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How to build a digital FM receiver for recording audio in MP3 format? Preferably directly to Android phone? Answered

Hi!

I have this thing:
http://www.phonak.com/com/b2c/en/products/fm/transmitters/smartlink_plus/overview.html

Which I use during lectures so that I could properly hear the lecturer, and it works very very well - I can hear him perfectly when he "wears" it so that microphones are close to him.
I also have the FM receiver part which works in conjunction with a hearing aid - no issues.

However, I also would like to RECORD everything he says, a technician told me the FM frequency used by the Phonak system is Channel 16 frequency: 174.1200 MHz (174120.0 HZ)


I tried a few Google searches, but I did not come up with any leads or ideas, how to record this transmission - best would be to an MP3 file or something, I could store on Evernote or something along with the lecture notes I take.


I should also point out, I have an Arduino Uno at my disposal (with Prototyping shield).


I am open for any and all ideas, and suggestions how to get this done.
I might require some help as electronics is unfortunately not my strong suite (software development is, however).


Thanks!

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steveastrouk
steveastrouk

7 years ago

So how does this link into your hearing aid ? By the loop input ?

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Carmageddon
Carmageddon

Answer 7 years ago

Yes, using the loop which has built in FM receiver and is creating the magnetic resonance picked up by the Telecoil built into the hearing aid.

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steveastrouk
steveastrouk

Answer 7 years ago

In that case, just pick up the loop signal from the receiver straight into your recorder. No need for an arduino. Your standard plugin earphone-mic might well be all you need.

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Carmageddon
Carmageddon

Answer 7 years ago

What do you mean by plugin earphone-mic? can you give an example?

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steveastrouk
steveastrouk

Answer 7 years ago

The thing that plugs into your phone for headphones and microphone

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Carmageddon
Carmageddon

Answer 7 years ago

The Loop cable is integrated with the receiver, so took me a while to figure out what you (possibly) meant:
According to: http://www.phonak.com/content/dam/phonak/b2b/C_M_tools/FM/Receivers/UserGuides/MyLinkPlus-User-Guide.PDF
On page 9, it has a Headphone socket (2.5mm) - did you mean to use this output, as microphone input for the phone? if so, how?

Googling a bit further, I found this: http://forum.xda-developers.com/showthread.php?t=1548401

Apparently it is a 4 contact miniature jack - so I am not sure what to look for, that would work bridging the two together...

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steveastrouk
steveastrouk

Answer 7 years ago

That helps enormously, just get the 4 pin jack off a mic/headphone cable and wire a 2.5mm jack by removing the microphone from the cable.

I don't guarantee it will work without a bit of extra circuitry, but it might. Try it.

My original idea was to make a pickup coil and pick up the loop signal through that.

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Carmageddon
Carmageddon

Answer 7 years ago

Interesting idea, I will be looking for such a cable (along with 2.5mm male jack) that I could cut and solder instead of the microphone :)

BUT, this method has one BIG drawback: according to the above linked manual, once I plug in the external "output" (originally designed for say, headphones) - it will disable the Loop to save battery power!!

So, your idea of building a a pickup coil is still preferred - could you please give me instructions as to how to accomplish this? if its not much more complex, I would rather try that first.


And thanks so much for the help so far! I have hope :)

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steveastrouk
steveastrouk

Answer 7 years ago

Have you anyway of laying your hands on a "dead" hearing-aid receiver ? I'm not sure how the pickup is achieved: I know, of course, what it needs - basically a coil wrapped on a former.

I muse idly on the idea of using a tape-recorder pickup head as the coil... cheap and simple.

Try it. Its hard to suggest much else without experiments.

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Carmageddon
Carmageddon

Answer 7 years ago

I do have some older hearing aids which are no longer in use, but it is past midnight now, I will look into this tomorrow :)

PS: any idea how to recognize the telecoil? everything is miniaturized in that little thing :)

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steveastrouk
steveastrouk

Answer 7 years ago

We may need to make a tiny amp for the signal, we may not. This is getting interesting.

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Carmageddon
Carmageddon

Answer 7 years ago

Hi Again Steve :)
I have opened a very old hearing aid I had (of the generation before the digital ones) - based on the picture we saw online of the telecoil component, I MAY have identified it, but it is sooo small!
Like, really small! the connectors are as tiny as hairs almost... I am not sure how to solder that.

In addition, one connector got torn off while I opened the case :(

I am attaching two pictures - one of them taken using a magnifying glass :)





What do you think?

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steveastrouk
steveastrouk

Answer 7 years ago

I think you've nailed the identifcation, but I think soldering it will be tricky !

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Carmageddon
Carmageddon

Answer 7 years ago

That is an understatement, Steve!
I tried to get the wire off with some spare, but it tore off without spare :(

Any suggestions on how to solder this? perhaps there are special strategies for this scale?
Do I just drop a small drop of the solder over each contact, with the hope they will keep the touch to the tiny contacts remaining? The drop would pretty much cover the whole hole...

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steveastrouk
steveastrouk

Answer 7 years ago

You really need a little piece of prototyping board, solder the tracks to the board, solder the wires to the board - then there is no strain on the wires....or get the telephone pickup ;-)

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steveastrouk
steveastrouk

Answer 7 years ago

I think you look for a telephone pickup.....

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Carmageddon
Carmageddon

Answer 7 years ago

damn, instructables filters out HTML and image links.. I attached them here.

http://imageshack.us/a/img849/8663/xm1.png
http://imageshack.us/a/img404/3097/svb.png

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steveastrouk
steveastrouk

Answer 7 years ago

He.
All I can suggest is some GOOD photos ! Let's see if its detectable.

ALSO, you might be able to find a "telephone pickup coil" from somewhere. Like this http://www.maplin.co.uk/telephone-pick-up-coil-3519

Steve

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steveastrouk
steveastrouk

Answer 7 years ago

...or this http://compare.ebay.co.uk/like/321077321479?var=gv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=65&ff19=0

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Carmageddon
Carmageddon

Answer 7 years ago

Are you certain the above two are telecoil based?
I tend to think they are mic based...
Anyway this evening I will update with pictures once I take apart old hearing aid :)

Meanwhile, I found this:
http://www.grupopremo.com/in/new/152/
http://www.grupopremo.com/in/product/522/features/rfid/telecoils/tp0602-tc-microsmdhardferritetelecoil.html

In the shop: http://www.grupopremo.com/in/shop/

But I am not sure - is that the telecoil generator, or the receiver we are looking for?
Looking forward for your answer, because apparently I can order the one on the Shop online, and no extra shipping charges :)'

Thanks!!

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steveastrouk
steveastrouk

Answer 7 years ago

That looks like the receiver coil to me. Its VERY small though ;-)

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steveastrouk
steveastrouk

Answer 7 years ago

PS. All you do is wire the coil onto the microphone leads.

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Carmageddon
Carmageddon

Answer 7 years ago

Do you mean one edge to the ground, and the other to the Microphone?
Because as I understand it, the 4 jack receiver goes this way:
A headphone 4 pins (sound + mic) have 4 contact, beginning for the point are : Sound Left, Sound Right, Ground, Microphone.