极坐标系下的画图及其转换公式，特殊作图需要用到-Polar coordinates of the drawing and the conversion formula, need to use special drawing

DTMF是Dual Tone Multi Frequrency 的缩写，意为双音多频，广泛应用于电话机的拨号上.本文介绍使用单片机生成DTMF信号。-DTMF Dual Tone Multi Frequrency is the acronym meaning dual tone multi-frequency, widely used in telephone dial-up paper describes the use of S