pinMode() function behavior in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set pin 13 as an output.

Arduino

pinMode(13, [1]);

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

AINPUT

BINPUT_PULLUP

COUTPUT

DANALOG

Attempts:

3 left

💡 Hint

Common Mistakes

Using INPUT instead of OUTPUT will make the pin read signals, not send them.

Using INPUT_PULLUP is for input pins with a pull-up resistor.

The pinMode() function sets the mode of a pin. To make pin 13 an output, use OUTPUT.

2fill in blank

medium

Complete the code to set pin 7 as an input with an internal pull-up resistor.

Arduino

pinMode(7, [1]);

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

AOUTPUT

BINPUT

CANALOG

DINPUT_PULLUP

Attempts:

3 left

💡 Hint

Common Mistakes

Using INPUT alone does not enable the pull-up resistor.

OUTPUT mode is for sending signals, not reading buttons.

To use the internal pull-up resistor on pin 7, set the mode to INPUT_PULLUP.

3fill in blank

hard

Fix the error in the code to correctly set pin 2 as an input.

Arduino

pinMode([1], INPUT);

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

A2

BINPUT_PULLUP

COUTPUT

D13

Attempts:

3 left

💡 Hint

Common Mistakes

Putting OUTPUT or INPUT_PULLUP as the pin number causes errors.

Using the wrong pin number changes the wrong pin.

The first argument of pinMode() is the pin number. To set pin 2 as input, use 2.

4fill in blank

hard

Fill both blanks to create a dictionary that maps pin numbers to their modes for pins 4 and 5.

Arduino

pin_modes = {4: [1], 5: [2]

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

AINPUT

BOUTPUT

CINPUT_PULLUP

DANALOG

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up INPUT and OUTPUT modes.

Using ANALOG which is not a valid pinMode argument.

Pin 4 is set as INPUT and pin 5 as OUTPUT in the dictionary.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that sets pins as output only if their number is greater than 10.

Arduino

pin_modes = {pin: [1] if pin [2] 10 else [3] for pin in range(8, 15)}

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

AINPUT

B>

COUTPUT

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators like < instead of >.

Swapping INPUT and OUTPUT modes.

The code sets pins greater than 10 as OUTPUT, else INPUT.

Practice

1. What does the pinMode() function do in an Arduino sketch?

easy

A. It sets a pin as input or output to control how it behaves.

B. It reads the value from a pin.

C. It writes a value to a pin.

D. It resets the Arduino board.

Solution

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

   The pinMode() function tells the Arduino whether a pin will be used to read signals (input) or send signals (output).

2. Step 2: Differentiate from other functions

   Reading values is done by digitalRead(), writing by digitalWrite(), and resetting is unrelated to pinMode().

3. Final Answer:

   It sets a pin as input or output to control how it behaves. -> Option A

4. Quick Check:

   pinMode() sets pin direction = C [OK]

Hint: pinMode() sets pin direction: input or output [OK]

Common Mistakes:

• Confusing pinMode() with digitalRead() or digitalWrite()
• Thinking pinMode() reads or writes values
• Assuming pinMode() resets the board

2. Which of the following is the correct syntax to set pin 7 as an output pin?

easy

A. pinMode(7, OUTPUT);

B. pinMode(OUTPUT, 7);

C. pinMode(7, "OUTPUT");

D. pinMode(7);

Solution

1. Step 1: Recall pinMode() syntax

   The correct syntax is pinMode(pinNumber, mode); where mode is a constant like OUTPUT without quotes.

2. Step 2: Check each option

   pinMode(7, OUTPUT); matches the correct syntax. pinMode(OUTPUT, 7); reverses parameters. pinMode(7, "OUTPUT"); uses quotes incorrectly. pinMode(7); misses the mode parameter.

3. Final Answer:

   pinMode(7, OUTPUT); -> Option A

4. Quick Check:

   pinMode(pin, mode) correct order = B [OK]

Hint: pinMode(pin, mode) with mode as constant, no quotes [OK]

Common Mistakes:

• Swapping parameters order
• Using quotes around OUTPUT
• Omitting the mode parameter

3. What will be the output on the serial monitor after running this code?

void setup() {
  pinMode(3, INPUT_PULLUP);
  Serial.begin(9600);
  Serial.println(digitalRead(3));
}
void loop() {}

medium

A. No output

B. 0

C. Error: pinMode not set correctly

D. 1

Solution

1. Step 1: Understand INPUT_PULLUP behavior

   Setting pin 3 as INPUT_PULLUP activates an internal pull-up resistor, so the pin reads HIGH (1) if not connected to ground.

2. Step 2: digitalRead on pin 3

   Since nothing else is connected, digitalRead(3) returns 1, which is printed to the serial monitor.

3. Final Answer:

   1 -> Option D

4. Quick Check:

   INPUT_PULLUP reads HIGH = 1 [OK]

Hint: INPUT_PULLUP makes pin read HIGH if unconnected [OK]

Common Mistakes:

• Expecting 0 instead of 1 for INPUT_PULLUP
• Thinking pinMode causes error
• Assuming no output without loop code

4. Identify the error in this code snippet:

void setup() {
  pinMode(13, "OUTPUT");
  digitalWrite(13, HIGH);
}
void loop() {}

medium

A. Pin number 13 is invalid.

B. Missing Serial.begin() in setup().

C. The mode parameter in pinMode() should not be in quotes.

D. digitalWrite() cannot be used in setup().

Solution

1. Step 1: Check pinMode() parameter types

   The mode parameter must be a constant like OUTPUT without quotes. Using quotes makes it a string, causing a compile error.

2. Step 2: Verify other parts

   Pin 13 is valid. digitalWrite() can be used in setup(). Serial.begin() is not required here.

3. Final Answer:

   The mode parameter in pinMode() should not be in quotes. -> Option C

4. Quick Check:

   pinMode mode no quotes = D [OK]

Hint: Use OUTPUT without quotes in pinMode() [OK]

Common Mistakes:

• Putting mode in quotes
• Thinking pin 13 is invalid
• Believing digitalWrite() can't be in setup()

5. You want to connect a push button to pin 2 and read its state without an external resistor. Which pinMode() setting should you use to ensure the pin reads HIGH when the button is not pressed?

hard

A. pinMode(2, OUTPUT);

B. pinMode(2, INPUT_PULLUP);

C. pinMode(2, INPUT);

D. pinMode(2, INPUT_PULLDOWN);

Solution

1. Step 1: Understand button wiring without external resistor

   Without an external resistor, the internal pull-up resistor must be enabled to keep the pin HIGH when the button is not pressed.

2. Step 2: Choose correct pinMode()

   Using INPUT_PULLUP activates the internal pull-up resistor. INPUT alone leaves the pin floating. OUTPUT is wrong for reading. INPUT_PULLDOWN is not standard on Arduino.

3. Final Answer:

   pinMode(2, INPUT_PULLUP); -> Option B

4. Quick Check:

   Use INPUT_PULLUP for internal resistor = A [OK]

Hint: Use INPUT_PULLUP to avoid external resistor on button pin [OK]

Common Mistakes:

• Using INPUT without pull-up resistor causes floating pin
• Trying OUTPUT mode to read button
• Assuming INPUT_PULLDOWN exists on all Arduino boards