trigger LED

[John Larkin]

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[whit3rd]

On Monday, January 6, 2020 at 12:01:45 PM UTC-8, John Larkin wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

If you trigger a toggle flipflop, the Q and /Q make an AC signal; bridge
rectifier into a resistor-parallel(LED, capacitor) will light the LED
as long as events happen, and fade the LED out at an RC time...
it looks like you want an 'activity' light to look.

There's lots of designs for logic probes (a common project forty years ago)
that also would have clever ways to indicate pulses.

 

[bitrex]

On 1/6/20 3:01 PM, John Larkin wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

Differential transistor pair with one base biased to half the nominal
pulse amplitude, and the other gets the pulses through an RC lowpass to
its base is pretty bug-free. Put the LED in the appropriate collector
line for whether you want it to blink for positive or negative logic signal.

 

[bitrex]

On 1/6/20 3:54 PM, bitrex wrote:

On 1/6/20 3:01 PM, John Larkin wrote:


I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.


Differential transistor pair with one base biased to half the nominal
pulse amplitude, and the other gets the pulses through an RC lowpass to
its base is pretty bug-free. Put the LED in the appropriate collector
line for whether you want it to blink for positive or negative logic
signal.

Or rather use PNP or NPN transistors depending.

 

[whit3rd]

On Monday, January 6, 2020 at 12:42:27 PM UTC-8, whit3rd wrote:

If you trigger a toggle flipflop, the Q and /Q make an AC signal; bridge
rectifier into a resistor-parallel(LED, capacitor)

I omitted the (kinda important) coupling capacitor from that AC signal
into the bridge rectifier; the RC time that sets the pulse decay is
from the coupling capacitor and the impedance of the LED being
driven. I liked about a half-second decay, used a 10 uF nonpolar
electrolytic.

 

[LM]

A 2 input Xor and a cap between inputs detects changes.

On Mon, 06 Jan 2020 12:01:35 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

 

[John Larkin]

On Mon, 06 Jan 2020 23:44:12 +0200, LM <sala.nimi@mail.com> wrote:

A 2 input Xor and a cap between inputs detects changes.

But what drives the LED?

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Mon, 6 Jan 2020 15:54:24 -0500, bitrex <user@example.net> wrote:

On 1/6/20 3:01 PM, John Larkin wrote:


I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.


Differential transistor pair with one base biased to half the nominal
pulse amplitude, and the other gets the pulses through an RC lowpass to
its base is pretty bug-free. Put the LED in the appropriate collector
line for whether you want it to blink for positive or negative logic signal.

That would miss a fast (say, 5 ns wide) trigger pulse.

A retriggerable one-shot is ideal, if that would work at 100 MHz input
rate.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Monday, January 6, 2020 at 3:01:45 PM UTC-5, John Larkin wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

Section 6.6 gives timing. You're good with 5ns triggers at Vcc 2.5V or more.. But retrigger, trr, times climb into us for Cext in the range you're talking about. And there's no mention of some kind of metastability if exceeded.. Those are the pulse durations for predictable guaranteed operation. You will probably need to lockout the trigger input for reliable operation.
http://www.ti.com/lit/ds/symlink/sn74lvc1g123.pdf

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Why do you want the LED to go out at high trigger rates? Seems an ambiguous indication confusing no activity with high activity.

 

[piglet]

On 07/01/2020 17:53, bloggs.fredbloggs.fred@gmail.com wrote:

On Monday, January 6, 2020 at 3:01:45 PM UTC-5, John Larkin wrote:
I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

Section 6.6 gives timing. You're good with 5ns triggers at Vcc 2.5V or more. But retrigger, trr, times climb into us for Cext in the range you're talking about. And there's no mention of some kind of metastability if exceeded. Those are the pulse durations for predictable guaranteed operation. You will probably need to lockout the trigger input for reliable operation.
http://www.ti.com/lit/ds/symlink/sn74lvc1g123.pdf

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Why do you want the LED to go out at high trigger rates? Seems an ambiguous indication confusing no activity with high activity.

How about using two monostables, 100ms led-on followed by an enforced
100ms led-off before the first trigger is re-enabled. Then the led will
blink once for a single event and flash at 5Hz for sustained event bursts?

piglet

 

[LM]

Yes, my answer does not really answer your question. But what about a
circuit with fast rise time and 100ms fall time. A capacitor, diode or
two, a couple of resistors, second capacitor and a smith gate to drive
a led.
On Mon, 06 Jan 2020 15:43:18 -0800, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Mon, 06 Jan 2020 23:44:12 +0200, LM <sala.nimi@mail.com> wrote:


A 2 input Xor and a cap between inputs detects changes.

