import RPi.GPIO as GPIO,time,os

GPIO.setmode(GPIO.BOARD)

TRIG=38
ECHO=40

GPIO.setup(TRIG,GPIO.OUT)
GPIO.setup(ECHO,GPIO.IN)

GPIO.output(TRIG,False)
time.sleep(2)

GPIO.output(TRIG,True)
time.sleep(0.00001)
GPIO.output(TRIG,False)

while GPIO.input(ECHO)==0:
    pulse_start=time.time()
while GPIO.input(ECHO)==1:
    pulse_end=time.time()

pulse_duration=pulse_end-pulse_start
distance = pulse_duration*17150
distance=round(distance,2)
print "Distance : ",distance," cm"