Re: gEDA-user: minor problems with ngspice + gschem tutorial

[John Doty <jpd@xxxxxxxxx>]

On Aug 2, 2009, at 12:24 PM, Mike Kordosky wrote:

>
>    Hi,
>    I'm learning to use ngspice and gschem via the excellent tutorial
>    [1]http://geda.seul.org/wiki/geda:ngspice_and_gschem
>    I think there are a few small problems which if fixed would make  
> the
>    tutorial even better. I am not sure if this is the relevant mailing
>    list, I thought about geda-bug, but my problems are not software  
> bugs.
>    Anyway, please advise if this is not the right list.
>    Issues:
>    * I'm using gschem 1.4.3.20081231  and ngspice v19 on Ubuntu  
> 9.04. I
>    compiled ngspice from source but the gEDA suite came as a  
> collection
>    of ubuntu packages.
>    * I followed the tutorial all the way through and ran ngspice  
> but got
>    the following message:
>    Supplies reduced to   0.1000% Warning: singular matrix:  check  
> nodes
>    2n3904 and 2n3904
>    ** Most users will know this output indicates a problem. But, it  
> would
>    be nice to point users to a sample file showing correct output.
>    ** I'd be surprised if this isn't a fairly well known problem.  I
>    found a hint via google. My solution was to edit
>    Q1 1 Vbase 2  2N3904
>    to
>    Q1 1 Vbase 2 0 2N3904
>    I think the leading 2 in 2N3904 is being interpreted as a node  
> number
>    (for the substrate)  by ngspice.

Yep. Ancient problem inherited from Berkeley.

>   The naive user needs to be helped
>    through this,

Indeed. Old SPICE codgers recognize this problem, but it's hard to  
find an explanation.

> perhaps by modifying 2N3904 to Q2N3904 in the text or
>    just by suggesting the hand edit.
>    * It would be helpful if the reader could download a correct  
> copy of
>    the netlist to compare with theirs.
>    * It would be helpful to "close the loop" and get the user to
>    graphical output, also introducing them to ngspice in interactive
>    mode.  I'm suggesting:
>    ngspice [2]spice.net
>    ngspice 1 -> ac dec 20 1 100Meg
>    ngspice 2 -> plot vout vin vbase
>    which produces the attached plot for me.
>    Mike Kordosky
>
> References
>
>    1. http://geda.seul.org/wiki/geda:ngspice_and_gschem
>    2. http://spice.net/<output.png>

Why don't you ask Ales for access to the wiki? Go ahead and fix it.  
That's how we make progress.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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