Home Automation with Raspberry Pi

The RPi's GPIO pins are shown in Figure 2. The RPi's IO ports operate at 3.3v, and the relay module works at 5v. However, the relays are isolated from the RPi's GPIO pins using optocouplers. The optocouplers may be supplied 3.3v over the Vcc pin. The Vcc pin of the relay module may be supplied 3.3v from the GPIO header of the Pi. Make sure you have removed the jumper that bridges the Vcc and JDVcc on the relay module board. The JDVcc pin should be supplied 5v for proper operation of the relay. The relay module is designed to be active low. This means that you have to ground the terminals IN1-IN8 to switch on a relay.

Figure 2. The RPi's GPIO Pins

Warning: handle all wiring with caution. Getting a shock from the line can be fatal!

Cut the remaining extension cables at the plug end, and screw in the wire end to the relay. Also daisy-chain the live wire from the wall outlet to the relay terminals. The entire setup can be housed in a pencil box or something similar. Plan this out in advance to avoid having to unwire and rewire the terminals. Additionally, I added a few screw cable clamps to the holes I made in my housing to act as a strain relief (Figure 3).

Figure 3. The Hardware Setup

Environment

I built my environment starting with a fresh install of Raspbian. For the initial installation, you need an HDMI-capable display, a USB keyboard, mouse and a wired Ethernet connection. You also optionally may connect a Wi-Fi adapter. Build the SD card for the first boot by following the instructions given at http://www.raspberrypi.org/documentation/installation/installing-image. During the first boot, the installer sets up the OS and expands the image to fill the entire card. After the first boot, you should be able to log in using the default credentials(user "pi" and password "raspberry").

Once you successfully log in, it's good practice to update the OS. The Raspbian image is based on Debian and uses the aptitude package manager. You also will need python, pip and git. I also recommend installing Webmin to ease administration processes. Instructions for installing Webmin are at http://www.webmin.com/deb.html (follow the directions in the "Using the Webmin APT repository" section):


sudo apt-get update && sudo apt-get dist-upgrade
sudo apt-get install python python-pip git git-core

Next, you need to set up the Wi-Fi connection. You can find detailed instructions for this at http://www.raspberrypi.org/documentation/configuration/wireless. I recommend the wicd-curses option. At this point, you can make changes to the RPi setup using the sudo raspi-config command. This will bring up a GUI that lets you choose options like the amount of RAM you share with the GPU, overclocking, GUI Boot and so on.

Another useful tool is the Cloud 9 IDE. The Cloud9 IDE allows you to edit your code on the RPi using a Web browser. It also gives you a shell interface in the browser. You can develop and execute all your code without leaving the Web browser. The Cloud 9 IDE requires a specific version of NodeJS. Using the wrong version will cause frequent crashes of the Cloud 9 server, resulting in constant frustration. Instructions for installing NodeJS on the Raspberry Pi are outlined at http://weworkweplay.com/play/raspberry-pi-nodejs.

Software

I decided to build my front-end UI using HTML5, CSS3 and JavaScript. The combination of these three form a powerful tool for building UIs. JavaScript provides easy communication APIs to servers. There also are a lot of JavaScript libraries like JQuery, Bootstrap and so on from which to choose. HTML5 supports the WebSocket API that allows the browser to keep a connection alive and receive communication over this connection. This makes WebSocket useful for implementing live and streaming apps, such as for games and chat interfaces. CSS is useful for styling the various HTML elements. When used properly, it lets one build dynamic UIs by switching the styles on an element in response to events. For this project, I chose JQuery to handle events, Bootstrap CSS to lay out the buttons in a grid form and pure JavaScript to handle WebSocket communications.

Libraries

The back-end server on the Raspberry Pi needs to control the GPIO pins on the Raspberry Pi board. It also needs an HTTP interface to serve the UI and a WebSocket interface to pass command and status messages. Such a specific server did not exist for off-the-shelf deployment, so I decided to write my own using Python. Python has prebuilt modules for the Raspberry Pi GPIO, HTTP server and WebSockets. Since these modules are specialized, minimum coding was required on my part.

However, these modules are not a part of Python and need to be installed separately. First, you need to be able to control the RPi's GPIO pins. The easiest way to do this from Python is by using the RPi.GPIO library from https://pypi.python.org/pypi/RPi.GPIO. Install this module with:


sudo pip install RPi.GPIO

Using the RPi.GPIO module is very simple. You can find examples of its usage at http://sourceforge.net/p/raspberry-gpio-python/wiki/Examples. The first step in using the module is to import it into the code. Next, you need to select the mode. The mode can be either GPIO.BOARD or GPIO.BCM. The mode decides whether the pin number references in the subsequent commands will be based on the BCM chip or the IO pins on the board. This is followed by setting pins as either input or output. Now you can use the IO pins as required. Finally, you need to clean up to release the GPIO pins. Listing 1 shows examples of using the RPi.GPIO module.

Listing 1. Using the RPi.GPIO Module


import RPi.GPIO as GPIO          # import module
GPIO.setmode(GPIO.BOARD)         # use board pin numbering
GPIO.setup(0, GPIO.IN)           # set ch0 as input
GPIO.setup(1, GPIO.OUT)          # set ch1 as output
var1=GPIO.input(0)                       # read ch0
GPIO.output(1, GPIO.HIGH)        # take ch1 to high state
GPIO.cleanup()                           # release GPIO.
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Bharath Bhushan Lohray is a PhD student working on his dissertation on image compression techniques at the Department of Electrical & Computer Engineering, Texas Tech University. He is interested in machine learning.