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From: John Larkin on 4 Oct 2007 23:38
Does LTspice have a potentiometer component? I'd like to do transient
analysis sweeps, as a function of pot rotation.

I can't find this. Any other way to simulate the function? I really
need the varying resistances, so I can't just use a multiplier.


John

From: John Popelish on 4 Oct 2007 23:53
John Larkin wrote:
> Does LTspice have a potentiometer component? I'd like to do transient
> analysis sweeps, as a function of pot rotation.
>
> I can't find this. Any other way to simulate the function? I really
> need the varying resistances, so I can't just use a multiplier.

For a resistance value, use a variable name enclosed in
curly braces (to solve the variable before each run), e.g.
{RV}. Then add a parameter step command to the schematic,
e.g. .step param RV 1 10k 1k
using the Edit, Spice directive menus.

To make a potentiometer, define the values the two halves of
the pot (on each side of the wiper) with a position formula
in curly braces), e.g. {1+Rtotal*position} and
{1+Rtotal*(1-position)}.

Then add a parameter to define Rtotal,
..param Rtotal=10k
and a step command for the position,
..step param position 0 1 .1

The extra ohm in the formulas prevents the section
resistance from reaching zero ohms which blows the math up,
and sort of represents the wiper resistance.

If you want to run single position runs, add a position
parameter definition
..param position=.5
and comment out the step position by right clicking on the
command and clicking the comment button.

Later you can comment out the position parameter and
uncomment the position step command, if needed.
From: Tam/WB2TT on 4 Oct 2007 23:54

"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message
news:n9cbg3h2ie7enqpurmsg350lr3ata4nsjl(a)4ax.com...
> Does LTspice have a potentiometer component? I'd like to do transient
> analysis sweeps, as a function of pot rotation.
>
> I can't find this. Any other way to simulate the function? I really
> need the varying resistances, so I can't just use a multiplier.
>
>
> John
>
Interesting you should ask. I was 100% certain that there was a
potentiometer. But, using the latest version, like you, I could not find it.

Tam


From: Jim Thompson on 5 Oct 2007 10:37
On Thu, 04 Oct 2007 20:38:57 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>Does LTspice have a potentiometer component? I'd like to do transient
>analysis sweeps, as a function of pot rotation.
>
>I can't find this. Any other way to simulate the function? I really
>need the varying resistances, so I can't just use a multiplier.
>
>
>John

Posted many moons ago...

http://analog-innovations.com/SED/PotentiometerForSpice.pdf

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave
From: Joel Kolstad on 5 Oct 2007 12:49
"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message
news:n9cbg3h2ie7enqpurmsg350lr3ata4nsjl(a)4ax.com...
> Does LTspice have a potentiometer component?

Nope! From hearing Mike Engelhardt (the author) answer the question, I'm
pretty sure it's that way on purpose -- he really does prefer two resistors,
with one set to, e.g., {10k*x} and the other set to {10k*(1-x)}. (And then
you use a .param statement to have LTspice step through the various values of
x you're interested in.)

I'm told that someone has posted (presumably on the Yahoo! group) a
potentiometer just bundling up the two resistors into a single package (as
Jim's .pdf demonstrates) in case you want something that looks "nicer."

It's interesting that Mike seems to feel so strongly about pots one way
whereas John Warner of SIMetrix fame seems to like pots so much he added the
ability to use the cursor keys to "turn" the pot and automatically re-run
simulation each time!

---Joel


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