How earphone remotes (with play/skip buttons) work on a single wire

How earphone remotes (with play/skip buttons) work on a single wire(unix.stackexchange.com)

76 points by inghoff 14 years ago | 17 comments

rcfox 14 years ago |

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?)

abailin 14 years ago | |

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

rcfox 14 years ago | | |

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.

kmm 14 years ago | |

Thank you. I was wondering if such headphones with a microphone would need five connections.

eidorb 14 years ago | |

I guess you could use a series arrangement to get a binary encoding.

dag11 14 years ago |

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

mbell 14 years ago | |

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.

dfc 14 years ago |

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.

mbell 14 years ago | |

> 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.

TazeTSchnitzel 14 years ago | |

It's a single additional wire.

gus_massa 14 years ago |

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 14 years ago | |

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.

omegant 14 years ago |

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 14 years ago | |

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.

throwaway_95014 14 years ago |

"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...

zokier 14 years ago |

http://en.wikipedia.org/wiki/1-Wire

Probably not used in headphones, but it could be.

its_so_on 14 years ago |

This is kind of lacking.