说明：  设计一个简单的数字电压表，输入电压范围0~2.5V，用4位数码管显示，精确到小数点后3位。
(A simple digital voltmeter is designed. The input voltage ranges from 0 to 2.5V. It is displayed with a 4-digit digital tube and is accurate to 3 digits after the decimal point.)