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Short pulse output

AnalogKid

Jun 10, 2015
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Will the 555 not still continue the pulse output if the it is triggered past the duration of its timing cycle??
Correct. Post #7.

A 555 is neither a true monostable (output pulse width completely independent of trigger pulse width) nor a true retriggerable monostable (output pulse period restarts if the input is triggered in the middle of an output pulse). To make a 555 a true monostable, you have to add a differentiator circuit to the input. Usually, this is one resistor and one capacitor.

ak
 

Harald Kapp

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Will the 555 not still continue the pulse output if the it is triggered past the duration of its timing cycle??
The typical 555 monostabel circuit is not retriggerable. New trigger pulses while the output is active will not reset the timerr and thus will not influence the timing of the monostable circuit.
If, however, the trigger occurs after the monostable timer has stopped, it will of course be triggered anew and output a new pulse. That is what a monostable circuit is designed for.
 

kellys_eye

Jun 25, 2010
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will do the job with only a few lines of programming.
I have no disregard for microcontrollers and their abilities (vast and capable) but it's not as simple as 'a few lines of code' since (1) you need the programmer and (2) you need the coding experience and the ICE/development software. Of course, any modern designer would leap for the uC solution but I find it wise to consider the other aspects such as time, accessibility, capability, operability and the actual circumstances that may even preclude the use of uC's.

I recall, some years ago, designing a controller to allow two switching stations to select control of a propulsion system (on a boat) with system indicators and station lock-out (with emergency override) facilities. I did it using RELAYS! Yes, I could have designed and built a small uC'd board but that would have left the vessel owner in a pickle if it went mammaries skywards (tits up) as it would have been a one-off controller. I took the decision to use a series of identical plug-in relays (multi-contact) that were (and still are) generally available such that 'anyone' could fix it in the event of a problem - not that modern relays can't handle millions of operations without fault that is.....

No reported issues to this day (some 20 years later...).
 

danadak

Feb 19, 2021
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You are quite correct sir
What is the tolerances you are seeking for the 2 sec pulse ?

Do you care about T & V and Device tolerances for the pulse above ?

If you use CMOS gate logic to create the time delays preference is to
use a Schmidt input device, like 74HC14, to insure you dont get this in
your pulse production :

1670434503615.png
Cause of this is time slow moving input rise / fall time staying in active region of gate
and system noise causing the gate to flip logic levels :

Lastly here is classic switch bounce from mechanical buttons, switches that should be
debounced as well :


1670435779643.png


I worked with switches that bounced in the 100's of mS, they were truly crappy cheap
switches. "Normally" one designs for debounce problems around 100 mS, in other
words a switch is only valid if it is stable for at least 100 mS. That is very simple code
for a processor. Attached some background material.

One last, do not hang a large value C on a CMOS logic pin. That can cause device
failure due to excess current flow thru input protection diodes when power is cyckled on
part. . Use a series R of a 1K or so to prevent this.







Regards, Dana.
 

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danadak

Feb 19, 2021
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Here is a simulation showing a 10 mS slow ramp 0 - 5 V being applied to
a CMOS gate input (with no Schmidt input) and 50 mV RMS of noise super imposed
on that input. As you can see it has a very unstable output as its input passes
thru gate threshold point (~ 2V) :

1670437141249.png


Regards, Dana.
 

bigkim100

Apr 17, 2013
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Thank you very much to everyone that has supplied an answer to this. I have read them all carefully and have decided that what I thought was a simple problem is actually quite complex (a frequent outcome of one of my questions). I think I will place this problem on the Back-Burner for now.
 

dragon

Oct 31, 2022
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Thats a little depressing Kim... cant even get a 2 second pulse out, theres alot tougher problems than this, this is just the very basics!!!!
 

Harald Kapp

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One thing to say -> The circuit I posted here works.
Maybe even in the real world, but the pulse it creates is totally unsuitable to activate a relay for 2 s.
So effectively: No, doesn't work in the real world.
 

bigkim100

Apr 17, 2013
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Thats a little depressing Kim... cant even get a 2 second pulse out, theres alot tougher problems than this, this is just the very basics!!!!
Naaah...in the grand scheme of things a Microprocessor would do the job, its just I know nothing about them. I did learn a lot tho, from the responses I got. At 61, Im building power supplies for 3 military receivers, and many other circuits for various other things, so you may say that my knowledge is dated. Nothing Im doing is of absolute necessity...usually, and 99.9% of the time, I can cobble something together with the various pieces of help I receive here, from various responses. Overall, this forum is extremely helpful, and populated by EXTREMELY talented people. most of the time if I cannot comprehend an answer here, its because of MY lack of knowledge of answers.

Only in a sim - it will NOT work in the world we live in.
LOL...its a nice world then!

One thing to say -> The circuit I posted here works.
Im sorry Dragon, I didnt see your corrected circuit. I will try it in REAL LIFE, and report back on it.
 

dragon

Oct 31, 2022
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Im sorry Dragon, I didnt see your corrected circuit. I will try it in REAL LIFE, and report back on it.

I would be very happy if you did give it a go! it works! its not as good as the transistor "monostable" circuit, but it should work to get a pulse out of a switch, but it doesnt work off a tiny bit of power, it requires the switch so it can short the power in the cap before it comes out the timing resistor.
 
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danadak

Feb 19, 2021
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Naaah...in the grand scheme of things a Microprocessor would do the job, its just I know nothing about them. I did learn a lot tho, from the responses I got. At 61, Im building power supplies for 3 military receivers, and many other circuits for various other things, so you may say that my knowledge is dated. Nothing Im doing is of absolute necessity...usually, and 99.9% of the time, I can cobble something together with the various pieces of help I receive here, from various responses. Overall, this forum is extremely helpful, and populated by EXTREMELY talented people. most of the time if I cannot comprehend an answer here, its because of MY lack of knowledge of answers.


