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Chroma Wheeler

Reinventing the wheel on RGB lighting systems just for fun

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Power LEDs, communication, electronics, programming and feeling good. Sometimes only few things are a matter of interest to some geeky people. But it is also known that the color of the environment play a role in feelings - and feeling good. So, gettign the chance to play with high power LEDs, heatsinks, PCBs, protocols and microcontrollers, it's ended up in a RGBW lamp project and it is turn out to be a simple but nice design experience.

This is the first project that let me play with something different than mere fimware and PCBs, but finally a bit of boxes and acrylic planes. It is a multicolor lamp, which is developed 100% from scratch, both firmware and software, for a challenge and for seeing how things can be optimized with standard code and a new concept of power handling. The LEDs are also implemented in a 100% self-developed thermal PCB because there were no other little boards available with a given density in terms of power LEDs per square inch.

I started to build some LED drivers, then a small MCU board with a power path handler, with a built-in safety feature of power priority in made in hardware and other short circuit protections, since it is supposed to deliver more than 10W. With these loads, one need an high energy source and so a bit if protection never hurts. Those boards are Lino and Glighter

At the end, it turns out that I can use those boards together, with additional PCB for connecting the LED and with some thermal handling, to build a first draft of my desk/ambiance lamp. In the log will be present some eventual progress on how things are going.

I will keep the updates in the log as soon as I have more details ready to be published.

  • LED engine history

    Enrico09/10/2017 at 22:14 0 comments

    The issue

    When I started to breadoard the lamp, I was using this PCB, carrying on the LEDs (from now on called LED engine). The one shown in the breadboard was this one:

    Chosen to reach, according to thermal analysis of the LEDs (from datasheet) and the given suggested thermal pad on the PCB, no more than somewhere 70°C at full power.

    Making this in reality shows that my calculations were imperfect: the heatsink could reach almost 75°C and more, showing that this thermal pad


    wasn't probably conceived to be thermally closed within traces as shown in the picture. I say this because was the only variation from the specified layout: even the right amount of copper was used, according to the application engineers. The calculations were simply done in this way:

    Where the case-heatsink term is the thermal resistance given from the LED pad design provided from the application note. But what in the end make me realize that calculations were even more far, is that the LED power were overestimated, because I assumed that all the power is generated in heat, while in reality the LED have a given efficacy (around 30/40%), meaning that the 40% of power is generated in light and not in heat (well.. the heat is light per se, but not useful here). So in reality, it shall be even 40% cooler than it was.

    In the end, I also realized that if such heatsink shall be touched (I want to use those LED at desk height ideally), even 70°C were too much, forcing me to use either a fan (but I am against them were their usefulness is not proven) or a bigger heatsink.

    The monster

    When you get betrayed by a small heatsink, you go big. So I decided to look for some nice heatsinks available, and made a board for them. I came out with the third revision of the LED engine, as big and round as a coin, overcompensated with an heatsink beneath it.


    The big size has also the purpose of being helpful for supporting mechanically the lights somehow. As you can see from the picture below, designing the PCB was quite interesting too:

    The little brothers

    When I was taking a picture of the big one, I have also realized how many attempts I've made in the past. You can see them here one next to each other:

    On the left, the first ever board made was described in detail here. It was a first design trial implementing a linear LED driver, with firsts experiments with OSHPark and SMD soldering. Despite errors and imperfections, each LED was surprisingly cooled.
    Then the second attempt, still with a linear approach, with a different layout was described here and corresponds to the second from the left.
    The third one is the one used up to now and the biggest one is the final revision. Actually, there was a middle version of a bigger heatsink in the second revision of the LED engine, just to get things done, from a previous project:


    After this refreshing (with heatsinks.........) update, I can go forward with the assembly of my lamp, while improving the firmware. Stay tuned!

  • Board first assembly

    Enrico08/15/2017 at 09:16 0 comments

    When I had started the project, I had (and usually have) no idea on how to integrate stuff. So as a natural consequence was to use my already developed LED drivers. But I had in my mind some use cases of this lamp.

    It must be connected to a PC, because I want it to be smart, but it need to deliver more power than a USB can do, so it must work also from a DC power supply - this already triggered the firmware generation in my mind, mind compilation has started.

    This is the board currently used for providing power to one or more series LED:


    And I need 4 of them, because I want my lamp to execute light algorithm with the white too, in order to be an improved RGBW system. That is why I was able to easily use my other board, initially started for general purpose "high power" Arduino equivalent, thought for 4 LED driving system. Here the board, Lino, with no tweaks, still a "vanilla" version:


    And I startede thinking to them. So I had this connections in mind:

    It turns out that I can directly put them on a breadboard when soldering some headers on the boards. So I have also crinched together an encoder recovered from an old car radio. So that I can do some functional tests and start working on the firmware, too. The LEDs that can be seen in the picture are the classic Luxeon Rebel series, soldered on a board, a satellite board. I was able to use a small heatsink which I bought, being sure that was thermally compatible with my calculations. But the satellite history is something that deserves a separate log.

    In the picture above, you can spot that the process of testing the Lino in various operating modes, debug and stresses, added to the board the signs of the mods.

    The overall effect with some basic firmware I have to say it is quite interesting in terms of light and its ambient effect.

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oshpark wrote 08/17/2017 at 08:09 point

Great project!

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