How long bright flashing LED last on AA cells?

[Palindr☻me]

All of them - because the OP did not tell us the current.




The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

IME,YMMV, almost all OPs contain insufficent information to be certain
of the requirement.

Now in many cases, where safety and/or the law is involved, all a
respondent can do is to ask for more information. AS an example, when
someone asks about domestic electrical wiring and how to do something -
it cannot be answered without knowing where they are and what
regulations apply. So, if uncertain, the only response can be "Where are
you?"

With posts where safety and/or law aren't immediately involved,
responding to everything with "insufficient information, please clarify"
makes sense but is a tad boring - treating the information as clues to a
puzzle is more fun..It is never possible to eliminate the "ass" in
assumptions - but no harm is done. Putting the clues together correctly
can be a bit like doing the Times crossword..

I would imagine that most posters here enjoy solving puzzles and trying
to produce the answer that they think the OP would have got, had he
given enough information to be certain...

 

[nospam]

Doesn't matter though, there are two ways to go, either demand exact specs from
someone who might not have a clear idea yet, or post a response based on your
own carefully judged assumption. The latter is usually easier that waiting and
second-guessing your response before you've made one, and it gives the OP
something to think about.

A third and the easiest way to go is ignore dumb questions like "I have an
application for some string, what length do I need?".

Dumb questions like this often generate long threads of, frankly, dumb
answers.

The OP remains notable by his absence. If the OP can't be bothered to ask
properly why do so many feel inclined to answer?

Perhaps it is because letting the reader choose the question allows them to
pick one they have an answer for.
--

 

[Clive Mitchell]

If you really want to go all out, get an InGaN green LED (nominal
wavelength usually 525 to 530 nm) of the common 5 mm "bullet" style and
give it the sandpaper treatment described above. Then give it half a
milliamp or maybe a quarter of a milliamp. Most Nichia 5 mm green ones
and those trying to compete with them (ETG, and others) should at half
a milliamp have a brightness that I consider "fully that of a usual
green LED indicator light". Furthermore, the wavelength of these tends
to shift a little inversely with current, and at half a milliamp the
color is likely to be about that of LEDs with nominal wavelength in the
550's nm, maybe close to 560 - a yellowish shade of green likely to
look enough like a usual 565 nm green LED indicator lamp to look like a
usual indicator LED to most criminals.

I was demonstrating the efficiency of Gallium Nitride green LEDs to a
friend yesterday. I plugged it in to a simple tester that runs the LED
at either 75uA or 20mA and showed him it lit at 75uA. I was surprised
myself when I saw the beam actually move across his face as I pointed it
at him.

Given the distance most people are from a camera I would say that filing
it down is not required.

A set of four or more AA Alkalines with a suitable resistor (39K?)
should theoretically keep the Gallium Nitride green LED glowing at 75uA
for about three years.

 

[William P.N. Smith]

If it looks like a duck, how long do you wait to see if it quacks like a duck?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94030
works remarkably well, it senses motion and scans while flashing a
light.

 

[William P.N. Smith]

A third and the easiest way to go is ignore dumb questions like "I have an
application for some string, what length do I need?".

Thank you for your input.

 

[William P.N. Smith]

Doesn't matter though, there are two ways to go, either demand exact specs from
someone who might not have a clear idea yet, or post a response based on your
own carefully judged assumption.

Yeah, what "Lost" said.

Lastly, consider a low power laser diode, UNLENSED. These are eye safe at
distances beyond a few inches, (take care NOT to use a microlensed version
though) as they diverge strongly. Their output is highly monochromatic,
specular, very eye-catching, and their conversion of electricity to light is
second to none, so they can make ideal beacons.

This sounds interesting, do you have any sources?

Thanks!

[I think the discussion engendered by this particular "How long a
piece of string?" query has been useful and enlightening [sic].]

 

[Bob]

All of them - because the OP did not tell us the current.


The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

The OP did not provide enough information. In fact, he asked how long an LED
would last - He did not ask how long the cells powering the LED would last.

He did not specify duty cycle. His interpretation of "flashing" could range
from 1/2 second on, 1/2 second off (think traffic signal on flash), which
would likely average 10 ma (20 ma LED / 50% duty cycle) + power consumption
of whatever you are driving it with , down to sub millisecond pulses every
10 seconds, which could result in the cell(s) lasting for their self
discharge life.

He did not say what he would be flashing it with. He could be using a relay
with a capacitor to provide a time constant, which would likely make for a
very short battery life, or, with enough cells in series, and no current
limiting for the LED, could answer the question as to how long the LED would
last (not very long), or he could be using an LM3903.

He could be talking about something like this
http://www.lc-led.com/View/itemNumber/144 Even reading the datasheet for
that device does not provide enough information where you could provide an
accurate answer to either interpretation of the OP's question.


You could change the wording of the original question to address a different
technology, and have similar questions:

Very approximately how long would a lawn mower engine last?
The power source would be one (or more but how many?) gas cans each with a
capacity of 20 liters?


None of this is meant to put down the original poster. He just did not
provide enough info to answer his question without assuming just about
everything about it.

