off based on the received command.

📋 What You'll Learn

Create a variable for the LED pin number

Create a variable for the Bluetooth serial communication

Write code to read data from the Bluetooth module

Control the LED based on the received data

Print the LED status to the serial monitor

💡 Why This Matters

🌍 Real World

Bluetooth modules like HC-05 and HC-06 are commonly used to add wireless control to devices such as home automation systems, robots, and wearable gadgets.

💼 Career

Understanding Bluetooth communication and Arduino programming is useful for embedded systems developers, IoT engineers, and hobbyists working on wireless device projects.

1

Set up the LED pin

Create an integer variable called ledPin and set it to 13. Then, in the setup() function, set the ledPin as an output using pinMode.

Arduino

int ledPin = 13;

void setup() {
  // Set ledPin as output
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use pinMode(ledPin, OUTPUT); inside setup() to prepare the LED pin.

2

Initialize Bluetooth serial communication

Create a SoftwareSerial object called bluetooth using pins 10 for RX and 11 for TX. In the setup() function, start the bluetooth serial communication at 9600 baud rate. Also, start the default serial communication at 9600 baud rate.

Arduino

#include 

int ledPin = 13;
SoftwareSerial bluetooth(10, 11); // RX, TX

void setup() {
  pinMode(ledPin, OUTPUT);
  // Start bluetooth serial at 9600
  // Start serial monitor at 9600
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use bluetooth.begin(9600); and Serial.begin(9600); inside setup().

3

Read Bluetooth data and control LED

In the loop() function, check if bluetooth.available() is greater than zero. If yes, read the incoming byte using bluetooth.read() and store it in a variable called incomingByte. If incomingByte is the character '1', turn the LED on using digitalWrite(ledPin, HIGH). If incomingByte is the character '0', turn the LED off using digitalWrite(ledPin, LOW). Also, print "LED ON" or "LED OFF" to the serial monitor accordingly.

Arduino

#include 

int ledPin = 13;
SoftwareSerial bluetooth(10, 11); // RX, TX

void setup() {
  pinMode(ledPin, OUTPUT);
  bluetooth.begin(9600);
  Serial.begin(9600);
}

void loop() {
  if (bluetooth.available() > 0) {
    // Read incoming byte
    // Your code here
  }
}

Hint

Use bluetooth.read() to get the data and digitalWrite to control the LED.

4

Test and display LED status

Print the message "Waiting for Bluetooth command..." once in the setup() function to the serial monitor. This will help you know the program is ready.

Arduino

#include 

int ledPin = 13;
SoftwareSerial bluetooth(10, 11); // RX, TX

void setup() {
  pinMode(ledPin, OUTPUT);
  bluetooth.begin(9600);
  Serial.begin(9600);
  // Print waiting message
  // Your code here
}

void loop() {
  if (bluetooth.available() > 0) {
    char incomingByte = bluetooth.read();
    if (incomingByte == '1') {
      digitalWrite(ledPin, HIGH);
      Serial.println("LED ON");
    } else if (incomingByte == '0') {
      digitalWrite(ledPin, LOW);
      Serial.println("LED OFF");
    }
  }
}

Hint

Use Serial.println("Waiting for Bluetooth command..."); inside setup().

Practice

1. What is the main purpose of using an HC-05 or HC-06 Bluetooth module with an Arduino?

easy

A. To enable wireless serial communication between Arduino and other Bluetooth devices

B. To increase the Arduino's processing speed

C. To provide power supply to the Arduino

D. To connect Arduino to the internet via Wi-Fi

Solution

1. Step 1: Understand the function of HC-05/HC-06 modules

   These modules are designed to allow wireless serial communication using Bluetooth technology.

2. Step 2: Compare options with module purpose

   Only To enable wireless serial communication between Arduino and other Bluetooth devices correctly describes enabling wireless serial communication; others describe unrelated functions.

3. Final Answer:

   To enable wireless serial communication between Arduino and other Bluetooth devices -> Option A

4. Quick Check:

   HC-05/HC-06 = Wireless serial communication [OK]

Hint: HC-05/HC-06 = Bluetooth serial communication module [OK]

Common Mistakes:

• Confusing Bluetooth with Wi-Fi connectivity
• Thinking it powers the Arduino
• Assuming it speeds up Arduino processing

2. Which of the following is the correct way to create a SoftwareSerial object for HC-05 on pins 10 (RX) and 11 (TX)?

easy

A. SoftwareSerial BT(11, 10);

B. SoftwareSerial BT(10, 11);

C. SoftwareSerial BT(9, 8);

D. SoftwareSerial BT(0, 1);

Solution

1. Step 1: Recall SoftwareSerial constructor syntax

   The constructor is SoftwareSerial(rxPin, txPin), so RX is first, TX second.

