Receiving commands from computer in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start serial communication at 9600 baud.

Arduino

void setup() {
  Serial.[1](9600);
}

void loop() {
  // your code here
}

Drag options to blanks, or click blank then click option'

Astart

Bbegin

Copen

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using Serial.start() instead of Serial.begin()

Forgetting to set the baud rate

The Serial.begin(9600); command starts serial communication at 9600 baud rate.

2fill in blank

medium

Complete the code to check if data is available to read from the serial port.

Arduino

void loop() {
  if (Serial.[1]() > 0) {
    // read data
  }
}

Drag options to blanks, or click blank then click option'

Aread

Bpeek

Cavailable

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using Serial.read() to check availability

Using Serial.peek() incorrectly

Serial.available() returns the number of bytes available to read from the serial buffer.

3fill in blank

hard

Fix the error in reading a byte from the serial port.

Arduino

void loop() {
  if (Serial.available() > 0) {
    char data = Serial.[1]();
    // process data
  }
}

Drag options to blanks, or click blank then click option'

Aread

Bbegin

Cprint

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using Serial.write() to read data

Using Serial.print() instead of reading

Serial.read() reads one byte from the serial buffer.

4fill in blank

hard

Fill both blanks to read a string from the serial port until a newline character.

Arduino

void loop() {
  if (Serial.[1]() > 0) {
    String input = Serial.[2]('\n');
    // use input
  }
}

Drag options to blanks, or click blank then click option'

Aavailable

BreadStringUntil

Cread

Dbegin

Attempts:

3 left

💡 Hint

Common Mistakes

Using Serial.read() to read the whole string

Not checking if data is available before reading

Use Serial.available() to check data and Serial.readStringUntil('\n') to read until newline.

5fill in blank

hard

Fill all three blanks to read a command character and an integer value from serial input.

Arduino

void loop() {
  if (Serial.[1]() > 0) {
    char command = Serial.[2]();
    int value = Serial.[3]();
    // process command and value
  }
}

Drag options to blanks, or click blank then click option'

Aavailable

Bread

CparseInt

Dbegin

Attempts:

3 left

💡 Hint

Common Mistakes

Using readString instead of parseInt for numbers

Not checking if data is available before reading

Check availability, read one byte as command, then parse integer value from serial.

Practice

1. What is the purpose of Serial.begin(9600); in an Arduino sketch?

easy

A. It reads data from the serial port.

B. It starts serial communication at 9600 bits per second.

C. It sends data to the computer automatically.

D. It stops the serial communication.

Solution

1. Step 1: Understand Serial.begin()

   Serial.begin(9600); initializes the serial communication at a speed of 9600 bits per second.

2. Step 2: Identify its role in communication

   This function sets up the Arduino to send and receive data through the serial port at the specified speed.

3. Final Answer:

   It starts serial communication at 9600 bits per second. -> Option B

4. Quick Check:

   Serial.begin() = start communication [OK]

Hint: Serial.begin() always starts communication at given speed [OK]

Common Mistakes:

• Thinking Serial.begin() reads or sends data
• Confusing Serial.begin() with Serial.read()
• Assuming Serial.begin() stops communication

2. Which of the following is the correct way to check if data is available to read from the serial port?

easy

A. if (Serial.available()) { }

B. if (Serial.write()) { }

C. if (Serial.begin()) { }

D. if (Serial.read() > 0) { }

Solution

1. Step 1: Identify function to check data availability

   Serial.available() returns the number of bytes available to read from the serial buffer.

2. Step 2: Understand usage in condition

   Using if (Serial.available()) checks if there is any data to read (non-zero means data is available).

3. Final Answer:

   if (Serial.available()) { } -> Option A

4. Quick Check:

   Serial.available() checks data presence [OK]

Hint: Use Serial.available() to check before reading [OK]

Common Mistakes:

• Using Serial.read() to check availability
• Calling Serial.begin() inside loop
• Using Serial.write() to check data

3. What will be the output on the Serial Monitor if the following code receives the input string "HELLO"?

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

void loop() {
  if (Serial.available()) {
    String command = Serial.readStringUntil('\n');
    Serial.println(command);
  }
}

medium

A. HELLO\n

B. H

C. HELLO

D. No output

Solution

1. Step 1: Understand Serial.readStringUntil()

   This function reads characters from the serial buffer until it finds the newline character '\n'. It returns the string without the '\n'.

2. Step 2: Analyze the code output

   The input "HELLO" followed by Enter sends "HELLO\n". The code reads "HELLO" and prints it exactly.

3. Final Answer:

   HELLO -> Option C

4. Quick Check:

   readStringUntil('\n') returns string without newline [OK]

Hint: readStringUntil('\n') excludes newline from output [OK]

Common Mistakes:

• Expecting newline character printed
• Thinking only one character is read
• Assuming no output without delay

4. Identify the error in this Arduino code snippet that tries to read a command from the serial port:

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

medium

A. Serial.available is used without parentheses

B. Serial.read() is missing a parameter

C. Serial.print() cannot print char variables

D. The if condition should check for Serial.read() instead

Solution

1. Step 1: Check Serial.available usage

   Serial.available is a function and must be called with parentheses: Serial.available().

2. Step 2: Verify other function calls

   Serial.read() correctly reads one byte without parameters; Serial.print() can print chars.

3. Final Answer:

   Serial.available is used without parentheses -> Option A

4. Quick Check:

   Functions need parentheses to call [OK]

Hint: Always use parentheses when calling functions like Serial.available() [OK]

Common Mistakes:

• Forgetting parentheses on function calls
• Thinking Serial.read() needs parameters
• Assuming Serial.print() can't print chars

5. You want to receive a command string from the computer and turn on an LED if the command is "ON" and turn it off if "OFF". Which code snippet correctly implements this?

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

void loop() {
  if (Serial.available()) {
    String cmd = Serial.readStringUntil('\n');
    // What goes here?
  }
}

hard

A. if (cmd === "ON") digitalWrite(13, HIGH); else if (cmd === "OFF") digitalWrite(13, LOW);

B. if (cmd = "ON") digitalWrite(13, HIGH); else if (cmd = "OFF") digitalWrite(13, LOW);

C. if (cmd.equal("ON")) digitalWrite(13, HIGH); else if (cmd.equal("OFF")) digitalWrite(13, LOW);

D. if (cmd == "ON") digitalWrite(13, HIGH); else if (cmd == "OFF") digitalWrite(13, LOW);

Solution

1. Step 1: Understand String comparison in Arduino

   Arduino String objects overload the == operator to compare contents with string literals like "ON".

2. Step 2: Check each option's correctness

   if (cmd == "ON") correctly compares string contents. if (cmd = "ON") performs assignment, not comparison. cmd.equal("ON") fails--no such method (it's equals()). === is invalid C++ syntax.

3. Final Answer:

   if (cmd == "ON") digitalWrite(13, HIGH); else if (cmd == "OFF") digitalWrite(13, LOW); -> Option D

4. Quick Check:

   Arduino String == compares content [OK]

Hint: Use cmd == "ON" to compare Arduino Strings [OK]

Common Mistakes:

• Using = instead of == for comparison
• Calling non-existent cmd.equal()
• Using JavaScript === operator in Arduino