 

[Palindr☻me]

The OP did not provide enough information. In fact, he asked how long an LED
would last - He did not ask how long the cells powering the LED would last.

He did not specify duty cycle. His interpretation of "flashing" could range
from 1/2 second on, 1/2 second off (think traffic signal on flash), which
would likely average 10 ma (20 ma LED / 50% duty cycle) + power consumption
of whatever you are driving it with , down to sub millisecond pulses every
10 seconds, which could result in the cell(s) lasting for their self
discharge life.

He did not say what he would be flashing it with. He could be using a relay
with a capacitor to provide a time constant, which would likely make for a
very short battery life, or, with enough cells in series, and no current
limiting for the LED, could answer the question as to how long the LED would
last (not very long), or he could be using an LM3903.

He could be talking about something like this
http://www.lc-led.com/View/itemNumber/144 Even reading the datasheet for
that device does not provide enough information where you could provide an
accurate answer to either interpretation of the OP's question.


You could change the wording of the original question to address a different
technology, and have similar questions:

Very approximately how long would a lawn mower engine last?
The power source would be one (or more but how many?) gas cans each with a
capacity of 20 liters?


None of this is meant to put down the original poster. He just did not
provide enough info to answer his question without assuming just about
everything about it.

Yes but it is fun guess-timating what he had in mind... Incidently,
indefinately - I can never start the bloody thing unless I have someone
to hold the thing down whilst I pull on the cord with both hands...

 

[JohnR66]

Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?

You asked how long the LED would last. Did you mean whow long the batteries
would last?

The LED can last a second to many years depending on the dropping resistor
or the lack thereof.
John

 

[Palindr☻me]

You asked how long the LED would last. Did you mean whow long the batteries
would last?

The LED can last a second to many years depending on the dropping resistor
or the lack thereof.

The OP also didn't indicate the environment. Did he mean at normal room
temperatures?

The LED can last a few seconds to many years, depending on being located
inside the central heating furnace, or outside it...

 

[Lostgallifreyan]

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94030
works remarkably well, it senses motion and scans while flashing a
light.

Nice. Judging by the combination of visceral response to physical action,
and the fact that few people other than the builders of such things can
separate the practical requirements for that kind of machine vision, and
that needed for recording images, that thing should deter criminals both
smart and dumb.

 

[Lostgallifreyan]

Doesn't matter though, there are two ways to go, either demand exact
specs from someone who might not have a clear idea yet, or post a
response based on your own carefully judged assumption.

Yeah, what "Lost" said.

Lastly, consider a low power laser diode, UNLENSED. These are eye safe
at distances beyond a few inches, (take care NOT to use a microlensed
version though) as they diverge strongly. Their output is highly
monochromatic, specular, very eye-catching, and their conversion of
electricity to light is second to none, so they can make ideal
beacons.

This sounds interesting, do you have any sources?

Thanks!

[I think the discussion engendered by this particular "How long a
piece of string?" query has been useful and enlightening [sic].]

Agreed. 'Nospam', we do it for us. It amuses, interests... There are
ters questions with terse answers with immensely high SNR for those
involved, but they are often so specific that they offer nothing to anyone
but those who ask and answer. When a few people get to put in ideas threads
get interesting to many at once. Some verge on the inane but I don't care,
I take as I find it, I don't have to read them all.

William, there's laser diodes from roithner-laser.com, intellite.com, and
if you're in the UK, photonic-products.com have some especially nice ones
made by Opnext (Hitachi). Sometimes the most cost effective way is eBay,
seller milasers (Meredith Instruments) was selling boxes of 100 5 mW 635 nm
5.6 mm packaged diodes. They want around 45 to 70 mA to get full output,
but pulsed, these could form excellent small beacons, extremely visible as
the wavelength is a lot shorter than most red LED's. Even unlensed, a
distance of a few feet is wise if you're going to look into them directly.
Lensed to collimate parallel, that should not be done at all. Nice
advantage: collimated, you can project the beacon on a high wall or post
without the expense of wires. Totally weatherproof too, that way.

 

[Palindr☻me]

Nice. Judging by the combination of visceral response to physical action,
and the fact that few people other than the builders of such things can
separate the practical requirements for that kind of machine vision, and
that needed for recording images, that thing should deter criminals both
smart and dumb.

LOL, you might think so. However, around here, all of these fake cameras
are the same make and model and crims can easily identify one and all.

One idea is to take some of these fake cameras and retrofit real camera
modules. The crims will treat them as fakes and operate quite openly in
front of them, rather than try and find somewhere not covered by a camera..

Of course, all you have to do is spread the rumour that this has been
done..and then not bother..

etc..

 

[Clive Mitchell]

Nice. Judging by the combination of visceral response to physical
action, and the fact that few people other than the builders of such
things can separate the practical requirements for that kind of machine
vision, and that needed for recording images, that thing should deter
criminals both smart and dumb.

No. It looks completely fake and will drain the batteries quickly with
it's prolonged motorised sweeping movement.

Although it uses light level movement sensing it does trigger easily. I
got a couple cheap and took 'em to bits. (As I tend to do.)

