Multiple LED and button control in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set pin 13 as an output.

Arduino

void setup() {
  pinMode([1], OUTPUT);
}

void loop() {
  // Empty loop
}

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

A13

B12

C11

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pin number that is not connected to an LED.

Forgetting to set the pin mode before using it.

Pin 13 is commonly used for the built-in LED on many Arduino boards. Setting it as OUTPUT allows us to control the LED.

2fill in blank

medium

Complete the code to read the state of a button connected to pin 7.

Arduino

int buttonState = digitalRead([1]);

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

A8

B6

C5

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong pin number for digitalRead.

Not setting the pin mode to INPUT before reading.

To read a button connected to pin 7, use digitalRead(7).

3fill in blank

hard

Fix the error in the code to turn on the LED connected to pin 9.

Arduino

digitalWrite([1], HIGH);

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

A7

B10

C9

D8

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pin number not connected to the LED.

Confusing HIGH and LOW values.

The LED is connected to pin 9, so digitalWrite should use pin 9 to turn it on.

4fill in blank

hard

Fill both blanks to create a dictionary that maps LED pins to button pins.

Arduino

const int ledPins[] = { [1] };
const int buttonPins[] = { [2] };

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

A9, 10, 11

B7, 8, 12

C5, 6, 13

D2, 3, 4

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up LED and button pin numbers.

Forgetting commas between pin numbers.

LED pins are 9, 10, 11 and button pins are 7, 8, 12 to match each LED with a button.

5fill in blank

hard

Fill all three blanks to complete the loop that turns on LEDs when their buttons are pressed.

Arduino

for (int i = 0; i < [1]; i++) {
  int buttonState = digitalRead([2][i]);
  if (buttonState == [3]) {
    digitalWrite(ledPins[i], HIGH);
  } else {
    digitalWrite(ledPins[i], LOW);
  }
}

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

A3

BbuttonPins

CHIGH

DLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using HIGH instead of LOW for pressed button state.

Looping beyond the array length.

The loop runs 3 times for 3 LEDs and buttons. It reads each button pin from buttonPins array. If the button is pressed (LOW because buttons often connect to ground when pressed), the LED turns on; otherwise, it turns off.

Practice

1. What is the main advantage of using arrays to control multiple LEDs and buttons in Arduino?

easy

A. It allows controlling many LEDs and buttons efficiently with loops.

B. It makes the LEDs brighter.

C. It reduces the power consumption of the Arduino.

D. It automatically fixes wiring errors.

Solution

1. Step 1: Understand arrays usage

   Arrays store multiple pin numbers for LEDs and buttons in one place.

2. Step 2: Use loops for control

   Loops can iterate over arrays to read buttons and control LEDs easily.

3. Final Answer:

   It allows controlling many LEDs and buttons efficiently with loops. -> Option A

4. Quick Check:

   Arrays + loops = efficient control [OK]

Hint: Think how arrays help repeat actions for many pins [OK]

Common Mistakes:

• Thinking arrays make LEDs brighter
• Confusing arrays with power saving
• Assuming arrays fix wiring automatically

2. Which Arduino pin mode is best to use for buttons to avoid external resistors?

easy

A. OUTPUT

B. INPUT_PULLUP

C. INPUT

D. ANALOG

Solution

1. Step 1: Recall button wiring

   Buttons need a way to avoid floating input pins, usually with pull-up resistors.

2. Step 2: Use built-in pull-up

   INPUT_PULLUP mode activates Arduino's internal pull-up resistor, no external resistor needed.

