Idea: Smart LED front door light with PIR detector and light sensor

Hello to all.

I searched the forums for the project I plan to do, but found no real answer.

Here is the idea:

I want to have a front door light using CREE high power LEDs that would:
- stay off during the day
- turn on at 10% current level when night falls
- ramp up the current gradually to 100% current when a movement is detected, stay at 100% for a preselected amount of time, then return back to 10%.

This would make a very efficient front door light.

I have some experience making headlamps using buckpucks and power LEDs (thanks to dan from this site), but I have no idea on how to make the "gradually changing" current driver for that project. I guess it would involve a microcontroller of some sort.

Has anyone some insights on this ?

Thanks for reading,

Mike, Switzerland

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If the buck-puck has an enable line, try modulating that with a PWM signal. You'd probably make THAt simplest with a microcontroller, but you might be able to do it with analogue electronics too, though not as easily.

4fontaines (author)  steveastrouk6 years ago
Thank you for your answer. Yes, the buck-puck has an enable line (the one I use to use can be modulated from 10% to 100% current by varying the resistance between to pins).
I'll need to get more info in those PWM and such. I'm not very familiar with the terminology, and although I can comprehend rudimentary electronic circuits, I think my comprehension sort of ends when other components than transistors, resistors and capacitors are used :-)
TRY putting a MOSFET transistor on the pair of wires that you can dim with. Set it up so a small potentiometer can vary the base drive to the transistor and see what happens....

If you then arrange it so your PIR switches on, and charges a capacitor attached between the base and ground, you should get a slow turn on effect.
*thats what I was on about with an adjustable driver...leave it to steve to have the obvious answer :D
frollard6 years ago
You could use an existing 'variable constant current driver' with a simple detection circuit, couple that with an ambient light sensor and you have the basics of your design. Microcontroller would help, but might not be necessary depending on how much you learn your analog circuits.
. Owww! Variable constants make my head hurt. :)
They get you every time. I should say "adjustable constant current driver"
. My guess is that neither is more correct - they both yield over a million hits. I just thought variable constant was kinda funny. Adjustable constant looks almost as funny.
4fontaines (author)  frollard6 years ago
Thank you for your input. As I said, I'm no pro, but willing to learn... I'll google some info on such an analog 'variable constant current driver'...