from machine import Pin,PWM 
from time import sleep 

pwm=PWM (Pin(9))

pwm.freq(1000)

while True:
    for duty  in range(65535):
        pwm.duty_u16(duty)
        sleep(0.0001)
    sleep(0.5)
    for duty in range (65535,0,-1):
        pwm.duty_u16(duty)
        sleep(0.0001)
    sleep(0.5)