4538 monostable input rise/fall restriction

[Pimpom]

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with an
inverter at one of the OR inputs.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.

 

[Jim Thompson]

On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are no TR/TF
restrictions. The inputs have hysteresis.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.

Are you wanting to have one monostable trigger the second?

You need to describe your situation in more detail.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Pimpom]

"Jim Thompson"
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote in
message news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...

On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and RCA

(really the same) and they say that the inputs have Schmitt
triggers. Don't know how I missed that. Thanks for pointing
it out. NatSemi and Fairchild don't mention it.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one
is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is this:

One monostable is triggered first to produce a pulse of ~50
msec. The second mono is triggered a little later while the
first one's Q output is still high, that is, before it has
reverted to the idle state. It doesn't matter if the second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence. The
two outputs go to different sections of the overall circuit.

 

[Pimpom]

Jim Thompson wrote:

On Fri, 25 Jan 2013 23:16:36 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:


"Jim Thompson"
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote
in
message
news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...
On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The
block
logic diagram shows the trigger input as an OR gate
with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are
no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and RCA
(really the same) and they say that the inputs have
Schmitt
triggers. Don't know how I missed that. Thanks for
pointing
it out. NatSemi and Fairchild don't mention it.


Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay
after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second
one
is
triggered. I can think of some ways to do this using
other
logic gates or another monostable. But I'd like to
avoid
adding another active device if possible. The delay is
not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output
of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the
second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is
this:
One monostable is triggered first to produce a pulse of
~50
msec. The second mono is triggered a little later while
the
first one's Q output is still high, that is, before it
has
reverted to the idle state. It doesn't matter if the
second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence.
The
two outputs go to different sections of the overall
circuit.


What does the trigger pulse for the first mono look
like...
pulsewidth?

Probably a manual switch - a momentary tactile type. The

design is still in the early stages and many factors are not
yet clearly defined.

 

[Jim Thompson]

On Fri, 25 Jan 2013 23:16:36 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

"Jim Thompson"
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote in
message news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...
On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and RCA
(really the same) and they say that the inputs have Schmitt
triggers. Don't know how I missed that. Thanks for pointing
it out. NatSemi and Fairchild don't mention it.


Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one
is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is this:
One monostable is triggered first to produce a pulse of ~50
msec. The second mono is triggered a little later while the
first one's Q output is still high, that is, before it has
reverted to the idle state. It doesn't matter if the second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence. The
two outputs go to different sections of the overall circuit.

What does the trigger pulse for the first mono look like...
pulsewidth?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Fields]

On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with an
inverter at one of the OR inputs.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.

---
Yes, it will.

View using a fixed-pitch font:


.. +----------------->OUT1
.. 4538A | 4538B
.. +-----+ | +-----+
..TRIG>-------|T1 Q1|-+-[R]-+-|T2 Q2|--->OUT1 + DT
.. +-----+ | +-----+
.. [C]
.. |
.. GND

--
JF

 

[Jim Thompson]

On Fri, 25 Jan 2013 23:59:22 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

Jim Thompson wrote:
On Fri, 25 Jan 2013 23:16:36 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:


"Jim Thompson"
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote
in
message
news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...
On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The
block
logic diagram shows the trigger input as an OR gate
with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are
no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and RCA
(really the same) and they say that the inputs have
Schmitt
triggers. Don't know how I missed that. Thanks for
pointing
it out. NatSemi and Fairchild don't mention it.


Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay
after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second
one
is
triggered. I can think of some ways to do this using
other
logic gates or another monostable. But I'd like to
avoid
adding another active device if possible. The delay is
not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output
of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the
second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is
this:
One monostable is triggered first to produce a pulse of
~50
msec. The second mono is triggered a little later while
the
first one's Q output is still high, that is, before it
has
reverted to the idle state. It doesn't matter if the
second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence.
The
two outputs go to different sections of the overall
circuit.


What does the trigger pulse for the first mono look
like...
pulsewidth?

Probably a manual switch - a momentary tactile type. The
design is still in the early stages and many factors are not
yet clearly defined.

Make that manual switch a SPDT... switch an R/C up to some V+.

That positive transition triggers monostable #1 (set for
positive-going trigger).

Release the switch and the R/C decays downward.

That negative-going transition triggers monostable #2 (set for
negative-going trigger).

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Pimpom]

"John Fields" <jfields@austininstruments.com> wrote in
message news:vmv5g89o4nnk2d45ad6teldaqc72c5voo8@4ax.com...

On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The block
logic diagram shows the trigger input as an OR gate with
an
inverter at one of the OR inputs.

Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second one
is
triggered. I can think of some ways to do this using other
logic gates or another monostable. But I'd like to avoid
adding another active device if possible. The delay is not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output of
the first mono and the input of the second will work.

---
Yes, it will.

