LED blink pattern in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LED blink code?

Consider the following Arduino code that blinks an LED connected to pin 13. What will be the LED's behavior?

Arduino

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

void loop() {
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

A The LED turns on for 0.5 seconds, then off for 0.5 seconds, repeatedly.

B The LED stays off continuously without blinking.

C The LED blinks very fast, about every 0.1 seconds.

D The LED stays on continuously without blinking.

💡 Hint

Look at the delay times and the order of turning the LED on and off.

The code turns the LED on, waits 500 milliseconds, then turns it off and waits another 500 milliseconds. This cycle repeats, causing the LED to blink on and off every half second.

❓ Predict Output

intermediate

What is the LED blink pattern of this code?

Analyze this Arduino code. What pattern will the LED on pin 13 follow?

Arduino

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

void loop() {
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(200);
}

A The LED blinks on and off every 0.5 seconds.

B The LED is on for 0.2 seconds and off for 1 second repeatedly.

C The LED stays on continuously.

D The LED is on for 1 second and off for 0.2 seconds repeatedly.

💡 Hint

Check the delay times after turning the LED on and off.

The LED is turned on, then the program waits 1000 milliseconds (1 second), then turns off and waits 200 milliseconds before repeating.

🔧 Debug

advanced

What error does this LED blink code cause?

Look at this Arduino code snippet. What error will occur when compiling or running it?

Arduino

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

void loop() {
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

A No error, code runs and blinks LED correctly

B SyntaxError due to missing semicolon after pinMode(13, OUTPUT)

C SyntaxError due to missing curly braces in loop function

D Runtime error because pin 13 is not set as output

💡 Hint

Check punctuation carefully in the setup function.

The original code was missing a semicolon after pinMode(13, OUTPUT), causing a syntax error. This corrected code includes the semicolon, so it compiles and runs correctly.

❓ Predict Output

advanced

What is the LED blink pattern of this code with variable delay?

What pattern will the LED on pin 13 follow when running this Arduino code?

Arduino

int delayTime = 200;

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

void loop() {
  digitalWrite(13, HIGH);
  delay(delayTime);
  digitalWrite(13, LOW);
  delay(delayTime * 2);
}

A LED blinks on and off every 0.2 seconds.

B LED on for 0.4 seconds, off for 0.2 seconds repeatedly.

C LED on for 0.2 seconds, off for 0.4 seconds repeatedly.

D LED stays on continuously.

💡 Hint

Look at how delayTime is used for on and off durations.

The LED is on for delayTime (200 ms) and off for delayTime * 2 (400 ms), creating an uneven blink pattern.

❓ Predict Output

expert

What is the LED blink pattern of this code with nested loops?

Analyze this Arduino code. What is the total number of LED blinks before the pattern repeats?

Arduino

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

void loop() {
  for (int i = 0; i < 3; i++) {
    digitalWrite(13, HIGH);
    delay(300);
    digitalWrite(13, LOW);
    delay(300);
  }
  delay(1000);
}

A The LED blinks 6 times continuously without pause.

B The LED blinks 3 times, then pauses for 1 second before repeating.

C The LED blinks once, then pauses for 1 second before repeating.

D The LED blinks 3 times with no pause before repeating.

💡 Hint

Count how many times the loop runs and the delays involved.

The for loop runs 3 times, blinking the LED on and off each time with 300 ms delays, then the code waits 1 second before repeating the whole pattern.

Practice

1. What does the delay(1000); command do in an Arduino LED blink program?

easy

A. Pauses the program for 1000 milliseconds (1 second)

B. Turns the LED on for 1000 milliseconds

C. Turns the LED off for 1000 milliseconds

D. Sets the LED brightness to 1000

Solution

1. Step 1: Understand the delay function

   The delay() function pauses the program for the given time in milliseconds.

2. Step 2: Interpret the argument 1000

   1000 milliseconds equals 1 second, so the program waits for 1 second before continuing.

