简易数字交流电压表，测出交流电压的峰峰值和平均值，并设置报警电压，设置独立键盘实现调整报警电压和采样周期的功能。-Simple digital AC voltmeter, measure the AC voltage peak-to-peak and average, and set the alarm voltage, set up a separate keyboard to adjust the alarm voltage and function of the sampling peri