

How earphone remotes (with play/skip buttons) work on a single wire - inghoff
http://unix.stackexchange.com/a/41989/11724

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rcfox
The linked answer is close, but not entirely correct. There isn't a
specialized wire for buttons; it uses the microphone line.

Play/pause will usually be connected directly to ground. The other functions
connect to ground through different impedances. While each impedance level is
roughly twice the last one (which makes the detection circuit simpler) having
one level at 1 ohm and the next at 2 ohms is not practical due to noise. Also,
due to the way that parallel impedances work, you do not get a binary encoding
of the buttons pressed. (Do you ever really want to skip the track and
increase the volume at the same time anyway?)

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abailin
Would increasing the resistances to something more significant like 1k, 2k, 4k
ohm make any difference wrt noise?

~~~
rcfox
Not really. You only need to space out the levels by a few ohms.

Microphone impedances start around 500 ohms, so if you go higher than that,
you can't distinguish between a button and a working mic.

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dag11
But what I want to know is then how the microphone signal is implemented with
the 4-wire system, in addition to playback controls.

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mbell
The microphone is in-operable when a button is pushed, at least for all
intents and purposes. The resistance of an average headset microphone is
relatively high, 100-500 ohms if i were to guess. When you put a small
resistor in parallel with a resistance this high it has a negligible effect on
the resistance of the combination. For example if the microphone were 500 ohms
and your switch put a 5 ohm resistor in parallel with it you would expect to
read ~4.95 ohms of resistance total.

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dfc
Why does the title include "on a single wire"?

The current stackexchange question does not use the phrase "single wire" and
more importantly nothing about your headphones will work with a single wire.

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mbell
> The current stackexchange question does not use the phrase "single wire" and
> more importantly nothing about your headphones will work with a single wire.

Its pretty common in the electronics world to not count the ground as a wire
in a communication protocol, only wires carrying data are counted. For example
the "1-Wire" inter-IC bus create by Maxim.

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gus_massa
A little off topic, but this not standard additional features reminds me about
fictitious features of the _Martian Headsets_ models in
<http://www.joelonsoftware.com/items/2008/03/17.html>

~~~
rcfox
His headset analogy is pretty accurate. It even goes one step further though:
In China, some headsets have the mic and ground pin swapped. So before putting
a signal on the mic line to see if it exists, you have to detect which pin is
ground.

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omegant
It's cool to know how this works, I've been trying to repair a couple of
senhaisher plug headPhones+mic for the Iphone (they broke at the jack) and I
couldn't make them work. I am courrently able to use them to listenimg only.
The mic and the controls are not working. And I tried all the combinations at
the jack...(well maybe not all or it would be working perfectly).

I tried to find some diagrams but was unable. Maybe this will help me.

~~~
joering2
Same issues here. I had three pairs of amazing Rocksford inear headset with
huge bass chamber 14mm drive I believe. Anything after that plugged into the
ear sounded dead flat. Anyways, of course the problem is jack and wearing it
with ipod it died withn month. What a frustration. $120 headset that are junk
only because of broken jack.

We need a robust 3.5mm jack short cord extention. Something that would be
robust in built but protect oryginal jack the same time. I think plenty of
people that appreciate quality music on the go would chip in for such a cord.
I would definitely give $15 to protect jack of my high quality headsets. If
someone starts a kickstarter on this, I will pledge.

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throwaway_95014
"modern" headset remotes that work with devices from a major vendor have long
since abandoned the analog resistor approach in favor of a digital system.

The details of the implementation aren't disclosed, but people have seen a
whiff of it, e.g. here:

[http://superuser.com/questions/107378/what-is-the-apple-
mike...](http://superuser.com/questions/107378/what-is-the-apple-mikey-hid-
driver-for)

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zokier
<http://en.wikipedia.org/wiki/1-Wire>

Probably not used in headphones, but it could be.

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its_so_on
This is kind of lacking.

