from machine import Pin,PWM
import time

led=PWM(Pin(14),freq=1000)

while True:
    # 逐渐点亮
    for i in range(1024):
        led.duty(i)
        time.sleep_ms(1)
    # 逐渐熄灭
    for i in range(1023,0,-1):
        led.duty(i)
        time.sleep_ms(1)