Sourcing 5mm RGB LEDs for LED Cube - Page 1
Forum section: electronics / projects

author: Oleenick
author_rank: Contributor
timestamp: December 23, 2019, 09:28:37 am
content: Hello EEVblog forum!I'm working on an 8 x 8 x 8 LED Cube. I'm at the stage where I need to order ~600 5mm RGB LEDs. Specifically, 5mm RGB common anode diffused lens LEDs.My main question for today is: How should I source these? Here are my thoughts so far...I was considering buying from somewhere like LCSC:TOGIALEDhttps://lcsc.com/product-detail/Others_TOGIALED-TJ-L5FYTXHMCYLCRGB-A5_C331057.htmlAUD$57.35for 600<---This one is my current best pickMEIHUAhttps://lcsc.com/product-detail/Light-Emitting-Diodes-LED_MEIHUA-MHLA5319URGBDWT_C417349.htmlAUD$123.85for 600I can get some for great prices on ebay here:https://www.ebay.com.au/itm/1000pcs-5mm-RGB-LED-Common-anode-Tri-Color-Emitting-Diodes-Diffused/2914984581961000 forAUD$46.52Trouble is, I don't know whether to trust the brightness of any of the afformentioned LEDs.The specs of the TOGIALED one from LCSC state that the avg. brightness isR: 400,G: 1500,B: 300 mcd. (@20mA)While the MEIHUA also from LCSC has an avg. brightness ofR: 600,G: 1500,B: 300 mcd. (@20mA)The ebay one doesn't give a brightness, only a part number (F51BW9RGB-C) for which I can't find a brightness elesewhere online.Just the brightness is throwing me off. The high variation in mcd for each colour is strange. Is it because they're using percieved brightness values, where green is more predominant due to the human eye?Even larger brands like Kingbright have LEDs with high variations between colour brightness:https://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KCRound+Tri%2DColor&Page=1So... Should I be worried about these brightness differences or is there something else I don't know?What are your experiences with ordering LEDs in bulk from eBay or other places like element14?Thanks in advance, I really appreciate any help.

author: ataradov
author_rank: Super Contributor
timestamp: December 23, 2019, 11:06:16 pm
content: Why not order a few samples, test them and then decide if they will work for your application?It is really hard to order LEDs just based on their parameters.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 23, 2019, 11:29:15 pm
content: 5mm is pretty big for an LED, maybe it's the size you want for your design, but 3mm will probably offer much better prices and pretty comparable brightness.The output difference is the inherent difference in output efficiency, and one way or another, your driver circuit will have to compensate for it. This is going to be true for basically every LED or set of LEDs unless you have wildly different packages or current limits for each, so the approach is probably just to do your RGB value to actual PWM value as a mapping table or function in software to get things closer to what you'd expect from something rendering true color. That also means the difference between your lowest output to your highest output divided by your pwm step size is the effective resolution of the output - so wider variation in intensity of the diodes means fewer of your pwm step distinctions are usable because the lowest intensity LED will need several steps to match the brightness of a single step of a brighter one.Then you've got the issue of human eye color sensing, and honestly I'm not sure how mcd or candela in general is specified for that, since it's supposedly a reference to a green monochromatic source, the datasheet values may actually need to be scaled somewhat to figure out what it would "look like" rather than what it measures on a test apparatus, but I don't know the standard test setup well enough to say how.

author: tooki
author_rank: Super Contributor
timestamp: December 25, 2019, 08:54:28 am
content: 3mm (T1) and 5mm (T1¾) are the most common THT LED sizes, making them both exceedingly cheap. No idea why you think 5mm is “pretty big”, nor why it’d be “much” cheaper. It’s also hands-down the standard LED size used for LED cube builds.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: December 25, 2019, 12:05:35 pm
content: Ebay 8 dollar per 100.Mouser 80 dollar per 100.

author: Oleenick
author_rank: Contributor
timestamp: December 26, 2019, 10:00:30 am
content: Thanks for all of your feedback, it's been a great help.I'll go with ebay but I can't decide between these two.1.https://www.ebay.com.au/itm/1000pcs-5mm-RGB-LED-Common-anode-Tri-Color-Emitting-Diodes-Diffused/2914984581962.https://www.ebay.com.au/itm/1000pcs-5mm-4-Pin-Tri-Color-RGB-Diffused-Common-Anode-Red-Green-Blue-LED-Leds/221175446363Both are good prices, 1 does not give brightness information while 2 does.I'm not sure to believe any brightness claim even if its present. In the case of not believing brightness values, even if they are present, I think I'll go with 1 as its much cheaper.Reply if you think I should do otherwise. If not, I think I've found my solution.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 26, 2019, 10:23:52 am
content: Yes, cd or lm numbers for green LEDs are higher even if the LEDs happened to be of same power efficiency (% of converted into energy of photons), because cd, lm units exist to describe perceived brightness as per human eye's sensitivity curve.If you want neutral white out of an RGB LED, or similar-looking red, green and blue indications, you need to tune the currents. If you have full digital brightness control, then this is easy with software. If you don't, play around with one of the LEDs first to find best series resistor values per color before assembling all 600...Random Ebay LEDs are high-risk items: they may be OK, but they may have high failure rate, which would be definitely a problem at qty 600, and not verifiable by sampling a few.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: December 26, 2019, 02:05:43 pm
content: Big chance they all the same.

