Re: [Discuss-gnuradio] Using USRP w/o Daughterboard's

[Eric Blossom]

On Thu, Nov 03, 2005 at 11:40:42AM -0700, Robitaille, Michael wrote:
> The project I am working is for remote sensing via an optic link.  For the
> proof of concept I am using ASK (ON/OFF Keying) modulation at low data rate
> and low carrier frequencies (500Hz to 2.0 KHz - Yep real low).  At a later
> date it will be changed to different modulation technique and higher
> frequencies to get the data rate up some.  Based on my current
> specification, none of the DB would be of much use so I am trying to use the
> USRP w/o daughterboard's.
> 
> Any insight/examples on how I can do this would be appreciated.
> 
> I have been looking through all the documentation (Doxygen documents, usrp
> header files, examples, Dawei Shen Tutorial) to find what I need but I am
> coming up short.  For instance, I can't find usage information for commands
> like usrp.determine_rx_mux_value or options.rx_sugdev_spec and many more
> that I have found being used in examples or mention in post on this board
> (read_io).  Could someone point me to where I can find
> information/headers/code for these?

The code that defines determine_rx_mux_value is in

   gr-usrp/src/usrp.py

It's pretty short.

> The fist task that I am trying to do is make the example usrp_oscope.py and
> usrp_fft.py work without the daughterboard.  First I am not sure what inputs
> these use and second I need to find out some information on some of the
> function they use.  The examples work but not sure how to connect the input
> w/o daughter boards.

You are going to need some kind of daughterboard to get access to the
high-speed A/D and D/A inputs and output respectively.  On the other
hand, you may be able to just read a digital i/o pin for your very low
data rate.  The Basic Tx and Basic Rx daughterboards bring out 16
uncommitted digital i/o pins to headers.  To read then periodically,
you'd need to hack up some custom FPGA code.  You might need to build
a small amount of circuitry to inteface your analog signal to the 
0 to 3.3 V levels the i/o pins expect.

> Any help in how to modify these examples and where to find the information
> on all the function/header/class would be appreciated.

Almost all of the high level USRP functionality is defined in two C++
header files:  usrp/host/lib/usrp_basic.h and usrp/host/lib/usrp_standard.h.
Through a somewhat convoluted path, the public interfaces of those
classes end being methods in the Python usrp.source_c and/or
usrp.sink_c classes.

Hope this helps.  If not, please ask again.

Eric