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I've a circuit that makes sounds through an a standard audio jack (3.5mm) and I would like to connect it to a smartphone (let's say iPhone).

When I connect it to an iPhone, it will be detected as headphones, so it would listen not only to my circuit but also on the iPhones built-in mic. If I take my jack and connect it to a microphone - it would detect a HeadSet connection and then listen only on the audio jack mic input. If I substitute the microphone with a resistor - it loses that detection and goes back to headphones (my assumption was it detects resistance. probably was wrong).

Any ideas how a smartphone would detect a microphone connected and how that could be simulated?

Many thanks!

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  • \$\begingroup\$ What resistor did you put in? \$\endgroup\$
    – Kellenjb
    Commented Aug 4, 2011 at 14:48
  • \$\begingroup\$ 2.2K resistor. The question is what does it expect? \$\endgroup\$
    – roman
    Commented Aug 4, 2011 at 15:10
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    \$\begingroup\$ Do you have a 10k ohm to throw in there and try? \$\endgroup\$
    – Kellenjb
    Commented Aug 4, 2011 at 15:34
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    \$\begingroup\$ The way I have always understood it was it was looking to see the resistance between the mic pin and the ground pin. If it is a short then the plug doesn't have a separate ring for a mic. It could be that it is looking for a higher resistance, which is why I am wondering. \$\endgroup\$
    – Kellenjb
    Commented Aug 4, 2011 at 15:40
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    \$\begingroup\$ Some small piezoelectric microphones can have megaohms of impedance so if resistance is being measured the values suggested so far may be out by a few orders of magnitude. Do you have the equipment to measure your microphone's impedance and then match that? A digital multimeter would be fine. \$\endgroup\$
    – jbarlow
    Commented Aug 31, 2011 at 10:45

1 Answer 1

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The the problem is probably the standard 3.5mm jack. Smart phones use four pole 3.5mm jacks to add a mic to a headset. There are two configurations used but the most common (read what Apple pushes) is to have the sleeve as mic in, ground on the adjacent ring, right audio on the next ring then left on the tip.

Pinout with list of phones

I know that most recent Samsung phones reverse ground and mic in. I actually built a small crossover cable to get around this issue.

According to this page the mic should work if the resistance is about 2.2k ohms.

I only assume this works based on the success of using my crossover cable to use a headset/mic with button designed for iPhone on my Galaxy S.

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  • \$\begingroup\$ Thanks for the response. I've used an apple cord so that the pins will be correct. (for now just using for the iPhone). I've found that the impedance it expects is about 1.25k ohms. After simulating this impedance - it really would detect it. \$\endgroup\$
    – roman
    Commented Sep 26, 2011 at 13:32

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