if lucky, get a web page vs a data sheet.
- if unlucky, mostly works but doesn't.
- cross reference.

always check stupid stuff.
- wasted 5 minutes b/c unaligned jumper.

(1) Using IO trigger for at least 10us high level signal,

(2) Module automatically sends eight 40 kHz and detect
    whether there is a pulse signal back.  

(3) If the signal back, through high level , time of high output
    IO duration is the time from sending ultrasonic to returning.
    Test distance = (high level time×velocity of sound (340M/S) / 2,