LOL...its a nice world then!


Im sorry Dragon, I didnt see your corrected circuit. I will try it in REAL LIFE, and report back on it.

If you have used a 4 function calculator over the years than you have been programming,
in your head. You know when to create a variable, to store a temporary result, you know
order of operations, you know what an operation is......

The block programming languages getting pretty good. Here is an example using mBlock,
where I want to convert a variable V to a variable pulse width.

1670774820095.png

So those blocks are dragged out of the block lib tool and dropped onto design area of
tool.

First block tells tool where program starts
Second block creates a variable to hold voltage that will be read on a pin
Third block tells program run all the code inside it forever, just keep running it
Forth block reads the voltage on pin 0 and puts it into the variable
Fifth block updates PWM setting with the V read

Then you hit program button and mBlock takes the code it generated and programs the
board you use. Code by the way is Arduino type code,

I would not mislead you into believing you magically become an expert after five minutes
doing the above. But its quite visual and easy to use for many projects.

There are videos on it, and once you get comfortable with it there are many block languages
that have various capabilities and they all operate very similar to this. And youc an look at the
C code it generates to get a feel for classic languages like C should you desire to go further
into the parts and designs at a later time.

Get a Nano board, ~ $3, and have some fun. You also have to install Arduino IDE on your POC
as it uses its programmer software to program the board. All software is free.

Here is an example of a fairly sophisticated timer / pulse sequencer, and an example of a talking
voltmeter :



In above block language used was Snap4Arduino, very similar to mBlock.



Regards, Dana.
 

hevans1944

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Jun 21, 2012
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I recall, some years ago, designing a controller
Yeah, me too!

In early 1970s I was tasked with designing a controller for a raster-scanned X-Y positioning stage. This was part of a new laser window-test facility that we had been asked to spin up for the Air Force. I didn't know it at the time, but this was the beginning of our involvement in the so-called Star Wars Ballistic Missile Defense Initiative or BMDI. That program lasted for several years (it is still ongoing) but yielded no reliable, battle-ready hardware until decades later, long after my involvement.

Although discrete-logic integrated circuits were available, especially TTL (transistor-transistor-logic) ICs, I decided to implement the controller using diode-relay logic because we had a short window of opportunity. This turned out to be a very robust solution that was quickly implemented with commercial off-the-shelf components. It worked perfectly the first time it was turned on. It has probably long since been scrapped because we built another one bigger and better. If asked to do it again today, I would surely use a microcontroller instead of diode-relay logic. The state of the art in both processors and programming for embedded systems has advanced a LOT in fifty years. I still prefer assembly language programming versus high-level abstract coding methods because it allows me to be as close as possible to manipulating actual hardware, banging on the bits so to speak. @danadak has opened my eyes to graphical programming, which is another step closer to actually speaking to the computer to tell it what to do. Still, there is a long way to go because the graphical programming paradigm still generates high-level "C" or "C++" code that must then be translated into executable machine code... the ones and zeroes that machine logic "understands."

This being the early part of the 21st century, I can understand the reluctance of earlier generations (Boomers, X, Millenniums, etc.) to embrace unfamiliar paradigms. But it really is better to learn the new while still appreciating and cherishing the old... IMHO. Those who forget the mistakes of the past are doomed to repeat those mistakes in the present.

Word got around quickly. A few weeks later a team of high-level Air Force personnel visited our test facility and were suitably impressed. We were then awarded a contract to build a full-scale laboratory, to be used to test laser windows of weapons-grade size... at the Air Force Weapons Laboratory in Albuquerque, New Mexico. I didn't participate much in that effort initially, but instead worked to establish a smaller version of the laser window test facility on campus. Those were indeed fun times.

Meanwhile, technology sped ahead and microprocessors were invented. I got involved with using the Intel 8080 µP as an embedded controller for scientific instruments, later "moving up" to the Intel 8085 which was easier to use. The last time I implemented an 8085 system was in the 1980s when tasked with upgrading a tourist exhibit of the Apollo mission control room for NASA. During that same period, microprocessors became embedded in personal computers, but acceptance was slow during the early years of the 1980s. That all changed with the introduction of software-based (instead of paper) spread-sheets on PCs. IBM and Microsoft were alleged to have a motto for their operating systems' software development: it ain't done 'til Lotus won't run! But open-source "free" software put the damper on that.

So, fast forward to June 2012. I turned 68 that month and was now only working part-time. Somehow I found Electronics Point and met @KrisBlueNZ (deceased) who was trying to help @TenderTendon use a mosfet switch, controlled by a PIC microprocessor, to operate a custom-machined, high-brightness, five ampere LED flashlight. You can look up this thread to see how that worked out. Jeff hasn't abandoned that project, but he is taking it in another direction that I will help him with.

So, I stand by my statement: "integrated circuit processors are not sledge hammers, and they are really "dirt cheap" solutions." Yes, you do need certain inexpensive tools (anyone still use a multimeter?) and there is a learning curve, but once you have dipped your toes into those new waters, you will find the swimming is a lot of fun. The solutions that @danadak is offering are almost free, with a few bux needed to buy a Arduino Nano that can be used for programming other micros (such as the ATTiny) using free software that can be downloaded from the Internet. You do need a personal computer, but most of us here have at least one of those, even if it's in the form of a "smart" cell phone.
 
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