用74系列数字器件设计一个频率计。要求： ① 用4位7段数码管显示待测频率，格式为0000Hz。 ② 测量频率范围：10~9999Hz。 ③ 测量信号类型：正弦波、方波和三角波。 ④ 测量信号幅值：0.5~5V。 ⑤ 设计的脉冲信号发生器，以此产生闸门信号，闸门信号宽度为1S。 -74 series of digital devices designed to use a frequency counter. Requirements: ① with four 7-seg

Universal timer and counter build with three seven-segment digits and three buttons for control of operation.

GM计数管电路，集成升压电路，采样电路，波型处理-GM counter circuit, the integrated boost circuit, sampling circuit, waveform processing