from machine import Pin, PWM
from utime import sleep
freq = 5000
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.off()
    led.duty(duty_cycle)
    sleep(0.005)
  for duty_cycle in range(1024,0):
    led.duty(duty_cycle)
    sleep(0.005)
  for duty_cycle in range(0,1024):
    IN1.off()
    IN2.on()
    led.duty(duty_cycle)
    sleep(0.005)
  for duty_cycle in range(1024,0):
    led.duty(duty_cycle)
    sleep(0.005)