3. Final Answer:

   Pauses the program for 1000 milliseconds (1 second) -> Option A

4. Quick Check:

   delay(1000) = 1 second pause [OK]

Hint: delay(ms) pauses program for ms milliseconds [OK]

Common Mistakes:

• Thinking delay turns LED on or off
• Confusing delay time with brightness
• Assuming delay is in seconds

2. Which of the following is the correct syntax to set pin 13 as an output in Arduino?

easy

A. pinMode(OUTPUT, 13);

B. pinMode(13, OUTPUT);

C. digitalWrite(13, OUTPUT);

D. digitalWrite(OUTPUT, 13);

Solution

1. Step 1: Recall pinMode syntax

   The correct syntax is pinMode(pin, mode); where pin is the pin number and mode is INPUT or OUTPUT.

2. Step 2: Match the correct order

   pinMode(13, OUTPUT); uses pinMode(13, OUTPUT); which matches the correct order and parameters.

3. Final Answer:

   pinMode(13, OUTPUT); -> Option B

4. Quick Check:

   pinMode(pin, OUTPUT) sets pin as output [OK]

Hint: pinMode(pin, OUTPUT) sets pin as output [OK]

Common Mistakes:

• Swapping pin and mode parameters
• Using digitalWrite instead of pinMode to set mode
• Missing semicolon at end

3. What will be the output of this Arduino code snippet?

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

void loop() {
  digitalWrite(13, HIGH);
  delay(500);
  digitalWrite(13, LOW);
  delay(500);
}

medium

A. LED on pin 13 blinks on and off every 0.5 seconds

B. LED on pin 13 stays on continuously

C. LED on pin 13 stays off continuously

D. LED on pin 13 blinks on and off every 1 second

Solution

1. Step 1: Analyze the delay times

   The LED is turned on, then the program waits 500 ms, then turned off, then waits 500 ms again.

2. Step 2: Calculate total blink cycle

   On time + off time = 500 ms + 500 ms = 1000 ms (1 second) per full blink cycle. Each on or off state lasts 0.5 seconds.

3. Final Answer:

   LED on pin 13 blinks on and off every 1 second -> Option D

4. Quick Check:

   delay(500) means 0.5 second blink intervals [OK]

Hint: Sum delays to find blink cycle time [OK]

Common Mistakes:

• Confusing total blink time with single delay
• Ignoring delay after turning LED off
• Assuming delay is in seconds

4. Identify the error in this Arduino code that tries to blink an LED on pin 13:

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

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

medium

A. Missing semicolon after delay(1000)

B. pinMode should be in loop()

C. digitalWrite needs pinMode first

D. delay cannot be used in loop()

Solution

1. Step 1: Check syntax line by line

   Look at each statement for missing semicolons or syntax errors.

2. Step 2: Find missing semicolon

   The line delay(1000) is missing a semicolon at the end, causing a syntax error.

3. Final Answer:

   Missing semicolon after delay(1000) -> Option A

4. Quick Check:

   Every statement must end with ; [OK]

Hint: Check each line ends with semicolon [OK]

Common Mistakes:

• Putting pinMode inside loop instead of setup
• Thinking delay can't be used in loop
• Ignoring missing semicolon errors

5. You want an LED on pin 13 to blink twice quickly, then pause for 2 seconds, and repeat. Which code snippet achieves this pattern?

hard

A. digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); delay(2000);

B. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000); } delay(2000);

C. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000);

D. digitalWrite(13, HIGH); delay(500); digitalWrite(13, LOW); delay(500); delay(2000);

Solution

1. Step 1: Understand the blink pattern

   The LED should blink twice quickly (short on/off), then pause 2 seconds before repeating.

2. Step 2: Analyze each option's timing

   for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); blinks twice with 200 ms on and off delays, then pauses 2000 ms. This matches the pattern.

3. Step 3: Check other options

   digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); delay(2000); blinks once only. for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(1000); digitalWrite(13, LOW); delay(1000); } delay(2000); blinks twice but with 1 second delays (too slow). digitalWrite(13, HIGH); delay(500); digitalWrite(13, LOW); delay(500); delay(2000); blinks once with 500 ms delays.

4. Final Answer:

   for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); -> Option C

5. Quick Check:

   Loop twice fast blinks + long pause = for(int i=0; i<2; i++) { digitalWrite(13, HIGH); delay(200); digitalWrite(13, LOW); delay(200); } delay(2000); [OK]

Hint: Use loop for repeated quick blinks, then delay for pause [OK]

Common Mistakes:

• Using delay too long for quick blinks
• Not looping for multiple blinks
• Pausing before blinking instead of after