from machine import Pin, PWM
from time import sleep

frequency = 1
led = PWM(Pin(13), frequency)
led.duty(512)
#while True:
#    for up_duty_cycle in range(0, 1024):
#        led.duty(up_duty_cycle)
#        sleep(0.05)
#    for down_duty_cycle in range(1023, 1, -1):
#        led.duty(down_duty_cycle)
#        sleep(0.05)
while True:
    pass