from machine import Pin, PWM
import time
led2 = PWM(Pin(2))
led2.freq(1000)
while True:
# 从不亮到，慢慢亮
for i in range(0,1024):
led2.duty(i)
time.sleep_ms(1)
for i in range (1023,-1):
led2.duty(i)
time.sleep_ms(1)
