Bluetooth with HC-05/HC-06 module in Arduino

Introduction

Bluetooth modules like HC-05 and HC-06 let your Arduino talk wirelessly to other devices. This helps you send and receive data without wires.

You want to control an Arduino robot from your phone without cables.

You need to send sensor data from Arduino to a computer wirelessly.

You want to make a wireless remote control for a device.

You want to connect two Arduinos to share information without wires.

Syntax

Arduino

SoftwareSerial bluetooth(10, 11); // RX, TX pins

void setup() {
  Serial.begin(9600);          // Start serial monitor
  bluetooth.begin(9600);       // Start Bluetooth serial
}

void loop() {
  if (bluetooth.available()) {
    char data = bluetooth.read();
    Serial.print(data);        // Show data on serial monitor
  }
  if (Serial.available()) {
    char data = Serial.read();
    bluetooth.print(data);     // Send data to Bluetooth
  }
}

Use SoftwareSerial to create a serial connection on other pins because Arduino Uno has only one hardware serial port.

Make sure baud rates match between Arduino and Bluetooth module (usually 9600).

Examples

Set up Bluetooth on pins 2 and 3 with 9600 baud rate.

Arduino

SoftwareSerial bluetooth(2, 3); // RX=2, TX=3

void setup() {
  Serial.begin(9600);
  bluetooth.begin(9600);
}

Read one character from Bluetooth and print it to serial monitor.

Arduino

if (bluetooth.available()) {
  char c = bluetooth.read();
  Serial.print(c);
}

Send characters typed in serial monitor to Bluetooth device.

Arduino

if (Serial.available()) {
  char c = Serial.read();
  bluetooth.print(c);
}

Sample Program

This program reads data from the Bluetooth module and prints it on the serial monitor. It also sends anything typed in the serial monitor to the Bluetooth device.

Arduino

/*
  Simple Bluetooth communication with HC-05/HC-06
  Connect HC-05 RX to Arduino pin 10 (RX), TX to pin 11 (TX)
  Use SoftwareSerial to communicate
*/
#include <SoftwareSerial.h>

SoftwareSerial bluetooth(10, 11); // RX, TX

void setup() {
  Serial.begin(9600);          // Start serial monitor
  bluetooth.begin(9600);       // Start Bluetooth serial
  Serial.println("Bluetooth ready");
}

void loop() {
  if (bluetooth.available()) {
    char data = bluetooth.read();
    Serial.print("Received: ");
    Serial.println(data);
  }
  if (Serial.available()) {
    char data = Serial.read();
    bluetooth.print(data);
  }
}

Important Notes

HC-05 can be master or slave; HC-06 is slave only.

Make sure to connect HC-05 TX to Arduino RX pin and RX to Arduino TX pin (cross connection).

Use a voltage divider on HC-05 RX pin if Arduino uses 5V to avoid damage (HC-05 RX is 3.3V tolerant).

Summary

HC-05/HC-06 modules let Arduino communicate wirelessly using Bluetooth serial.

Use SoftwareSerial to connect Bluetooth module on different pins.

Match baud rates and connect pins correctly for communication.

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