import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18,GPIO.OUT)
pwm=GPIO.PWM(18,50)

print "starting"
pwm.start(40)
time.sleep(2)

pwm.ChangeDutyCycle(2)
time.sleep(.5)

pwm.ChangeDutyCycle(40)
time.sleep(2)

pwm.ChangeDutyCycle(2)
time.sleep(.5)

pwm.ChangeDutyCycle(40)
time.sleep(2)

print "done"
GPIO.cleanup()