Writing HIGH and LOW to output pins in Embedded C - Mini Project: Build & Apply

Writing HIGH and LOW to Output Pins

📖 Scenario: You are working with a simple microcontroller board. You want to control two LEDs connected to output pins. One LED should be turned ON (HIGH) and the other LED should be turned OFF (LOW).

🎯 Goal: Write a program that sets two output pins: one to HIGH and the other to LOW, to control two LEDs.

📋 What You'll Learn

Create two variables representing output pins named pin1 and pin2 with values 5 and 6 respectively.

Create a variable called HIGH with value 1 and a variable called LOW with value 0.

Write code to set pin1 to HIGH and pin2 to LOW using a function called digitalWrite.

Print the states of pin1 and pin2 to the console.

💡 Why This Matters

🌍 Real World

Controlling LEDs or other devices by setting microcontroller pins HIGH or LOW is a basic task in embedded systems.

💼 Career

Embedded software engineers often write code to control hardware pins to turn devices on or off.

1

Define Output Pins

Create two integer variables called pin1 and pin2 and set them to 5 and 6 respectively.

Embedded C

# Define output pins
// Your code here

Hint

Use int to declare the pins and assign the numbers 5 and 6.

2

Define HIGH and LOW Values

Create two integer variables called HIGH and LOW and set them to 1 and 0 respectively.

Embedded C

int pin1 = 5;
int pin2 = 6;
// Define HIGH and LOW values
// Your code here

Hint

HIGH means ON (1), LOW means OFF (0).

3

Set Pins to HIGH and LOW

Use the function digitalWrite to set pin1 to HIGH and pin2 to LOW.

Embedded C

int pin1 = 5;
int pin2 = 6;
int HIGH = 1;
int LOW = 0;
// Set pin1 to HIGH and pin2 to LOW
// Your code here

Hint

Call digitalWrite twice, once for each pin and value.

4

Print Pin States

Print the states of pin1 and pin2 using printf in the format: "Pin 5 is HIGH" and "Pin 6 is LOW".

Embedded C

int pin1 = 5;
int pin2 = 6;
int HIGH = 1;
int LOW = 0;
digitalWrite(pin1, HIGH);
digitalWrite(pin2, LOW);
// Print pin states
// Your code here

Hint

Use printf with %d to insert pin numbers and print the states.

Practice

1. Which function is used to set a pin as an output before writing HIGH or LOW to it?

easy

A. setPinMode(pin, HIGH)

B. digitalWrite(pin, OUTPUT)

C. pinMode(pin, OUTPUT)

D. writePin(pin, OUTPUT)

Solution

1. Step 1: Understand pin configuration

   Before writing HIGH or LOW, the pin must be set as an output to control voltage.

2. Step 2: Identify the correct function

   The function to set pin mode is pinMode(pin, OUTPUT), which configures the pin for output.

3. Final Answer:

   pinMode(pin, OUTPUT) -> Option C

4. Quick Check:

   Set pin as output = pinMode(pin, OUTPUT) [OK]

Hint: Set pin mode with pinMode before writing HIGH or LOW [OK]

Common Mistakes:

• Using digitalWrite to set pin mode
• Confusing HIGH/LOW with OUTPUT/INPUT
• Forgetting to set pin mode before writing

2. Which of the following is the correct syntax to turn pin 5 ON (HIGH) in embedded C?

easy

A. digitalWrite(5, 1);

B. digitalWrite(5, ON);

C. digitalWrite(5, OUTPUT);

D. digitalWrite(5, HIGH);

Solution

1. Step 1: Identify the function to write pin state

   The function digitalWrite(pin, value) sets the pin voltage HIGH or LOW.

2. Step 2: Use correct constants

   Use HIGH to turn the pin ON. The correct syntax is digitalWrite(5, HIGH);.

3. Final Answer:

   digitalWrite(5, HIGH); -> Option D

4. Quick Check:

   Turn pin ON = digitalWrite(pin, HIGH) [OK]

Hint: Use HIGH constant, not ON or numbers, for clarity [OK]

Common Mistakes:

• Using ON instead of HIGH
• Using OUTPUT instead of HIGH
• Using numeric 1 instead of HIGH constant

3. What will be the output state of pin 3 after running this code?

pinMode(3, OUTPUT);
digitalWrite(3, LOW);
digitalWrite(3, HIGH);

medium

A. Pin 3 will be LOW

B. Pin 3 will be HIGH

C. Pin 3 will be in input mode

D. Pin 3 will be undefined

Solution

1. Step 1: Set pin 3 as output

   The code sets pin 3 as output with pinMode(3, OUTPUT);.

2. Step 2: Write LOW then HIGH to pin 3

   First, pin 3 is set LOW, then immediately set HIGH, so final state is HIGH.

3. Final Answer:

   Pin 3 will be HIGH -> Option B

4. Quick Check:

   Last digitalWrite sets pin state = HIGH [OK]

Hint: Last digitalWrite sets the pin state [OK]

Common Mistakes:

• Assuming pin stays LOW after writing HIGH
• Forgetting pinMode sets output mode
• Thinking pin state is undefined without delay

4. Identify the error in this code snippet:

pinMode(7, OUTPUT);
digitalWrite(7, HIGH)
digitalWrite(7, LOW);

medium

A. Missing semicolon after digitalWrite(7, HIGH)

B. pinMode should be called after digitalWrite

C. HIGH and LOW are not valid constants

D. Pin number 7 cannot be used

Solution

1. Step 1: Check syntax line by line

   The second line digitalWrite(7, HIGH) is missing a semicolon at the end.

2. Step 2: Confirm other lines are correct

   pinMode(7, OUTPUT); and digitalWrite(7, LOW); are correct syntax.

3. Final Answer:

   Missing semicolon after digitalWrite(7, HIGH) -> Option A

4. Quick Check:

   Every statement must end with semicolon [OK]

Hint: Check each line ends with a semicolon [OK]

Common Mistakes:

• Forgetting semicolon after function calls
• Calling pinMode after digitalWrite
• Misusing HIGH/LOW constants

5. You want to toggle pin 10 ON and OFF every second in a loop. Which code snippet correctly sets pin 10 HIGH then LOW with a 1-second delay between states?

hard

A. pinMode(10, OUTPUT);
digitalWrite(10, HIGH);
delay(1000);
digitalWrite(10, LOW);
delay(1000);

B. digitalWrite(10, HIGH);
delay(1000);
digitalWrite(10, LOW);
delay(1000);

C. pinMode(10, INPUT);
digitalWrite(10, HIGH);
delay(1000);

D. pinMode(10, OUTPUT);
digitalWrite(10, LOW);
digitalWrite(10, HIGH);

Solution

1. Step 1: Set pin 10 as output

   Use pinMode(10, OUTPUT); to configure pin 10 for output.

2. Step 2: Write HIGH, wait, then LOW, wait

   Use digitalWrite(10, HIGH); then delay(1000); to wait 1 second, then digitalWrite(10, LOW); and delay again.

3. Final Answer:

   pinMode(10, OUTPUT); digitalWrite(10, HIGH); delay(1000); digitalWrite(10, LOW); delay(1000); -> Option A

4. Quick Check:

   Set output, write states with delay between [OK]

Hint: Always set pinMode before toggling with delays [OK]

Common Mistakes:

• Forgetting to set pinMode as OUTPUT
• Missing delay between HIGH and LOW
• Setting pinMode to INPUT instead of OUTPUT