gertlex (gertlex) wrote in hearingaidhacks,

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Some bluetooth goodness

Hi all, I'm new to this community (skimmed it a few times over the past few months), and created a new LJ account with the sole purpose of contributing and learning in this community.  (My past screenname is unfashionable these days ;) )... I've got a project that I'll be attempting in the next couple weeks which I'm going to throw the preliminary basics of at you.  But first a bit about me and my hearing aids.  Jump down past the ººººººººº's if you want to go to the technical side of stuff right off.

I was born hearing impaired, roughly 50 % loss in both ears, slightly worse in the left.  Got hearing aids at 3, when grandpa suggested to my parents that such might be the case.  I've worn BTEs ever since then, and plainly visible too.  I've adapted fairly well to regular life.  I went through public school and am now a sophomore studying nuclear engineering at the University of Michigan.  I love my music... hate loud places, not least because I can't communicate much at all there... highly prefer captions everywhere, but generally watch almost no TV... I can do phones, but you won't like it unless I know your voice really well.  If I had to pick the thing that annoys me most at the current time about how I'm limited by hearing impairment, it's that I can't in good conscience take up a leadership role on the UM Solar Car team (or anything similar).  It's the limit of my capabilities to follow a group meeting, never mind contributing and thinking too.  I'll admit, the impression I get from reading this LJComm is that hearing aids aren't doing all they can for me.  I'm wary of subscribing to that after 17 years of the same old, I admit, but I'll search around harder the next time I get new HAs (a couple years from now, alas).

I finally got digital hearing aids just shy of two years ago.  I had tried them 4 years prior, and not liked them.  The ones now are better than then, of course.  The winning feature is the ability to turn off the microphone and receive only DAI input (is that redundant? :D).  I've been using DAI cables for 3 years now, and have four sets of said wires... Like many, I used the telecoil feature on my analog BTEs, originally.

Yes, four sets of wires.  Three of them are monaural Phonak wires.  They work for a year, but the insulating material is nothing short of crap.  I'm tempted to say the same of the materials that my BTEs are made of (always been phonak).  My last pair had cracks in it after 4 years. My original pair, 17 years old now, are crack-free... or were until I cracked those ones open a year or so ago (all but one screw came out)...  The fourth wire set is from Connevans in the UK, but I got them cheapish... HARC Mercantile, an hearing aid accessory sales-place had a "trial" set of wires from a product fair.  I bought those from them.  Currently they are working on determining whether they want to sell them.  Naturally, they have to import them and pay quite a bit in shipping.  Send them an email at to encourage them if this is something you'd like them to do!   Ah yes, the wires themselves; they're stereo, which makes them far better for listening to music.

I suppose you could say I'm done with the intro stuff, but really, I've done an excellent job transitioning into the hacking part of this, if I do say so myself ;)

Bluetooth has a magical allure to it for me.  Not exactly sure why, though the name and logo are catchy (and blue LEDs are awesome too).  I of course know about the ELI modules.  I'm glad I never splurged on those, as I know now they're definitely not what I want for music.  I've got my bluetooth enabled laptop accompanied by bluetooth mouse, keypad, serial connector, MP3 player and headphones.


We all know we look ridiculous when wearing headphones with BTEs though :)  (and they don't want to stay there, often)

I'm sure you're not going to be surprised at this point when I tell you that my plan is to take the remains of some of those old wires and splice them into the bluetooth headphones.  Not that simple of course, but read on.

My primary guide for this stuff so far is Neil's guide, which does a similar thing.  Doing it my way though :).  Beyond that, so far, what I know is from what I've gleaned via opening stuff and measuring stuff with my multimeter.

Currently, the end goal is to:
- Maintain regular headphone functionality
- short DAI cables plug into the hearing aids, one from each side of the headphones (each "phone")
- Switches on the outside of each phone
- Monoaural jacks on the outside of each phone
- The switches will toggle each phone and each DAI cable individually
- A resistor between each phone's circuitry and it's respective jack

Here are some pics of relevant parts... Let me know if you want pics of other components :)
- Side by side, Connevan's DAI plug and the Phonak plugs. (1)
- The circuit board in the left phone (2)
- The two severed loops from the 2nd oldest of the Phonak sets (3)
- The wiring of one of the phones' speaker (4)
- The mangled circuitry that is contained in the junction of the Phonak set. (5)
These and future pictures are stored here.

