kCube - LED cube design revisited

[tatus1969]

No, this is just a reference picture from a different project, which they sent me to show how transparent the material is. The substrate is actually PET, which I find funny. I hope that they are not making the PCBs from old Coca Cola bottles? 

This means to me that I'll have to use low-temp solder, which I was expecting anyway. This way I'll do the LEDs a favor as well. A reel of the with 600pcs just arrived today.

[tatus1969]

Here is a first picture of my PET flex boards that I just got from the manufacturer 

[perkinsb1024]

Very neat, I can't wait to see it assembled! Can you say which manufacturer you're using for the flex PCBs?

[tatus1969]

I ordered them from wonderfulpcb.com: 10 sets for USD150.

[tatus1969]

Got caught by Chinese counterfeit fraud, even though I took a sample from the reel and made a genuine check (the window must be made from silicone, fakes are mostly glass). What the seller did was taking 150 genuine parts from one reel, and then adding another 450 counterfeit parts attached with tape. If someone would have feeded that into a pick&place machine, then he would'nt probably even notice.

The most facepalming moment tough was the reply from the vendor (Shenzhen Shijibaike Electronics Co., Ltd.), after my feedback that I had received partly counterfeit parts in a clear act of fraud, and telling them that they do not work (they do electrically, but they do not match in color, nor brightness, nor appearance):
[...] We understand but how does it not work? there is no reaction at all? We have sent those parts to many different clients last month mostly the same time as per your order. But the other feedback is good. We agree to send you another new 450pcs original part [...]

They don't even seem to realize that they are admitting having done this kind of fraud many times, nor that this is a fraud anyway.

I'm not complaining because I was expecting this in one or the other way anyway, just what astonishes me is the inventiveness that they develop in winding up their customers.

Anyway, I will have to wait for more parts now before I can continue. The genuine parts were good to populate two boards, and this is how it looks like. When being submersed in clycerine (board is covered with Plastik 70 spray), the effect is even better than I had expected. There fluid creates a glow around each light, which looks great. The last picture cannot fully reproduce this. The flex PCB and copper traces are visible when the light is turned off, but that disappears almost completely as soon as they turn on.

The signal and power supply integrities are spot on. With good stabilization at the connector, the voltage ripple is less than 200mV (peak) at full brightness. I can definitely recommend this topology. The board's continuous current limit is 1.2A in free air (hottest spot is the main power trace at 60°C). The indivdual legs can be made even thinner, 0.1mm will work equally well (now 0.2mm). This corresponds to an intensity level of 200/200/200 (R/G/B).

[tatus1969]

I haven't found much time to work on this recently, but I managed to make a few steps nevertheless. One of them was deciding to change the transparent flex PCB construction. The first design required to glue all flex PCBs onto acrylic base plates. It is almost impossible to do that without having bubbles inbetween. The next design will use a completely different approach. You can see this in the below picture.

I also used this opportunity to change to APA102-2020 LEDs, because they are much smaller and will drastically reduce the amount of obsticles in the light paths. Populated sample flex PCBs are ordered and should arrive in a few weeks.

[tatus1969]

I just got this picture from my PCB assembly service 

[firehopper]

looks nice! cant wait to see the finished project, take a video too!

[tatus1969]

thanks, I'll definitely make a YT video as soon as possible. This projec is running in my spare time between customer projects, but I'm on it :-)

[firehopper]

wonder how much a finished project would cost, I dont have the skills to make something like this.

[tatus1969]

The most expensive parts will be the 512 LEDs which alone will cost me USD86. These are original brand APA parts sourced locally in China. There may be cheaper sources but I don't want to risk getting counterfeit parts. I'm not close yet to being able to calculate a kit price, but I target something in the order of 150 to 200€. Edit: forgot to mention, I am going to sell kits for self assembly. No soldering or machining involved, but for this kit glueing and working with fluid (glycerine).

[tatus1969]

it took me quite a few redesigns of the mechanical support framework for the flex PCBs in place, but it finally works now. A lot of thought had to go into finding a solution that would be as easy to assemble as possible, without the need of glue. This is how that looks like at the moment. I haven't lit up the new boards yet, but MultiCB is already making adapter boards. I'll be able to show the completed cube soon :-)

[Ysjoelfir]

Sorry for digging up this old thread, but I am really curious how your project turned out. Did you go on with the project?

[tatus1969]

Sorry for digging up this old thread, but I am really curious how your project turned out. Did you go on with the project?

I have the almost-finished prototype sitting here on a shelf, because I wasn't happy with two aspects. The one is that the refraction indices between PET (PCB material) and glycerine don't differ much on the paper, but the difference is still visible quite clearly (photo). That's likely unavoidable because that was the best combination that I could find. The bigger problem is that the sealing concept didn't work out. My plan was to glue the 8 flex cables together, and then put glue into the cutout where they exit. This didn't work and I have to rethink. But the main "problem" is that the business that I had started in 2017 goes so well that I have virtually no time to drive smaller side projects like this. However that doesn't mean that I want to cancel this project :-)