基于at89s52@12MHz的频率计，使用lm311比较器，手动切换量程，最大可检测1MHz频率，大约0.5 误差。使用lcd1602显示，界面友好。-Based on the of at89s52 @ 12MHz frequency counter, use the lm311 comparator, manual switching range, the maximum detectable frequency of 1MHz, about 0.5　error. Where use lcd1602 friendly interface.