I have a COB LED 50W Lamp Light 12V Circular LED Bulb powered by a 12V battery. I also have a ARDUINO MEGA 2560 (if needed).
I would like to linearly increase the intensity through the COB LED with variable programmable time steps. This is used to simulate the sun rising light from dawn so i can't use PWM technics, just analogical. I can handle the programming but i need some help to figure out the hardware.
Thank you very much
Why is this? Who is going to observe this light?
I do not understand why PWM will not work. It sounds like a plant application, they do not know what PWM is. I would highly using something else, LEDs are current devices not voltage devices. You can get some control with analog but the range will be very narrow.
Hello gzonus
Take some time and describe the desired function of the sketch in simple words and this very simple and short form.
Have a nice day and enjoy coding in C++.
Дайте миру шанс!
It's probably not dimmable without adding/building a dimmable driver circuit (and removing or bypassing the existing driver). 
PWM should work fine. And if just appearing dim or (appearing off) isn't good enough in your application there are some PWM-controlled dimmable LED drivers that put-out continuous-variable DC current. **ALL ** switch-mode power supplies use a kind-of PWM "internally" while putting-out nice-smooth DC.
Since LEDs are "current operated" most high-power LEDs are driven by a switch-mode constant current (or variable controlled-current) power supply.
That's not an easy thing to build yourself but you can find boards/modules as long as you can find one with the correct voltage/current rating. The dimmable modules can usually use PWM but the "industry standard" is 10V PWM (or 0-10VDC) and in that case you need to add a little (low-power) transistor to "boost" the 5V PWM from the Arduino. (The driver itself often provides the 10V.)
With regular little LEDs we just use a resistor to limit/control current but with high power LEDs this is rarely done because the resistor wastes about as much power and generates about as much heat as the LED itself. Or, with "cheap" LED flashlights sometimes they'll rely on the battery's internal resistance. In either of those cases you can simply use a MOSFET Driver Circuit with PWM for dimming.
If you already have a constant-current driver, I've seen a "neat trick" where a MOSFET is used to "short-out" the LED (for part of the PWM cycle). In theory that works because the constant-current supply just keeps happily pumping-out constant current at nearly zero voltage. And (almost) no power is wasted because power requires a combination of voltage and current at the same time. But not all constant-current power supplies are designed for that.
flowers photosynthesis
Sunrise and sunset duration is different relative to latitude and season (axis orientation during orbit). Two and one half minutes for close to the equator to "never" at the pole. You probably know this already...
I see.
Are plants not fooled by PWM like we are? I am not very familiar with plant biology.
Thank you
Are you sure that your bulb provides the correct portions of the spectrum?
Genuinely curious why sunrise would matter to a plant.
I grow loads of fruit and vegetables year-round and I've never simulated sunrise, Does it help? Do you have a link to reference material to that effect?
Sounds like an interesting project.
Hello DVDdoug,
Thank you for very much for your help. I must admit that even if i pretty much understand the theory, it's still a long way to be able to realize what i need. The main reason is that my domain of expertise is biology and my knowledge in electronic is unfortunately insufficient.
A PWM controlled dimmable LED drivers that put-out continuous-variable DC current sounds like what i need because i'm convinced that PWM would not stimulate properly the photosynthesis at low light intensity. To be more specific i study photosynthesis during what is called the blue hour just before the sun rises.
So my question is could you help me a little further by providing more specific infos about such driver and a rough design of the device i need to properly operate my 50W Lamp Light 12V Circular LED Bulb powered by a 12V battery. I will use it only at low amp, i don't need the full brightness of it, only say one fourth of the current will be enough.
I have a small budget for my thesis, i could give you a couple hundred dollars for your time. I know it's not a lot for this kind of expertise.
So thank you DVDdoug for your precious help.
Regards
Cool white light LEDs are a pretty good approximation of the sun spectrum specially in the blue portion of the spectrum which is what i study (the sky is blue before sunrise)
If you have a COB LED, all you need is to buy an appropriate LED driver with PWM dimming input.
For example, if you have this COB LED, and a 12V DC power source, you could use that LED driver, which has a PWM dimming input that you can control from any PWM capable pin of your microcontroller. No other parts needed. It's really that simple.
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