otacustes

Hi, I'm hoping that someone will know the answer to this question regarding the simulation speed on multisim 8. This is a great simulation tool for electronics but it has one major drawback – the documentation doesn't seem to cover everything, or if it does then it is in too much detail.

What I am trying to do is run the simulation in realtime. The software is great for "slow speed" where a circuit can be diagnosed but what happens if you want to see the circuit run as if it has been built in real life?

Looking at the settings, I can see that you can change the maximum time the simulation runs for and limit the maximum step that can be taken, but there is nothing that I can find that indicates the speed at which the simulation is to be run at.

Any help is greatly appreciated.

Kind regards

Ota

Roff

Does your simulation have independent sources? If so, you just need to set them to have the correct pulse widths, frequencies, etc. The simulation controls that you mention have no effect on these parameters.

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Ron

Optikon

You'll have to explain more. You don't need the simulation to run in real time. For example:

Lets say I build a circuit in the simulator that also conatins a button pressed by the user which, activates some function. In real life the button press might not occur for many seconds. All I would need to do is simulate the button press happeing at say a time of 3 seconds. Setup the simulator to run for 4 seconds. Now when it simulates this, it wont take 4 seconds - that depends on step size _AND_ what the circuit is doing. If I simulate with a step size of 1 second - it will still be finished in much less than 1 second (if the circuit has no dynamics happening faster than this).

BUT the final simulation result will be time-accurate.

You see, you have to understand, the simulator is solving circuit equations not showing you real time response- for 99% of the time we dont want real time response anyways! That takes too long.

I see no need for any circuits high speed or low speed that require a real time simulation. Why is it you think you need it to be?

Roff

Optikon, I actually opened my post for editing to add similar comments, like:
1. You will never get a 1GHz pulse generator to sim in real time, and you couldn't see it even if it were possible.
2. You wouldn't want to wait for a real-time sim if an oscillator with a 3 week period. :lol:
But then I thought, naaaahhh, he can't really mean actual real time. So I canceled the edit. But maybe he does..... :?: :?:

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Ron

Optikon

Not to mention the fact that the simulator software is likely not running in a real time OS anywhoo... so it has a limited concept of what real time is anyways (10 us clock tick interrupts on processor etc..)

I think the OP has real time confused with setting up the simulation to run for a fixed amount of time. He'll prolly not respond anyways.. :cry:

otacustes

Thanks guys for your replies......

Being a little new to this sort of thing I am a a little curious as to what independent sources are defined as? What I am trying to simulate is a flashing circuit that runs off the mains supply. It consists of, unsuprisingly an AC source, and some diodes and some logic circuitry. What I am trying to see is whether the circuit actually works but the simulation runs at fractions of mS which is really slow when I am looking at the oscilloscope trying to see what is happening.
Perhaps my desription of real time was a little inaccurate??

I can post the file here if anyone is interested?

Thanks guys.

Roff

Otacustes, I was hoping Optikon would reply, because I am baffled as to what you expect to see. Can you expand on this?
Your AC source is an independent source - it's voltage is not dependent on any other voltage or current in the circuit.

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Ron

Optikon

Well, it's not quite clear to me what your actual "speed" problem is. So, the oscilloscope is a multisim waveform viewer of sorts? So maybe this oscilloscope tool is trying to emulate a real time response and it is too "fast" to see since your circuit does all its tricks in mS? Is this right?

You can post the file, but that doesn't really help you with your simulation setup. I am not familiar with the multisim environment, but I'm sure there is a way to configure the scope viewer tool. Things to consider or try:

Can you forget about the scope widget and use a real post processor waveform viewer? I'm sure it has one.

Since your viewer is an oscilloscope, you have to trigger on a repeatable event (like AC source) for a waveform to stay on the CRT? If it is a digital O'scope, then you could also work in single shot trigger mode so that your waveforms are captured and displayed after the trigger event.

otacustes

The problem is that at the bottom of the screen there is a clock which is running in 0.1mS increments. Looking at the oscilloscope the waveform generated is very slowly as the clock ticks.

I'll try and see if there is a post processor viewer and try that.

Thanks