Dotstar Light Strip Low Update Frequency

Question

I've built the start of a persistence of vision display. The rotation platform itself is built and I have just mounted the LEDs. After doing some testing, I can only get very slow update speeds of the lights themselves. I am using a very simple for loop in Python3 on a Raspberrypi 3B+ using GPIO 10 and 11 to control the strip. The strip is managed by the Adafruit Dotstar library and is controlled by the SPI bus. I choose this Light Strip as it is a clone of the APA102c and is ideal for Persistence of Vision displays. The code below works as design it will travel down the strip and update each LED but quite slowly. Could this be a limitation of the Pi's speed? I feel as if it would have more than enough power for a list update of this nature.

import board
import time
import adafruit_dotstar as dotstar

#Reversed Order
dots = dotstar.DotStar(board.MOSI, board.SCK, 72, brightness=.2)
#Default From Adafruit
#dots = dotstar.DotStar(board.SCK, board.MOSI, 72, brightness=.2)

n_dots = len(dots)
for dot in range(n_dots):
        dots[dot] = (0, 0, 0)
#time.sleep(1)
start = time.time()
for dot in range(n_dots):
        dots[dot] = (255, 255, 255)
end = time.time()
timetoloop = end-start

print ('Finished %.2f'%timetoloop + " Seconds")

Answer 1

I note your pins SCK and MOSI are the other way around from the adafruit examples which say

dots = dotstar.DotStar(board.SCK, board.MOSI, 30, brightness=0.2)

So it's possible that although you're using the SPI pins, the clock and data can't take advantage of the hardware transceiver. You might be forcing it to send the bits in software, which in Python, won't be very fast.

Try swapping the pins in hardware, and in your code, see if that's faster.