code.py

import RPi.GPIO as GPIO          
import time

GPIO.setwarnings(False)

in1=22   #pin15
in2=23   #pin16
in3=24   #pin18
in4=25   #pin22

PIN_TRIGGER = 4  #pin 7
PIN_ECHO = 17    #pin 11

GPIO.setmode(GPIO.BCM)

GPIO.setup(in1,GPIO.OUT)
GPIO.setup(in2,GPIO.OUT)
GPIO.setup(in3,GPIO.OUT)
GPIO.setup(in4,GPIO.OUT)
GPIO.setup(PIN_TRIGGER, GPIO.OUT)
GPIO.setup(PIN_ECHO, GPIO.IN)

def forward():
	GPIO.output(in1,GPIO.LOW)
	GPIO.output(in2,GPIO.HIGH)
	GPIO.output(in3,GPIO.LOW)
	GPIO.output(in4,GPIO.HIGH)

def back():
	GPIO.output(in1,GPIO.HIGH)
	GPIO.output(in2,GPIO.LOW)
	GPIO.output(in3,GPIO.HIGH)
	GPIO.output(in4,GPIO.LOW)
	
def stop():
	GPIO.output(in1,GPIO.LOW)
	GPIO.output(in2,GPIO.LOW)
	GPIO.output(in3,GPIO.LOW)
	GPIO.output(in4,GPIO.LOW)
	
def left():
	GPIO.output(in1,GPIO.LOW)
	GPIO.output(in2,GPIO.HIGH)
	GPIO.output(in3,GPIO.HIGH)
	GPIO.output(in4,GPIO.LOW)
	
def right():
	GPIO.output(in1,GPIO.HIGH)
	GPIO.output(in2,GPIO.LOW)
	GPIO.output(in3,GPIO.LOW)
	GPIO.output(in4,GPIO.HIGH)
	
def dist():
      GPIO.output(PIN_TRIGGER, GPIO.LOW)
      print ("Waiting for sensor to settle")
      time.sleep(0.5)
      print ("Calculating distance")
      GPIO.output(PIN_TRIGGER, GPIO.HIGH)
      time.sleep(0.00001)
      GPIO.output(PIN_TRIGGER, GPIO.LOW)
      while GPIO.input(PIN_ECHO)==0:
            pulse_start_time = time.time()
      while GPIO.input(PIN_ECHO)==1:
            pulse_end_time = time.time()

      pulse_duration = pulse_end_time - pulse_start_time
      distance = round(pulse_duration * 17150, 2)
      print ("Distance:",distance,"cm")
      return distance

forward()
Flag=True
while Flag:
	d=dist()
	if d<50:
		right()
		time.sleep(0.5)
		forward()
	if d<20:
		back()
		time.sleep(0.5)
		right()
	if d<10:
		Flag=False
		

stop()
GPIO.cleanup()