树莓派科学小实验4B--05_跑马灯

小实验目录

树莓派科学小实验
001 点亮第一盏LED灯
002 点亮LED灯组
003_开关控制LED灯
004_获取温湿度
005_跑马灯（ws2812b））

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前言

由于未知的原因，在一阵青烟中，我的树莓派4B主板和接口板都报销了。 直到今天我才接到高价从京东购买的新板子（做硬件开发真的很费钱啊！）新年第一烧，希望今年能红红火火的！
长话短说，回归正题：这个实验依然从github上导入所需的库文件。
https://github.com/rpi-ws281x/rpi-ws281x-python

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提示：以下是本篇文章正文内容，下面案例可供参考

一、实验元件

带有8颗RGB灯珠的WS2812元器件板

GPIO扩展板一块 or 面包板一块

二、 ws2812b原理

这里是引用的2812原理说明，实际连接中使用3.3v的输出即可
大致的接线图如下：

VCC： 3.3v 从树莓派的3.3v供电GPIO接出
GND： 接在了树莓派的共地接口上
控制脚：接在了IO12上（这里是需要接在PWM脚上，因为后面我们需要调整频率）
每一个灯珠都是串联在一起的。从DI到DO 在VCC和GND间需要一个滤波电容（100MF）

对于ws2812b可以从github上下载现成的库，没有必要去重新底层应用，我们可以直接调用。

三、 代码部分：

1）导入并安装ws2812的库

sudo pip install rpi_ws281x

2）设定公共部分

中文标准的部分是需要根据实际需要修改的，其他的可改可不改

# LED strip configuration:
LED_COUNT = 8        # 设定灯珠的数量，我的灯珠只有8颗.
LED_PIN = 12          #设定控制脚连接的位置（我的是12脚，注意这里需要使用PWM，如果是10脚将需要使用SPI控制）  
LED_FREQ_HZ = 800000  # 设定PWM的频率（就是灯珠的频率，800KHZ）
LED_DMA = 10          # DMA channel to use for generating signal (try 10)
LED_BRIGHTNESS = 255  # Set to 0 for darkest and 255 for brightest
LED_INVERT = False    # True to invert the signal (when using NPN transistor level shift)
LED_CHANNEL = 0       # set to '1' for GPIOs 13, 19, 41, 45 or 53

3）定义一个函数用来点亮
color：RGB格式的颜色值。
strip：初始化后的灯组

def colorWipe(strip, color, wait_ms=50):
    """Wipe color across display a pixel at a time."""
    for i in range(strip.numPixels()):
        strip.setPixelColor(i, color)
        strip.show()
        time.sleep(wait_ms / 1000.0)

4）定义一个渐变色的函数

def rainbow(strip, wait_ms=20, iterations=1):
    """Draw rainbow that fades across all pixels at once."""
    for j in range(256 * iterations):
        for i in range(strip.numPixels()):
            strip.setPixelColor(i, wheel((i + j) & 255))
        strip.show()
        time.sleep(wait_ms / 1000.0)
def rainbowCycle(strip, wait_ms=20, iterations=5):
    """Draw rainbow that uniformly distributes itself across all pixels."""
    for j in range(256 * iterations):
        for i in range(strip.numPixels()):
            strip.setPixelColor(i, wheel(((i * 256 // strip.numPixels()) + j) & 255))
        strip.show()
        time.sleep(wait_ms / 1000.0)

5）定义一个跑马灯的函数

def theaterChaseRainbow(strip, wait_ms=50):
    """Rainbow movie theater light style chaser animation."""
    for j in range(256):
        for q in range(3):
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, wheel((i + j) % 255))
            strip.show()
            time.sleep(wait_ms / 1000.0)
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, 0)

