newleft_sensor.py

# Written and Debugged by: Vishal Venkateswaran and Shantanu Ghosh
import RPi.GPIO as GPIO
import time
while True:
	try:
		GPIO.setmode(GPIO.BOARD)
		#assign gpio pin numbers to trigger&echo
		PIN_TRIGGER = 13
		PIN_ECHO = 15

		#assign trigger&echo to proper gpio i/o status
		GPIO.setwarnings(False)
		GPIO.setup(PIN_TRIGGER, GPIO.OUT)
		GPIO.setup(PIN_ECHO, GPIO.IN)

		#set trigger to low
		GPIO.output(PIN_TRIGGER, GPIO.LOW)

		#sensor calibration/settle time
		time.sleep(1.4)

		#set trigger to high
		GPIO.output(PIN_TRIGGER, GPIO.HIGH)
		time.sleep(0.00001)
		GPIO.output(PIN_TRIGGER, GPIO.LOW)

		#condition to set start/stop time based on echo
		while GPIO.input(PIN_ECHO)==0:
			pulse_start_time = time.time()
		while GPIO.input(PIN_ECHO)==1:
			pulse_end_time = time.time()

		#calculate distance based on times. assume speed of sound to  be 17150 cm/s. round distance to 2 decimal places
		pulse_duration = pulse_end_time - pulse_start_time
		distance = round(pulse_duration * 17150, 2)

		#write distance to a file so the webpage can use the data from the sensors
		with open('leftsensor.txt', 'w') as num_file:
			num_file.write(str(distance))

	#allow keyboard interrupt to stop program
	except KeyboardInterrupt:
		print("Measurement stopped by User")
		GPIO.cleanup()
		break