Audio Jack P2 Problems


Hi everyone,

I’m a new user of DragonBoard 410c and I need to record and play sounds with it.
I’m trying to use the configuration gave in this link:

I’ve soldered a female stereo connector with 4 terminals: pin 10 (CDC_HPH_L), pin 8 (CDC_HPH_R), pin 4 (GND) and pin 6 (CDC_MIC2_P).

To record an audio file I use the follow lines:

tinymix ‘MultiMedia1 Mixer TERT_MI2S_TX’ 1

tinymix ‘DEC1 MUX’ ‘ADC2’

tinymix ‘ADC2 MUX’ ‘INP2’

tinycap /data/test.wav

And to play a audio file I do:

tinymix ‘PRI_MI2S_RX Audio Mixer MultiMedia1’ 1

tinymix ‘RX1 MIX1 INP1’ ‘RX1’

tinymix ‘RX2 MIX1 INP1’ ‘RX2’

tinymix ‘RDAC2 MUX’ ‘RX2’

tinymix ‘HPHL’ ‘Switch’

tinymix ‘HPHR’ ‘Switch’

tinymix ‘MI2S_RX Channels’ ‘Two’

tinyplay /data/test.wav

The problem is:
If I use a speaker with a 2 rings Jack P2 (left, right and gnd) it works normally with those commands. If I use a microphone with a 2 rings Jack P2, it works normally too, but it has a buzz in the back of the sound.
If I use a headset with a tip and 3 rings (left, right, gnd and microphone) it doesn’t work with those commands. So I have two question:

  1. Does someone know how I can take off the buzz in the sound recorded?
  2. Why doesn’t the Jack P2 with tip and 3 rings work with my commands?

I’m really sorry for my bad english and thanks for your time and considerations.


Hi Vitor

This is partially my fault. I missed one connection when I wrote the app note, and in fact I am in the process of updating the app note to correct this omission. Please add one more wire from J9 pin 9 (HPH_REF) to GND at the jack. This should resolve the buzz when you are recording.

The next ‘issue’ is the headset mic needs a 1.8V Bias signal. Without a Bias voltage, the mic doesn’t work very well. The bias voltage (CDC_MIC_BIAS2) was supposed to be provided on the main board by R160 (2k Ohms), unfortunately all of the boards have been built without having R160 installed.

We have you have a 3 options to provide a bias voltage to the mic.

  1. The best solution is to install R160 in the board, unfortunately this requires soldering on an extremely tiny resistor and most of us don’t have the necessary dexterity to do this. When I update the app note I will show the location of R160 for the brave few who can do the rework.

I have not yet tested options 2 and 3 so I can’t be sure they work.

  1. connect CDC_MIC_BIAS1 (J7 pin 12) through a 2k resistor to CDC_MIC2_P (J2 pin 6), I have not yet checked that CDC_MIC_BIAS1 is turned on, you can use a volt meter and confirm the presence of 1.8V on pin 12 (measure between J7 pin 4 and J7 pin 12). If the 1.8V is not present, then you can try option 3.

  2. There is a 1.8V supply on the low-speed connector (J8 pin 35, LS_EXP_1V8), this supply may be a little noisy if you have a mezzanine card plugged into the low speed connector, but if there is no mezzanine board plugged in it should be quite quiet. Use a 2k resistor to connect LS_EXP_1V8 (J8 pin 35) to CDC_MIC2_P (J7 pin 6).

The last thing to check is the pin-out on your jack and the headset. Every jack seems to have different terminals for different rings make sure you read the correct manufacturer’s datasheet. The other thing to check is your headset, there are two common pinouts and you might have either one. Starting at the tip, the order of the rings can be either Left,Right,Ground,Mic, or Left,Right,Mic,Ground (Note: how Mic and Ground are swapped). if you have a swapped headset for your 3-ring headset it will not work until you swap the terminals.

Full Disclosure, I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


Hi @ljking,

Thanks for your reply. I’ve tried and tested your solutions and for the first one (eliminate the buzz) it’s true that now it’s working pretty better. And I’ve tried the option 3 (connect 2K resistor to J8 pin 35 and J7 pin 6.

Now I think that my problems were solved but the sound recorded is low. I don’t know if the problem is the sound recorded or the sound played is low. Do you know what I can do?




Hi @ljking,

In the app note you’ve said:

“You should be able to hear playback on the earphone connected to the stereo connector.
Playback using Android Music player would play the audio over HDMI, as that is the default
setting. To change the default behavior, edit the file
device/qcom/msm8916_32/mixer_paths_sbc.xml based on the use case and push the file
into DragonBoard 410c via adb to /system/etc/.”

In fact, I don’t want to play any sound in Android Music player, but I want to start up the DragonBoard with the configurations to record and play music as I’ve said before with my Jack P2. I’ve tried to modify the file ‘mixer_paths_sbc.xml’ but I didn’t succeed, may you know how I can start the system with these configurations. Should I modify any boot file? Could you help me?



Hi Vitor:

Unfortunately modifying the .xml file is also beyond my skill level. I am hoping an Android expert can step in here and help out.

About the low recording levels, there is a programmable gain stage in the hardware and I suspect the gain can be set using the .xml file…

Full Disclosure, I am an employee of Qualcomm Canada, any opinions expressed in this or any other post may not reflect the opinions of my employer.


Hi @ljking,

I update this topic because I’m actually designing a jack-audio output on my mezzanine board and I’m meeting some troubles.

I rode here that you are actually updating the application note about routing the audio output from the DragonBoard 410c.

It seems that there is a mistake in the figure at the 2.3 of the app. note.
I was looking for a jack connector with a dedicated contact for TIP switch (offering the ability to detect a jack plug) and it seems that the common symbolic usage of jack connector looks like this:


This image is from CUI Inc. from the topic “Understanding Audio Jack Switches and Schematics.”

It should be the Sleeve connected to the “rectangular part” on the schematic (currently, on the figure at the 2.3, it’s the TIP signal connected to it). It just something that will help a bit the cabling of a jack audio to the DragonBoard 410c, personnaly, I had to cross several source to understand that point.

Thanks for considering this.

EDIT: Image integration + Sorry, I didn’t saw that the topic was so old (I followed a link you posted on another topic).


Hi @Will

There are an astoundingly huge number of connectors out there all with different pinouts and switch organisations. There are also numerous ways to number the tip, sleeve and rings on the connector, and finally there are two common types of headset with microphone: the European and the North American varieties which have two contacts swapped. The app note has been updated and is (as far as I know) correct. I was very careful to NOT use pin numbers and I only described the connector for a North American headset in the app note.

Follow the diagrams in the app note, but you will need to “translate” it to the pin numbers of the specific headset plug and the jack you have selected.

No longer a Qualcomm employee
Looking for a new opportunity.


Awh ok, I wasn’t sure it was a mistake, I’m in EU that’s why I misunderstood the pins diagram.

Yep, my conclusion was the same, so thanks for the confirmation :slight_smile: