digitalWrite() for output control in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the digitalWrite() function do in Arduino?

digitalWrite() sets a digital pin to either HIGH (on) or LOW (off), controlling output devices like LEDs.

beginner

What are the two main values you can use with digitalWrite()?

The two main values are HIGH (to turn the pin on) and LOW (to turn the pin off).

beginner

Why do you need to use pinMode() before digitalWrite()?

You must set the pin as OUTPUT with pinMode() so Arduino knows you want to control something like an LED.

intermediate

What happens if you use digitalWrite() on a pin set as INPUT?

The pin will not properly control output devices; it may cause unexpected behavior because the pin is set to read signals, not send them.

beginner

Write a simple Arduino code snippet to turn an LED on pin 13 on and off every second using digitalWrite().

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

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

What does digitalWrite(8, HIGH); do?

A Reads the value from pin 8

B Sets pin 8 to output and turns it on

C Turns pin 8 on if it is set as output

D Sets pin 8 to input mode

digitalWrite() sets the pin HIGH or LOW but does not change pin mode. The pin must be set as output first.

Which function must be called before digitalWrite() to control an LED?

A pinMode(pin, OUTPUT);

B digitalRead(pin);

C delay(time);

D analogWrite(pin, value);

You must set the pin as OUTPUT using pinMode() before using digitalWrite().

What value turns a pin off using digitalWrite()?

A HIGH

B OUTPUT

C INPUT

D LOW

LOW turns the pin off (0 volts).

If you want to blink an LED every second, which function helps create the delay?

A pinMode()

B delay()

C digitalWrite()

D analogRead()

delay() pauses the program for a set time in milliseconds.

What will happen if you call digitalWrite() on a pin set as INPUT?

A The output may not work as expected

B The pin will read the input value

C The pin will output the value correctly

D The Arduino will reset

Using digitalWrite() on an input pin can cause unexpected behavior because the pin is not set to output mode.

Explain how digitalWrite() controls an LED connected to an Arduino pin.

Think about turning a light switch on and off.

Describe the steps to blink an LED using digitalWrite() and delay().

Imagine turning a flashlight on and off with pauses.

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