from machine import Pin as pin, PWM as pwm
from time import sleep 

frequency = 5000
led = pwm(pin(14),frequency)

while True:
    for dc in range(0,1024,1):
        led.duty(dc)
        sleep(0.001)

    for dc in range(1023,0,-1):
        led.duty(dc)
        sleep(0.001)