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 determine whether the button is pressed.