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Raspberry Pi LED Blueprints

Chapter 1. Getting Started with LED Programming through Raspberry Pi GPIO

In this chapter, you will learn the basics of Raspberry Pi GPIO and LED development so that you can be sure that you have the basic required knowledge to develop LED programming through Raspberry Pi GPIO.

The following topics will be the major takeaways from this chapter:

Setting up Raspberry Pi
Introducing Raspberry Pi GPIO
Blinking LEDs
Turning an LED on/off using a push button
Changing color through an RGB LED

Introducing Raspberry Pi GPIO

General-purpose input/output (GPIO) is a generic pin on Raspberry Pi, which can be used to interact with external devices, such as sensor and actuator devices. You can see the Raspberry Pi GPIO pinouts in the following figure (source: http://www.element14.com/community/docs/DOC-73950/l/raspberry-pi-2-model-b-gpio-40-pin-block-pinout):

To access Raspberry Pi GPIO, we can use several GPIO libraries. If you are working with Python, Raspbian will have already installed the RPi.GPIO library to access Raspberry Pi GPIO. You can read more about RPi.GPIO at https://pypi.python.org/pypi/RPi.GPIO. You can verify the RPi.GPIO library from a Python terminal by importing the RPi.GPIO module, as shown in the following screenshot:

If you don't find this library on Python runtime or get the error message ImportError: No module named RPi.GPIO, you can install it by compiling from the source code. For instance, we want to install RPi.GPIO 0.5.11, so type the following commands:

wget https://pypi.python.org/packages/source/R/RPi.GPIO/RPi.GPIO-0.5.11.tar.gz
tar -xvzf RPi.GPIO-0.5.11.tar.gz
cd RPi.GPIO-0.5.11/
sudo python setup.py install

Tip

To install and update through the apt command, your Raspberry Pi must be connected to the Internet.

Another way to access Raspberry Pi GPIO is to use WiringPi. It is a library written in C for Raspberry Pi to access GPIO pins. You can read information about WiringPi from the official website http://wiringpi.com/.

To install WiringPi, you can type the following commands:

sudo apt-get update
sudo apt-get install git-core
git clone git://git.drogon.net/wiringPi
cd wiringPi
sudo ./build

Please make sure that your Pi network does not block the git protocol for git://git.dragon.net/wiringPi. This code can be browsed on https://git.drogon.net/?p=wiringPi;a=summary.

The next step is to install the WiringPi interface for Python, so you can access Raspberry Pi GPIO from a Python program. Type the following commands:

sudo apt-get install python-dev python-setuptools
git clone https://github.com/Gadgetoid/WiringPi2-Python.git
cd WiringPi2-Python
sudo python setup.py install

When finished, you can verify it by showing a GPIO map from the Raspberry Pi board using the GPIO tool:

gpio readall

If this is successful, you should see the GPIO map from the Raspberry Pi board on the terminal:

You can also see values in the wPi column, which will be used in the WiringPi program as GPIO value parameters. I will show you how to use it in the WiringPi library in the next section.

Blinking LEDs

In this section, we will build a simple app that interacts with Raspberry Pi GPIO. We will use three LEDs, which are attached to the Raspberry Pi 2 board. Furthermore, we will turn the LEDs on/off sequentially.

The following hardware components are needed:

Raspberry Pi 2.(you can change this model)
Three LEDs of any color
Three resistors (330 Ω or 220 Ω)

The hardware wiring can be implemented as follows:

LED 1 is connected to Pi GPIO18
LED 2 is connected to Pi GPIO23
LED 3 is connected to Pi GPIO24

The following image shows the hardware connection for LED blinking:

Now you can write a program using WiringPi with Python. The following is the complete Python code for blinking LEDs:

# ch01_01.py file

import wiringpi2 as wiringpi
import time

# initialize
wiringpi.wiringPiSetup()

# define GPIO mode
GPIO18 = 1
GPIO23 = 4
GPIO24 = 5
LOW = 0
HIGH = 1
OUTPUT = 1
wiringpi.pinMode(GPIO18, OUTPUT)
wiringpi.pinMode(GPIO23, OUTPUT)
wiringpi.pinMode(GPIO24, OUTPUT)


# make all LEDs off
def clear_all():
    wiringpi.digitalWrite(GPIO18, LOW)
    wiringpi.digitalWrite(GPIO23, LOW)
    wiringpi.digitalWrite(GPIO24, LOW)

# turn on LED sequentially
try:
    while 1:
        clear_all()
        print("turn on LED 1")
        wiringpi.digitalWrite(GPIO18, HIGH)
        time.sleep(2)
        clear_all()
        print("turn on LED 2")
        wiringpi.digitalWrite(GPIO23, HIGH)
        time.sleep(2)
        clear_all()
        print("turn on LED 3")
        wiringpi.digitalWrite(GPIO24, HIGH)
        time.sleep(2)

except KeyboardInterrupt:
    clear_all()

print("done")

Save this script in a file named Python ch01_01.py.

