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: |
| Function D control event | Required | Input event: KEY_VOICECOMMAND
Android key: |
| Function B control event | Required | Input event: KEY_VOLUMEUP
Android key: |
| Function C control event | Required | Input event: KEY_VOLUMEDOWN
Android key: |
| 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 |