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Basic queries on using LT Spice

T

Terry Pinnell

Jan 1, 1970
0
These are very basic questions, some no doubt in the Duh! category.
FWIW I've read the tutorial, albeit quickly. But a few quick pointers
from the established LT Spice users could save me hours please! Or
maybe there is an existing source for learning practical details which
I've not yet found? I'm so familiar with CM that getting comfortable
with LT Spice may take me a while, but I'd like to master it as its
simulation facilities are plainly superior.

1. What's the difference between Move and Drag? (Both appear to move a
selected part or group of parts around, until left click fixes them in
new position.)

2. With a circuit drawn, I click Run and get the 'Select Visible
Waveforms' dialogue, with choices like V(n001),V(n002),etc. But how do
I know what those nodes are? IOW how do I first ensure the nodes are
displayed on the schematic.

3. In the absence of such indicators, suppose I just choose the first
and get a plot headed
'V(n001)'. Can I *now* get the schematic to show that choice? Is there
any other way of finding what voltage or current I'm seeing, apart
from clicking each node with the cursor and observing the result?

4. If I decide to take the Help's advice "The easiest method is to
simply probe the schematic. You simply point and click at a wire to
plot the voltage on that wire," how do I by-pass that initial
dialogue? Even with none of its choices selected, if I click Cancel,
it still plots V(n001). I could of course then close that, to get a
clean slate ... if I knew which node to click!

5. With several voltages plotted, how do I separate them into
individual windows?

6. To edit the schematic, I take it you must first close all plots?

7. In CM I can select a 'component' called '.IC' and connect it at a
node. In LTS I see I add this as a Spice Directive. But how do I
connect it?

8. Is there any way to re-assign shortcuts? For example, I have ctrl-z
ingrained for Undo, and Ctrl-c for Copy, not F9 and F6.

9. Where can I find step by step examples of adding/importing new
models?

10. For a Transient Analysis, with whatever defaults running, what are
the steps for changing the key parameters: Start Time, Stop Time, Step
Time, Max Step Time. Are these all entered as Spice Directives? If so,
is there a succinct summary of the main directives and their syntax
please? (In CM, I use only the GUI.)
 
T

Tony Williams

Jan 1, 1970
0
These are very basic questions, some no doubt in the Duh!
category. FWIW I've read the tutorial, albeit quickly. But a few
quick pointers from the established LT Spice users could save me
hours please! Or maybe there is an existing source for learning
practical details which I've not yet found? I'm so familiar with
CM that getting comfortable with LT Spice may take me a while,
but I'd like to master it as its simulation facilities are
plainly superior.

LTSpice is my first Spice ever, so can't really answer
many of your questions Terry..... but I do have to say
that I'm mightily impressed with some of the simulations
it has done on known circuits.

3. In the absence of such indicators, suppose I just choose the
first and get a plot headed 'V(n001)'. Can I *now* get the
schematic to show that choice? Is there any other way of finding
what voltage or current I'm seeing, apart from clicking each node
with the cursor and observing the result?

Left click in the schematic window to make that window the
one with the input focus. Then wander around around nodes
and components to see the scope probe or current display
being offered. As each one is offered it's description
in given down in the bottom left corner, in text.
6. To edit the schematic, I take it you must first close all
plots?

No, just left-click in the schematic window to make it the
active window. When done, re-run the simulation and a new
plot will overwrite the old one.
10. For a Transient Analysis, with whatever defaults running,
what are the steps for changing the key parameters: Start Time,
Stop Time, Step Time, Max Step Time.

Drop down the 'Simulate' pane, 'Edit Simulation Cmd' is
the bottom option.
 
T

Terry Pinnell

Jan 1, 1970
0
Tony Williams said:
LTSpice is my first Spice ever, so can't really answer
many of your questions Terry..... but I do have to say
that I'm mightily impressed with some of the simulations
it has done on known circuits.



Left click in the schematic window to make that window the
one with the input focus. Then wander around around nodes
and components to see the scope probe or current display
being offered. As each one is offered it's description
in given down in the bottom left corner, in text.


No, just left-click in the schematic window to make it the
active window. When done, re-run the simulation and a new
plot will overwrite the old one.


