Learning BeagleBone Python Programming

By Alexander Hiam
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About this book

BeagleBone is a barebone computer that can be configured and customized for different applications and is almost half the price of a standard computer. This book will cover the basics of how BeagleBone Black's hardware interface subsystems work, and can be controlled using two popular Python libraries for BeagleBone Black. You will be introduced to BeagleBone Black's GPIO, PWM, ADC, UART, SPI, I2C, and eQEP subsystems. We will then dive deep into more complex built-in peripherals, demonstrating different ways to receive input from a user including buttons, potentiometers, and rotary encoders with the eQEP module. We will also learn about interfacing with external devices; this will be demonstrated using the serial modules to interface with external devices such as temperature sensors and accelerometers. Towards the end of the book, we will present a couple of real-world problems and demonstrate how to solve them with the skills you've acquired.

Publication date:
July 2015
Publisher
Packt
Pages
196
ISBN
9781784399702

 

Chapter 1. Before We Begin

Before we start hooking up hardware and writing code, we'll need to have an understanding of what we're working with. This chapter will introduce you to the BeagleBone and highlight the various interfaces it provides to connect to external devices. It will cover:

  • An overview of the BeagleBone system

  • An overview of the BeagleBone's peripheral interfaces, and what types of external devices each can connect to

  • Some additional hardware and tools that you will need if you want to duplicate the examples given throughout the book, and where you can buy them

 

An overview of BeagleBone


The BeagleBone boards are a series of small, powerful, and affordable Linux computers that are perfect for embedded applications such as home automation, robotics, industrial control, and much more. They are designed by BeagleBoard.org (http://beagleboard.org/) and are fully open source. They are based on the Texas Instruments AM335x 1GHz ARM Cortex-A8 series of microprocessors, and can run a number of different operating systems, including various GNU/Linux distributions, Android, and even Windows Embedded CE. The current BeagleBone model being produced is the BeagleBone Black rev C, which ships with a Debian GNU/Linux distribution. Therefore, this book will focus on using Debian on the BeagleBone Black, though much of the information given will apply to other BeagleBone models and Linux distributions as well.

The following screenshot shows the BeagleBone board:

The BeagleBone Black's AM335x microprocessor contains a number of built-in peripheral interface subsystems, enabling it to accept and generate many different forms of inputs and outputs. The BeagleBone Black includes two 2 x 23 pin rows of female header pins, giving a total of 92 connection points for hardware expansion using the processor's peripheral interface subsystems.

General purpose input/output

The general purpose input/output (GPIO) module handles all the digital input and output. In this context, digital refers to the fact that the signals are binary; they are either 1 or 0, represented by fully on and fully off respectively. In the case of the AM335x, the fully-on level is 3.3V, and the fully-off level is 0V. The GPIO module is used for inputs such as switches and buttons, which are either on or off. Its outputs can be used to control devices, such as LEDs, buzzers, and relays.

Analog-to-digital converter

The analog-to-digital converter (ADC) module is used to measure analog voltages. The AM335x ADC can only measure voltages between 0V and 1.8V (and voltages outside this range may damage your BeagleBone), but, in later chapters, you will learn how to divide larger voltages to be within this range. The ADC can be used to receive inputs from devices such as potentiometers, which can be used to create varying voltages, measure the voltage output of analog sensors for temperature, light, sound, and different types of gases, and with some additional external components it can be used to measure electrical current.

 

Pulse width modulation


The pulse width modulation (PWM) module is essentially used to generate a square wave signal at a fixed frequency, and then vary its duty cycle. It gives us the ability to accurately generate pulses of a configured duration, repeating at a configured frequency. Like the GPIO module, the PWM module on the BeagleBone Black operates at 3.3V. These PWM signals can be used to control servo motors, vary the speed of DC motors and the brightness of LEDs, and with some additional external components they can be used to generate varying voltages.

Universal asynchronous receiver/transmitter

The universal asynchronous receiver/transmitter (UART) modules are used to transmit and receive RS-232 style serial signals, which is an industry standard for serializing and transferring information between two devices using a pair of unidirectional digital signals. They can be used to communicate with PCs, Bluetooth and Wi-Fi radio modules, and GPS receivers. The BeagleBone Black's UART modules also operate at 3.3V.

Serial peripheral interface

The serial peripheral interface (SPI) module is used to communicate over SPI, which is another industry standard serial protocol. Whereas UARTs are generally used to connect two devices, SPI is made to connect one master device to one or many slave devices. It is commonly used on devices such as small character and graphics LCD screens, external ADCs, and DACs (Digital-to-Analog converters), as well as on many different types of sensor. The BeagleBone Black's SPI modules operate at 3.3V as well.

Inter-Integrated Circuit

Inter-Integrated Circuit (I2C) is yet another industry standard serial protocol. It also allows a master device to communicate with a bus of many slave devices, but it requires fewer pins than SPI. It is commonly used by real-time clocks (RTCs), as well as in many types of sensors, including Micro-Electro-Mechanical Systems (MEMS) devices, such as accelerometers, magnetometers, and gyroscopes. The BeagleBone's I2C modules operate at 3.3V.

 

Tools and additional hardware


The majority of the demo programs in this book use external hardware that must be purchased separately. Each time a demo program is given, which requires additional parts, they will be listed by part number and/or description. We will do our best to use the most readily available and lowest cost parts. All of the parts used can be purchased from one or more of the following resources:

The circuits in each demo will be assembled using solderless breadboard and jumper wires. Both come in many different shapes and sizes.

