text: import RPi.GPIO as GPIO
  import time
  from AlphaBot2 import AlphaBot2
  
  TRIG = 22
  ECHO = 27
  
  Ab = AlphaBot2()
  
  GPIO.setmode(GPIO.BCM)
  GPIO.setwarnings(False)
  GPIO.setup(TRIG,GPIO.OUT,initial=GPIO.LOW)
  GPIO.setup(ECHO,GPIO.IN)
  
  def Distance():
  	GPIO.output(TRIG,GPIO.HIGH)
  	time.sleep(0.000015)
  	GPIO.output(TRIG,GPIO.LOW)
  	while not GPIO.input(ECHO):
  		pass
  	t1 = time.time()
  	while GPIO.input(ECHO):
  		pass
  	t2 = time.time()
  	return (t2-t1)*34000/2
  	
  print("Ultrasonic_Obstacle_Avoidance")
  try:
  	while True:
  		Dist = Distance()
  		print("Distance = %0.2f cm"%Dist)
  		if Dist <= 20:
  			Ab.right()
  #			Ab.left()
  		else:
  			Ab.forward()
  		time.sleep(0.02)
  
  except KeyboardInterrupt:
  	GPIO.cleanup();
  