LED BLINK

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Introduction

In this tutorial, you’ll make a real LED blink using Arduino UNO or ESP32 in under 5 minutes.
This is the classic first project that teaches how software controls real hardware using digital output pins.

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What you’ll learn

• How digital output pins work
• How to safely connect an LED
• What pinMode() and digitalWrite() actually do
• How changing delays affects hardware behavior

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Components Needed

Component	Quantity	Purpose
Arduino UNO or ESP32	1	Runs the program
LED	1	Visual output
Resistor (220Ω)	1	Protects the LED from damage
Breadboard	1	Easy wiring without soldering
Jumper Wires	3–4	Connects everything

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Circuit & Schematic

The circuit diagram shows physical connections.
The schematic shows how electricity flows.

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Wiring Instructions

1. Insert the LED into the breadboard
2. Connect a 220Ω resistor to the long leg (anode) of the LED
3. Connect the other end of the resistor to digital pin 13
4. Connect the short leg (cathode) of the LED to GND
5. Plug your Arduino or ESP32 into your computer using USB

⚠️ Important

• If the LED is reversed, it won’t light up (this is safe)
• Never connect an LED directly to a pin without a resistor

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Arduino Code

This program turns the LED ON for 1 second and OFF for 1 second, repeatedly.

arduino-led-blink.ino

#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// ================= JOYSTICK =================
const int joyX = A0;
const int joyY = A1;
const int joyBtn = 2;

// ================= SNAKE ====================
const int gridSize = 4;
const int maxLength = 100;

int snakeX[maxLength], snakeY[maxLength];
int length = 3;

int dirX = 1, dirY = 0;
int nextDirX = 1, nextDirY = 0;

int foodX, foodY;

unsigned long lastMove = 0;
int speed = 150;

int score = 0;
bool gameRunning = true;

// ============== LONG PRESS ==================
unsigned long upPressedTime = 0;
bool upHeld = false;

unsigned long downPressedTime = 0;
bool downHeld = false;

const unsigned long holdDuration = 1500;

// ===========================================

void setup() {
  pinMode(joyBtn, INPUT_PULLUP);

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.display();

  showStartScreen();
  startGame();
}

void loop() {
  if (gameRunning) {
    handleInput();

    if (millis() - lastMove > speed) {
      lastMove = millis();

      // Apply direction ONCE per move (fix flicker)
      dirX = nextDirX;
      dirY = nextDirY;

      moveSnake();
      drawGame();
    }
  } else {
    showGameOverScreen();

    // Hold joystick button to restart
    if (digitalRead(joyBtn) == LOW) {
      if (!downHeld) {
        downPressedTime = millis();
        downHeld = true;
      } else if (millis() - downPressedTime > holdDuration) {
        startGame();
        gameRunning = true;
      }
    } else {
      downHeld = false;
    }
  }
}

// ===========================================

void showStartScreen() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(30, 20);
  display.print("Mini Snake");
  display.setCursor(12, 40);
  display.print("Press joystick");
  display.display();

  while (digitalRead(joyBtn) == HIGH) {
    // wait
  }

  delay(300);
}

void startGame() {
  length = 3;
  score = 0;

  dirX = 1;
  dirY = 0;
  nextDirX = 1;
  nextDirY = 0;

  gameRunning = true;

  for (int i = 0; i < length; i++) {
    snakeX[i] = 20 - i * gridSize;
    snakeY[i] = 20;
  }

  spawnFood();
}

// ===========================================

void handleInput() {
  int xVal = analogRead(joyX);
  int yVal = analogRead(joyY);

  const int deadLow = 350;
  const int deadHigh = 650;

  // ----- Direction selection (NO flicker) -----
  if (yVal < deadLow && dirY != 1) {
    nextDirX = 0;
    nextDirY = -1;
  }
  else if (yVal > deadHigh && dirY != -1) {
    nextDirX = 0;
    nextDirY = 1;
  }
  else if (xVal < deadLow && dirX != 1) {
    nextDirX = -1;
    nextDirY = 0;
  }
  else if (xVal > deadHigh && dirX != -1) {
    nextDirX = 1;
    nextDirY = 0;
  }

  // ----- HOLD UP to quit -----
  if (yVal < deadLow) {
    if (!upHeld) {
      upPressedTime = millis();
      upHeld = true;
    } else if (millis() - upPressedTime > holdDuration) {
      gameRunning = false;
    }
  } else {
    upHeld = false;
  }
}

// ===========================================

void moveSnake() {
  for (int i = length - 1; i > 0; i--) {
    snakeX[i] = snakeX[i - 1];
    snakeY[i] = snakeY[i - 1];
  }

  snakeX[0] += dirX * gridSize;
  snakeY[0] += dirY * gridSize;

  // Screen wrap
  if (snakeX[0] < 0) snakeX[0] = SCREEN_WIDTH - gridSize;
  if (snakeX[0] >= SCREEN_WIDTH) snakeX[0] = 0;
  if (snakeY[0] < 0) snakeY[0] = SCREEN_HEIGHT - gridSize;
  if (snakeY[0] >= SCREEN_HEIGHT) snakeY[0] = 0;

  // Self collision
  for (int i = 1; i < length; i++) {
    if (snakeX[0] == snakeX[i] && snakeY[0] == snakeY[i]) {
      length = 3;
      score = 0;
    }
  }

  // Eat food
  if (snakeX[0] == foodX && snakeY[0] == foodY) {
    if (length < maxLength) length++;
    score++;
    spawnFood();
  }
}

// ===========================================

void drawGame() {
  display.clearDisplay();

  // Food
  display.fillRect(foodX, foodY, gridSize, gridSize, SSD1306_WHITE);

  // Snake
  for (int i = 0; i < length; i++) {
    display.fillRect(snakeX[i], snakeY[i], gridSize, gridSize, SSD1306_WHITE);
  }

  // Score
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(84, 0);
  display.print("Score:");
  display.print(score);

  display.display();
}

// ===========================================

void spawnFood() {
  bool valid = false;
  while (!valid) {
    foodX = random(0, SCREEN_WIDTH / gridSize) * gridSize;
    foodY = random(0, SCREEN_HEIGHT / gridSize) * gridSize;
    valid = true;

    for (int i = 0; i < length; i++) {
      if (foodX == snakeX[i] && foodY == snakeY[i]) {
        valid = false;
        break;
      }
    }
  }
}

// ===========================================

void showGameOverScreen() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(10, 20);
  display.print("Player: Sanele");
  display.setCursor(10, 35);
  display.print("Final Score: ");
  display.print(score);
  display.setCursor(10, 50);
  display.print("Hold BTN restart");
  display.display();
}

How the code works

• pinMode(13, OUTPUT) tells the board that pin 13 will control an output device
• digitalWrite(13, HIGH) sends voltage to the LED and turns it ON
• delay(1000) pauses the program for 1 second (1000 milliseconds)

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Try This

Change the delay value in the code:

delay(200);

• What happens when you make it smaller?
• What happens when you make it larger?

This is how you start learning by experimenting.

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Common Problems

• LED not blinking → Check LED direction
• Nothing happens → Verify pin number and wiring
• Board not detected → Try a different USB cable

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🚀 What’s Next?

• Blink using a different pin
• Control LED using a button
• Learn smooth fading using PWM

🤖 Tip: Ask the AI assistant to modify this code for PWM or button control.

Notes

Add more images by copying one <figure> block and changing the file + caption.

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