simple oneshot(2)

G

George Herold

Guest
Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)
 
On Wednesday, April 16, 2014 11:58:56 AM UTC-4, RobertMacy wrote:
On Wed, 16 Apr 2014 08:28:32 -0700, George Herold <gherold@teachspin.com

wrote:



Hi all, OK a silly basic question.

I'm doing some digital stuff.

I wanted a one shot to reset some things, but didn't want to put in an

entire chip

(74HC123.. or whatever the number is.)

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG

Is this OK?



Thanks,

George H.

(This didn't appear the first time I posted it...

trying again.)



didn't look at the pic, but first thought, "What happens when the

unexpected happens?"
Oh just an RC high pass and diode to ground to "eat up" the reverse voltage spike.
Click to expand...

Like power up, up then off then up again, or very slow up. those kinds of
things.
Click to expand...
Hmm that shouldn't be a problem. It only "sees" internal sharp pulses.
I was more worried about too much current in the diode,
or if the -0.3 volt from the diode clamp would be an issue.
It seems like this must be (or must have been*) either a standard trick..
or something that is frowned upon.

George H.
*does anyone do pieces parts digital circuits anymore?
Or is it all FPGA's and their ilk.
 
On Wed, 16 Apr 2014 08:28:32 -0700, George Herold <gherold@teachspin.com>
wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an
entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)
Click to expand...

didn't look at the pic, but first thought, "What happens when the
unexpected happens?"

Like power up, up then off then up again, or very slow up. those kinds of
things.
 
On Wednesday, April 16, 2014 8:28:32 AM UTC-7, George Herold wrote:
Hi all, OK a silly basic question.

I'm doing some digital stuff.

I wanted a one shot to reset some things, but didn't want to put in an entire chip

(74HC123.. or whatever the number is.)

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG

Is this OK?
Click to expand...

If the inverter weren't CMOS, and you can tolerate multiple
edges near the end of the delay, yes.

For CMOS, slow-slewing inputs are highly discouraged (can
cause high power consumption) unless the gate is one that
has hysteresis (i.e. a Schmitt inverter).

At/near the logic threshold, a slow ramp voltage might result in power
supply noise getting amplified (and that means lots of
hash on the output), so hysteresis is your friend. Two
thresholds, so you're never near both of 'em.
 
On Wed, 16 Apr 2014 09:10:27 -0700, George Herold <gherold@teachspin.com>
wrote:

..snip...
*does anyone do pieces parts digital circuits anymore?
Or is it all FPGA's and their ilk.
Click to expand...

Naw, today the 'component' is an iPod, or such. people are writing apps as
the product and think in terms of a super complex system as the component.
Whole new ballgame.
 
On Wednesday, April 16, 2014 8:28:32 AM UTC-7, George Herold wrote:

I wanted a one shot to reset some things, but didn't want to put in an entire chip

(74HC123.. or whatever the number is.)

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Click to expand...

Either a '555 or a SN74LVC1G123 (both in SO-8 nowadays) would
work. In CMOS, a slow-slewing input that approaches threshold
will result in lots of hash (because power supply noise gets
amplified), and possibly in high power consumption, UNLESS you
have a Schmitt gate. The hysteresis of a Schmitt trigger solves
both problems. Switching to TTL solves the transient power consumption
issue.
 
"George Herold" schreef in bericht news:e9caced1-21a9-4345-9eb3-bad0b02c6584@googlegroups.com...

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)

If you need a clean reset puls like a 74HC121 or similar circuit will provide, this is *not* OK. You will need some more components like in the schematic below.

|| D2 |\
----||----+--->|---+---+----| >O------
|| | | | |/
C1 | .-. | HCT14
- | | ---
^ D1 R| | --- C2
| '-' |
| | |
---------+--------+---+---------------
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

There are some thing you have to mention:
- The starting pulse need to be able to provide the required power i.e. provide enough current during it’s on-time to load C2.
- So C1>>C2
- D1 eats the negative pulse on the falling edge of the input pulse.
- D2 isolates the one shot from the input once it has started.
- R*C2 determines the resulting pulsewidth (along with the thresholds of the 74HC14).
- To trigger this one shot again, it requires a new rising edge i.e. a new pulse on its input.
- C1 and D1 can be omitted if you can couple the input pulse directly. But in this case the timing will start when the input pulse has gone.

petrus bitbyter
 
On Wednesday, April 16, 2014 8:28:32 AM UTC-7, George Herold wrote:

I wanted a one shot to reset some things, but didn't want to put in an entire chip

(74HC123.. or whatever the number is.)

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Click to expand...

Either a '555 or a SN74LVC1G123 (both in SO-8 nowadays) would
work. In CMOS, a slow-slewing input that approaches threshold
will result in lots of hash (because power supply noise gets
amplified), and possibly in high power consumption, UNLESS you
have a Schmitt gate. The hysteresis of a Schmitt trigger solves
both problems. Switching to TTL solves the transient power consumption
issue.

(having posting problems, hope this isn't a repeat send!)
 
