digitalRead() for input reading in Arduino - Mini Project: Build & Apply

Using digitalRead() to Read a Button Press

📖 Scenario: You have a simple Arduino setup with a button connected to a digital pin. You want to read whether the button is pressed or not.

🎯 Goal: Build a program that reads the button state using digitalRead() and prints "Button Pressed" or "Button Released" to the Serial Monitor.

📋 What You'll Learn

Create a variable for the button pin number

Set the button pin as input in setup()

Use digitalRead() to read the button state in loop()

Print "Button Pressed" if the button is pressed (HIGH), else print "Button Released"

💡 Why This Matters

🌍 Real World

Reading button presses is common in many devices like remote controls, game controllers, and home appliances.

💼 Career

Understanding how to read digital inputs is essential for embedded systems programming and hardware interfacing jobs.

1

Set up the button pin variable

Create an int variable called buttonPin and set it to 2.

Arduino

# Your code here

Hint

Use int buttonPin = 2; to store the pin number where the button is connected.

2

Initialize the button pin as input

Write the setup() function. Inside it, use pinMode(buttonPin, INPUT); to set the button pin as input. Also start serial communication with Serial.begin(9600);.

Arduino

int buttonPin = 2;

void setup() {
  // Your code here
}

Hint

Use pinMode(buttonPin, INPUT); inside setup() to prepare the pin for reading the button.

3

Read the button state using digitalRead()

Write the loop() function. Inside it, create an int variable called buttonState and set it to digitalRead(buttonPin);.

Arduino

int buttonPin = 2;

void setup() {
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  // Your code here
}

Hint

Use digitalRead(buttonPin) to get the current state of the button.

4

Print the button state to Serial Monitor

Inside loop(), add an if statement that checks if buttonState == HIGH. If true, print "Button Pressed" using Serial.println(). Otherwise, print "Button Released".

Arduino

int buttonPin = 2;

void setup() {
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  int buttonState = digitalRead(buttonPin);
  // Your code here
}

Hint

Use if (buttonState == HIGH) to check if the button is pressed and print the messages accordingly.

Practice

1. What does the digitalRead() function do in Arduino?

easy

A. Sets a digital pin to HIGH or LOW

B. Reads the voltage level (HIGH or LOW) from a digital input pin

C. Configures a pin as an output

D. Reads analog voltage from a pin

Solution

1. Step 1: Understand the purpose of digitalRead()

   The function digitalRead() checks the voltage level on a digital pin and returns HIGH or LOW.

2. Step 2: Differentiate from other functions

   Unlike digitalWrite() which sets pin output, digitalRead() only reads input state.

3. Final Answer:

   Reads the voltage level (HIGH or LOW) from a digital input pin -> Option B

4. Quick Check:

   digitalRead() reads pin state [OK]

Hint: digitalRead() always reads input pin state [OK]

Common Mistakes:

• Confusing digitalRead() with digitalWrite()
• Thinking digitalRead() sets pin output
• Mixing digitalRead() with analogRead()

2. Which of the following is the correct syntax to read a digital pin 7 in Arduino?

easy

A. digitalReadPin(7);

B. digitalRead = 7;

C. digitalRead(7);

D. readDigital(7);

Solution

1. Step 1: Recall the correct function syntax

   The correct function call is digitalRead(pinNumber); where pinNumber is the pin to read.

2. Step 2: Check each option

   Only digitalRead(7); matches the correct syntax digitalRead(7); others are invalid function calls or assignments.

3. Final Answer:

   digitalRead(7); -> Option C

4. Quick Check:

   Correct function call [OK]

Hint: digitalRead(pinNumber) reads pin state correctly [OK]

Common Mistakes:

• Using assignment instead of function call
• Wrong function name like readDigital()
• Adding extra words like digitalReadPin()

3. What will be the output on the Serial Monitor if the button connected to pin 2 is pressed (assuming HIGH when pressed)?

void setup() {
  pinMode(2, INPUT);
  Serial.begin(9600);
}

void loop() {
  int buttonState = digitalRead(2);
  Serial.println(buttonState);
  delay(500);
}

medium

A. 1

B. Error: pinMode missing

C. 0

D. Random values

Solution

1. Step 1: Analyze pinMode and digitalRead usage

   Pin 2 is set as INPUT, so digitalRead(2) reads the button state correctly.

2. Step 2: Understand button press state

   When the button is pressed, the pin reads HIGH which is 1, so Serial.println prints 1 repeatedly.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Pressed button = HIGH = 1 [OK]

Hint: Pressed button reads HIGH (1) on digitalRead() [OK]

Common Mistakes:

• Assuming pressed button reads 0 instead of 1
• Forgetting to set pinMode to INPUT
• Confusing analogRead with digitalRead

4. Identify the error in this code snippet that reads a button state on pin 4:

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

void loop() {
  int state = digitalRead(4);
  Serial.println(state);
  delay(1000);
}

medium

A. delay() cannot be used with digitalRead()

B. digitalRead() cannot be used in loop()

C. Serial.begin() should be in loop()

D. Missing pinMode(4, INPUT) in setup()

Solution

1. Step 1: Check pin configuration

   The code does not set pin 4 as INPUT using pinMode(), which is required before reading.

2. Step 2: Verify other parts

   digitalRead() can be used in loop(), Serial.begin() must be in setup(), and delay() is allowed.

3. Final Answer:

   Missing pinMode(4, INPUT) in setup() -> Option D

4. Quick Check:

   Always set pinMode before digitalRead() [OK]

Hint: Always set pinMode(INPUT) before digitalRead() [OK]

Common Mistakes:

• Forgetting pinMode() setup
• Moving Serial.begin() to loop() incorrectly
• Thinking delay() breaks digitalRead()

5. You want to detect if a switch connected to pin 3 is pressed, but the switch is wired so it connects the pin to GND when pressed (active LOW). Which code snippet correctly reads the switch state and prints "Pressed" or "Not Pressed" accordingly? A)

pinMode(3, INPUT);
if (digitalRead(3) == HIGH) {
  Serial.println("Pressed");
} else {
  Serial.println("Not Pressed");
}

B)

pinMode(3, INPUT);
if (digitalRead(3) == LOW) {
  Serial.println("Pressed");
} else {
  Serial.println("Not Pressed");
}

C)

pinMode(3, OUTPUT);
if (digitalRead(3) == LOW) {
  Serial.println("Pressed");
} else {
  Serial.println("Not Pressed");
}

D)

pinMode(3, INPUT_PULLUP);
if (digitalRead(3) == HIGH) {
  Serial.println("Pressed");
} else {
  Serial.println("Not Pressed");
}

hard

A. Code snippet B

B. Code snippet A

C. Code snippet C

D. Code snippet D

Solution

1. Step 1: Understand active LOW switch wiring

   The switch connects pin 3 to GND when pressed, so digitalRead(3) returns LOW when pressed.

2. Step 2: Check pinMode and condition

   pinMode must be INPUT (not OUTPUT). The condition to detect press is digitalRead(3) == LOW.

3. Final Answer:

   Code snippet B -> Option A

4. Quick Check:

   Active LOW switch reads LOW when pressed [OK]

Hint: Active LOW means pressed when digitalRead() returns LOW [OK]

Common Mistakes:

• Using OUTPUT mode instead of INPUT
• Checking for HIGH instead of LOW for active LOW switch
• Using INPUT_PULLUP but checking wrong logic