[Arduino] Arduino Timers and Interrupts

大家都推得這篇, 我倒是覺得這篇寫得比較好

reference:
* https://arduino-info.wikispaces.com/Timers-Arduino
* http://www.robotshop.com/letsmakerobots/arduino-101-timers-and-interrupts
* http://maxembedded.com/2011/07/avr-timers-ctc-mode/