说明：  软件A/D所能实现的精度有限，测量电压范围是2-15V， 而且速度低(约1KHz),但仅用一个电容和一个电阻的诱惑 力，我想大虾您会笑纳的。用于某些场合是有用的。
(Software A/D can achieve the accuracy is limited, measuring voltage range is 2-15V, and low-speed (approximately 1 KHz), but only a capacitance and resistance of a temptation, I think you will prawns to the heart. For certain occasions is useful.)