View using a fixed-pitch font:


. +----------------->OUT1
. 4538A | 4538B
. +-----+ | +-----+
.TRIG>-------|T1 Q1|-+-[R]-+-|T2 Q2|--->OUT1 + DT
. +-----+ | +-----+
. [C]
. |
. GND

Yes, that's exactly what I had in mind. What I didn't know
when I made my opening post (because I missed seeing it in
the datasheet) was whether the mono trigger inputs have a
Schmitt trigger that accepts slow rise times.

 

[John Fields]

On Fri, 25 Jan 2013 23:59:22 +0530, "Pimpom" <Pimpom@invalid.invalid>
wrote:

Jim Thompson wrote:
On Fri, 25 Jan 2013 23:16:36 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:


"Jim Thompson"
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote
in
message
news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...
On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The
block
logic diagram shows the trigger input as an OR gate
with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there are
no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and RCA
(really the same) and they say that the inputs have
Schmitt
triggers. Don't know how I missed that. Thanks for
pointing
it out. NatSemi and Fairchild don't mention it.


Why I'd like to know: I want to trigger one of the two
monostables in the package with a slight time delay
after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second
one
is
triggered. I can think of some ways to do this using
other
logic gates or another monostable. But I'd like to
avoid
adding another active device if possible. The delay is
not
critical - anything from 1 to several milliseconds will
do.
So I wondered if a simple RC filter between the output
of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the
second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is
this:
One monostable is triggered first to produce a pulse of
~50
msec. The second mono is triggered a little later while
the
first one's Q output is still high, that is, before it
has
reverted to the idle state. It doesn't matter if the
second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence.
The
two outputs go to different sections of the overall
circuit.


What does the trigger pulse for the first mono look
like...
pulsewidth?

Probably a manual switch - a momentary tactile type. The
design is still in the early stages and many factors are not
yet clearly defined.

---
The 4538 is a good choice, then, since it can be level-triggered by
transitions from GND to Vcc or from Vcc to GND and can be wired to be
retriggerable or not, relaxing the debounce requirements on the
trigger input(s).

Can you tell us a little more about your application?


--
JF

 

[Pimpom]

"John Fields" <jfields@austininstruments.com> wrote in
message news:l2j8g8p843crbr60hc4gu28s3k0keavi5k@4ax.com...

On Fri, 25 Jan 2013 23:59:22 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Jim Thompson wrote:
On Fri, 25 Jan 2013 23:16:36 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:


"Jim Thompson"
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com
wrote
in
message
news:cah5g81ffnsan2tl6rneb8h1u85l14omsb@4ax.com...
On Fri, 25 Jan 2013 22:34:34 +0530, "Pimpom"
Pimpom@invalid.invalid
wrote:

Does the 4538 monostable have any restriction on the
rise/fall time of the triggering pulse? None of the
datasheets I have mentions any such restriction. The
block
logic diagram shows the trigger input as an OR gate
with
an
inverter at one of the OR inputs.

All the 4538 data sheets I've seen state that there
are
no
TR/TF
restrictions. The inputs have hysteresis.

Oops! I had another look at the datasheets by TI and
RCA
(really the same) and they say that the inputs have
Schmitt
triggers. Don't know how I missed that. Thanks for
pointing
it out. NatSemi and Fairchild don't mention it.


Why I'd like to know: I want to trigger one of the
two
monostables in the package with a slight time delay
after
the other one. The first mono has to be still in the
triggered state (Q output still high) when the second
one
is
triggered. I can think of some ways to do this using
other
logic gates or another monostable. But I'd like to
avoid
adding another active device if possible. The delay
is
not
critical - anything from 1 to several milliseconds
will
do.
So I wondered if a simple RC filter between the
output
of
the first mono and the input of the second will work.


Are you wanting to have one monostable trigger the
second?

You need to describe your situation in more detail.

Question answered above^. Anyway, what I want to do is
this:
One monostable is triggered first to produce a pulse of
~50
msec. The second mono is triggered a little later while
the
first one's Q output is still high, that is, before it
has
reverted to the idle state. It doesn't matter if the
second
mono is triggered by the first or they are triggered
separately, as long as they are in the proper sequence.
The
two outputs go to different sections of the overall
circuit.


What does the trigger pulse for the first mono look
like...
pulsewidth?

Probably a manual switch - a momentary tactile type. The
design is still in the early stages and many factors are
not
yet clearly defined.

---
The 4538 is a good choice, then, since it can be
level-triggered by
transitions from GND to Vcc or from Vcc to GND and can be
wired to be
retriggerable or not, relaxing the debounce requirements
on the
trigger input(s).

Can you tell us a little more about your application?

The first monostable *was* intended to set up a circuit

before and during application of the pulse from the second
mono. But I've changed the design of the controlled circuit
so that, although the mono pair will still be used, they now
work independently and sequential triggering is no longer
needed. What I didn't mention before was that the second
mono was to have the option of either manual direct
triggering or being triggered by the first mono.