Raspberry Pi A, User Manual, Page: 243 / 314

C H A P T E R 1 4
T H E G P I O P O R T
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The last line tells the GPIO library that Pin 11 on the Raspberry Pi’s GPIO port should be set
up as an output. If you were controlling additional devices, you could add more
GPIO.setup
lines into the project. For now, however, one will suffice.
With the pin configured as an output, you can switch its 3.3 V supply on and off in a simple
demonstration of binary logic. The instruction
GPIO.output(11, True)
will turn the pin
on, while
GPIO.output(11, False)
switches it off again. The pin will remember its last
state, so if you only give the command to turn the pin on and then exit your Python pro-
gram, the pin will remain on until told otherwise.
Although you could just add
GPIO.output(11, True)
to the Python project to switch the
pin on, it’s more interesting to make it blink. First, add the following line to create an infinite
loop in the program:
while True:
Next, add the following lines to switch the pin on, wait two seconds, and then switch it off
again before waiting another two seconds. Make sure each line starts with four spaces, to
signify that it is part of the infinite
while
loop:
GPIO.output(11, True)
time.sleep(2)
GPIO.output(11, False)
time.sleep(2)
The finished program should look like this (see Figure 14-4):
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.OUT)
while True:
GPIO.output(11, True)
time.sleep(2)
GPIO.output(11, False)
time.sleep(2)
Save the file as
gpiooutput.py
. If you’re using a Python development environment such
as SPE, don’t try to run the program from within the editor. Most Raspberry Pi Linux distri-
butions restrict the use of the GPIO port to the
root user, so the program will need to be run
using the command
sudo python gpiooutput.py
at the terminal to get it started. If all
has gone well, you should see the LED begin to blink on and off at regular intervals—and
you’ve created your first home-made output device for the Pi.