On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)
Click to expand...

This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

It's all "logic legal" electrically.

Use an XOR gate, and it fires on both input edges.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Wed, 16 Apr 2014 17:24:06 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)

This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

It's all "logic legal" electrically.

Found of any old text book.
Use an XOR gate, and it fires on both input edges.
Click to expand...

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 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.
 
On Wed, 16 Apr 2014 17:55:14 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Wed, 16 Apr 2014 17:24:06 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)

This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

It's all "logic legal" electrically.

Found of any old text book.
Use an XOR gate, and it fires on both input edges.

...Jim Thompson
Click to expand...

The book that you need is "Killfiles for Dummies."


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
 
On Wednesday, April 16, 2014 11:28:32 AM UTC-4, George Herold wrote:
Hi all, OK a silly basic question.

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Click to expand...

Hi guys, Well a follow-up on the oneshot.
So this is with a 74HC14. (Schmitt trigger inverter.)
Here's a link to a dropbox file. (I'm really loving dropbox.)
(It's turning into a notebook supplement.)
https://www.dropbox.com/sh/kj73ftaajd3532w/-Vtjx2t9tX
The sheets of paper describe the circuit and the 'scope shots.
The first three scope shots are w/o the series resistor.
(Lots of loading as Phil warned.)
I then added the 1k in series, and measured pulse width versus the capacitor.
At the lowest C (12 pF... I couldn't find 10 pF in my box.), the 'scope probe loaded the input.
So TEK008 is just the output. And then TEK009 is 'scope probe with 3.3pF series capacitor.
The picture is of probing w/3.3pF series cap.. circuit in upper right hand side.
(the rest is some other bit's and pieces.)

George H.
 
On Wednesday, April 16, 2014 2:27:26 PM UTC-4, petrus bitbyter wrote:
"George Herold" schreef in bericht
news:e9caced1-21a9-4345-9eb3-bad0b02c6584@googlegroups.com...



So I just used a cap, resistor, diode and
inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?


If you need a clean reset puls like a 74HC121 or
similar circuit will provide, this is *not* OK. You will need some more
components like in the schematic below.
snipping nice Ascii art circuit.

There are some thing you have to
mention:

- The starting pulse need to be able to provide
the required power i.e. provide enough current during it's on-time to load
C2.

- So C1>>C2

- D1 eats the negative pulse on the falling edge
of the input pulse.

- D2 isolates the one shot from the input once it
has started.

- R*C2 determines the resulting pulsewidth (along
with the thresholds of the 74HC14).

- To trigger this one shot again, it requires a
new rising edge i.e. a new pulse on its input.
Click to expand...
OK that seems to work too.
you might want to add some series resistance so as to not load the input as much when D1 conducts.
- C1 and D1 can be omitted if you can couple the
input pulse directly. But in this case the timing will start when the input
pulse has gone.
Click to expand...

Hmm..If you take out C1 and D1 then it like a pulse stretcher.
(I've done that sometime in the dim past.)
I guess that's also part of mickey mouse logic.

George H.
petrus bitbyter
Click to expand...
 
On Wed, 16 Apr 2014 20:09:40 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 16 Apr 2014 17:55:14 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Wed, 16 Apr 2014 17:24:06 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)

This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

It's all "logic legal" electrically.

Found of any old text book.
Use an XOR gate, and it fires on both input edges.

...Jim Thompson

The book that you need is "Killfiles for Dummies."
Click to expand...

---
Invoking such a killfile would likely rid USENET of much of its
traffic.

BTW, discounting metastability, your one-shot only works if the
input is wider than the output.
 
On Wednesday, April 16, 2014 8:24:06 PM UTC-4, John Larkin wrote:
On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold

gherold@teachspin.com> wrote
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JP
Click to expand...

<snipping>
This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

OK that'll be a fairly short pulse.

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.
Click to expand...

Once I've put in enough other stuff I might as well just stick in a "real" one-shot. I had a few extra inverters, so the above was what I thought of.

It's all "logic legal" electrically.
Click to expand...
Grin.. Ya mean my logic aint legal?
The digital police will be after me :^)
Use an XOR gate, and it fires on both input edges.
Click to expand...

OK I'll try and remember that trick.

George H.
--



John Larkin Highland Technology, Inc



jlarkin att highlandtechnology dott com

http://www.highlandtechnology.com
Click to expand...
 
On Wednesday, April 16, 2014 6:54:21 PM UTC-4, whit3rd wrote:
On Wednesday, April 16, 2014 8:28:32 AM UTC-7, George Herold wrote:



I wanted a one shot to reset some things, but didn't want to put in an entire chip
snip

Either a '555 or a SN74LVC1G123 (both in SO-8 nowadays) would
work. In CMOS, a slow-slewing input that approaches threshold
will result in lots of hash (because power supply noise gets
amplified), and possibly in high power consumption, UNLESS you
have a Schmitt gate. The hysteresis of a Schmitt trigger solves
both problems. Switching to TTL solves the transient power consumption
issue.

Yeah I wanted to avoid another IC.

