Try adding a load (e.g. 1k-10k) to the 121 output.

What issue is this to address? The output is totem pole.

 

What issue is this to address?

Depending on the accuracy and any quirks of the '121 and scope input models used, it may make Multisim happy. It shouldn't be necessary, but it costs nothing to try.

 

Try adding a load (e.g. 1k-10k) to the 121 output.

Thanks for the sugestion. I did but it does not change its behaviour

If the one shot period is 3.4s, you need the trigger signal to be slower than 0.29Hz. 5Hz gives you trigger pulses every 200ms and that isn't what you want.

Yes, you are completly right. I got it wrong thinking about the output in simulation instead of the real output I want to get. I did simulate it with 200mHz and the result is shown in picture "trigger input .2Hz.PNG", where you can see that it does not trigger the output and the simulation stop by itself with an error of "running out of memory", that is why it stops around 8 or 9 seconds.

I need to see the trigger pulses and the output pulses on the same screen.

Hi crutschow. There it is in the picture "trigger input 10kHz and output.PNG" where trigger is in green colour and output comes in red.

After all these simulation, I had to create a copy of the circuit because it was not giving me any output at all. Actually I had to copy the long timer circuit and modify RC components in order to establish the almost 4s output.
Hope to give all the right answers your asked me guys and, please, feel free to keep asking me things as I am really dying to get to the bottom of this matter. It will be easier for me to fill the report I need to do for the assignment. However, I would go for dividing the circuit and trying to get what it suppose to be giving the inputs from instrumentation rather than simulating the whole circuit. It is a shame but I need to move on this. I really hope when I breadboard it, it will work

 

here it is in the picture "trigger input 10kHz and output.PNG" where trigger is in green colour and output comes in red.

The trigger is just solid green which is no help.
You need to simulate a shorter time so I can see the relation between the trigger pulse and the output pulse.

 

The trigger is just solid green which is no help.
You need to simulate a shorter time so I can see the relation between the trigger pulse and the output pulse.

Right. In order to be able to see the trigger pulses and the output signal I had to perform a simulation in 20ms however it does only shows an active output pulse. See picture "trigger input 10kHz and output in 20ms.PNG". Also, I did a simulation in 25Hz in 5s time so the output appears "more as normal" (. See picture "trigger input 25Hz and output in 5s.PNG".

 

Also, I did a simulation in 25Hz in 5s time so the output appears "more as normal" (. See picture "trigger input 25Hz and output in 5s.PNG".

What is the point of triggering the one shot at 25Hz when it's non-retriggerable and the time period is 5 seconds?

Why is the trigger signal voltage -5V to 5V?

Why don't you change the timebase so we can see the more relevant information?

 

What is the point of triggering the one shot at 25Hz when it's non-retriggerable and the time period is 5 seconds?

Well, I uploaded two simulations. One is trigger at 10kHz (which is the main design frequency) in 20ms just because crutschow suggested to simulate a shorter time. The output signal in that simulation does not show the behaviour it is having the whole time the 74121. That is why I also uploaded another simulation, the one you are refering to. In this last simulation and as I mentioned, the output signal seems abit more to the normal behaviour that the 74121 is showing in the circuit. Resume: It was just for some clarification and answering crutscshow's question.

Why is the trigger signal voltage -5V to 5V?

It was the standard conf in the function generator from multisim. I did not care much about it because I think it does not interfiere on the results, as the results in previous simulations with trigger voltage 0 to 5V were exactly the same as now. Nonetheless, it is configured again in trigger input voltage 0V to 5V.

Why don't you change the timebase so we can see the more relevant information?

I may not be getting what you guys really want me to do. I have already simulated in several timebases so far but apparently it does not show what you need to see. Please, could you tell me specifically what timebase would be the right one?

 

I may not be getting what you guys really want me to do. I have already simulated in several timebases so far but apparently it does not show what you need to see. Please, could you tell me specifically what timebase would be the right one?

The problem is that you have some objective in mind and we don't know what that is.

What is the point of triggering the one shot at such a high frequency?

I see a variable on period from the one shot in the clip I posted, but you have the time scale too compressed to be able to look for why.

 

could you tell me specifically what timebase would be the right one?

Use a time base that show about two pulses from the one-shot.

As previously asked, what is the purpose of using such a high frequency trigger for a low pulse from the one-shot?

The problem is, it still isn't clear exactly what you are trying to do(?).