| page.title=3.5 mm Headset: Accessory Specification |
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| <div id="qv-wrapper"> |
| <div id="qv"> |
| <h2>In this document</h2> |
| <ol id="auto-toc"> |
| </ol> |
| </div> |
| </div> |
| |
| <p>This article specifies requirements for 3.5 mm plug headsets to |
| function uniformly across the Android ecosystem.</p> |
| |
| <p>Device manufacturers should consult the <a href="jack-headset-spec.html">3.5 mm |
| jack specification</a> and the |
| <a href="{@docRoot}compatibility/android-cdd.html">Android Compatibility Definition Document</a> |
| (CDD) for additional requirements.</p> |
| |
| <h2 id="functions">Functions</h2> |
| |
| <table style="width:50%"> |
| <tr> |
| <th>Function</th> |
| <th>Accessory Support</th> |
| </tr> |
| <tr> |
| <td>Stereo Audio Out</td> |
| <td>Required</td> |
| </tr> |
| <tr> |
| <td>Audio in (Mic)</td> |
| <td>Required</td> |
| </tr> |
| <tr> |
| <td>Ground</td> |
| <td>Required</td> |
| </tr> |
| </table> |
| |
| <h2 id="control-function_mapping">Control-function mapping</h2> |
| |
| <table> |
| <tr> |
| <th style="width:33%">Control Function</th> |
| <th style="width:33%">Accessory Support</th> |
| <th style="width:33%">Description</th> |
| </tr> |
| <tr> |
| <td>Function A</td> |
| <td>Required</td> |
| <td>Play/pause/hook (Short Press), Trigger Assist (Long Press), Next |
| (Double Press)</td> |
| </tr> |
| <tr> |
| <td>Function B</td> |
| <td>Optional</td> |
| <td>Vol+</td> |
| </tr> |
| <tr> |
| <td>Function C</td> |
| <td>Optional</td> |
| <td>Vol-</td> |
| </tr> |
| <tr> |
| <td>Function D</td> |
| <td>Optional</td> |
| <td>Reserved (Nexus devices use this to launch Voice Assist) |
| </td> |
| </tr> |
| </table> |
| |
| <p>Assign functions to buttons as follows:</p> |
| |
| <ul> |
| <li> All one-button headsets must implement Function A. |
| <li> Headsets with multiple buttons must implement functions according to the |
| following pattern: |
| <ul> |
| <li> 2 functions: A and D |
| <li> 3 functions: A, B, C |
| <li> 4 functions: A, B, C, D |
| </ul> |
| </ul> |
| |
| <h2 id="mechanical">Mechanical</h2> |
| |
| <table> |
| <tr> |
| <th style="width:33%">Function</th> |
| <th style="width:33%">Accessory Support</th> |
| <th style="width:33%">Notes</th> |
| </tr> |
| <tr> |
| <td>4 conductor 3.5 mm plug</td> |
| <td>Required</td> |
| <td>Ref: EIAJ-RC5325A standard</td> |
| </tr> |
| <tr> |
| <td>CTIA pinout order (LRGM)</td> |
| <td>Required</td> |
| <td>Except in regions with legal requirements for OMTP pinout</td> |
| </tr> |
| <tr> |
| <td>OMTP pinout order (LRMG)</td> |
| <td>Optional</td> |
| <td></td> |
| </tr> |
| <tr> |
| <td>Microphone</td> |
| <td>Required</td> |
| <td>Must not be obstructed when operating headset controls</td> |
| </tr> |
| </table> |
| |
| <h2 id="electrical">Electrical</h2> |
| |
| <table> |
| <tr> |
| <th style="width:33%">Function</th> |
| <th style="width:33%">Accessory Support</th> |
| <th style="width:33%">Description</th> |
| </tr> |
| <tr> |
| <td>Ear speaker impedance</td> |
| <td>16 ohms or higher</td> |
| <td>Recommend 32 - 300 ohms</td> |
| </tr> |
| <tr> |
| <td>Mic DC resistance</td> |
| <td>1000 ohms or higher |
| </td> |
| <td>Mic characteristics must be compliant with section 5.4 |
| <em>Audio Recording</em> of the current |
| <a href="{@docRoot}compatibility/android-cdd.html#5_4_audio_recording">Android CDD</a></td> |
| </tr> |
| <tr> |
| <td rowspan="4">Control Function Equivalent impedance*</td> |
| <td>0 ohm</td> |
| <td>[Function A] Play/Pause/Hook</td> |
| </tr> |
| <tr> |
| <td>240 ohm +/- 1% resistance</td> |
| <td>[Function B]</td> |
| </tr> |
| <tr> |
| <td>470 ohm +/- 1% resistance</td> |
| <td>[Function C]</td> |
| </tr> |
| <tr> |
| <td>135 ohm +/- 1% resistance</td> |
| <td>[Function D]</td> |
| </tr> |
| </table> |
| |
| <p><em>*Total impedance from positive mic terminal to GND when button is |
| pressed with 2.2 V mic bias applied through 2.2 kOhm resistor</em></p> |
| |
| <p>In the following diagrams, Button A maps to Function A, Button B to |
| Function B, and so on.</p> |
| |
| <h2 id="reference_headsets">Reference headset test circuits</h2> |
| |
| <p>The following diagram for Reference Headset Test Circuit 1 shows the CTIA |
| pinout for a 4-segment plug. For the OMTP pinout, switch the positions of the |
| MIC and GND segments.</p> |
| |
| <img src="images/headset-circuit1.png" alt="Reference Headset Test Circuit 1" /> |
| <p class="img-caption"><strong>Figure 1.</strong> Reference headset test circuit 1</p> |
| |
| <p>The following diagram for Reference Headset Test Circuit 2 shows how the |
| actual resistor values (R1 - R4) are altered to meet this specification.</p> |
| |
| <img src="images/headset-circuit2.png" alt="Reference Headset Test Circuit 2" /> |
| <p class="img-caption"><strong>Figure 2.</strong> Reference headset test circuit 2</p> |
| |
| <p>The actual resistance of the buttons parallel with the microphone (R1-R4) is |
| based on the microphone capsule resistance (Rmic) and the equivalent impedance |
| values (ReqA-ReqD). Use the following formula:</p> |
| |
| <p><em>Req<sub>N</sub>=(R<sub>mic</sub>*R<sub>n</sub>)/(R<sub>mic</sub>+R<sub>n</sub>)</em></p> |
| |
| <p>Where R<em>n</em> is the actual resistance of a button, Req<em>N</em> is the |
| equivalent impedance value of that button (provided), and Rmic is the |
| microphone impedance value.</p> |
| |
| <p>The example above assumes a 5 kohm microphone impedance (Rmic); to achieve |
| an equivalent R4 impedance of 135 ohm (ReqD), the actual resistor value (R4) |
| must be 139 ohms.</p> |
| |