2. Step 2: Match pins to constructor

   Given RX=10 and TX=11, the correct call is SoftwareSerial BT(10, 11);

3. Final Answer:

   SoftwareSerial BT(10, 11); -> Option B

4. Quick Check:

   SoftwareSerial(rx, tx) = SoftwareSerial(10, 11) [OK]

Hint: SoftwareSerial(rxPin, txPin) order matters [OK]

Common Mistakes:

• Swapping RX and TX pins
• Using default hardware serial pins (0,1) for SoftwareSerial
• Choosing pins not supported by SoftwareSerial

3. Given the code snippet below, what will be printed on the Serial Monitor if the HC-05 sends the string "Hello"?

SoftwareSerial BT(10, 11);
void setup() {
  Serial.begin(9600);
  BT.begin(9600);
}
void loop() {
  if (BT.available()) {
    char c = BT.read();
    Serial.print(c);
  }
}

medium

A. No output

B. Random characters

C. Error: BT not initialized

D. Hello

Solution

1. Step 1: Understand data flow in code

   The code reads characters from Bluetooth (BT) and prints them to Serial Monitor.

2. Step 2: Analyze input and output

   If HC-05 sends "Hello", BT.read() reads each character and Serial.print outputs them, so "Hello" appears.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   BT.read() + Serial.print = "Hello" [OK]

Hint: BT.read() prints incoming Bluetooth data directly [OK]

Common Mistakes:

• Assuming no output without Serial.println
• Forgetting to call BT.begin()
• Confusing BT with Serial hardware pins

4. Identify the error in this Arduino code snippet for HC-05 communication:

SoftwareSerial BT(10, 11);
void setup() {
  Serial.begin(9600);
  BT.begin(115200);
}
void loop() {
  if (BT.available()) {
    Serial.write(BT.read());
  }
}

Assuming the HC-05 module is set to 9600 baud.

medium

A. Serial.begin is missing

B. SoftwareSerial pins are incorrect

C. BT.begin baud rate does not match HC-05 baud rate

D. BT.read() should be inside setup()

Solution

1. Step 1: Check baud rate consistency

   HC-05 default baud is 9600, but BT.begin uses 115200, causing communication failure.

2. Step 2: Verify other code parts

   SoftwareSerial pins and Serial.begin are correct; BT.read() is correctly placed in loop.

3. Final Answer:

   BT.begin baud rate does not match HC-05 baud rate -> Option C

4. Quick Check:

   Baud rates must match for communication [OK]

Hint: Match BT.begin baud with HC-05 baud rate [OK]

Common Mistakes:

• Using different baud rates between Arduino and HC-05
• Placing BT.read() in setup() instead of loop()
• Confusing Serial and SoftwareSerial pins

5. You want to send the string "LED ON" from your phone to Arduino via HC-05. The Arduino should turn on an LED connected to pin 13 when it receives this exact string. Which code snippet correctly implements this behavior?

hard

A. SoftwareSerial BT(10, 11);
String input = "";
void setup() {
pinMode(13, OUTPUT);
Serial.begin(9600);
BT.begin(9600);
}
void loop() {
while (BT.available()) {
char c = BT.read();
input += c;
}
if (input == "LED ON") {
digitalWrite(13, HIGH);
input = "";
}
}

B. SoftwareSerial BT(10, 11);
void setup() {
pinMode(13, OUTPUT);
Serial.begin(9600);
BT.begin(9600);
}
void loop() {
if (BT.read() == 'LED ON') {
digitalWrite(13, HIGH);
}
}

C. SoftwareSerial BT(10, 11);
void setup() {
pinMode(13, OUTPUT);
Serial.begin(9600);
BT.begin(9600);
}
void loop() {
if (BT.available()) {
digitalWrite(13, HIGH);
}
}

D. SoftwareSerial BT(10, 11);
String input = "";
void setup() {
pinMode(13, OUTPUT);
Serial.begin(9600);
BT.begin(9600);
}
void loop() {
if (BT.available()) {
input = BT.read();
}
if (input == "LED ON") {
digitalWrite(13, HIGH);
}
}

Solution

1. Step 1: Collect full string from Bluetooth input

   The correct code declares a global String input = ""; and uses while (BT.available()) { char c = BT.read(); input += c; } to accumulate all available characters into the string.

2. Step 2: Compare the full input string and control LED

   After accumulating, if (input == "LED ON") { digitalWrite(13, HIGH); input = ""; } turns on the LED and clears the input for next message.

3. Step 3: Analyze other options

   One option incorrectly compares a single BT.read() char to 'LED ON'; another turns on the LED on if (BT.available()) without checking content; the last captures only a single char per loop with input = BT.read().

4. Final Answer:

   The code snippet that accumulates characters into a String using while(BT.available()) -> Option A

5. Quick Check:

   Read full input string before comparing [OK]

Hint: Build full string from BT.read() before comparing [OK]

Common Mistakes:

• Comparing single char to full string
• Not accumulating all characters before checking
• Turning LED on without input check