Documentation and pin mapping in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino pin mapping code?

Consider the following Arduino code that maps pins and prints their states. What will be printed on the serial monitor?

Arduino

const int ledPin = 13;
const int buttonPin = 7;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  int buttonState = digitalRead(buttonPin);
  if (buttonState == LOW) {
    digitalWrite(ledPin, HIGH);
    Serial.println("LED ON");
  } else {
    digitalWrite(ledPin, LOW);
    Serial.println("LED OFF");
  }
  delay(1000);
}

A LED ON always, no output printed

B LED OFF always, no output printed

C LED ON (if button pressed), LED OFF (if not pressed) every second

D Syntax error due to missing semicolon

💡 Hint

Remember that INPUT_PULLUP mode means the button reads HIGH when not pressed and LOW when pressed.

The buttonPin is set with INPUT_PULLUP, so when the button is pressed, the pin reads LOW. The code turns the LED on and prints "LED ON" when the button is pressed (LOW). Otherwise, it turns the LED off and prints "LED OFF". This repeats every second.

🧠 Conceptual

intermediate

Which Arduino pin is best for PWM output?

Given an Arduino Uno, which pin below is typically used for PWM (Pulse Width Modulation) output?

A Pin 13

B Pin 0

C Pin 7

D Pin 9

💡 Hint

Look for pins marked with a tilde (~) on the Arduino board.

On Arduino Uno, pins 3, 5, 6, 9, 10, and 11 support PWM output. Pin 9 is one of these PWM pins. Pin 13 is usually connected to the onboard LED and is not PWM. Pins 7 and 0 are digital pins without PWM capability.

🔧 Debug

advanced

Why does this Arduino code fail to turn on the LED?

Examine the code below. The LED connected to pin 8 never turns on. What is the reason?

Arduino

int ledPin = 8;

void setup() {
  pinMode(ledPin, INPUT);
}

void loop() {
  digitalWrite(ledPin, HIGH);
}

A Missing semicolon after pinMode line

B The pinMode is set to INPUT, so digitalWrite has no effect

C LED is connected to wrong pin number

D digitalWrite should be called in setup, not loop

💡 Hint

Think about the difference between INPUT and OUTPUT pin modes.

When a pin is set as INPUT, digitalWrite does not drive the pin HIGH or LOW. To turn on an LED, the pin must be set as OUTPUT. Here, pinMode is incorrectly set to INPUT, so the LED never receives power.

📝 Syntax

advanced

What error does this Arduino code produce?

Look at the code snippet below. What error will the Arduino IDE show when compiling?

Arduino

const int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  digitalWrite(ledPin, HIGH);
  delay(1000);
  digitalWrite(ledPin, LOW);
  delay(1000);
}

A Syntax error: missing semicolon after const int ledPin = 13

B Type error: ledPin must be declared as volatile

C Runtime error: delay function not defined

D No error, code compiles and runs correctly

💡 Hint

Check the end of each statement for proper punctuation.

The line 'const int ledPin = 13' is missing a semicolon at the end. This causes a syntax error during compilation.

🚀 Application

expert

How many pins are configured as OUTPUT after this Arduino setup?

Given the following Arduino setup code, how many pins are set as OUTPUT?

Arduino

const int pins[] = {2, 3, 4, 5, 6};

void setup() {
  for (int i = 0; i < 5; i++) {
    if (pins[i] % 2 == 0) {
      pinMode(pins[i], OUTPUT);
    } else {
      pinMode(pins[i], INPUT);
    }
  }
}

void loop() {}

A 3

B 0

C 5

D 2

💡 Hint

Count how many pins in the array are even numbers.

The pins array contains 2, 3, 4, 5, 6. The code sets pins with even numbers as OUTPUT. Even pins are 2, 4, and 6, so 3 pins are OUTPUT.