If you don't want to read through the information, the source code is available for download here . (Also included in that download is the excel spreadsheet used to quickly convert messages into binary arrays) The LED Sign itself is a 48x10 soldered together matrix of red LED's. I soldered them together sparsely in a mesh so it could be mounted in the back window without losing rear visibility. The rows are controlled using a 4017 decade counter for POV. The columns are controlled using six 959 shift registers.
Input from the vehicle is recieved from the trailer light hookup through a cable and into the cab. The signal from the trailer lights hookup is connected to the arduino using optocouplers. The arduino can sense both turn signals and the lights using this setup. The 12v signal is regulated down to 5v for the optocoupler using 7805 voltage regulators. There was probably somewhere in the cab to get the turning signal input from, but it was easier to use the trailer hookup, although uglier.
Unfortunately, the sign itself is fairly dim and only visible at night, however, it is highly visible at night as seen in the demo videos. During normal driving the sign will display URLs for personal advertisment. The advertisements are only displayed when the vehicle's lights are on. This is helpful because I can leave the arduino plugged in without draining the battery in my pickup (unless I forget and leave the headlights on). When either of the turning signals or brake lights are activated, any other animations are haulted immediately and the animation arrows are displayed as can be seen on the demo videos page.
Since I am using an Arduino ADK, it would seem like a waste to not use the ADK part of it. I'm planning on using that for quick messages to the drivers behind me like "back off", or "pass me now", etc. (you get the idea). That's the next phase of the project coming when I get to it.
Have any questions? Email me using the email at the bottom of the page.