1.5ms pulse generator switched

[zorbzz]

Hi guys is there an easy way to make a pulse generator out of a 555 that when power is applied to the circuit it will generate a 1.5 ms pulse, turn off and then wait till power is applied then make another one etc?
I have fiddled around but cant do it how I want.

Ultimately when power is applied to the circuit the power can be about 5ms long, I need to find a way to turn that 5 ms pulse into a 1.5 ms one but only for each pulse. Then re triggered from the next pulse etc.
If a 555 isnt right for this job please steer me in the right direction.

All of the circuits I have tried have to have the circuit powered up all the time and then triggered but I havent found a way to make it so that the triggering pulse width of 5ms is converted to 1.5ms each time.

Thanks for your help Im only new to this and my knowledge is limited.

 

[william_rx]

Hi guys is there an easy way to make a pulse generator out of a 555 that when power is applied to the circuit it will generate a 1.5 ms pulse, turn off and then wait till power is applied then make another one etc?
I have fiddled around but cant do it how I want.

Ultimately when power is applied to the circuit the power can be about 5ms long, I need to find a way to turn that 5 ms pulse into a 1.5 ms one but only for each pulse. Then re triggered from the next pulse etc.
If a 555 isnt right for this job please steer me in the right direction.

All of the circuits I have tried have to have the circuit powered up all the time and then triggered but I havent found a way to make it so that the triggering pulse width of 5ms is converted to 1.5ms each time.

Thanks for your help Im only new to this and my knowledge is limited.

interesting way. i had a project to generate a pulse ,but it is at 4GHz and 4ns width.
i guess 555 is for low frequency operation, thus it cutoff frequency 1/T (rising) is not enough for this pulse( narrow pulse means rich frequency component).

 

[colin55]

I would never use a 555. It is not an "engineers" chip. It may be ok for an automotive application but it is certainly not suitable for any electronic circuitry.

Use a Hex Schmitt trigger.

 

[ericgibbs]

Ultimately when power is applied to the circuit the power can be about 5ms long, I need to find a way to turn that 5 ms pulse into a 1.5 ms one but only for each pulse. Then re triggered from the next pulse etc.
If a 555 isnt right for this job please steer me in the right direction.

All of the circuits I have tried have to have the circuit powered up all the time and then triggered but I havent found a way to make it so that the triggering pulse width of 5ms is converted to 1.5ms each time.

hi,
Look at this image of the required trigger pulse width.

If you want to 'convert' a 5mS pulse width into a 1.5mS, 'ac' couple the 5mS such that the 5mS pulse width is less than say, 1mSec.

If you need to, you can use the 555 RESET to hold off, the 555 while the power supply is stable, then apply the trig pulse. OK.?

The 555 ic is perfectly suitable for all engineering applications where a simple pulse is required.

 

[colin55]

Is your 5mS pulse "negative going?" In other words, does the pulse line sit HIGH and then go LOW for 5mS.

 

[Mikebits]

I would never use a 555. It is not an "engineers" chip. It may be ok for an automotive application but it is certainly not suitable for any electronic circuitry.

Use a Hex Schmitt trigger.

Isn't a Schmitt trigger just a threshold detection circuit?
________________edit__________________________

Also, I would think the auto industry has to maintain very high design standards. After all, an automobile can be an instrument of death.

 

[zorbzz]

Thanks guys for the quick replies.

First to Eric, my signal which is 5ms is dc and is 9v I dont know how to do what you are saying with ac coupling sorry.

Colin55 Its a positive pulse not a negative thats why I am having trouble and was thinking the easiest way to do it would be to make a pulse generator that when I applied the 9v 5ms pulse I have now, it would simply produce a pulse that is 1.5ms and then do nothing until the next pulse arrived etc. Is there such a thing like that?

My existing pulses are 5ms long and run at only 10 hz to 30hz so its relatively slow compared to a lot of other things.

I just need to make them 5 ms pulses into 1.5 if there is a way.

Thanks alot for your help.

 

[colin55]

You are mixing up a lot of different points, like mixing fruit, ice-cream and nails in a basket.

A 555 produces a lot of noise and cannot be included in a circuit with other digital chips.
Its mode of operation is very primitive.
It has a “crowbar” method of discharging the capacitor.
It also consumes a lot of current when doing nothing.
The output voltage is very poor.

It’s not until you try to combine it with other chips that all these faults materialize.

That’s why they tried to improve it with a CMOS version.


The only advantage is: It is cheap, 17 cents.


”Isn't a Schmitt trigger just a threshold detection circuit? “
That’s exactly what we are detecting: THRESHOLD.


If your pulse is positive-going, just use Schmitt gates:

 

[Mikebits]

Hans R. Camenzind would be hurt. Probably one of the biggest selling IC's ever, and you claim engineers never use it. Surely someone had to buy it to put it in the rankings for a title.

 

[ericgibbs]

A 555 produces a lot of noise and cannot be included in a circuit with other digital chips.
It can and is included in logic circuits if the appropiate decoupling is used.

It’s not until you try to combine it with other chips that all these faults materialize.

That’s why they tried to improve it with a CMOS version.
They did greatly improve the 555 with the CMOS version

The only advantage is: It is cheap, 17 cents.

