由于按键是通过一个4.7KΩ的电阻上拉到3.3V电压，因此当按键未按下时一直处于高电平，当按下时为低电平。在程序设计中可以检测低电平来判断是否有按键按下。-The button is a 4.7KΩ resistor pulled to 3.3V voltage, so when the button is not pressed, has been in high low when pressed. In the program design can detect low to determi