Re: gEDA-user: How to do transient analysis?

[David Logan]

Daniel Nilsson wrote:
On Fri, Apr 08, 2005 at 05:34:14PM -0600, David Logan wrote:
 

What would be the best way to do transient analysis using geda? I have 
pspice instructions, which are easy enough. I just define a circuit like:

gnd -> IDC -> t_Close (t=0) -> R -> L -> gnd. Then I go into "Transient 
analysis" setup, set "Print Step" and "Final Time", and I get a graph of 
my capcitor voltage or inductor current.
   

I'm not sure I understand what your circuit is supposed to do, are you
sending a DC current through an inductor ? That should not produce
anyting interesting in simulation at all...
 

It actually does produce something interesting between t=0 and t=L/R, 
because current changes at a rate of If+(Ii-If)e^(-t/(L/R)), and the 
voltage changes at L*di/dt of that.

The transient analysis that I am doing now is showing that rate of 
change of capacitors or inductors over that (usually) short time frame.

In ngspice you should be able to do something like this to simulate an
inductor in transient analysis:
*Simulation for inductor circuit
I1 0 source pwl (0 0 10n 0 12n 1)
R1 source 1 10
L1 1 0 10nH
.tran 100ps 50ns
.end
Save that to a file filename.sp, run:
ngspice -b filename.sp -r filename.raw -o filename.out
Then load filename.raw into gwave.
 

I'll give that a shot. For simple circuits, this will probably be fine. 
However, when it gets into the multi-switch circuits, the pspice 
simulations have actual settable switches. Transient analysis takes into 
account switch locations at the specified time frames, and correctly 
calculates/graphs voltages and currents respectively.

So I presume there is no equivalent in geda?
I can show you a single switch example and a corresponding graph: 
http://www.loganshouse.net/problem
(Keep in mind that there can be multiple switches, open or closed by 
default at t=0, and switched at t values > 0. This simple example just 
doesn't happen show one.)

Thanks!
David Logan