[OZAPRS] DreamPlug as an IGate???

[Andrew Errington]

On Sun, 10 Jul 2011 15:28:45 Steve wrote:
> Andrew,
>
> That sounds fantastic.
> Can you offer any examples of tested USB units that have the required
> chipset and that have good access to the required GPIO signal?
> I'll be hitting eBay, etc, the minute you do ;-)

It sounds fantastic, but the way is fraught with difficulty and danger.

For other examples of this technique look at TheLinkBox, the 
pcrepeatercontroller project, and Asterisk app_rpt.  Or search Google 
for 'CM108 PTT'.  So, it's not a new idea, but adding support to soundmodem 
is.  Upon reflection I should have added it to hamlib, then soundmodem and 
fldigi could both make use of it, but I am leaving this as an exercise for 
others.

Firstly, you have to find a USB audio dongle with a supported chipset.  There 
are many of them, you've probably seen them, shot in bright translucent 
plastic with the logo "3D Sound" on them.  They cost about $5 or something 
cheap like that.  Inside is probably a C-Media CM108 chip (or later variants, 
CM109 or CM119).  But... you can only use them if you get a packaged chip on 
the PCB.  These days a lot of them are epoxy blobbed, and I don't think the 
GPIO lines are bonded out to the PCB.

There are compatible chips from 3S, the SSS1620/21/23.  These have a different 
pinout, but they are software compatible.  These, and the CM119 are often 
found in the slightly bigger plastic moulding with "Virluul 7.1Ch Sound" 
(or 'Virtual') printed on them.  These have buttons for Volume up/down and 
mic and speaker mute.  Again, you need a packaged chip.

I have two SSS1623 units which I have modified, but I have not extensively 
tested them so I don't know if they stutter or lock up under load, or other 
bad things.  I have two CM119 units which do not expose a HID interface under 
Linux, so the buttons don't work, and I can't write to GPIO.  I am hoping 
this is fixed in a later version of Linux, since the buttons work properly 
under Windows.

So, you will find hundreds of vendors on ebay selling these devices, but 
unless your vendor is willing to inspect their stock carefully they might not 
be able to sell you exactly what you want (or expect).

73,

Andrew
ZL3AME