Breadboards and jumper wires can be purchased from any of the preceding links, and you'll probably want to start out with one standard-sized breadboard and a jumper wire kit, such as that from Adafruit:

That should provide enough breadboard space and jumper wires to assemble most, if not all, of the demo circuits in this book.

Just like with software, it is inevitable when assembling hardware that things won't always work the first time. There are many tools that can greatly reduce the time it takes to fix these problems. The most useful for the circuits in this book will be a multimeter, which is a tool that measures voltage and current, and often additional properties such as resistance, capacitance, and frequency. Both SparkFun and Adafruit carry very affordable digital multimeters. While these are not high quality measurement tools, they are certainly suitable for these circuits. Though not essential, I would highly recommend having some sort of multimeter on hand when building the circuits in this book.

More helpful than a multimeter for debugging tools such as PWM and serial protocols is an oscilloscope, which shows you a plot of voltage over time to visualize many different signals in a circuit. This is a more expensive tool, and will be less necessary for these circuits. Throughout the book, however, you will see screen captures of an oscilloscope to show various signals, and it should become evident just how helpful they can be. Again, Adafruit and SparkFun carry affordable oscilloscopes.

 

The BeagleBone design


The BeagleBone was designed with prototyping in mind. If its shape and size look familiar to you, it's probably because the board was designed to fit inside an Altoids tin, which is great for both transportation and making custom enclosures. All of the expansion pins are broken out on to two female headers with a 2.54 mm pin pitch, which is one of the most commonly used spacings in the hobby and DIY world, and mating male header pins can easily be soldered by hand to add-on boards or wires. The board can be powered through USB or with a standard DC barrel jack, and power can also be supplied through the expansion headers.

 

Board comparison


There are a number of low-cost single-board GNU/Linux computers on the market these days, so let's take a look at how the BeagleBone Black stacks up against a couple of its most popular competitors.

 

BeagleBone Black

Intel Edison

Raspberry Pi 2 B

CPU

1 GHz single-core ARM Cortex-A8

500 MHz dual-core Intel Atom

900 MHz quad-core ARM Cortex-A7

Flash

4 GB eMMC, expandable with uSD

4 GB eMMC

uSD card

RAM

512 MB

1 GB

1 GB

Video

microHDMI

N/A

HDMI, Composite

Network

10/100 Mbit Ethernet

Dual-band a/b/g/n Wi-Fi, Bluetooth 4.0

10/100 Mbit Ethernet

GPIO pins

65

20

40

ADC channels

7

6

N/A

PWM channels

8

4

2

UARTs

4

1

1

SPI ports

2

1

1

I2C ports

2

1

2

Coprocessor

2x 200 MHz 32-bit PRU microcontrollers

100 MHz 32-bit Intel Quark

N/A

Price (USD)

$49

$49.95

$39.95

The BeagleBone Black offers great performance and far more hardware expansion capabilities at about the same cost as the Edison and Raspberry Pi 2 B. That combined with its active open source community makes it a great choice for a huge variety of projects.

Another important feature of the BeagleBone is the two built-in PRU (programmable real-time unit) microcontrollers. These are built right into the AM335x CPU and are on the ARM interconnect, so they can share memory with the ARM processor as well as provide direct access to the peripherals. This means high-speed, real-time tasks can be executed on the PRUs asynchronously without any interruption from the Linux kernel. With growing kernel driver support and documentation to compile and load firmware to PRUs, and for communicating with the code running on them from GNU/Linux user space, they really set the BeagleBone apart from much of its competition. The PRUs are outside the scope of this book, but there are plenty of tutorials and examples to be found on the Web.

 

Helpful resources


One of the BeagleBone Black's strong suits is the large community surrounding it.

The official site at http://beagleboard.org/ has lots of great information.

The main source for help with BeagleBone-related issues is the mailing list at https://groups.google.com/forum/#!forum/beagleboard.

There are also plenty of helpful people on the #beagle IRC channel at http://beagleboard.org/Community/Live%20Chat.

There are also many resources online that can help fill the gaps this book leaves on the electrical side. For instance, the Element14 community at http://www.element14.com/community/welcome and the EEVBlog at http://www.eevblog.com/, both contain a wealth of great material, as well as very active electronics forums.

 

Summary


You should now have a better understanding of what the BeagleBone has to offer, and maybe even some insight into the types of devices we will be interfacing with in later chapters.

In the next chapter, you will be plugging in your BeagleBone Black and learning how to log in and get everything we need installed and up to date.

About the Author
  • Alexander Hiam

    Alexander Hiam is a freelance embedded systems designer. He has a bachelor's degree in computer science (embedded systems) from Marlboro College. He is the sole proprietor of Gray Cat Labs, where he has been doing contract software and hardware development since 2012.

    Alex developed and actively maintains the PyBBIO Python library for BeagleBone. He has designed BeagleBone Capes professionally for clients, and he also actively contributes to the BeagleBone community by helping provide support on the mailing list and IRC channel and mentoring for the BeagleBoard.org organization during Google Summer of Code.

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Latest Reviews (2 reviews total)
The sections I have read have been very approachable.
Well written. Code works after some struggles, because I was not aware about required Debian version 7.9 (I was using Debian 8.*). I've not yet finished the book.
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