One 、 Results the preview

Two 、 Implementation process

# -*- coding: utf-8 -*-
import RPi.GPIO as GPIO
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#  Use actual physical pins to GPIO mouth 
GPIO.setmode(GPIO.BOARD)
#  Set the pin to input mode , Pull up to high level (3.3V)
GPIO.setup(11, GPIO.IN, pull_up_down=GPIO.PUD_UP)  
​
# LED Pin settings 
#  Set up Pin The mode is output mode 
GPIO.setup(12, GPIO.OUT)  
#  Set up Pin The pin is low level (0V) close LED
GPIO.output(12, GPIO.LOW)  
#  Set the frequency to 2KHz
Led = GPIO.PWM(12, 2000)  
Led.start(0)
​
#  Infinite loop 
def loop():
    while True:
        if (0 == GPIO.input(11)):
            #  Appear barrier , Light up 
            Led.ChangeDutyCycle(100.0)
        else:
            #  Remove barriers , Turn off the lights 
            Led.start(0)
​
#  Program entrance 
if __name__ == '__main__':
    try:
        #  Infinite loop 
        loop()
        #  When pressed Ctrl+C when , Will perform destroy() Subroutines 
    except KeyboardInterrupt:
        #  Call to release resources 
        GPIO.cleanup()