順便簡單說明Digital和Analog Signal,Arduino論壇有非常淺顯易懂的說明
Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means.
由定義和上圖我們可知道PWM和DAC是一家親的,藉由定義PWM(Digital Singal)的佔空比去轉換Analog值高低,反之亦然
附上原文網址
https://www.arduino.cc/en/Tutorial/PWM