author: Oleenick
author_rank: Contributor
timestamp: December 27, 2019, 11:52:16 pm
content: QuoteThank you thats a good clarification. I'd be testing them all before I used any of them to check brightness against a standard. But do you mean a high failure rate in that they will fail quickly or that they will be dead on arrival? Since I'm ordering 1000 and I only need 512, that should help.I'll be running them at constant current as well so I can tune the current to match colour channels if needed.

author: james_s
author_rank: Super Contributor
timestamp: December 28, 2019, 01:22:20 am
content: Forget the specs, just buy a small quantity of any type you are considering and test them out, specs will only tell you so much, you have to see them with your own eyes. LEDs are cheap and you can always build something else with the samples.

author: djacobow
author_rank: Super Contributor
timestamp: December 28, 2019, 04:39:23 am
content: Quote from: Jan Audio on December 26, 2019, 02:05:43 pmThis. But regardless, LCSC is legit and the LEDs will arrive packaged properly and they won't be floor sweepings. Can't say the same for eBay and AliExpress.And you just don't want to buy LEDs from legit US distributors. The pricing is not acceptable for "LED heavy" designs.

author: mariush
author_rank: Super Contributor
timestamp: December 28, 2019, 05:19:25 am
content: You should consider surface mount leds.Here's a couple examples:1206https://www.tme.eu/gb/details/rf-w2s155ts-a41/smd-colour-leds/refond/1204https://www.tme.eu/gb/details/rf-w2s118ts-a41/smd-colour-leds/refond/The first one has something like 1mm or 1.27mm spacing between the half-holes , the 2nd one is even narrower ... both could be usedYou could custom make a circuit board for each "level" in the cube to hold the 64 leds of that level (have traces on both top and bottom of pcb to make the lengths of pcb thinThe first led could also be soldered onto a pcb that has through holes you could just have a bit of copper wire come out the pcb and you'd place the led and just put a drop of solder to connect the wire to the led.

author: tooki
author_rank: Super Contributor
timestamp: December 28, 2019, 11:33:09 am
content: Quote from: Oleenick on December 27, 2019, 11:52:16 pmIn the case of an LED cube, the concern isn’t DOA LEDs, but rather the longevity. Since replacing an LED in a cube is extremely difficult, you don’t want to risk LEDs that don’t last long. So I’d avoid random eBay sellers, and use LCSC, or at minimum the eBay/Ali store of an LED vendor that’s been around a while.Quote from: mariush on December 28, 2019, 05:19:25 amThat makes no sense. Using PCBs blocks the view. Additionally, for an LED cube, you want a diffused LED body to blend the color of the 3 LED dice within the LED, as well as to provide a wide viewing angle. SMD RGB LEDs simply aren’t large enough for this blending to occur, even if they use diffused epoxy, and SMD LEDs tend to be much more directional than diffused THT LEDs.

author: StillTrying
author_rank: Super Contributor
timestamp: December 28, 2019, 12:51:07 pm
content: An 8 x 8 x 8ColouredLED Cube seem like a job and a half to me.Min. 200 outputs ?https://www.instructables.com/id/Led-Cube-8x8x8/

author: Jan Audio
author_rank: Frequent Contributor
timestamp: December 28, 2019, 01:14:30 pm
content: If you gonna build something like this, you need at least a 3D printer with transparant filament, or some plexiglass around it for the case you squash your thing.Good luck, place some pictures in the year 2021.

author: StillTrying
author_rank: Super Contributor
timestamp: December 28, 2019, 01:21:31 pm
content: Quote from: Jan Audio on December 28, 2019, 01:14:30 pmI guess you think it's a job and a half as well,>2,200 soldered connections just on the cube itself.

author: mariush
author_rank: Super Contributor
timestamp: December 28, 2019, 01:37:08 pm
content: QuoteJLCPCB does thin pcbs, as low as 0.4mm thick. If you can make cutouts to have 1-3 mm wide segments, you'd basically have wire like pcb between leds but it would probably be more rigid.As for something to be inspired from, Kevin Darrah did 8x8x8 rgb cubes, here's his videos:Playlist (12 videos):Part 1Part 2Part 3

author: tooki
author_rank: Super Contributor
timestamp: December 28, 2019, 02:06:17 pm
content: Quote from: Jan Audio on December 28, 2019, 01:14:30 pmTransparent 3D prints are not glass-clear, they end up rather milky, defeating the purpose of a 3D cube. If you're going to make a case for it, make it from plexiglas or similar.Quote from: mariush on December 28, 2019, 01:37:08 pmDoubtful. Thin PCBs are quite flexible. There's little reason to assume it'd be more rigid than wire, and for sure it'd be more brittle, insofar as wire can be bent back and forth a few times, but FR-4 will fracture.And you completely ignored the issue of diffusion that I went into.SMD is just a stupid idea for this project, sorry.

