Covid-19 is here, and I’ve been keeping to myself a lot more after work. For reference, our office is currently an old school that we have been squatting in for a couple years, and one of the old buildings had an LED sign that dated back to the late 80’s. This thing came with a power supply and nothing else. No documents and no keyboard to program it, nada. Also, no documentation was found for this specific model online.
After digging through any and all archives, taking whatever model numbers or post information I could obtain from the screen, I was able to locate a couple of things. These signs have the ability to be networked together, using almost any medium and also a lot of others with similar home projects. I found a couple of documents that were essential to figuring out how this dumb thing operated.
Turns out the networking document from Adaptive Displays gives you enough info to get started. All examples and documentation I could find point me to using a serial connection or RJ11 cable to interface with. My stupid sign had a DIN connector. So, I popped it off. I figured if it was a serial connection, it need a +/- and a ground, right? I guess so. The sign was fed from an AC power supply, and offered a 13 volt, AC connection to the sign itself. The DIN connector had three wires that were not AC power related, which I assumed to be the needed for a serial connection. I knew from previous documents that networking was possible, so I had a hunch that the DIN would have to be the connector. It was easy to identify the ground, it was the smallest gauge wire and was soldered to a separate location on the board. The networking document stated that the serial connection would require a RS-485 adapter, so I went digging for a USB to serial adapter. I actually had an RS-485 serial to USB adapter available, and got to work. Pin 5 was ground and Pin 1 and 2 were +/- 5v. I soldered a cat5e cable into the back of the DIN port and wired it to the USB adapter.
Using a document from MIT, I was able to find the serial information for the connection. My sign used the EZKEY II or EZKEY protocol, and required a 1200, 2400 or 4800 baud rate. I used the AlphaNET software trial to see if I could get the sign to interface with the serial connection. It could.
I had found the appropriate connection settings. 2400 Baud, 7 data bits, two stop bits and even parity. I could send text to the sign.
Now it was time to use the dumb thing. I found out through a lot of trial and error that my sign is too old to use strings, and must only write and read TEXT files. I began working on my own interface to handle sign text in nodejs. Once I was able to write string buffers of hex ASCII codes, I could use strings and convert them into packets. But whats the point of that? Why not make an express HTTP server to handle requests and use parameters to create messages that do things?
Great! Now we just need a front end to interface with the user and hang it in our office