用於Python和Raspberry Pi的FFT的LED條形矩陣

Question

我被Python和LED燈條卡住了。 具有WS2801芯片且可通過SPI尋址的LED燈帶已安排為如下矩陣：

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

每個破折號代表一個LED（一個像素）。 一列有16個像素，組成8行。

從右下角開始編號。 因此，最右邊的列從索引0開始，到索引15結束。行之間的四個像素不會點亮。 因此，第二最右邊的列從索引為20的頂部向下到索引為35的底部。最左邊的列的范圍從頂部的140到底部的155。

我要做的是在播放歌曲時可視化其頻譜。 較低的頻率應顯示在左列中，較高的頻率應顯示在右列中。

我的代碼基於PixelPi（ https://github.com/scottjgibson/PixelPi ）。 我忽略了FFT，因為那不是問題。

# 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()

問題在於此代碼僅點亮最右邊的列（0到15）。 所有其他列似乎都是黑色的。

當我在col循環中放置spidev.write(pixel_output)和spidev.flush()以便為每一列寫入pixel_output時，至少其他列中的某些燈會亮起。 但是，它們以某種方式隨機出現，並且聲音不再平滑。

順便說一下，LED燈條在PixelPi實例（例如褪色和追趕）中表現不錯。 可能是由於我不知道的WS2801芯片的某些特性嗎？ 還是我沒有正確計算pixel_output矩陣？

更新 ：另外一件奇怪的事情：

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()

實際上，這應該將像素0點亮到最后一個像素，並在執行16次循環后遺漏4個像素。 但是，它不會遺漏一個像素，因此會在到達最后一個像素之前停止。

Answer 1

弄清楚了！

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

不僅復制了3個數組元素，而且符合我的預期。 它將filter_pixel返回的值從整個緩沖區的pixel_index復制到末尾。

設置復制上限解決了我的問題。

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