Raspberry Pi Sensors

Before we get started, it's time to reintroduce our good friend, the Raspberry Pi. Kudos to the designers of the board, who have packed everything we need to accomplish our projects in a credit-card-sized printed circuit, also called a credit-card-sized single-board computer. There are two versions of Raspberry Pi: Raspberry Pi 1 and Raspberry Pi 2. Due to earlier developments, the Raspberry Pi 1 family consists of model A, model A+, model B, and model B+. The recently launched model is Raspberry Pi 2, the new addition to the model B category. Nowadays, the most widely used Raspberry Pi is model B+, which is also called the original Raspberry Pi board in the Raspberry Pi 1 family. The predecessor of the Raspberry Pi models B and B+ was model A, which is not widely used in the hobbyist space compared to other models such as A+ and B+. If you are not aware of the specifications of these boards, take a look at the complete comparison in the following table, which contains the comparable parameters of the current models of Raspberry Pi 1 and 2. Then you can choose a board that you want.

Raspberry Pi 1 has a Broadcom BCM2835 processor with a 256 MB or 512 MB RAM on top of it. The processors and RAM are integrated as Package on Package (POP). On the other hand, Raspberry Pi 2 has a Broadcom BCM2836 processor, which comes with a 1024 MB RAM interfaced beneath the board. Raspberry Pi 1 model A+ is still loved by minimal RasPi users who need low-powered performance when they are running on batteries. There's lots of good stuff here: RAM states the temporary memory available to run the current processes and applications. Multimedia processing ensures smooth graphical processing to run high-resolution videos through HDMI and video-extensive applications on Raspberry Pi.

Your new friend has all the capabilities that your computer has. The RasPi can be used to understand how a computer works, to learn programming, for word processing, and for gaming. Here are the small and shiny hacks that we can do with RasPi:

All of these features come in such a small piece of board.

Because of its ability to interact with the outside world, the major applications developed using RasPi include recognizing the surrounding parameters using sensors and converting them into useful data to analyze and control the appliances that we are going to experiment in the upcoming chapters.

I assume that you have the RasPi (model B or B+) in your hand, and you might be wondering what are the different connectors and electronic elements on the board. Rather than introducing the jargon of specifications, I will introduce what we need to make our projects. Take a look at the different connectors in the following diagrams. The nomenclature presented here will be used throughout the book.

The Raspberry Pi 1 model B connectors

The Raspberry Pi 1 model B+ and Raspberry Pi 2 model B look identical to each other, and the difference is only in performance.

The Raspberry Pi 1 model B+ and Raspberry Pi 2 model B connectors

Due to a more powerful processor and an upgraded RAM, Raspberry Pi 2 Model B improves on performance by six times. In a clockwise direction in the diagram of the RasPi 1 model B, the short description of the important connectors is as follows:

Following your recent purchase of the RasPi, you now have to make it ready to work for you. In this section, we are going to install an operating system on which our RasPi will run. The most popular, stable, and widely used operating system for RasPi is the Wheezy-Raspbian.

The Raspbian runs on an open platform, Debian Linux. Why are we going to use Raspbian instead of directly using Linux and other flavors of Linux? Simply because Raspbian has all device drivers written for the RasPi. In brief, the device driver is a program that gives the details of the hardware to the running operating system and supports the user interface to take/give commands from/to the hardware. As our RasPi has different hardware than a personal computer or general-purpose computer, the modified operating system is needed to completely use all resources on the hardware. It is best for those who want to follow the default standards.

You can download the Wheezy-Raspbian install file (known as an image file) from the Raspberry Pi foundation's website at http://downloads.raspberrypi.org/raspbian_latest. If you want to install the GUI-free flavor of Linux (Direct CLI), you can try Arch Linux. It can be downloaded from the ArchLinuxArm web page at http://archlinuxarm.org/os/ArchLinuxARM-rpi-latest.tar.gz.

Once you have finished setting up the RasPi, it's time to connect it to the Internet. Basically, there are two very common ways of connecting the RasPi to Internet: the first (and easiest way) is via Wi-Fi connection using a Wi-Fi dongle, or transceiver; the second is somewhat tricky but it's the most economical and practical way to utilize everything you have and without an additional Wi-Fi dongle. This will require a laptop/desktop computer (a PC) and an Ethernet cable. We will see how to follow each of the ways.

netstat -nr

Internet connection through Ethernet from a PC

All of the preceding steps require a dedicated display, mouse, keyboard, and all other cables to get the view of the working RasPi. For regular uses, this is somewhat bulky to carry all of these along with your RasPi. At this stage, I assume that you have already installed Raspbian OS.

