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Support for 3.5mm plug keys

asked 2014-11-26 02:45:55 +0200

Aonsaithya gravatar image

updated 2014-11-26 09:20:27 +0200

eric gravatar image

I recall hearing that one design goal of Sailfish (and the Jolla phone itself) was minimizing the number of hardware buttons. I'm not a big fan of this approach, and would certainly love a mappable extra hardware button, be it for answering/ending a call, turning on flashlight, switching bluetooth, going to launcher, etc.

So, would it be possible to add OS-level support for remapping those 3.5mm plug buttons, and obviously not enabling headset functions when just a button plug is installed (assuming it's possible to detect whether the plugged-in device is a proper headset or just a button plug).

Example of a button plug: image description

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Are those button plugs available for other devices? Or is this just an idea to create one? If so, see my answer below: I'd rather create a TOH for extra buttons than this one.

naytsyrhc ( 2014-11-26 09:55:54 +0200 )edit

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answered 2014-11-26 09:52:39 +0200

naytsyrhc gravatar image

Wouldn't that be something for a TOH? You could create one with several buttons on the back. You wouldn't block the 3.5 jack and wouldn't be limited to just one button. It would also be easy to recognize and integrate I presume. And that's what the TOH idea is for, isn't it? Such a 3.5 plug-button seems to me as a work around as there are no other possibilities on other phones.

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That'd certainly be possible, but for those of us that are going for the keyboard TOH, another TOH isn't an option. I'd also rather have an extra button on one side of the phone than the back.

Aonsaithya ( 2014-11-26 11:02:29 +0200 )edit

answered 2014-11-26 09:21:20 +0200

marsch gravatar image

Great device, would be a simple solution to a seemingly controverse issue.

The plug state of audio jacks is generally detected on a pure mechanical basis, i.e. the plug causes 2 contacts to touch.

Without knowing about the inner workings of the plug, I assume that would require an additional measurement of a specific resistance between two contacts of the plug instead of just detecting the logical state of an IO line.

Otherwise it might be impossible to differentiate between plug and headphones.

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But it could be enough. The plug can be detected as headphone with "answering" button. The rest is up to software. Just get some daemon recognizing pressing of that answering button and let it do something...

naytsyrhc ( 2014-11-26 09:54:37 +0200 )edit

You still have to provide a way then to not block audio, as it would be the case with your said headphone.

There doesn't seem to be any datasheet available for this device, so it makes barely sense to discuss this issue further without looking inside the hardware.

marsch ( 2014-11-26 10:46:22 +0200 )edit

I'd assume these plug keys are more or less identical in terms of inner workings. Here's a picture I found from

I myself have three different ones from Dealextreme, 315648, 317684 and 322540. I can try to crack open one or more of them to have a look inside?

Aonsaithya ( 2014-11-26 10:59:31 +0200 )edit

@marsch Good point. Which is another argument for not doing it via headphone but by creating a TOH, which is designed for just that (see my answer below).

naytsyrhc ( 2014-11-26 10:59:46 +0200 )edit

Isn't this plug the same as a headset with buttons on the cable? ...without the earphones and cable, of course...

vattuvarg ( 2014-11-27 14:46:19 +0200 )edit
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Asked: 2014-11-26 02:45:55 +0200

Seen: 268 times

Last updated: Nov 26 '14