Bluetooth with HC-05/HC-06 module in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output on Serial Monitor?

Consider this Arduino code using HC-05 Bluetooth module. What will be printed on the Serial Monitor when the module receives the character 'A' from a paired device?

Arduino

void setup() {
  Serial.begin(9600); // Serial Monitor
  Serial1.begin(9600); // HC-05 module
}

void loop() {
  if (Serial1.available()) {
    char c = Serial1.read();
    if (c == 'A') {
      Serial.println("Received A");
    } else {
      Serial.println("Other char");
    }
  }
}

A Received A

B Other char

C No output

D Compilation error

💡 Hint

Check what happens when Serial1 reads 'A'.

The code reads from Serial1 (HC-05). If the character is 'A', it prints 'Received A' on Serial Monitor.

❓ Predict Output

intermediate

What will be the output of this code snippet?

This Arduino sketch reads data from HC-06 module and echoes it back. What will be printed on Serial Monitor if the paired device sends 'Hello'?

Arduino

void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);
}

void loop() {
  while (Serial1.available()) {
    char c = Serial1.read();
    Serial.print(c);
    Serial1.print(c);
  }
}

A No output

B olleH

C Hello

D Compilation error

💡 Hint

Look at how characters are read and printed.

The code reads each character from Serial1 and prints it to Serial Monitor and back to Serial1, so 'Hello' is printed as is.

❓ Predict Output

advanced

What error does this code produce?

This code tries to initialize HC-05 module but has a mistake. What error will occur when compiling?

Arduino

void setup() {
  Serial.begin(9600);
  Serial1.begin(38400); // Missing semicolon fixed
}

void loop() {}

A SyntaxError: missing semicolon

B TypeError: wrong baud rate

C No error, runs fine

D Runtime error: Serial1 not found

💡 Hint

Check punctuation at the end of lines.

The line 'Serial1.begin(38400)' misses a semicolon, causing a syntax error.

🧠 Conceptual

advanced

Which statement about HC-05 and HC-06 modules is correct?

Choose the correct statement about HC-05 and HC-06 Bluetooth modules.

A HC-06 can act as master or slave; HC-05 only as slave

B Both HC-05 and HC-06 can only act as master

C Both HC-05 and HC-06 can only act as slave

D HC-05 can act as master or slave; HC-06 only as slave

💡 Hint

Think about flexibility of module roles.

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

🚀 Application

expert

How many bytes will be stored in buffer after this code runs?

Given this Arduino code snippet reading from HC-05, how many bytes will be stored in the buffer array after receiving the string 'BT123'?

Arduino

char buffer[10];
int index = 0;

void loop() {
  while (Serial1.available()) {
    char c = Serial1.read();
    if (c == '\n') break;
    buffer[index++] = c;
  }
}

A 6

B 5

C 4

D 0

💡 Hint

Count characters before newline.

The string 'BT123' has 5 characters; no newline received yet, so all 5 are stored.