If that's true, it won't deter a thief. Bear with me here, the logic gets
interesting.. >
If it won't deter a thief, it's very important that cameras with flashing
LEDs on them actually contain lenses and working circuits to gather video
evidence of the events that they might seem to encourage. Therefore it
makes sense to always have something real in there, so in practise, you'd
be wrong.
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])