树梅派（十）：超声波传感器用于测量距离

    #from __future__ import print_function
    import time
    import RPi.GPIO as GPIO
    
    # Use BCM GPIO references
    # instead of physical pin numbers
    GPIO.setmode(GPIO.BCM)
    
    # Define GPIO to use on Pi
    GPIO_TRIGGER = 23
    GPIO_ECHO    = 24
    
    # Speed of sound in cm/s at temperature
    temperature = 20
    speedSound = 33100 + (0.6*temperature)
    
    print("Ultrasonic Measurement")
    print("Speed of sound is",speedSound/100,"m/s at ",temperature,"deg")
    
    # Set pins as output and input
    GPIO.setup(GPIO_TRIGGER,GPIO.OUT)  # Trigger
    GPIO.set