trigger LED

[George Herold]

On Wednesday, January 8, 2020 at 3:23:07 PM UTC-5, dagmarg...@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

LED's keep getting better!
Looking at the 'transfer ratio' of an led,
electrons in to photons out, is kinda fun.

Led's I looked at years ago would start to 'crap out'* at a few mA..
I wonder if they are better these days.

George H.
*transfer ratio became non-linear... you needed to add three electrons
to make two photons at low current/voltage.

 

On Fri, 10 Jan 2020 18:00:49 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Wednesday, January 8, 2020 at 3:23:07 PM UTC-5, dagmarg...@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

LED's keep getting better!
Looking at the 'transfer ratio' of an led,
electrons in to photons out, is kinda fun.

Led's I looked at years ago would start to 'crap out'* at a few mA..
I wonder if they are better these days.

George H.
*transfer ratio became non-linear... you needed to add three electrons
to make two photons at low current/voltage.

I got visible light from a green LED at 1 nA.



--

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"