[petabeda]

Good day,
does anybody know how work three buttons (play, next, back) on Nokia Stereo Headset WH-701 or any other headset? On jack there are 4 contacts:
1. - left earphone
2. - right earphone
3. - common ground
4. - other use (microphone,..)

Possibly, 4. contact is used for these buttons.
But how? Are they 3 resistors of same value in serial connect and a button will short one of these? Or something else? I have tried many ways, but with bad luck.

Thank for possible answers.

[tanz1987]

The fourth contact is actually used for all functions except the first three. Different signals are multiplexed, possibly using some encoding. Try searching Forum Nokia for hardware details.

[petabeda]

Hello,

Thanks for your asnwer

I have tried "Nokia AV Hardware Interface Specification" but I found that "Control data and advanced accessories are proprietary of Nokia and are not covered in this document.".

So there is only one solution, buy it. I don't understand why this information about control data and advanced accessories is not public, when anyone is able to open this headset and discover it.

[petabeda]

If somebody knew about Nokia's ECI (Enhancement Control) interface, could he write some informations about?

[tanz1987]

I've never opened a headset myself, but I can expect some DSPs and other programmable chips inside doing the encoding/multiplexing. Their contents would be trade secrets of Nokia.

[petabeda]

I wanted try to use audio interface as serial data line, therefore I will be able to connect any serial data device (keyboard, voltage measurement)

But even if I solved how these headset buttons work, I don't know whether delay between "simulated press of play button" and notify of J2ME application wasn't be very large.

[petabeda · Accepted solution]

For completion of this discussion I have disassembled the headset.

 You are right, tanz1987, actually, there is a one IC, probably DSP.

Nevermind, it is very amazing solution how to transfer signal from microphone and control data from headset.at the same time over just one pin.