说明：  本设计通过proteus仿真实现一量程自动转换的数字电压表，数码管显示，采用AT89C51、ADC0808、74HC4051、LM358N等器件，共有200mV、2V、20V、145V四档量程。
(This design by proteus simulation to achieve a range of automatic conversion of digital voltmeter, digital display, using AT89C51, ADC0808,74HC4051, LM358N and other devices, there are 200mV, 2V, 20V, 145V fourth gear range.)