Moreover, you can run this file on the terminal. Type the following command:

sudo python ch01_01.py

You should see three LEDs blinking sequentially. To stop the program, you can press CTRL+C on the Pi terminal. The following is a sample of the program output:

Based on our wiring, we connect three LEDs to GPIO18, GPIO23, and GPIO24 from the Raspberry Pi board. You can see these WiringPi GPIO values from the gpio readall command and find GPIO18, GPIO23, and GPIO24 recognized as (the wPi column) 1, 4, and 5, respectively.

First, we initialize WiringPi using wiringpi.wiringPiSetup(). Then, we define our GPIO values and set their modes on Raspberry Pi as follows:

GPIO18 = 1
GPIO23 = 4
GPIO24 = 5
LOW = 0
HIGH = 1
OUTPUT = 1
wiringpi.pinMode(GPIO18, OUTPUT)
wiringpi.pinMode(GPIO23, OUTPUT)
wiringpi.pinMode(GPIO24, OUTPUT)

Each LED will be turned on using wiringpi.digitalWrite(). time.sleep(n) is used to hold the program for n seconds. Let's set a delay time of two seconds as follows:

clear_all()
print("turn on LED 1")
wiringpi.digitalWrite(GPIO18, HIGH)
time.sleep(2)

The clear_all() function is designed to turn off all LEDs:

def clear_all():
    wiringpi.digitalWrite(GPIO18, LOW)
    wiringpi.digitalWrite(GPIO23, LOW)
    wiringpi.digitalWrite(GPIO24, LOW)

Turning an LED on/off using a push button

In the previous section, we accessed Raspberry Pi GPIO to turn LEDs on/off by program. Now we will learn how to turn an LED on/off using a push button, which is used as a GPIO input from Raspberry Pi GPIO.

The following hardware components are needed:

A Raspberry Pi 2 board
An LED
A push button (https://www.sparkfun.com/products/97)
1 KΩ resistor

You can see the push button connection in the following figure:

Turning an LED on/off using a push button

Our hardware wiring is simple. You simply connect the LED to GPIO23 from Raspberry Pi. The push button is connected to Raspberry Pi GPIO on GPIO24. The complete hardware wiring can be seen in the following figure:

Furthermore, you can write a Python program to read the push button's state. If you press the push button, the program will turn on the LED. Otherwise, it will turn off the LED. This is our program scenario.

The following is the complete code for the Python program:

# ch01_02.py file

import wiringpi2 as wiringpi

# initialize
wiringpi.wiringPiSetup()

# define GPIO mode
GPIO23 = 4
GPIO24 = 5
LOW = 0
HIGH = 1
OUTPUT = 1
INPUT = 0
PULL_DOWN = 1
wiringpi.pinMode(GPIO23, OUTPUT)  # LED
wiringpi.pinMode(GPIO24, INPUT)  # push button
wiringpi.pullUpDnControl(GPIO24, PULL_DOWN)  # pull down


# make all LEDs off
def clear_all():
    wiringpi.digitalWrite(GPIO23, LOW)

try:
    clear_all()
    while 1:
        button_state = wiringpi.digitalRead(GPIO24)
        print button_state
        if button_state == 1:
            wiringpi.digitalWrite(GPIO23, HIGH)
        else:
            wiringpi.digitalWrite(GPIO23, LOW)

        wiringpi.delay(20)

except KeyboardInterrupt:
    clear_all()

print("done")

Save this code in a file named ch01_02.py.

Now you can run this program via the terminal:

$ sudo python ch01_02.py

After this, you can check by pressing the push button; you should see the LED lighting up.

First, we define our Raspberry Pi GPIO's usage. We also declare our GPIO input to be set as pull down. This means that if the push button is pressed, it will return value 1.

GPIO23 = 4
GPIO24 = 5
LOW = 0
HIGH = 1
OUTPUT = 1
INPUT = 0
PULL_DOWN = 1
wiringpi.pinMode(GPIO23, OUTPUT)  # LED
wiringpi.pinMode(GPIO24, INPUT)  # push button
wiringpi.pullUpDnControl(GPIO24, PULL_DOWN)  # pull down

We can read the push button's state using the digitalRead() function from WiringPi as follows:

button_state = wiringpi.digitalRead(GPIO24)

If the push button is pressed, we turn on the LED; otherwise, we turn it off:

print button_state
if button_state == 1:
    wiringpi.digitalWrite(GPIO23, HIGH)
else:
    wiringpi.digitalWrite(GPIO23, LOW)

Changing color through an RGB LED

The last demo of basic LED programming is to work with an RGB LED. This LED can emit monochromatic light, which could be one of the three primary colors—red, green, and blue, known as RGB.

