from machine import Pin, PWM
from time import sleep


led = PWM(Pin(15))

led.freq(100000)

while True:

    for duty in range(0, 100000, 500):
        led.duty_u16(duty)
        sleep(0.01)

    for duty in range(100000, 0, -500):
        led.duty_u16(duty)
        sleep(0.01)