author: james_s
author_rank: Super Contributor
timestamp: December 28, 2019, 06:54:58 pm
content: Lots of people have built 8x8 LED cubes, it's not that different from knitting a sweater. It's the sort of thing you build because you enjoy creating a work of art.

author: Oleenick
author_rank: Contributor
timestamp: December 29, 2019, 09:31:38 am
content: Quote from: Jan Audio on December 28, 2019, 01:14:30 pmYeah I'll be posting the finished project once its done. Aiming for having it finished within the next couple months. As for a enclosure for the cube... I think I'll run the risk of not having something covering it. Yes I know dust is the enemy but I don't really like the effect that the internally reflective acryllic has on the clarity of the cube. Nit picking yes. Maybe I'll eventually make a case for it.Quote from: mariush on December 28, 2019, 01:37:08 pmThat's what I'm basing this project on. Kevin Darrah's overview of the entire cube architecture is fantastic. As for the SMD LED cube idea... Not so sure. There's a lot more challenges to overcome with a design like that. I'm sure it can be done in some capacity but that's not what I'm looking to achieve with this project. Although the PCB that the cube goes into will use SMD components to hide them on the bottom. My idea was to have only the MCU on the top of the board so you can see the brains on display. Might also trick some passers by that its entirely controlled with that one component haha.Quote from: StillTrying on December 28, 2019, 12:51:07 pmYeah I'm using 200 outputs (192 LED cathode control for 64RGB common anode leds). The last 8 are for the anodes which are commoned for each layer driven by mosfets to accomodate the modulated layer architecture.Thanks everyone for the great discussions. I'll go with LCSC.

author: mark03
author_rank: Frequent Contributor
timestamp: December 29, 2019, 06:49:14 pm
content: Quote from: tooki on December 28, 2019, 11:33:09 amWait a minute, surely you have this backwards? SMD LEDs have *wider* beamwidth than THT LEDs, not narrower.The interconnect certainly become more difficult with SMD, but it has been done:https://www.eevblog.com/forum/projects/kcube-led-cube-design-revisited/

author: tooki
author_rank: Super Contributor
timestamp: December 29, 2019, 07:10:25 pm
content: Quote from: mark03 on December 29, 2019, 06:49:14 pmNope. I specifically (and repeatedly) saiddiffusedTHT LED. As in, with the milky body that changes it from a beam to just a glowing plastic blob. Very different from the water-clear LEDs that have (perplexingly) become the norm. A diffused THT LED can be seen even from well beyond 90˚ off-axis, even from behind.Quote from: mark03 on December 29, 2019, 06:49:14 pmJust because onecandoesn't mean oneshould, and that thing is a perfect example thereof. Having to have transparent PET flex PCBs made, which then require an external frame to support them, and require low-temperature solder, turns that into a totally different type of project, and for what?

author: james_s
author_rank: Super Contributor
timestamp: December 29, 2019, 09:44:05 pm
content: The whole point of one of these LED cubes is to have a freestanding sculpture without any PCBs in the way. The bare minimum required to hold the LEDs in space. The only reasonable way for it to look right is to use through-hole LEDs.

author: mark03
author_rank: Frequent Contributor
timestamp: December 29, 2019, 11:54:57 pm
content: I didn't mean to suggest that one *ought* to use SMD LEDs for a cube; I merely took issue with the claim that they have narrower beam patterns. I still disagree with this. It is true that you can see THT LEDs from behind, but if you plot the actual brightness profile in the elevation (?) plane, I think they are still more focused than the wide-angle SMD type. For example, if you looked at the ratio of brightness, say, on axis and 70 degrees off axis, I think the SMD LEDs would still win.

author: tooki
author_rank: Super Contributor
timestamp: December 30, 2019, 11:11:08 am
content: Quote from: mark03 on December 29, 2019, 11:54:57 pmI didn't say they have narrower beam patterns. I said they have a narrower viewing angle. And that's NOT the same thing! Why? Because a non-diffused LED is very nearly a point light source. In a water-clear THT LED (and many SMD ones), the body is a lens that focuses it in some way or another, depending on the design. But in a diffused THT LED, it's not a point source any more, it becomes a diffuse body, with little to no focused beam at all. The light output of a point source LED has a pattern that varies significantly by angle. In a diffused one, the angle is damned near irrelevant, and that's desirable. In an LED cube, you don'twantthe light output to be directional. 70˚ off-axis is still looking at the front of the LED. But in this application, you want an LED that is visible from well beyond that. An SMD LED, even wide-angle, will have little to no light output at or beyond 90˚, and even before then, you start to get color shifting as the LED housing blocks your line of sight to one or more of the individual LED dice.You're thinking flashlights, where brightness is the main criterion. But in this application, the ideal would be a fluorescent sphere emitting all its light equally in all directions.And again, you want the large diffuse body to provide a place for the colors to blend. Without this, much of the blending doesn't happen until the light beam hits a surface like a wall. Totally opposite of what you want in an LED cube.