Author Topic: kCube - LED cube design revisited  (Read 10542 times)

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Offline tatus1969Topic starter

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kCube - LED cube design revisited
« on: March 26, 2018, 09:38:40 pm »
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 for your cool 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 above  8)
 
That 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  :)









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Offline mikeselectricstuff

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Re: kCube - LED cube design revisited
« Reply #1 on: March 26, 2018, 10:05:55 pm »
Quote
- (almost) invisible power and signal wiring of 8x8x8 full RGB dimmable LED's
So how exactly is that going to work then ?
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Online ataradov

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Re: kCube - LED cube design revisited
« Reply #2 on: March 26, 2018, 10:15:55 pm »
Yes, if you actually plan to use NeoPixel strips, then you should add them to the model, and see how invisible they actually are.
Alex
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #3 on: March 26, 2018, 10:22:37 pm »
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 :-)
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Online ataradov

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Re: kCube - LED cube design revisited
« Reply #4 on: March 26, 2018, 10:24:24 pm »
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 :-)
Where 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.
Alex
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #5 on: March 26, 2018, 10:32:53 pm »
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 :-)
Where 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.
I 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):



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Online ataradov

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Re: kCube - LED cube design revisited
« Reply #6 on: March 26, 2018, 10:35:42 pm »
That's more effort than I expected. Please update with the results, it would be interesting to see it in action.
Alex
 

Offline mikeselectricstuff

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Re: kCube - LED cube design revisited
« Reply #7 on: March 26, 2018, 10:38:31 pm »
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
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Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #8 on: March 26, 2018, 10:59:41 pm »
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
Each 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 cooled   ;)

Right, i'm also curious how transparent that thing actually will become. But I think the flex PCB part will be good enough, for example:
« Last Edit: March 26, 2018, 11:07:11 pm by tatus1969 »
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Offline MasterT

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Re: kCube - LED cube design revisited
« Reply #9 on: March 26, 2018, 11:11:03 pm »
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
 

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Re: kCube - LED cube design revisited
« Reply #10 on: March 26, 2018, 11:14:15 pm »
Right, i'm also curious how transparent that thing actually will become. But I think the flex PCB part will be good enough, for example:
That look like a 3D render.
Alex
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #11 on: March 26, 2018, 11:25:02 pm »
Right, i'm also curious how transparent that thing actually will become. But I think the flex PCB part will be good enough, for example:
That look like a 3D render.
not necessarily, look at the dirt spots and reflections on the right. But anyway, I'll show you once I have it here.
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Offline firehopper

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Re: kCube - LED cube design revisited
« Reply #12 on: March 27, 2018, 01:04:32 am »
they make ws2812b in led 5mm led form too you know..
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #13 on: March 27, 2018, 08:44:42 am »
they make ws2812b in led 5mm led form too you know..
I 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??)...

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. 
Do you have pictures or videos of your cube? I would be interested.

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.
I 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  ;)
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Offline firehopper

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Re: kCube - LED cube design revisited
« Reply #14 on: March 27, 2018, 12:51:15 pm »
they make ws2812b in led 5mm led form too you know..
I 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??)...

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. 
Do you have pictures or videos of your cube? I would be interested.

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.
I 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  ;)
the apa102 2020 sized ones are clear I think. at least the ones I saw for sale on evilbay seemed to have a clear housing.
 
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Offline MasterT

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Re: kCube - LED cube design revisited
« Reply #15 on: March 27, 2018, 01:16:08 pm »
Do you have pictures or videos of your cube? I would be interested.
No, don't have a video.  On youtube there are similar
It's all about transparency, leds should not  create obstruction. Even spacing in-between leds is important.
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #16 on: March 27, 2018, 01:22:18 pm »
the apa102 2020 sized ones are clear I think. at least the ones I saw for sale on evilbay seemed to have a clear housing.
Thanks, didn't know them yet. They look really good, and they are very small  :-+ :-+
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Offline Kevman

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Re: kCube - LED cube design revisited
« Reply #17 on: March 27, 2018, 04:29:31 pm »
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.

 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #18 on: March 27, 2018, 06:09:20 pm »
have it respond to the sound in the room. People really like it.
Looks great! A mic will also be integrated in my kit.
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Offline cowana

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Re: kCube - LED cube design revisited
« Reply #19 on: March 28, 2018, 08:58:44 am »
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.

« Last Edit: March 28, 2018, 09:02:50 am by cowana »
 

Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #20 on: March 28, 2018, 09:34:23 am »
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?
The 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.
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Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #21 on: March 28, 2018, 10:13:14 am »
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.

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Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #22 on: April 02, 2018, 09:28:24 am »
The first parts arrived, and I am curious of how that will work together  8)

The 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.

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Offline tatus1969Topic starter

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Re: kCube - LED cube design revisited
« Reply #23 on: April 03, 2018, 07:36:45 am »
Just got a picture from the PCB fab, this is a reference picture that shows how my PCBs will look like:
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Online ataradov

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Re: kCube - LED cube design revisited
« Reply #24 on: April 03, 2018, 04:16:01 pm »
Sol there is no cutouts, it is just a continuous sheet of plastic? That will also add up in opacity over 8 layers.
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