digitalRead() for input reading in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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'

A7

B13

C0

DLED_BUILTIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong pin number in digitalRead()

Confusing digitalRead() with analogRead()

The button is connected to pin 7, so digitalRead(7) reads its state.

2fill in blank

medium

Complete the code to check if the button on pin 4 is pressed (HIGH).

Arduino

if (digitalRead([1]) == HIGH) {
  // button pressed
}

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

A13

B2

C7

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pin number not connected to the button

Comparing digitalRead() result to LOW instead of HIGH

We check pin 4 because the button is connected there. digitalRead(4) reads its state.

3fill in blank

hard

Fix the error in reading the button state on pin 9.

Arduino

int state = digitalRead([1]);

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

AdigitalPin9

B9

Cpin9

DINPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name instead of the pin number

Passing a mode like INPUT instead of a pin number

digitalRead() requires the pin number as an integer, so 9 is correct.

4fill in blank

hard

Fill both blanks to read a button on pin 5 and check if it is LOW.

Arduino

if (digitalRead([1]) == [2]) {
  // button not pressed
}

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

A5

BHIGH

CLOW

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong pin number

Comparing to HIGH instead of LOW

Pin 5 is where the button is connected. Checking if digitalRead(5) == LOW means button is not pressed if wired with pull-up.

5fill in blank

hard

Fill all three blanks to create a dictionary-like structure mapping pin names to their digitalRead values, only for pins with HIGH state.

Arduino

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

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

void loop() {
  for (int i = 0; i < 3; i++) {
    int pin = pins[i];
    if (digitalRead(pin) == HIGH) {
      Serial.print("Pin ");
      Serial.print(pin);
      Serial.println(" is HIGH");
    }
  }
  delay(1000);
}

// Create a map-like structure:
// { [1]: [2] for [3] in pins if digitalRead([3]) == HIGH }

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

Apin

BdigitalRead(pin)

Dpins

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names

Not matching the loop variable in the condition

This comprehension-like structure maps each pin to its digitalRead value if that value is HIGH.

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