Bluetooth with HC-05/HC-06 module in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the HC-05 Bluetooth module used for?

The HC-05 module is used to add wireless Bluetooth communication to Arduino projects, allowing devices to send and receive data wirelessly.

beginner

How do you connect the HC-05 module to an Arduino board?

Connect HC-05 VCC to 5V, GND to GND, TXD to Arduino RX pin, and RXD to Arduino TX pin (usually through a voltage divider to protect the module).

intermediate

What is the difference between HC-05 and HC-06 modules?

HC-05 can act as both master and slave device, while HC-06 works only as a slave device. HC-05 is more versatile for Bluetooth communication.

beginner

How do you send data from Arduino to a Bluetooth device using HC-05?

Use the Serial communication commands like Serial.write() or Serial.print() to send data through the HC-05 module connected to Arduino's serial pins.

intermediate

Why is a voltage divider needed on the HC-05 RX pin?

Because the HC-05 RX pin works at 3.3V logic level, and Arduino TX pin outputs 5V, a voltage divider reduces 5V to 3.3V to protect the module.

Which pin on the HC-05 module should be connected to Arduino's RX pin?

A HC-05 TXD pin

B HC-05 RXD pin

C HC-05 VCC pin

D HC-05 GND pin

The HC-05 TXD pin sends data to Arduino's RX pin.

What role does the HC-05 module play in Bluetooth communication?

A It powers the Arduino board

B It controls the Arduino's motor

C It stores data permanently

D It acts as a wireless communication bridge

HC-05 enables wireless data transfer between devices.

Which Arduino function is commonly used to send data via HC-05?

A delay()

B Serial.print()

C analogRead()

D digitalWrite()

Serial.print() sends data over serial communication to HC-05.

What voltage level should the HC-05 RX pin receive?

A 12V

B 5V

C 3.3V

D 1.8V

HC-05 RX pin works at 3.3V logic level to avoid damage.

Which module can act as both master and slave in Bluetooth communication?

A HC-05

B HC-06

C Both HC-05 and HC-06

D Neither HC-05 nor HC-06

HC-05 supports master and slave modes; HC-06 supports only slave mode.

Explain how to connect and communicate with an HC-05 Bluetooth module using Arduino.

Think about wiring and serial communication steps.

Describe the main differences between HC-05 and HC-06 Bluetooth modules.

Focus on device roles and flexibility.

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