Receiving commands over Bluetooth in Arduino

Introduction

Receiving commands over Bluetooth lets your Arduino talk wirelessly to other devices. This helps control your project without wires.

You want to control a robot using your phone.

You need to change settings on a device without plugging it in.

You want to send simple commands from a computer to Arduino wirelessly.

You are building a remote control for lights or motors.

You want to receive sensor data from another Bluetooth device.

Syntax

Arduino

void setup() {
  Serial.begin(9600); // Start serial communication
  bluetoothSerial.begin(9600); // Start Bluetooth serial
}

void loop() {
  if (bluetoothSerial.available()) {
    char command = bluetoothSerial.read();
    // Use the command
  }
}

Use bluetoothSerial.available() to check if data is ready to read.

Use bluetoothSerial.read() to get one byte (character) from Bluetooth.

Examples

This reads one character from Bluetooth and prints it to the normal Serial Monitor.

Arduino

if (bluetoothSerial.available()) {
  char c = bluetoothSerial.read();
  Serial.print("Received: ");
  Serial.println(c);
}

This reads all available characters from Bluetooth and stores them in a string.

Arduino

String command = "";
while (bluetoothSerial.available()) {
  command += (char)bluetoothSerial.read();
}
Serial.println(command);

Sample Program

This program listens for commands over Bluetooth. When it gets '1', it turns the built-in LED on. When it gets '0', it turns the LED off. It also prints the commands and actions to the Serial Monitor.

Arduino

#include <SoftwareSerial.h>

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

void setup() {
  Serial.begin(9600);
  bluetoothSerial.begin(9600);
  Serial.println("Bluetooth Command Receiver Ready");
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  if (bluetoothSerial.available()) {
    char command = bluetoothSerial.read();
    Serial.print("Command received: ");
    Serial.println(command);

    // Example: turn on LED if command is '1'
    if (command == '1') {
      digitalWrite(LED_BUILTIN, HIGH);
      Serial.println("LED ON");
    } else if (command == '0') {
      digitalWrite(LED_BUILTIN, LOW);
      Serial.println("LED OFF");
    }
  }
}

Important Notes

Make sure your Bluetooth module is connected to the correct Arduino pins (here pins 10 and 11).

Set the same baud rate on both Arduino and Bluetooth device (usually 9600).

Use SoftwareSerial library if your Arduino has only one hardware serial port.

Summary

Bluetooth commands let you control Arduino wirelessly.

Use available() and read() to get data from Bluetooth.

Test commands by printing them to Serial Monitor and acting on them.

Practice

1. What does the available() function do when receiving Bluetooth commands on Arduino?

easy

A. It sends data to the Bluetooth device.

B. It checks if there is data ready to be read from the Bluetooth module.

C. It resets the Bluetooth connection.

D. It closes the Bluetooth communication.

Solution

1. Step 1: Understand the role of available()

   The available() function returns the number of bytes available to read from the Bluetooth serial buffer.

2. Step 2: Identify its use in receiving commands

   It is used to check if any data has arrived and is ready to be read, so the program knows when to read incoming commands.

3. Final Answer:

   It checks if there is data ready to be read from the Bluetooth module. -> Option B

4. Quick Check:

   available() checks data presence [OK]

Hint: Remember: available() means data is ready to read [OK]

Common Mistakes:

• Thinking available() sends data instead of checking
• Confusing available() with read()
• Assuming available() resets connection

2. Which of the following is the correct way to read a single character from Bluetooth in Arduino?

easy

A. char command = Bluetooth.read();

B. char command = Bluetooth.available();

C. char command = Bluetooth.write();

D. char command = Bluetooth.begin();

Solution

1. Step 1: Identify the function to read data

   The read() function reads one byte (character) from the Bluetooth serial buffer.

2. Step 2: Confirm correct syntax

   Assigning Bluetooth.read() to a char variable correctly stores the incoming character.

3. Final Answer:

   char command = Bluetooth.read(); -> Option A

4. Quick Check:

   Use read() to get one char [OK]

Hint: Use read() to get data, not available() or write() [OK]

Common Mistakes:

• Using available() to read data instead of read()
• Using write() which sends data, not reads
• Calling begin() which initializes, not reads

3. What will be printed on the Serial Monitor when the following Arduino code receives the character 'L' over Bluetooth?

if (Bluetooth.available()) {
  char cmd = Bluetooth.read();
  if (cmd == 'L') {
    Serial.println("LED ON");
  } else {
    Serial.println("UNKNOWN COMMAND");
  }
}

medium

A. LED ON

B. UNKNOWN COMMAND

C. L

D. No output

Solution

1. Step 1: Check if data is available

   The code first checks if Bluetooth data is available, which it is since 'L' is sent.

2. Step 2: Read and compare the character

   The character 'L' is read and compared to 'L', which matches, so it prints "LED ON".

3. Final Answer:

   LED ON -> Option A

4. Quick Check:

   Received 'L' triggers "LED ON" print [OK]

Hint: Match received char to command to print correct message [OK]

Common Mistakes:

• Assuming it prints the character itself
• Ignoring the if condition and expecting UNKNOWN COMMAND
• Thinking no output if Bluetooth.available() is true

4. Identify the error in this Arduino Bluetooth command reading code:

if (Bluetooth.available > 0) {
  char cmd = Bluetooth.read();
  Serial.println(cmd);
}

medium

A. Bluetooth.read() should be Bluetooth.readChar().

B. The if condition should check for Bluetooth.read() instead.

C. Serial.println() cannot print characters.

D. Bluetooth.available should be called as a function with parentheses.

Solution

1. Step 1: Check usage of available()

   The code uses Bluetooth.available without parentheses, but it is a function and must be called as Bluetooth.available().

2. Step 2: Verify other parts

   Bluetooth.read() is correct to read a char, and Serial.println() can print characters, so no errors there.

3. Final Answer:

   Bluetooth.available should be called as a function with parentheses. -> Option D

4. Quick Check:

   available() needs parentheses [OK]

Hint: Remember functions need () to work [OK]

Common Mistakes:

• Forgetting parentheses on available()
• Thinking read() is readChar()
• Believing Serial.println() can't print chars

5. You want your Arduino to turn an LED on when it receives the command '1' and off when it receives '0' over Bluetooth. Which code snippet correctly implements this behavior?

if (Bluetooth.available()) {
  char cmd = Bluetooth.read();
  switch (cmd) {
    case '1':
      digitalWrite(LED_PIN, HIGH);
      Serial.println("LED ON");
      break;
    case '0':
      digitalWrite(LED_PIN, LOW);
      Serial.println("LED OFF");
      break;
    default:
      Serial.println("Invalid command");
  }
}

hard

A. digitalWrite cannot be used with Bluetooth commands.

B. The code should use if-else instead of switch for Bluetooth commands.

C. This code correctly reads commands and controls the LED accordingly.

D. Bluetooth.read() returns an integer, so char cmd is wrong.

Solution

1. Step 1: Analyze command reading and control

   The code reads a character from Bluetooth and uses a switch to check if it is '1' or '0'.

2. Step 2: Verify LED control and feedback

   It sets the LED pin HIGH or LOW accordingly and prints the status, which matches the requirement.

3. Final Answer:

   This code correctly reads commands and controls the LED accordingly. -> Option C

4. Quick Check:

   Switch-case handles commands and controls LED [OK]

Hint: Use switch-case to handle multiple commands cleanly [OK]

Common Mistakes:

• Thinking if-else is required instead of switch
• Believing digitalWrite can't be used with Bluetooth input
• Confusing data types returned by Bluetooth.read()