This article written by Emanuele Palazzetti, the author of Getting Started with UDOO, will teach us about home automation and using sensors to monitor the CO2 emission by the wood heater in our home.

(For more resources related to this topic, see here.)

During the last few years, the maker culture greatly improved the way hobbyists, students, and, more in general, technology enthusiasts create new hardware devices. The advent of prototyping boards such as Arduino together with a widespread open source philosophy, changed how and where ideas are realized. If you're a maker or you have a friend that really like building prototypes and devices, probably both of you have already transformed the garage or the personal studio in a home lab. This process is so spontaneous that nowadays newcomers in the Makers Community begin to create their first device at home.

UDOO and Home Automation

Like other communities, the makers family self-sustained their ideas joining their passion with the Do It Yourself (DIY) philosophy, which led makers to build and use creative devices in their everyday life. The DIY movement was the key factor that triggered the Home Automation made with open source platforms, making this process funnier and maker-friendly. Indeed, if we take a look at some projects released on the Internet we can find thousands of prototypes, usually composed by an Arduino together with a Raspberry Pi, or any other combinations of similar prototyping boards.

However, in this scenario, we have a new alternative proposed by the UDOO board—a stand alone computer that provides a multidevelopment-platform solution for Linux and Android operating systems with an integrated Arduino Due. Thanks to its flexibility, UDOO combines the best from two different worlds: the hardware makers and the software programmers. Applying the UDOO board to home automation is a natural process because of its power and versatility. Furthermore, the capability to install the Android operating system increases the capabilities of this board, because it offers out-of-the-box mobile applications ecosystem that can be easily reused in our appliances, enhancing the user experience of our prototype.

Since 2011, Android supports the interaction with an Arduino compatible device through the Android Accessory Development Kit (ADK) reference. Designed to implement compelling accessories that could be connected to Android-powered devices, this reference defines the Android Open Accessory (AOA) protocol used to communicate with an Arduino device through an USB On-The-Go (OTG) port or via Bluetooth. UDOO makes use of this protocol and opens a serial communication between two processors soldered in the same board, which run the Android operating system and the microcontroller actions respectively.

Mastering the ADK is not so easy, especially during the first approach. For this reason, the community has developed an Android library that simplifies a lot the use of the ADK: the Android ADKToolkit (http://adktoolkit.org).

To put our hands-on code, we can imagine a scenario in which we want to monitor the carbon dioxide emissions (CO2) produced by the wood heater in our home. The first step is to connect the CO2 sensor to our board and use the manufacturer library, if available, in the Arduino sketch to retrieve the detected CO2. Using the ADK implementation, we can send this value back to the main UDOO's processor that runs the Android operating system, so it can use its powerful APIs, and a more powerful processor, to visualize or compute the collected data. The following example is a part of an Arduino sketch used to send sensor data back to the Android application using the ADK implementation:

uint8_t buffer[128];
int co2Sensor = 0;
void loop() {
Usb.Task();
if (adk.isReady()) {
   // Hypothetical function that
   // gets the value from the sensor
   co2Sensor = readFromCO2Sensor();
   buffer[0] = co2Sensor;
   // Sends the value to Android
   adk.write(1, buffer);
   delay(1000);
}
}

On the Android side, using a traditional AsyncTask method or a more powerful ExecutorService method, we should read this value from the buffer. This task is greatly simplified through the ADKToolkit library that requires the initialization of the AdkManager class that holds the connection and exposes a handler to open or close the communication with Arduino. This instance could be initialized during the onCreate() activity callback with the following code:

private AdkManager mAdkManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.hello_world);
mAdkManager = new AdkManager(this);
mAdkManager.open();
}

In a separated thread, we can use the mAdkManager instance to read data from the ADK buffer. The following is an example that reads the message from the buffer and uses the getInt() method to parse the value:

private class SensorThread implements Runnable {
@Override
public void run() {
   // Reads detected CO2 from ADK
   AdkMessage response = mAdkManager.read();
   int co2 = response.getInt();
   // Continues the execution
   doSomething(co2);
}
}

Once we retrieve the detected CO2 value from the sensor, we can use it in our application. For instance, we may plot this value using an Android open source chart library or send collected data to an external web service.

These preceding snippets are just examples to show how it's easy to implement the communication in UDOO between the Android operating system and the onboard Arduino. With a powerful operating system such as Android and one of the most widespread prototyping platform provided in a single board, UDOO can play a key role in our home automation projects.

Summary

As makers, if we manage to make enough experience into the home automation field, chances are that we will be able to develop and build a high-end system for our own house, flexible enough to be easily extended without any further knowledge. When I wrote Getting started with UDOO, the idea was to make a comprehensive guide and a collection of examples, to help developers grabbing quickly the key concepts of this prototyping board, focusing in the Android development to bring back to light the advantages provided by this widespread platform, if used in our prototypes and not only in our mobile devices.