from machine import Pin, PWM
from utime import sleep

Freq = 5.000
led = PWM(pin(21), Freq)

IN1 = Pin (5, Pin.Out)
IN2 = Pin (18, Pin.Out)

  while True:
  For duty_cycle in range(0,1024):
  IN1.On()
  IN2.Of()
  led.duty (duty_cycle)
  sleep(0.005)

for duty_cycle in range (1024,0):
  led.duty(duty_cycle)
  sleep(0.005)