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[aprssig] Re: Single Board PC

Stephen H. Smith wa8lmf2 at aol.com
Thu Sep 8 18:27:20 UTC 2005

bruninga at usna.edu wrote:

>Can anyone point to a source of single-
>board PC's with 2 serial ports, and sound 
>card that comes with WIndows.  Something to
>put in a box and forgetabout.  But
>can plug in a monitor and Keyboard to
>set up.
>It will run ALOGGER, and ECHOLINK, etc...
>for a stand-alone remote controlled satgate.
>Dont want hamfest specials, but something that
>is reproducible...

It's not a complete boxed PC with OS installed,  but the VIA Computer 
micro-ITX "EPIA" series motherboards are perfect for this kind of 
application.  Several versions have dual serial ports and sound 
built-into the motherboard.     My combination APRS UI-Webserver--APRN 
System--EchoLink  "Ham Superserver" runs on the EPIA-TC board which has 
the added twist of operating directly on a single +12 VDC supply at less 
than 1.2A. It has DC-DC converters on-board that generate the other 
voltages required including +5 and +12 for external devices like hard 
disks and CD-ROM drives.   

My version of the EPIA has TWO serial ports, 6 USB 2.0 ports, XGA video, 
standard PS/2 mouse and kbd jacks,  and one Ethernet port.  The sound 
system has both line and mic level inputs.  (The LINE level input, which 
an increasing number of laptops and motherboards omit, is vastly 
preferrable to a MIC input for soundcard applications like Echolink or 

Other versions of the EPIA board require a conventional ATX-type PC 
power supply, but have FOUR serial ports and TWO Ethernet ports on 
board.     These boards are small (about 8" square) and can fit into 
special small-footprint cases,  but the tooling (mounting holes, 
connector panels and backplane slot alignment) lets the board fit 
standard ATX tower cases.  

Full details on my installation, including links to the board 
manufacturer's technical data and vendors are at:


Important Warning:   The on-board sound on many systems is a severely 
cost-reduced "brain dead" approach to PC sound that does away with much 
of the specialized hardware traditionally found on add-in sound cards. 
Instead they use the host CPU, bus clocks and interrupt handlers to do  
work formerly done by specialized sound chips and timing chains with 
accurate dedicated oscillators.    The exact timing and sample rate of 
the sound system then varies depending on how many other programs and 
processes are running on the CPU at the same time.    This usually isn't 
a problem  for  the normal voice and music applications of the sound 
system, but can cause major calibration problems on PSK31 and SSTV.   
Gradually accumulating timing errors (relative to the system at the 
other end of a link) can cause periodic phase slips, hiccups and 
stuttering audio on EchoLInk,    slanted pictures on SSTV,    and an 
effect like a drifting analog VFO on PSK31. 

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com

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