 

[William P.N. Smith]

William, there's laser diodes from roithner-laser.com, intellite.com

Many thanks!

 

[Jaxx]

Victor Roberts wrote:

On Sun, 02 Jul 2006 15:37:34 +0100, Palindr?me

[snip]


What duty cycle would you use?


It depends on the application

For example:

For a torch with a super bright LED running off a single cell, I
would probably have an adjustable duty cycle from 5 - 50%. That
would give adjustable brightness (and run-time).

For a "walker on road setting", one 10 mSec flash, 3 times a
second. Cyclically varying the repetition rate is more likely to
get it seen.

For a "power on" indicator where power is limited, one 5mSec flash
every 10 secs is a starting point.

That's quite a large duty cycle range. 50% to 0.05% or a
range of 1000. Which do you think the OP was referring to
when he asked about his battery life?

If he had to ask the question posed, I shouldn't imagine that he
knew either.

As OP, I can say there is some truth in that. I want the flash rate to
be one that is noticed but I would have to try it out in real life to
see which rate worked best for me.

What I really wanted to know was whether an NIMH was going to give me
such a short life (say under 4 days) that I would be better using a
mains PSU. This is an outdoor application so a battery setup has quite
a lot of advantages from portability and wider choice of location.

 

[Jaxx]

I'll have a guess at the application.....

They probably wanted to add a flashing LED to a fake camera that
could run for a long time on a battery.

In reality, a short duty cycle blinking LED on a camera immediately
says FAKE!

As OP I can say that's not quite it but it is reasonably close in
principle to what I had in mind.

In fact, the flashing is not for humans to notice though but for
animals. That's why I am vague about the correct flash rate.

 

[Jaxx]

No. It looks completely fake and will drain the batteries quickly
with it's prolonged motorised sweeping movement.

Although it uses light level movement sensing it does trigger
easily. I got a couple cheap and took 'em to bits. (As I tend to
do.)

The price of real cameras seems to be falling so much that a very
basic "starter" real camera is not all that much more expensive than
a dummy.

It's perhaps true that the cheaper sort of real camera look even more
fake than the fake cameras do.

 

[Palindr☻me]

As OP I can say that's not quite it but it is reasonably close in
principle to what I had in mind.

In fact, the flashing is not for humans to notice though but for
animals. That's why I am vague about the correct flash rate.

You might want to consider some CMOS low power internally linked shift
registers, to give a pseudo-random variable flash rate.

It puzzles the heck out of my squirrels, when connected to a motorised
table. They can manage up to 3 bits of this "Simon" memory game,
correctly jumping to the table at the correct time. But not 4 bits.

 

[Jaxx]

I have some ideas...

1. If this is to be used in the home, power the LED from a wall
wart. And maybe power the LED through two steering diodes coming
together - one from the wall wart and the other from a backup
battery.

For that matter, get the cheapest actual security camera you can
find from a hobbyist/surplus catalog - even if it's incompatible
with anything practical.

Or further for that matter, find some little professional looking
case and fit some cheap webcam into it and you have a fake security
camera that may actually be made to work in some way as a real one!
Put a red LED on the case...

2. I have an idea for the red LED - make it glow continuously like
those on real cameras that have LEDs do. Get a GaAlAsP red LED,
peak wavelength 660 nm, 3000 mcd (with a usual beam width of 15
degrees but sometimes claimed more), such as Radio Shack 276-307.
Red LEDs of same/similar chemistry and efficiency are Agilent
HLMP-8103 and HLMP-C124.

Get some fine sandpaper and sand down the tip by about a millimeter
then restore the "bullet" shape but about a millimeter shorter and
with the tip very slightly more blunt, then get some really fine
sandpaper and get the LED good and evenly frosted. After that, you
have a super high efficiency diffused wide angle red LED that works
well and reliably at 1 milliamp, and may be bright enough at half a
milliamp. It will glow with a color close enough to that of lower
efficiency red LEDs.

If you really want to go all out, get an InGaN green LED (nominal
wavelength usually 525 to 530 nm) of the common 5 mm "bullet" style
and give it the sandpaper treatment described above. Then give it
half a milliamp or maybe a quarter of a milliamp. Most Nichia 5 mm
green ones and those trying to compete with them (ETG, and others)
should at half a milliamp have a brightness that I consider "fully
that of a usual green LED indicator light". Furthermore, the
wavelength of these tends to shift a little inversely with current,
and at half a milliamp the color is likely to be about that of LEDs
with nominal wavelength in the 550's nm, maybe close to 560 - a
yellowish shade of green likely to look enough like a usual 565 nm
green LED indicator lamp to look like a usual indicator LED to most
criminals.

A pack of (4) AA alkaline cells with a 6.8K resistor should power
such a green LED reasonably well 24/7 for at least half a year.

If you want an LED to falsely indicate presence of a security
system in an automobile, don't worry about conserving every
milliamp since the battery has self-discharge in the 10's of
milliamps. You can afford a few milliamps to protect a car.

- Don Klipstein ([email protected])

There are some nice hints and tips above which I had not thought of,
Such as filing down LED case to extract more light.