LED control patterns in Embedded C - Mini Project: Build & Apply

LED Control Patterns

📖 Scenario: You are programming a simple embedded system with 4 LEDs connected to a microcontroller. You want to create different light patterns by turning LEDs on and off in a sequence.

🎯 Goal: Build a program that controls 4 LEDs using an array to represent their states, then create a pattern that turns LEDs on one by one, and finally print the LED states to simulate the output.

📋 What You'll Learn

Create an array called leds with 4 elements initialized to 0 (off).

Create a variable called current_led to track which LED to turn on.

Write a loop that sets the current_led element in leds to 1 (on) and others to 0 (off).

Print the leds array states to show which LEDs are on or off.

💡 Why This Matters

🌍 Real World

Embedded systems often control LEDs to show status or alerts. Learning to manage LED patterns is a basic skill for hardware programming.

💼 Career

Embedded software developers and hardware engineers use similar code to control lights and indicators on devices.

1

Create the LED array

Create an integer array called leds with 4 elements, all initialized to 0 to represent LEDs turned off.

Embedded C

int leds[4] = {0, 0, 0, 0}; // Your code here

Hint

Think of leds as a row of 4 light switches, all starting off.

2

Add a variable to track the current LED

Create an integer variable called current_led and set it to 0 to track which LED will be turned on.

Embedded C

int leds[4] = {0, 0, 0, 0};
int current_led = 0; // Your code here

Hint

This variable will help you choose which LED to turn on.

3

Turn on the current LED and turn off others

Write a for loop with variable i from 0 to 3 that sets leds[i] to 1 if i equals current_led, otherwise sets it to 0.

Embedded C

int leds[4] = {0, 0, 0, 0};
int current_led = 0;
for (int i = 0; i < 4; i++) {
    // Your code here
}

Hint

Use the if statement inside the loop to set the LED states.

4

Print the LED states

Write a for loop with variable i from 0 to 3 that prints the value of leds[i] followed by a space, then print a newline after the loop.

Embedded C

int leds[4] = {0, 0, 0, 0};
int current_led = 0;
for (int i = 0; i < 4; i++) {
    if (i == current_led) {
        leds[i] = 1;
    } else {
        leds[i] = 0;
    }
}
// Your code here

Hint

Use printf inside the loop to show each LED state, then print a newline.

Practice

1. What is the main purpose of using LED control patterns in embedded C programming?

easy

A. To create visual effects by turning LEDs on and off in specific sequences

B. To increase the processing speed of the microcontroller

C. To store data in the microcontroller's memory

D. To connect the microcontroller to the internet

Solution

1. Step 1: Understand LED control patterns

   LED control patterns are used to create visual effects by controlling LEDs.

2. Step 2: Identify the purpose in embedded systems

   They help show device status or create decorative light sequences by turning LEDs on and off.

3. Final Answer:

   To create visual effects by turning LEDs on and off in specific sequences -> Option A

4. Quick Check:

   LED patterns = visual effects [OK]

Hint: LED patterns control lights, not speed or memory [OK]

Common Mistakes:

• Confusing LED patterns with data storage
• Thinking LED patterns improve processing speed
• Assuming LED patterns connect to the internet

2. Which of the following is the correct syntax to turn on an LED connected to pin 5 using embedded C?

easy

A. digitalWrite(HIGH, 5);

B. digitalWrite(5, ON);

C. digitalWrite(5, HIGH);

D. digitalWrite(ON, 5);

Solution

1. Step 1: Recall digitalWrite syntax

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

2. Step 2: Match correct parameters

   Pin number comes first, then the value HIGH to turn LED on.

3. Final Answer:

   digitalWrite(5, HIGH); -> Option C

4. Quick Check:

   digitalWrite(pin, HIGH) = turn LED on [OK]

Hint: Pin number first, then HIGH or LOW [OK]

Common Mistakes:

• Swapping pin and value order
• Using ON instead of HIGH
• Using lowercase for HIGH

3. What will be the output on the LED connected to pin 3 after running this code snippet?

for(int i = 0; i < 3; i++) {
  digitalWrite(3, HIGH);
  delay(500);
  digitalWrite(3, LOW);
  delay(500);
}

medium

A. LED stays OFF continuously

B. LED stays ON continuously for 1.5 seconds

C. LED blinks once and stays OFF

D. LED blinks 3 times with 0.5 second ON and 0.5 second OFF

Solution

1. Step 1: Analyze the loop iterations

   The loop runs 3 times, each time turning LED ON then OFF with delays.

2. Step 2: Understand delay timing

   Each ON and OFF lasts 500ms, so LED blinks 3 times with equal ON/OFF intervals.

3. Final Answer:

   LED blinks 3 times with 0.5 second ON and 0.5 second OFF -> Option D

4. Quick Check:

   Loop 3 times with delay = 3 blinks [OK]

Hint: Count loop runs and delays for blink count [OK]

Common Mistakes:

• Ignoring the loop count
• Confusing delay units
• Assuming LED stays ON

4. Identify the error in this LED blinking code:

void loop() {
  digitalWrite(2, HIGH);
  delay(1000);
  digitalWrite(2, HIGH);
  delay(1000);
}

medium

A. delay() function is used incorrectly

B. LED never turns OFF because digitalWrite(2, HIGH) is used twice

C. Pin 2 is not set as OUTPUT

D. digitalWrite() syntax is wrong

Solution

1. Step 1: Check LED ON/OFF commands

   Both digitalWrite calls set pin 2 to HIGH, so LED stays ON.

2. Step 2: Identify missing OFF command

   LED never turns OFF because digitalWrite(2, LOW) is missing.

3. Final Answer:

   LED never turns OFF because digitalWrite(2, HIGH) is used twice -> Option B

4. Quick Check:

   Same HIGH twice = no OFF [OK]

Hint: LED needs HIGH then LOW to blink [OK]

Common Mistakes:

• Assuming delay is wrong
• Forgetting to set pin mode
• Thinking syntax is incorrect

5. You want to create a running LED pattern on 4 LEDs connected to pins 2, 3, 4, and 5. Which code snippet correctly implements this pattern?

hard

A. for(int i = 2; i <= 5; i++) {
digitalWrite(i, HIGH);
delay(200);
digitalWrite(i, LOW);
}

B. for(int i = 2; i <= 5; i++) {
digitalWrite(i, LOW);
delay(200);
digitalWrite(i, HIGH);
}

C. digitalWrite(2, HIGH);
digitalWrite(3, HIGH);
digitalWrite(4, HIGH);
digitalWrite(5, HIGH);
delay(200);
digitalWrite(2, LOW);
digitalWrite(3, LOW);
digitalWrite(4, LOW);
digitalWrite(5, LOW);

D. for(int i = 5; i >= 2; i--) {
digitalWrite(i, HIGH);
delay(200);
}

Solution

1. Step 1: Understand running LED pattern

   Running LED means turning ON one LED at a time in sequence, then OFF before next.

2. Step 2: Analyze each option

   for(int i = 2; i <= 5; i++) { digitalWrite(i, HIGH); delay(200); digitalWrite(i, LOW); } loops from pin 2 to 5, turns each LED ON, delays, then OFF, creating running effect.

3. Final Answer:

   for(int i = 2; i <= 5; i++) { digitalWrite(i, HIGH); delay(200); digitalWrite(i, LOW); } -> Option A

4. Quick Check:

   Loop ON then OFF per LED = running pattern [OK]

Hint: Turn ON then OFF each LED in order [OK]

Common Mistakes:

• Turning all LEDs ON at once
• Not turning off the LED after delay
• Turning LEDs OFF before ON