While we are on the subject of Multisim, I have a question.

[L.W.]

I have Multisim 2001 Power Pro edition. For some reason I am having
dificulty simulating the 555 timer on long delays. By long I mean in
the area of 20 seconds. I am designing an astable multivibrator with a
20 second off pulse (space) and a one second on pulse (mark). I know
my component calculations are correct, but it seems that Multisim
hangs or has difficulty after about 5.2 seconds. Is it possible that
the program is sucking all my RAM memory? Or am I running out of
virtuall memeory under Windows 98? If there is something I am not
doing or there is something I could do (other than dumping it for
another program) please let me know.


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[Paul Burridge]

On Tue, 27 Jul 2004 11:09:46 -0700, L.W. <lacy@cwv.net> wrote:

I have Multisim 2001 Power Pro edition. For some reason I am having
dificulty simulating the 555 timer on long delays. By long I mean in
the area of 20 seconds. I am designing an astable multivibrator with a
20 second off pulse (space) and a one second on pulse (mark). I know
my component calculations are correct, but it seems that Multisim
hangs or has difficulty after about 5.2 seconds. Is it possible that
the program is sucking all my RAM memory? Or am I running out of
virtuall memeory under Windows 98? If there is something I am not
doing or there is something I could do (other than dumping it for
another program) please let me know.

Why not dump it for a free program that works better, anyway? LT Spice
(from www.linear.com) comes with (inter-alia) a decent model of a 555.
Give it a try and see for yourself if you might not be better off
adopting it full-time.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[L.W.]

This is a follow up to my question that was not truly answered. I did
figure out the solution on my own. Out of the kindness of my heart I
am going to post my finding so that others who have Multisim and are
having porblems can try this and see if it solves some of their
problems.

1. Go to the SIMULATION tab and click on it.

2. Go down to DEFAULT INSTRUMENT SETTINGS and click on it.

3 Click the drop down menu at the very top of the dialog box. You will
find about 4 options there to set INTIAL CONDITIONS for your
circuit. I chose SET TO ZERO. You can use whatever suits your
particular need.

4. The next Step is to look down and find the box that says SET
MAXIMUM TIMESTEP (TMAX)). Click on the box that says MAXIMUM
TIMESTEP (TMAX). Once this is done, you can set TMAX in the
adjacent box. The default is .00001 which is equivalent to 10us.
I adjust mine down to .0001 which is equivalent to 100us.

This little change did wonders for my simulation of my circuit. The
TMAX option I beieve is the accuracy resolution of the simulator. The
smaller the number the more accurate the output and the slower
Multisim runs. I would also ventrue to say that the higher the
accuracy the more resources are required to simulate the circuit.
Since most circuits don't need to be simulated that precisely, it may
help to try this if you are running into problems getting the program
to perform as you expect it.

Anyway that is what I have found and I hope it helps others.


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