Reverse Engineering a LED Display Board

Hello Everyone again!

The question: "What protocol / communication uses 3 wires?" I am hoping this will be an easy question, but probably not...

I have a small hobby here working on intelligent lighting / moving heads for stage and DJ use. These are simply lights on stepper motors controlled by microcontrollers. (for the most part) It is wonderful to see how companys have taken these parts and made working products out of them. Also great to see how limit switches, and sensors work in the real world (or during a show!) Highly suggest others do the same thing... You will recognize a lot of the parts. ;)

Anyway, one light I picked up recently has a broken display board, which is a total bummer because it is a custom made board/display. On the back of the board is an Atmel microcontroller! This makes me think I can make my own board.

Not so fast, first things first, need to understand what protocol is used between the main CPU board and this display board. Following traces and cables it uses 3 wires. I have never worked with chip-chip communication before but have been looking for a reason to do this. I have a cheap logic analyzer also a great time to learn how to use this too. Perhaps it'd be better to do this on a known protocol to see how it works first. Nahhh

Once the protocol is figured out, the messages / codes should be fun. This is a bi-directional protocol because there are also buttons on this display board that trigger menu functions.

It sounds like a fun project to learn on, it also sounds like it can be over my head.. Anyone have experience in this area? It interests me.

Thanks!!

How many options are there in the menu? If there are 8 or less items so it could be only easy binary code.

There are many menu options.

I realize this might be a bit of a naive question now that I've done some digging a research. Possibly serial? Possibly ISP? Possibly custom. If I were to bit bang, how would I accomplish this?

Without a working system to study I think it would be extremely difficult, if not impossible, to figure out the protocol.

It uses I2C to communicate! What is next? :)

I am guessing plug in logic analyzer and capture some stuff, then write an arduino program to send some bits back?