#!/usr/bin/python

import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(12, 880)  # channel=12 frequency=50Hz
p.start(0)

for dc in range(0, 3):
 p.ChangeDutyCycle(50)
# p.ChangeFrequency(1000)
 time.sleep(0.15)
p.stop()
GPIO.cleanup()