Drop down the 'Simulate' pane, 'Edit Simulation Cmd' is
the bottom option.

Thanks Tony. 3 down, 7 to go. Until my next 10 <g>.
 
T

Tony Williams

Jan 1, 1970
0
Terry Pinnell said:
Thanks Tony. 3 down, 7 to go. Until my next 10 <g>.

I forgot to say. After the schematic is drawn, and
before a run, you can wander the cursor around the
schematic and the identity of each node also comes
up in the bottom left corner.
 
T

Terry Pinnell

Jan 1, 1970
0
YD said:
You can also place a label (F4) at the nodes of interest. Press F4 to
give it a name and definiton (In, Out, Bi, None). Then drag and drop
it onto a wire in the node. Or place it somewhere and connect it.

- YD.

Thanks YD. Discovered that one a little later <g>. How about
connecting the .IC command though?
 
Y

YD

Jan 1, 1970
0
I forgot to say. After the schematic is drawn, and
before a run, you can wander the cursor around the
schematic and the identity of each node also comes
up in the bottom left corner.

You can also place a label (F4) at the nodes of interest. Press F4 to
give it a name and definiton (In, Out, Bi, None). Then drag and drop
it onto a wire in the node. Or place it somewhere and connect it.

- YD.
 
J

John Smith

Jan 1, 1970
0
----- Original Message -----
From: "Terry Pinnell" <[email protected]>
Newsgroups: sci.electronics.cad,sci.electronics.design
Sent: Tuesday, November 30, 2004 3:42 AM
Subject: Basic queries on using LT Spice

These are very basic questions, some no doubt in the Duh! category.
FWIW I've read the tutorial, albeit quickly. But a few quick pointers
from the established LT Spice users could save me hours please! Or
maybe there is an existing source for learning practical details which
I've not yet found? I'm so familiar with CM that getting comfortable
with LT Spice may take me a while, but I'd like to master it as its
simulation facilities are plainly superior.


A dedicated LT Spice newsgroup:
http://groups.yahoo.com/group/LTspice/?yguid=161100399

1. What's the difference between Move and Drag? (Both appear to move a
selected part or group of parts around, until left click fixes them in
new position.)


If the component is connected in the schematic, using drag will pull the
wires along with the component when you move it. Move moves the component
without stretching the wires. Note that you can draw a rectangle with drag
or move to select an entire area to move or drag.

See Help/Schematic Editing.
2. With a circuit drawn, I click Run and get the 'Select Visible
Waveforms' dialogue, with choices like V(n001),V(n002),etc. But how do
I know what those nodes are? IOW how do I first ensure the nodes are
displayed on the schematic.


I believe this question has been answered. If you don't want to pass the
crosshairs over the wire to read the node ID below, you can label the wire.
See Help/Trace Selection.
3. In the absence of such indicators, suppose I just choose the first
and get a plot headed
'V(n001)'. Can I *now* get the schematic to show that choice? Is there
any other way of finding what voltage or current I'm seeing, apart
from clicking each node with the cursor and observing the result?


No. Not that I aware of. Note that you single click a node to plot it.
Clicking the same node twice in succession discards all plots but that node.
This is not what you asked, but it is handy to know.

4. If I decide to take the Help's advice "The easiest method is to
simply probe the schematic. You simply point and click at a wire to
plot the voltage on that wire," how do I by-pass that initial
dialogue? Even with none of its choices selected, if I click Cancel,
it still plots V(n001). I could of course then close that, to get a
clean slate ... if I knew which node to click!


On a new schematic, or when you have closed the plot window, LT Spice
doesn't know which node you want plotted, so it asks. You must either tell
it which node to plot or it will plot node 001. After the initial run, it
will continue to display the node or nodes previously selected until you
close the plot window again. If you have a display which you like, you can
click on the plot window somewhere to make it the focus, then save the plot.
Save the plot with the same name as the schematic. The next time you do a
run after closing the plot window (or after closing LT Spice and then
reloading), LT Spice will look for a plot file and use it to display your
plots as selected previously.

See Help/Save Plot Configurations
5. With several voltages plotted, how do I separate them into
individual windows?


I think this has been answered, but, right click the plot pane. Select Add
Plot Pane. Click the node of interest.

