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..
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
It's perhaps true that the cheaper sort of real camera look even more
fake than the fake cameras do.
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.
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.
Did you read the answers? Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?
I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?
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. If the result is confusion and an apparent grasping
at each offered straw in turn, then it is probably wise to demand some kind of
focussed assessment of the original situation. At least this way the OP is not
considered stupid until proven intelligent. :)
My own thoughts on the topic are: you can have a 'super-bright' LED and long
life, but a few things should be managed to do it. Use a lithium battery
preferably, then alkaline, and avoid Nimh types. Use a power converter to
efficiently make use of the entire battery charge. Use a narrow viewing angle
on the LED, so that it projects strongly for only a limited point of view. Use
a clear LED not a coloured plastic. Use a short duty cycle, less than 1% and
pulse length no longer than 50 milliseconds even when the flash period is
longer than 5 seconds, with that period never being longer than 10 seconds
unless you're really going to be staring at that LED for 30 seconds or more
regardless of what it might be doing. These are not hard and fast rules. :)
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. They're much harder to use
though, easily damaged, and initial power requirements are higher. Also, while
you can make an LED stand much higher currents than their nominal rating, often
tenfold increase, with a laser diode, the pulse rating for a CW diode is
usually less than twofold higher.
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
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.
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.
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
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...
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
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...
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