(having posting problems, hope this isn't a repeat send!)
Click to expand...
Hmm google groups? It's a bit weird lately, my original post appeared (to me)
several hours after I posted in.. and long after Phil responded.

George h.
 
On Thu, 17 Apr 2014 08:15:54 -0500, John Fields <jfields@austininstruments.com>
wrote:

On Wed, 16 Apr 2014 20:09:40 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 16 Apr 2014 17:55:14 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Wed, 16 Apr 2014 17:24:06 -0700, John Larkin
jlarkin@highlandtechnology.com> wrote:

On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

Hi all, OK a silly basic question.
I'm doing some digital stuff.
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?

Thanks,
George H.
(This didn't appear the first time I posted it...
trying again.)

This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

It's all "logic legal" electrically.

Found of any old text book.
Use an XOR gate, and it fires on both input edges.

...Jim Thompson

The book that you need is "Killfiles for Dummies."

---
Invoking such a killfile would likely rid USENET of much of its
traffic.
Click to expand...

A week or so ago, JT claimed that he installed a script to killfile me and all
followups. Of course, he's claimed that many times before, and lied every time.
He claims he kills me, and then lurks. I bet he peeks in his neighbors windows,
too... that's his personality.

BTW, discounting metastability, your one-shot only works if the
input is wider than the output.
Click to expand...

Metastability? What can go metastable?

As far as width goes, it's similar to George's RC glitcher. Better, actually, in
not having long time constants that will introduce pattern dependencies.



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
 
On Thu, 17 Apr 2014 10:21:18 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Wednesday, April 16, 2014 8:24:06 PM UTC-4, John Larkin wrote:
On Wed, 16 Apr 2014 08:28:32 -0700 (PDT), George Herold

gherold@teachspin.com> wrote
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JP

snipping
This is a prop-delay one-shot:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Oscillators/Prop_Delay_One-shot.JPG

OK that'll be a fairly short pulse.

That one makes a pulse that is one gate delay wide, but you can add
any delay element in series with the lower inverter: coax, RC, more
gates, or just a cap from the inverter output to ground, if you're
feeling tacky.

Once I've put in enough other stuff I might as well just stick in a "real" one-shot. I had a few extra inverters, so the above was what I thought of.


It's all "logic legal" electrically.
Grin.. Ya mean my logic aint legal?
The digital police will be after me :^)
Click to expand...

The RC glitcher can have problems if C is small, and undershoots zero
volts. Misdemeanors, probably not a felony.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 4/17/2014 12:39 PM, George Herold wrote:
On Wednesday, April 16, 2014 11:28:32 AM UTC-4, George Herold wrote:
Hi all, OK a silly basic question.

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG


Hi guys, Well a follow-up on the oneshot.
So this is with a 74HC14. (Schmitt trigger inverter.)
Here's a link to a dropbox file. (I'm really loving dropbox.)
(It's turning into a notebook supplement.)
https://www.dropbox.com/sh/kj73ftaajd3532w/-Vtjx2t9tX
The sheets of paper describe the circuit and the 'scope shots.
The first three scope shots are w/o the series resistor.
(Lots of loading as Phil warned.)
I then added the 1k in series, and measured pulse width versus the capacitor.
At the lowest C (12 pF... I couldn't find 10 pF in my box.), the 'scope probe loaded the input.
So TEK008 is just the output. And then TEK009 is 'scope probe with 3.3pF series capacitor.
The picture is of probing w/3.3pF series cap.. circuit in upper right hand side.
(the rest is some other bit's and pieces.)

George H.
Click to expand...

I suspect you may be over-thinking this. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Thu, 17 Apr 2014 19:52:24 -0400, Phil Hobbs
<hobbs@electrooptical.net> wrote:

On 4/17/2014 12:39 PM, George Herold wrote:
On Wednesday, April 16, 2014 11:28:32 AM UTC-4, George Herold wrote:
Hi all, OK a silly basic question.

So I just used a cap, resistor, diode and inverter.

https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG


Hi guys, Well a follow-up on the oneshot.
So this is with a 74HC14. (Schmitt trigger inverter.)
Here's a link to a dropbox file. (I'm really loving dropbox.)
(It's turning into a notebook supplement.)
https://www.dropbox.com/sh/kj73ftaajd3532w/-Vtjx2t9tX
The sheets of paper describe the circuit and the 'scope shots.
The first three scope shots are w/o the series resistor.
(Lots of loading as Phil warned.)
I then added the 1k in series, and measured pulse width versus the capacitor.
At the lowest C (12 pF... I couldn't find 10 pF in my box.), the 'scope probe loaded the input.
So TEK008 is just the output. And then TEK009 is 'scope probe with 3.3pF series capacitor.
The picture is of probing w/3.3pF series cap.. circuit in upper right hand side.
(the rest is some other bit's and pieces.)

George H.


I suspect you may be over-thinking this. ;)

Cheers

Phil Hobbs
Click to expand...

AKA "Creeping Elegance" ?>:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 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.
 
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