通过压力传感器把大气压力转化为电信号，通过单片机模数转换，判断并提示示过压还是欠压-Through the pressure sensor to atmospheric pressure into electrical signals through the microcontroller analog-digital conversion, judge and prompt show overvoltage or undervoltage

双电源转换开关自动转换程序，能实现断相检测过压，欠压检测-Dual power switch automatic conversion process, to achieve the Phase-cut overvoltage, undervoltage detection