import threading
import RPi.GPIO as GPIO
import time

# The value used to hold the distance
global distance
distance = 0

#GPIO Mode (BOARD / BCM)
GPIO.setmode(GPIO.BCM)
 
#set GPIO Pins
GPIO_TRIG = 23
GPIO_ECHO = 24
 
#set GPIO direction (IN / OUT)
GPIO.setup(GPIO_TRIG, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)

class Sensor(threading.Thread):
 
    def __init__(self,interval):    
        self.inter = interval
        self.terminated = False
        self.start()

    def run(self):
        global distance
        while not self.terminated:
            # set Trigger to HIGH
            GPIO.output(GPIO_TRIG, True)
         
            # set Trigger to LOW after 0.01ms 
            time.sleep(0.00001)
            GPIO.output(GPIO_TRIG, False)
         
            StartTime = time.time()
            StopTime = time.time()
         
            # save StartTime
            while GPIO.input(GPIO_ECHO) == 0:
                StartTime = time.time()
         
            # save time of arrival
            while GPIO.input(GPIO_ECHO) == 1:
                StopTime = time.time()
         
            # time difference between start and arrival
            TimeElapsed = StopTime - StartTime
            # multiply by sonic speed (34300 cm/s)
            # and divide by 2, because there and back
            distance = (TimeElapsed * 34300) / 2
         
            time.sleep(self.inter)

SensorA = Sensor(1)

# Example bit of code to read the value from the thread
global distance
try:
    while True:
        print("Measured Distance = %.1f cm" % distance)
        time.sleep(1)
except KeyboardInterrupt:
    GPIO.cleanup()
    SensorA.terminated = True