Inline Media Controls for Mobile to Car Audio

This Instructable will show you how to create a 3.5mm male to male audio cable to use between your mobile phone and car to give you simple media control without having to touch or look at your phone.

I have only tested it with a Samsung Galaxy S2, and am not sure if it will work or be safe with any other models, although I have reason to believe it should work with many Android based phones, as the operating system should be looking for the same commands, assuming that the hardware supports it (that the phone has a 4 pole connection in its headphone socket).


EDIT:
Since upgrading my phone to the latest version of Android (Ice Cream Sandwich, v4.0.3) the controls have changed! My cord now does nothing when the button is pressed, volume up on skip track back, volume down on track forward. If anyone else finds this problem with their phone please leave a comment below with the phone version and operating system version. I am working on a new cable, but I have to try to find the new values to perform the desired functions!

EDIT 2:
I have tried resistance values from 0 ohm to 1200 ohms and have only been able to increase or decrease the volume on my Samsung Galaxy S2 running Android 4.0.3.
Decreasing volume occurs between 300 - 720 ohms
Increasing volume occurs between 150 - 290 ohms
The original values (used in this Instructable) should still work with earlier versions of Android, and possibly on other phones.


I don't think that this it will work with iPhones, as they look for a series of impulses rather than varied resistance as inline media controls.

I also need to give credit to WideBread.com and author Rich Kappmeier for doing the leg work on this one. Without his article
         http://www.wisebread.com/build-a-cable-to-control-your-android-phone-while-you-drive
I would not have been able to get very far with my idea (which as it turns out wasn't very original, at least in this phase).

At one point I forgot to take photos so I made a second cable to get photos of the final steps, thus the different cord colour.


Materials:
1 x 3.5mm 4 pole headphone jack
1 x 3.5mm stereo headphone jack
4 core cable
1 x 220 ohm resistor
1 x 620 ohm resistor
1 x push button (Play/Pause)
1 x 2 way switch (Skip Forward/Back)
Short length of wire
Solder
Sugru or other joining/finishing product

Step 1: Striping the wire

You will need to strip your 4 core wire.

My cable was very well insulated against chemical corrosion, far more than it needed to be for this purpose, which meant it was fairly hard to strip.

The outer jacket was a rubbery plastic which my wire stripper had trouble getting through without destroying the wire inside. After a few attempts I ended up using a sharp blade and bending the cable away from the cut and using the extra tension on the side facing up to make careful cuts till I got to the inner wires.

Only strip one end of your wire at this point. if you make a mistake you will need to cut it off and start again, making your cable shorter each time. Make sure you have plenty of excess cable and cut to length when you need to strip the other end.

This first end is going to be used for the 4 pole 3.5mm jack as it is the most tricky end of the cable, but more on that in the next step.

Comments

[DustySeven7]

Nice design, but technically speaking this is not really a "inline" control. That would be where the controls are somewhere in the length of the cable. Hence "inline". What would be interesting to see is if you could run the cable to the steering wheel and have the controls there. I think this would be safer as both hands would stay on the wheel.

[RandomIdeaMan]

Inline control is any control of your media player (phone) which is on the audio cable. In this case the controls are at the end of the cable, but are still before the connector. Even if you ran more wire for the 4th pole and ground to put the buttons on (as you mentioned) the steering wheel it is still technically in line with the audio cable.

While putting the controls on the steering wheel may be safer for use, having the cable long enough to allow full lock in both directions would require a fair amount of slack, this slack could inter fear with your driving and make it more dangerous than ever! The best solution for that would be to use a springy cord (think telephone cord) to keep it against the steering column.

If you do decide to try that please do be careful with the cable, and make sure the controls on the wheel don't inter fear with your hands on the wheel.

[zack247]

very cool. i have an android phone and was hoping play/pause wasnt the only thing i could do.

im going to do this and mount the controls either on or by my steering wheel for easy access.

also, this shouldnt void your warranty since you arent modifying the phone in any way.

[RandomIdeaMan]

If you are planning to mount the controls on your steering wheel make sure you allow plenty of cable so you can turn to full lock without breaking the wires.

I've seen that the Samsung galaxy note comes with headphones with inline play/pause, track skip and volume controls. If you can get your hands on the headphones from one of those you could measure the resistance across the 4th pole when changing the volume and add that to your controls too.

[rblee]

I'm guessing that the volume control will be either one or two (ganged) pots simply attenuating the output, which is normally how they do it. IME just a single pot between the ground from the two outputs and the ground going back to the phone.



Please comment if it's actually signalling the phone.



Very nice instructable - Really useful but no CNC milling machines or laser cutters :). Thanks for taking the time to post it. 

[RandomIdeaMan]

Actually I think the volume control would be the same as track skipping, a specific resistance between the 4th pole and ground for volume up and another for volume down.

The inline volume control used in simple headphones does use pots to change the resistance on the speaker wire, and thus the volume, but the idea of inline volume control in this case would be to change the setting on the phone. The only way the phone is receiving and input from these controls is via the 4th pole on the jack.

If I can get my hands on a headset with inline volume I will try to figure it out and post my findings, however it is fairly difficult to find them these days.

[rblee]

Check out:

http://www.androidzoom.com/android_applications/tools/headset-volume-controller_jpyc.html

The important bit seems to be:

"Turn your headset previous/next buttons into a volume controller while playing back music. Pause playback and you can skip tracks again."

Not great, but do-able. They don't do anything convenient like providing a DC offset to power tiny circuits with, do they?

Anyone got an oscilloscope?

[rblee]

Yarg - What happened to the formatting?
Sorry

[zack247]

I never thought about the volume, thats a good idea!

[Awesome-aniac]

Cool, I didn't even know that this could be done.

[RandomIdeaMan]

I don't think many people do, the big manufacturers are all focused on Bluetooth accessories and simple things like this get missed!

Luckily it's not very hard to do your self.

[RandomIdeaMan]

Also don't forget to vote for it in the Car Audio competition if you like it!