Relevant comments on pics:
1. Yes, the connevans plug is white.  The ones on the website are black.  Both have the same blue right angle plug.  I've verified that the white set has the same resistance as documented on Neils page (330kOhm)
2. The blue circle near the bottom is the two wires I anticipate I will need to desolder and rewire, etc.
3. These should be perfect length as is...  That curl is sort of permanent.  The polymer hardens with time.  Curled up in my pocket for thousands of hours has dictated their curl.  I've examined the wiring of these.  There are three wires, essentially: insulated red and white wires, and the copper strands elsewhere which I presume are ground.  The red/white wires are almost definitely for redundancy.  They go to the same pin (the short thin one), and are soldered together on the circuitry.  You can see the wires better in pic (1).
4. Same two wires as were see attached to the circuit board
5. I've destroyed two of these.  The first time I didn't realize there was circuity in there.  Second time, I took a more conservative approach to dissection, but still mangling abounded.  Were I do to this to my third one, I wouldn't have to mangle it  :/.  I'm not sure why it has so much circuitry, though most of it just seems to be splitting the single channel into two directions and making sure none the wires touch each other.

I've already ordered these:
- Switches (need two, ordered four) (I)
- Audio jacks (need two, ordered four) (II)

If I recall correctly, I have the power to edit this post indefinitely in the future.  As such, I will continue at a later time as I work through this project.  I finish up exams for the semester Monday... so I need to get sleep :)  I need to do some more research on the wiring though.  If anyone sees any glaring flaws, *please* let me know.

Thanks and insane props if you read all of that!
Dec. 16, 2007


Dec. 18 (barely), 2007

Been a long day, but I'm home from the dorms and done with exams.  I made sure to bring everything I needed back home with me (I keep a lot of my tools with me).

My shipment from Digi-key arrived, eliminating any worries of it taking weeks to come (ordered Friday, came Monday, cheapest shipping!).  Said package has the switches and audio jacks.

I started off with testing what connects to what on each set of DAI cables.  The Connevans match the schematic on Neil's guide.  The Phonaks, however, confuse me greatly.  I can match the ground pin (short, fat) to the "sleeve" part of the audio plug, but the tip doesn't seem to have connection to any DAI pins... Might it be that the circuitry in the junction of the DAI cable is something that is an electrically activated switch of a sort?  Electronics are not my forte; electrical engineering scares me, thus.  Alas, electronics are the key to hardware hacks these days.

Finding my continued foolery with the multimeter to be useless I fled to Wikipedia.  A couple results set me back on track:
- Explanation of the basic wiring of an audio jack, properly known as a TRS (or TS or TRRS) connector
- Additional diagram with clear explanation (for me) of the schematic drawings of TRS connectors

After this, I crudely disassembled one of the mono plugs of the Phonak DAI cables.  Crude = scissors + pliers + dremel.  I can use this piece though!  A picture will be forthcoming.  This mono plug is a TS connector... It has a tip and a sheath, but no ring (i.e. two metal contacts)

It does occur to me that there might be a diode or two in the circuitry of the Phonak DAI cable (but I mangled it so badly I can't tell ;) ).  I'll be sure to check for continuity from conditions tomorrow (red to DAI, black to audio plug, vice versa).  Some other tests I have planned for later today (after some sleep):
- I've got a 300something kOhm diode-resistor which I will put in series with one of the severed loops (3) and the TS connector using alligator clips... I'll test it with one of my older hearing aids to see if that's as simple as the circuit has to be.
- Make sure I have the wiring for the mono jacks from Digi-key right by plugging in some junk earbuds and connecting terminals with a male-male cable connected to one of my old mp3 players (mmmm, electronic junk; it's toxic, don't throw it away!; and you never know when you might want to scrap it for a hack).
- Throw in the switches into some circuits
- Actually draw up some electrical diagrams, and perhaps post them here.
- Figure out how I want mount the switch/jack to the headphones.  Ultimately I'm going to be drilling holes or cutting out larger holes in my brand new bluetooth headphones.  *wince*

Another note... my current hearing aids are a pair of Phonak Eleva 411 dAz BTEs.  The previous pair (and maybe the pair before that? I forget...) are Phonak PicoForte 3 PP-C-P BTEs

That's all for now.


Dec 20, 2007 (barely)

I've got it working.  The left phone is essentially done.  Yesterday was the wiring of the audio jack and added wires, and then epoxying the audio jack in.  I was barely able to get the battery back in, and ended up trimming the plastic bag that it was in... I shouldn't have to remove it ever again, I'm sure.

I'm feeling a bit ADD right now so that's all for now!

Dec 21, 2007

And here's the part you've been waiting for.... pictures!

Slowly working on the right side.  Much more of a pain to do.  I got particularly frustrated when I noticed that I had accidentally melted a small spot on the left phone while trying to solder a particularly stubborn wire.  Rawr.  I really need a steadier hand, a third hand, and maybe even someone else to do the soldering for me.

Dec 26, 2007

I'm nearly done with the right side.  The soldering was indeed trickier.  I've finished the soldering and epoxied the audio jack in place.  Tomorrow I'll be cutting out the slot in the phone's cover and calling that part done.

For the wires, I want to use right angle TS connectors and much more flexible wire.  I need to look into doing the wire splicing at the Europlug (i.e. right behind the hearing aid).

