Re: gEDA-user: A little puzzled about the purpose of gschem

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On 22/04/10 07:26, Madhusudan Singh wrote:
>    Hello,
> 
>    I am not new (though a tad rusty) to spice, or the usual design
>    process. Years ago, I went through an analog circuit design, followed
>    by a VLSI design class that involved the use of H-Spice, Mentor
>    Graphics and Cadence software, basically Design Architect, (Modelsim
>    for digital design), Accusim, IC Station, DRC, LVS workflow, with the
>    (IIRC) AMI05 library.
> 
>    I am finding myself in need of doing some circuit design for a lab
>    application, and without access to the aforementioned software and
>    having developed a slight preference for the faster GUI based work (as
>    opposed to using MacSpice - I am on Mac OSX where geda, pcb, etc. are
>    all installed using MacPorts, and seem to launch ok), I decided to give
>    geda a spin. The overall workflow looks superficially similar to the
>    one I outlined above.
> 
>    So, I fire up gschem and decide to test it with a rudimentary inverting
>    op amp circuit using a 741. I wire the net, and then discover I need to
>    use command line gnetlist to generate the actual spice netlist. No
>    biggie, years of Sun and Linux experience (and importantly, zero
>    windows experience) make this a piece of cake. gschem editor experience
>    is remarkably like DA.
> 
>    But, I get a truckload of errors. I start researching and find this
>    gem:
> 
>    [1]http://www.brorson.com/gEDA/SPICE/x150.html
> 
>    Basically, I need to painfully enter all the parameters for a 741 !
>    There is even a file parameter where I can presumably enter the
>    filename containing the spice model by hand.
> 
>    At that point I stopped to take stock of the whole thing. Correct me if
>    I am wrong, but isn't the entire point of having a GUI entry to ease
>    and more importantly, speed, the development process ? So, precisely in
>    which way is using gschem more efficient than typing in a spice script
>    if I have to painfully pointy-and-clicky every damn single attribute
>    into this ? Some might say that after defining a symbol, I can copy and
>    paste it to create more complicated circuits, but that is what a subckt
>    definition is for.
> 
>    I guess I am asking - what purpose does gschem serve (other than to
>    create pretty pictures, and being a humongous waste of time otherwise
>    since its basically asking you to enter the entire spice script, albeit
>    in disparate pretty boxes) ?
> 
>    Thanks.
> 
> References
> 
>    1. http://www.brorson.com/gEDA/SPICE/x150.html
> 
> 
> 
> 
> 
> 
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gschem isn't a SPICE frontend, and in fact it is only tangentially
related to SPICE. As such, it doesn't ship with any SPICE models, and as
a result, including default model parameters would make no sense (since
any spice models that may or may not be available on the system would
probably have a different name than the default anyway).

That said, you only need to enter the model names/paths for your .subckt
models. If you have your schematic ready, you can also use gattrib to
edit the parameters of all components at once in a tabular fashion. The
advantage gschem gives over manual writing of SPICE files is that you
have a visual representation of your eventual netlist, and an integrated
circuit symbol with the pin names included is much more obvious than
"X1" followed by some numbers and an obscure name.

However, if you want a quick, graphical SPICE, I suggest using LTSpice
through Darwine. In my personal experience, LTSpice's simulator is a lot
better than ngspice/gnucap, and it is definitely an easier workflow than
gschem->gattrib->gnetlist->ngspice if you're only interested in simulation.


Peter


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