LED matrix sign

I feel like I’ve done this before. It really seems like I’ve made a post about this before. At least the code for the arduino that proves these sign segments out. Well, now I have a full sign driven by a raspberry pi.

Original sign with reverse engineered code.

I got these sign segments from a friend who got them at a scrap yard. They weren’t all perfect, but they were pretty darn good. I reverse engineered the whole drive circuit for one of the boards and generated code to drive them from an arduino. I originally bit banged the whole thing, but then I moved to hardware SPI because that’s really what these signs talk. They use tb62726afg constant current LED drivers as well as some addressing to pick which line you are streaming data into. These are red/green only, but other than that they are reeeeeeeally close to the RGB ones adafruit sells. They are compatible with “HUB75” panels, electrically. That means that all the adafruit code and documentation will work, with some slight wiring modifications.

The adafruit bonnet was out of stock when I did this, so I cloned the hardware, kinda, I stole the pinout and used some buffers I had and adapted the wiring to my displays. These days I’d lay out a board, but at the time this was faster and easier.

These boards have soldered on mounting posts, and not all of them are present anymore. There are enough, however, to make the whole thing go together on a big lasered backer board.

There were some ghosting problems, but Frank helped me sort them out.

Brandon helped me laser the mounts and Frank supplied the 40A 5v power supply.

It all tucks away very nicely. Now there needs to be some sort of script on boot that pulls from a rotating set of ‘slides’ that can display images, text, moving images, or moving text. I’m thinking a python script that iterates over a folder full of text files.

photos of the thing are here

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