import RPIO, time

sonic_pin=17
stop=time.time()

# Shoot pulse
RPIO.setup(sonic_pin, RPIO.OUT, initial=RPIO.LOW)
time.sleep(0.5)
RPIO.output(sonic_pin, True)
time.sleep(0.00001)
RPIO.output(sonic_pin, False)

# Capture pulse
RPIO.setup(sonic_pin, RPIO.IN)

while RPIO.input(sonic_pin)==0:
        start = time.time()

while RPIO.input(sonic_pin)==1:
        stop = time.time()

# Calculate pulse length
elapsed = stop-start

# Calculate distance in cms.
distance = elapsed * 17000

print distance

# Reset GPIO settings
RPIO.cleanup()