Simulating a monostable

alec_t

Well-Known Member

Most Helpful Member

• Oct 23, 2012

• #1

It's easy enough to model monostable action using e.g. a CD4000 series monostable model, or logic gate models etc, but these all involve external R and C.
Is it possible to use just a behavioral (or standard) voltage source instead, with trigger instant and period both set by parameters? I've faffed around with a bvs but can't come up with a suitable formula to get from it, for example, a voltage which goes low for a period T in response to the falling edge of some other signal.

 

MikeMl

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• Oct 23, 2012

• #2

Are you using LTSpice? If so, read the help file on the Behavioral Source, specifically the function:absdelay(x,t[,tmax]) x delayed by t.

 

alec_t

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Most Helpful Member

• Oct 24, 2012

• #3

Yes, LTSpice (sorry; thought everyone here was using LTSpice ). Read that. That's what I was faffing with. It just delays an input waveform rather than start a pulse in response to a falling edge of the waveform. So no joy so far. Maybe that function can be tweaked, but I haven't yet found how. But thanks anyway MikeMl.

 

K

kubeek

Well-Known Member

Most Helpful Member

• Oct 24, 2012

• #4

Well if you combine that with an RS latch, you might get what you wanted.
Remember that this is how a 555 monostable works. Also you might want the latch with priority on one of the inputs in case there is a long control impulse.

 

Last edited: Oct 24, 2012

alec_t

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• Oct 25, 2012

• #5

Thanks, kubeek. That gives me another way to cobble together something. I was hoping to avoid multiple devices and to use only a single LTS parameterised voltage source. Looks like that's not going to be doable.

 

Roff

Well-Known Member

• Oct 25, 2012

• #6

Post deleted.

 

Last edited: Oct 25, 2012

Roff

Well-Known Member

• Oct 26, 2012

• #7

Here's a start (unless you've already been this far already). Note that the input pulse must be wider than the output (param PW). I know that's not good, but it's as far as I got.
Also, I see no way to control output transition times in a B element.

Note that the input pulse amplitude may be anything (I think it has to be constant (flat). The output will swing between 0V and Vhigh.

 

alec_t

Well-Known Member

Most Helpful Member

• Oct 26, 2012

• #8

it's as far as I got

Click to expand...

...and further than I got.
That looks handy in many situations. Thanks Roff.