digitalWrite() for output control in Arduino - Mini Project: Build & Apply

Control an LED with digitalWrite()

📖 Scenario: You have a small LED light connected to your Arduino board. You want to turn it on and off using code.

🎯 Goal: Write a program that turns an LED on and off by controlling the output pin using digitalWrite().

📋 What You'll Learn

Create a variable for the LED pin number

Set the LED pin as an output in setup()

Use digitalWrite() to turn the LED on and off in loop()

Add a delay between turning the LED on and off

💡 Why This Matters

🌍 Real World

Controlling lights and indicators is a common task in electronics projects and devices.

💼 Career

Understanding how to control outputs like LEDs is fundamental for embedded systems and hardware programming jobs.

1

Set up the LED pin variable

Create an integer variable called ledPin and set it to 13.

Arduino

# Your code here

Hint

Use int ledPin = 13; to store the pin number.

2

Configure the LED pin as output

In the setup() function, use pinMode() to set ledPin as an output.

Arduino

int ledPin = 13;

void setup() {
  // Your code here
}

void loop() {
}

Hint

Use pinMode(ledPin, OUTPUT); inside setup().

3

Turn the LED on and off using digitalWrite()

In the loop() function, use digitalWrite() to turn ledPin HIGH, then LOW with a delay of 1000 milliseconds between each.

Arduino

int ledPin = 13;

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

void loop() {
  // Use digitalWrite to turn LED on and off
  // Add delay(1000) between changes
}

Hint

Use digitalWrite(ledPin, HIGH); to turn on and digitalWrite(ledPin, LOW); to turn off the LED.

4

Upload and observe the LED blinking

Upload the program and observe the LED connected to pin 13 blinking on and off every second. Use Serial.println() to print "LED ON" when the LED turns on and "LED OFF" when it turns off.

Arduino

int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  // Initialize serial communication
}

void loop() {
  digitalWrite(ledPin, HIGH);
  // Print "LED ON"
  delay(1000);
  digitalWrite(ledPin, LOW);
  // Print "LED OFF"
  delay(1000);
}

Hint

Use Serial.begin(9600); in setup() and Serial.println() in loop().

Practice

1. What does the digitalWrite() function do in Arduino programming?

easy

A. It sets the analog value of a pin.

B. It reads the voltage from a digital pin.

C. It initializes the serial communication.

D. It sets a digital pin to HIGH or LOW voltage.

Solution

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

   The function digitalWrite() is used to control the voltage level on a digital pin, setting it either HIGH (on) or LOW (off). It does not read values (that's digitalRead()), nor does it set analog values or initialize serial communication.

2. Final Answer:

   It sets a digital pin to HIGH or LOW voltage. -> Option D

3. Quick Check:

   digitalWrite() controls pin voltage = D [OK]

Hint: digitalWrite sets pin ON or OFF voltage [OK]

Common Mistakes:

• Confusing digitalWrite() with digitalRead()
• Thinking digitalWrite() reads pin values
• Mixing digitalWrite() with analogWrite()

2. Which of the following is the correct syntax to turn on an LED connected to pin 13 using digitalWrite()?

easy

A. digitalWrite(13, HIGH);

B. digitalWrite(13, LOW);

C. digitalWrite(13, ON);

D. digitalWrite(13, TRUE);

Solution

1. Step 1: Recall correct constants and check options

   digitalWrite() uses HIGH and LOW constants. To turn on, use HIGH. A uses ON (not valid), B uses LOW (turns off), D uses TRUE (not valid). Only C: digitalWrite(13, HIGH); is correct.

2. Final Answer:

   digitalWrite(13, HIGH); -> Option A

3. Quick Check:

   Use HIGH or LOW with digitalWrite() = C [OK]

Hint: Use HIGH or LOW, not ON or TRUE [OK]

Common Mistakes:

• Using ON or TRUE instead of HIGH
• Using LOW instead of HIGH
• Forgetting to set pinMode to OUTPUT first

3. What will be the output on pin 8 after running this code snippet?

pinMode(8, OUTPUT);
digitalWrite(8, LOW);
digitalWrite(8, HIGH);
digitalWrite(8, LOW);

medium

A. Pin 8 will toggle rapidly.

B. Pin 8 will be HIGH (on).

C. Pin 8 will be LOW (off).

D. Pin 8 will cause a syntax error.

Solution

1. Step 1: Trace the digitalWrite() calls

   pinMode sets OUTPUT, then LOW, HIGH, LOW. Final LOW so pin off.

2. Final Answer:

   Pin 8 will be LOW (off). -> Option C

3. Quick Check:

   Last digitalWrite sets pin LOW = A [OK]

Hint: Last digitalWrite() sets pin state [OK]

Common Mistakes:

• Assuming pin toggles automatically
• Confusing initial and final pin states
• Thinking multiple digitalWrite calls cause errors

4. Identify the error in this Arduino code snippet:

digitalWrite(12, HIGH);
pinMode(12, OUTPUT);

medium

A. No error, code runs fine.

B. pinMode() must be called before digitalWrite().

C. digitalWrite() cannot use pin 12.

D. HIGH is not a valid value for digitalWrite().

Solution

1. Step 1: Check order of pinMode() and digitalWrite()

   pinMode() must set OUTPUT before digitalWrite(), otherwise unexpected behavior. Here digitalWrite first.

2. Final Answer:

   pinMode() must be called before digitalWrite(). -> Option B

3. Quick Check:

   Set pinMode before digitalWrite = A [OK]

Hint: Always set pinMode(OUTPUT) before digitalWrite() [OK]

Common Mistakes:

• Calling digitalWrite before pinMode
• Assuming pinMode defaults to OUTPUT
• Using invalid pin numbers

5. You want to blink an LED connected to pin 9 on and off every second. Which code snippet correctly uses digitalWrite() inside the loop() function to achieve this?

hard

A. digitalWrite(9, HIGH);
delay(1000);
digitalWrite(9, LOW);
delay(1000);

B. digitalWrite(9, HIGH);
digitalWrite(9, LOW);
delay(1000);

C. pinMode(9, OUTPUT);
digitalWrite(9, HIGH);
delay(1000);

D. digitalWrite(9, HIGH);
delay(500);
digitalWrite(9, HIGH);
delay(500);

Solution

1. Step 1: Understand blinking and analyze options

   Blink: HIGH, delay(1000), LOW, delay(1000). A: HIGH immediate LOW, no on time. C: pinMode in loop inefficient, no LOW. D: HIGH twice, always on. Only B correct.

2. Final Answer:

   digitalWrite(9, HIGH); delay(1000); digitalWrite(9, LOW); delay(1000); -> Option A

3. Quick Check:

   Turn ON, delay, turn OFF, delay = B [OK]

Hint: Turn ON, delay, turn OFF, delay for blinking [OK]

Common Mistakes:

• Missing delay between ON and OFF
• Not turning LED OFF after ON
• Setting pinMode inside loop repeatedly