Phone going nuts when using 3.5mm plug- Need schematic..

[Allen_B]

Very strange problem using my HTC One (2013 model) when using it with the stereo on my motorcycle...

The bike uses a standard 3.5mm input cable that plugs into the stereo's wiring harness. The problem is for some reason, the phone will think it is connected to a mic/button headset and will freak out skipping songs (Pandora) redialing the last number (dozens of times) or launch Google One- generally freaking the frack out until I unplug the cable.

I say for some reason but it is obvious the phone thinks it is connected to a headset with a button and the button is being pressed repeatedly and randomly. When I initially plug in the phone (and when I'm not having problems) it shows the normal headphone icon but during one of it's "seizures" it clearly indicates it thinks it has a headset connected.

I am at a disadvantage in that I don't know how the button press is signaled (no pinout or schematic) so I am unsure where to start. My initial thought would be a short somewhere but the 3.5mm plug is a standard "3-ring" plug. The audio cable actually plugs into a harness in the bike's sound system (3 wire plug) and the strange part is when the phone is having a "seizure", I have disconnected the cable from the harness (and subsequently the stereo) with no change- it continued to freak out. Unplug the cable from the phone and it stops...

Phone works perfectly with 3 other vehicles, several standard sets of headphones and a button/mic headset.

Any ideas??


/r

Allen

 

[B. Diddy]

Re: Phone going nuts when using a standard 3.5mm plug?!

I'm not going to pretend that I have a solution, but this Wikipedia entry is worth reading, specifically this passage:

"Three- or four-conductor (TRS or TRRS) 2.5 mm and 3.5 mm sockets are common on cell phones, providing mono (three conductor) or stereo (four conductor) sound and a microphone input, together with signaling (e.g., push a button to answer a call). Three-conductor 2.5 mm connectors are particularly common on older phones, while four-conductor 3.5 mm connectors are more common on newer smartphones. These are used both for handsfree headsets (esp. mono audio plus mic, also stereo audio plus mic, plus signaling for call handling) and for (stereo) headphones (stereo audio, no mic). For wireless connection of headsets or headphones, Bluetooth is the standard protocol, and does not use a connector.

Due to possibility of three rings in the plug versus four rings in the socket and to differing pin assignment on the rings, many physically compatible connections are not electrically compatible. For example, plugging TRS headphones into a TRS headset socket (or the reverse), plugging TRS headphones or headsets into a TRRS socket, or plugging TRRS headphones or headsets from one manufacturer into a TRRS socket from another may not function. Most commonly mono audio will work, but stereo audio or mic may or may not work, depending on wiring. Signaling compatibility depends both on wiring compatibility and the signals sent by the hands-free/headphones controller being correctly interpreted by the phone.[original research?] Specialized adapters are available,[12][original research?] though adapters that are wired for headsets will not work for stereo headphones and conversely. Further, as TTY/TDDs are wired as headsets, TTY adapters can also be used to connect a 2.5 mm headset to a phone.

3.5 mm TRRS (stereo-plus-mic) sockets are particularly common on recent smartphones, and have been used e.g. by Nokia since 2006; this is often compatible with standard 3.5 mm stereo headphones. 2 different forms are frequently found, both of which place left audio on the tip and right audio on the first ring (mirroring the configuration found on stereo connectors). Where they differ is in the placement of the microphone and return contacts. The first, which places the return signal on the second ring and the microphone on the sleeve, is used by Apple's iPhone line, HTC devices, latest Samsung, Nokia and Sony phones, among others. The second, which reverses these contacts, is used by older Nokia mobiles, Samsung smartphones and some Sony Ericsson phones.[13] Some computers now include a TRRS headset socket, compatible with headsets intended for smartphones. One such pin assignment, with ground on the sleeve, is standardized in OMTP[14] and has been accepted as a national Chinese standard YDT 1885-2009."

Bottom line is that maybe the plug leading from the bike to the phone's jack is the wrong orientation.

 

[Allen_B]

Re: Phone going nuts when using a standard 3.5mm plug?!

...Bottom line is that maybe the plug leading from the bike to the phone's jack is the wrong orientation.

That is the problem (in a way)... The 3.5mm plug from the bike is a standard (TRS as described above) 3-wire plug vice the 4 wire stereo-plus-mic plug- That is a big reason I am confused. There isn't an extra "4th" ring or wire to be wired incorrectly or backwards.

The other problem is this is an intermittent problem- the phone will correctly identify the cable as a standard 3-ring headphone connection MOST of the time. While riding, the phone will schiz-out and indicate it has a headset connected.


/r

Allen

 

[B. Diddy]

Re: Phone going nuts when using a standard 3.5mm plug?!

Any way you can replace that particular connecting cable?

 

[Allen_B]

Re: Phone going nuts when using a standard 3.5mm plug?!

Any way you can replace that particular connecting cable?

That is the current plan but I am trying to understand the nature of the problem. Swapping the cable is sort of easter-egg troubleshooting...

Can anyone post a wiring diagram of a typical OMTP wired headset? I am particularly interested in how a button is wired- i.e. when the button is pressed is this a normally open or normally closed circuit? What contact is actually closed or opened (i.e. tip to GND)?


/r

Allen

 

[Allen_B]

Re: Phone going nuts when using a standard 3.5mm plug?!

Ok, can anyone tell me what (electronically) is happening when you press a button on a headset?

That would assist in looking for an intermittent short or open in the cable...


/r

Allen