digitalWrite() for output control in Arduino

Introduction

digitalWrite() lets you turn a pin on or off to control things like lights or motors.

Turning an LED on or off.

Controlling a buzzer to make sounds.

Switching a relay to turn appliances on or off.

Activating a motor or fan.

Sending signals to other electronic parts.

Syntax

Arduino

digitalWrite(pin, value);

pin is the number of the pin you want to control.

value can be HIGH (on) or LOW (off).

Examples

Turns pin 13 on (usually lights up the built-in LED).

Arduino

digitalWrite(13, HIGH);

Turns pin 8 off.

Arduino

digitalWrite(8, LOW);

Turns pin 5 on, maybe to power a motor.

Arduino

digitalWrite(5, HIGH);

Sample Program

This program makes the built-in LED on pin 13 blink on and off every second.

Arduino

void setup() {
  pinMode(13, OUTPUT); // Set pin 13 as output
}

void loop() {
  digitalWrite(13, HIGH); // Turn LED on
  delay(1000);           // Wait 1 second
  digitalWrite(13, LOW);  // Turn LED off
  delay(1000);           // Wait 1 second
}

Important Notes

Always set the pin mode to OUTPUT before using digitalWrite().

Use delay() to create pauses between turning pins on and off.

Pin numbers depend on your Arduino board model.

Summary

digitalWrite() controls a pin's voltage: HIGH for on, LOW for off.

Use it to turn devices like LEDs and motors on or off.

Remember to set the pin as OUTPUT first with pinMode().

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