In this article, you'll learn the simple steps to control a light using a Raspberry Pi and Java.

Hardware (Total Cost: $43):

• Raspberry Pi (I have chosen the Raspberry Pi 3 model B, which has a built-in Wi-Fi dongle, ethernet cable support, 4 USB ports, and 2 GB of RAM) — $35 on Amazon.

• Arduino relay module (1 pin) — less than $5 on eBay.

• Female-to-female connector wires — $1 on eBay.

• Light bulb and a conducting wire — $2 on eBay.

Setup

• Install Apache Tomcat on your Raspberry Pi to enable connectivity between the Pi and your other devices. I know it might be heavy to run a container on small scale devices. We can also achieve our goals by using a card reader or voice recognizer, but I chose this easy way to establish the connection.

• Include the pi4j library to send signals to the Raspberry Pi GPIO to control the power.

        <dependency>
            <groupId>com.pi4j</groupId>
            <artifactId>pi4j-core</artifactId>
            <version>1.1</version>
        </dependency>

• Connect the GPIO pins and Arduino module using the female-female connector wires. GPIO pin numbers and Raspberry Pi pin numbers are different, so look at the diagram below for clear info. Also take a look at the video at the bottom of this article. Connect your Raspberry Pi:

  • Ground pin (6) to Arduino GRND.

  • VDC power pin (2) to Arduino VCC.

  • Any GPIO pin (22) to Arduino IN1.

• Use the below code snippet to switch on/off (or) control the power using the pi4j lib. More examples of pi4j can be found here.

// create gpio controller
        final GpioController gpio = GpioFactory.getInstance();

        // lookup the pin by address
        Pin pin = CommandArgumentParser.getPin(
                RaspiPin.class,    // pin provider class to obtain pin instance from
                RaspiPin.GPIO_06);             // argument array to search in
// We are using PIN 06 as per the attached diagram

        GpioPinDigitalOutput output = gpio.provisionDigitalOutputPin(pin, "My Output", PinState.HIGH);

// switch ON
        output.high();
      // switch OFF
        output.low();

I have designed a web-app with JSP and a controller to send commands from the broswer. Based on the request parameter, we can send signals to GPIO pins. The complete web-app code is available here. Download and building it will generate smart-home-ui.war.

if("on".equalsIgnoreCase(request.getParameter("control"))) {
            output.high();
        } else {
            output.low();
        }

After following the above steps, copy  smart-home-ui.war to the Tomcat/webapps directory and start Tomcat. Enter the URL (https://<raspberry pi hostname (or) ip address>:8080/smarthome-ui/index) and click the Switch On/Off buttons and control the light in your home. Here is the sample UI.

Video

I hope you have enjoyed it. Any constructive comments/suggestions are than more welcome.