【转】Android系统3.5mm耳机插口说明

本文详细介绍了3.5mm耳机接口的设备规范,包括必须支持的功能如立体声输出、麦克风输入等,软件映射及按钮阻值检测标准,并强调了兼容性和机械、电气特性的重要性。

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【声明】

    本文转自《3.5 mm Headset Jack: Device Specification》


【正文】

3.5 mm Headset Jack: Device Specification


To achieve compatibility with the 3.5 mm plug headset specification, devices that include a 4 conductor 3.5 mm audio jack must meet the following specifications. For Android compatibility requirements, refer to the Analog audio ports section of the Android CDD.

Functions


Function Device Support
Stereo Audio Out Required
Audio in (Mic) Required
Ground Required

Software mapping


Function Device Support Description
Function A control event Required Input event: KEY_MEDIA

Android key: KEYCODE_HEADSETHOOK

Function D control event Required Input event: KEY_VOICECOMMAND

Android key: KEYCODE_VOICE_ASSIST

Function B control event Required Input event: KEY_VOLUMEUP

Android key: VOLUME_UP

Function C control event Required Input event: KEY_VOLUMEDOWN

Android key: VOLUME_DOWN

Headset insertion detection Required Input event: SW_JACK_PHYSICAL_INSERT 7
Headset type detection Mic Input event: SW_MICROPHONE_INSERT 4
No Mic Input event: SW_HEADPHONE_INSERT 2
Headset speaker impedance Required Headphone (low) Failure mode is to indicate headphones so limitation would be on
Required Line In (high) Input event: SW_LINEOUT_INSERT 6

Mechanical


Function Device Support Description
4 conductor 3.5 mm jack Required  
CTIA pinout order (LRGM) Required 3 Pin & Mono Plug Compatible
OMTP pinout order (LRMG) Optional but strongly recommended  
Headset detect sequence Required Plug insert notification must be triggered only after all contacts on plug are touching their relevant segments (this prevents unreliable headset detection due to slow insertion.

Electrical


General

Function Device Support Notes
Maximum output voltage drive 150mV >= 150mV on 32 ohm

Test conditions: EN50332-2

Mic bias resistance Required Flexible on detection method used and microphone bias resistor selection. Require that all button resistance value ranges specified below be detected and related to their respective function
Mic bias voltage 1.8V - 2.9V To guarantee compatibility to common microphone capsules.

Function impedance and threshold detection

Devices must detect the following resistor ladder on the accessories. The accessories will be tested to the standardized circuit diagram in the diagram illustrated earlier (Reference Headset Test Circuit) where the total impedance is measured from MIC terminal to GND when a button is pressed with 2.2V mic bias applied through 2.2 kOhm resistor. This is the same effective resistance as the button detection circuit with the microphone in parallel with the button resistor.

Button Impedance Level Device Support Notes
70 ohm or less Required [Function A]
110 - 180 ohm Required [Function D]
210 - 290 ohm Required [Function B]
360 - 680 ohm Required [Function C]
Headset Speaker Impedance Level Device Support Notes
Low Threshold Detection Required Headphone (low) < 1 Kohm
High Threshold Detection Required Line In (high) > 5 Kohm
4-Segment Plug Detection Resistance (between 3rd and 4th segment) Device Support Notes
4-Segment Plug Threshold Required Resistance >= 100 ohms
3-Segment Plug Threshold Required Resistance < 100 ohms

### 3.5mm线控耳机原理图及设计方案分析 #### 一、3.5mm线控耳机基本组成 3.5mm线控耳机通常由以下几个主要部分构成: - **音频信号传输组件**:包括左声道(L)、右声道(R)以及麦克风输入(MIC),这些信号通过TRRS插头连接到设备。 - **控制按键模块**:用于实现音量调整、播放暂停等功能。这类按键通常是基于电阻分压网络或者专用编码芯片实现的[^2]。 - **麦克风拾取单元**:负责捕捉语音信号并将之化为电信号发送给主机设备处理。 --- #### 二、具体设计方案详解 ##### 1. **SSS1530 芯片为基础的设计方案** - SSS1530 是一种高度集成化的单芯片USB音频控制器,能够提供完整的音频编解码功能,同时支持硬件均衡器调节和灵活的产品配置选项[^2]。 - 它包含了立体声 ADC 和 DAC 功能,并且可以直接驱动耳机负载而无需额外功率放大级电路。 - 下面是一个典型的基于此芯片的应用框图示例: ```plaintext +-------------------+ | Host Device | +-------------------+ ↓ +-------------------+ | USB Port | +-------------------+ ↓ +-------------------+ | SSS1530 Chip | +-------------------+ ↓ +-------------------+ | 3.5mm Audio Jack | +-------------------+ ``` 在该框架下,SSS1530 不仅完成了数字模拟换的任务,还简化了整个系统的复杂度,减少了所需元件数量从而降低了成本。 --- ##### 2. **CS201为核心的简易型设计思路** - 如果目标是制作更加紧凑小巧的产品,则可以选择像 CS201 这样的小型化封装解决方案[^4]。 - 此类芯片同样具备良好的性能指标,尤其适合应用于那些对外形尺寸敏感场合下的产品开发工作当中。 - 关键特性对比表如下所示: | 特性 | SSS1530 | CS201 | |---------------------|-------------------------------|------------------------------| | 封装形式 | QFN | QFN | | 支持标准切换 | 否 | 是 | | 外围元件需求 | 较多 | 更少 | 因此,在追求极致简约的情况下,CS201 或许会成为更优的选择之一。 --- #### 三、内部结构剖析 为了更好地理解3.5mm线控耳机的实际运作机制,下面给出一段简化的电气连接描述: 假设我们正在讨论的是一个具有三个按钮(音量加减与播放/暂停)的标准配置版本,则其大致布局可表示为: ```plaintext +------------+ +---------+ +-------+ | Volume Up Btn|--->| Resistor|--->| GPIO Pin A| +------------+ +---------+ +-------+ +--------------+ +----------+ +--------+ |Volume DownBtn|--->|Resistors|--->|GPIO Pin B| +--------------+ +----------+ +--------+ +------------------+ +-----------+ +---------+ |Play/Pause Button|--->|Switches |--->|GND Line | +------------------+ +-----------+ +---------+ ``` 这里利用不同大小的固定值电阻串联形成特定电压等级反馈至主控单元相应管脚处被识别解读成对应命令动作[^3]。 --- #### 四、总结说明 综上所述,无论是采用高性价比路线还是高端定制策略,都可以找到合适的软硬件搭配方式来达成预期效果。而对于初学者而言,优先考虑成熟商用平台所提供的参考设计不失为一条捷径;随着经验积累和技术水平提升后再逐步探索个性化改进途径亦未尝不可。 --- ###
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