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I have a circuit and I am trying to integrate it with an iPhone via a TRRS headphone jack's microphone input. I have a generic TRRS cord and am trying to send a signal through it. However, the iPhone does not detect that a mic is even plugged in. However, if I plug it into my Mac via line-in and record, I can record the signal I am sending perfectly.

I have read online that it needs to detect resistance between the ground and mic, which I have. Are there any other things I need to do? It seems like this is an issue that stems from Apple's proprietary technology, as the earbuds are from a Windows Phone before they were spliced.

Thanks so much!

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  • \$\begingroup\$ Schematic, please. \$\endgroup\$
    – Brian Carlton
    Apr 27, 2012 at 21:44
  • \$\begingroup\$ @BrianCarlton, knowing Apple I seriously doubt it. They don't want anybody making accessories without paying them kickbacks. \$\endgroup\$
    – Joe Stavitsky
    Apr 27, 2012 at 22:31
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    \$\begingroup\$ I think he means of what he built \$\endgroup\$
    – Journeyman Geek
    Apr 28, 2012 at 2:05

4 Answers 4

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You might want to take a look at this and check if you have the same config.
http://www.wisebread.com/build-a-cable-to-control-your-android-phone-while-you-drive
I'm sure android and apple are the same kind (I've used them interchangeably) though samsung android phones have two rings swapped.

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From my testing, the iPhone seems to need some capacitance in the circuit for it to detect a microphone.

I used a variation of the schematic found at http://www.creativedistraction.com/demos/sensor-data-to-iphone-through-the-headphone-jack-using-arduino/ and was successfully able to get audio into my iPhone.

This is what my schematic looked like for hooking up my iPhone to a Baofeng UV5R radio:

Schematic

I've put the Eagle files up for this here: https://github.com/johnboiles/BaofengUV5R-TRRS

UPDATE: @jose.angel.jimenez in the comments says the capacitance isn't necessary. That may well be. My testing wasn't the most scientific. Still, this was the circuit that definitely worked best for me.

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    \$\begingroup\$ In fact, the iPhone does need to "see" an equivalent ohmic resistor of about 1.6K, tough 2.2K will work also fine. It has nothing to do with the capacitance. \$\endgroup\$
    – jose.angel.jimenez
    Feb 4, 2014 at 1:00
  • \$\begingroup\$ @jose.angel.jimenez Thank you! It works. Where is the 1.6K documented? \$\endgroup\$
    – Mark Adler
    May 27 at 16:57
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Impedance (the iPhone mic input) is a little trickier than straight DC resistance. Impedance line-matching has always involved a few passive components (cap's and/or coils). johnboiles' schematic uses some series RC for (I assume) signal matching/conditioning to the iPhone's mic input and he's apparently using the left (?) channel of the iPhone's output to feed the mic input on the ham radio(??). A 1.6Kohm resistor is a workable approximation, but isn't really impedance-matching.

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The Apple implementation swaps the standard Ring2 (normally microphone) and Sleeve (normally Ground) functions as used in OMTP TRRS

The Apple CTIA TRRS is Tip- Left Audio, Ring1- Right Audio, Ring2- Ground, Sleeve- microphone.

(source: Wikipedia https://en.wikipedia.org/wiki/Phone_connector_(audio))

--This pinout switch on same-connector implementation, will be familiar to those who used Avid's products in the late 1990's.---

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