The working principle and the functions of the monostability multivibrator composed of 555 timer are introduced in the paper,and the time switches are designed.

• 介绍了用555定时器构成的单稳态触发器的工作原理,对其功能作了进一步探讨,在此基础上设计了一种具有实用价值的定时-非定时两用开关。