from machine import Pin, PWM
from time import sleep

pwm = PWM(Pin(12))

pwm.freq(5000)

while True:
  for duty in range(65025):
    pwm.duty_u16(duty)
    sleep(0.0005)
  for duty in range(65025, 0, -1):
    pwm.duty_u16(duty)
    sleep(0.0005)