Where to find embedded developers for start-up?

I don't know where to find developers, but can you describe your concept in more detail? E.g. I don't see the advantage of a RGB LED, blinking with 25 kHz, compared to a RGB LED, which is driven with a adjustable constant current, for stills or video. But maybe with 25 kHz there are some interesting stroboscope effects.

BTW: You can get some interesting effects with the opposite direction, not illuminating, but when scanning each image for a movie line by line:

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

Hi Varying the current causes a color shift in the LEDs. This is avoided by controlling brightness by PWM. Frequencies 25kHz and above have two main advantages, avoid pickup from audio equipment and even illumination at high shutter speeds.

Cheers, Morten

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Temperature causes chromatic shifts, too, so PWM doesn't help. There are some researches about this topic:

The only solution for no noticable chromatic shifts with RGB LEDs is an optical feedback scheme, but this can be implemented with both concepts.

That's true, but I think the disadvantage would be more electromagnetic interference, because a PWM of 25 kHz requires fast rising and falling times, with lots of high frequency harmoncics, especially if you do this with 100 W or more for some video scene illumination.

So I still don't see the advantage of your concept. And PWM is less efficient than constant current:

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

Well, from the photographers point of view, the concept is pretty revolutionary. The overall point is that a very fast light source controlled by a microcontroller, opens up completely new creative (and technical) possibilities.

I have great results from using PWM to switch the LEDs. Some features needs the light to actually turn on and off very fast. Other times a lower average might work just as well. If we can combine switching with current reduction to improve efficiency, that is great.

This is actually a good example of why more brainpower is needed on the project :-)

Morten

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A few things... Here in c.a.e you will find many people (e.g. myself :) who will be happy to work on such things on a contract project basis. However, through random trawling, you will not find many professional embedded devs interested in putting sweat equity into a business idea that might or might not turn into a cash payout. Of course here and there you may find someone who is particularly interested in this application and willing to invest in it, but that's what it is - an investment (with risk), i.e. a partnership not "joining a startup".

If you already have something close to a viable product, maybe you are better off looking for an investor and then hiring someone who will continue to develop the product according to your original vision, rather than trying to find a partner with better technical skills who will most likely dilute your input into the project.

Well, I think it is really the same as with constant current. But maybe just the concept of adjusting the color is revolutionary for photographers and maybe this is a market niche.

Do you have an example where your 25 kHz switching frequency gives other results for photographers than with constant current? I don't believe it, but maybe you can convince some photographers with buzz words like "digital light" and make some money with it :-)

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

So how is this different from existing LED theater stage lighting and their DMX controllers?

By the way although you can get many color combinations from RGB leds you can't get an infinite number of them. For some colors you still need gels.

Cameras use other protocols to communicate with lights, they are proprietary and different for each manufacturer and a real hassle.

I guess you could say that this light is different from a stage light the same way a truck is different from a sedan. This is a small battery powered light. The optics are intended for photography, control of light properties is done on the unit itself, or from the back of the camera.

Spectral power distribution and fine control over correlated color temperature is more important for photography than it is for stage lighting (I assume :-)). This light understands exposure times and frame rates and is able to modulate parameters during individual frames and over a series of frames. It is like High Speed Sync on, well, speed :-) It can measure and mirror the color temperature of ambient light.

You are right that there are colors that fall outside the color triangle you get by colormixing this or any kind of tripple cromaticity luminaire. Deep violet is probably a good example. I guess this is more of an issue for stage lighting where you may want a very saturated effect color? Photography is 99% about controlling white light and the ability to emit a particular color is icing on the cake.

Morten

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Yea verily. You have to deliver value for value -- if you aren't delivering money, then you'll be delivering ownership. If your development partner feels that a different direction is necessary for success (or to stroke his/her ego) then that's the direction thing's will get pulled.

'course, your hypothetical investor will want to do the same thing. If you're lucky you'll find an investor whose skill set compliments yours (i.e. finance vs. marketing, or technical vs. business -- whatever).

If you get someone who's vision of how a business ought to be run is markedly different from yours, it'll be a nightmare.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

I actually had a specific incubator company in mind when I wrote this, but the name escapes me due to the evening's dose of ~325mL of shiraz. The company in question listens to the business plan, decides whether or not to cut a check, and keeps their hands off the business management.

s I

=A0 =A0 =A0

From a microcontroller point of view it's a trivial piece of software, many have multiple pwm generators built in. The problem I see is the basic application. You cannot "dial in any colour" as you only have three colour sources. You can of course mix them but that does not give you a different colour! just a mixture of three colours.

Controlling the spectral spread of the more or less monochromatic LEDs would in fact be a good idea :-). Three monochromatic light sources (RGB) will not produce an equivalent illumination compared to a true white light source (e.g. a 6000 K black body radiation).

