from machine import Pin, PWM 
from time import sleep 

pwm = PWM(Pin(3))
 
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)