I've got the parts for that third hand forthcoming as an xmas gift from my brother, and I'll be buying some heat-shrink tubing, having discovered that mom has a heat gun she's almost never used.

More pictures to be added to the flickr album tomorrow, probably.

Jan 1, 2008

I'm essentially done.  A problem out of my control with the headphones has cropped up, though.  It seems the battery is electrically discharging itself (even when disconnected), but rather slowly.  I'll probably have to redo the terminal wiring, as something is (hopefully) wrong there, probably.  I've been testing the battery, and still am.

I did one of the wires to completion in a very satisfactory way.  This approach was:
1. cut a euro plug right at the base of the three pins.
2. force out the two relevant pins for soldering.  The plastic melts really fast if you leave the metal in there...
3. solder 270k Ohm resistor to one pin.

I used the wires from some junk stereo headphones I had.  Specifically, these Jensen headphones.  Each strand of the wire has two wires in it, ground and whichever channel that strand is for.  Ground/Right, and Ground/Left.

4. Strip the wires a bit, trim the wire not needed in each pair (Right, from ground/right, and ground, from left/right)
5. Solder Left to the resistor, and ground to the ground pin.
6. Test to make sure it works.

The first time I did it, I got the wires mixed up.  The wires were very fine, so I'm not too surprised I messed up with the multimeter when determining which wire was the Right wire.  The second time, I checked the other end of the wire cut... that which goes to the headphones.  Made it much more obvious.

7. Put tape of some sort on one side of this assembly, and then fill the gap with glue.  I used Gorilla glue because I had that sitting around, and the fact that it expands 4x helps fill up gaps.  (I trimmed excess with a dremel)  Once dry, an inch of 1/4" diameter heat-shrink tubing was enough to cover the whole thing.

Some pictures in the album of this.

Also, it occurs to me that I have not stated which headphones I've been working with.  Said headphones are Sony DR-BT22 bluetooth stereo headphones.

A note about the resistance.... I found that the 270k Ohm resistor results in the sound level being for me when listening to the headphones normally, and listening with the wires.  I need to obtain another resistor of that size from a friend.  Pulled that one out of a radio...

Hope you all had a great new years.

Gotta say though, I'm surprised at the lack of comments o_O


Jan. 10, 2008

So I lost the cable pictured below.  It really pisses me off.  Probably got dragged out of my pocket by accident when I pulled my keys out.  I have a guess as to where to look for the cable, but it's been a few days, plus rain.  (it's near my house, not my dorm, so not taking a bus all the way home just to look... though I'll look tomorrow as I go home then anyways)

And I went home to get stuff that came in the mail, namely a second pair of those headphones so I'd have matching wires.  Oh the irony.

I talked to a fellow Solar Car teammate who is an electrical engineer about the lithium battery.  His guess was that the funny smell was lithium (he had his own description of the smell) and concluded that the battery had been air-tight until I had trimmed the packaging...

Along those lines, I've yet to get a reply back from either of two potential sources for replacement batteries of the same size type... This is quite annoying.  I had hoped to quite literally show off the headphone hack to my audiologist in a week or two.

'Tis a working hack; I just had some crap luck towards the end.

May 13, 2008

Heh. Haven't edited this entry in ages.  Some further updates.

-Finally got a replacement battery from Sony.  Took 3 weeks to arrive, or so, and cost me ~$43. Ouch.  But I hear of people paying ~$50ish for replacement cellphone batteries....
-I use these regularly. I get strange looks, but they're so excellent.
-I've had the epoxy break where it attaches to the plastic a few times... Just using more epoxy and not leaving the wires plugged in when I put the headphones in my pockets has saved me this problem.  You never lose the jacks either, as they're soldered to three wires...
-I've been working on documenting a how-to here:
-It might be possible to do the exact same thing with this tiny beauty: Ebay link
But questions include sound quality and battery life.
-I got the whole setup to work with my brother's bluetooth phone, and had a conversation with a friend from the internets.  Amazing quality with hearing in both ears and no telecoil buzz!

May 17, 2010
Dang. 2 years later...!!!
The same headphones are still working perfectly fine! The battery might be slightly going bad, e.g. maybe 6 hours instead of 9... but I bought a second pair of headphones off ebay for ~$30 a couple months ago :)

There's no real damage to the headphones... they've survived regular use amazingly.  The only damage has been

I now use the headphones with three things: my laptop, my ipod touch, and my cellphone, which I got in Dec 09.  The cellphone is a Samsung Alias 2, and has bluetooth, of course.  I so very much love the ability to make "easy" phone calls now.

I've never really gotten around to finishing the guide, though.

I've done a fair amount of thinking in my head, and I'm pretty sure I can "manufacture" new DAI connectors myself now.  I've yet to take the time to do the necessary experimenting, but I hope to this summer.
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