So I have an issue — I want to use an 8x8 APA102 matrix

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So I have an issue — I want to use an 8x8 APA102 matrix as a real display. Not an installation or a something at home that can be cobbled together with some kind of diffusion material etc

Light pipes are out as they can get fiddly and I am not sure I trust them — the only way to do this is probably to use a piece of dark tinted acrylic. It doesn’t look 100% but it’s fairly ok.

My next option to explore would be an older style RGB 8x8 matrix where all the LEDs are separate, like the one in this tutorial except RGB:

http://arduino.cc/en/Tutorial/RowColumnScanning

I guess I could use a driver like the TLC5947 — I presume I need one of those and something else to do the control the rows.

Anyone got any experience of either using APA102 or WS2812 as a “real” display or using “dumb” RGB matrix with controllers?

James

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When you say “real display” you mean you want an addressable 8 x 8 matrix made of APA102s? It’s pretty straight forward: you just snake the signal wires back and forth across each row and sort the addressing out in software. Take a look at https://github.com/FastLED/FastLED/tree/FastLED3.1/examples/XYMatrix for a demo.

You can even buy pre-made matrices in various sizes, take a look at Ray Wu’s site on Alibaba.

Or is that not what you meant?

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Funny I had exactly the same question from @Robert_Atkins but hesitated to ask for clarifications as I am the guy that ‘cobbled’ his WS2812b RGB matrix together with some kind of diffuser (parchment
paper actually cause it works for me and it is the cheapest I could find !!)

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When I say a “real” display — I mean one that could actually be used in a product that would sell. Something that is reliable and relatively simple for the manufacturing house to put together.

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Hi @James_Carruthers ,

The closest I have seen to your description of a ‘Real’ display is the one displayed by these folks…

http://docs.pixelmatix.com/SmartMatrix/index.html

I think they use a 3rd party frame kit normally intended for pictures and small 3-d objects. Is this kinda what you are looking for ?

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Thanks for the mention @JP_Roy . I took a deep dive on driving those epoxy filled RGB matrices a couple years ago which lead to the SmartMatrix products.

Take a look at the EMS Peggy series of products for an open source reference design of how to drive multiplexed LED arrays:
http://wiki.evilmadscientist.com/Peggy_2

Basically you want to have shift registers that are capable of sourcing or sinking a lot of current. There are some specialized chips that can do that, or you can combine two chips like a 74HC595 shift register that drives a ULN2803 transistor array.

Unless you really need the low resolution of 8x8, or even 16x16, I think you’re better off using the multiplexed RGB displays like SmartMatrix uses. They come in different sizes, check out Adafruit as they sell a lot. The price per pixel is pretty low, and the driver circuitry is already taken care of so your design is much simpler. They are not as bright as WS/APA discrete LEDs which can be on 100% of the time, but that can be a good thing depending on the application. I’ve never seen displays smaller than 16x32 pixels.

On a previous rev of the product I tried hiding diffusion material (thin pearl white BOPP) behind dark acrylic, but found it wasn’t manufacturable though it looked great.
http://docs.pixelmatix.com/SmartMatrix/projects.html#aurora-display-bay-area-maker-faire-2014

I’m currently using Acrylite Satinice in the product, which diffuses the light and hides the LEDs a little bit. They have a dark version which diffuses and does a great job of hiding the LEDs but only transmits 20% or so of the light.

  • Louis