1 page.title=Custom Accessories 2 @jd:body 3 4 <!-- 5 Copyright 2014 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 <div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25 </div> 26 27 <p>An accessory for Android can be anything: keyboard, thermometer, robot, lighting control or 28 anything else you can imagine. Accessories for Android all have one thing in common; they all 29 connect to an Android device in some way. When starting out to build an accessory, you should 30 decide how your accessory will connect to Android devices. This page gives you quick overview of 31 your options for connecting your Android accessory and resources to help you get started.</p> 32 <h2 id="connecting-over-usb">Connecting over USB</h2> 33 <p>An accessory that connects to an Android device through a USB cable must support the Android 34 Open Accessory (AOA) protocol, which specifies how an accessory can establish communication with 35 an Android device over a USB cable. Due to the low power output of Android devices, the AOA 36 protocol requires the accessory act as a USB host, which means that the connecting accessory must 37 power the bus.</p> 38 <p>The AOA protocol has two versions which support different types of communication. Version 39 1.0 supports a generic accessory communication and adb debugging. This version of the protocol is 40 supported by the platform in Android 3.1 (API Level 12) and higher, and supported through an 41 <a href="https://developers.google.com/android/add-ons/google-apis/">Add-On Library</a> in Android 42 2.3.4 (API Level 10) and higher. Version 2.0 of the protocol is available in Android 4.1 (API Level 43 16) and adds audio streaming and human interface device (HID) capabilities.</p> 44 <p>If you use the general accessory protocol to communicate with your accessory (rather than the 45 adb or audio protocol), you must provide an Android application that can detect the connection of 46 your USB accessory and establish communication.</p> 47 <h3 id="next-steps">Next steps</h3> 48 <p>To get started on building an Android accessory that uses a USB connection:</p> 49 <ul> 50 <li>Select a hardware platform or build a hardware device that can support USB host mode.</li> 51 <li>Review the <a href="{@docRoot}accessories/index.html">AOA protocol</a> specifications to understand 52 how to implement this protocol on your accessory hardware. Implementing the 53 <a href="{@docRoot}accessories/aoa2.html">AOA 2.0 protocol</a> is recommended for all new Android USB 54 accessories.</li> 55 <li>Review the ADK 2012 <a href="http://developer.android.com/tools/adk/adk2.html#src-download">firmware source code</a> 56 (<code><adk-src>/adk2012/board/library/ADK2/</code>), which demonstrates an implementation of an accessory 57 using a USB connection for general data communications and audio streaming.</li> 58 <li>If you are planning to build an Android application that communicates with your accessory 59 via USB, review the ADK 2012 Android 60 <a href="http://developer.android.com/tools/adk/adk2.html#src-download">application source code</a> 61 (<code><adk-src>/adk2012/app/</code>).</li> 62 </ul> 63 <h2 id="connecting-over-bluetooth">Connecting over Bluetooth</h2> 64 <p>An accessory that connects with Android devices over a Bluetooth connection can use the 65 various connection profiles supported by Android, including the Simple Serial Protocol (SSP) and 66 Advanced Audio Distribution Profile (A2DP) profile. An accessory that uses Bluetooth to connect to 67 Android devices must support Bluetooth communications and at least one of the supported connection 68 profiles.</p> 69 <p>Users must enable Bluetooth on their Android device and pair with your accessory in order to 70 use it. You can also provide a secondary Android application that handles any specialized 71 communication, such as data input or control outputs, to interface with your accessory.</p> 72 <h3 id="next-steps_1">Next steps</h3> 73 <p>To get started on building an Android accessory that uses a Bluetooth connection:</p> 74 <ul> 75 <li>Select a hardware platform or build an hardware device that can support Bluetooth 76 communications and an Android supported connection profile, such as SSP or A2DP.</li> 77 <li>Review the ADK 2012 <a href="http://developer.android.com/tools/adk/adk2.html#src-download">firmware source code</a> 78 (<code><adk-src>/adk2012/board/library/ADK2/</code>), which includes an example implementation 79 of general data communications and audio streaming using a Bluetooth connection.</li> 80 <li>If you are planning to build an Android application that communicates with your accessory 81 via Bluetooth, review the ADK 2012 Android 82 <a href="http://developer.android.com/tools/adk/adk2.html#src-download">application source code</a> 83 (<code><adk-src>/adk2012/app/</code>).</li> 84 </ul> 85 <p><strong>Note:</strong> The ADK 2012 source code includes an open source Bluetooth stack which 86 is built for the Texas Instruments CC2564 chip, but can work with any Bluetooth chip that 87 supports a standard Host/Controller Interface (HCI).</p> 88 89 <h2 id="audio-over-usb">Connecting audio over USB</h2> 90 <p>An accessory that connects with Android over USB connection may use the Android Open 91 Accessory (AOA) protocol version 2.0. This version of the AOA protocol is supported on Android 4.1 92 (API Level 16) and higher. Once an Android device connects to an accessory that supports this 93 protocol, the Android system treats it as a standard audio output device and routes all audio to 94 that accessory. No secondary software application is required on the Android device.</p> 95 <p><strong>Note:</strong> Due to the low power output of Android devices, the Android Open Accessory 96 Protocol requires that accessories act as a USB host, which means that the connecting accessory 97 must power the bus.</p> 98 <h3 id="next-steps">Next steps</h3> 99 <p>To get started on building an audio accessory that uses a USB connection:</p> 100 <ul> 101 <li>Select a hardware platform or build a hardware device that can support USB host mode.</li> 102 <li>Review the <a href="{@docRoot}accessories/aoa2.html">AOA 2.0 protocol</a> specification to understand 103 how to implement this protocol on your accessory hardware.</li> 104 <li>Review the ADK 2012 <a href="http://developer.android.com/tools/adk/adk2.html#src-download">firmware source code</a> 105 (<code><adk-src>/adk2012/board/library/ADK2/</code>), which includes an example implementation 106 of an audio playback accessory using a USB connection.</li> 107 </ul> 108 <p><strong>Note:</strong> The AOA 2.0 protocol also supports the 109 <a href="{@docRoot}accessories/aoa2.html#hid-support">human interface device</a> (HID) protocol through a USB 110 connection, enabling accessories such as audio docks to provide hardware play back controls such 111 as pause, fast-forward or volume buttons.</p> 112
