Re: gEDA-user: Simulation with Potentimeter

[John Doty <jpd@space.mit.edu>]

Remember: dependent sources are your friends when synthesizing nonstandard
SPICE components.

Most SPICE variants give you a way to make a bilinear dependent source. In
ngspice, for example, you can use a "B" device to make a resistor whose
voltage is proportional to the product of the applied current (measured by
a series "ammeter") and a control voltage. A pair of these with
complemetary control voltages should make a voltage-controlled pot
(although I haven't tried this particular trick).

This is enormously more flexible than a swept resistor. You can sweep the
control voltage if you wish, but you can also do a transient analysis
using an arbitrary function for the control voltage.


John Doty		"You can't confuse me, that's my job."
Home: jpd@w-d.org
Work: jpd@space.mit.edu

On Mon, 5 Jan 2004, John Sheahan wrote:

> On Sun, Jan 04, 2004 at 09:15:55PM +0100, mailinglists@my-mail.ch wrote:
> > Hi Stuart,
> > 
> > I did some simulations today using ".dc name start end stepsize" so that
> > would mean for your example
> > 
> > Resistor sweep test circuit
> > r1 0 1 100
> > r2 1 2 1k
> > v1 0 2 1v
> > .dc r1 100 1k 100
> > .end
> > 
> > This way it works and generates values, but shouldn't the result be a
> > straight line?
> > 
> > 
> > Tobias
> 
> this circuit has the transfer function vout = v1 . r1 / (r1+r2)
> which is not a linear function of r1 (not a straight line)
>