How long bright flashing LED last on AA cells?

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.

In message , Don Klipstein writes

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.

remarkably well, it senses motion and scans while flashing a light.

Thank you for your input.

Yeah, what "Lost" said.

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].]

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

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...

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

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...

William P.N. Smith wrote in news: snipped-for-privacy@4ax.com:

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.

William P.N. Smith wrote in news: snipped-for-privacy@4ax.com:

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.

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..

In message , Lostgallifreyan writes

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.)

Many thanks!

I have an electric lawn mower, and I changed its capacitor last week, 10 uF,

400V.Lasted exactly 10 years,manufacturing date 5/1995(the capacitor, the mower is still working after the change).

Can I borrow it? Or do you want a swap for a petrol 2 stroke one that needs two people to start?

;)

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.

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.

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.