LED modules used in Japanese train station readerboards - Page 1
Forum section: electronics / projects

author: kmm
author_rank: Regular Contributor
timestamp: November 05, 2024, 08:20:54 pm
content: Mostly wondering if anyone else has visited Japan, saw the displays for things like train departure times, and went down the rabbit hole of finding the display modules they use in them.They look very much like they come in (approximately) 50x50mm square sub-units of something like 32x32 RGB LED pixels with around a 1-2mm dot pitch and tight pixel spacing, and are usually cascaded horizontally on the signage to make a longer display suitable for maybe 20-40 characters. Looking at an angle you can often see variances in reflections that seem to give away a cascade of squares rather than long strips. Overall very similar to some of the the easy to find but much larger LED matrix modules used for video walls in appearance, just smaller and seem to be more designed for displaying a row of nicely-rendered characters than general video use.I've checked the usual places for electronic tat and while I can find many video wall modules that have a similar look to the pixels, they're all much larger (64 pixels to a row/column and up) and generally rectangular. While I can find blocks of a similar size, geometry, pitch, and overall "look" in monochrome, I haven't seen any in RGB like used on these signs. Totally possible I just haven't hit the right combination of power words in my searches but I suspect these might be a Japanese product intended mostly for the domestic Japanese market, possibly specifically the transport signage market, without a lot of marketing presence in the English sphere and not something China has widely cloned. Checked around here too in search and didn't see much relating to Japanese train sign LEDs, but also totally possible I just didn't hit the right query terms.I never thought to take a pic that shows the module block structure revealing itself, but this stock photo of a Shinkansen sign at least illustrates the signs I'm talking about.I just think it would be fun to have a strip of Shinkansen status display hanging in my house being a glorified wall clock, that's all.

author: coppice
author_rank: Super Contributor
timestamp: November 05, 2024, 08:28:17 pm
content: I think they may be Japan only products. Most places lived with limited colour low resolution LEDs until LCDs took over with full colour high definition information for trains. Japan is the only place where I've seen LED displays for trains with white characters, and quite high definition.

author: kmm
author_rank: Regular Contributor
timestamp: November 05, 2024, 08:45:01 pm
content: Quote from: coppice on November 05, 2024, 08:28:17 pmYeah first time I've ever encountered signs like these. Unique and I found them very aesthetically pleasing, all the transit displays around North America are just LCD TVs now. Don't even see the classic 1-2" 5x7 or 8x8 LED matrices much any more.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 06, 2024, 10:43:19 pm
content: Quote from: kmm on November 05, 2024, 08:20:54 pmAliExpress have many outdoor/indoor sign modules of varying LED pitch and size ?One example: P1.25 high density LED Modules 320*160mm (256x128) full color 32 Scan 3840Hz RGB Full Color Small Pitch For LED DisplayFewer LEDs on a more coarse pitch, are of course cheaperP2 led module 256mm x 128mm, (128x64 ) P2 HD led video wall led screen module 128x64

author: kmm
author_rank: Regular Contributor
timestamp: November 07, 2024, 03:53:26 pm
content: Quote from: PCB.Wiz on November 06, 2024, 10:43:19 pmDefinitely, and I'll probably end up ordering a few different varieties of these video wall modules to play with since it sounds fun anyway. I suspect even if I do end up finding a part number for the actual modules they'll either be something no one will to sell me or cost a LOT more than I'm willing to pay in low quantity. The main thing the about the video wall modules is just the aspect ratio is pretty far off from the sign units, they're more for making big rectangular panels than long skinny strips of text, but I'm thinking just masking off part of the displays with a bezel could get pretty close to the same look, even if the pixel density isn't quite as high.I'm also pondering if maybe making my own modules using 3D printed "pixel masks" with an array of addressable LEDs behind. I think getting the density the same would be tough since the smallest addressable LEDs I've seen are all pretty much in the 5mm realm (if anyone knows of an addressable LED in something around the size of 0805 I'd love a link or part number), but getting the overall aesthetic seems relatively easy with resin printed masks and pixel holes filled with light diffusing epoxy or silicone.

author: BennoG
author_rank: Frequent Contributor
timestamp: November 07, 2024, 05:36:25 pm
content: They are controlled via HUB75 protocolhttps://github.com/hzeller/rpi-rgb-led-matrixThere are more sources for the HUB75 hat but this is the one i encounter the most.attached of a setup I made for a customer.Benno

