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4538 monostable input rise/fall restriction

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.

Reply to
Pimpom
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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

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.

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.

Reply to
Pimpom

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

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  |             | 
| Voice:(480)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.
Reply to
Jim Thompson

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

Reply to
Pimpom

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  |             | 
| Voice:(480)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.
Reply to
Jim Thompson 

--
Yes, it will. 

View using a fixed-pitch font: 


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

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  |             | 
| Voice:(480)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.
Reply to
Jim Thompson

"John Fields" wrote in message news: snipped-for-privacy@4ax.com...

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.

Reply to
Pimpom 

--
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?
Reply to
John Fields

"John Fields" wrote in message news: snipped-for-privacy@4ax.com...

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.

Reply to
Pimpom

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