说明：  此为电子开发中最常用的一种元器件，555定时器，文档中有报警，门铃，技数，触摸按键等功能，和555定时器常见的单稳态电路，震荡电路等。
(This is the electronic development of a kind of the most commonly used components, 555 timer, document in alarm, doorbell, technical data, touch keys and other functions, and 555 timer common monostable circuit, oscillating circuit.)