🎇 Node.js – Flowing LEDs – Create LED Chaser Effect with Raspberry Pi & Node.js

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🧲 Introduction – What Is a Flowing LED (Chaser)?

A Flowing LED, also called an LED Chaser, is a classic electronics project where LEDs light up one after another in a sequence, creating a “flow” or “running” light effect. Using Node.js and Raspberry Pi GPIO, you can programmatically control this flow, giving your project a futuristic or dynamic look.

🎯 In this guide, you’ll learn:

• How to wire multiple LEDs to Raspberry Pi GPIO
• Use Node.js and the onoff library to sequence LEDs
• Create loop logic for left-to-right and reverse chasing
• Add timing, effects, and cleanup logic

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🔌 Hardware Required

🧰 Component	📋 Description
Raspberry Pi	Any model with GPIO support
4–6 LEDs	Red, green, blue, etc.
330Ω Resistors	One per LED to prevent overcurrent
Breadboard	For connecting components
Jumper Wires	Male-to-male wires

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🧾 Wiring Overview (Example with 4 LEDs)

• LED1 → GPIO 17 (Pin 11)
• LED2 → GPIO 18 (Pin 12)
• LED3 → GPIO 27 (Pin 13)
• LED4 → GPIO 22 (Pin 15)
• Each LED’s anode goes through a 330Ω resistor to GND (Pin 6)

🛠️ Use pinout.xyz to check GPIO layout.

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📦 Install Required Package

npm install onoff

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🎇 Node.js Code – Flowing LEDs

const Gpio = require('onoff').Gpio;

// Define GPIO pins for each LED
const ledPins = [17, 18, 27, 22];
const leds = ledPins.map(pin => new Gpio(pin, 'out'));

let current = 0;
let direction = 1;

// Flow function
const interval = setInterval(() => {
  // Turn all LEDs off
  leds.forEach(led => led.writeSync(0));

  // Turn current LED ON
  leds[current].writeSync(1);

  // Move to next LED
  current += direction;

  // Reverse direction at ends
  if (current === leds.length || current < 0) {
    direction *= -1;
    current += direction;
  }
}, 200); // 200ms per step

// Cleanup on exit
process.on('SIGINT', () => {
  clearInterval(interval);
  leds.forEach(led => {
    led.writeSync(0);
    led.unexport();
  });
  console.log('\n🧹 Cleaned up and exiting...');
  process.exit();
});

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🧪 Output – What You’ll See

• LEDs light up one after another:
  LED1 → LED2 → LED3 → LED4 → LED3 → LED2 → …
• Repeats continuously until the process is stopped.

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🧱 Best Practices for Flowing LED Projects

✅ Practice	💡 Why It’s Useful
Use writeSync(0) before each step	Ensures only one LED is ON at a time
Clean up GPIO with unexport()	Prevents pin locking on reruns
Use SIGINT handling	Gracefully stop script with Ctrl+C
Modularize LED flow logic	Makes it reusable for other effects
Use setTimeout() or setInterval()	Time control for animations

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📌 Summary – Recap & Next Steps

Creating flowing LEDs with Node.js is a fun and visual way to learn GPIO programming. You control the timing, direction, and animation entirely with JavaScript—making it a great bridge between frontend logic and embedded control.

🔍 Key Takeaways:

• Use onoff to control GPIO pins via JavaScript
• Create flowing/chaser effects using intervals and loops
• Clean up with unexport() to prevent errors
• Reverse direction with logic for back-and-forth animation

⚙️ Real-world relevance:
Used in status displays, vehicle lighting effects, wearables, interactive art, and IoT dashboards.

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❓FAQs – Node.js Flowing LEDs

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❓ Can I use more than 4 LEDs?
✅ Yes! Just expand the ledPins array:

const ledPins = [17, 18, 27, 22, 23, 24];

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❓ How can I reverse the flow direction manually?
✅ Add a button input on another GPIO pin and toggle direction *= -1 on press.

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❓ Why do LEDs stay ON after the script ends?
❌ If you don’t run unexport(), the GPIO stays active. Use cleanup logic on SIGINT.

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❓ Can I slow down the blinking?
✅ Yes. Increase the interval from 200ms to 500ms, for example.

setInterval(..., 500);

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❓ Do I need root permissions to run this script?
✅ Sometimes. If you get a permissions error, use:

sudo node flowing-leds.js

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