🌈 Running Light Experiment (ESP32 + Arduino)

In the previous lesson, we learned how to blink a single LED. This time, we’re going a step further and building a running light effect using multiple LEDs. It’s a classic project that helps you understand arrays, loops, and GPIO control in embedded systems.

🔧 Hardware Circuit Design

Option A: Use Your ESP32 Extension Board (Recommended)

✅ Wiring Plan

Use female-to-male jumper wires

ESP32 GPIO Pin	ESP32 Label	Connects To	LED on Module
GPIO13	D13	LED1	D1 (Red)
GPIO12	D12	LED2	D2 (Yellow)
GPIO14	D14	LED3	D3 (Yellow)
GPIO27	D27	LED4	D4 (Green)
GND	GND	GND	Common GND

⚠️ Important: The LED module expects you to connect each GPIO pin to the LEDx pin (anode), and share a common GND with ESP32.

🧠 Understanding the Circuit

Each LED already has a series resistor on the board, so you can connect the ESP32 GPIO pins directly to the LEDx inputs — no external resistors needed.

Option B: Use a Breadboard (Alternative)

🧰 Bill of Materials (BOM)

Item	Quantity
5mm LED (through-hole)	5
1kΩ Resistor	5 (or 1 shared)
Jumper wires	Several
Breadboard	1

Each LED’s positive leg (anode) is connected to a different GPIO pin. Each LED is connected in series with a resistor, and the negative leg (cathode) goes to GND.

⚠️ You can use a single resistor for all LEDs if you multiplex carefully, but we recommend one resistor per LED for safety and clarity.

🧩 Using Your Extension Board

If you’re using your custom ESP32 extension board, simply plug the LEDs directly into the labeled GPIO ports like this:

[D13] --> LED1 (anode)
[D12] --> LED2 (anode)
[D14] --> LED3 (anode)
[D27] --> LED4 (anode)
[D26] --> LED5 (anode)
Each LED cathode --> Resistor --> GND

✅ No breadboard required if your extension board exposes GPIO headers!
⚠️ Still remember to add resistors to limit current.

💻 Software: Program Design

We’ll walk through 3 variations of the running light effect:

🔹 1. Standard Running Light (One-way ON → OFF)

Each LED turns on one by one from left to right, then turns off in the same order.

// Define the GPIO pins connected to the 4 LEDs
int pin_list[4] = {13, 12, 14, 27};

// Calculate the number of LEDs using the array size
int size = sizeof(pin_list) / sizeof(pin_list[0]);

void setup() {
  // Set each pin in the list as OUTPUT
  for (int i = 0; i < size; i++) {
    pinMode(pin_list[i], OUTPUT);
  }
}

void loop() {
  // Turn on LEDs one by one from left to right
  for (int i = 0; i < size; i++) {
    digitalWrite(pin_list[i], HIGH);  // Set the pin HIGH to turn on LED
    delay(50);                         // Wait for 50 milliseconds
  }

  // Then turn them off one by one from left to right
  for (int i = 0; i < size; i++) {
    digitalWrite(pin_list[i], LOW);   // Set the pin LOW to turn off LED
    delay(50);                         // Wait before turning off next LED
  }
}

🔁 2. Back-and-Forth Running Light (ON → ← OFF)

Now we make the LEDs light up from left to right and then back from right to left, like a wave.

int pin_list[4] = {13, 12, 14, 27};
int size = sizeof(pin_list) / sizeof(pin_list[0]);

void setup() {
  for (int i = 0; i < size; i++) {
    pinMode(pin_list[i], OUTPUT);  // Initialize all LEDs as OUTPUT
  }
}

void loop() {
  // Turn on LEDs from left to right
  for (int i = 0; i < size; i++) {
    digitalWrite(pin_list[i], HIGH);
    delay(100);
  }

  // Then turn them off from right to left (reverse)
  for (int i = size - 1; i >= 0; i--) {
    digitalWrite(pin_list[i], LOW);
    delay(100);
  }
}

➡️ 3. Shifting Light (Single LED “Moving”)

This version creates a “moving dot” effect. Only one LED is on at any time, giving a clean shifting illusion.

int pin_list[4] = {13, 12, 14, 27};
int size = sizeof(pin_list) / sizeof(pin_list[0]);

void setup() {
  // Set all pins as OUTPUT
  for (int i = 0; i < size; i++) {
    pinMode(pin_list[i], OUTPUT);
  }
}

void loop() {
  for (int i = 0; i < size; i++) {
    // Turn on the current LED
    digitalWrite(pin_list[i], HIGH);

    // Turn off the previous LED
    if (i > 0) {
      digitalWrite(pin_list[i - 1], LOW);
    } else {
      // If it's the first LED, turn off the last one to complete the loop
      digitalWrite(pin_list[size - 1], LOW);
    }

    delay(250);  // Slower speed to visualize movement
  }
}