[code python]
import RPi.GPIO as GPIO
 import time
 import threading 

GPIO.setmode(GPIO.BCM)
 
TRIG = 14
ECHO = 15
 
L = 24
 
TRIG_W = 23
ECHO_W = 18
 
distance1 = 0
distance2 = 0
 
a = 0
b = 0
c = 0
 
GPIO.setup(TRIG,GPIO.OUT)
GPIO.setup(ECHO,GPIO.IN)
GPIO.setup(TRIG_W,GPIO.OUT)
GPIO.setup(ECHO_W,GPIO.IN)
GPIO.setup(L,GPIO.OUT)
 
def ultrasonic1():
        try:
                        GPIO.output(TRIG, False)
                        time.sleep(1)
                 
                        GPIO.output(TRIG, True)
                        time.sleep(0.00001)
                        GPIO.output(TRIG, False)
                 
                        while GPIO.input(ECHO)==0:
                                pulse_start = time.time()
         
                        while GPIO.input(ECHO)==1:
                                pulse_end = time.time()
         
                        pulse_duration = pulse_end - pulse_start
               
                        global distance1       
                        distance1 = pulse_duration * 17150
         
                        distance1 = round(distance1, 2)
                 
                        print "Distance1:",distance1,"cm"
                        if distance1 < 20:
                                global a
                                a += 1
                        time.sleep(0.2)
        except KeyboardInterrupt:
                print "KeyboardInterrupt detected!"
                GPIO.cleanup()
def ultrasonic2():
        try:
                        GPIO.output(TRIG_W, False)
                        time.sleep(1)
 
                        GPIO.output(TRIG_W, True)
                        time.sleep(0.00001)
                        GPIO.output(TRIG_W, False)
 
                        while GPIO.input(ECHO_W)==0:
                                pulse_start = time.time()
         
                        while GPIO.input(ECHO_W)==1:
                                pulse_end = time.time()
         
                        pulse_duration = pulse_end - pulse_start
                        global distance2
                        distance2 = pulse_duration * 17150
 
                        distance2 = round(distance2, 2)
 
                        print "Distance2:",distance2,"cm"
                        if distance2 < 20:
                                global b
                                b += 1
                        time.sleep(0.2)
        except KeyboardInterrupt:
                print "KeyboardInterrupt detected!"
                GPIO.cleanup()
 
try:
        while True:
                e1 = threading.Event()
                e2 = threading.Event()
                t1 = threading.Thread(target=ultrasonic1)
                t2 = threading.Thread(target=ultrasonic2)
                t1.start()
                t2.start()
                if b > a:
                        c = 1
                elif a > b:
                        c = 0
                if c <= 0:
                        print "a = ", a, "b = ", b
                        print "c = ", c
                        print "turn off"
                        GPIO.output(L,GPIO.LOW)
                elif c >= 1:
                        print "a = ", a, "b = ", b
                        print "c = ", c
                        print "turn on"
                        GPIO.output(L,GPIO.HIGH)
                time.sleep(0.5)
except KeyboardInterrupt:
        print "KeyboardInterrupt detected!"
        t1.join()
        t2.join()
        GPIO.cleanup()[/code]