The RGB LED connection is shown in the following figure:

In this section, we will build a simple program to display red, green, and blue colors through the RGB LED.

The following hardware components are needed:

A Raspberry Pi 2 board
An RGB LED (https://www.sparkfun.com/products/9264).

Our hardware wiring can be implemented as follows:

RGB LED pin 1 is connected to Raspberry Pi GPIO18
RGB LED pin 2 is connected to Raspberry Pi VCC +3 V
RGB LED pin 3 is connected to Raspberry Pi GPIO23
RGB LED pin 4 is connected to Raspberry Pi GPIO24

The complete hardware wiring can be seen in the following figure:

Returning to the Raspberry Pi terminal, you could write a Python program to display color through RGB LED. Let's create a file named ch01_03.py and write this script as follows:

# ch01_03.py file

import wiringpi2 as wiringpi
import time

# initialize
wiringpi.wiringPiSetup()

# define GPIO mode
GPIO18 = 1  # red
GPIO23 = 4  # green
GPIO24 = 5  # blue
LOW = 0
HIGH = 1
OUTPUT = 1
wiringpi.pinMode(GPIO18, OUTPUT)
wiringpi.pinMode(GPIO23, OUTPUT)
wiringpi.pinMode(GPIO24, OUTPUT)


# make all LEDs off
def clear_all():
    wiringpi.digitalWrite(GPIO18, HIGH)
    wiringpi.digitalWrite(GPIO23, HIGH)
    wiringpi.digitalWrite(GPIO24, HIGH)


def display(red, green, blue):
    wiringpi.digitalWrite(GPIO18, red)
    wiringpi.digitalWrite(GPIO23, green)
    wiringpi.digitalWrite(GPIO24, blue)


try:
    while 1:
        clear_all()
        print("red")
        display(0, 1, 1)
        time.sleep(2)
        clear_all()
        print("green")
        display(1, 0, 1)
        time.sleep(2)
        clear_all()
        print("blue")
        display(1, 1, 0)
        time.sleep(2)
        clear_all()
        print("white")
        display(0, 0, 0)
        time.sleep(2)
        clear_all()
        print("110")
        display(1, 1, 0)
        time.sleep(2)
        clear_all()
        print("101")
        display(1, 0, 1)
        time.sleep(2)
        clear_all()
        print("011")
        display(0, 1, 1)
        time.sleep(2)

except KeyboardInterrupt:
    clear_all()

print("done")

Save this script. You can run this file by typing the following command:

$ sudo python ch01_03.py

Then, you should see that the RGB LED displays a certain color every second. The program output can also write a message indicating which color is currently on the RGB LED:

The RGB LED can display a color by combining three basic colors: red, green, and blue. First, we initialize Raspberry Pi GPIO and define our GPIO usage:

# initialize
wiringpi.wiringPiSetup()

# define GPIO mode
GPIO18 = 1  # red
GPIO23 = 4  # green
GPIO24 = 5  # blue
LOW = 0
HIGH = 1
OUTPUT = 1
wiringpi.pinMode(GPIO18, OUTPUT)
wiringpi.pinMode(GPIO23, OUTPUT)
wiringpi.pinMode(GPIO24, OUTPUT)

For instance, to set a red color, we should set LOW on the red pin and HIGH on both green and blue pins. We define the display() function to display a certain color on the RGB LED with the red, green, and blue values as parameters as follows:

def display(red, green, blue):
    wiringpi.digitalWrite(GPIO18, red)
    wiringpi.digitalWrite(GPIO23, green)
    wiringpi.digitalWrite(GPIO24, blue)

In the main program, we display a color via the display() function by passing red, green, and blue values, as shown in the following code:

clear_all()
print("red")
display(0, 1, 1)
time.sleep(2)
clear_all()
print("green")
display(1, 0, 1)
time.sleep(2)
clear_all()
print("blue")
display(1, 1, 0)
time.sleep(2)
clear_all()
print("white")
display(0, 0, 0)
time.sleep(2)
clear_all()
print("110")
display(1, 1, 0)
time.sleep(2)
clear_all()
print("101")
display(1, 0, 1)
time.sleep(2)
clear_all()
print("011")
display(0, 1, 1)
time.sleep(2)

Description

Blinking LED is a popular application when getting started in embedded development. By customizing and utilising LED-based modules into the Raspberry Pi board, exciting projects can be obtained. A countdown timer, a digital clock, a traffic light controller, and a remote light controller are a list of LED-based inspired project samples for Raspberry Pi. An LED is a simple actuator device that displays lighting and can be controlled easily from a Raspberry Pi. This book will provide you with the ability to control LEDs from Raspberry Pi, starting from describing an idea through designing and implementing several projects based on LEDs, such as, 7-segments, 4-digits 7 segment, and dot matrix displays. Beginning with step-by-step instructions on installation and configuration, this book can either be read from cover to cover or treated as an essential reference companion to your Raspberry Pi. Samples for the project application are provided such as a countdown timer, a digital clock, a traffic light controller, a remote light controller, and an LED-based Internet of Things, so you get more practice in the art of Raspberry Pi development. Raspberry Pi LED Blueprints is an essential reference guide full of practical solutions to help you build LED-based applications.

