1 <html devsite> 2 <head> 3 <title>3.5 mm Headset: Accessory Specification</title> 4 <meta name="project_path" value="/_project.yaml" /> 5 <meta name="book_path" value="/_book.yaml" /> 6 </head> 7 <body> 8 <!-- 9 Copyright 2017 The Android Open Source Project 10 11 Licensed under the Apache License, Version 2.0 (the "License"); 12 you may not use this file except in compliance with the License. 13 You may obtain a copy of the License at 14 15 http://www.apache.org/licenses/LICENSE-2.0 16 17 Unless required by applicable law or agreed to in writing, software 18 distributed under the License is distributed on an "AS IS" BASIS, 19 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 20 See the License for the specific language governing permissions and 21 limitations under the License. 22 --> 23 24 25 26 <p>This article specifies requirements for 3.5 mm plug headsets to 27 function uniformly across the Android ecosystem.</p> 28 29 <p>Device manufacturers should consult the <a href="jack-headset-spec.html">3.5 mm 30 jack specification</a> and the 31 <a href="/compatibility/android-cdd.html">Android Compatibility Definition Document</a> 32 (CDD) for additional requirements.</p> 33 34 <h2 id="functions">Functions</h2> 35 36 <table style="width:50%"> 37 <tr> 38 <th>Function</th> 39 <th>Accessory Support</th> 40 </tr> 41 <tr> 42 <td>Stereo Audio Out</td> 43 <td>Required</td> 44 </tr> 45 <tr> 46 <td>Audio in (Mic)</td> 47 <td>Required</td> 48 </tr> 49 <tr> 50 <td>Ground</td> 51 <td>Required</td> 52 </tr> 53 </table> 54 55 <h2 id="control-function_mapping">Control-function mapping</h2> 56 57 <table> 58 <tr> 59 <th style="width:33%">Control Function</th> 60 <th style="width:33%">Accessory Support</th> 61 <th style="width:33%">Description</th> 62 </tr> 63 <tr> 64 <td>Function A</td> 65 <td>Required</td> 66 <td>Play/pause/hook (Short Press), Trigger Assist (Long Press), Next 67 (Double Press)</td> 68 </tr> 69 <tr> 70 <td>Function B</td> 71 <td>Optional</td> 72 <td>Vol+</td> 73 </tr> 74 <tr> 75 <td>Function C</td> 76 <td>Optional</td> 77 <td>Vol-</td> 78 </tr> 79 <tr> 80 <td>Function D</td> 81 <td>Optional</td> 82 <td>Reserved (Nexus devices use this to launch voice commands) 83 </td> 84 </tr> 85 </table> 86 87 <p>Assign functions to buttons as follows:</p> 88 89 <ul> 90 <li> All one-button headsets must implement Function A. 91 <li> Headsets with multiple buttons must implement functions according to the 92 following pattern: 93 <ul> 94 <li> 2 functions: A and D 95 <li> 3 functions: A, B, C 96 <li> 4 functions: A, B, C, D 97 </ul> 98 </ul> 99 100 <h2 id="mechanical">Mechanical</h2> 101 102 <table> 103 <tr> 104 <th style="width:33%">Function</th> 105 <th style="width:33%">Accessory Support</th> 106 <th style="width:33%">Notes</th> 107 </tr> 108 <tr> 109 <td>4 conductor 3.5 mm plug</td> 110 <td>Required</td> 111 <td>Ref: EIAJ-RC5325A standard</td> 112 </tr> 113 <tr> 114 <td>CTIA pinout order (LRGM)</td> 115 <td>Required</td> 116 <td>Except in regions with legal requirements for OMTP pinout</td> 117 </tr> 118 <tr> 119 <td>OMTP pinout order (LRMG)</td> 120 <td>Optional</td> 121 <td></td> 122 </tr> 123 <tr> 124 <td>Microphone</td> 125 <td>Required</td> 126 <td>Must not be obstructed when operating headset controls</td> 127 </tr> 128 </table> 129 130 <h2 id="electrical">Electrical</h2> 131 132 <table> 133 <tr> 134 <th style="width:33%">Function</th> 135 <th style="width:33%">Accessory Support</th> 136 <th style="width:33%">Description</th> 137 </tr> 138 <tr> 139 <td>Ear speaker impedance</td> 140 <td>16 ohms or higher</td> 141 <td>Recommend 32 - 300 ohms</td> 142 </tr> 143 <tr> 144 <td>Mic DC resistance</td> 145 <td>1000 ohms or higher 146 </td> 147 <td>Mic characteristics must be compliant with section 5.4 148 <em>Audio Recording</em> of the current 149 <a href="/compatibility/android-cdd.html#5_4_audio_recording">Android CDD</a></td> 150 </tr> 151 <tr> 152 <td rowspan="4">Control Function Equivalent impedance*</td> 153 <td>0 ohm</td> 154 <td>[Function A] Play/Pause/Hook</td> 155 </tr> 156 <tr> 157 <td>240 ohm +/- 1% resistance</td> 158 <td>[Function B]</td> 159 </tr> 160 <tr> 161 <td>470 ohm +/- 1% resistance</td> 162 <td>[Function C]</td> 163 </tr> 164 <tr> 165 <td>135 ohm +/- 1% resistance</td> 166 <td>[Function D]</td> 167 </tr> 168 </table> 169 170 <p><em>*Total impedance from positive mic terminal to GND when button is 171 pressed with 2.2 V mic bias applied through 2.2 kOhm resistor</em></p> 172 173 <p>In the following diagrams, Button A maps to Function A, Button B to 174 Function B, and so on.</p> 175 176 <h2 id="reference_headsets">Reference headset test circuits</h2> 177 178 <p>The following diagram for Reference Headset Test Circuit 1 shows the CTIA 179 pinout for a 4-segment plug. For the OMTP pinout, switch the positions of the 180 MIC and GND segments.</p> 181 182 <img src="images/headset-circuit1.png" alt="Reference Headset Test Circuit 1" /> 183 <p class="img-caption"><strong>Figure 1.</strong> Reference headset test circuit 1</p> 184 185 <p>The following diagram for Reference Headset Test Circuit 2 shows how the 186 actual resistor values (R1 - R4) are altered to meet this specification.</p> 187 188 <img src="images/headset-circuit2.png" alt="Reference Headset Test Circuit 2" /> 189 <p class="img-caption"><strong>Figure 2.</strong> Reference headset test circuit 2</p> 190 191 <p>The actual resistance of the buttons parallel with the microphone (R1-R4) is 192 based on the microphone capsule resistance (Rmic) and the equivalent impedance 193 values (ReqA-ReqD). Use the following formula:</p> 194 195 <p><em>Req<sub>N</sub>=(R<sub>mic</sub>*R<sub>n</sub>)/(R<sub>mic</sub>+R<sub>n</sub>)</em></p> 196 197 <p>Where R<em>n</em> is the actual resistance of a button, Req<em>N</em> is the 198 equivalent impedance value of that button (provided), and Rmic is the 199 microphone impedance value.</p> 200 201 <p>The example above assumes a 5 kohm microphone impedance (Rmic); to achieve 202 an equivalent R4 impedance of 135 ohm (ReqD), the actual resistor value (R4) 203 must be 139 ohms.</p> 204 205 206 </body> 207 </html> 208
