🛎️ Node.js – LED + Pushbutton – Control GPIO Input & Output on Raspberry Pi

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🧲 Introduction – Why Combine LED with a Push Button?

Combining an LED and a pushbutton with Node.js on a Raspberry Pi allows you to build interactive hardware applications. From doorbells to voting machines, this simple project teaches you how to handle GPIO input (button) and output (LED) using the onoff library in Node.js.

🎯 In this guide, you’ll learn:

• How to wire an LED and button to Raspberry Pi GPIO
• Detect button press and control LED using Node.js
• Use GPIO input events (rising, falling)
• Handle cleanup and debounce for smooth interactions

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🔌 Hardware Required

🧰 Component	📋 Description
Raspberry Pi	Any model with GPIO header
LED (any color)	Visual indicator
330Ω Resistor	For LED current protection
Push Button Switch	Standard tactile switch
10kΩ Resistor	Pull-down resistor for stable signal
Breadboard + Jumper Wires	For easy prototyping

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🧾 Wiring Overview

🔋 LED Circuit

• GPIO 17 (Pin 11) → 330Ω Resistor → LED Anode (long leg)
• LED Cathode (short leg) → GND (Pin 6)

🔘 Button Circuit

• One leg of the button → GPIO 4 (Pin 7)
• Same leg → 10kΩ Resistor → GND (Pin 6)
• Other leg → 3.3V (Pin 1)

📌 The 10kΩ pull-down resistor ensures the input stays LOW when button is unpressed.

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📦 Install Required Library

npm install onoff

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💡 Node.js Code – LED with Push Button

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

// GPIO17 for LED (output), GPIO4 for Button (input with interrupt)
const led = new Gpio(17, 'out');
const button = new Gpio(4, 'in', 'rising', { debounceTimeout: 10 });

// Listen to button press
button.watch((err, value) => {
  if (err) {
    console.error('❌ Error:', err);
    return;
  }
  
  console.log('🔘 Button pressed!');
  led.writeSync(1); // Turn LED ON
  
  // Turn off LED after 500ms
  setTimeout(() => {
    led.writeSync(0);
  }, 500);
});

// Cleanup on exit
process.on('SIGINT', () => {
  led.writeSync(0);
  led.unexport();
  button.unexport();
  console.log('\n🧹 Clean GPIO and Exit.');
  process.exit();
});

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🧪 Output – What Happens

• Each button press turns the LED ON for 500ms.
• Output in terminal: 🔘 Button pressed!

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🧱 Best Practices for GPIO Input/Output

✅ Practice	💡 Why It’s Useful
Use debounceTimeout	Prevents multiple triggers from button bounce
Always unexport GPIOs on exit	Frees up pins and avoids lock issues
Test button logic with LEDs	Easy visual feedback for button state
Avoid floating GPIO input	Always use pull-down or pull-up resistors
Use rising, falling, or both	Choose based on action trigger (press/release)

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📌 Summary – Recap & Next Steps

By combining an LED and a button using Node.js on a Raspberry Pi, you learned how to respond to physical events using GPIO. This is the foundation of many real-world IoT and embedded system projects.

🔍 Key Takeaways:

• Use Gpio(pin, 'in', 'rising') to detect button press
• Use watch() to listen for GPIO changes asynchronously
• Combine GPIO input and output for interactive circuits
• Debounce input to avoid multiple unwanted triggers

⚙️ Real-world relevance:
Used in IoT dashboards, home automation, security systems, voting booths, and educational tools.

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❓FAQs – Node.js with Button & LED on Raspberry Pi

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❓ Why does the LED stay on sometimes?
✅ Make sure led.writeSync(0) is called after use. Also check wiring or remove debounce delay.

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❓ What does debounceTimeout do?
✅ It prevents repeated triggers caused by switch bouncing. A value like 10ms usually works well.

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❓ Can I detect button release too?
✅ Yes. Change the input mode to 'both' and check the value parameter (1 for press, 0 for release).

const button = new Gpio(4, 'in', 'both');

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❓ Can I use more than one button or LED?
✅ Absolutely! Just create more Gpio() instances with different pin numbers.

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❓ Do I need sudo to run this code?
✅ On some systems, GPIO access requires root. Run with sudo if you get permission errors:

sudo node led-button.js

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