6. To edit the schematic, I take it you must first close all plots?

No.



7. In CM I can select a 'component' called '.IC' and connect it at a
node. In LTS I see I add this as a Spice Directive. But how do I
connect it?
8. Is there any way to re-assign shortcuts? For example, I have ctrl-z
ingrained for Undo, and Ctrl-c for Copy, not F9 and F6.


I've never used this, but look under Help in Shortcuts.

9. Where can I find step by step examples of adding/importing new
models?


Look in Help/FAQs/Adding Third Party Models

10. For a Transient Analysis, with whatever defaults running, what are
the steps for changing the key parameters: Start Time, Stop Time, Step
Time, Max Step Time. Are these all entered as Spice Directives? If so,
is there a succinct summary of the main directives and their syntax
please? (In CM, I use only the GUI.)


With focus on the schematic, click Simulate/Edit Simulation Command. A
dialog box opens for you to insert the values without resorting to
directives. Otherwise, see Help/Dot Commands.

Note that my answers here are based on my experience and there may be other
and better answers.

LT Spice comes with example programs and pretty good help, especially for a
free, powerful program. I strongly recommend you read the Help and run the
examples. I should do this, too.

Good luck.

John
 
T

Terry Pinnell

Jan 1, 1970
0
John Smith said:
----- Original Message -----
From: "Terry Pinnell" <[email protected]>
Newsgroups: sci.electronics.cad,sci.electronics.design
Sent: Tuesday, November 30, 2004 3:42 AM
Subject: Basic queries on using LT Spice




A dedicated LT Spice newsgroup:
http://groups.yahoo.com/group/LTspice/?yguid=161100399




If the component is connected in the schematic, using drag will pull the
wires along with the component when you move it. Move moves the component
without stretching the wires. Note that you can draw a rectangle with drag
or move to select an entire area to move or drag.

See Help/Schematic Editing.



I believe this question has been answered. If you don't want to pass the
crosshairs over the wire to read the node ID below, you can label the wire.
See Help/Trace Selection.



No. Not that I aware of. Note that you single click a node to plot it.
Clicking the same node twice in succession discards all plots but that node.
This is not what you asked, but it is handy to know.




On a new schematic, or when you have closed the plot window, LT Spice
doesn't know which node you want plotted, so it asks. You must either tell
it which node to plot or it will plot node 001. After the initial run, it
will continue to display the node or nodes previously selected until you
close the plot window again. If you have a display which you like, you can
click on the plot window somewhere to make it the focus, then save the plot.
Save the plot with the same name as the schematic. The next time you do a
run after closing the plot window (or after closing LT Spice and then
reloading), LT Spice will look for a plot file and use it to display your
plots as selected previously.

See Help/Save Plot Configurations



I think this has been answered, but, right click the plot pane. Select Add
Plot Pane. Click the node of interest.





I've never used this, but look under Help in Shortcuts.




Look in Help/FAQs/Adding Third Party Models




With focus on the schematic, click Simulate/Edit Simulation Command. A
dialog box opens for you to insert the values without resorting to
directives. Otherwise, see Help/Dot Commands.

Note that my answers here are based on my experience and there may be other
and better answers.

LT Spice comes with example programs and pretty good help, especially for a
free, powerful program. I strongly recommend you read the Help and run the
examples. I should do this, too.

Good luck.

John
Thanks for that very thorough and helpful reply, John. Much
appreciated. Have now joined the Yahoo Forum.
 
J

john jardine

Jan 1, 1970
0
Terry Pinnell said:
Thanks YD. Discovered that one a little later <g>. How about
connecting the .IC command though?

It's added as one of those arcane, bloody, directives. Eg. " .IC V(n003)=0 "
regards
john
 
J

Jim Thompson

Jan 1, 1970
0
Terry Pinnell said:
[snip]

Thanks YD. Discovered that one a little later <g>. How about
connecting the .IC command though?

It's added as one of those arcane, bloody, directives. Eg. " .IC V(n003)=0 "
regards
john

In PSpice you just place an IC marker on your schematic... "IC1"
establishes initial conditions for a point relative to ground, "IC2"
establishes initial conditions between two points.

Generally you can also establish initial conditions within the setups
for capacitors and inductors.

...Jim Thompson
 
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