import threading
import RPi.GPIO as GPIO
import time
 
#GPIO Mode (BOARD / BCM)
GPIO.setmode(GPIO.BCM)
 
class Sensor(threading.Thread):

    """ultrasonic sensor continous distance reading at given interval in seconds"""

    def __init__(self,interval, gpio_trig, gpio_echo):    
        super(Sensor, self).__init__()
        self.inter = interval
        self.trig = gpio_trig
        self.echo = gpio_echo 

        #set GPIO pins direction (IN / OUT)
        GPIO.setup(self.trig, GPIO.OUT)
        GPIO.setup(self.echo, GPIO.IN)

        self.dist = 0        
        self.terminated = False
        self.start()

    def run(self):
        while not self.terminated:
            # set Trigger to HIGH
            GPIO.output(self.trig, True)
      
            # set Trigger to LOW after 0.01ms 
            time.sleep(0.00001)
            GPIO.output(self.trig, False)
      
            StartTime = time.time()
            StopTime = time.time()
      
            # save StartTime
            while GPIO.input(self.echo) == 0:
                StartTime = time.time()
      
            # save time of arrival
            while GPIO.input(self.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
            self.dist = (TimeElapsed * 34300) / 2
          
            time.sleep(self.inter)

#Sensor object initiated with GPIO programmable pins 23 and 24
SensorA = Sensor(interval=.7, gpio_trig=23, gpio_echo=24)

try:
    while True:
        print("Measured Distance = %.1f cm" % SensorA.dist)
except KeyboardInterrupt:
    SensorA.terminated = True
    GPIO.cleanup()