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Neeraj Sharma Oct 22, 2015

Very well documented step by step approach to understand Raspberry Pi and the its interaction with the real world examples. Enjoyed the detail oriented approach - a must have for beginners to intermediate use.

Amazon Verified review

Neal A Gordon Oct 21, 2015

Packt consistently creates well written, applicable books on electronics and programming with good examples. I have learned Linux personal computing and servers, python, and specific python modules with great detail from Packt.This book in particular is a great introduction to Linux with Raspberry Pi and electronics. The code examples and a pdf can be downloaded or viewed on their website. The examples are fun and useful and you will learn faster than learning from forums.Help support open source software by buying books from Packt!

Annette Herbst Oct 29, 2015

When I first saw the title of the book I thought by my self, why for god sake does someone publish a book on such a seemingly simple task on how to switch LEDs on and off with a Raspberry Pi (RPi). But curiosity won and I bought the book.Chapter 1 shortly introduces the raspberry and gives hints to install the required software. The first project starts already on page 7: It is (of course) a "Hello World project”: Three LEDs will blink, a GPIO will be read and several colors will be displayed using a RGB LED.Chapter 2 deals with 7-segment displays, shift registers and the design and implementation of a countdown timer.Chapter 3 describes a 4-digit-7-segment digital clock, introduces the I2C Bus and implements a digital clock using an OLED Graphic display.In Chapter 4 the author "plays" with an 8x8 LED dot matrix display in connection with the integrated circuit MAX7219.Chapter 5 describes a traffic light controller. In course of this project a channel relay module is introduced, a method is presented which allows the expansion of the number of GPIOs of the RPI. Finally, the author connects several integrated circuits of type MCP23017 to build a cascaded traffic light controller.Chapter 6 shows how to set up Bluetooth and establishing Bluetooth communication between a RPi und an Android Device in order to build a remote LED light controller.Chapter 7 is the most interesting part of the book because it deals with controlling LEDs via the Internet ("Internet of Things"). The chapter starts showing how to connect the RPI to a network (cable and WiFi), it then demonstrates how to implement Node.js on the RPi. After building a simple webserver using Node.js the author implements a RESTful system using Express for Node.js. He uses JSON to exchange data between the server and the client. Then he develops a program that allows the user to control LEDs connected to the RPi by a browser running on another (distant) computer. In the final part of this chapter the author develops an Android App by means of PhoneGap, a tool developed to build a cross-platform mobile app. This PhoneGap App combined with the above mentioned program enables the user to switch on 3 LEDs with his mobile Android device.To summarize:I don’t regret that I bought the book. It is well written and you don't have to be an EE-student to understand the technical content of chapter 1-6. The material presented in chapter 7 is quite ambitious for a newbie and it takes further reading of the given references to fully understand what’s going on.In order to really benefit from this book the reader should have some knowledge of Python, Java, Node.js, JSON etc. But even if he doesn't have prior knowledge, this book will provide him with well-documented "blueprints" which enables him to build the projects described therein himself. With minor changes he may use the blueprints to control other sensors or actuator.

Christoph Lipp Oct 27, 2015

I really liked the book. Reading through it was a breeze and following the example provided a lot of insight in gpio programming in python and with the raspberry in general. I'm looking forward to get a bigger led matrix panel and build a huge led clock :-DNext I'd like to try a few of the examples on the windows 10 iot core operating system, since working with visual studio and c# is also a lot of fun.

Philip Verhoeven Oct 24, 2015

I bought the e-book and I liked that the book goes (far) beyond the basics.The experiments are fun tot try (after reading this book, I look different at traffic lights :-)), but challenging and rewarding.In my opinion previous experience with the RaspberryPi is necessary.

Raspberry Pi LED Blueprints: Design, build, and test LED-based projects using the Raspberry Pi

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Raspberry Pi LED Blueprints

Chapter 1. Getting Started with LED Programming through Raspberry Pi GPIO

Setting up Raspberry Pi

Introducing Raspberry Pi GPIO

Tip

Blinking LEDs

Turning an LED on/off using a push button

Changing color through an RGB LED

Summary

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