频率的测量实际上就是在1s时间内对信号进行计数，计数值就是信号频率。用单片机设计频率计通常采用两种办法，第一种方法是使用单片机自带的计数器对输入脉冲进行计数；第二种方法是单片机外部使用计数器对脉冲信号进行计数，计数值再由单片机读取。-In the measurement of frequency is actually 1s to count time signal, numerical is signal frequency. Using single-chip microcomputer frequency plan by using two kinds of method, usually the first approach is to use own counter chip counting input pulses, The second method is to use external counter pulse signal count by MCU, numerical read again.