I am happy with a sense of accomplishment after I deciphered all the information necessary to utilize this circuit board, formerly the faceplate for a salvaged car tape deck. I started this investigation when I found I could power it up under control of the original mainboard. Now, I can work with the LCD and read all knobs and buttons with an Arduino, independent of the original mainboard. My original intent was just to see if I could get to this point. I thought I would learn a lot whether I succeeded or failed trying to control this faceplate. I have gained knowledge and experience I didn't have before, and a faceplate I can control.

Now what?

It feels like I should be able to build something nifty with this faceplate, there's room to be creative in repurposing it. At the moment I don't have any ideas that would creatively utilize the display and button/knob input, but I could build a simple demo. This LCD is wide and not very tall, so I thought I would make it into a simple Larson Scanner. (a.k.a. Cylon lights a.k.a. K.I.T.T. lights.)

First, I divided the LCD segments into 16 groups of roughly similar size. I started using my segment map to generate the corresponding bit patterns by hand but then decided I should make a software tool to do it instead. I've already written code to light up one segment at a time for generating the segment map, it took only a bit of hacking to make it into a drawing tool. I use the knob to move segments as I did before, but now I could press the knob to toggle the selected segment. Every time I pressed the knob, I print the corresponding bit pattern out to serial terminal in a format that I could copy into C source code.

I then added a different operating mode to my Arduino test program. Pressing the Volume knob would toggle between drawing mode and Larson Scanner mode. While in Larson Scanner mode, I would select two of those 16 groups based on scanner position, and bitwise OR them together into my display. This gives me a nice little demo that is completely unrelated to this LCD's original purpose, and confidence I no longer need this tape deck's original mainboard.

https://twitter.com/Regorlas/status/1526424801404850176

Source code for this demo is publicly available on GitHub.