Q:

How do I build a TRRS headphone jack with a jack that is detectable by an iPhone

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! 

A:

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.

