trigger LED

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 ...
Click to expand...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.


--
Thanks,
- Win
 
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
Click to expand...

OK, this would work, with a few more parts,

https://www.dropbox.com/s/l0r5tmg1thaopwl/LED_Stretcher_1.JPG?raw=1

and maybe a little math.

Is on the fast schottky diodes is maybe 100 nA or so, so 100K stretch
per stage is possible, maybe 10K to be conservative. Even 1K would
work in three stages.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 7 Jan 2020 18:56:21 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.
Click to expand...

A stretch ratio of 1e7 might just be possible in one stage. Discharge
at 100 mA, charge at 10 nA.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, January 7, 2020 at 10:29:00 PM UTC-5, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020 18:56:21 -0800, Winfield Hill <winfieldhill@yahoo.com
wrote:

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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one stage. Discharge
at 100 mA, charge at 10 nA.
Click to expand...

-+-
|
.-.
| | R1
'-'
|
V ~~>
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

:)

Cheers,
James
 
On Tue, 7 Jan 2020 19:34:23 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, January 7, 2020 at 10:29:00 PM UTC-5, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020 18:56:21 -0800, Winfield Hill <winfieldhill@yahoo.com
wrote:

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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one stage. Discharge
at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

:)

Cheers,
James
Click to expand...

That's my trick! The Is of the diode is the discharge. Cgs is 20 pF or
so, maybe some Miller added, so we need a diode that leaks maybe 1 nA
reverse. Not a schottky.

A 123 type one-shot has two inputs. I could clock B, and connect Q to
A, so it locks its own triggers out while it's active. That might
help.

(Note proper use of its and it's )

(Not to be confused with Is )



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, January 7, 2020 at 7:55:19 PM UTC-5, Phil Hobbs 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.
Huh, no bleed resistor? leakage from the Schottky? (or cmos gate?)
Click to expand...

George H.
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
Click to expand...
 
On 2020-01-06, 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.
Click to expand...

not at all, or not visibly?

--
Jasen.
 
dagmargoodboat@yahoo.com wrote...
On January 7, 2020, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020, Winfield Hill wrote:
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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one
stage. Discharge at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---
Click to expand...

Here's my favorite fault-indicator LED circuit.
Its input is a /dis line, accepting wire-or'd
outputs from multiple o/c comparators and gates.
The /dis signal makes a BSS84 MOSFET charge the
cap. It's discharged by base current of an NPN
pulling current through an LED at some higher V.

.. LED Fault Indicator
.. 40ms stretch
..
.. 3.3V 5,12V etc
.. | 3.3V |
.. 10k | A
.. | S K LED
.. +- G pMOS |
.. | D |
.. | | C NPN
.. /dis +---- B
.. | E
.. 0.1 |
.. | 680
.. Gnd |
.. Gnd
..


--
Thanks,
- Win
 
On Tue, 7 Jan 2020 21:27:20 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Tuesday, January 7, 2020 at 7:55:19 PM UTC-5, Phil Hobbs 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.
Huh, no bleed resistor? leakage from the Schottky? (or cmos gate?)
Click to expand...

Low-barrier schottkies have predictable reverse leakage in the 100 nA
range, and a CMOS gate has pA of input current, so it works.

Here's an RF detector. Works fine.

https://www.dropbox.com/s/0yysocb7cxp4bxu/P348_RF_Detector.jpg?raw=1



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 8 Jan 2020 05:07:37 -0800, Winfield Hill <winfieldhill@yahoo.com>
wrote:

dagmargoodboat@yahoo.com wrote...
On January 7, 2020, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020, Winfield Hill wrote:
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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one
stage. Discharge at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

Here's my favorite fault-indicator LED circuit.
Its input is a /dis line, accepting wire-or'd
outputs from multiple o/c comparators and gates.
The /dis signal makes a BSS84 MOSFET charge the
cap. It's discharged by base current of an NPN
pulling current through an LED at some higher V.

