[clue-tech] Everex mini PC

[Nate Duehr]

On Mar 3, 2008, at 3:55 PM, marcus hall wrote:

> On Mon, Mar 03, 2008 at 02:34:35PM -0700, Michael J. Hammel wrote:
>> Audio out is kind of limited.  I wonder if Linux supports USB audio
>> hardware?
>
> Definately is supported.  Even as far back as 2.4 kernels.


Yeah, most certainly -- some chipsets (like most USB things) better  
than others.  There's been some ham radio operators who have been  
hacking open $8 USB audio devices and finding the logic output/input  
pins on some of the chipsets for use in controlling radios, etc... an  
$8 interface between the PC and a radio, the logic output used to key  
the radio's push-to-talk and the logic input used to determine when  
the radio is hearing a signal (squelch or "COS" circuit, or similar).

They take these little $8 devices, hack them up for the additional  
signals needed, hack up the USB driver so they can get programmatic  
access to those pins on the chipset, and then hook it all together via  
Asterisk and/or custom C code for handling the VoIP conversions/CODECs  
etc.  Pretty cool.

Some have been working on "DSP" software to detect things like DTMF  
tones, so-called "sub-audible" tones (used for signaling in many FM 2- 
way applications) etc... finding zero-crossings of say a 100 Hz tone  
superimposed on an audio signal that's carrying voice is some ugly  
heavy-hitter math, when trying to do it in real-time in a user  
application under the linux kernel.  Quite difficult, but a neat  
programming challenge for those that are "into" such things.  (I don't  
think they have a working prototype of that code yet, but anyone who  
could pull it off will probably have a job for life in the telco low- 
level DSP programming world...)

--
Nate Duehr
nate at natetech.com