from machine import Pin,PWM
from time import sleep,sleep_ms

led=PWM(Pin(22))
led.freq(5000)

while True:
    for i in range(65535):
        led.duty_u16(i)
        sleep(0.0001)
    for i in range(65535, 0 , -1):
        led.duty_u16(i)
        sleep(0.0001)