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Reverse engineering an LED display from eBay [Permalink]

I decided to try doing a video for this post instead of just writing about it.
As a result, most of the content for this post is in the video, some of it is repeated here.

I recently came across some LED displays from eBay. They were so cheap (£15 each plus about £5 postage) that I bought two.
I think the seller had pulled apart a sign from a railway station departure board or a bus stop sign or something like that.

So here is a quick look; The signs were made by "shorekarn". They each have 40 columns and 7 rows of LEDs (280 in total). Each board has a chain of shift registers that effectively make one large SIPO (Serial-in-parallel-out) 40-bit shift register. There is a 3 to 8 line decoder (that has a redundant line) which selects the row to light up. Therefore the signs must be actively scanned to maintain an image. The boards can be daisy chained together to make larger signs.

This was fairly easy to figure out, googling part numbers I didn't know and then following traces back and referring to pin diagrams of the chips, I was able to identify the function of each pin on the main data connector.

I wrote some arduino code to control it, it turns out that was remarkably easy thanks to the simplicity of the sign's design.

So, without further ado, here is the vid:

I'm not sure what I want to do with these signs, I just couldn't resist them at that price.
I have written a snake game for it that also has sounds, I might turn it into a really odd arcade machine.

Hope you liked it.

Links to datasheets for the chips on the board:

Logic

3 to 8 line decoder 74138
Quad NAND gate 7400 Not that there's anything we haven't seen in this one.
8 bit SIPO shift register 74164

Drivers

Row drivers (darlington transistors) TIP125
Row driver IC (hex buffer) 7407
Column driver IC (darlington transistor array) MC1413P

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