1 Reply Latest reply: Sep 22, 2009 1:13 PM by danotron
danotron Level 1 Level 1 (0 points)
Hey all. I am trying to figure a couple of things out in regards to the function button as on the standard iPhone headset.

I have a motorcycle, and an older Autocom system (a helmet radio / voice switcher / etc), and am trying to integrate my iPhone. To do so, I need to make a male-male 3.5mm 4-pole TRRS cable, as nobody really seems to make one anywhere that I've been able to find. I've seen the various pin-outs for the wires if one wanted to simply go from connector A to connector B, but I am trying to find out how to wire in a function button (this way I can reject a call, pause playback, skip tracks, etc, without having to actually look at or touch the phone while I'm riding).

I have found several pretty useful diagrams, the best of which is at this link:

The overall schematic of what I need to do here (as near as I can tell) is as follows:

Tip (right speaker) --> Tip (right speaker)
Ring1 (left speaker) --> Ring1 (left speaker)
Ring2 (ground) --> Sleeve (microphone)
Sleeve (microphone --> Ring2 (microphone)

Supposedly one should be able to wire in a momentary switch, on the Ring2 and Sleeve wires. When this switch is activated, is how the phone interprets the function button being pressed, and does whatever it is the phone is programmed to do when that happens.

What I am trying to figure out, basically, is how this switch works: a typical momentary switch is in either an always-open or always-closed state, and the switch action occurs when the circuit is either closed (as in an always-open switch) or opened (as in an always-closed switch). Push a button, switch is activated. Let go of the button, it returns to its normal default state.

That would, however, imply that either Ring2 (ground, on the iPhone side), or Sleeve (the microphone, on the iPhone side) is either always disconnected, and the phone recognizes a function-button action when that circuit is completed momentarily; or, that the phone interprets a headset-function-button-push when that connection is interrupted. It could also be that the connections should be switched (Ring2 -> Ring2, Sleeve -> Sleeve) in order for that to happen. I really don't know.

Does anybody here have any insight? In a nutshell, what I am trying to find out is how the iPhone recognizes that the function button on the headset has been pushed.

Thanks very much, all!


iPhone 3G, iPhone OS 3.0.1