Note

For this method, you just need your laptop/desktop (it already has an inbuilt Wi-Fi module, which is why we don't purchase an additional Wi-Fi dongle for RasPi until we have a special requirement), the Windows operating system, and an Internet connection. You do not need any add-on displays, keyboard, mouse, or Wi-Fi dongles connected with the RasPi.

So all we need is an Ethernet cable, a power supply to RasPi, the SD card with Raspbian, a Windows-based PC with an Ethernet port, an SD card reader for the PC (just required for the first time, either inbuilt or as an add-on SD card reader), and the RasPi (obviously!).

Assemble all of these on a neat table and just start your laptop without starting up the RasPi. I will run you through the step-by-step process. If you follow it, you'll have a working Internet connection provided from your PC to your RasPi with no added costs of Wi-Fi dongles.

Editing the command-line file of the RasPi

The first step is to edit the file that RasPi checks when it starts booting. Try inserting the SD card of the RasPi into your PC's SD card reader. Open Explorer (where all the drives are listed); there, you can find the removable media. You will be amazed to see that the partition is about 15 MB to 20 MB, but your card is actually 8 GB or 16 GB! Don't panic; it's just the boot space of RasPi. You will be able to see the multiple files on this media. We are interested in editing the cmdline.txt file. Just double-click on the file (or open it in standard Notepad), and you will be able to see the following startup commands:

dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait

You can change some settings by adding the static IP address of your RasPi at the end of the line (take a look at the following code). There is no need to understand the meaning of all of these parameters at this stage; I will introduce them when they will be useful.

dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait ip=169.254.0.2

In bold, you will see the static IP we have provided for the RasPi.

Note

From now onwards, you'll always have to access your Pi using this IP address, when you access it from your PC.

Tip

If you are a Linux or Mac OS X user, insert the SD card into the SD card reader. There will be two partitions visible. Open the boot partition and follow the same process explained to add the IP address to the cmdline.txt file.

Save the file, safely remove the SD card from the PC, and move on to the next step.

Turning on the RasPi

Now it's time to start and boot the RasPi by inserting the SD back into the RasPi. Establish an Ethernet connection between the RasPi and your PC before powering up the RasPi. You will see now multiple LEDs blinking on RasPi, stating that the Ethernet connection is being established and there is a transfer of data occurring between the PC and the RasPi. Check the working connection of PC and RasPi by entering ping 169.254.0.2 in Command Prompt (Start Menu | Run | cmd.exe). Note that we are using the same IP address as entered in the cmdline.txt file. It should give a response like this:

The ping command allows us to send the predefined size of packets to the host systems and expects them to be reflected back. The Lost = 0 section in the response shows that all the packets sent from the PC to the RasPi are reflected back and the connection is working.

For Linux and Mac OS X users, the connection can be verified by entering the ping 169.254.0.2 command in the terminal. Enter the ping command in the same Command Prompt to get the Ethernet port IP address of your PC. Following this, enter ipconfig (ifconfig in the case of Mac OS X and Linux users) and note down the IP address of the LAN connection (Ethernet), which is 169.254.121.232 in the following screenshot:

Tip

You will be able to see these Ethernet IP addresses only if the RasPi is in the "powered on" state. Otherwise, you will see no IP address.

Changing cmdline.txt again to add the PC's Ethernet port IP address

Shut down the RasPi (sudo poweroff), remove the SD card, insert it back into your PC, and follow the Editing the command-line file of RasPi section. Add the noted IP address (in this case, it's 169.254.121.232) at the end of the cmdline.txt file, as shown in the following code:

dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait ip=169.254.0.2 ::169.254.121.232

Here, the double colon (::) is the most important part to be put between the RasPi's IP address and your PC's IP address. Then, save the cmdline.txt file.

Sharing the Internet connection between your PC and an Ethernet connection

Turn on the RasPi after safely inserting the SD card back into RasPi and plugging in the micro USB adapter. On a Windows PC, you need to open Network and Sharing Center by navigating to Control Panel | Change adapter settings, right-clicking on the adapter where you are getting Internet connection, and going to its properties.

Note

Look out for possible Internet connectivity on your PC through a wireless Internet connection.

