Multiple LED and button control in Arduino - Mini Project: Build & Apply

Multiple LED and button control

📖 Scenario: You have three LEDs and three buttons connected to an Arduino board. Each button controls one LED. When you press a button, the matching LED should turn on. When you release the button, the LED should turn off.

🎯 Goal: Build a program that reads the state of three buttons and controls three LEDs accordingly. Each LED lights up only when its button is pressed.

📋 What You'll Learn

Use three LED pins: 2, 3, and 4

Use three button pins: 5, 6, and 7

Set LED pins as outputs and button pins as inputs with pull-up resistors

Read each button state and turn on the matching LED when pressed

Turn off the LED when the button is not pressed

💡 Why This Matters

🌍 Real World

Controlling multiple devices or indicators with buttons is common in home automation, robotics, and interactive projects.

💼 Career

Understanding how to read inputs and control outputs with microcontrollers is a key skill for embedded systems and hardware programming jobs.

1

Set up LED and button pins

Create three integer variables called ledPins and assign the values 2, 3, and 4 in an array. Create another integer array called buttonPins with the values 5, 6, and 7.

Arduino

int ledPins[] = {2, 3, 4};
int buttonPins[] = {5, 6, 7};
// Your code here

Hint

Use arrays to store the LED and button pin numbers exactly as given.

2

Configure pins in setup()

In the setup() function, use a for loop with variable i to set each pin in ledPins as OUTPUT. Then use another for loop with variable i to set each pin in buttonPins as INPUT_PULLUP.

Arduino

int ledPins[] = {2, 3, 4};
int buttonPins[] = {5, 6, 7};

void setup() {
  // Your code here
}

Hint

Use two separate for loops to set pin modes for LEDs and buttons.

3

Read buttons and control LEDs

In the loop() function, use a for loop with variable i to read each button pin from buttonPins. If the button is pressed (reads LOW), turn on the matching LED by writing HIGH to ledPins[i]. Otherwise, turn off the LED by writing LOW.

Arduino

int ledPins[] = {2, 3, 4};
int buttonPins[] = {5, 6, 7};

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

void loop() {
  // Your code here
}

Hint

Use digitalRead to check button state and digitalWrite to control LEDs inside a loop.

4

Test and observe LED behavior

Upload the program to your Arduino. Press each button and observe that the matching LED lights up only while the button is pressed. Release the button to turn off the LED. Write Serial.println("Test complete") in the loop() function after the for loop to confirm the program runs.

Arduino

int ledPins[] = {2, 3, 4};
int buttonPins[] = {5, 6, 7};

void setup() {
  for (int i = 0; i < 3; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
  for (int i = 0; i < 3; i++) {
    pinMode(buttonPins[i], INPUT_PULLUP);
  }
  Serial.begin(9600);
}

void loop() {
  for (int i = 0; i < 3; i++) {
    if (digitalRead(buttonPins[i]) == LOW) {
      digitalWrite(ledPins[i], HIGH);
    } else {
      digitalWrite(ledPins[i], LOW);
    }
  }
  // Add Serial.println here
  // Your code here
}

Hint

Use Serial.println("Test complete") to print the confirmation message.

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