Raspberry Pi A, User Manual, Page: 248 / 314

P A R T I V
H A R D W A R E H A C K I N G
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Save the file as
gpioinput.py
, and then execute it from the terminal with
sudo python
gpioinput.py
. At first, nothing will happen—but if you press the push-button switch, the
program will print the message from line seven to the terminal (see Figure 14-6). Release the
button and press it again, and the message will be repeated.
Figure 14-6:
The output
of the
gpioinput.
py
program
As with the previous input example, this is a deceptively simple program that can be used for
many purposes. In addition to being able to read when a switch is pressed, the same code can
be used to read when the pins of a separate device—such as a sensor or external microcon-
troller—have been pulled high or low.
By extending the code to look for multiple push-buttons, each on an individual GPIO pin, you
could even create a simple four-button game controller. For example, you could combine the
preceding code with the Raspberry Snake game from Chapter 12, “An Introduction to Python”,
to turn the Raspberry Pi into a simple games console. You can also combine both input and
output examples into a single program, which waits for the button to be pushed and then turns
on the LED by sending the output pin high. To ensure that you’ve understood the concepts in
this section, try creating that combined program now. If you get stuck, or you want to check
your method, turn to Appendix A, “Python Recipes”, for a sample solution.