Google empowers hardware hackers with the Android ADK

Google wants thousands of peripherals connected to Android devices; if you don't see what you like, you can build it yourself

The annual Google I/O developers' conference has always been a hot spot for mobile devices. In recent years, Google has taken to giving out the latest Android smartphones free to attendees, sending gadget lovers into a feeding frenzy as the show approaches. Tickets to this year's event, which took place this week in San Francisco, sold out in under an hour. But next year, the hottest Android hardware at the conference might not be what Google hands out, but what attendees bring with them.

Past Android devices could only interact with other hardware in a limited way, via Bluetooth and some rudimentary USB functions. But beginning with Android 3.1, an update for Android tablets that ships this week, Google has greatly expanded the USB capabilities of its mobile OS. Devices running Android 3.1 will be able to interact with the full range of existing USB input devices -- including keyboards, mice, and game controllers -- further cementing Android as a general-purpose OS not limited to smartphones and tablets.

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Even more tantalizing, however, Google envisions a whole new class of USB devices, ones purpose-built to interact with Android. Google is calling these devices Android Open Accessories, and their capabilities go far beyond what you'd expect from your everyday PC peripheral.

These peripherals are PCs
To demonstrate the power of Android Accessories, Google presenters showed off an exercise cycle that could interact with an Android handset via USB. When plugged into the bike, the handset automatically launched a game that players could control by varying their rate of pedaling.

That such a device could connect via USB should come as no surprise. But to connect to the full range of USB peripherals, a PC must act as a USB host. According to the USB specification, a device that supports USB Host Mode must supply 500mA of power at 5 volts. That's no problem for a PC, but it's too much for the humble batteries of most phones, so handset manufacturers typically don't built the hardware necessary to support USB Host Mode into their products.

To get around this limitation, Android Accessories take on the role of USB host themselves. In effect, an Android device plugged into an Android Accessory becomes a kind of smart controller, with the Android Accessory doing the major work. This means the Android Accessory must supply enough power for itself and the Android device, but that's easier to do when the device isn't designed to travel everywhere in your shirt pocket.

All the tools you need
This is no pie-in-the-sky concept. Google wants developers to start building their own Android Accessories today. To get them started, Google has released the Android Open Accessory Development Kit (ADK). There's no fee to download it and no developer plan to join. Everything about the ADK is offered under an open, royalty-free license -- right down to the plans and specifications needed to build the reference hardware.

Android Open Accessory Development Kit tablet
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