3. Final Answer:

   INPUT_PULLUP -> Option B

4. Quick Check:

   Button mode = INPUT_PULLUP [OK]

Hint: Use INPUT_PULLUP to simplify button wiring [OK]

Common Mistakes:

• Using OUTPUT mode for buttons
• Forgetting pull-up resistor causes unstable reads
• Using ANALOG mode for digital buttons

3. What will be the output on the LEDs if the following code runs and button 2 is pressed?

const int buttonPins[] = {2, 3, 4};
const int ledPins[] = {8, 9, 10};

void setup() {
  for (int i = 0; i < 3; i++) {
    pinMode(buttonPins[i], INPUT_PULLUP);
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  for (int i = 0; i < 3; i++) {
    if (digitalRead(buttonPins[i]) == LOW) {
      digitalWrite(ledPins[i], HIGH);
    } else {
      digitalWrite(ledPins[i], LOW);
    }
  }
}

medium

A. Only LED on pin 8 turns ON.

B. All LEDs turn ON.

C. Only LED on pin 9 turns ON.

D. No LEDs turn ON.

Solution

1. Step 1: Identify button pressed

   Button 2 is pressed, which is buttonPins[1] (pin 3).

2. Step 2: Match LED to button

   LED on ledPins[1] (pin 9) turns ON because buttonPins[1] is LOW.

3. Final Answer:

   Only LED on pin 9 turns ON. -> Option C

4. Quick Check:

   Button 2 pressed lights LED 9 [OK]

Hint: Match button index to LED index in arrays [OK]

Common Mistakes:

• Assuming all LEDs turn on when one button pressed
• Confusing pin numbers with array indexes
• Ignoring INPUT_PULLUP logic (LOW means pressed)

4. The following code is intended to turn ON an LED when its matching button is pressed, but the LED never lights up. What is the error?

const int buttonPins[] = {2, 3};
const int ledPins[] = {8, 9};

void setup() {
  for (int i = 0; i <= 2; i++) {
    pinMode(buttonPins[i], INPUT_PULLUP);
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  for (int i = 0; i <= 2; i++) {
    if (digitalRead(buttonPins[i]) == LOW) {
      digitalWrite(ledPins[i], HIGH);
    } else {
      digitalWrite(ledPins[i], LOW);
    }
  }
}

medium

A. digitalRead should be replaced with analogRead.

B. Buttons should be set as OUTPUT, not INPUT_PULLUP.

C. LED pins should be set as INPUT.

D. The for loops use <= 2 instead of < 2, causing out-of-bounds access.

Solution

1. Step 1: Check loop conditions

   Loops run from i = 0 to i <= 2, which means i = 0,1,2 (3 iterations).

2. Step 2: Check array sizes

   buttonPins and ledPins have only 2 elements (indexes 0 and 1). Accessing index 2 causes error.

3. Final Answer:

   The for loops use <= 2 instead of < 2, causing out-of-bounds access. -> Option D

4. Quick Check:

   Loop index out of range causes failure [OK]

Hint: Use < array length, not <=, in loops over arrays [OK]

Common Mistakes:

• Using <= instead of < in loops
• Setting button pins as OUTPUT
• Confusing digitalRead with analogRead

5. You want to control 4 LEDs with 4 buttons so that pressing a button toggles its LED ON or OFF (not just ON while pressed). Which approach is best to implement this behavior?

hard

A. Use arrays for pins and track LED states in a separate boolean array, toggling state on button press detection.

B. Use digitalWrite to turn LED ON when button is pressed and OFF otherwise.

C. Use INPUT mode for buttons and analogWrite for LEDs.

D. Connect LEDs directly to buttons without Arduino code.

Solution

1. Step 1: Understand toggle behavior

   Toggle means LED changes state only when button is pressed, not continuously.

2. Step 2: Track LED states

   Store LED ON/OFF states in a boolean array and change state only on button press event.

3. Step 3: Use arrays for pins

   Arrays help manage multiple buttons and LEDs efficiently with loops.

4. Final Answer:

   Use arrays for pins and track LED states in a separate boolean array, toggling state on button press detection. -> Option A

5. Quick Check:

   Toggle needs state tracking + arrays [OK]

Hint: Track LED states in array to toggle on button press [OK]

Common Mistakes:

• Turning LED ON only while button pressed
• Using analogWrite for simple ON/OFF LEDs
• Wiring LEDs directly to buttons without control