Click on the Sharing tab. Keep the Allow other network users to connect through this computer's Internet connection option checked and click on OK. This setting changes the IP address of the Ethernet port of the PC; we need to reset it.

In the same window of the adapter settings, go to the properties of the Local Area Network connection (Ethernet), double-click on the IPv4 settings, and click on Obtain an IP Address Automatically as well as Obtain DNS server address automatically.

Tip

The IP address we provide for the RasPi may have a subnet class different from the network in your home. The interesting point is that this subnet class remains between the RasPi and PC. Don't panic if the Wi-Fi adapter of your PC is getting IPs in range of 192.x.x.x. This method still works, as Windows allows the Internet sharing between cross subnets. This is because we have enabled the Internet sharing and Ethernet settings as automatic. Therefore, it is clear that the Wi-Fi-to-PC (192.x.x.x) and PC-to-RasPi (169.254.x.x) scenarios work successfully.

Mac OS X user can follow the same steps by navigating to Preferences | Sharing and it would be very easy to follow the GUI.

Linux users can click on network menu in the top panel and navigate to Edit Connections... and then double click your wired connection and keep the wireless connection untouched. Navigate to the IPv4 Settings tab and select method: Shared to other computers.

Installing and opening the free SSH client on your PC

Secure Shell (SSH) is a cryptographic network protocol for secure data communication. It means remote command-line login and remote command execution between two networked computers. Here, we use it for the command-line login and remote command execution between the PC and the RasPi. A one-of-a-kind and free SSH client is PuTTY (www.putty.org) for Windows, and since it is an open source, you can download it for free. Run PuTTY on your Windows PC and change the settings as follows:

Tip

For Linux and Mac OS X users, there is no need to install the PuTTY client, as they can directly perform this task from their terminal window by the ssh pi@169.254.0.2 command.

1. In the Host Name textbox of PuTTY, provide the same IP address that you entered in cmdline.txt (which is 169.254.0.2, as per the example given in the previous section).

2. Following this, navigate to Category | Connection | SSH | X11 and check the Enable X11 forwarding option.

3. In the left-side Category menu, click on Session, enter the session name in the Saved Sessions field, and save it so that you don't have to save the settings every time you connect the RasPi with the PC.

4. Double-click on the saved connection and enter the ID and password; you will get the CLI on the screen of your laptop. Now how do we check the working Internet connection on the RasPi?

5. The answer to the preceding question is simple; enter the following command to check the Internet connection:

   ping -c 4 www.google.com
   

You should get the same response with 0 percent packet loss, and now you have a working Internet connection on your RasPi. All of this is one-time hard work; later on, if you just have to keep your settings unchanged, log in to PuTTY, and enjoy the Internet on the RasPi. For the first time, setting up is somewhat a long process, but you know you've saved almost 10 USD for a Wi-Fi dongle. Isn't that a great thing?

Note

Here is a beautiful tip: you can install Xming from http://www.straightrunning.com/XmingNotes/, which is an X Windows System Server. Once it is installed, run it and you should see that there is no window. Worry not because as soon as you magically input the command lxsession in PuTTY, you will see the entire desktop of the RasPi on your PC's screen. A program similar to Xming is VNC Viewer, which directly opens the desktop of the RasPi by entering the IP address of the RasPi without logging in from PuTTY. Amazing, right?

Many authors and books will teach you the concepts of the Linux operating system, so I will just quickly introduce Linux here. You can refer to Beginning Linux Programming 4th Edition, Wrox Publishing, written by Neil Matthew and Richard Stones. For shell scripting, you can refer to Linux Shell Scripting Cookbook Second Edition, Packt Publishing, written by Shantanu Tushar and Sarath Lakshman. This operating system is mostly known for its non-user-friendliness to beginners! When users start using Linux, they often wonder, "Why is this operating system widely used and famous?" Linux is the biggest open source platform for hobbyists like us, and it allows us to modify the kernel of the operating system the way we want. Some advantages of using Linux include (and are certainly not restricted to) being free, stable, quick, and dependable under the General Public License (GPL).

You can build your own personalized operating system using Linux kernel distributions, for example, a Raspbian developed on the Debian flavor of Linux. We need our customized operating systems because if we develop our personalized hardware, we know how it should be programmed and we develop the drivers according to our needs on top of the Linux kernel. We will now go through the most powerful tool in any Linux operating system—the terminal.

