How to Control WS2818 LED Strips with Raspberry Pi

				
					#!/usr/bin/env python3
from rpi_ws281x import PixelStrip, Color
import time
import math
import signal
import sys

# === LED Strip Configuration ===
LED_COUNT = 100        # Number of LEDs
LED_PIN = 18           # GPIO pin (must support PWM)
LED_FREQ_HZ = 800000   # Signal frequency (Hz)
LED_DMA = 10           # DMA channel
LED_BRIGHTNESS = 150   # Brightness (0-255)
LED_INVERT = False     # Signal inversion
LED_CHANNEL = 0        # PWM channel

# Initialize LED strip
strip = PixelStrip(LED_COUNT, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL)
strip.begin()

# === Color Generation Functions ===
def wheel(pos):
    """Convert 0-255 value to rainbow color (red→green→blue cycle)"""
    pos = 255 - pos  # Reverse color direction (optional)
    if pos < 85:
        return Color(pos * 3, 255 - pos * 3, 0)
    elif pos < 170:
        pos -= 85
        return Color(255 - pos * 3, 0, pos * 3)
    else:
        pos -= 170
        return Color(0, pos * 3, 255 - pos * 3)

def smooth_wheel(pos):
    """Smoother rainbow transition (trigonometric version)"""
    r = int(255 * (0.5 + 0.5 * math.sin(pos * 0.0245)))
    g = int(255 * (0.5 + 0.5 * math.sin(pos * 0.0245 + 2.094)))  # +120°
    b = int(255 * (0.5 + 0.5 * math.sin(pos * 0.0245 + 4.188)))  # +240°
    return Color(r, g, b)

# === Main Effect Function ===
def rainbow_flow(speed_ms=20, smooth=True):
    """Rainbow chasing effect
    :param speed_ms: Base animation speed (milliseconds)
    :param smooth: Use smooth color transitions
    """
    step = 0
    try:
        while True:
            # Dynamic speed control (optional)
            dynamic_speed = speed_ms * (0.8 + 0.2 * math.sin(step * 0.01))
            
            for i in range(strip.numPixels()):
                # Calculate color hue (creates chasing effect)
                hue = int((i * 256 / strip.numPixels()) + step) % 256
                color = smooth_wheel(hue) if smooth else wheel(hue)
                strip.setPixelColor(i, color)
            
            strip.show()
            time.sleep(dynamic_speed / 1000.0)
            step += 1
    except KeyboardInterrupt:
        pass

# === Graceful Exit Handler ===
def signal_handler(sig, frame):
    print("\nTurning off LED strip...")
    for i in range(strip.numPixels()):
        strip.setPixelColor(i, Color(0, 0, 0))
    strip.show()
    sys.exit(0)

signal.signal(signal.SIGINT, signal_handler)

# === Main Program ===
if __name__ == '__main__':
    print("=== Rainbow Chasing Effect for LED Strip ===")
    print("Press Ctrl+C to exit")
    
    # Configuration parameters
    USE_SMOOTH_COLOR = True  # Enable smooth color transitions
    BASE_SPEED_MS = 15       # Base animation speed (milliseconds)
    
    rainbow_flow(speed_ms=BASE_SPEED_MS, smooth=USE_SMOOTH_COLOR)