But what drives the LED?

 

[Bill Sloman]

On Tuesday, January 7, 2020 at 7:01:45 AM UTC+11, John Larkin wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

Why not read the data sheet?

http://www.farnell.com/datasheets/2151614.pdf

The data you want is on page 11.

You haven't specified your supply voltage, but with a blue LED you will need more than 3V, and that would give minimum pulse widths of 3nsec, which is compatible with 100MHz operation.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

Reading the data sheet would have been even easier, but that takes electronic design skills.

Building you own monostable with a couple of 5GHz transistors would have taken you even further.

Ghiggino, K.P., Phillips, D., and Sloman, A.W. "Nanosecond pulse stretcher",Journal of Physics E: Scientific Instruments, 12, 686-687 (1979).

I should have used an emitter-coupled monostable (as is mentioned in the letter), but the traditional circuit worked in the application we needed it for.

--
Bill Sloman, Sydney

 

[Phil Hobbs]

On 2020-01-06 18:43, John Larkin wrote:

On Mon, 06 Jan 2020 23:44:12 +0200, LM <sala.nimi@mail.com> wrote:


A 2 input Xor and a cap between inputs detects changes.

But what drives the LED?

One of your patented 'Schottky + capacitor + no bleed resistor' level
detectors running into a SC70 CMOS comparator might be the business,
unless the trigger pulses are super short.

Same number of parts.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[bitrex]

On 1/6/20 6:45 PM, John Larkin wrote:

On Mon, 6 Jan 2020 15:54:24 -0500, bitrex <user@example.net> wrote:

On 1/6/20 3:01 PM, John Larkin wrote:


I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.


Differential transistor pair with one base biased to half the nominal
pulse amplitude, and the other gets the pulses through an RC lowpass to
its base is pretty bug-free. Put the LED in the appropriate collector
line for whether you want it to blink for positive or negative logic signal.

That would miss a fast (say, 5 ns wide) trigger pulse.

A retriggerable one-shot is ideal, if that would work at 100 MHz input
rate.

How about turning the problem upside-down and generating a pulse train,
and have the incoming user trigger gate it off momentarily. Then into a
missing-pulse detector.

I'd expect detecting missing pulses in a train of them would be an
easier thing to do reliably than detect isolated pulses of such short
duration.

 

On Monday, January 6, 2020 at 3:01:45 PM UTC-5, John Larkin wrote:

I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Min. trigger pulse for an 'AC123 is 5ns, but I don't
think it'll re-trigger immediately, 10ns later...

https://www.ti.com/lit/an/scla014/scla014.pdf
"If the input retrigger pulse follows the initial input pulse
after 0.30 × the initial output pulse duration, the output
is retriggered."

But does it matter? If you have a 10ns pulse triggering a 100ms
one-shot, does it matter than the one-shot isn't re-triggered
until 30ms into its timing cycle, instead of immediately? The
LED will appear continuously lit, either way.

If you wanted to be sure without having to try things, a
flip-flop in front of the 'AC123 could latch on the trigger
pulse, and then be reset by the 'AC123 -- two small parts,
minimal glue.

Cheers,
James

 

[John Larkin]

On Tue, 7 Jan 2020 20:05:48 -0500, bitrex <user@example.net> wrote:

On 1/6/20 6:45 PM, John Larkin wrote:
On Mon, 6 Jan 2020 15:54:24 -0500, bitrex <user@example.net> wrote:

On 1/6/20 3:01 PM, John Larkin wrote:


I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.


Differential transistor pair with one base biased to half the nominal
pulse amplitude, and the other gets the pulses through an RC lowpass to
its base is pretty bug-free. Put the LED in the appropriate collector
line for whether you want it to blink for positive or negative logic signal.

That would miss a fast (say, 5 ns wide) trigger pulse.

A retriggerable one-shot is ideal, if that would work at 100 MHz input
rate.


How about turning the problem upside-down and generating a pulse train,
and have the incoming user trigger gate it off momentarily. Then into a
missing-pulse detector.

Gate it off momentarily? With a one-shot!

I'd expect detecting missing pulses in a train of them would be an
easier thing to do reliably than detect isolated pulses of such short
duration.

Schematic?


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Wed, 08 Jan 2020 01:18:43 +0200, LM <sala.nimi@mail.com> wrote:

Yes, my answer does not really answer your question. But what about a
circuit with fast rise time and 100ms fall time. A capacitor, diode or
two, a couple of resistors, second capacitor and a smith gate to drive
a led.
On Mon, 06 Jan 2020 15:43:18 -0800, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Mon, 06 Jan 2020 23:44:12 +0200, LM <sala.nimi@mail.com> wrote:


A 2 input Xor and a cap between inputs detects changes.

