Re: gEDA-user: Simulation with Potentimeter

[Stuart Brorson <sdb@cloud9.net>]

Quoting "mailinglists@my-mail.ch" <mailinglists@my-mail.ch>:
> I am trying to simulate a circuit that uses a potentiometer, but can't
> figure out how to do that. Anybody can tell what a commandfile would
> look like to do so? I read somewhere that it should be possible to
> sweep
> resistor values, but didn't find any further explanation or an example.
> 
> Tobias

Hi Tobias --

It's hard to answer this question without a clearer idea of where you
are stuck.  Also, what simulator do you want to use?  To answer your
question, I'll assume you want to use gschem to draw your circuit,
and then use tclspice/ngspice to simulate.  Right?

Plain Berkeley SPICE (which is what tclspice is) doesn't support pots. 
(i.e. there is no built-in pot component recognized by the program.)
Therefore, if you want to simulate a circuit with a pot in it 
using plain SPICE, you should just use two series resistors & 
vary the ratio between the two resistor values.  Yes, it's a PITA, but
life is full of sorrows. . . . .  If the TCL facilities in tclspice
worked better, you could write a TCL prog to do this automaticaly.
However, the TCL stuff rarely seems to work for me.  :-(

Commercial simulators like PSpice *do* incorporate pot symbols and 
models.  We have previously discussed incorporating this kind of 
facility into gschem & gnetlist/spice-sdb.  However, without the ability
to simulate using an open-source simulator, it's hard to know what 
SPICE code syntax should be spit out from the netlister.  And yes, I
suppose somebody could hack tclspice to support pots, but it seems
like a lot of work to me. . . .

Does anybody know what (if anything) gnucap does with pots?  Does it have
a native pot component?

Stuart