Receiving commands over Bluetooth in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Bluetooth command receiver sketch?

Consider this Arduino code that reads characters from a Bluetooth serial connection and prints them to the Serial Monitor. What will be printed if the Bluetooth device sends the characters 'HELLO'?

Arduino

void setup() {
  Serial.begin(9600); // Serial monitor
  Serial1.begin(9600); // Bluetooth module
}

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

A hello

B No output because Serial1 is not initialized

C HELLO

D HELLOHELLO

💡 Hint

Think about what Serial1.read() returns and how Serial.print() works.

The code reads each character sent over Bluetooth (Serial1) and prints it exactly as received to the Serial Monitor. Since the device sends 'HELLO', the output is 'HELLO'.

🧠 Conceptual

intermediate

Which Arduino function checks if Bluetooth data is ready to read?

You want to read incoming data from a Bluetooth module connected to Serial1. Which function tells you if there is data waiting to be read?

A Serial1.read()

B Serial1.available()

C Serial1.begin()

D Serial1.print()

💡 Hint

This function returns how many bytes are ready to read.

Serial1.available() returns the number of bytes available to read from the Bluetooth serial buffer. It is used to check if data has arrived.

🔧 Debug

advanced

Why does this Bluetooth command receiver code not print anything?

Look at this Arduino code snippet. It should print characters received from Bluetooth on Serial1 to the Serial Monitor. But nothing appears on the Serial Monitor. What is the problem?

Arduino

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

void loop() {
  if (Serial1.available() > 0) {
    char c = Serial1.read();
    Serial.print(c);
  }
}

A Serial1.available is missing parentheses, so it does not call the function

B Serial1.read() is called before Serial1.available()

C Serial.begin(9600) should be Serial1.begin(9600)

D Serial.print(c) should be Serial.println(c)

💡 Hint

Check how functions are called in Arduino code.

Serial1.available is a function and must be called with parentheses: Serial1.available(). Without parentheses, it refers to the function itself, which is always true, but does not return the number of bytes available. So the if condition never works as intended.

📝 Syntax

advanced

Which option correctly reads a full command string from Bluetooth until newline?

You want to read a full command sent over Bluetooth ending with a newline character '\n'. Which code snippet correctly reads characters into a string until '\n' is received?

Arduino

String command = "";
void loop() {
  while (Serial1.available()) {
    char c = Serial1.read();
    if (c == '\n') {
      // command complete
      Serial.println(command);
      command = "";
    } else {
      command += c;
    }
  }
}

A Reads characters but uses Serial.read() instead of Serial1.read()

B Reads characters but never clears the command string

C Reads characters but prints command before '\n' is received

D Reads characters until '\n', then prints the command and clears it

💡 Hint

Look for the code that resets the command string after printing.

Option D correctly accumulates characters until '\n' is found, then prints the full command and resets the string for the next command.

🚀 Application

expert

How many commands will be stored in the array after this Bluetooth input?

This Arduino code reads commands separated by commas from Bluetooth and stores them in an array. If the Bluetooth device sends 'ON,OFF,TOGGLE,STATUS', how many commands will be stored?

Arduino

String commands[5];
int index = 0;
String current = "";

void loop() {
  while (Serial1.available()) {
    char c = Serial1.read();
    if (c == ',') {
      commands[index++] = current;
      current = "";
    } else {
      current += c;
    }
  }
  // After input ends, store last command
  if (current.length() > 0) {
    commands[index++] = current;
    current = "";
  }
}

A 4

B 3

C 5

D 1

💡 Hint

Count the number of commas and remember the last command after the last comma.

The input has 3 commas, so 4 commands: 'ON', 'OFF', 'TOGGLE', 'STATUS'. The code stores each command when a comma is found and also stores the last command after input ends.