I compare this section to an ice cream with chocolate sauce (yummy! ssrupp!). If you have a vanilla ice cream in your hand, you can enjoy the ice cream, but once you pour chocolate sauce on that, it becomes more delicious, doesn't it? Adding and installing libraries in the RasPi is the same scenario. The RasPi is amazing with the added libraries, which can give you the functionalities you want, whether it is on the GPIO or on the camera port. A library is a particular set of functions that gives you easiness while writing the programs.

Step by step, we will install the useful libraries. To install the libraries, all you need is an Internet connection on the RasPi via PuTTY, as explained in previous sections.

sudo apt-get update
sudo apt-get upgrade

sudo apt-get install git-core

git clone git://git.drogon.net/wiringPi

The latest distribution of the RasPi comes with python-gpio installed, but this library will be necessary for those who have an old distribution installed. The python-gpio library allows you to easily access and control the GPIO pins while running the Python script. This library can be downloaded from the Python organization's website, but we will install it using the LXTerminal or PuTTY. Let's proceed by downloading the .tar file:

wget https://pypi.python.org/packages/source/R/RPi.GPIO/RPi.GPIO-0.5.7.tar.gz

If you aren't aware, let me tell you that a TAR file is a kind of bundled file used to make the download compact and easy. We need to extract the downloaded file in a directory:

tar -xf RPi.GPIO-0.5.7.tar.gz

Let's rename this folder for ease of use; use this command:

mv RPi.GPIO-0.5.7 python_gpio

Move to the python-gpio directory to install the library using this command:

cd python_gpio

Now, we will install this library:

sudo python setup.py install

There is a possibility that it gives you a response that the library is already installed with the latest version. After this process, if you want to remove the downloaded file, you can use the rm command and remove it. Finally, one more library that provides support for the Python Serial Peripheral Interface (SPI) protocol on GPIO is spidev. You can install it using the following command. You can refer to the Serial Peripheral Interface section of Chapter 2, Meeting the World of Electronics, to learn more on SPI protocol. We will be using the SPI protocol in Chapter 6, Uploading Data Online – Spreadsheets, Mobile, and E-mails, when we build the sensor station project to send sensor data on web pages.

sudo pip install spidev

We'll use Python because it is a very simple, yet powerful, language and is easy to write and read because of its indentation and standard English keywords.

The C programming language offers ample benefits when developing the projects using already available libraries, such as wiringPi, which can give you full control of GPIO pins. If you have previously developed a project on C, you can integrate the wiringPi functions and get the same functionalities as your previous project. Also, you can simultaneously use GPIO.

Let's play around with both the languages; this will not give you the whole idea of the programming, but it will give you a good start and will create interest. We will see both the languages one by one.

name = "World"
name = "Hello " + name
print name
for i in range(3):
    print "Whoa"
import this

#include<stdio.h>
int i;
int main()
{
for(i=0;i<3;i++)
printf("Harder you work, Luckier you get");
return 0;
}

gcc -o example2 example2.c

This section includes some practice problems, which should be exercised with shell, C, and Python. The reason behind this practice is that it will make you stronger in understanding the problems and logic of programs, which can really help you to easily make the sensor project. This practice will not cover or give you the idea of entire language or script, but will make you comfortable enough to understand the codes used in the next chapters.

I advise you to connect the Raspberry Pi through an Ethernet cable with your PC, and use the methods stated in the preceding sections to execute the programs. You can take help of the Internet (www.cprogramming.com/quiz/) to understand the logic and the syntax. The problem statements shown here should be attempted in all three languages/scripts, which will give you enough idea to work with scripts and languages:

The skills acquired by performing these exercises will allow you to better understand the projects in the upcoming chapters. You can expect an easy programming level in upcoming chapters. These chapters will focus more on Python and C programs. Hence, more practice on programs will help you gain a better understanding of the language and increase logical thinking.

In this chapter, you learned about the different connectors and functionalities available on the Raspberry Pi board. We successfully installed the operating system on the RasPi and shared an Internet connection with it. After these processes, you learned the basic Linux commands and a glance of the Linux terminal and shell scripting, which will be used frequently while developing applications and projects. Then we installed the useful libraries (in the same way as we add a chocolate topping on top of a vanilla ice cream). A brief introduction to compiling and executing C and Python programs was given to kick-start work on the Raspberry Pi.

In the next chapter, you will be learning the basics of electronics so that you can easily develop the projects. These basics are essential for interfacing the sensors. You will also learn how sensors communicate with the Raspberry Pi. We will run simple codes to drive LEDs on GPIO pins.