Re: Dimmers and auto-iris lenses

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Ian Shef" <invalid@xxxxxxxxxxxxx> wrote in message
news:Xns98EE7FBA71843vaj4088ianshef@xxxxxxxxxxxxxxxxxx
> "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in
> news:p5CdnZEN4qMCDm3YnZ2dnUVZ_tijnZ2d@xxxxxxx:
>
> > I've got an odd issue monitoring the dog crate for my little bad-eyed
> > Boodle.  I monitor the crate with an auto-iris IR cam and therein lies
> > the problem.  It's very hard to tell remotely whether the light is
> > barely dimmed or dimmed 90% because the autoiris compensates for the
> > dimming.  All you see when you hit the DIM button on the X-10 controller
> > is a slight "flaring" of the image as the light dims and the iris open
> > up.  I thought sharpness might be a cue, but the auto-iris probably
> > isn't an iris in the traditional mechanical sense.  I'm betting it's
> > electronic because as it adjusts there seem to be no corresponding depth
> > of field changes.
> >
> > The camera's got enough resolution to usefully image a 3" dial
> > thermometer in the heated water bath along the side of her crate so I
> > thought I'd get a solar cell and small electrical meter with a dial I
> > could see via the remote cam and a potentiometer to calibrate lo and hi
> > ranges.  That setup would consume no power, but it's probably going to
> > be hard to read.  Any suggestions cheerfully accepted.  In the meantime
> > I'm going to search the junkbox.
> >
> > --
> > Bobby G.
>
> How about an LED (or even a nightlight) that is within the image.  Its own
> brightness is constant, so an open iris (due to dim lights) makes the LED
> look bright.  A closed down iris (due to bright lights) makes the LED look
> dim.
> Dim LED implies bright room lights.
> Bright LED implies dim room lights.
>
> The LED could blink to reduce battery drain if battery powered.  Blinking
> LEDs for decorative purposes can be picked up in many places.  I don't
know
> if there is going to be an interaction between the duration of the blink
> and the scanning period of the video camera.
>
> Could be cheap but consumes more power than your solution.

Thanks, Ian.  I've got a *very* old Lafayette meter calibrated from 1 to
50ma that's just about exactly what I need except the damn needle is too
small to see via the camera!

I hooked it up to a solar panel salvaged from a garden lamp and it responds
to the range of illumination provided by the lamp.  After I read your note I
realized that's almost enough power to light up an LED so it might turn out
that a fusion of our techniques will fill the bill.   I'm going to the LED
junk box right now to see if I can generate enough power to light one.  A
nicer design would be to light up a row of LEDs to correspond to the
lighting level but I'll take a single LED if I can calibrate to fire before
the camera's internal IR LEDs fire because that seems to wake up the dog.

[Time passes]

Great!  I just checked out the panels.  While one didn't do the trick (they
put out about 1.3V each) three of them easily power a flashing red LED

http://www.allelectronics.com/cgi-bin/category/340200/Flashing.html

quite nicely under full output with no power other than the room light.
I've got a whole box of these recycled solar panels got some time back from
Allectronics so ganging them together will make something a little bigger
than I would like, but will allow me to determine when the camera's IR
illuminator is about to come on.  Red LEDs show up VERY nicely when imaged
via IR cameras, so this will work out quite well.

If I can figure out how to vary the flash rate with the illumination levels
that would be even better but the flashing LED's I use have the flashing
circuitry built into the base of the LED and are not adjustable, I believe.
Even without flashing, mounting the LED near the lens will tell me what I
need to know about lighting levels.  It doesn't need to be in sharp focus,
like the meter would, to give me an indication of the light level.

Now to see if there's any way to have three LEDs to indicate dim, medium and
bright conditions.  I'm not sure how to create a circuit that lights
additional LEDs in response to an increase in amperage.  The voltage on the
panels appears to be fairly constant over the range of illumination provided
by a 60W lamp.

Thanks for the input, Ian!  I like the nightlight idea, too, and am going to
try one of the little electroluminescent jobs before I finalize on a
solution.  The amount of electricity used by those panels is negligible and
it could be that it images even better than LEDs will.  It's certainly
easier to implement.

--
Bobby G.