1 page.title=3.5 mm Headset: Accessory Specification 2 @jd:body 3 4 <!-- 5 Copyright 2015 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>This article specifies requirements for 3.5 mm plug headsets to 28 function uniformly across the Android ecosystem.</p> 29 30 <p>Device manufacturers should consult the <a href="jack-headset-spec.html">3.5 mm 31 jack specification</a> and the 32 <a href="{@docRoot}compatibility/android-cdd.html">Android Compatibility Definition Document</a> 33 (CDD) for additional requirements.</p> 34 35 <h2 id="functions">Functions</h2> 36 37 <table style="width:50%"> 38 <tr> 39 <th>Function</th> 40 <th>Accessory Support</th> 41 </tr> 42 <tr> 43 <td>Stereo Audio Out</td> 44 <td>Required</td> 45 </tr> 46 <tr> 47 <td>Audio in (Mic)</td> 48 <td>Required</td> 49 </tr> 50 <tr> 51 <td>Ground</td> 52 <td>Required</td> 53 </tr> 54 </table> 55 56 <h2 id="control-function_mapping">Control-function mapping</h2> 57 58 <table> 59 <tr> 60 <th style="width:33%">Control Function</th> 61 <th style="width:33%">Accessory Support</th> 62 <th style="width:33%">Description</th> 63 </tr> 64 <tr> 65 <td>Function A</td> 66 <td>Required</td> 67 <td>Play/pause/hook (Short Press), Trigger Assist (Long Press), Next 68 (Double Press)</td> 69 </tr> 70 <tr> 71 <td>Function B</td> 72 <td>Optional</td> 73 <td>Vol+</td> 74 </tr> 75 <tr> 76 <td>Function C</td> 77 <td>Optional</td> 78 <td>Vol-</td> 79 </tr> 80 <tr> 81 <td>Function D</td> 82 <td>Optional</td> 83 <td>Reserved (Nexus devices use this to launch Voice Assist) 84 </td> 85 </tr> 86 </table> 87 88 <p>Assign functions to buttons as follows:</p> 89 90 <ul> 91 <li> All one-button headsets must implement Function A. 92 <li> Headsets with multiple buttons must implement functions according to the 93 following pattern: 94 <ul> 95 <li> 2 functions: A and D 96 <li> 3 functions: A, B, C 97 <li> 4 functions: A, B, C, D 98 </ul> 99 </ul> 100 101 <h2 id="mechanical">Mechanical</h2> 102 103 <table> 104 <tr> 105 <th style="width:33%">Function</th> 106 <th style="width:33%">Accessory Support</th> 107 <th style="width:33%">Notes</th> 108 </tr> 109 <tr> 110 <td>4 conductor 3.5 mm plug</td> 111 <td>Required</td> 112 <td>Ref: EIAJ-RC5325A standard</td> 113 </tr> 114 <tr> 115 <td>CTIA pinout order (LRGM)</td> 116 <td>Required</td> 117 <td>Except in regions with legal requirements for OMTP pinout</td> 118 </tr> 119 <tr> 120 <td>OMTP pinout order (LRMG)</td> 121 <td>Optional</td> 122 <td></td> 123 </tr> 124 <tr> 125 <td>Microphone</td> 126 <td>Required</td> 127 <td>Must not be obstructed when operating headset controls</td> 128 </tr> 129 </table> 130 131 <h2 id="electrical">Electrical</h2> 132 133 <table> 134 <tr> 135 <th style="width:33%">Function</th> 136 <th style="width:33%">Accessory Support</th> 137 <th style="width:33%">Description</th> 138 </tr> 139 <tr> 140 <td>Ear speaker impedance</td> 141 <td>16 ohms or higher</td> 142 <td>Recommend 32 - 300 ohms</td> 143 </tr> 144 <tr> 145 <td>Mic DC resistance</td> 146 <td>1000 ohms or higher 147 </td> 148 <td>Mic characteristics must be compliant with section 5.4 149 <em>Audio Recording</em> of the current 150 <a href="{@docRoot}compatibility/android-cdd.html#5_4_audio_recording">Android CDD</a></td> 151 </tr> 152 <tr> 153 <td rowspan="4">Control Function Equivalent impedance*</td> 154 <td>0 ohm</td> 155 <td>[Function A] Play/Pause/Hook</td> 156 </tr> 157 <tr> 158 <td>240 ohm +/- 1% resistance</td> 159 <td>[Function B]</td> 160 </tr> 161 <tr> 162 <td>470 ohm +/- 1% resistance</td> 163 <td>[Function C]</td> 164 </tr> 165 <tr> 166 <td>135 ohm +/- 1% resistance</td> 167 <td>[Function D]</td> 168 </tr> 169 </table> 170 171 <p><em>*Total impedance from positive mic terminal to GND when button is 172 pressed with 2.2 V mic bias applied through 2.2 kOhm resistor</em></p> 173 174 <p>In the following diagrams, Button A maps to Function A, Button B to 175 Function B, and so on.</p> 176 177 <h2 id="reference_headsets">Reference headset test circuits</h2> 178 179 <p>The following diagram for Reference Headset Test Circuit 1 shows the CTIA 180 pinout for a 4-segment plug. For the OMTP pinout, switch the positions of the 181 MIC and GND segments.</p> 182 183 <img src="images/headset-circuit1.png" alt="Reference Headset Test Circuit 1" /> 184 <p class="img-caption"><strong>Figure 1.</strong> Reference headset test circuit 1</p> 185 186 <p>The following diagram for Reference Headset Test Circuit 2 shows how the 187 actual resistor values (R1 - R4) are altered to meet this specification.</p> 188 189 <img src="images/headset-circuit2.png" alt="Reference Headset Test Circuit 2" /> 190 <p class="img-caption"><strong>Figure 2.</strong> Reference headset test circuit 2</p> 191 192 <p>The actual resistance of the buttons parallel with the microphone (R1-R4) is 193 based on the microphone capsule resistance (Rmic) and the equivalent impedance 194 values (ReqA-ReqD). Use the following formula:</p> 195 196 <p><em>Req<sub>N</sub>=(R<sub>mic</sub>*R<sub>n</sub>)/(R<sub>mic</sub>+R<sub>n</sub>)</em></p> 197 198 <p>Where R<em>n</em> is the actual resistance of a button, Req<em>N</em> is the 199 equivalent impedance value of that button (provided), and Rmic is the 200 microphone impedance value.</p> 201 202 <p>The example above assumes a 5 kohm microphone impedance (Rmic); to achieve 203 an equivalent R4 impedance of 135 ohm (ReqD), the actual resistor value (R4) 204 must be 139 ohms.</p> 205 206