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 07, 2024, 08:44:15 pm
content: Quote from: kmm on November 07, 2024, 03:53:26 pmThey come as small as 0606 these days !https://www.lcsc.com/products/RGB-LEDs-Built-in-IC_13484.html

author: nctnico
author_rank: Super Contributor
timestamp: November 07, 2024, 09:14:53 pm
content: Quote from: kmm on November 07, 2024, 03:53:26 pmYou didn't look hard enough (*)I have used these (1x1 mm) in a recent design:https://www.bestsmd.com/1010-rgb-led/62269470.htmlVery affordable and very bright. Be aware though that LEDs need large copper pads for proper cooling.* Actually, I did spend quite a bit of time finding these tiny RGB LEDs.

author: kmm
author_rank: Regular Contributor
timestamp: November 07, 2024, 09:28:59 pm
content: These LED suggestions are great, thanks! I'm not sure how i haven't ever run across these, maybe it's just because I've been searching for "addressable" rather than "IC included" and similar permutations, smallest I was able to find despite searching around for this on and off for years are the ubiquitous 5050, and was puzzled why smaller ones didn't seem to exist. Some of them in the LCSC catalog are even the super easy to drive clock-and-data variants.

author: kmm
author_rank: Regular Contributor
timestamp: November 09, 2024, 09:43:52 pm
content: I've started sketching out a module using the 1x1mm LEDs. Specifically XL-1010RGBC-WS2812B mostly just because LCSC has a gazillion of them in stock and I seem to recall JLC and LCSC are either the same company or partnered and JLC has access to a lot of LCSC's catalog without extra fees.After finding some higher resolution stock photos of the signs and counting dots, the array height looks like 24 pixels, so I started with a 24x24 module (576 LEDs) with thin margins on the sides so I can stack them horizontally with a minimal gap.This is by far the most dense thing I've attempted and MSOP/LQFP ICs are about as fine as I go, never attempted a BGA or WLCSP design. I'm not 100% sure if JLC will let me do via-in-pad if I'm not using an actual BGA footprint; I don't see why not since this should be well within the fab rules for their 4/6 layer cheapo promo process but I'm not aware of what goes on on the backside and if there's maybe a software constraint or something in the fab process that relies on standard BGA footprints for this to work.Layer stack I'm thinking ground on top for heat sinking, signals in the middle (in my example I have signals on top for the LED-LED data lines but I'll probably do VIP and route these internally too), and power on the back layer. Datasheet for these parts doesn't seem to have a suggested pattern for thermal management but I'm guessing gnd is the closest coupling. One thing I'm not sure about is decoupling capacitors, datasheet suggests one per LED but I'm hoping I can get away with one every 4 at most. I'd like to avoid the costs of a double side assembly load and just experiment with populating the back in various numbers to get it stable. I've used WS2812 LEDs in other things and they seem to be fairly forgiving in terms of decoupling, so I'm hoping a 1:4 or 1:8 density of caps to LEDs is enough.I haven't fully routed this (need to figure out KiCad scripting to change all the LED refs rather than doing it >500 times by hand), but here's a couple examples of what I'm thinking, comment welcome and appreciated.I've ordered probably in the hundreds of boards over 10 or 20 jobs from JLC but mostly lower density stuff and max 4 layers, and have never tried their (or anyone else's) assembly services so if anyone has any protips regarding that I'd appreciate it.Here's the schematic if anyone's interested; this is by far the most components I've ever thrown into one KiCad drawing and it handled it respectably even on this ~8th gen i7 X1 Carbon I use for travel.I don't intend to run this full bright ever as a wall clock but it looks like from the datasheet each element can max out at 12mA for a total of just under 7A demand, so I've gone excessive with the plans for power inputs.array-24x24x2mm.pdf(1095.08 kB - downloaded 58 times.)If anyone wants the KiCad sources I'm happy to share. This is just a for fun project and I may end up getting sticker shock and not even going to fab with it, but I enjoy designing and laying out stuff.

author: kmm
author_rank: Regular Contributor
timestamp: November 12, 2024, 12:51:44 am
content: Fleshed out the sketch a bit, haven't gotten into designing the 3D printed dot mask/diffuser part and probably won't unless I have a few assembled units in hand; the cost aspect is still a looming unknown.Not sure how much I like the 2.54mm pin headers on top but with the number of vias perforating the board and wanting narrow margins on the sides it was difficult to fit in SMT contact pads on the back that could be feasibly soldered to.Had to do a 6 layer to qualify for JLC's via-in-pad promo deal, went with this stackup that I think will provide sufficient power even at full bright:GNDSignal [mostly LED data line interconnects, not much effective plane from the GND fill]GND [broken by the board D out return line to the header on the right side, but otherwise continuous]V+V+GNDWent with a 1:4 ratio of LEDs to decoupling caps evenly distributed across the LED array, don't know if that's adequate or not but it'll be something to experiment with if I get some fabbed.