Richard,

To keep costs as low as possible 
you might want to find a microprocessor
with onboard ADC and USB ports.  I am
using a PIC14000 with onboard 16 bit
ADC ports, but it can only do a software
based standard serial I/O.   There is a PIC16c77
that has onboard 12 bit ADC ports, plus a port
that can be used for software based USB, all for
about $5.   See my web page for some PIC
programming links.  
http://www.infiltec.com/seismo/#micro
Also see Jan Axelson's book "USB Complete".  
http://www.amazon.com/exec/obidos/tg/detail/-/0965081958/
Unfortunately USB I/O is a lot more 
complicated than serial.

Hope this helps,

Dave
http://www.infiltec.com/seismo/

> From:    Richard Diaz 
> Date:    Sun, 23 Feb 2003 19:23:26 -0700
> 
> I am from Colorado School of Mines and currently am working on a 
> seismometer to be mass produced for general education classroom use.  
> We have been using the DATAQ instruments DI-194RS starter kit, but is 
> not really streamlined for what we need it for.  I was thinking about 
> an AD converter that only has two input, and outputs to a USB port, 
> since it is becoming a mainstream method of PC input.  I am not really 
> sure how to go about modifying and AD converter in such a manner.  If 
> anyone has any insight, could you please assist?


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