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[SOLVED] Need help understanding the right way to wire up a headset for an Android phone

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Hyerman

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This is my first post on this forum. My apologies if it is the wrong section or I get anything wrong.

I am trying, and failing, to create a simple headset for an android phone out of basic components. My design only has one speaker rather than the two that a headset normally has. It also doesn't have any of the fancy control buttons. It just has a single speaker and a microphone. I have been trying for about a week to get it to work and I haven't been able to create a headset that android will recognize.

The android spec for audio pugs can be found here. https://source.android.com/devices/accessories/headset/plug-headset-spec#electrical
The jack side of the android spec can be found here.

The datasheet for the microphone I have been using can be found here.
The datasheet for the speaker I have been using can be found here. NOTE: this is a link to a pdf download rather than a web page.

The CTIA wiring for 3.5mm plugs is described rather well in this post.

I wired my headphone up the same way as the CTIA diagram in the prior link with a few exceptions:
1) I only used one speaker rather than two. I wired up the right speaker and not the left speaker.
2) I added a 110 ohm resistor in front of the speaker so that the combined resistance on that line would be 117 ohms. The android plug spec indicates that the resistance should be between 32 and 300 ohms.
3) I added a 520 ohm resistor upstream of the microphone so that the combined resistance on that line would be 1120 ohms. The android plug spec indicates that the resistance should be greater than 1000 ohms.

When I plug in my headset I get nothing. Nothing comes thru the microphone or out thru the speakers. My phone will continue to use its built in speakers and microphone. I also use an app that detects and indicates headphone insertion. An app that works pretty well to determine if a headset with-or-without a microphone is attached is called “Headset Notifier” on Google Play. I turn off all the options for it so that it only comes on when I want it to.

For comparison, I have a cheapo Skull Candy headset with a microphone. It works great in my android phone.

I checked the resistance of the various plug contacts on both my headset and the Skull Candy headset. I see what I expect on my headset. The Skull Candy headset has infinite resistance on the sleeve connections, which I don't understand.

Here is my naming conventions for the plug from the tip down to the sleeve.
Tip-Spkr-L
Ring-Spkr-R
Ring-Ground
Sleeve-Mic

Contact 1Contact 2Skull CandyMy headset
Ring-Spkr-RTip-Spkr-L40 ohmsInf
Ring-GroundTip-Spkr-L20 ohmsInf
Ring-GroundRing-Spkr-R20 ohms117 ohms
Sleeve-MicTip-Spkr-LInfInf
Sleeve-MicRing-Spkr-RInf1120 ohms
Sleeve-MicRing-GroundInf1120 ohms

I appreciate any guidance that can be provided. I am a software person, but 30 years ago I had an aerospace engineering degree and took basic 200-level circuit courses. My understanding of your comments won't go much beyond that.

Thanks,

Hyer
 

BradtheRad

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I have computers that are able to discern what I have plugged into the audio output. It's a combination of hardware sensing and software switching. How it operates is a mystery to me.

The high (infinite) ohm reading may in fact be a capacitor which blocks DC yet lets through AC. Your device may sense a finite impedance is attached even though you measure infinite with a DC ohmmeter.

Now I notice your headset has infinite resistance at the left channel. Perhaps you merely need to install a resistor to act as a mimic of an earphone. Then your device ought to detect headphones are plugged in.
 
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Hyerman

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I have computers that are able to discern what I have plugged into the audio output. It's a combination of hardware sensing and software switching. How it operates is a mystery to me.

The high (infinite) ohm reading may in fact be a capacitor which blocks DC yet lets through AC. Your device may sense a finite impedance is attached even though you measure infinite with a DC ohmmeter.

Now I notice your headset has infinite resistance at the left channel. Perhaps you merely need to install a resistor to act as a mimic of an earphone. Then your device ought to detect headphones are plugged in.
Thanks Brad. I'll try adding a speaker to the left channel. As for the the capacitor, the datasheet for the microphone shows a capacitor and a resister outside of the microphone case. At that point you then have three wires and I don't see how that matches up with the CTIA spec which only has two channels (one for the mic and one for the ground). This is exceeding my electrical knowledge.
 

Hyerman

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@BradtheRad , Sorry, but your suggestion to add a resistor to the other channel didn't work. Android still won't recognize my homemade headset. Any other suggestions?
 

BradtheRad

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Sleeve-MicRing-Spkr-RInf1120 ohms

Looking at your first table, you measure some connection between the mic & speaker, 1120 ohms. Should that be the case? (Because the skull candy phones show infinite.)

The speaker circuit doesn't require connection to the Mic circuit. Not all headphones have a mic anyway.

However you may intend to add a bit of your own vocal to what comes through the headphones. (Research found most people prefer this.) My computer amplifies the mic audio and sends it out the speaker port. (Does your android phone do so?) Did you put in home-made circuitry to do the same thing? You may need to increase the resistance between them.
 
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Hyerman

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My headset works now. For the benefit of anyone else searching with the same problem:

- android sees the headset (without a mic) being attached if ground and mic (ring2 and sleeve) are shorted.
- android see the headset also having a mic if ground and mic have reasonable resistance across them (I have tried 1K, 1.5K, and 1250 ohms). I have not tried any other resistance to simulate button presses.
- my mic and speakers work fine with a 8 ohm speaker and a 1250 ohm mic. The datasheets for both of them are above. It records my voice fine and I can hear the speaker in my ear. I have only hooked up one speaker and android doesn't seem to care if I use one or two speakers.
 

FvM

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Regarding 1120 ohm measurement, I see a similar value with my android headset if connecting the multimeter inversed (- to microphone terminal, + to ground terminal). No electret microphone has a low resistance when connected correctly. Hence the series resistor thing is probably nonsense.
 

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