'''
PIR 只能做動態偵測, 無法做靜態偵測。
設定 Pin 物件外部硬體中斷只要呼叫 irq() 方法, 並傳入 trigger 以及 callback 參數即可.
Pin.IRQ_LOW_LEVEL (LOW 觸發)
Pin.IRQ_HIGH_LEVEL (HIGH觸發)
Pin.IRQ_RISING  (上升緣都觸發)
Pin.IRQ_FALLING (下降緣都觸發)
handler is an optional function to be called when the interrupt triggers. 
The handler must take exactly one argument which is the Pin instance.
'''