dimmer/brighten with timer

[bwells]

One of my hobbies is using motion activated cameras to capture footage of wildlife in the Maine wilderness. I am using a pre-built sensor system that is based on a PIC chip and is triggered via motion/heat detection.  When an animal moves in front of the sensor, it sends a trigger via LANC to an HD camcorder to turn on the camcorder to record for some set length of time (~2 minutes).  The motion card also has an external light port that will turn on a light when the camera turns on (only at night).  This light can be up to 4.2amps. Right now, I am using 5.5amps of light and did this with the use of a relay in the circuit that actually turns on/off the lights.  I plan to switch to LED lights soon, so I will no longer need the relay once I do that.  The light system is 12volts (I did not say that previously).

The animals I am trying to video tape are bear, bobcat, coyote, moose, porcupine, skunk, etc. Many of these critters are startled by a light suddenly coming on.  I have used infrared light in the past, but my new HD camcorder needs full spectrum white light to get sharp color videos at night. 

One trick I have heard about is to use a dimmer circuit so the light will gradually get brighter over a 1-2 minute duration instead of coming on with full-brightness at the beginning.  Animals apparently don’t realize the light has come on when it slowly brightens, and they will then go about their business, oblivious to the fact that a bright light is shining on them.  After doing lots of searching, I discovered I will probably want to use a Pulse Width Modulation circuit.  This is also handy for LED lights too.

I have virtually no experience building electronic circuits. I think that with enough time and reading, I might be able to build the circuit I need to control my lights

I would like to know if someone here could build me the circuit I need. I am willing to pay a reasonable price.  Or with enough instruction, I could do it myself.  I have no idea where to begin.

Here are a few videos I have captured so far with my system:

http://remotecameras.blip.tv/posts/?topic_name=wildlife


Thanks
Bryan
http://www.oakleafs.com

[Rob]

Welcome to the boards.

Have you considered infrared lights?

[bwells]

I have always used infrared light in the past, but the new HD camcorders do not easly support color daytime and infrared night time.  I have to select either night-time only IR, or full color white light night and day.  My older analog Sony camcorders were easy to modify so I could run IR day and night and for those cameras, I used IR at night for the old Sony analog camcorders.  I might be able to figure out a way to modify the new HD camcorder so it could do IR day recording, but that kind of defeats the purpose of going with HD.  I could also go with two camcorders; one for day and one for night.  But that would be an expensive option.

[cadstarsucks]

well i am assuming you are using a 12V battery since you did not say...

12V*4A=50W  if you are lucky enough to get 15Lm/W you have 750Lm

http://www.dealextreme.com/details.dx/sku.8405 puts out 145Lm at 700mA, so about 5 would do it.  make it an even six...3 sets of two in series. 

If you really must you can follow the mundane advice normally given-LM317 current sources.  Then a simple FET in line to do the PWM switching ... accept I am not sure if the LM317s would tolerate it.

[justDIY]

using a buckpuck with a big cap and resistor across the analog dimming control will give you a soft start (fade-in) effect.  not sure you'd be able to stretch it out 2 minutes, but you should get several seconds worth of fade from it.

[cadstarsucks]

With the LM317s if you put a 1K between the output and sense of each, tie together the senses and PWM the set resistor with a cap from the sense to GND it should work.

You would still want the separate FET to turn them off all the way since LM317s will present a continuous 3-5mA from the battery.