完整的测试用例：

# NeoPixel library strandtest example
# Author: Tony DiCola ([email protected])
#
# Direct port of the Arduino NeoPixel library strandtest example.  Showcases
# various animations on a strip of NeoPixels.
import time

from rpi_ws281x import Color, PixelStrip, ws


# LED strip configuration:
LED_COUNT = 40         # Number of LED pixels.
LED_PIN = 18           # GPIO pin connected to the pixels (must support PWM!).
LED_FREQ_HZ = 800000   # LED signal frequency in hertz (usually 800khz)
LED_DMA = 10           # DMA channel to use for generating signal (try 10)
LED_BRIGHTNESS = 255   # Set to 0 for darkest and 255 for brightest
LED_INVERT = False     # True to invert the signal (when using NPN transistor level shift)
LED_CHANNEL = 0
LED_STRIP = ws.SK6812_STRIP_RGBW
# LED_STRIP = ws.SK6812W_STRIP


# Define functions which animate LEDs in various ways.
def colorWipe(strip, color, wait_ms=50):
    """Wipe color across display a pixel at a time."""
    for i in range(strip.numPixels()):
        strip.setPixelColor(i, color)
        strip.show()
        time.sleep(wait_ms / 1000.0)


def theaterChase(strip, color, wait_ms=50, iterations=10):
    """Movie theater light style chaser animation."""
    for j in range(iterations):
        for q in range(3):
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, color)
            strip.show()
            time.sleep(wait_ms / 1000.0)
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, 0)


def wheel(pos):
    """Generate rainbow colors across 0-255 positions."""
    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 rainbow(strip, wait_ms=20, iterations=1):
    """Draw rainbow that fades across all pixels at once."""
    for j in range(256 * iterations):
        for i in range(strip.numPixels()):
            strip.setPixelColor(i, wheel((i + j) & 255))
        strip.show()
        time.sleep(wait_ms / 1000.0)


def rainbowCycle(strip, wait_ms=20, iterations=5):
    """Draw rainbow that uniformly distributes itself across all pixels."""
    for j in range(256 * iterations):
        for i in range(strip.numPixels()):
            strip.setPixelColor(i, wheel(((i * 256 // strip.numPixels()) + j) & 255))
        strip.show()
        time.sleep(wait_ms / 1000.0)


def theaterChaseRainbow(strip, wait_ms=50):
    """Rainbow movie theater light style chaser animation."""
    for j in range(256):
        for q in range(3):
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, wheel((i + j) % 255))
            strip.show()
            time.sleep(wait_ms / 1000.0)
            for i in range(0, strip.numPixels(), 3):
                strip.setPixelColor(i + q, 0)


# Main program logic follows:
if __name__ == '__main__':
    # Create NeoPixel object with appropriate configuration.
    strip = PixelStrip(LED_COUNT, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL, LED_STRIP)
    # Intialize the library (must be called once before other functions).
    strip.begin()

    print('Press Ctrl-C to quit.')
    while True:
        # Color wipe animations.
        colorWipe(strip, Color(255, 0, 0))  # Red wipe
        colorWipe(strip, Color(0, 255, 0))  # Blue wipe
        colorWipe(strip, Color(0, 0, 255))  # Green wipe
        colorWipe(strip, Color(0, 0, 0, 255))  # White wipe
        colorWipe(strip, Color(255, 255, 255))  # Composite White wipe
        colorWipe(strip, Color(255, 255, 255, 255))  # Composite White + White LED wipe
        # Theater chase animations.
        theaterChase(strip, Color(127, 0, 0))  # Red theater chase
        theaterChase(strip, Color(0, 127, 0))  # Green theater chase
        theaterChase(strip, Color(0, 0, 127))  # Blue theater chase
        theaterChase(strip, Color(0, 0, 0, 127))  # White theater chase
        theaterChase(strip, Color(127, 127, 127, 0))  # Composite White theater chase
        theaterChase(strip, Color(127, 127, 127, 127))  # Composite White + White theater chase
        # Rainbow animations.
        rainbow(strip)
        rainbowCycle(strip)
        theaterChaseRainbow(strip)

效果：
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