from machine import Pin,PWM
from time import sleep
frequency=4000 
led=PWM(Pin(5),frequency)
while True:
    for duty_cycle in range(0,1024,1):
        led.duty(duty_cycle)
        print(duty_cycle)
        sleep(0.0005)
    for duty_cycle in range(1023,-1,-1):
        led.duty(duty_cycle)
        print(duty_cycle)
        sleep(0.0005)