Raspberry Pi Cookbook

Chapter 11. Digital Inputs

11.0. Introduction

In this chapter, we look at recipes for using digital inputs, such as switches and keypads. This chapter also covers modules that have a digital output that can be connected to a Raspberry Pi input.

Most of the recipes require the use of a solderless breadboard and male-to-male jumper wires (see Recipe 8.10).

11.1. Connecting a Push Switch

Note

Be sure to check out the accompanying video for this recipe at http://razzpisampler.oreilly.com.

Problem

You want to connect a switch to your Raspberry Pi so that when you press it, some Python code is run.

Solution

Connect a switch to a GPIO pin and use the RPi.GPIO library in your Python program to detect the button press.

To make this recipe, you will need:

• Breadboard and jumper wires (see Prototyping Equipment)
• Tactile push switch (see Miscellaneous)

Figure 11-1 shows how to connect a tactile push switch, using a breadboard and jumper wires.

Figure 11-1. Connecting a push switch to a Raspberry Pi

Open an editor (nano or IDLE) and paste in the following code. As with all the program examples in this book, you can also download the program from the Code section of the Raspberry Pi Cookbook website, where it is called switch.py.

This example code displays a message when the button is pressed:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

GPIO.setup(18, GPIO.IN, pull_up_down=GPIO.PUD_UP)

while