Assuming a reflecting surface with different colour stripes illuminated with truly white light. Only a narrow wavelength band is going to be reflected by each stripe.

Take a look at the human spectral sensitivity for different cells

and notice a strong overlap between the LMS (or RGB) cells. Thus a yellow or blue green reflective stripe is going to give a strong response. Also a monochromatic yellow low pressure sodium lamp is going to be easily visible.

When there are only three RGB monochromatic light sources, the reflected light from the yellow or blue-green stripe will be zero, no matter how much the eye (or camera) spectral channel response will overlap and those stripes are seen as black.

Thus, in order to generate for _illuminations_ purposes white light, you need more than three monochromatic sources. Using more than three different LED colours (and of course LEDs are not truly monochromatic) will help to generate reflective light from "difficult" colour surfaces, so that the overlapping spectral response from the eye or camera can register that colour properly.

It will be not black, because the surface doesn't reflect just a single wavelength and the LED doesn't emit just a single wavelength, but it will be darker. You can measure the ability of a light source of how many refelective wavelengths it can produce with the CRI:

And it is important for photographers.

Yes, this would be a good idea. A good mix of different LED colors could increase the CRI value. Maybe 8 different LEDs from the some 20 different LED types of this chart:

and you could create really any spectrum you want. But I guess a device like this is already invented, but if not, this would be a real novel idea.

And maybe you should add ultraviolet light, because some interesting fluorescent effects can be seen with UV, only:

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

BTW: This one looks slightly different and has an additional curve for the rod cells:

Which one is the right one?

--
Frank Buss, http://www.frank-buss.de
piano and more: http://www.youtube.com/user/frankbuss

Looking at some 1-2 W single colour LEDs and the half power (-3 dB) bandwidth appears to be 25-50 nm or 5-10 % relative bandwidth. Should some other measure of bandwidth (such as -10 dB bandwidth) be used for bandwidth comparison ?

How the reflectivity coefficient of a specific pigments drops around the dominant wavelength will determine the colour saturation of the reflected light.

When a white (0 % saturation) car and a pure yellow car (100 % saturation) is illuminated during the night with a monochromatic yellow 589 nm light from a low pressure sodium lamp, both will appear as "bright".

Pure (100 % saturated) blue, green or red cars would appear as black, (or at least non-yellow :-), while a pink (low saturation red) car would look grayish or brownish.

If the light source does not contain photons with a specific energy (wavelength), neither does the reflected light contain those photons, thus neither the eye nor the camera can convert those non-exiting photons to electrons to be sensed :-).

The LPS example is of course an extreme case, but it shows what happens with a peaky light source spectrum.

Re the various posts about RGB color mixing.

Colors are additive when it comes to light, so you can indeed produce "any" color by mixing the 3 primary colors.

RGB follows the entire work flow: Our eyes are trichromatic, with red, green and blue sensitive cones. The screen you are looking at uses RGB pixels, the camera sensor uses RGB filters to record the image. Illuminating with a RGB light source fits nicely into this scenario.

That being said, every part of this system has its own color reproduction capability. The color space is determined by the cromaticity coordinates of the red, green and blue emitter. The weakest link will determine the result.

Of course, photography is usually about more that one color, that is why white light is used for illumination. There need to be energy present at all wavelengths to reproduce all colors hence the need for a broadspectrum light. If the red, blue and green emitters have a narrow spectral bandwidth, you will have 'holes' in the spectrum. I'm investigating an additional amber or white emitter to the RGBs. Right now it actually looks like the white one gives the best results. The problem is that whit is slow, but that is another story.

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The problem with the whole approach is that LEDs are small-bandwidth monochromatic primaries. You can mix light from them that'll appear white to the human eye, but that doesn't mean that it'll illuminate coloured objects the same way that actual, full-sprectrum white light would. In other words, it's probably useless for general ghotography.

Only as far as image synthesis and manipulation on computers is concerned. It stops as soon as the image leaves the computing domain. Printers don't use RGB, pigments of actual object in your everyday environment don't use RGB, and the eye doesn't actually use RGB, either.

Close, but not close enough. It's really red and two different greens, with a funny side effect in the violet end of the spectrum for the green one.

... and one might wish those to be the same R, G and B in all of those. Alas, the world refuses to be that simple.

And that's before we start considering that some people might actually still be using analog film. Or they might want to output those photos on something else than a computer monitor.

Let's face it: for quite a while being, the best source for natural white light is still going to be a piece of material heated to several thousand Kelvins.

It will be hard to create a spectrum with LED's anywhere near as smooth as produced by incandescent light sources. By their very nature LED's peak at a certain wavelength and emit very little light beyond that.

Most white LED's have significant gaps in their spectrum as well, not surprisingly considering a white LED is often just a blue LED with some yellow phosphor so it appears 'white' to the human eye.