Uploading and running a sketch in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What happens when you upload this sketch?

Consider this Arduino sketch. What will the LED connected to pin 13 do after uploading and running this code?

Arduino

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

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

A The LED will stay off permanently.

B The LED will stay on permanently.

C The LED will blink on and off every second.

D The sketch will not compile due to a syntax error.

💡 Hint

Look at the loop function and the delay times.

The loop turns the LED on, waits 1 second, turns it off, waits 1 second, then repeats. This causes blinking every second.

❓ Predict Output

intermediate

What is the output on the Serial Monitor?

What will be printed on the Serial Monitor when this sketch is uploaded and run?

Arduino

void setup() {
  Serial.begin(9600);
  Serial.println("Start");
}

void loop() {
  Serial.println("Running");
  delay(500);
}

A

Start
Running
Running
Running... (repeats every 0.5 seconds)

B

Start
Running (printed once, then stops)

C Only Start is printed repeatedly.

D Nothing is printed because Serial.begin is missing.

💡 Hint

Check where Serial.println is called inside the loop.

Serial.println("Running") is inside loop(), so it prints repeatedly every 0.5 seconds after printing "Start" once in setup().

🔧 Debug

advanced

Why does this sketch fail to upload?

This sketch fails to upload to the Arduino board. What is the cause?

Arduino

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

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

A pinMode cannot be used on pin 13.

B digitalWrite is used incorrectly; it needs two arguments.

C delay function is not allowed in setup().

D Missing semicolon after pinMode(13, OUTPUT) causes a syntax error.

💡 Hint

Check punctuation carefully in setup().

The line pinMode(13, OUTPUT) is missing a semicolon at the end, causing a syntax error that prevents uploading.

❓ Predict Output

advanced

What is the state of pin 12 after running this sketch?

After uploading and running this sketch, what will be the voltage state of pin 12?

Arduino

void setup() {
  pinMode(12, OUTPUT);
  digitalWrite(12, HIGH);
}

void loop() {
  // empty loop
}

A Pin 12 will output LOW voltage (0V).

B Pin 12 will output HIGH voltage (5V).

C Pin 12 will be an input pin by default.

D Pin 12 will toggle between HIGH and LOW every second.

💡 Hint

Check what happens in setup() and if loop() changes pin 12.

Pin 12 is set as OUTPUT and immediately set HIGH in setup(). Since loop() does nothing, pin 12 stays HIGH.

🧠 Conceptual

expert

What happens if you upload a sketch with an empty loop()?

If you upload this sketch to an Arduino, what will be the behavior of the board?

Arduino

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

void loop() {
  // empty
}

A The LED on pin 13 will stay on permanently.

B The LED on pin 13 will blink rapidly.

C The LED on pin 13 will stay off.

D The Arduino will reset continuously causing no output.

💡 Hint

Think about what setup() does and what an empty loop() means.

setup() runs once and sets pin 13 HIGH. loop() does nothing, so pin 13 stays HIGH and LED stays on.

Practice

1. What happens immediately after you upload a sketch to an Arduino board?

easy

A. The Arduino board sends the sketch back to the computer.

B. You need to press the reset button to start the sketch.

C. The sketch starts running automatically on the board.

D. The sketch is saved but does not run until you power cycle the board.

Solution

1. Step 1: Understand the upload process

   Uploading sends the program to the Arduino's memory.

2. Step 2: Recognize sketch behavior after upload

   The Arduino automatically runs the sketch once upload finishes.

3. Final Answer:

   The sketch starts running automatically on the board. -> Option C

4. Quick Check:

   Upload triggers automatic run [OK]

Hint: Upload means program runs immediately after transfer [OK]

Common Mistakes:

• Thinking you must press reset to start sketch
• Believing sketch waits for manual start
• Confusing upload with download

2. Which of the following is the correct step to upload a sketch to an Arduino board?

easy

A. Connect the board, then type the sketch in the serial monitor.

B. Write the sketch, then press the reset button before uploading.

C. Select the board, then save the sketch without uploading.

D. Select the board and port, then click the Upload button.

Solution

1. Step 1: Identify correct upload procedure

   You must select the correct board and port in the IDE.

2. Step 2: Perform upload action

   Clicking the Upload button sends the sketch to the board.

3. Final Answer:

   Select the board and port, then click the Upload button. -> Option D

4. Quick Check:

   Board + port selected, then upload [OK]

Hint: Always pick board and port before uploading [OK]

Common Mistakes:

• Skipping board or port selection
• Trying to upload without connecting board
• Using serial monitor to upload code

3. Consider this Arduino sketch snippet:

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

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

What will happen after uploading and running this sketch?

medium

A. The built-in LED on pin 13 will blink on and off every second.

B. The LED will stay on permanently without blinking.

C. The sketch will cause a compilation error due to missing semicolons.

D. Nothing will happen because the loop function is empty.

Solution

1. Step 1: Analyze setup function

   Pin 13 is set as an output pin.

2. Step 2: Analyze loop function behavior

   The LED on pin 13 turns HIGH (on), waits 1 second, then LOW (off), waits 1 second, repeating.

3. Final Answer:

   The built-in LED on pin 13 will blink on and off every second. -> Option A

4. Quick Check:

   Pin 13 output toggles every 1s [OK]

Hint: Pin 13 blinking means HIGH and LOW with delay [OK]

Common Mistakes:

• Confusing delay units (milliseconds vs seconds)
• Assuming LED stays on without blinking
• Thinking loop is empty

4. You tried uploading a sketch but got an error saying "avrdude: stk500_recv(): programmer is not responding." What is the most likely cause?

medium

A. The sketch code has syntax errors.

B. The wrong board or port is selected in the Arduino IDE.

C. The USB cable is connected properly and working.

D. The Arduino IDE is not installed.

Solution

1. Step 1: Understand the error message

   This error means the IDE cannot communicate with the board.

2. Step 2: Identify common communication issues

   Usually caused by wrong board or port selection or bad connection.

3. Final Answer:

   The wrong board or port is selected in the Arduino IDE. -> Option B

4. Quick Check:

   Communication error = wrong board/port selected [OK]

Hint: Check board and port if upload communication fails [OK]

Common Mistakes:

• Assuming syntax errors cause communication errors
• Ignoring USB cable connection
• Thinking IDE installation causes this error

5. You want to upload a sketch to an Arduino Uno but your computer shows multiple COM ports. How do you ensure you upload to the correct port?

hard

A. Disconnect the Arduino, check ports, reconnect it, then select the new port shown.

B. Select any COM port randomly; the IDE will find the board automatically.

C. Upload without selecting a port; the sketch will upload anyway.

D. Restart the Arduino IDE and it will select the correct port.

Solution

1. Step 1: Identify the correct COM port

   Disconnect Arduino and note available ports, then reconnect and see which port appears.

2. Step 2: Select the newly appeared port in the IDE

   This port corresponds to the Arduino board for uploading.

3. Final Answer:

   Disconnect the Arduino, check ports, reconnect it, then select the new port shown. -> Option A

4. Quick Check:

   New port after reconnect = correct port [OK]

Hint: Unplug and replug board to spot correct COM port [OK]

Common Mistakes:

• Guessing COM port without checking
• Assuming IDE auto-selects port
• Uploading without port selection