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film grade controller for rgbww leds

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Syntax Error:
Thanks for posting those images.  :-+

I assume that you're just using the CCD and have no in between mechanical shutter?

Certainly some aliasing going on with the digital shutter speed and the lights. The Yeelight looks reminiscent of the way aircraft propellers look bent because they are sweeping across a progressive scanned CCD.

Out of curiosity, what happens to the patterns if you turn the camera on it's side, so the scanning at 90 degrees?

Really though, the only way to nail this is to see the RGBWW data timings on an oscilloscope.

Very nice camera btw  8)

vns:
There is a mechanical shutter, and it used for pictures, but obviously not for video.

The images at 90 degress show the same pattern.

Yeah, it would be nice to see a disasembly of one of the yeelight bulbs and see what's going on with a scope but I don't have one.

tooki:

--- Quote from: vns on June 22, 2020, 05:58:09 am ---Hi,

I want to design/implement a controller for rgbww leds to use in film/photography illumination.

It has to be flicker and banding free, and also it cannot emit any sound in the audible range, which means that leds need to be controlled with pwm above 20khz, my plan is to use 25khz.

All leds will be emitting the same color.

rgbww leds integrate 5 different leds, red, green, blue, and two white leds with different color temperatures, to create different colors and intensities I need 5 pwm pins with different duty cycles running at 25khz, I need enough precision to have a good color spectrum coverage while I am able to dimm intensity, I am not sure how many bits I need, but probably no less than 12, maybe 16.

I will use wifi to control the color/intensity.

These are the leds I will be using: https://a.aliexpress.com/_BO6lwY

the question is, how do I get 5 pwm pins at high frequencies with enough resolution?

Mi initial idea was to use a eps12 or esp8266 module with a pca9685 or pca9635,  but the first one doesn’t provide enough frequency and the second one lacks the precision.

PWM dithering to increase resolution could be an option, but I don’t know what hardware I can use...

This is something I am doing as a hobbyist, so my resources are limited. There are out there illumination products providing what I want, but I really want to learn how to do this.

Thanks in advance.

--- End quote ---
If you decide not to use a commercial controller chip, then I’d recommend using this dimmer circuit: https://www.electro-tech-online.com/articles/simple-pwm-circuit-for-lamp-dimming-etc-improves-on-555-pwm-circuits.797/

I built one using a 20KHz PWM frequency, which I use to dim my under-desk lighting. (The page says frequencies of 100KHz should be doable.) It supports far better low-end dimming than any 555 based circuit I’ve tried, and it doesn’t flicker. To control it from an MCU, you need to generate a control voltage, which you can do with a DAC, or by using the slow PWM from the MCU and filtering it through an LC filter.

fcb:
You'll need to go at something like 200KHz to 500KHz to eliminate all the shutter issues.  If you need finer control at higher frequencies (to blend colours) then probably some sort of dithering scheme might help, only watch for artifacts caused by a predicatable jitter sequence, you might need to add a pseudo random element to this.

Could you use DC constant-current control and then correct the mix for the change in colour temperature at lower currents?

Syntax Error:
There are a few teardowns for those yeelights, because hackers love wifi IoT stuff. Unsurprisingly, inside it's an Arm microcontroller doing all of the color mixing/muxing.  So not a practical option for practcals :(

As @Tooki suggests, your going to need a very fast PWM with dithering, or a constant-current DC, which makes color matching a real pain. Pehaps a super simple solution; a bank of variable resistors per channel and a DC supply?

btw I've been looking at other led video lighting, and I have found nowhere that gives a clue on operating frequencies on their lights!

Fyi: FadeCandy
https://github.com/scanlime/fadecandy/blob/master/README.md

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