import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

GPIO_TRIGGER = 18
GPIO_ECHO = 24

GPIO.setup(GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)

def distance():
    GPIO.output(GPIO_TRIGGER, True)
    time.sleep(0.00001)
    GPIO.output(GPIO_TRIGGER, False)

    StartTime = time.time()
    StopTime = time.time()

    while GPIO.input(GPIO_ECHO) == 0:
        StartTime = time.time()

    while GPIO.input(GPIO_ECHO) == 1:
        StopTime = time.time()

    TimeElapsed = StopTime - StartTime
    distance = (TimeElapsed*34300)/2

    return distance

if __name__ == '__main__':
    while True:
        dist = distance()
        print ("Measured Distance = %.1f cm" % dist)
        time.sleep(1)