. LED Fault Indicator
. 40ms stretch
.
. 3.3V 5,12V etc
. | 3.3V |
. 10k | A
. | S K LED
. +- G pMOS |
. | D |
. | | C NPN
. /dis +---- B
. | E
. 0.1 |
. | 680
. Gnd |
. Gnd
.
Click to expand...

Beta-graded transistors, like BCX70, help things like this. The old
rule "never design around beta" doesn't always apply.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Wed, 8 Jan 2020 07:40:45 -0000 (UTC), Jasen Betts
<jasen@xnet.co.nz> wrote:

On 2020-01-06, 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.

not at all, or not visibly?
Click to expand...

It's just a visual trigger indicator, so it's not fussy.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Tuesday, January 7, 2020 at 11:21:59 PM UTC-5, jla...@highlandsniptechnology.com wrote:
On Tue, 7 Jan 2020 19:34:23 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Tuesday, January 7, 2020 at 10:29:00 PM UTC-5, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020 18:56:21 -0800, Winfield Hill <winfieldhill@yahoo.com
wrote:

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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one stage. Discharge
at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

:)


That's my trick! The Is of the diode is the discharge. Cgs is 20 pF or
so, maybe some Miller added, so we need a diode that leaks maybe 1 nA
reverse. Not a schottky.

A 123 type one-shot has two inputs. I could clock B, and connect Q to
A, so it locks its own triggers out while it's active. That might
help.
Click to expand...

I think that's a winner -- triggers the '123 doesn't see, can't
confuse it.

Cheers,
James
 
On Wednesday, January 8, 2020 at 8:07:51 AM UTC-5, Winfield Hill wrote:
dagmargoodboat@yahoo.com wrote...
On January 7, 2020, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020, Winfield Hill wrote:
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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one
stage. Discharge at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

Here's my favorite fault-indicator LED circuit.
Its input is a /dis line, accepting wire-or'd
outputs from multiple o/c comparators and gates.
The /dis signal makes a BSS84 MOSFET charge the
cap. It's discharged by base current of an NPN
pulling current through an LED at some higher V.

. LED Fault Indicator
. 40ms stretch
.
. 3.3V 5,12V etc
. | 3.3V |
. 10k | A
. | S K LED
. +- G pMOS |
. | D |
. | | C NPN
. /dis +---- B
. | E
. 0.1uF |
. | 680
. Gnd |
. Gnd
.


--
Thanks,
- Win
Click to expand...

Hey, I tried to look at your cute circuit but that 4mA
LED poked my eye out! .-)

(I get complaints about LEDs being too bright at 2mA
these days.)

Cheers,
James Arthur
 
On Wed, 8 Jan 2020 12:23:02 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Wednesday, January 8, 2020 at 8:07:51 AM UTC-5, Winfield Hill wrote:
dagmargoodboat@yahoo.com wrote...
On January 7, 2020, jla...@highlandsniptechnology.com wrote:
On 7 Jan 2020, Winfield Hill wrote:
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 ...

I'm not happy with oneshots, with all their rules,
for this application. I feed the pulse to a 2n7000
to discharge a cap, with a pullup R. A comp circuit
detects whenever the cap is below 0.6Vcc. If the
first pulse is very short, repeat using the comp
circuit's output. Never miss a trigger.

A stretch ratio of 1e7 might just be possible in one
stage. Discharge at 100 mA, charge at 10 nA.

-+-
|
.-.
| | R1
'-'
|
V ~~
---
|
||--'
||<-. 2n7002
trig >-->|--'|--+
|
---

Here's my favorite fault-indicator LED circuit.
Its input is a /dis line, accepting wire-or'd
outputs from multiple o/c comparators and gates.
The /dis signal makes a BSS84 MOSFET charge the
cap. It's discharged by base current of an NPN
pulling current through an LED at some higher V.

. LED Fault Indicator
. 40ms stretch
.
. 3.3V 5,12V etc
. | 3.3V |
. 10k | A
. | S K LED
. +- G pMOS |
. | D |
. | | C NPN
. /dis +---- B
. | E
. 0.1uF |
. | 680
. Gnd |
. Gnd
.