But what drives the LED?

That's a pulse stretcher, but with a 20 million stretch ratio.

That's hard to do in one stage. Three or four cascaded stretchers
would work, but that's a lot of parts.

Top posting is confusing on usenet.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 7 Jan 2020 19:55:09 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-01-06 18:43, John Larkin wrote:
On Mon, 06 Jan 2020 23:44:12 +0200, LM <sala.nimi@mail.com> wrote:


A 2 input Xor and a cap between inputs detects changes.

But what drives the LED?


One of your patented 'Schottky + capacitor + no bleed resistor' level
detectors running into a SC70 CMOS comparator might be the business,
unless the trigger pulses are super short.

Same number of parts.

Cheers

Phil Hobbs

Say I'd want to stretch a 5 ns pulse to a 50 ms LED flash. 1e7:1
ratio. That's tricky to do analog.

I like the one-shot, if it will work. I guess I'll try it.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 7 Jan 2020 17:20:59 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, January 6, 2020 at 3:01:45 PM UTC-5, John Larkin wrote:
I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Min. trigger pulse for an 'AC123 is 5ns, but I don't
think it'll re-trigger immediately, 10ns later...

https://www.ti.com/lit/an/scla014/scla014.pdf
"If the input retrigger pulse follows the initial input pulse
after 0.30 × the initial output pulse duration, the output
is retriggered."

But does it matter? If you have a 10ns pulse triggering a 100ms
one-shot, does it matter than the one-shot isn't re-triggered
until 30ms into its timing cycle, instead of immediately? The
LED will appear continuously lit, either way.

As long as the LED stays lit, I don't care how confused the one-shot
is, or how confused I am.

If you wanted to be sure without having to try things, a
flip-flop in front of the 'AC123 could latch on the trigger
pulse, and then be reset by the 'AC123 -- two small parts,
minimal glue.

I previously built a fast one-shot from a 1 ns Tiny flop that reset
itself, and use that to fire a second one-shot. But I want something
simpler.

I was just wondering if anyone had done this.

It ought to work. I'll try it.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

On Tuesday, January 7, 2020 at 9:10:39 PM UTC-5, John Larkin wrote:

On Tue, 7 Jan 2020 17:20:59 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, January 6, 2020 at 3:01:45 PM UTC-5, John Larkin wrote:
I'm doing a small box that accepts a user trigger. I'd like to flash
an LED every time it gets triggered. Something like 100 ms, on a blue
LED.

The obvious circuit is a 74lvc1G123 one-shot, set to 100 ms pulse
width. But how fast will that work? I'd like to go to 50 or maybe 100
MHz. Would it keep retriggering? I wouldn't want the LED to go out at
high trigger rates.

There is a specified "retrigger time", but I'm not sure what that
means. Has anyone really over-triggered these things?

I guess I could breadboard and try it, but asking is easier.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Min. trigger pulse for an 'AC123 is 5ns, but I don't
think it'll re-trigger immediately, 10ns later...

https://www.ti.com/lit/an/scla014/scla014.pdf
"If the input retrigger pulse follows the initial input pulse
after 0.30 × the initial output pulse duration, the output
is retriggered."

But does it matter? If you have a 10ns pulse triggering a 100ms
one-shot, does it matter than the one-shot isn't re-triggered
until 30ms into its timing cycle, instead of immediately? The
LED will appear continuously lit, either way.

As long as the LED stays lit, I don't care how confused the one-shot
is, or how confused I am.


If you wanted to be sure without having to try things, a
flip-flop in front of the 'AC123 could latch on the trigger
pulse, and then be reset by the 'AC123 -- two small parts,
minimal glue.

I previously built a fast one-shot from a 1 ns Tiny flop that reset
itself, and use that to fire a second one-shot. But I want something
simpler.

I was just wondering if anyone had done this.

It ought to work. I'll try it.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

I had a similar situation but with re-trigger rates closer
to kHz, not MHz. I used an 'AC123 with a 100ms period.

But I can't really tell you if the thing was retriggering
promptly -- the LED just stayed lit to the eye, which was
all I cared about.

If extreme re-trigger rates befuddle the '123, I think a single
flip-flop fixes it.

-+-
|
Rt
+-Ct-.
| |
.----. .-------.
.-|D | | |
| | Q|------|> Q|----> LED
trig >---|> | |'AC123 |
| '----' | _|
| | Q|--.
| '-------' |
'------------------------'

Cheers,
James