Why digital I/O is the foundation in Arduino - Test Your Understanding

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

BOUTPUT

CHIGH

DLOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using INPUT instead of OUTPUT

Using HIGH or LOW in pinMode

To control an LED or other device, the pin must be set as OUTPUT.

2fill in blank

medium

Complete the code to turn the LED on by setting pin 13 HIGH.

Arduino

digitalWrite(13, [1]);

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

AHIGH

BLOW

CINPUT

DOUTPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOW to turn LED on

Confusing pinMode with digitalWrite

Setting the pin HIGH sends voltage to turn the LED on.

3fill in blank

hard

Fix the error in the code to read a button state from pin 7.

Arduino

int buttonState = digitalRead([1]);

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

A7

BINPUT

C13

DOUTPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin mode constants instead of pin number

Using output pins for input reading

digitalRead needs the pin number, here pin 7, to read the button state.

4fill in blank

hard

Fill both blanks to create a dictionary of pin states for pins 2 and 3.

Arduino

int states[] = {digitalRead([1]), digitalRead([2])};

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

A2

B3

C4

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using pins not set as input

Using wrong pin numbers

We read the states of pins 2 and 3 to store in the array.

5fill in blank

hard

Fill all three blanks to create a map of pin numbers to their digital states.

Arduino

int pinStates[] = {digitalRead([1]), digitalRead([2]), digitalRead([3])};

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

A6

B7

C8

D9

Attempts:

3 left

💡 Hint

Common Mistakes

Using pins not configured as inputs

Mixing pin order

We read pins 9, 7, and 8 to get their states in order.

Practice

1. What is the main purpose of digital I/O pins on an Arduino board?

easy

A. To read or send simple ON/OFF signals

B. To store large amounts of data

C. To connect to the internet directly

D. To power the Arduino board

Solution

1. Step 1: Understand digital I/O function

   Digital I/O pins can read or send signals that are either ON (HIGH) or OFF (LOW).

2. Step 2: Compare options with function

   Only To read or send simple ON/OFF signals describes this simple ON/OFF signal role correctly.

3. Final Answer:

   To read or send simple ON/OFF signals -> Option A

4. Quick Check:

   Digital I/O = ON/OFF signals [OK]

Hint: Digital I/O means simple ON or OFF signals [OK]

Common Mistakes:

• Confusing digital I/O with memory storage
• Thinking digital I/O connects directly to internet
• Assuming digital I/O powers the board

2. Which of the following is the correct way to set a digital pin 7 as output in Arduino code?

easy

A. pinMode(7, INPUT);

B. pinMode(7, OUTPUT);

C. digitalWrite(7, OUTPUT);

D. digitalRead(7, OUTPUT);

Solution

1. Step 1: Recall pinMode function usage

   pinMode(pin, mode) sets a pin as INPUT or OUTPUT.

2. Step 2: Identify correct syntax for output

   pinMode(7, OUTPUT); correctly sets pin 7 as output.

3. Final Answer:

   pinMode(7, OUTPUT); -> Option B

4. Quick Check:

   pinMode + OUTPUT = pinMode(7, OUTPUT); [OK]

Hint: Use pinMode(pin, OUTPUT) to set output pin [OK]

Common Mistakes:

• Using digitalWrite instead of pinMode to set pin mode
• Setting pin as INPUT instead of OUTPUT
• Passing OUTPUT to digitalRead or digitalWrite incorrectly

3. What will be the output on the LED connected to pin 13 after running this code?

void setup() {
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
}

medium

A. LED stays ON permanently

B. LED stays OFF permanently

C. LED blinks ON and OFF every second

D. Code causes a compile error

Solution

1. Step 1: Analyze pinMode and digitalWrite usage

   Pin 13 is set as output, then turned HIGH (ON) and LOW (OFF) with 1 second delay each.

2. Step 2: Understand loop behavior

   The loop repeats turning LED ON for 1 second, then OFF for 1 second, causing blinking.

3. Final Answer:

   LED blinks ON and OFF every second -> Option C

4. Quick Check:

   digitalWrite + delay = blinking LED [OK]

Hint: HIGH then LOW with delay makes LED blink [OK]

Common Mistakes:

• Thinking LED stays ON or OFF permanently
• Confusing delay units (milliseconds vs seconds)
• Assuming code has syntax errors

4. Identify the error in this Arduino code snippet that tries to read a button state on pin 2:

void setup() {
  pinMode(2, OUTPUT);
}

void loop() {
  int buttonState = digitalRead(2);
}

medium

A. pinMode is not needed for digital pins

B. digitalRead cannot be used inside loop

C. buttonState must be declared globally

D. Pin 2 should be set as INPUT, not OUTPUT

Solution

1. Step 1: Check pinMode for reading input

   To read a button, pin 2 must be set as INPUT, not OUTPUT.

2. Step 2: Verify digitalRead usage

   digitalRead reads the state of an input pin correctly if pinMode is INPUT.

3. Final Answer:

   Pin 2 should be set as INPUT, not OUTPUT -> Option D

4. Quick Check:

   Reading pin requires INPUT mode [OK]

Hint: Set pin as INPUT to read button state [OK]

Common Mistakes:

• Setting pin as OUTPUT when reading input
• Thinking digitalRead is invalid inside loop
• Declaring variables only globally is required

5. You want to control two LEDs on pins 8 and 9 so that when a button on pin 2 is pressed, LED on pin 8 turns ON and LED on pin 9 turns OFF. Which code snippet correctly implements this behavior?

hard

A. pinMode(2, INPUT); pinMode(8, OUTPUT); pinMode(9, OUTPUT); if(digitalRead(2) == HIGH) { digitalWrite(8, HIGH); digitalWrite(9, LOW); }

B. pinMode(2, OUTPUT); pinMode(8, OUTPUT); pinMode(9, OUTPUT); if(digitalRead(2) == HIGH) { digitalWrite(8, HIGH); digitalWrite(9, LOW); }

C. pinMode(2, INPUT); pinMode(8, INPUT); pinMode(9, INPUT); if(digitalRead(2) == HIGH) { digitalWrite(8, HIGH); digitalWrite(9, LOW); }

D. pinMode(2, INPUT); pinMode(8, OUTPUT); pinMode(9, OUTPUT); if(digitalRead(2) == LOW) { digitalWrite(8, HIGH); digitalWrite(9, LOW); }

Solution

1. Step 1: Set pin modes correctly

   Button pin 2 must be INPUT to read its state; LEDs pins 8 and 9 must be OUTPUT to control them.

2. Step 2: Check button press condition

   When button is pressed, digitalRead(2) returns HIGH, so LEDs are set accordingly.

3. Final Answer:

   pinMode(2, INPUT); pinMode(8, OUTPUT); pinMode(9, OUTPUT); if(digitalRead(2) == HIGH) { digitalWrite(8, HIGH); digitalWrite(9, LOW); } -> Option A

4. Quick Check:

   Button INPUT + LEDs OUTPUT + condition HIGH = correct [OK]

Hint: Button pin INPUT, LEDs pins OUTPUT, check HIGH for press [OK]

Common Mistakes:

• Setting button pin as OUTPUT instead of INPUT
• Setting LEDs as INPUT instead of OUTPUT
• Checking LOW instead of HIGH for button press