--
Thanks,
- Win

Hey, I tried to look at your cute circuit but that 4mA
LED poked my eye out! .-)

(I get complaints about LEDs being too bright at 2mA
these days.)

Cheers,
James Arthur
Click to expand...

We ran the first Cree blue LEDs at 50 mA. As they got better,
customers started complaining.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 1/7/20 8:56 PM, John Larkin wrote:
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?
Click to expand...

Somethin like

<https://imgur.com/a/QqqKCjl>

The red blip is a burst of 7 5ns wide pulses, the blue spike is a pulse
through the LED connected to the HIGHLY _ILLEGAL_ 555's discharge
transistor pin.
 
On Wed, 8 Jan 2020 16:27:39 -0500, bitrex <user@example.net> wrote:

On 1/7/20 8:56 PM, John Larkin wrote:
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?



Somethin like

https://imgur.com/a/QqqKCjl

The red blip is a burst of 7 5ns wide pulses, the blue spike is a pulse
through the LED connected to the HIGHLY _ILLEGAL_ 555's discharge
transistor pin.
Click to expand...

Kind of a lot of parts to light an LED.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.

"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
 
On 1/8/20 10:51 PM, jlarkin@highlandsniptechnology.com wrote:
On Wed, 8 Jan 2020 16:27:39 -0500, bitrex <user@example.net> wrote:

On 1/7/20 8:56 PM, John Larkin wrote:
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?



Somethin like

https://imgur.com/a/QqqKCjl

The red blip is a burst of 7 5ns wide pulses, the blue spike is a pulse
through the LED connected to the HIGHLY _ILLEGAL_ 555's discharge
transistor pin.

Kind of a lot of parts to light an LED.
Click to expand...

Sometimes there's an advantage to using a few extra parts to convert a
problem you don't know how to solve into one you do; detecting missing
pulses in a low-frequency train of them is easier than detecting
isolated pulses in the vast expanse of time when maybe nothing happens
from like an "information theory" perspective, or something.
 
On Wednesday, January 8, 2020 at 4:27:46 PM UTC-5, bitrex wrote:
On 1/7/20 8:56 PM, John Larkin wrote:
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?



Somethin like

https://imgur.com/a/QqqKCjl

The red blip is a burst of 7 5ns wide pulses, the blue spike is a pulse
through the LED connected to the HIGHLY _ILLEGAL_ 555's discharge
transistor pin.
Click to expand...

Logic is flawed and it takes 2xtpd to latch a discrete gate latch like that.
 
On 1/9/20 3:51 PM, bloggs.fredbloggs.fred@gmail.com wrote:
On Wednesday, January 8, 2020 at 4:27:46 PM UTC-5, bitrex wrote:
On 1/7/20 8:56 PM, John Larkin wrote:
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?



Somethin like

https://imgur.com/a/QqqKCjl

The red blip is a burst of 7 5ns wide pulses, the blue spike is a pulse
through the LED connected to the HIGHLY _ILLEGAL_ 555's discharge
transistor pin.

Logic is flawed and it takes 2xtpd to latch a discrete gate latch like that.
Click to expand...

?????????????????????????
 
On Wednesday, January 8, 2020 at 10:26:17 AM UTC-5, jla...@highlandsniptechnology.com wrote:
On Tue, 7 Jan 2020 21:27:20 -0800 (PST), George Herold
ggherold@gmail.com> wrote:

On Tuesday, January 7, 2020 at 7:55:19 PM UTC-5, Phil Hobbs 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.
Huh, no bleed resistor? leakage from the Schottky? (or cmos gate?)

Low-barrier schottkies have predictable reverse leakage in the 100 nA
range, and a CMOS gate has pA of input current, so it works.

Here's an RF detector. Works fine.

https://www.dropbox.com/s/0yysocb7cxp4bxu/P348_RF_Detector.jpg?raw=1
Thanks, I guess there's no reason not to use a diode both ways.
Click to expand...

As long as you can live with the temp dependence.

George H.
--

John Larkin Highland Technology, Inc

lunatic fringe electronics
Click to expand...
 
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