MicroPython meteor light on a Pico’s LED bar, PWM

# A meteor: a bright head and a fading tail of PWM levels run along the
# LED bar graph and back. Every one of the ten pins has a PWM channel.
from machine import Pin, PWM
import time

pins = [16, 17, 18, 19, 20, 21, 22, 26, 27, 28]
leds = [PWM(Pin(n)) for n in pins]
for led in leds:
    led.freq(10000)

tail = [65535, 16384, 4096, 1024, 256]   # each step a quarter of the last

def draw(head, step):
    for n, led in enumerate(leds):
        behind = (head - n) * step       # how far n is behind the head
        led.duty_u16(tail[behind] if 0 <= behind < len(tail) else 0)

while True:
    for head in range(10 + len(tail)):
        draw(head, 1)
        time.sleep_ms(60)
    for head in range(9, -len(tail) - 1, -1):
        draw(head, -1)
        time.sleep_ms(60)
    print("meteor")