Electronic – How do media buttons on a plain wired headset work


I mean the simple analog headset pluggable into the jack of a phone. Not USB, not bluetooth, not fancy proprietary plugs with extra connectors – just a generic stereo+mic jack.

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The four "bands" on the jack plug are GND, right earphone, left earphone and microphone. And there's nothing to cover the buttons – usually "Volume up/down" + "Media key" for receiving the call.

How do these buttons communicate being pressed to the phone?

Best Answer

Each switch bridges the high-impedance microphone with a low resistance, allowing internal circuitry to sense the buttons. Here's a helpful image:

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The MIC+ line has a bias voltage (to supply the mic), and by adding some additional circuitry to the mic preamp, it's easy to differentiate those resistor values.

This is the most common scheme for "on-headphone" controls. Additionally, it's very easy to implement in the headphones, allowing for cheap headphones and requires only a little bit more circuitry in the phone.