import RPi.GPIO as GPIO
import time


led = 25
GPIO.setmode(GPIO.BCM)
 
GPIO_TRIGGER = 5
GPIO_ECHO = 6
 
GPIO.setup(GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(GPIO_ECHO, GPIO.IN)

GPIO.setup(led,GPIO.OUT)
GPIO.output(led,GPIO.LOW)

p1 = GPIO.PWM(led, 50) # GPIO PWM with 50Hz
p1.start(0) # Initialization
 
def distance():
    # set Trigger to HIGH
    GPIO.output(GPIO_TRIGGER, True)
 
    # set Trigger after 0.01ms to LOW
    time.sleep(0.00001)
    GPIO.output(GPIO_TRIGGER, 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 with the sonic speed (34300 cm/s)
    # and divide by 2, because there and back
    distance = (TimeElapsed * 34300) / 2
 
    return distance

print "CTRL+C = STOP program"
 
if __name__ == '__main__':
    try:
        while True:
            dist = distance()
            print ("Distance = %.1f cm" % dist)
            if dist > 100:
                dist = 100
            p1.ChangeDutyCycle(dist)
            time.sleep(0.1)

    except KeyboardInterrupt:
        GPIO.cleanup()  # must be executed before program stop