接着上一篇ESP8266-NodeMCU-闪灯实验的接线，我们调整一下代码，使LED灯的显示亮度发生变化。

参考代码

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from machine import Pin,Timer,PWM
pwm =PWM(Pin(14),100)     #create PWM object from a pin,and set frequency
polar = 0
duty = 0

def setLed(t):            #create a variate,and change it between 0 and 1008
  global duty,polar
  if(polar == 0):
    duty+=16
    if(duty >= 1008):
      polar = 1
  else:
    duty -= 16
    if(duty <= 0):
      polar = 0
  pwm.duty(duty)           #set duty of the PWM

tim = Timer(1)          #create Timer object from Virtual timers with timer ID=1
tim.init(period=10,mode=Timer.PERIODIC, callback=setLed)     #init Timer,Call the callback function with per second

try:                            #The catching
  while True:
    pass
except:                         #Capture anomaly, deinit Timer and PWM
  tim.deinit()
  pwm.deinit()