Olimex Support Forum

OLinuXino Android / Linux boards and System On Modules => A10 => Topic started by: SetV on April 15, 2015, 11:46:38 pm

Title: A10 Lime Stereo Audio Out Pin
Post by: SetV on April 15, 2015, 11:46:38 pm
Hi,

Is here a way to take Stereo Audio out from a A10-Lime device, by accessing GPIO pin.

Few reference are seen accessing Composite Video out by accessing GPIO_1 Pin 20 and Pin 4 (http://wot.lv/tv-out-on-olimexs-a10-lime.html)

I want to connect A10-Lime to an old TV where RCA connector is alone supported (Yello, Red and White cable connectors).

Thanks,
SetV
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: Gerrit on April 16, 2015, 01:07:48 am
Audio is on GPIO-1 pin 14/16/18

14 HPOUTL
16 HPCOM
18 HPOUTR

But use capacitors between all the the pins and the TV (+ side at the board)

An alternative is to use a converter like this, so you can connect other HDMI devices to the TV also.

http://www.tinydeal.com/hdmi-to-av-video-converter-adapter-p-96139.html
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: SetV on April 16, 2015, 11:26:46 pm
Hi Gerrit,

Thanks for the reply, I shall go with your former solution for now.

I am having one more question, What should be the value of capacitor used? Is there any soft/hard limit to be applied?
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: Gerrit on April 17, 2015, 12:27:12 am
Quote from: SetV on April 16, 2015, 11:26:46 pm
I am having one more question, What should be the value of capacitor used? Is there any soft/hard limit to be applied?


It is not critical just to filter out the DC components anything from 1uF to 47uF.
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: SetV on April 22, 2015, 11:18:46 am
Thanks Gerrit, I shall try and update the same.
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: SetV on April 29, 2015, 03:04:52 pm
Hi Gerrit,

I tried to get Stereo Audio from Pin 14 and 18 using Pin 4 as ground, could not get stereo audio yet, I don't know what I am missing.

GPIO_1 Pin 14 is connected to 1uF 63V Capacitor positive and negative is connected to RCA white cable inner connector, same way GPIO_1 Pin 18 is connected to another 1uF 63V Capacitor positive and negative is connected to RCA Red cable inner connector. GPIO_1 Pin 4 is connected to both White and Red cable negative point (outer connectors).

I don't know how to use Pin 16 (HPCOM), is it Headphone Jack Composite Audio/Video Out? searched in GPIO sheet and user manual to get some info, could not find any.

Is FEX settings need to be modified to get Stereo Audio out, as done in case of TV out? Please share your input.

Thanks!
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: Gerrit on April 29, 2015, 05:33:56 pm
QuoteI don't know how to use Pin 16 (HPCOM)


This is the common for L and R out, if you measure the voltage against ground (pin 4) then you will see all 3 audio pins are about 1.5 Volts, that is why the capacitors are needed, it should work the way you connected it now, but also connect a 1uF between pin 14 and the negative point from the red and  white cable to be sure.

If you don't have that 1.5 Volt or sound then most likely the output is on mute.

most easily to see and correct is to start alsamixer from the command line
if you don't have it install it with

sudo apt-get install alsa-utils

if you start it, you see the controls,
first is the slider for the volume "Master"
second "Master Capture Mute" MM = muted 00 = not muted

after selecting it, you can toggle it with the M key make you sure it is on 00

also make sure the player selected the right output and is not sending it to the HDMI

to make it default open  /etc/asound.conf and change
pcm.dmixer {
      type dmix
      ipc_key 1024
      ipc_key_add_uid false
      ipc_perm 0660
      slave {
          pcm "hw:1,0"   <==== this line
          rate 48000
          channels 2
          period_time 0
          period_size 1024
          buffer_time 0
          buffer_size 4096
      }
  }


pcm.dmixer {
      type dmix
      ipc_key 1024
      ipc_key_add_uid false
      ipc_perm 0660
      slave {
          pcm "hw:0,0"   <=== into this
          rate 48000
          channels 2
          period_time 0
          period_size 1024
          buffer_time 0
          buffer_size 4096
      }
  }


After a reboot it will take effect
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: SetV on May 04, 2015, 08:26:04 pm
Hi Gerrit,

Thanks for the extensive help!

I am getting Stereo Audio now, your second setting helped to get the audio, the audio was pointing to HDMI, after the 'pcm' value change, audio was detectable.

Quote from: Gerrit on April 29, 2015, 05:33:56 pm
but also connect a 1uF between pin 14 and the negative point from the red and  white cable to be sure.


The point you mentioned is for pin 16, I guess, I took it that way!

Does 1uF capacitor applies to A20-Lime board as well? I am occasionally using this board too, but the video is somewhat dim compared to A10-Lime. Do I need to reduce the value of the capacitor?

Thanks for the support!
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: Gerrit on May 04, 2015, 11:28:32 pm
Quote from: SetV on May 04, 2015, 08:26:04 pm


Quote from: Gerrit on April 29, 2015, 05:33:56 pm
but also connect a 1uF between pin 14 and the negative point from the red and  white cable to be sure.


The point you mentioned is for pin 16, I guess, I took it that way!

Yes you are right

Quote
Does 1uF capacitor applies to A20-Lime board as well? I am occasionally using this board too, but the video is somewhat dim compared to A10-Lime. Do I need to reduce the value of the capacitor?


Same for the A20 don't know why you would reduce the value, the capacitors are for the audio, not for the video output.
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: SetV on May 06, 2015, 06:06:22 pm

Thanks Gerrit!

I thought video out would also emit DC volts and capacitor is required to eliminate that. I am not using capacitor any more for video and things are fine now.
Title: Re: A10 Lime Stereo Audio Out Pin
Post by: balenbalen on June 07, 2015, 10:38:53 am
I totally agree with Gerrit about that......well done