I have trying to play around with this PULSE source to make it one-shot pulse, but the voltage always looks constant. I do have a couple of .tran statements that I switch between, but now when I attempt to change the values, it puts all the original values back. Basically the statements appear to be non-modifiable. Don't worry though about the multiple .trans statements, because I get rid of them by Making them into a text comment on the schematic. Before I modified my .trans I was seeing flat readings for anywhere I probed in the circuit. When I use the other .trans, I get complaints about my timestep being too small for schmidt triggers.

Here is the Circuit INtro

 

Did you try adjusting the time step?

You need to add a resistor from the input of U6 to ground or the positive logic supply. Pick one.

 

I tried adjusting the time step as well as other option, but any changes i attempt to make are instantaneously erased after pressing ENTER.

Even if I get rid of the whole circuit, the PULSE waveform doesn't work.

 

Hi WU,
From that collection of circuits in your opening post asc file, which of the circuits do you want to use?

Trying to run them all at the same time is going to cause problems.

E
Updated:
This is the circuit from post #1, Note R1.

 

I tried adjusting the time step as well as other option, but any changes i attempt to make are instantaneously erased after pressing ENTER.

It's seldom that you need to adjust the timestep. LTspice normally picks the proper value for the simulation.

I don't understand the changes being erased.
Exactly all what steps are you doing when you try to change a parameter?

As eric noted, you shouldn't have all those separate and different circuits in the same file, as it slows down the simulation and, if there's a problem, it's difficult to know which of the many circuits is at fault.

Cut and paste each one to separate file and run only one circuit at a time.

 

Since it hasn't been pointed out explicitly - there is an error in the schematic in post #1.

Where R_1M is connected now, it has no function. R_1M should be connected between the right side of C9 and GND. This will form a conventional monostable circuit. A negative-going edge out of V5 will produce a positive pulse across R13.

ak

 

As pointed out, all inputs must have a proper DC bias.
See R1 in post #4.

 

Where R_1M is connected now, it has no function.

Yes, it would seem there was a typo in the original schematic.
Happens to the best of us.

 

I tried adjusting the time step as well as other option, but any changes i attempt to make are instantaneously erased after pressing ENTER.

Even if I get rid of the whole circuit, the PULSE waveform doesn't work.

Hi WU,
From that collection of circuits in your opening post asc file, which of the circuits do you want to use?

Trying to run them all at the same time is going to cause problems.

E
Updated:
This is the circuit from post #1, Note R1.


View attachment 317932

Lesson Learned! I copied that one circuit into a new .asc file, and everything started working beautifully! Now that I think about it, it seems as if my simulations became more sluggish and unreliable the more circuits I packed into the .asc

 

I think the circuit will oscillate without C2/R2.

 

I think the circuit will oscillate without C2/R2.

The feedback connection from U2 to U1 is not the standard design for a true monostable.

Among other things, U2 now is driving U1 through an R-C network. This might indeed cause the circuit to oscillate, but that usually is not a good thing.

Without R2, the U1 input has no DC termination. This can cause problems.

Post #4 shows the traditional circuit, basically the same as post #1 with the error corrected.

ak