”Isn't a Schmitt trigger just a threshold detection circuit? “
That’s exactly what we are detecting: THRESHOLD.
He is not detecting a threshold, but a period or duration of an incoming trigger pulse

If your pulse is positive-going, just use a Schmitt gates(s)
What has the polarity of the pulse to do with a using a Schmitt.?

Some of posts you are making are very misleading to any student who may not be aware of the inaccuracy.

 

[colin55]

"He is not detecting a threshold, but a period or duration of an incoming trigger pulse."

He is actually detecting a THRESHOLD (more accurately the presence of a signal or voltage of 5v or 12v) and producing a pulse of 1.5mS duration. The duration of the pulse does not matter. The circuit I have created produces an output of 1.5mS, no matter how long the input signal is present.

The poster had a problem with a positive going pulse, just as I did, using a 555. That's why I suggested using a Schmitt gate.

 

[ericgibbs]

"He is not detecting a threshold, but a period or duration of an incoming trigger pulse."

He is actually detecting a THRESHOLD (more accurately the presence of a signal or voltage of 5v or 12v) and producing a pulse of 1.5mS duration. The duration of the pulse does not matter. The circuit I have created produces an output of 1.5mS, no matter how long the input signal is present.

The poster had a problem with a positive going pulse, just as I did, using a 555. That's why I suggested using a Schmitt gate.

That is rubbish.

If you read his post, he wants to generate a 1.5mS PULSE from a 5mS trigger PULSE.... no mention of thresholds as I can see.

If he needs to invert the signal, all that is needed is a simple transistor invertor between the source and 555 trigger.

 

[colin55]

I really don't to be involved with discussions like this.

 

[ericgibbs]

I really don't to be involved with discussions like this.

Why not, this is a technical forum.?

EDIT:
On an open Forum you should be prepared to explain to your peers any technical statements that you make, that they disagree with.

 

[k7elp60]

Hi guys is there an easy way to make a pulse generator out of a 555 that when power is applied to the circuit it will generate a 1.5 ms pulse, turn off and then wait till power is applied then make another one etc?
I have fiddled around but cant do it how I want.

Ultimately when power is applied to the circuit the power can be about 5ms long, I need to find a way to turn that 5 ms pulse into a 1.5 ms one but only for each pulse. Then re triggered from the next pulse etc.
If a 555 isnt right for this job please steer me in the right direction.

All of the circuits I have tried have to have the circuit powered up all the time and then triggered but I havent found a way to make it so that the triggering pulse width of 5ms is converted to 1.5ms each time.

Thanks for your help Im only new to this and my knowledge is limited.

After reading the thread, I think I can help you. A 555 as a one-shot should do fine and I will be happy to post a schematic, but I need some more information.
You said the 5ms pulse is 9V. Is this pulse being generated from a 9V battery supply and do you have access to the 9V power leads?

 

[zorbzz]

Hi
No the source 5ms pulse is genetated from a 12 volt dc power source but It comes out as a 5ms 9volt pulse.
The final voltage doesnt really matter as long as it is 1.5ms and 3 to 12 volts.

My main problem is triggering the 555 from a positive pulse to produce 1.5 ms pulse everytime the initial 5ms pulse triggers it.

I can do it with a negative trigger but not a positive one.

Maybe I could use an optocoupler to trigger the 555?
Im stuck. I will be experimenting on the weekend but any ideas would help me alot.
Thanks again.

 

[ericgibbs]

Hi
No the source 5ms pulse is genetated from a 12 volt dc power source but It comes out as a 5ms 9volt pulse.
The final voltage doesnt really matter as long as it is 1.5ms and 3 to 12 volts.

My main problem is triggering the 555 from a positive pulse to produce 1.5 ms pulse everytime the initial 5ms pulse triggers it.

I can do it with a negative trigger but not a positive one.

Maybe I could use an optocoupler to trigger the 555?
Im stuck. I will be experimenting on the weekend but any ideas would help me alot.
Thanks again.

hi,
add a simple transistor invertor before the trigger circuit.
Its not a 'negative' trigger but a 'negative going' trigger.

Do you follow.??

EDIT:

 

[Mikebits]

What about using a 74LS123. It can trigger active hi or active low. It also has built in schmitt.
https://www.electro-tech-online.com/custompdfs/2009/03/sn74ls123.pdf

I should add, this part will not run at 12v. But you said level did not matter.

 

[zorbzz]

hi,
add a simple transistor invertor before the trigger circuit.
Its not a 'negative' trigger but a 'negative going' trigger.

Do you follow.??

EDIT:

Yep that looks like its what I'm after thanks alot, ill experiment with it and let you know how it went.


Mikebits if this doesnt work ill have to try something else like that.

Thanks alot for your help everyone.

 

[k7elp60]

Here is a schematic that may work depending upon theenergy of the 5mS pulse. I used a comos 555 as a 5mS one shot from my function generator to trigger it. You will notice that the power for the 555 is also obtained from the 5mS pulse.
I have used this circuit on occasion with the input + terminal going to +Vcc. On power up it generates a short + trigger.

Correction: The two capacitors on pins 6&7 and pin 2 should be reversed. The .01uf should be on pin 2 and the 0.1uF should be on pins 6&7. And the 13K and the 10K should be exchanged.