Question

我坚持使用Python和LED灯条。 LED灯条具有WS2801芯片并可通过SPI寻址，其排列方式如下：

     ----      ----      ----      ----
140 |    |    |    |    |    |    |    | 15
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
    |    |    |    |    |    |    |    |
155 |    |    |    |    |    |    |    | 0
          ----      ----      ----

每个破折号代表一个LED（一个像素）。一列中有16个像素，占8行。

编号从右下角开始。因此，最右边的列以索引0开始，以索引15结束。行之间的四个像素将不会被点亮。所以第二个最右边的列从顶部开始，索引20下降到底部，索引为35。最左边的列的范围从顶部的140到底部的155。

我想要做的是在播放时想象一首歌曲的频谱。较低的频率应显示在左列中，较高的频率显示在右列中。

我的代码基于PixelPi（https://github.com/scottjgibson/PixelPi）。我将FFT部分省略掉，因为那部分不是问题。

# Each pixel consumes 3 bytes
PIXEL_SIZE = 3 

# Lots of colors
BLACK = bytearray(b'\x00\x00\x00')
AQUA = bytearray(b'\x00\xff\xff')
AQUAMARINE = bytearray(b'\x7f\xff\xd4')

def filter_pixel(input_pixel, brightness):
    output_pixel = bytearray(PIXEL_SIZE)

    input_pixel[0] = int(brightness * input_pixel[0])
    input_pixel[1] = int(brightness * input_pixel[1])
    input_pixel[2] = int(brightness * input_pixel[2])

    output_pixel[0] = gamma[input_pixel[0]]
    output_pixel[1] = gamma[input_pixel[1]]
    output_pixel[2] = gamma[input_pixel[2]]
    return output_pixel

# Initialize LED strip matrix
height  = 16
base    = [155, 120, 115, 80, 75, 40, 35, 0]
# Do the indexes of this column go from bottom to top?
up      = [False, True, False, True, False, True, False, True]
color   = [NAVY, RED, MAROON, DARKBLUE, DARKCYAN, PALEGREEN, YELLOWGREEN, YELLOW]

# Output matrix, filled with black pixels
empty_output = bytearray(args.num_leds * PIXEL_SIZE + 3)
for led in range(args.num_leds):
    empty_output[led * PIXEL_SIZE:] = filter_pixel(BLACK, 1)

current_color = bytearray(PIXEL_SIZE)
corrected_color = bytearray(PIXEL_SIZE)

while True: # (Actually while song is playing)

    # Returns an array of length 8 with values between 0 and 4095
    matrix = calculate_levels(matrix, weighting, data, CHUNK_SIZE, sample_rate)

    # Copy the matrix with only black pixels. Copying seems to be faster than resetting all not needed pixels to black
    pixel_output[:] = empty_output


    for col in range(len(base)):
        current_color[:] = color[col][:]
            # Do some gamma correction
        corrected_color[:] = filter_pixel(current_color[:], 1)

            # Each column is 16 pixels high. The maximum value of the FFT to be returned for each column is 4095. 4096 / 256 = 16
        lighted_height = round(matrix[col]/float(1 << 8), 2)

        for row in range(max(16, int(lighted_height) + 1)):
            pixel_index = base[col] + row if up[col] == True else base[col] - row
            pixel_index = pixel_index * PIXEL_SIZE

            if (row < int(lighted_height)):
                # Pixel's brightness in 100%
                pixel_output[pixel_index:] = corrected_color[:]
            elif (row <= int(lighted_height) and row + 1 > int(lighted_height)):
                # Pixel's brightness is between 0 and 1
                pixel_output[pixel_index:] = filter_pixel(current_color[:], lighted_height - int(lighted_height))

            #print "[col:", col, ", row:", row, "] : ", pixel_index, "lighted_height:", lighted_height, "int(lighted_height)", int(lighted_height), "lighted:", lighted

            # As I uncomment these two lines, at least all pixels on the other columns are displayed.
            #spidev.write(pixel_output)
            #spidev.flush()

    spidev.write(pixel_output)
    spidev.flush()

问题是此代码仅点亮最右侧的列（0到15）。所有其他列似乎都是黑色的。

当我将spidev.write(pixel_output)和spidev.flush()放在col循环中，以便为每列写入pixel_output时，其他列中的至少一些灯会亮起。然而，它们以某种方式随机出现，声音不再平滑。

顺便说一句，LED条带在PixelPi示例中表现得很好，如褪色和追逐。可能这是由于我不知道的WS2801芯片的一些特性？或者我没有正确计算pixel_output矩阵？

更新：还有一件奇怪的事情：

i = 0
x = 0
while x < 160:
    if i != 0 and i % 16 == 0:
    x = x + 4

    pixel_index = x * PIXEL_SIZE
    pixel_output[pixel_index:] = filter_pixel(WHITE, 1)

    i = i + 1
    x = x + 1

    print "i, x", i, x

    time.sleep(0.1)
    spidev.write(pixel_output)
    spidev.flush()

这应该实际上将像素0点亮到最后一个并且在循环执行16次之后省略4个像素。但是，它不会遗漏像素，因此会在到达最后一个像素之前停止。

Answer 1

想出来了！

pixel_output[pixel_index:] = filter_pixel(WHITE, 1)

不仅复制了我预期的3个数组元素。它将filter_pixel返回的值从pixel_index复制到整个缓冲区。

设置复制的上限解决了我的问题。

pixel_output[pixel_index:(pixel_index + PIXEL_SIZE)] = filter_pixel(WHITE, 1)

使用Python和Raspberry Pi进行FFT的LED条带矩阵

1 个答案: