kCube - LED cube design revisited - Page 1
Forum section: electronics / projects

author: tatus1969
author_rank: Super Contributor
timestamp: March 26, 2018, 09:38:40 pm
content: Long time ago, I wanted to make my own LED cube - mainly because I had an interesting idea of what to show on them. Sadly, I never started building it because of the huge amount of work that comes with soldering hundreds of LEDs together, bending each leg such that it can connect with the next, then adding even more wires to be able to create a multiplexing grid. Plus tons of logic, power switches and current sources to drive them all. And I wasn't even daring to dream of full color RGB...Then came Worldsemi and made LED's smart.I just started experimenting with some NeoPixel rings, when suddenly my old idea came back into my mind. But I didn't want to design yet another LED cube. My goals are:- (almost) invisible power and signal wiring of 8x8x8 full RGB dimmable LED's- easy to assemble (I estimate 2-4 hours - no soldering needed)- lowest possible cost (full kit will proably around 150 .. 200€)- open source hardware and software foryourcool ideas (STM32 based, Bluetooth, USB?)- ability to immerse the LED arrangement in de-ionized water to reduce refractions of inner transparent structures- plus some new features that are related to my untold idea aboveThat was two days ago, and the overall construction is finished and ordered. I have some first rendered pictures (can't wait how that will look in reality) and am eager to read your comments

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 26, 2018, 10:05:55 pm
content: QuoteSo how exactly is that going to work then ?

author: ataradov
author_rank: Super Contributor
timestamp: March 26, 2018, 10:15:55 pm
content: Yes, if you actually plan to use NeoPixel strips, then you should add them to the model, and see how invisible they actually are.

author: tatus1969
author_rank: Super Contributor
timestamp: March 26, 2018, 10:22:37 pm
content: the layers will be made from transparent flex circuit board material, with WS2812B chips and some passives soldered directly onto them. NeoPixel strips are of course not suitable :-)

author: ataradov
author_rank: Super Contributor
timestamp: March 26, 2018, 10:24:24 pm
content: Quote from: tatus1969 on March 26, 2018, 10:22:37 pmWhere are you going to manufacture that transparent flex? Also, how is no soldering needed? You plan to order PCBA as well? That can get pricey for a one-off.

author: tatus1969
author_rank: Super Contributor
timestamp: March 26, 2018, 10:32:53 pm
content: Quote from: ataradov on March 26, 2018, 10:24:24 pmI don't plan to let this end as a one-off, my idea is to turn this into a pre-assembled kit for others to build. The flex boards are already ordered, I pay USD150 for 10 copies. One LED cube needs four of these boards. This is how one LED layer looks like (I made green stop layer to show the board traces):

author: ataradov
author_rank: Super Contributor
timestamp: March 26, 2018, 10:35:42 pm
content: That's more effort than I expected. Please update with the results, it would be interesting to see it in action.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 26, 2018, 10:38:31 pm
content: I think you have somewhat optimistic expectations of the transparency of the PCB, and of the copper needed to carry sufficient current without too much voltage drop

author: tatus1969
author_rank: Super Contributor
timestamp: March 26, 2018, 10:59:41 pm
content: Quote from: mikeselectricstuff on March 26, 2018, 10:38:31 pmEach invidual leg has 0.2mm power traces carrying 0.4A when fully on. The FPC cable for one plane has 0.8mm traces for 3.2A. The full cube would draw 25.6A at full on, which makes it obvious that this is not a realistic scenario. The microcontroller firmware will need power limiting feature by globally scaling down the commanded brightness when a certain power limit is reached. And remember, the circuit is water cooledRight, i'm also curious how transparent that thing actually will become. But I think the flex PCB part will be good enough, for example:

author: MasterT
author_rank: Frequent Contributor
timestamp: March 26, 2018, 11:11:03 pm
content: I made 8x8x8 led cube, and created a software. It was not clear to me in the beginning, what exactly I want to see, just need something for Christmas. Tweaking light show I realized, why led cube so magnificent, because you can walk around it and have 360 degree view from all sides. Common crystal clear led is lighting in all direction, even from the back side, so less efficient. It's like a holography, fully 3D. And here is your mistake, the best you can get from ws2812 is about 120-130 degree. Flat image, white plastic cases would ruin all perfection whenever you slightly move your head. Sorry for disappointing.https://e-radionica.com/productdata/RGB5050LED.pdf

author: ataradov
author_rank: Super Contributor
timestamp: March 26, 2018, 11:14:15 pm
content: Quote from: tatus1969 on March 26, 2018, 10:59:41 pmThat look like a 3D render.

author: tatus1969
author_rank: Super Contributor
timestamp: March 26, 2018, 11:25:02 pm
content: Quote from: ataradov on March 26, 2018, 11:14:15 pmnot necessarily, look at the dirt spots and reflections on the right. But anyway, I'll show you once I have it here.

author: firehopper
author_rank: Frequent Contributor
timestamp: March 27, 2018, 01:04:32 am
content: they make ws2812b in led 5mm led form too you know..

author: tatus1969
author_rank: Super Contributor
timestamp: March 27, 2018, 08:44:42 am
content: Quote from: firehopper on March 27, 2018, 01:04:32 amI was considering them, and would have wanted them for their "non-directivity", but that would have ruined my no-soldering-DIY and cost-effectiveness goals. And it would have been a PITA to solder them to FPC (maybe bent wires??)...Quote from: MasterT on March 26, 2018, 11:11:03 pmDo you have pictures or videos of your cube? I would be interested.Quote from: MasterT on March 26, 2018, 11:11:03 pmI have them here and visually tested their directivity. Their inner supporting frame reflects quite some light, which makes them usable for almost 180 degrees (half sphere). I say usable, because the intensity at large angles is limited of course. This is the reason why I placed them horizontally. A vertical orientation facing to the viewer would have ruined that 360 degree walk-around impression. I'm dreaming of asking Worldsemi to make a variant with clear housing, in a far far future

author: firehopper
author_rank: Frequent Contributor
timestamp: March 27, 2018, 12:51:15 pm
content: Quote from: tatus1969 on March 27, 2018, 08:44:42 amthe apa102 2020 sized ones are clear I think. at least the ones I saw for sale on evilbay seemed to have a clear housing.

author: MasterT
author_rank: Frequent Contributor
timestamp: March 27, 2018, 01:16:08 pm
content: Quote from: tatus1969 on March 27, 2018, 08:44:42 amNo, don't have a video. On youtube there are similarIt's all about transparency, leds should not create obstruction. Even spacing in-between leds is important.

author: tatus1969
author_rank: Super Contributor
timestamp: March 27, 2018, 01:22:18 pm
content: Quote from: firehopper on March 27, 2018, 12:51:15 pmThanks, didn't know them yet. They look really good, and they are very small

author: Kevman
author_rank: Regular Contributor
timestamp: March 27, 2018, 04:29:31 pm
content: I built an 8x8x8 LED cube a number of years ago, before the kits were available. I take it to demoparties and have it respond to the sound in the room. People really like it.This is mine:I think that unless you can see the light well when looking at it straight on it won't look very good, but that should be fixable.

author: tatus1969
author_rank: Super Contributor
timestamp: March 27, 2018, 06:09:20 pm
content: Quote from: Kevman on March 27, 2018, 04:29:31 pmLooks great! A mic will also be integrated in my kit.

author: cowana
author_rank: Frequent Contributor
timestamp: March 28, 2018, 08:58:44 am
content: It's hard to see in your 3D model of the flexi PCB design - are the 100nF decoupling capacitors mounted on the underside beneath each LED?Every commercial LED strip you can buy with WS2812B LEDs includes one capacitor per LED - without that the latched data stored in each LED can easily become corrupted due to the PWM noise on the supply rails, and you get flickering of random colours. This becomes more of an issue the further you get from the power supply, as the impedance of the long traces along the strip starts to add up.

author: tatus1969
author_rank: Super Contributor
timestamp: March 28, 2018, 09:34:23 am
content: Quote from: cowana on March 28, 2018, 08:58:44 amThe flex PCB is single sided to reduce cost, and there is only one 1uF capacitor at the end of each leg. The WS2812B chips have an internal constant current source delivering roughly 30-50mA, which is then PWMed. The second LED on the leg is the most critical. As there are 8 on each leg, the second supply trace (0.2mm wide, 13.6mm long) will see a voltage ripple of ( 7*50e-3 ) * ( 0.0171 * 13.6e-3 / 0.2 / 0.035 ) = 0.01V. The trace inductance will add more switching noise, but my first tests didn't show any problems.

author: tatus1969
author_rank: Super Contributor
timestamp: March 28, 2018, 10:13:14 am
content: Now I got worried over my own explanations, and did another experiment. I removed *all* capacitors from this 24-LED ring. And it still worked flawless (!) I measured 1.5V switching spikes at the last LED, which coincides with 0.3*VDD and suggests that the system is probably just about to fail. Adding one single 1uF MLCC at the first LED reduced the spikes to ~ 250mV.

author: tatus1969
author_rank: Super Contributor
timestamp: April 02, 2018, 09:28:24 am
content: The first parts arrived, and I am curious of how that will work togetherThe flex PCBs are also being manufactured, and I have got an interesting information. The base material will be PET, which is great because it surely is transparent, and its refraction index (1.585) almost matches that of acrylic glass (1.49). The PCB tracks will be immersion silver coated.

author: tatus1969
author_rank: Super Contributor
timestamp: April 03, 2018, 07:36:45 am
content: Just got a picture from the PCB fab, this is a reference picture that shows how my PCBs will look like:

author: ataradov
author_rank: Super Contributor
timestamp: April 03, 2018, 04:16:01 pm
content: Sol there is no cutouts, it is just a continuous sheet of plastic? That will also add up in opacity over 8 layers.

author: tatus1969
author_rank: Super Contributor
timestamp: April 03, 2018, 04:32:46 pm
content: 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.

author: tatus1969
author_rank: Super Contributor
timestamp: April 12, 2018, 08:38:37 am
content: Here is a first picture of my PET flex boards that I just got from the manufacturer

author: perkinsb1024
author_rank: Newbie
timestamp: April 13, 2018, 11:30:58 pm
content: Very neat, I can't wait to see it assembled! Can you say which manufacturer you're using for the flex PCBs?

author: tatus1969
author_rank: Super Contributor
timestamp: April 14, 2018, 01:09:50 pm
content: I ordered them from wonderfulpcb.com: 10 sets for USD150.

author: tatus1969
author_rank: Super Contributor
timestamp: April 19, 2018, 08:09:59 am
content: 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).

author: tatus1969
author_rank: Super Contributor
timestamp: May 29, 2018, 07:34:12 am
content: 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.

author: tatus1969
author_rank: Super Contributor
timestamp: June 14, 2018, 02:22:52 pm
content: I just got this picture from my PCB assembly service

author: firehopper
author_rank: Frequent Contributor
timestamp: June 15, 2018, 02:35:31 am
content: looks nice! cant wait to see the finished project, take a video too!

author: tatus1969
author_rank: Super Contributor
timestamp: June 15, 2018, 09:46:57 am
content: 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 :-)

author: firehopper
author_rank: Frequent Contributor
timestamp: June 15, 2018, 11:41:12 am
content: wonder how much a finished project would cost, I dont have the skills to make something like this.

author: tatus1969
author_rank: Super Contributor
timestamp: June 15, 2018, 12:08:57 pm
content: 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).

author: tatus1969
author_rank: Super Contributor
timestamp: July 17, 2018, 10:27:50 am
content: 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 :-)

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: July 01, 2019, 09:01:27 am
content: Sorry for digging up this old thread, but I am really curious how your project turned out. Did you go on with the project?

author: tatus1969
author_rank: Super Contributor
timestamp: July 02, 2019, 09:33:23 am
content: Quote from: Ysjoelfir on July 01, 2019, 09:01:27 amI 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 :-)