User Guide

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5. On the Menu, click File and then click Save As.
6. Save the file to your folder, as doorbell.py.
7. Add the Python code below, and then save your
script again:
import RPi.GPIO
RPi.GPIO.setmode(RPi.GPIO.BCM)
RPi.GPIO.setup(2, RPi.GPIO.IN,
pull_up_down=RPi.GPIO.PUD_UP)
def Ring():
pass
while True:
if RPi.GPIO.input(2) == RPi.GPIO.LOW:
Ring()
This code detects a button press in the same way as described
in Chapter 7 – Controlling Input and Output Pins on page154. It
then calls the function Ring(), which does nothing yet.
To play a sound file from Python, you can use mpg321. This is a
command line tool for playing MP3 files on Raspbian, but you
can start it from a Python script. To install mpg321:
• In LXTerminal, type the following command and then
press Enter:
sudo apt-get install mpg321
Copy the sound effect .mp3 into your Doorbell folder.
Add the following import directive to the top of the script:
import os
Then in the Ring() function, remove the pass statement and add
the following code; replace the file name of the MP3 file if
necessary.
os.system("mpg321 ring.mp3")
The system() function in the os module runs command line tools
from Python scripts. To run the script: